| 00:02 | This is lecture 11 of Neuroscience. we ended last time when we started |
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| 00:07 | about the different ways that neurons have integrate the signals and different ways that |
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| 00:13 | turn neurons may want to impact the depolarization of the synoptic neuron. So |
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| 00:20 | talked about spatial summation where multiple synopsis target the same dendrites and will produce |
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| 00:27 | potentials at the same time. And have the highest ST response when you |
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| 00:33 | across the space at the same And another way is temporal summation. |
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| 00:38 | the same axon produces a train or number of action potentials very closely dispersed |
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| 00:45 | space and time. And that also for the E ESB to grow, |
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| 00:53 | it doesn't reach the same aptitude as would have in the cases of spatial |
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| 01:00 | . Another thing that happens that we is that dendrites are not insulated. |
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| 01:06 | , dendrites are sort of like leaky and the maximal current that you may |
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| 01:14 | here either through synaptic stimulation, depolarization an electrical electro physiological stimulation, the |
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| 01:23 | immediately at the point of stimulation, will have very large depolarization and some |
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| 01:30 | of that depolarization is going to die over distance. So this current is |
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| 01:35 | to decode and we talked about this value. This is LAMBDA which refers |
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| 01:42 | length constant. So by the time 100% of injection here, this is |
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| 01:50 | 100% current that the side a over distance, that current decays exponentially to |
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| 02:00 | of its value. And that distance space is LAMBDA is the length |
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| 02:10 | So the longer the length constant, further along the dendrite that signal can |
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| 02:16 | transmitted. Uh In reality, dendrites not just one straight cable. It's |
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| 02:23 | complicated. They have complex branches, have primary secondary tertiary branches and many |
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| 02:31 | dendrites have voltage gated sodium calcium and channels. So in addition to those |
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| 02:38 | gated sodium and potassium channels and the of nodes of Ron beer, there |
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| 02:43 | also some voltage gated channels that will placed in the dendrites. And one |
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| 02:47 | the strategies of neuron is how to the channels and many channels far away |
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| 02:55 | the. So, so that these channels would still communicate information from these |
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| 03:00 | distal aspects of the sounds. So these channels can amplify the depolarization f |
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| 03:13 | versus just passively allowing for the signal leak out. Because if you open |
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| 03:18 | gated channels, you can increase more along this pathway rather than the |
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| 03:24 | just passively leaking out uh been reading channels. And some cells may carry |
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| 03:32 | signals in the opposite direction from SOMA in the dendrite. So we saw |
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| 03:38 | the back propagating action potential which came the hack on the lock and went |
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| 03:43 | the SOMA and went into the Den . And we're also seeing that there's |
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| 03:48 | of current along the den drive and not always moving toward the SOMA, |
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| 03:53 | can move away from the SOMA. we're actually just starting to wrap our |
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| 03:58 | around what these different movements of the along the dendrite actually mean and how |
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| 04:04 | play into the communication between the So these quite often you'll see the |
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| 04:11 | inputs that are located distally on the and the inhibitory inputs quite often will |
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| 04:18 | located in what we call these para areas in areas around the SOMA. |
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| 04:24 | if you have a strong excited or you have a pretty large epsp that |
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| 04:30 | can record in the den drive. there is no inhibition, then the |
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| 04:36 | of this depolarization will subscribe into the will potentially be enough to uh activate |
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| 04:44 | gated sodium channels in the axon vlock produce action potential. However, as |
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| 04:51 | mentioned with excitatory inputs and excitatory also a lot of inhibitory synopsis. |
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| 04:59 | if they're located closer to the they can very much impede with the |
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| 05:05 | of the signal and the current traveling the SOMA. So if all of |
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| 05:10 | sudden you have an exci or that's really strong has really largely PSP |
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| 05:16 | the site of that stimulus and that is traveling down the dendrid, some |
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| 05:22 | it is being lost due to the we saw the length, constant and |
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| 05:27 | of the current. And then if have inhibitor synapse here that gets |
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| 05:33 | it actually will cancel out at the of the SOMA. Instead of seeing |
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| 05:39 | small depolarization when there's no inhibition, you have an inhibition, all of |
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| 05:44 | sudden, it's going to cancel out excitation, it's gonna shun some of |
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| 05:49 | currents and essentially inhibit the cell from an action potential. So that's why |
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| 05:58 | often a single inhibitory neuron can have really small impact on many excitatory inputs |
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| 06:06 | this excitatory input will be located more . So greater chance of leak current |
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| 06:12 | and that inhibitory ones have greater impact this area. That's really important for |
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| 06:18 | all of the information of producing the potentials inners when we talk about modulation |
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| 06:26 | uh modulatory diffuse systems. In with the exception of acetyl comin, |
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| 06:32 | in the CNS acts through nicotinic and inic. So, isotropic and metabotropic |
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| 06:38 | , most of the uh signaling through protein coupled receptors that we'll be |
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| 06:45 | It's linked to the amine signaling to by acetylcholine which is nicotinic muscarinic. |
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| 06:53 | the others norepinephrine dopamine and serotonin, only uh interact through these G protein |
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| 07:01 | complexes. So they are receptors, beta is a receptor that's linked to |
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| 07:07 | protein complex. So lag and binding receptor is not a channel. This |
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| 07:12 | metabotropic signaling that can activate a then little cycles downstream. We can activate |
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| 07:19 | messenger cyclic A MP cyclic A P produce protein kin AIS protein kinas will |
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| 07:30 | potassium channel. So they will add po four group on these potassium |
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| 07:36 | And by phosphorylation nearby potassium channel, can influence the opening of this channel |
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| 07:44 | it can do so for prolonged manner . So it's modulatory because it doesn't |
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| 07:51 | open up the actual came again and signaling, but rather, it's modulating |
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| 07:58 | physiology of the membrane through these enzymes and secondary messengers. So, |
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| 08:07 | we have learned so far is that have rich diversity of different types of |
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| 08:16 | and synopsis, excitatory inhibitory chemical We also have electrical synopsis. We |
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| 08:24 | start explaining a lot of drug effects we're looking at synoptic transmission. So |
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| 08:29 | discussed uh botulinum toxin and we discussed toxin in the light of Alzheimer's |
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| 08:38 | which is not really bum toxin. it's cyl cholinesterase inhibitor, but it's |
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| 08:44 | the cholinergic system. We discuss boum as release of neurotransmitter for acetyl |
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| 08:51 | And that's for Botox and for we also discussed the G phosphates. |
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| 08:57 | you can start understanding, we also poynt receptor antagonist such as cr when |
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| 09:03 | talk about potential. So we can understanding drug drug effects, we can |
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| 09:11 | start understanding how specific neurotransmitter systems are or correlated or are a part of |
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| 09:22 | of specific neurological disorders. If we how the cells transmit the information and |
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| 09:30 | with each other, we can understand those synopsis can strengthen or weaken. |
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| 09:36 | we really can start understanding the basis what we call synaptic plasticity at the |
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| 09:42 | of the cells plasticity and the their capacity, their strength or their |
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| 09:47 | , their sizes. And also this a cellular mechanism for learning and memory |
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| 09:55 | of new synapsis, strengthening of new and driving away of the synopsis that |
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| 10:01 | not being utilized. And again, one of these chemicals as we will |
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| 10:09 | even further, when we talk about means will be responsible for slightly different |
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| 10:15 | . We already saw that the adenosine we discuss go off in the evening |
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| 10:20 | that makes you more sleep and they down in the morning and that makes |
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| 10:24 | more weak. So this is sleepy, behavior versus alert and engaged |
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| 10:34 | . Ok. So now we're moving to our next lecture material which is |
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| 10:42 | glutamate and Gaba. And as a , we're talking about all of these |
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| 10:48 | neurotransmitter systems. Uh And when we about amino acids, and if you |
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| 10:54 | my drawing, when I drew the , and I said that if you |
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| 10:57 | at the expression of glutamate and G the brain, there will be billions |
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| 11:03 | billions of cells that are expressing glutamate gama throughout the CMX. But we |
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| 11:10 | about amines and we mentioned that amines as acetyl codeine such as dopamine, |
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| 11:17 | confined to these nuclei. The production acetylcholine is just done in these small |
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| 11:27 | . And these nuclei contain tends to sometimes hundreds of thousands of units or |
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| 11:34 | that are responsible for synthesizing all of acetyl colon or all of the |
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| 11:40 | all of the serotonin in the entire . So that is very different. |
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| 11:46 | from here, we have axons that project and that will supply dopamine to |
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| 11:52 | frontal cortex or dopamine to the striatum these subcortical regions. And that's very |
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| 11:59 | . We also saw that neuropeptides and can be co expressed by cells and |
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| 12:04 | released by cells. You will find core vassals or secret Granules that are |
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| 12:11 | with neuropeptides together with the neurotransmitter, and the same synopsis. So they |
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| 12:18 | be co expressed and core released. , in general, when we're talking |
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| 12:24 | this whole neurotransmitter system, we already that in order for the cell to |
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| 12:31 | a cholinergic cell, a glutamatergic cell cell. If it's cholinergic cell, |
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| 12:37 | has to have a synthesis uh machinery enzymes to produce acetylcholine. So this |
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| 12:45 | chat cen acetyl transferase, acetylcholine vesicles have their own transporters so that the |
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| 12:56 | for acetylcholine on this vesicle is going bring in only acetylcholine and on another |
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| 13:07 | there will be a transporter for And it's going to bring in only |
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| 13:13 | into these vesicles. So you have load them up into the vesicles through |
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| 13:20 | . Then these molecules get released in synaptic cleft. And what we saw |
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| 13:25 | the acetylcholine is that in the synaptic , we had a degradating enzyme. |
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| 13:30 | we had acetylcholinesterase that was breaking down acetyl code. And once this molecule |
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| 13:40 | broken down and in some instances, is not broken down. Like we'll |
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| 13:44 | with dopamine or we'll see with it gets reuptake back. So this |
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| 13:49 | transporters that will react take this molecule the synaptic cleft. The reason for |
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| 13:55 | is that once you release neurotransmitter, neurotransmitter binds to the receptors is binding |
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| 14:01 | reversible. It's not gonna get stuck the receptor forever. It's going to |
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| 14:07 | , it's going to float off and it's gonna get reuptake back into the |
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| 14:11 | terminal. While synoptic, you have gated ion channels, there's an ionotropic |
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| 14:19 | protein coupled receptors is this metabotropic g complexes. But these G protein complexes |
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| 14:25 | modulate a community of the nearby ion as well as turn on secondary messenger |
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| 14:32 | by synoptic and those secondary messenger cascades even influence of transcription factors at the |
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| 14:39 | of the nucleus. So it could really long lasting effects. That's what |
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| 14:42 | call them modulatory effects. So if isolate uh acetyl codeine from a synapse |
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| 14:50 | you have that chemical acetyl colon and apply it on the cholinergic for synoptic |
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| 14:56 | . Here, you should get equivalent just like you would stimulate the presynaptic |
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| 15:01 | full of acetyl colon. We have diverse makeshift synopsis that use different |
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| 15:09 | Brain slice is often the model for neural transmission. So brain slice is |
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| 15:17 | in vitro preparation that is kept You can stimulate the pathways, you |
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| 15:23 | stimulate individual neurons, you can record miniature potential. So you can understand |
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| 15:29 | the mini, what's the number of or synopsis have been activated if the |
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| 15:35 | , if there's a big change in UBB. So you can collect electrophysiological |
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| 15:41 | , you can collect and measure chemicals are being released during the stimulation. |
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| 15:47 | this is really how these studies are . It's extremely difficult to try to |
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| 15:52 | chemicals in vivo in the whole Uh And in fact, even measure |
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| 15:58 | from single cells in the whole it's a lot, a lot more |
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| 16:02 | . So most of what we know through from um neurotransmission comes from either |
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| 16:08 | brain slide studies or more primitive organism like snails, for example. And |
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| 16:16 | you remember this, the optogenetics from first section? So now we have |
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| 16:22 | sorts of cool tools where we can the excitability with light. We don't |
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| 16:28 | have to poke electrode into the cell stimulate that cell with an electrode. |
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| 16:32 | can actually stimulate the cells with So channel or adoption depolarize the cells |
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| 16:38 | how adoption can hyperpolarize the cells. know, most of these studies are |
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| 16:43 | done in in vitro. Although optogenetics really nice uh applications in vivo as |
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| 16:52 | to localize our neurotransmitters of interest or degrading enzymes or the synthesizing enzymes. |
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| 17:00 | are two techniques that are very common chemistry and seo hybridization immuno is the |
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| 17:07 | utilizes antibodies that have a visible marker onto this antibody. So how do |
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| 17:16 | make the antibody? So in this , for example, it's a |
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| 17:19 | little rabbit, rabbit gets injected with candidate transmitter from a rat and then |
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| 17:27 | rabbit will have immune reaction to that invader molecule and will produce antibodies. |
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| 17:34 | so you can then withdraw specific you can withdraw the the the |
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| 17:43 | the blood and you can basically isolate antibodies. And now you know that |
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| 17:50 | you injected, for example, acetylcholine injected some other molecule, there might |
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| 17:56 | a reaction to that. So you create an antibody, you mark the |
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| 18:01 | with a visible marker. What do do next? You take a brain |
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| 18:07 | , learn to love the brain take the brain slice. Uh this |
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| 18:12 | slice will have thousands, maybe millions 1000 there. But this one just |
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| 18:19 | to, it's for simplicity purposes to what really happens. So how does |
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| 18:25 | procedure work? So have my antibody a tag is my tissue. I |
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| 18:31 | know which cells contain that neurotransmitter molecule interest and which ones do not. |
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| 18:37 | I'm gonna apply this antibody in the tissue here and I'm gonna apply a |
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| 18:42 | bit of trin X which is a and that detergent is gonna puncture little |
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| 18:49 | in the membrane. And then antibody the visible marker is gonna enter into |
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| 18:55 | cell, enter into this cell and into every cell. Then there's two |
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| 19:01 | the slice. We will enter into of them. And then we |
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| 19:05 | you do that. So this procedure a typically a couple of days long |
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| 19:10 | . Then you put your brain slice the shaker and you apply washes. |
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| 19:18 | you draw the fluid from around the , you discard that fluid, you |
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| 19:22 | fresh fluid and you shake it, it, shake it, shake it |
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| 19:28 | a shaker for six hours and then come back at 10 p.m. you're all |
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| 19:35 | and you suck out the fluid and apply new fluid and put it on |
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| 19:39 | shake overnight. And good thing, don't have to stay there while it's |
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| 19:43 | . So it's just shaking, shaking, shaking during that shaking |
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| 19:48 | If the antibody has something to bind inside the cell, it will stay |
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| 19:54 | stick in that cell or stick to membrane protein. However, if there |
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| 20:00 | nothing that, that antibody binds, just entered through this uh detergent punctured |
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| 20:06 | , there's nothing there that will wash . So now we understand that only |
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| 20:13 | cell in the last expresses a neurotransmitter interest. And this is a simple |
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| 20:19 | that you could have very complicated Again, this is a simplified network |
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| 20:25 | these cells. And you're gonna discover only these cells will be producing stain |
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| 20:35 | the cells are not staining or not , not being marked with that |
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| 20:42 | The really cool thing is that this not really, it can be used |
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| 20:47 | subcellular localization of different molecules and different and different enzymes. It really depends |
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| 20:53 | the resolution that the microscope has or have. The other cool thing is |
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| 21:00 | can do multiple antibodies. You can multiple antibody means the chemistry. So |
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| 21:07 | can tag one antibody green, you tag another antibody red, you can |
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| 21:14 | a third antibody in blue. So will have slightly different wavelengths for this |
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| 21:20 | marker. Now you can apply sometimes even more antibodies and determine which |
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| 21:29 | in the network are staining. Maybe green ones are gaba cells. The |
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| 21:34 | ones are glutamate cells and the blue are expressing serotonin something like that. |
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| 21:41 | , you can build that mosaic of network based on the chemical properties and |
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| 21:49 | staining. So you localize molecules to cells. The second method is in |
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| 21:56 | hybridization and pseudo hybridization, localized synthesis protein or peptide to a cell. |
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| 22:03 | you're detecting Mr and A, you're MRN A. And what you're doing |
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| 22:09 | you have a sequence that you put and that sequence that you put inside |
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| 22:16 | radioactively labeled. And you can order for uh for complementary nucleic acids that |
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| 22:25 | match specific messenger RNAs. And if is this, what I call sophisticated |
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| 22:32 | counterpart in the cell here, the RN A, the synthetic sequence here |
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| 22:40 | we produce as complementary sequence will reveal the cells that have this messenger RN |
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| 22:48 | . So it's not as much of spatial specificity or a subcellular localization. |
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| 22:56 | wouldn't use much of the pseudo divert in that case. But this is |
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| 23:00 | second technique that traces messenger RN A than a molecule. So it tells |
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| 23:06 | something about the expression of, of molecules and specific subtypes of cells, |
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| 23:18 | qualifying conditions. As I said, a chemical that you have isolated such |
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| 23:23 | acetylcholine. And uh there's a lot walking around today like there's no |
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| 23:31 | Now you go to the parking Yeah, that's it. That's what |
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| 23:35 | gonna do it next time. I'm lock the doors, no, |
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| 23:39 | no out, no in and out . But um so qualifying conditions. |
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| 23:47 | we study synoptic mimicry. That means we're going to mimic with this presynaptic |
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| 23:55 | does with this chemical synapse. So chemical synapse is glutamate synapse and when |
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| 24:01 | stimulate, it's going to release glutamate it's going to cause depolarization when I |
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| 24:07 | from the cells. OK. So I'm doing mimicry and I want to |
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| 24:13 | instead of stimulating the fibers, I to, for example, inject do |
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| 24:21 | ionophoresis. And I want to inject onto the dendrite here. And if |
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| 24:27 | supply this piece of dendrite with glutamate the pipette, then I should also |
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| 24:34 | a nice epsp or depolarization in the . So the electrode will measure the |
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| 24:42 | potential and there's an issue here. the issue is that so well, |
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| 25:03 | will work. The issue. The is that this is done and where |
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| 25:10 | the brain sls the best thing since bread instead of sliced bread, |
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| 25:21 | So uh now you have this electrode you have glutamate that you're applying from |
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| 25:27 | electrode right here. The problem is surrounded by fluids. So as you |
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| 25:35 | these glutamate molecules here, there will a higher concentration around here and there's |
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| 25:42 | to be almost like a ring of spreading everywhere. So it's it's a |
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| 25:49 | way to to to mimic but it's very specific spatially, right? You |
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| 25:54 | quite a bit of dilution, you quite a bit of diffusion of that |
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| 25:59 | molecule. So you're not really spatially specific with the synapse, not a |
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| 26:04 | way to really mimic individual synapses. it's kind of a good way to |
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| 26:09 | stimulate the dendrite with a lot of that has glutamate and you're gonna get |
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| 26:14 | response but it's not really going to the synapse. If it's going to |
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| 26:20 | here, it's going to represent synapses and it's going to be here. |
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| 26:24 | gonna represent synopses here and so on so forth. So, in the |
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| 26:30 | decade or so, there's a new that has been developed and that technique |
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| 26:35 | called uncaging neurotransmitters. So, what going on? So here we have |
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| 26:44 | dendrite with dendritic spines and we know this would be a synapse here, |
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| 26:54 | ? And I'm interested, I am interested in getting very specific to this |
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| 27:01 | synopsis because that's, that's what scientists . You know once we know that |
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| 27:06 | is a response and I want one , once I know there's one synapse |
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| 27:10 | I want one molecule. Uh I one vesicle, one visualized one vesicle |
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| 27:14 | visualize one molecule. So going deeper, deeper and understanding it |
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| 27:19 | at these different scales and micro Now what has been invented are the |
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| 27:28 | neurotransmitters. In this case, it's glutamine. What does that mean? |
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| 27:36 | means that glutamate molecule is literally placed the solution here and it's floating around |
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| 27:46 | . But that glutamate molecule is So it has no effect, it |
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| 27:51 | bind to any postsynaptic receptors, it activate any synopsis, it's enclosed in |
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| 27:57 | cage. And the way that this technique works is that you're using typically |
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| 28:06 | powerful microscopy and you're using UV the lasers these days are extremely |
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| 28:17 | So the fastest lasers in the world are femtosecond lasers. But just imagine |
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| 28:23 | you have a nanosecond laser, the and neuron are between nanoseconds and |
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| 28:31 | But really for integration of signals, milliseconds. Got it. So now |
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| 28:37 | you can do is now you can the laser to a specific location around |
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| 28:45 | one synapse and this is your laser and it only on cages, the |
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| 28:53 | in a very small area. So you can do is because these lasers |
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| 28:58 | so fast, you can move them one location to the next within nanoseconds |
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| 29:04 | within a fraction of a millisecond, can boom, boom, boom, |
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| 29:08 | , boom, boom, boom, , boom, boom, boom, |
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| 29:10 | uncaged glutamate allowed 10 different dendritic spikes gives you a lot more of the |
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| 29:18 | specificity and you can do it in dimensions. XYZ because with lasers and |
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| 29:29 | with the typical light microscopy, if looked on the brain slides with a |
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| 29:35 | microscope, you would only penetrate through 100 micrometers slice is typically about 400 |
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| 29:45 | in thickness. So you can really with infrared microscopy, we can only |
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| 29:51 | this top 100 micrometers. But with lasers and with confocal microscopes, you |
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| 30:00 | go deep into the tissue. So can get the Z axis XYZ three |
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| 30:06 | . Whereas the fourth one come So you are unleashing these uh uncaging |
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| 30:14 | unleashing these glutamate molecules over time Now, you can construct four dimensional |
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| 30:22 | of synaptic stimulation and integration by this . And while you're recording from this |
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| 30:28 | , now you can understand a lot than just kind of uh confusing with |
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| 30:34 | that the whole area of. So get a lot more spatial specificity, |
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| 30:39 | specificity and a lot better way to integration pretty cool. So you can |
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| 30:47 | glutamate, you can cage gaba, are also uh putting different chemicals in |
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| 30:52 | cages. Ions can be put in cages also, which is, which |
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| 30:57 | really cool. So the major amino that we'll be talking about is glutamate |
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| 31:04 | Gaba and glutamate right here. As can see, it is almost the |
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| 31:12 | molecule as Java. The only difference glutamate and Java is this carboxy. |
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| 31:19 | there's going to be a key synthesis inhibitory neurons are going to use glutamate |
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| 31:26 | synthesize Gaba. So we'll understand that a little greater details uh throughout the |
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| 31:33 | hour or so. And Gabor oric uh major source of synaptic inhibition in |
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| 31:39 | CNS. So, Glycine was in spinal cord, there's still uh gaba |
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| 31:43 | neurons in the spinal cord. But Gaba is dominating in the CNS and |
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| 31:48 | will serve a function of a cofactor glutamate an MD A receptors. |
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| 31:54 | in glum, a signaling, there three types of ionotropic r majors that |
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| 31:59 | responsible for what we call fast synoptic they are very sensitive detectors of both |
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| 32:08 | and voltage. And once you open these channels by MD A OK. |
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| 32:14 | channels, they will produce quite large and it will differentiate between similar |
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| 32:21 | So some of them will be permeable sodium and potassium and calcium, others |
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| 32:26 | permeable to sodium and potassium. The major subtypes are AMPA and MB A |
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| 32:32 | Kate AMPA has its own agonist, and M VA and M VA |
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| 32:37 | Kate glutamate is the endogenous molecule that an agonist to all three of |
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| 32:44 | These are the chemicals AMPA and MD and Kate, there are specific agonist |
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| 32:50 | either AMPA MD A or Kate So what is the difference between these |
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| 32:57 | receptors? First of all, they distinct agonists as we spoke and they |
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| 33:03 | distinct antagonists. So is blocked by and an ND A is blocked by |
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| 33:11 | PD or A P five. And will come back in the picture uh |
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| 33:16 | the score section. So there are gated channels and there are two sometimes |
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| 33:24 | and Kate is almost considered the same . Although they're different, they can |
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| 33:29 | distinguished chemically by agonist amper versus Kate kinetically. So their properties of these |
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| 33:38 | channels are similar. So a lot times you will have an MD A |
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| 33:44 | and Kate will group together or this will be an MD A versus |
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| 33:49 | an ND A glutamate receptors. And there is release of glutamate and there's |
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| 33:56 | synapse, glutamate will bind to alpha MD A receptors and alper receptor is |
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| 34:02 | Ln it. So as soon as binds to amper receptor, it produces |
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| 34:11 | in the form of EPSP. And early phase of this EPSP is mediated |
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| 34:21 | alpha. But an MD A receptor both an MD A receptor is Ln |
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| 34:30 | . So you need a Ln and also voltage gated. So you need |
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| 34:34 | change in voltage in order for this channel to open. The other difference |
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| 34:40 | these that are illustrated is that with the exception of some uh types |
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| 34:46 | receptors are mostly referable to sodium and . And an MD A serves as |
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| 34:53 | significant influx of calcium, an influx calcium through an MD A receptor. |
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| 34:58 | call that posy ally calcium is not an ion, it actually doesn't contribute |
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| 35:03 | much to a change in the membrane . The influx of that calcium posy |
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| 35:10 | associated with change of simplistic levels is with changes in posy cellular signaling because |
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| 35:19 | is also a secondary messenger in the , not just an ion. |
|
| 35:27 | So what why is this channel doesn't right away? And how is it |
|
| 35:33 | by voltage? So this channel doesn't right away. This channel which is |
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| 35:39 | MD A receptor channel is responsible for late phase of the EPSB. And |
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| 35:50 | reason for it is that if mate to immuno the channel, it's not |
|
| 35:55 | because it is actually plugged up with . So there's at least one if |
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| 36:01 | two magnesium ions that are bound inside inner lumen of this channel and are |
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| 36:10 | blocking the shell. So how do remove this magnesium? The only way |
|
| 36:16 | remove this magnesium is with a change voltage when you have depolarization from minus |
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| 36:25 | to minus 3030 millivolts or from minus to minus 55 to minus 50. |
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| 36:33 | alleviates magnesium lo so an MD A is in addition to Len gated, |
|
| 36:41 | also voltage dependent channel. It is to as coincident detector because it coincidentally |
|
| 36:50 | presynaptic glutamate release and postsynaptic depolarization of number. How does this depolarization of |
|
| 36:58 | number? It happened through ample receptions soon as Guam A gets released ample |
|
| 37:04 | open, they cause that initial depolarization minus 55 minus 50. Then N |
|
| 37:11 | A kicks in and now they're working to drive the number and potential to |
|
| 37:16 | threshold values because it is a coincident . That means it's detecting the presynaptic |
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| 37:25 | release and postsynaptic depolarization because it is coincidence detector. It plays a very |
|
| 37:31 | role in synaptic plasticity. It also a significant role in synaptic plasticity because |
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| 37:37 | is a source of a significant calcium inside the cells and impairments and an |
|
| 37:47 | A receptor are associated with many neurological and also mental disorders. It's also |
|
| 37:55 | target, a target for a lot uh pharmacological manipulations. Um And |
|
| 38:05 | one of the things that is shown , for example, is, do |
|
| 38:08 | remember voltage clamp, voltage clamp allows to clamp a number of potential you're |
|
| 38:14 | control, you're no longer following the mene potential. You're commanding and you're |
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| 38:20 | that number and potential. So, this example, what we're seeing is |
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| 38:25 | looking just at an MD A How can you be sure that you're |
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| 38:29 | looking at an MD A currents? there is a and an MD A |
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| 38:34 | , there's two receptors and you're stimulating cell with glutamate. How can you |
|
| 38:41 | you're only measuring an MD A What would you do? So |
|
| 38:55 | but glutamate is there. So al going to be open? Am I |
|
| 38:59 | just activate an MD A? It's good, it's a good thinking change |
|
| 39:05 | voltage. So you do polarizing. you're acting like, but now you're |
|
| 39:10 | seeing al activity you should block, . So agonist antagonist, right? |
|
| 39:17 | you block er receptor with CNQX, no current effect. Now you're releasing |
|
| 39:25 | , you're releasing glutamate and you're in concentration on magnesium 1.2 millimolar physiological concentration |
|
| 39:35 | magnes. You have a voltage plan minus 60 ample is blocked, you |
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| 39:42 | Liam minus 60 there's no an MD current minus 30 there is some in |
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| 39:50 | a current. So that's your change voltage that you mentioned that opens an |
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| 39:54 | a current. But now, you , it's only an MD a current |
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| 39:57 | your UT is blocked. Now you're the potential of whoops, there's nothing |
|
| 40:03 | zero. So recall that we discussed concept of equilibrium potential and we said |
|
| 40:13 | equilibrium potential also calculated for single So we talked about equilibrium potentials of |
|
| 40:22 | , equilibrium potentials for sodium calcium or and what happens with the equilibrium potential |
|
| 40:32 | these ions. So for example, we looked at the traces or inward |
|
| 40:37 | sodium, if you depolarize it, you depolarize it more, you get |
|
| 40:44 | in towards sodium. But if you the potential at some point, the |
|
| 40:49 | fluxes in a different direction. And this defined as equilibrium potential or sodium |
|
| 40:57 | inward currents. And if you cross equilibrium potential, the current fluxes in |
|
| 41:01 | different direction. Now, for an A and amper receptors, we cannot |
|
| 41:08 | equilibrium potential because equilibrium potentials are calculated just one ion sodium or potassium. |
|
| 41:17 | these channels are permeable to sodium potassium calcium. On top of that, |
|
| 41:23 | , the equilibrium potential for potassium is 80 millivolts or sodium positive 62 |
|
| 41:32 | And so what this reflects is sort like and reflects almost the combination of |
|
| 41:37 | potentials for sodium and potassium a little biased toward sodium. And also because |
|
| 41:44 | the calcium functioning through it to the potential, this is what we call |
|
| 41:49 | reversal cap, we call this reversal with equilibrium potentials because the ionic current |
|
| 41:56 | specific to sodium or potassium will reverse potential. But for an MD A |
|
| 42:03 | alpha receptors, we call it reversal because it's several ions that we're essentially |
|
| 42:10 | where this is an MD A receptor reverses. So reversal potential for an |
|
| 42:17 | A is zero or am it's And for acetylcholine receptors or employ |
|
| 42:32 | they are all equal zero millivolt reversal . And if you clamp your membrane |
|
| 42:42 | more positive potentials here, now you're that the currents have reversed and that |
|
| 42:48 | could flow pretty well once the neuron is depolarized. And in this |
|
| 42:58 | we removed magnesium from the extracellular So here it's regular magnesium like physiological |
|
| 43:07 | . So you'd expect that magnesium block the channel, then you would expect |
|
| 43:12 | to see any currents here for an A and the blockade or absence of |
|
| 43:19 | . But here you remove magnesium from solution altogether. And now it shows |
|
| 43:26 | that if you apply glutamate in the of magnesium and MD A receptors will |
|
| 43:32 | . So with this, with this showed that with this traces demonstrated, |
|
| 43:38 | of all the reversal potential for an A, there will also be the |
|
| 43:42 | reversal potential value for alpha and the one for potentials also. And it |
|
| 43:49 | essentially proves that it is magnesium that an MD a receptor and that you |
|
| 43:55 | need both lunate and depolarization or glutamate no magnesium if you want to have |
|
| 44:04 | channel open. But these hyperpolarize right? Any questions about anything so |
|
| 44:15 | ? Ok. So an MD A here and not an MD A |
|
| 44:25 | There's another difference here is that not MD A which is an ample kate |
|
| 44:31 | is an agonist and binding of glutamate enough to effectively open the ample kate |
|
| 44:37 | channels. Glycine. However, in spinal cord, it was a major |
|
| 44:44 | , neurotransmitter in the CNN gly seen a cofactor to an NBA receptor. |
|
| 44:51 | means that if glutamate is only the an MD A receptor will function |
|
| 44:56 | it's glutamate and depolarization, but it function most effectively to its maximal |
|
| 45:04 | If there is glycine as a co that is present and different molecules glutamate |
|
| 45:15 | magnesium, it also has a binding for zinc. Different molecules will bind |
|
| 45:22 | different parts of this channel. Some will compete for the same crevice for |
|
| 45:29 | same three dimensional amino acid sequence to in like a key into the |
|
| 45:36 | And that's exactly what this illustrates. they have their own distinct locks. |
|
| 45:41 | can think of these receptor channels as , but instead of having one handle |
|
| 45:47 | one lock, it has multiple one of them is sort of like |
|
| 45:53 | master lock, it can open the . But the other one glycine is |
|
| 45:59 | if you turn another lock and it fully open the door, swing it |
|
| 46:04 | . And then there's another call for to fit in that door and that |
|
| 46:10 | shuts the door. It's like fits the lock. A lot of uh |
|
| 46:16 | agents will be targeting uh an MD receptor. So we mentioned very briefly |
|
| 46:22 | we talked about acetyl cholinesterase inhibitors and disease. I mentioned that there is |
|
| 46:30 | memantine, a drug called memantine that open an MD A receptors that is |
|
| 46:36 | used as a medication for Alzheimer's but also a lot of illicit illegal |
|
| 46:43 | recreational drugs will be targeting the same . So and then the A receptor |
|
| 46:50 | also a target of PC P. this is why I always stress, |
|
| 46:56 | example, natural molecules or endogenous molecules synthetic molecules of synthetic drugs. From |
|
| 47:05 | we talk about ph ecological perspective, pharmacological companies, they do these things |
|
| 47:13 | studies of safety and efficacy. In , maybe we already have this |
|
| 47:19 | But in a lot of times, don't know exactly the mechanisms of action |
|
| 47:25 | a given drug. So that's not point of the pharmaceutical companies. They |
|
| 47:31 | to know how the drugs act, want to know the basic mechanisms of |
|
| 47:35 | and cellular mechanisms of action. But does your doctor really care about? |
|
| 47:40 | does the Pharma company really care about they have a molecule that's really effective |
|
| 47:49 | controlling disease, X disease, Y Z. So if you have a |
|
| 47:56 | that stops nausea, do you really for the mechanism of action if it's |
|
| 48:00 | and effective and it stops nausea? if there is five mechanisms of |
|
| 48:06 | And then two years later, there's mechanisms of action for that molecule. |
|
| 48:10 | that mean that drug all of a disappears? No, because it is |
|
| 48:14 | safe and ef applications. So it's scientists, the basic scientists and basic |
|
| 48:22 | that really care about the mechanisms of . What happens when this molecule |
|
| 48:28 | Is there cyclic MP goes to this and that goes inside the cell. |
|
| 48:32 | gonna spend five years chasing a molecule the cell. You know, for |
|
| 48:37 | companies that want to deliver safe and drugs and think about this, if |
|
| 48:42 | needed to know every mechanism of action every molecule and every dog in the |
|
| 48:49 | , that would take forever just to a drug that is affected. It |
|
| 48:54 | takes 10 years to deliver a neuro , 10 years and about a billion |
|
| 49:01 | , 95% will fail at stage three trials. So only 5% or so |
|
| 49:09 | the drugs that go from rats. two clinical trials to humans, stage |
|
| 49:15 | clinical trials because we're not quite like and we don't do things same |
|
| 49:20 | Exactly. But these are the systems we rely on and the models that |
|
| 49:24 | rely on to put drugs later into . And so there's a safe and |
|
| 49:30 | drugs, a lot of endogenous a lot of natural substances in |
|
| 49:35 | a lot of things that are pharma , they will mine to substances and |
|
| 49:40 | will leave them. So there will reversible agonists or reversible antagonists. And |
|
| 49:45 | problem with a lot of synthetic stuff there's a lot of synthetic stuff and |
|
| 49:49 | widely available in every gas station. can buy synthetic cannabinoids, delta eight |
|
| 49:55 | 10 HHCTHCP. It's all synthetic It means that they have, they |
|
| 50:02 | come from natural substances that are made chemicals in the lab, putting two |
|
| 50:06 | together. And we don't know a about when we synthesize molecules that have |
|
| 50:14 | , have not been researched for safety efficacy studies. A lot of them |
|
| 50:18 | out to be really potent agonists. if a natural molecule as a small |
|
| 50:26 | affinity and binds to that receptor and dissociates a synthetic agent may bind to |
|
| 50:34 | receptor and stick to it for For example, they have these irreversible |
|
| 50:42 | of sticking to the receptor proteins and channels. In this case. And |
|
| 50:50 | consequence of, for example, using CPA single time, it's an intoxicating |
|
| 50:56 | can actually set up a chronic chain events can upset this N MD A |
|
| 51:03 | and MD A receptor function for a time. So single use of these |
|
| 51:08 | can use can lead to acute schizophrenia by development of chronic psychosis symptoms. |
|
| 51:16 | , whatever is synthetic out there. the problem with synthetics is that they're |
|
| 51:22 | to, to make in the There's a lot of different chemicals and |
|
| 51:27 | variations, different carbons and tags, can add on molecules to make them |
|
| 51:34 | potent to cost people, higher really high highs and hallucinate hallucinations. |
|
| 51:43 | then yet there are other substances like causing drugs that have therapeutic and positive |
|
| 51:52 | too. And we'll talk a little about that next lecture. So, |
|
| 51:57 | life cycle, glutamate gets again released neurons. It will target ionotropic |
|
| 52:06 | esophagus, plus synoptic metabotropic glutamate receptor . Once it gets released in the |
|
| 52:12 | will get transported through glutamate transporters back neuron, it will get uploaded into |
|
| 52:19 | with glutamate transporters and it will get in the synapse. Well, what |
|
| 52:31 | happens? Remember the tripartite synopsis is cell right here. This is racy |
|
| 52:39 | have their own glutamate transporters. So will slurp up glutamate through the glutamate |
|
| 52:48 | . They will use glutamine synthetase to glutamine. They will transport this glutamine |
|
| 52:59 | and neurons will transport the glutamine in preoptic terminals. They will turn this |
|
| 53:07 | into glutamate using a TP and glutamine that glutamate will get loaded up into |
|
| 53:15 | vasic call and then release pre So, glia has a very significant |
|
| 53:25 | in regulating the amount of available glutamate neurons and also gaba it's not unique |
|
| 53:32 | glutamate. The same happens with Leo will slurp up Gaba as well |
|
| 53:38 | reprocess it and I'll tell you about in a second. Now, you |
|
| 53:44 | also understand what, what would happen the system if my astrocyte glutamate transporter |
|
| 53:52 | not working. What do you think happen in this and that there will |
|
| 54:01 | more glutamate here because it's not being , it's not being cycled. If |
|
| 54:08 | is more glutamate here, what happens the cells immediately? The sauce will |
|
| 54:15 | too much glutamate. But after some , there might be a decrease in |
|
| 54:21 | because part of the glutamate synthesis is through glutamine cycle, you know. |
|
| 54:28 | , all right. So I forgot copy this slide for you. But |
|
| 54:38 | would like to tell you that the thing is happening with, with, |
|
| 54:43 | gaba cycling. And uh let me , maybe it's a good time to |
|
| 54:49 | it now or maybe I'll come back it and do it. Yeah, |
|
| 54:51 | do it next lecture. So we'll finish up, continue on the |
|
| 54:56 | So in addition to the ND A that are inotropic and MD, a |
|
| 55:03 | source of calcium, you also have groups of metabotropic glutamate receptors. So |
|
| 55:07 | first one is oy and then group and group three are three synoptic. |
|
| 55:14 | it's the same molecule. But remember the fact of that molecule depends on |
|
| 55:19 | type of the receptor that molecule binds where it is located. Guess what |
|
| 55:26 | it's located pre cynically, is it really interfere with integration at the level |
|
| 55:31 | the SOMA or is it going to be affecting more of the exocytosis and |
|
| 55:37 | release? Yes, indeed. It's right here, presynaptic. So its |
|
| 55:43 | , the fact that these um Glu two and then GLU R three groups |
|
| 55:47 | be to control the release of its own release, its own glutamate |
|
| 55:54 | . So it's like almost like a feedback system. It can also uh |
|
| 56:00 | the exocytosis altogether. So that's why a negative feedback system. And what |
|
| 56:06 | it doing poop? Is that going control neurotransmitter muscle release? No, |
|
| 56:12 | likely it's going to be affecting some cellular cascade, cellular messengers and modulating |
|
| 56:20 | overall cellular molecular activity inside those Yeah. Is it just the astrocyte |
|
| 56:26 | regulates another variability or is there other cells? No, it's mostly Asy |
|
| 56:34 | . Yeah, they are part of tripartite synapse and that's where you have |
|
| 56:39 | glutamate transporters, you have them on . So I don't know if anybody |
|
| 56:43 | found them on Myco glia, not my knowledge. So, yeah, |
|
| 56:50 | they're in ostracized and now we're moving to Gaba. So remember that when |
|
| 56:58 | stimulate glutamate synopsis, you get Yeah. So if you have a |
|
| 57:12 | and it's epsp. Hm. If have Gaba, it's IP SB it's |
|
| 57:28 | to be hyper polarization if you have , this is sodium coming in |
|
| 57:36 | And this is potassium coming out through A and MD A receptor channels similar |
|
| 57:42 | we saw an action potential. But we're talking about Epsp and they're not |
|
| 57:48 | gated channels except for an MD A , partly voltage gated. Here you |
|
| 57:53 | influx of chloride for IP SP. when Gaba binds to, in this |
|
| 58:00 | , ionotropic Gaba receptor channel, Gaba cause influx of chloride. Gaba is |
|
| 58:07 | agonist. An influx of chloride will the inhibition. Gama media's most synaptic |
|
| 58:19 | in CNS. Last media's non Gaba inhibition which is mostly in the spinal |
|
| 58:27 | . Other molecules also just like an A receptor. Any one of these |
|
| 58:33 | in Gaba A receptor channel, it's huge target as well for pharmacological |
|
| 58:41 | Benzodiazepines arbitrates neuro steroids, ethanol, all agonists. All of these molecules |
|
| 58:54 | increase the levels of inhibition in the . Remember that you have certain amount |
|
| 59:00 | excitation. Certain amount of inhibitions are bombarded, depolarize, hyperpolarize, depolarized |
|
| 59:06 | and action potential. Go back to memory, hyperpolarize, depolarized, depolarize |
|
| 59:11 | fire and action potential. It goes and on and on this fluctuation. |
|
| 59:15 | it's happening within a certain dynamic right? You don't have your me |
|
| 59:21 | potential fluctuating positive 200 millivolts and sitting for two hours and then coming down |
|
| 59:26 | negative 200 millivolts for two hours. death within minutes of this village but |
|
| 59:32 | all of these substances increase inhibition which is alcohol. This is my |
|
| 59:40 | because you can talk about this and , almost everybody can relate to it |
|
| 59:45 | the sense that if you don't uh , you have observed this behavior before |
|
| 59:52 | when the person has one or two . But you know, pretty civilized |
|
| 59:57 | of wine and the lesser through uh binds to Gaba and it increases in |
|
| 60:05 | condition. So the person is sitting , you know, swing their |
|
| 60:08 | pretty chill reading a book. 10 later. What's happening? Shirt is |
|
| 60:20 | off dancing on the table. No , complete this inhibition. And you |
|
| 60:28 | literally desensitize these uh receptor channels. little bit of alcohol, you increase |
|
| 60:34 | addition to give it a lot of or ethanol is, ah, it's |
|
| 60:38 | , oh, I can't do anything . So there's no inhibition. The |
|
| 60:45 | are really strong sedatives, very uh are anti seizure medications, epilepsy, |
|
| 60:54 | or epilepsy, medications, barbiturates and will have equivalent of the fact that |
|
| 61:00 | have a doctor also. Uh you'll rap songs with Benzo thats Benzo |
|
| 61:06 | So it's referring to Benzodiazepines and it a medication. Uh you know, |
|
| 61:14 | people get into other people's uh medicine sometimes for no good reasons. All |
|
| 61:22 | . So this is the story of , increasing inhibition. But what else |
|
| 61:27 | Gaba do? Gaba also binds to B receptor and it's showing like whoa |
|
| 61:34 | is really significant what happens to Gaba receptor. So, poop the Gaba |
|
| 61:39 | receptor will interact with potassium channel and potassium channel positive charge leaving is gonna |
|
| 61:50 | second potential. This is Gaba A there early depolarization and this is Gaba |
|
| 62:00 | which is a late uh I'm uh hyper polarization and condition. Uh |
|
| 62:06 | that's because with some delay, you activate potassium channel and potassium leaving. |
|
| 62:13 | this is fluoride coming in and this potassium leaving potassium leaving will cause further |
|
| 62:20 | polarization inside the cell. Pre cynically B. Oh Really cool presyn Gaba |
|
| 62:30 | is similar to the metabotropic glutamate It will block its own exocytosis if |
|
| 62:37 | an auto receptor. So it will exocytosis because it will block influx of |
|
| 62:46 | through coptic. It also has this effect on an MD A receptor. |
|
| 62:54 | uh actually activation of an MD A . Gabba A will have its own |
|
| 63:02 | muscle. All Gabba B, Baclofen will be bicuculline and facin for Gabba |
|
| 63:10 | and Gabba B respectively. And this typically what we would see in neuronal |
|
| 63:21 | most of the time. The way experiments are done where in the brain |
|
| 63:30 | , most of the time, the experiments are done is that you place |
|
| 63:34 | the stimulating electrode and that stimulating electrode sizable. OK. And you're stimulating |
|
| 63:41 | number of fibers. So there's going be potentially hundreds of axons underneath here |
|
| 63:49 | and you're recording from your solid interest , this little cell in your |
|
| 63:55 | So when you stimulate these fibers and is what we observed. And this |
|
| 64:00 | part of my graduate work. We looking at the development from the retina |
|
| 64:06 | the thalamus of the visual inputs where would stimulate these fibers, the |
|
| 64:11 | the recording electrode would, this is stimulation right here with a little bit |
|
| 64:17 | synaptic chemical delay, we would see E TSB and then with a little |
|
| 64:23 | more delay, this EPSP is But yeah, but hey, and |
|
| 64:36 | B IP sp. OK. So does that tell you that tells you |
|
| 64:43 | you're trying to stimulate this neuron and neuron produces an EPSB. But immediately |
|
| 64:51 | is also Gaba release in this bundle fibers and you get inhibition. So |
|
| 64:57 | Gaba and Gaba B is keeping the of this Epsp in check sort of |
|
| 65:04 | the reins on the horse. It's as soon as it goes up |
|
| 65:07 | there's also inhibitory activation and goes pull . We're going back to hyperpolarize and |
|
| 65:15 | . A first followed by activation with tropic Gaba B later, right? |
|
| 65:21 | we have this significant hyper polarization and why we say that inhibition sculpts, |
|
| 65:30 | . It is like a sculptor. if you take away inhibition in this |
|
| 65:35 | , you apply by Kulin. This my Kulin which is uh antagonist or |
|
| 65:43 | A. OK. So you block A. This is what happens. |
|
| 65:52 | no sculpting. This is bicuculline traces excited response becomes massive, almost |
|
| 66:01 | And that tells you how precise his range is how you always have to |
|
| 66:08 | excitation inhibition. In order to have signaling. If you start losing |
|
| 66:14 | you start getting what we call hyper in the brain. Hyperexcitability is not |
|
| 66:21 | very good thing because it will open a lot of anor it will cause |
|
| 66:27 | of calcium and can lead to what call glutamate. And calcium like |
|
| 66:33 | Too much glutamate and too much calcium become toxic to the, to, |
|
| 66:38 | , to themselves, to neurons and essentially lead to cell death eventually. |
|
| 66:47 | . So this diagram puts everything together we are out of time. And |
|
| 66:53 | think that maybe if you guys uh a little bit of ethanol this |
|
| 66:58 | you will think about gamma um in uh before you reach the disinhibition |
|
| 67:08 | uh or C to aid the adenosine or, or block the R. |
|
| 67:14 | think about these things, I'm gonna those three lectures. So if you |
|
| 67:19 | to review them over the weekend, can and I'll leave the slide for |
|
| 67:23 | week because I think it is going be a good refresher of everything we've |
|
| 67:28 | today before we move into the final of neural transmission. Thank you very |
|
| 67:34 | all for being here. |
|
