The Enteric Nervous System: The Brain in the Gut, 2015 Refresher Course Pt. 4

and with that I’d like to introduce our final speaker last but certainly not least dr. MA who is from the University of Vermont and will be talking to us today about the little brain in the gut although correct me if I’m wrong I do believe the big brain also will make a guest appearance at some point so with that dr. MA thank you very much I’m pleased to be here to preach the gospel of gut neurobiology this morning and some of the things that I’ll try to cover today include just a just a word or two about the organization of the autonomic nervous system and how I try to introduce it to medical and physical therapy students when I’m covering these topics and then we’ll talk about the organization of parasympathetic and sympathetic innervation of the gut and how long reflexes regulate upper GI function but shorter intrinsic reflexes are largely responsible for controlling activity in the intestines then well I’ll show you an example of an experiment demonstrating very clearly how the central nervous system can override intestinal function even though that intestinal function is controlled locally and then finally we’ll talk about a couple of hot topics in enteric neurobiology so in terms of organization of this system as you know the peripheral nervous system is divided into somatic and autonomic and typically we see the autonomic nervous system being divided into parasympathetic and sympathetic divisions hopefully by the time I’m done today you’ll be convinced that there should be a third box they’re labeled enteric division so the autonomic nervous system differs from that somatic division in many ways but one of the things that I try to emphasize when I’m teaching these systems to let me see if there’s another one here nope to the medical and PT students is that striated muscle is relaxed in the absence of neural input and it contracts when it’s exposed to acetylcholine the target tissues that are innervated by autonomic neurons including cardiac muscle smooth muscle and gland cells have constitutive activity so if you take a cardiac muscle cell out and put it and grow it in culture you can see it contracting rhythmically smooth muscle cells generate tone on their own and gland cells can secrete on their own so rather than to cause or generate activity in these cells the role of the autonomic nervous system is to regulate the activity in these cells up and down regulate it and that’s why in most cases with the exception of vascular smooth muscle we are we often have dual innervation of a given tissue and this is the heart as the example where you have inhibitory input from the parasympathetic division and excitatory input from the sympathetic division and the response in a given tissue depends on the neurotransmitter the receptor and the signaling pathways that are involved and what those signaling pathways are doing to ion channels so if we take this this pattern of innervation and overlay it on the gastrointestinal tract this is the way netter drew it and it’s I think pretty accurate depictions in in some ways the vagal pre ganglionic projections are shown here as you know the vague of the board Vegas is from the latin term vagabond and this vagus nerve wanders down through the thorax and into the abdomen and it’s innervating much of the GI tract about as far as the splenic flexure from from there we have the sacral parasympathetics coming from the s 2 3 & 4 inhuman coming out into the distal colon in sigmoid colon with regard to sympathetic innervation it’s coming from thoracolumbar via pre vertebral ganglia the celiac ganglia superior mesenteric and inferior mesenteric ganglion and their projections follow the blood vessels so here’s the pattern for vagal innervation of the GI tract it goes it seems to go further than that splenic flexure but this is the innovation and the sacral pre ganglionic cover beyond that but let’s take a more careful look at the vagal input to the gut so this is from work by Hans rid off bear tude and Terry pally and what they were doing was they were labeling vagal efferent fibers and taking a careful look in the wall of the

gut it where those efferent fibers were going and what percent this graph is showing the percentage of ganglia that receive vagal efferent input and I should say this is my enteric ganglia so just to show you what’s going on here up in the stomach essentially 100% of the ganglia receive vagal efferent input and if you look in these ganglia and you look at the labeled fibers in the neurons it looks like essentially all of the gastric neurons have the vagal efferent fibers associated with them gall bladder ganglia are likely to be the same we haven’t this wasn’t looked at anatomically but I looked at it electro physiologically in my lab and all gallbladder neurons receive vagal efferent input the same is true of pancreatic ganglia but as you can see here is we work our way along the intestines there’s a rapid drop-off in the duodenum of the percentage of gangue my enteric anglia that are receiving vagal efferent input and if you look at micrographs of these ganglia you find that it’s only a small subpopulation of the neurons that are receiving that input so half or less than half of the ganglia receive vagal input and in those ganglia that do receive it half or less than half of the neurons are receiving that type of input so these you know from the terminology or postganglionic neurons but in the intestine most of them do not receive pre ganglionic input so this system is different and if we talk about the submucosal ganglia they don’t receive vagal efferent input they’re on their own so if we look at blood supply of the gut this is the the pattern of vascular perfusion from the cilia trunk superior mesenteric and inferior mesenteric and the pattern of innervation from those associated ganglia is the same but let’s look at the if the pattern of innervation of the GI tract from those ganglia and this is a schematic from a review by John Furness and it shows in the upper left-hand corner this is a pair of vertebral ganglion and then this represents one of these pre vertebral ganglia one type of innervation we have is vasoconstrictor innervation so they’re projections from pre vertebral ganglia and paravertebral ganglia to blood vessels in the gut because vasoconstriction we also have the ability to decrease motility and the neurons that are doing that are not projecting to the smooth muscle they’re projecting to my enteric ganglia where they largely have presynaptic inhibitory effect on synaptic communication within these Montera ganglia using alpha to adrenal receptors the way the sympathetic nervous system down regulates secretion in the gut is once again projecting to submucosal ganglia not to the epithelium in here we have inhibitory postsynaptic potentials and presynaptic inhibition in the submucosal ganglia we also have innervation of immune tissues from these sympathetic neurons but in terms of what we would have thought of is the classic example of sympathetic innervation of the gut projections to smooth muscle and to epithelial cells those projection patterns are very sparse so this this pattern of control is a little bit different we also have neurons shown here in the gut that are projecting out to the sympathetic pre vertebral ganglia and they represent one of the major simpson optic inputs a regulatory inputs to the pre vertebral ganglia it’s a local loop between the enteric nervous system and the sympathetic ganglia so if we look at the the pattern innovative innervation or a schematic as I drew you for the heart most of the neurons in the intestines don’t receive parasympathetic preganglionic input the target of the sympathetic division isn’t the effector tissues but it’s rather the enteric nervous system and the enteric nervous system actually sends projections to the to the sympathetic division to help it know when it should be down regulating gut activity so this is a different system and then the idea that the the innervation of the gut is different than other parts of our body is not necessarily new Bayless and Starling in a Journal of physiology paper that they published in 1899 proposed the law of the intestine which states that local stimulation of the gut produces excitation above an inhibition below the excited spot and these effects are dependent on activity of the local

nervous mechanism so what they appreciated at that time 116 years ago was that there’s complex complex neural reflex circuitry that it’s housed entirely within the wall of the gut that if you stimulate at one spot you can get excitation or contraction above and relaxation below and this is the underpinnings of peristalsis and it’s all within the gut so this means you have to have some way to sense that stimulation you have to be able to send that message upstream in the gut and cause contraction excitatory motor neuron activity above you have to send the message downstream and you have to have inhibitory neurotransmitter I’ll going on within the wall of the gut and this was a trick this was appreciated by John Langley when he wrote his big book the autonomic nervous system and he really laid out the organization of the nervous system as we know it or maybe as we should know it and as you can see here he divided the autonomic nervous system into three divisions that sympathetic the parasympathetic and the enteric division and and and I think that’s how it should be taught so let’s talk about the innervation of the gut and as I mentioned early on I usually talk about it as upper GI reflexes and then in intestinal reflexes and so in the case of the upper GI reflexes we’ve got innervation we’ve got sensory innervation or information coming from the vagus nerve or being generated in our cortex and that information is passed to the vagal motor nucleus and then we have output to the intestines that are to the gastrointestinal tract that cause different things to occur but let’s talk for a moment about the afferent end of this reflex we’ve got a lot of cells in the lining of our stomach and our intestines that are essentially acting as as taste cells these cells have micro villi with nutrient sensing receptors acid sensor receptors these can be activated so they’re actually like taste buds cells in the gut as you know they’re secretory vesicles are located on their basal surface and they put they when they secrete their secretory compounds can enter the bloodstream and they can activate receptors on nearby nerve fibers and we have a lot of different types of cells that fit within this entrĂ³ endocrine cell category and I’m not going to list them here but we’re learning to appreciate them more and more every year and this is a really exciting field I think the field of taste in the gut one of the recent findings along these lines Roger littles lab has shown that CCK producing cells this has been shown in for somatostatin cells in the stomach but Roger little has shown recently that in the intestine the CCK cells have these projections that he’s referring to as neural pods that seemed to be interfaces for neural input and for output from these cells to effort nerve fibers so this is like a kind of a synaptic type of communication that these cells are capable of so let’s talk about types of signals that that are being delivered by these cells to to stimulate vagal afferent fibers from the stomach we have Braylon and we have leptin and also stretch receptors on on the vagal afferents could activate vagal afferent input to the central nervous system and the upper small intestine three of the important signal signaling molecules include cholecystokinin serotonin and glucose dependent insulin a tropic peptide I should mention gel the the 5-htt 3 receptor is listed there for serotonin as you as you may or may not know when individuals are suffering from nausea and emesis associated with chemotherapy it’s due to an an overstimulation of the enteric romo fen cells and release of serotonin activating vagal 5-htt 3 receptors and this is why compounds like ondansetron 5h t3 receptor blockers have are now being used as such effective anti-nausea medications for people undergoing chemotherapy that as we get further along the GI tract a couple of the important signaling molecules to consider or glp-1 and pyy and there’s been a vast increase in our understanding of these these signaling molecules further along in the GI tract recently in part because of bariatric surgery so initially bariatric surgery the the the idea of it was that you would take away the accommodating

ability of the stomach and send these calories through the intestines at a rate faster than we’re able to digest and absorb them and that probably is true to some extent but what we’ve been learning is also these calories now that these nutrients are getting to the distal ileum they’re activating increased release of GLP and pyy and this is doing a couple of things the glp-1 is acting hormonal e to change our entire glucose handling ability and so this is why people who undergo bariatric surgery are miraculously cured from their type 2 diabetes within a matter of days and they have normalized glucose levels also these compounds are acting on vagus vagus nerves and changing satiety signaling in these individuals and they even change their their food preferences so you have people going through these surgeries who are meat and potato people all of a sudden they’re wanting to eat a salad which is something that they never wanted to do before in their life so this is I just wanted to point out that this is a pretty exciting field so some examples of some of these long reflexes that I’m talking about one example is transient lower oesophageal sphincter relaxations I don’t know if you’ve heard of these before but this is kind of a form of burping so stretching in the fundus air in the fundus leads to a transient relaxation of the lower esophageal sphincter and that causes venting of air from from the fundus and this is an important reflex from the perspective of gastroesophageal reflux disease the most common GI disorder it seems to be an abnormal signaling of this TL s TL ESR reflux that is responsible for that and these people have too many of these relaxations going on that Allah is allowing refluxes to occur and the pharma industry is interested in trying to get these under control and have been trying to aim at this with some of their their meds another long reflux that occurs in the cephalic oral and gastric phases of digestion includes gastric accommodation in which we have vagal projections to nitric neurons in the stomach that cause relaxation of the proximal stomach and then another type of reflex is the increase in antral pump activity that you see during the gastric phase of digest Jen so I’m going to take a moment here to show you an example of that and unfortunately one of these mac/pc things I’ve got to go to my movie thing here let’s see here okay so this is I will do it without sound but I wanted to show this to you as an example these these videos are available online they were produced by a professor airline at University of Hohenheim in Germany along with Michael Shimon who is an enteric neurobiologist who worked in his lab these are available online there are a lot of gastric physiology videos and a lot of intestinal motility videos there’s a real nice video showing emesis occurring a dog vomiting when after it’s been given a pill morphine but as you’ll see here they’re eating to the guest room body and the antrum the location of the pylorus and the duodenum are also indicated I think they’re very effective for sharing out stories how they have no work represent the gas big pump so here you can see the proximal stomach is just sitting there not doing any mounted waves originated at the gastric body and propagate towards the pylorus when the peristaltic wave reaches the antrum the constriction of the wave becomes deeper at the end from three parts can be differentiated okay we won’t go into that but it ‘nor ons in this area of the stomach that kind of the middle corpus or body of the stomach are activating the pacemaker activity in interstitial cells of qahal which in turn are involved in starting the central pump or the central pump ring of constriction that rolls its way towards the pylorus and so we can increase the rate and the strength of these events by increasing vagal input to gastric ganglia and in turn neuromuscular or

muscular activity okay another example of a long reflex is acid secretion the major driving force for acid secretion is vagal and in local gastric neural input to the stomach so it’s working in three different ways one way is directly on the this is a gastric neuron now receiving vagal input it release releases acetylcholine onto muscarinic receptors on the parietal cells it causes histamine release from enteric romo fat like cells in the region and it also can promote gastrin secretion from G cells and other of these types of entrĂ³ endocrine cells the gastric works through a hormonal mechanism to increase acid secretion and also to activate ECL activity before we add proton pump inhibitors and histamine blockers if somebody had really bad gastric ulcers one of the treatments for this was a bilateral vagotomy and this is also obviously before we knew about helical bacter pylori so parietal cell secretion it is a neural event also chief cell secretion involves a stimulus being acid in the lumen activating local enteric reflexes and vagal reflexes cause activated muscarinic receptor activation on the chief cells and they’re releasing lipase and pepsinogen and the acid and the pepsin converts pepsinogen to pepsin from there so we also have coordination of upper GI motor activity once the gastric contents are entering the small intestine and they’re activating eye cells that release cholecystokinin in response to proteins and fats in this CCK works through several different mechanisms to regulate upper GI motility one thing it does is act it acts hormonal e to increase gall bladder contraction so CCK I believe was the the second hormone discovered it was an American Journal of physiology paper by Ivan Goldberg in 1928 and they hooked up the vascular system of two dogs and shed that when they fed one of the dogs the other guy dogs gall bladder would contract or if they infused CCK into the one dog the other dogs gall bladder would contract we also have local enteric reflexes that can lead to swing curve OD relaxation and then we have vagal reflexes that are slowing down the stomach activity so so we’re further relaxing the fundus we’re slowing down the antral pump activity so what we’re saying is what the duodenum is saying to the stomach is okay we’ve got a lot of nutrients we’ve got to work on we need to slow down gastric emptying so we can digest and absorb these calories that reflux also contributes to gall bladder contraction and pancreatic secretion and the net result is decreased gastric emptying and increased bile flow within the pancreas we have long neural reflexes that are associated with the acid or cell secretion once again this is C CK acting on vagal afferents C CK itself but probably mainly acetylcholine coming from pancreatic ganglion cells activates muscarinic receptors on the acid or cells to increase acid or secretion and then we have seek the first hormone discovered entering the circulation and acting entirely through a hormonal mechanism to increase duxelle secretion and that duxelle secretion flushes the pancreatic enzymes into the small intestine so those are examples of long reflexes so these are all upper GI tract and they’re they’re involved in the initial phase of phases of the digestive process from here we get down into the small intestines and this is where everything is regulated a bit more locally so this is a schematic diagram by Furness and Costa of the enteric nervous system you can see layers of the gut peeled away here one thing that that this shows us this diagram shows both small intestine on the left and then on the right side you can see colon because we don’t have any villi here in the sub mucosal layer we’ve got a ganglion ated plexus that’s largely involved in regulating secretion in the gut and also regulating blood flow it is I’ll tell you about in a minute and then between the circular and longitudinal muscle layers we have the my enteric plexus so if you look at this in histology class it’s not very impressive because you’re looking at the enteric nervous system on edge on the other hand if you have an opportunity to look at it on fuss you begin to see that there’s this vast sea

of ganglia that stretches from the distal esophagus all the way to the anal canal and there are a lot of neurons in this system many of you probably heard this fun fact that there are more neurons in the GI tract than there are in the entire spinal cord over over a hundred million so this is this it shows the my enteric plexus in in the guinea pig so let’s focus in on a little section of one of these ganglia and look at it at the electron microscopic level and you’ll see another interesting feature of the enteric nervous system so this is the area of this micro graph that shows the my enteric ganglion to the left there’s like a basement membrane and then you see smooth muscle there but if we look at the ultra structural features of the gangly and you focus on this box you see something that’s very peculiar with knowing that this is peripheral nervous system these are unmyelinated axons that are running right next to one another normally you only see that in the central nervous system in the peripheral nervous system individual unmyelinated axons are typically wrapped by Schwann cell sheets there are a lotta so that so the ultra structurally the enteric nervous system looks more like the CNS than the pms also there’s quite a bit of neuronal diversity in this system there there’s diversity of morphological characteristics of these neurons there’s more diversity of electrical and synaptic activity in these neurons chemical coding patterns this micrograph shows a lot of different types of neurons I won’t go into you know what what we’re showing there but also different subpopulations of these neurons have different projection patterns so it took basically from 1899 when Bayliss and Starling we’re doing their work all the way to the late 80s in through the 90s for for we as enteric neurobiologists to figure out which neurons were doing what we knew that circuitry existed for peristalsis but but we were looking at the sea of ganglia and the sea of neurons and not knowing what was what but by combining morphological techniques intracellular injection with dyes with knowledge of the electrical properties of those neurons and then seeing where their axons project and then doing immunostaining we slowly were able to put together a picture of the different types of neurons that are found within the intestines in this sink and with this combined knowledge of these neurons we could start assigning functions to the different types of neurons so we have intrinsic sensory neurons these neurons that are purple and red intrinsic sensory neurons 100% of them project to the mucosa where they’re able to receive signals from those intro endocrine cells we have a lot of interneurons some are projecting upstream in the gut some of them are projecting downstream in the gut and then we have motor neurons motor neurons to the muscle motor neurons to the epithelial cells and also motor neurons to blood vessels there are a lot of different neurotransmitters in this enteric nervous system every class of neurotransmitter can be found here and there’s quite an array and a lot of co-expression of these neurotransmitters some of those that we have assigned pretty important functions too are shown in green or red green for excitatory read for inhibitory apologize to those of you who are red-green colorblind out there and ATP it can be both excitatory and inhibitory in this system along with all of this this vast array of neurotransmitters the enteric nervous system is a pharmacologist playground with regard to the number of receptors that are here this is a map from a schematic diagram from a review article that we published recently in Nature Reviews gie showing the distribution of serotonin receptors along the reflex circuitry of the gut so this is different types of reflexes here you can see serotonin receptors on the afferent terminals on cell bodies and on Pristina presynaptic Leon nerve terminals so this is a rich array of recent types of receptors along this system we can’t talk about the enteric nervous system in 2015 without acknowledging enteric glia there are a lot of presentations at this meeting by Brian gall Branson’s lab talk about enteric lee and he’s giving a talk tomorrow afternoon I believe this is staining of a guinea pig my entire gang lien stained for s100 showing the glial cells here these cells in the gut are positive for glial febrile area acidic protein which is known to be present synthesized by astrocytes in the central

nervous system the first efforts to see what gfa P does in astrocytes was a knockout mouse they looked in the brain didn’t see anything going on these animals were dying young they need crop seed them and they found all of these these these animals had widespread and to write us when they knocked out GF ap this is the same micrograph showing the glial wrapping around the neurons but now we know that there are enteric li out in the epithelial layer of the earth in the mucosal layer of the gut just underneath the epithelial cells and they seem to be integral for maintaining epithelial barrier function we’re also learning a lot of other functions of these enteric aliyah in terms of neuronal growth and survival and also neuronal communication so this is this is really an emerging field so the most unique feature of the enteric nervous system is the presence of intrinsic reflex circuitry this is the only part of our body where we have sensory neurons that are located outside of the dorsal root ganglia and cranial nerve ganglia and this is an example of one of these reflexes so this is layers of the gut orals to the left AB morals to the right stimulation and this can be in form of in the form of chemical stimulation and/or stretch leads to activate direct stretch activation of neurons and also release of compounds like serotonin from entero endocrine cells that activate the intrinsic sensory neurons once again all of which project to the mucosa these intrinsic sensory neurons activate a sending inter neurons that selectively synapse on excitatory motor neurons and cause a contraction primarily cholinergic contraction above the level of the stimulation those intrinsic sensory neurons also activate a descending limb of this pathway that involves inhibitory motor neurons that release purines such as ATP and beta nad and also nitric oxide to cause a relay relaxation downstream contraction above relaxation below generates a pressure gradient the luminal contents move along the gut and then it repeats itself because this circuitry is omnipresent along the intestines along the small intestine in the colon and so this I brought some movies along here to show you the enteric nervous system in action this is a segment of guinea pig distal colon and what we’ve done is we’ve taken guinea pig fecal pellets and coated them with nail polish this is the first job for new undergrads in my laboratory to really test their how interested they are in science but you can see that this pellet is moving in a pretty linear fashion down along that segment of guinea pig distal colon and it involves that reflex that I just showed you contraction above relaxation below and we know that this like Bayless and Starling we’re describing involves the activity of the local neural mechanism because if we block action potentials if we block voltage activated sodium channels and put the pellet in the same segment you can see some myogenic contractions but we’re no longer able to generate that pressure gradient and so the pellet just sits in that same spot I’ll also mention you know I’m not going to get into the data here but we’ve shown that if we activate all of the neurons in the enteric nervous system the pellet you know the pellet doesn’t move we wondered if it would shoot across the room but we call this we call this because we do a lot of inflammation induced neuroplasticity work in my lab where motility is disrupted even the neuronal excitability is increased and we where we think of this as attention deficit disorder in the enteric nervous system so let’s see here okay so these I just want to take a moment to talk just in passing about how these neuromuscular Sigma signals are are processed so there is like a neuromuscular motor unit in this system and it involves interstitial cells so the root cells in red here are stained for kit protein and these are interstitial cells of qahal this is another one of these things that were sent spending a lot of time studying these days the qahal described 110 or so years ago but these are interstitial cells of qahal they form a net work in this system so those are the pacemaker interstitial cells in the there are also cells shown in red and green here that are interstitial cells that seem to mediate neuromuscular transmission in this system so the red cell represents an interstitial cell of qahal and it’s mediating cholinergic neuromuscular transmission and also nitric inhibitory neuromuscular

transmission and it’s just in the last five years or so that it has been discovered that another type of interstitial cell that had been invisible to us and there all along this PD grf alpha cell mediates pure energic inhibitory neuromuscular transmission these cells are full of pure anarchic p2y one receptors and they’re full of sk3 potassium channels voltage activated potassium channels so when the pure energic receptors are activated in these cells they dive towards e k and that hyperpolarization spreads through the smooth muscle sensation so that’s how neuromuscular transmission seems to occur in this system there are other intrinsic reflexes in the gut I mentioned to you early on that sub mucosal ganglia do not receive vagal efferent input these ganglia are on their own so there we have basically sensory neurons and motor neurons in these ganglia the intrinsic sensory neuron is responding once again to release of serotonin release compounds like acetylcholine on to muscarinic receptors increasing the open state probability of the chloride channels in those epithelial cells it’s probably the same motor neurons that are causing vasodilation in this system so sub mucosal neurons can cause vasodilation so this is local vasodilation when we’re processing a meal we want more fluid coming to the gut so we can secrete water and we also want that vascular dilation because we’re absorbing a lot of nutrients into into the vessels in this area so we were increasing the blood flow in the area where digestion is occurring through these local reflux mechanisms there also up in the area of the stomach and duodenum there are also these local reflexes that appear to exist that we don’t know a whole lot about but they’re kind of interesting and I we’ve studied a couple of these in my lab one of these is a local neurons in the duodenum project to the sphincter to the pyloric sphincter so this is this could be a way of regulating gastric emptying from the duodenum in addition to those circuits that I was talking about earlier there are also neurons in the duodenum that project to the gallbladder this is something that I discovered when I was a postdoc in Mike Garr Sean’s lab there are also neurons in the duodenum the project to pancreatic ganglia and can increase pancreatic secretion and finally there are neurons in the duodenum that project to the sphincter of Oddi and what this was a lot of this work was done in my lab I had a grad student that showed that these neurons are intrinsic sensory neurons that are sensitive to CCK and projecting to the sphincter of Oddi so there’s kind of a lot of local control going on here so these in the intestines activity these functions fundamental functions motility secretion and vasodilation are controlled by local neural mechanisms but it’s important to note that the big brain can override the little brain in the gut this isn’t this is a slide that’s depicting an experiment that was done by Professor Tom all me a gastroenterologist at Dartmouth College this as you can see in the lower right this was this was published in 1947 and all me was interested in the relationship between stress and GI function and he invented this contraption that he has on his head there which is this metal crown with these screws that can be tightened and so what he would do would he would he would recruit one of the better experimental models at the time medical students into his lab and he would put this thing on them and then he would take a rigid sigmoidoscopy and put it up into their rectum now they didn’t have these really nice small flexible fiber-optic systems at the time this was kind of like a small telephone pole so all me would put this up in into into their rectum and he would look at the amount of motility going on it’s a reflection of motor activity and he would look at how red the mucosa was as a reflection of blood flow to the mucosa and as I mentioned to you both of these are regulated by local neural mechanisms he had these people put their hand in ice water and showed that they reported pain but they weren’t seeing any changes in their engorgement of the bow or

contractile state of the battle so then he would say okay I would like for you to tighten those screws on your head as tight as possible and so they would you know crank on these things good as well as in and all me would say so that’s all you can do there yeah that’s as tight as I can get them and so this guy’s let’s say his name was Paul Smith so it’s a Paul you’ve got a classmate named Mark O’Reilly right yeah and Tom mommy says in you and Mark are applying for that same residency at Beth Israel right mark also asked me to write a letter of recommendation for him and he was in here the other day and I have to say he tightened that crown a lot more tightly than your you seem to be tightening it here and at that point with this threat of not getting the good letter for Beth Israel all of a sudden can motor activity increased and also there was vasodilation so he published in 1947 and there was a lot you know it caused a bit of a stir but there were there were still people saying there’s a pain component to this this is not just stress this is pain so ami came up with another brilliant idea he had to wait a couple years I think for the med students to graduate and you know word of mouth to fall away and so what he did he did got that sigmoidoscope out again put it up in the rectum and did kind of like just basal baseline activity measurements and then dr. ami said to his nurse nurse I don’t think I’ve ever seen anything like this I’m gonna have to take some samples and could you call surgery and call pathology let’s have them do frozen sections right away and and so he even had a little container and he had like a little hunk of potato but just in the visual range of this medical student he would drop this piece of potato into a sample vial and have the nurse run off with it and so when this was going on this discovery of a rectal carcinoma you can see that this this is a stress response here and it fell away now this was before IRB approval right but it still I think serves as a good example of what’s going on here but another feature of this that I want to mention to you is that we’d really don’t know what is going on here you know what the first person who I show Asajj show this this slide was a jack wood who many of you might know very famous and Tarek neurobiologist now at Ohio State University when I was putting this talk together I call I’ve been using this but I called him and I said Jack let’s talk about that experiment do you I mean I don’t you know neural pathways don’t completely explain this in and stress hormones acting on the enteric nervous system don’t completely explain it and what but what Jack thinks is going on is that it might be stress hormones possibly released you know locally and/or through the the HPA axis acting on mast cells in the region and and we know that mast cells back to neural immune interactions mast cell degranulation is is really effective at flushing our GI tract from top of toxins and infectious agents if we need to do that because it causes a really big simultaneous secretory event and motor activity and it just pushes everything pushes everything along in it and it also goes along with vasodilation so that there might be a mass cell component to this so any self-respecting nervous system has disorders associated with it and we now know that there are a lot of motility disorders that are associated with changes in an enteric function we also know that IBD leads to neuroplastic changes that are responsible for altered motility secretion and sensitivity in the gut and also I have a question mark with with IBS but it’s becoming clear that there are changes in the wall of the gut in irritable bowel syndrome in my lab we’ve shown that there’s altered serotonin signaling in the gut others have shown a slightly elevated immune State in the gut the part those are probably interrelated this is likely leading to visceral hypersensitivity and altered motor activity in the system and believed before I leave this I want to

just show you how these sensory signals are processed we talked about the intrinsic afferents the vagal afferents seem to be involved primarily in homeostatic and digestive reflexes a lot of sites at ayat e signaling here but when we get to pain and discomfort these signals are being processed by way of the spinal afferents so if you’re trying to affect visceral hypersensitivity it’s a spinal efference that in their communication that you want to work on 5-htt three antagonists seem to inhibit these signals in somehow and we don’t understand it but 5-htt four agonists also seem to dampen peripheral visceral sensitivity through some sort of peripheral mechanism so in closing I just want to talk to you about a couple of things that are going going on in this system that are that are exciting not work that I’m doing in my lab or we’re doing in my lab but some some things of interest and one was really nicely described by dr. Abood in the second talk in this session and that has to do with vagal stimulation and so this is a list of things that vagal stimulation has been shown to do it’s pretty much everything but peace in the Middle East I think so rheumatoid arthritis your inflammatory bowel disease asthma diabetes obesity migraine seizures and depression so these are some things that we don’t completely understand how this is going on but there might be some cues in the next little section that I’ll give her the talk but the pathways involved in the in this vagal anti inflammatory pathway to the gut are being worked out so with regard to rheumatoid arthritis it’s that stuff that the the pathway that dr. bode mentioned that Kevin Tracy has been working on and Robin McCallum the details of this circuitry I don’t think have been clearly worked out this shows a vagal input to the celiac ganglion I don’t know if that really happens and then cilia neurons projecting to the spleen and here’s where we have those alpha 7 adrenal receptors I’m sorry colon or nicotinic receptors on the macrophages and we have t-cells in this model in the spleen releasing the acetylcholine work by D buckstein in his colleagues at University of Leuven in Belgium have been studying the the GI component of this reflex and they have found that vagal efferent fibers that are going down to the intestine which I mentioned to you are on the sparse side seemed to cause release of acetylcholine from my enteric neurons and it’s this local my enteric neuron input to the macrophages and their alpha seven nicotinic receptors that seems to be involved in this intestinal vagal anti inflammatory pathway but this is this is kind of a pretty cool story and I think if we can if we can take advantage of this this might represent a novel approach to treating IBD and other inflammatory disorders of the GI tract you can’t give a talk in 2015 without the microbiome coming up and especially if it’s a if it’s a gut talk but one of one of the most interesting aspects of the huge deep the deluge of information that we have about the microbiome has to do with the the microbiome and the gut brain axis there there there are a couple of of labs one at John Kriens group at Cork University Medical Center in in Cork Ireland and also the group at McMaster headed by Steve Collins Elaine aver do and przemek Burke has shown in in in this picture here have done some really elegant work showing that if you change the microbiome you can change animal behavior and brain neuro chemistry and one thing they’ve shown is that exploratory behavior is in increased in germ-free mice so you take the biome away from a Bobbsey mice which which are pretty timid animals and now they become more exploratory with this is a step down paradigm and also time in life this is a I think a plus maze but even more interesting to that than that in this paper by przemek burke ‘ok what they showed was if they took two different strains of mice that have different behaviors nih swiss mice are pretty a pretty exploratory and assertive Bobbsey mice like i said a pretty timid but if you take the

microbiome from nih swiss mice and you put it in germ-free see mice so they’ve become more exploratory and if you take bugs from Bob see mice and put it int NIH Swiss germ-free mice they become less exploratory so there’s something there’s something going on here and not only that but it seems to involve a critical period so there’s this period during development so it’s some time before ten weeks of age that you seem to have to make these changes in the microbiome to see these changes in behavior so this is kind of an interesting part of this how is this information communicated some of these changes are blocked by vagotomy others aren’t with with regard to those that are mediated by the vagus nerve how does the information get from the bugs to the vagus nerve work by Wolfgang Kansa also at McMaster University has shown that there seems to be a nicotinic synapse for my enteric neurons on to vagal afferents that is critical for this vagal signaling from the gut in response to bugs in the lumen so this is where we’re kind of redrawing our autonomic circuit diagrams here both with regard to how the autonomic nervous system contributes to organ function and in inflammation and also how signals from the lumen of the gut from the bacteria are getting front to the central nervous system so in summary one thing I want to try to drive home here is that the enteric nervous system is a distinct division of the autonomic nervous system that exhibits unique neuronal circuitry long reflexes that regulate upper GI tract functions while local reflexes regulate intestinal functions but we know from Amy’s work and many others that the big brain can override the little brain in the gut and finally advances in our understanding of the enteric nervous system could improve treatments for many GI disorders including IBD and and IBS so thanks for your attention you you