Marina Picciotto, PhD, Acetylcholine signaling in hippocampus: implications for anxiety and depression

December 01, 2020

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Charles B. G. Murphy Professor of Psychiatry and Professor in the Child Study Center, of Neuroscience and of Pharmacology; Interim Director Division of Molecular Psychiatry, Psychiatry; Deputy Chair for Basic Science Research, Dept. of Psychiatry; Deputy Director, Kavli Institute for Neuroscience; Co-Director, Neuroscience Research Training Program, Yale Department of Psychiatry

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00:00Hi everyone, welcome to the Yale Psychiatry
00:03and Child Study center datablitz.
00:06I'm happy to share with you some of
00:08my work on Astral cooling signaling
00:11and how it affects behaviors related
00:13to stress in mice and how that's
00:16translatable to human subjects.
00:19I'm going to share my screen now
00:21and show you some of the work
00:23that's going on in my lab.
00:25Our laboratory is interested in
00:26the receptors for nicotine in the
00:29brain and how those affect behaviors
00:31in typical situations and also
00:33related to psychiatric illness.
00:35One thing we know is that smoking
00:37anxiety and depression are highly
00:39correlated in human subjects.
00:41We know that major depressive
00:43disorder is a chronic, debilitating,
00:45relapsing illness.
00:46The huge cost to the individual
00:48to families and to society,
00:50and there's a bidirectional
00:51relationship with smoking.
00:53People who are depressed or
00:55more likely to smoke.
00:56And people who smoke are
00:58more likely to be depressed,
01:00so about 40 to 60% of patients with
01:02depression smoke versus now much less
01:04than 20% of the general population.
01:07So can we identify the neurobiological
01:10mechanisms underlying this comorbidity?
01:12Where should tell you that the primary
01:15targets for nicotine in the brain or
01:17the nicotinic acetylcholine receptors?
01:19These are a family of receptors
01:20that respond to the endogenous
01:22neurotransmitter acetal choline and
01:24there are two families of Astle calling
01:26receptors nicotinic and muscarinic.
01:28And I'm going to tell you about the
01:31relationship between the nicotinic
01:32receptors and Astle calling signaling.
01:34Today we have projects and muscarinic
01:36receptors as well as still calling
01:38neurons in the brain project very widely.
01:41Their cell bodies in the basil.
01:43Or bring complex and in the brainstem
01:46project pretty much everywhere in the brain,
01:48and in addition number of studies have shown,
01:51and here's one from the 1990s.
01:53That stress induces us to cooling
01:56release in many different brain areas.
01:58And so you can see here that
02:00using microdialysis, restraint,
02:02stress results in elevations of Astle
02:04calling signaling throughout the brain,
02:06including the hippocampus for as long
02:09as that restraint stress is applied.
02:12So what we've done is to use biochemical
02:14and molecular biological techniques
02:16to manipulate Astle calling signaling,
02:18and in this experiment from 2013,
02:21what we did was to block Astle
02:23calling breakdown throughout the
02:25brain and body by using the
02:28pharmacological antagonist Astle.
02:29Colon especial cholinesterase antagonist,
02:30physostigmine,
02:31and what we saw was that there was
02:34more immobility in this one test.
02:36We used many,
02:38but I'm showing you the tail
02:40suspension here as an example.
02:43You got more reactivity to stress
02:45as we increase the dose of this
02:47Astle cholinesterase blocker,
02:49which means as overall levels
02:51of actual calling increased,
02:52we got more stress related behaviors.
02:55These could be reversed by blockers
02:57of either nicotinic, muscarinic,
02:58or both families of astral choline
03:01receptors and that makes sense
03:03because that means that this increase
03:05in national calling resulted in
03:07behaviors that were sensitive
03:09to colon estel choline receptor
03:10blockers and you can see that.
03:13The behavior actually
03:14went down below baseline,
03:16with these blockers,
03:17suggesting that there's hostile
03:19calling tone that that is responsible
03:21for the baseline immobility.
03:23In this in this test.
03:26And this was also reversible by
03:28giving the SSRI fluoxetine Prozac.
03:30So first here's the increase in
03:32immobility that we see when we increase
03:35Estel coin signaling and that can also
03:37be reversed by this antidepressant
03:40that's widely prescribed in humans,
03:42suggesting that the model that we're
03:44looking at is more broadly relevant
03:46to depression related behaviors
03:48than just to the cholinergic system.
03:51And this is related to experiments
03:53done back in the 70s and 80s.
03:56By David Chrzanowski and his colleagues
03:58who gave the same drug Pfizer
04:00stigma to humans and saw depressive
04:02symptomatology even in human subjects,
04:04had never had a history of depression,
04:06suggesting that what we're looking
04:08at in mice is translatable to humans.
04:10Where in the brain is this
04:12happening where we were able to
04:14use molecular genetics to block,
04:16to downregulate Astle?
04:17Cholinesterase activity only locally
04:18in the hippocampus?
04:19I won't walk through all of this
04:21for the met up for reasons of time,
04:24but what you can see is that when
04:27we knocked down.
04:28Ask for cholinesterase only in
04:30the hippocampus.
04:31We see the same phenotype that we
04:33see when we pharmacologically block
04:34it everywhere and we can rescue
04:37that by expressing a human Estel
04:40cholinesterase transcript that can't
04:42be knocked down in here I'm showing
04:45you three different paradigms,
04:46both 2 models of immobility but one
04:49model of amorphism or ethologically.
04:51Relevant stressors.
04:52Social defeat stress where we give
04:55a subthreshold social defeat and
04:57now we see a very potent avoidance.
04:59After that social defeat by knocking
05:02down Astral cholinesterase only
05:04in the hippocampus.
05:05So I've shown you some data from our
05:08historical experiments showing the
05:10increasing Astle calling signaling
05:12in hippocampus by decreasing its
05:14breakdown increases stress related
05:15behaviors in mice to changes in
05:18Astral calling signaling than
05:19occur and oppressed human subjects.
05:21I'm going to show you some data
05:23that was gathered by our clinical
05:26colleagues in which we collaborated
05:28and it was using a tracer of this
05:31nicotinic acetylcholine receptor
05:32that was competitive for Astle
05:35choline at its binding site.
05:37And now what would we expect to see
05:39if human subjects who are depressed
05:41have more Astle calling signaling
05:43when we use this competitive tracer,
05:45well,
05:45there's going to be some astral
05:47calling in the brain that binds
05:49to these nicotinic receptors,
05:50and so when that radiotracers introduced,
05:52there are going to be others
05:54binding sites that it can bind to,
05:57and we will see changes in receptor
05:59availability when this tracer
06:00is administered.
06:01How about in patients or in subjects
06:03who might have elevated Astle calling,
06:05signaling they'll have more
06:06occupancy of their receptors.
06:08And now when the tracers introduced,
06:10they'll be fewer binding sites,
06:11and that's exactly what we see in the
06:14brains of depressed human subjects.
06:16So here's just an example.
06:17Human subject has to be a non
06:19smoker because This site is also
06:22competitive with nicotine.
06:23You can see the heat map of binding and
06:25that binding is decreased in a depressed
06:28and actively depressed nonsmoker.
06:29And when we do this in a large group
06:32of human subjects you can see that
06:34that decrease in availability is
06:36obvious throughout many cortical areas,
06:38but also through deeper.
06:40Brain structures.
06:41This could also have been due
06:43to decreases in the receptor
06:45itself and not to competition,
06:47and so that we were able to do
06:49was to take postmortem human brain
06:51tissue washout Astle calling and
06:53show that there is absolutely no
06:56change in the receptor number and
06:58what our colleague Irene Esther List
07:00was able to do was to reproduce the
07:03challenge study that Janowsky did
07:05and show that in the same person
07:07who at baseline had a relatively
07:09high level of Astle choline binding.
07:11Sites available after five cystic
07:13mean administration.
07:14The number of those bindings,
07:16the availability of those binding
07:17sites goes down just as you would
07:20expect with a competitive tracer,
07:21and this is allowed us to go back and
07:24forth between mouse models in human
07:26subjects and test our hypothesis
07:27generated from these pharmacological
07:29and molecular biology experiments
07:31in human subjects.
07:32So now can we use this mass model
07:34of an anxiety and depression like
07:36state to identify sites and receptors
07:38of cholinergic signaling?
07:40Important for these behaviors?
07:41I'm going to show you just a couple
07:44slides of ongoing experiments that
07:45are not yet published to show you
07:47a flavor of what we're doing.
07:48First of all,
07:50here's a diagram of the cholinergic
07:52innervation of the hippocampus,
07:54in particular the medial septum
07:56provides a large projection to
07:58the hippocampus.
07:59And what we've been able to do is to
08:02use designer receptors exclusively
08:04access activated by designer drugs,
08:07dreads that are targeted.
08:09Only two Astle choline neurons by
08:12infusing them into mice in which a
08:14recombinase is driven by the promoter
08:17for choline acetyl transferase,
08:19the synthetic enzyme for astral cooling,
08:22and to then direct these dreads
08:25locali to the hippocampus by
08:27infusing them into the hippocampus.
08:29Packaged in a virus that infects
08:32terminals of neurons and goes
08:33back to their cell bodies.
08:35So what does that look like?
08:37We infuse the retrograde dread
08:39here into the hippocampus.
08:40It goes back to the medial septum,
08:43and now when we give the chemical
08:45activator of this dread,
08:46we can exclusively activate this
08:48pathway in the brain and ask,
08:50does that also change behavior
08:52in ways relevant distress?
08:53And that's exactly what we see in a
08:56number of tests that I'm diagramming here.
08:59The light dark box,
09:00which is sensitive to anxiolytic
09:02medications that.
09:02Forced women tail suspension tests that
09:05are sensitive to acute administration
09:07of anti depressants and the social
09:09defeat test which is sensitive to
09:12chronic administration of antidepressants.
09:14All show changes in behavior
09:16when this dread activates the
09:18hippocampus that choline the astral.
09:20Colleen inputs to the big campus
09:22that are relevant that are consistent
09:25with the idea that increased
09:27hippocampal Estel cooling system
09:29signaling increases behaviors.
09:31Relevant distress, and we've now done.
09:33A number of experiments to show that this is
09:37actually mediated by Astle choline, not Co.
09:41Released neurotransmitters because if we
09:43locally infused and nicotinic antagonist
09:45mecamylamine into the hippocampus,
09:47we can reverse these effects of the dread.
09:51So here's the control plus
09:54Mecamylamine compared to the Dread
09:56activation in three different tests.
09:59So that means that.
10:01We can actually increase Astle calling
10:03signaling using this thread and reverse it
10:06using a nicotinic acetylcholine antagonist.
10:08So we have a number of studies that
10:10are dissecting the signaling of
10:12Astle calling in brain structures
10:14in addition to the hippocampus.
10:16For example, the amygdala,
10:18the prefrontal cortex,
10:19and then locally the basil forebrain
10:21complex where the cell bodies of
10:23those Astle calling neurons reside,
10:25and altogether what we are building
10:28is an integrated picture of how Astle
10:30calling signaling sets the threshold
10:32for behaviors relevant to stress.
10:34In mice and how we might translate
10:36those to understanding how I still
10:38calling signaling is affecting
10:40behavior in depressed human subjects,
10:41I want to thank the lab members
10:44who are contributing to this work.
10:46Particularly young men are a
10:47research scientist in the lab who's
10:49worked with me for many years.
10:51Thank you everybody for listening.
10:53I really enjoyed presenting
10:54this glimpse of the work.
10:56Please contact me if you'd
10:58like more information about
10:59the work going on in my lap.
11:02Bye bye.