 Now, this is the first lecture in by 150 on the neuroscience of disease. And most of the lectures from now on will be on that topic. And Ralph and I figure you have a pretty good background in elementary and fundamental neuroscience. And so now it's fun to apply that knowledge to diseases that you might see in your friends. We're going to talk about two neurodegenerative diseases today. Next time we will talk about diseases of emotion. And Ralph will be talking two lectures next week. Actually, he'll be talking about emotion and about other. And I will come and talk with you about schizophrenia as well. The two diseases that we're going to discuss today will be Alzheimer's and Parkinson's. This is Michael J. Fox, who has suffered from Parkinson's disease for many years, the actor. The two diseases Alzheimer's and Parkinson's are the most common neurodegenerative diseases in our society. We are going to follow a general description for all of the neural diseases. We'll talk about the clinical description about the genetics, at least what we know about the genetics. The pathophysiology, patho means sick, physiology means how things function. So how the disease gets started based on what we know about the fundamental problems. Biomarkers, easily accessible biochemical or functioning blood tests or other aspects that will allow us to give a quick summary of a disease so that we can follow both the time course of the disease and the therapy, as well as animal models. There is this interesting concept called a heterozygous advantage. And I won't say much about the heterozygous advantage until we get to one of the psychiatric diseases, bipolar. We'll talk about that in greater detail. And then about therapeutic approaches. So first off is Alzheimer's. And we have a lot to cover today. I hope we can get through it. But the typical case of Alzheimer, all right, now here's the usual question. Who first described Alzheimer's disease? Okay, so Alzheimer's disease usually begins with a rather pure impairment of a person's ability to think and his cognitive ability. Now, as I say to my friends my age, mild cognitive impairment does not always lead to a dementia, to a more severe case of Alzheimer's or other dementia. But there is a progression. First, the only symptom is forgetfulness. And people may have trouble remembering recent events, activities, names of familiar people or things. Maybe they can't do simple math problems. Did I already say that they repeat themselves every few minutes in conversation? No, okay. In the middle stages of Alzheimer's, people forget how to do simple tasks. Brushing their teeth, combing their hair. They can no longer think clearly. They begin to have problems speaking. Third stage, Alzheimer's patients actually may become aggressive or anxious because they are realizing that they have lost so much. They begin to wander away from home and they eventually need total care. Now, there is a scale called the mini mental status exam, which can be administered in a few minutes by either a psychologist or a neurologist or a psychiatrist. And the mini mental status exam says asks, well, the one of the toughest is please count back from 100 by seven. And then there are the simple questions like who's president, what day of the week is it, when were you born. There are a total of 30 questions. Everybody in this room would score 30. Sometime below 25 begin the symptoms and after a while patients score very poorly on the mini mental status exam. So it is, as we say, the most common neurodegenerative disease. And the number of people in age groups are given here. Alzheimer's is not a normal part of aging. And so you cannot say about a person. Well, quite normal to have Alzheimer's at his or her age. Late onset sporadic Alzheimer's occurs. And this is by far the most common late in life, no obvious inheritance. But we'll talk about some risk factor genes that do interact with each other. In fact, the most common risk factor gene to date remains a gene that makes one form of apolipoprotein E, which is a carrier for lipoproteins in the blood. So one polymorphism in APOE4 is in APOE is called APOE4 roughly 16%. And where there where a person has one copy of the gene, the probability of getting Alzheimer's is elevated to copies of the gene very severely all time elevated. Familiar Alzheimer's, which leads almost invariably to Alzheimer's is much rarer. It starts at age 30 to 60. So much earlier that typical hallmark of Alzheimer's pathology are the plaques and tangles in the brain. So here are these amyloid plaques. They contain a large amount of a very famous 42 amino acid peptide called beta amyloid or A beta 42. Now this is not the alpha 4 beta 2 nicotinic receptor. It is called A beta and it's 42 amino acids long. And it may very well be that beta amyloid is the initial cause of the pathophysiology that leads to dementia. Amyloid plaques probably contribute to the later stages. So the plaques are not what's doing the damage. It may be the beta amyloid itself. Then there are also neurofibrillary tangles that have a lot of cytoskeletal proteins, especially the microtubule associated protein tau or tau as most people call it. So in these tangles there are lots of phosphorylated proteins and these two could cause aggregation and precipitation. So it is important to realize that these plaques and tangles, although they are by far the most visible aspect of the disease, are probably not in the causal progression of the disease. They come much later. And in general, people with Alzheimer's have reduced brain volume, especially in regions that we've discussed the endo-rynal cortex and the hippocampus. So what is going on with Alzheimer's? Well, we don't know, but here is amyloid precursor protein APP. There are mutations associated with familial Alzheimer's disease. Now APP is amyloid precursor. These familial Alzheimer's is rather rare. There is also in this complex a protein called presanilin-1, and as we're going to see, presanilin-1 is itself a component of a protein called gamma secretase. So all of these mutations in presanilin-1 or in APP are associated with familial Alzheimer's disease. In addition to the beta amyloid plaques, there are the taupaties as well, and these are mutations in ta. These typically do not lead to a pure Alzheimer's. They cause frontotemporal dementia with Parkinsonism. And apparently within the last week, the comedian who killed himself, Williams, not Brian Williams, Robin Williams, thank you, was revealed to have been suffering from a form of frontotemporal dementia, and it is thought that this may have contributed to his suicide. So how does all of this work? Well, here is the amyloid precursor protein, APP. A beta 40 and 42 are thought to be proteolytic products. So A beta APP has this long extracellular region, has a little bit of a stub of the cytoplasmic region and the transmembrane domain. Within this stub region, there are several sites for proteolytic cuts, and so these are called alpha, beta, and gamma secretase. And then there are also some domains out here that are associated with Alzheimer's disease. And so it is thought that overproduced A beta and A beta 42 eventually arises because an altered ratio of proteolytic cleavages, and so the alpha, beta, and gamma proteolytic cleavages. And in fact, all of the known genetic risk factors proposing to true Alzheimer's disease do increase the accumulation of A beta peptides. And so there are APP mutations themselves on chromosome 21. There's the ApoE4 polymorphism, which we talked about already on chromosome 19, which also seems to increase the density of A beta plaques. There are mutations in PresaNLN1 and PresaNLN2, which increases the production of A beta 42. And there is a recently discovered protein called trim2, which increases the density of A beta plaques. And I believe there is a population in Iceland that has a mutation of trim2 and is actually protected against Parkinson's, sorry, against Alzheimer's. So one needs to understand that the amyloid hypothesis has indeed evolved over the years, and also different scientists have different takes on the amyloid hypothesis. So it was thought originally that these deposits were pathogenic, but it's now thought that A beta, which eventually causes the deposits, micro aggregates or soluble A beta oligomers are the neurotoxic species. And so it's important to realize that although many people publish papers saying, ah, I find that when I overexpress A beta, this molecule is affected, that molecule is affected, this one goes up, this one goes down. There is no clear single target for A beta. However, soluble oligomers, as we say, do apparently cause, which range from 40 to 42 peptides, do appear to interact with other proteins. They are toxic to neurons. It may very well be that the 12-mer is the most significant toxic form, but that changes year by year. And one of the more interesting hypotheses, also which holds for Parkinson's disease, is that misfolded alpha A beta 42 may actually act like a prion. If it develops in one cell, it may spread to another cell. A prion is a protein that seems to be infectious rather than DNA that seems to be infectious. So, what on earth is A beta, is APP there for? What on earth is presanelan there for? It may very well be that the normal function of the secretase and presanelan, which is part of the secretase, is to protealize notch. We learned about notch and delta in signaling. And the proteolysis of APP may be a side effect that also gets protealized. So, in the core gamma secretase complex, there is presanelan, either number one or two. Another protein that we know a little bit about. Another one that we know a little about and yet a third one. So, there's this complex of proteins called the gamma secretase. And it may be absolutely accidental that it cleaves APP, but it almost certainly cleaves notch. So, what are the general cellular processes? Well, here we get into the term for the first time protein homeostasis or proteostasis. And here, we're going to spend a lot of time talking about misfolded proteins today. And they are indeed a major and increasing theme in neurodegenerative disease. My lab is interested in them. Typically, when misfolded proteins accumulate, they do so in the endoplasmic reticulum. And this causes endoplasmic reticulum stress and a phenomenon called the unfolded protein response in which the cell responds homeostatically to the presence of lots of unfolded proteins in the ER. Now, ordinarily, the cell has mechanisms that overcome that. And we'll see a beautiful graph of that in a few slides. But if the unfolded protein response goes on too long, it becomes apoptotic. That is, cells begin to die. Then, there is also the usual hypothesis having to do with calcium, which is that excited toxicity occurs because the cell is stimulated too much because its channels are open too much. Calcium accumulates and eventually overwhelms the cell's ability to pump it out. And this allows various metabolites to accumulate in wrong compartments. And calcium also activates transduction systems, overactivates enzymes, and this causes necrosis of the cell. The cell dies. So, there are these two general hypotheses in which an insult can be caused either by misfolded proteins or the somewhat older hypothesis in which hyper-excitability, excited toxicity causes cell death, and both may be operative. Here's a, we're harking back now to our lecture on LTP and on learning and memory. Here's an example, a very specific example of how the beginning stage of Alzheimer's may be interfering with cognitive processes. And so, this is A-beta injected into a slice of the hippocampus, and people are monitoring long-term potentiation. So, here is a cell line that has been engineered to express A-beta. So, it's secreting A-beta into the medium. One takes the medium from that cell line, conditioned medium from this culture dish over here. And one puts it onto the slice that is being assessed for LTP. So, the conditioned medium containing A-beta oligomers decreases LTP, but the conditioned medium from another cell line next door that's also secreting lots of stuff, but has not been infected with A-beta and is therefore not secreting A-beta, doesn't have this effect. So, this is wild type CM conditioned medium. And there are a couple of other controls in the lower panel having to do with antibodies against A-beta. So, this is a highly specific and well controlled experiment showing that too much A-beta can indeed interfere with a model for a cognitive process. So, what are animal models for Alzheimer's? Probably the best animal models are mice that overexpress APP, amyloid precursor protein, especially mice that overexpress APP with Alzheimer's disease associated mutations, point mutations. Now, the question becomes, well, what about biomarkers for Alzheimer's? I've told you about the mini-metal status exam, the neurological slash psychiatric exam. And that is usually quite accurate in diagnosing dementia. But really for Alzheimer's, only an autopsy is the right way to do it, and only an autopsy shows decrease in the brain areas such as the basal forebrain, the hippocampus, and the entorhinal cortex. So, can you come up with a biomarker? Well, so various people are trying to do proteomics and metabolomics on cerebrospinal fluid, on the fluid in the ventricles, hoping to find a pattern that distinguishes a patient with Alzheimer's disease that would be much easier and more quantitative than waiting to autopsy, obviously. It might not be easier than a mini-metal status exam, but it's more objective. And then there are getting to be pet markers for APP deposits. Here is one of them. It's called Floor Beta Peer. Beta obviously is for beta amyloid. And this very careful paragraph, which you can read yourself, says, okay, we have FDA approval to give this pet test. And there are words like inconsistent with the neuropathological analysis of AD. So, if there's a negative scan that's inconsistent, if there's a positive scan like this one here, then moderate to frequent neurotic plaques, but not an absolute proof of Alzheimer's, other types of neurologic conditions, as well as older people with normal function. And so, this is a way of hemming and hawing around the fact that there is no biomarker, there is no good imaging procedure for Alzheimer's. We won't discuss heterozygic advantage yet. What about therapeutic approaches to Alzheimer's? Really, there are essentially no good therapeutic approaches. Basal forebrain cholinergic neurons are actually early death in Alzheimer's. And so, they produce acetylcholine. And so, the idea is let's make their remaining acetylcholine last longer and be more protective by using a cholinesterase inhibitor. You remember that acetylcholine esterase is broken down at the nerve muscle synapse by an enzyme acetylcholine esterase. And so, there are some brain penetrant acetylcholine esterases. The three that are on the market most prevalent now have these trivial names, and you will probably know them by their trademarks. A newer one, and so, it's not these work a little bit. They may delay symptoms by a couple of months. Then there are some inhibitors of NMDA receptors on the market. The idea, as you all know, is that NMDA receptors permeate calcium, and so, if you want to stop excited toxicity, you might stop the flow through NMDA receptors. And this is presumably the way the NMDA receptor blockers work. But inhibitors of beta secretase, which ought to be the answer, have pretty much either failed in the clinic or are still in development. And then there are gamma secretase inhibitors, which have failed. So there's a gamma secretase inhibitor, which is supposed to spare the notch system and block APP selectively. They haven't yet succeeded. How about antibodies against beta APP or amyloid beta? So here, biotech companies, including ones that we know well, such as Genentech and Amgen, have tried very hard to make antibodies against either beta APP or amyloid beta. And these have not yet panned out either. So we have a problem. Any questions about Alzheimer's? Okay, let's move on now to Parkinson's, which is the second most prevalent neurodegenerative disease. So we have the usual outline that we're going to apply to this disease. So James Parkinson was something like a dentist in 1817. And he observed these people in London during his daily walks. He found six of them. He called it paralysis agitans, agitated paralysis. So I'm going to show you a video, a YouTube video of a person who I believe is a professor of neurology, but I have not been able to track down this person's name. He does an excellent... This gate is the gate that is hypokinetic gate. The prototype is Parkinson's, a Parkinsonian type of gate in which the patient will have... This gate is the gate that... This gate is the gate that is hypokinetic gate. The prototype is Parkinson's, a Parkinsonian type of gate, in which the patient will have a posture which will be scooped over, leaned forward, and then will have difficulty as far as initiating gate. When the gate is initiated, there are small steps. Oftentimes there's a tremor associated with this. And as the gate progresses, there may be a picking up of speed of what's called a fenestrative gate. And then in turning, as they're having a normal turning, the patient will turn on block, which means they'll turn almost as a statue moving around. And then, again, having difficulty starting and the... Sit at Starbucks and watch people with that description walk by. Sometimes at the red door, we see people walking around campus with such a description also. What is not shown on this video are the small motor movements. The most common is a pill rolling movement, where a person just has his fingers together and does this for a large amount of time, and again, also a little bit of a shaking in the hands. However, one rarely sees this full blown because most Parkinson's patients have either been... have had electrical implants, deep brain stimulation, which we will discuss later in the lecture, or are medicated with Eldopa or another drug. But it's very tricky to get a patient medicated correctly, and sometimes overmedication occurs. And the easiest... You notice that the actor was leaning forward, and overmedicated Parkinson's patient actually leans too far back. They have often helped Parkinson's patients stand upright. Dopamine. The dopamine-ergic neurons in the brain. Here is a sagittal view of the human brain. As you know, the dopamine-ergic neurons in the human brain die in Parkinson's disease. As I'm going to tell you, you probably don't know, that dopamine-ergic neurons in the human brain project to all regions of the brain. So each neuron has a massive amount of axon, releases lots of neurotransmitter, has to work very hard to keep this axon up. In a mouse, I've showed... Now, this is a coronal section through a mouse brain, stained with tyrosine hydroxylase, which is the enzyme that makes dopamine. And so I've told you about the handlebar moustache in the brain, that is the set of neurons which make dopamine. And the handlebars are the substantia nigra. In fact, the substantia nigra pars compacta, because the neurons are fairly close together, and it is the handlebars which degenerate in Parkinson's disease. The upper lip of the handlebar moustache is the ventral tegmental area, still dopamine-ergic neurons, but they are responsible for a sense of pleasure. We'll get back to this concept in a few slides. One, we're going to use this schematic view, which comes from a nice book by Eric Nestler, Steve Hyman, and Rob Malenka of the relations between the basal ganglia and the rest of the brain. So the key here is that there are some excitatory neurons, especially high up in the cerebral cortex, and also in the subthalamic nucleus. While the subthalamic nucleus, it won't surprise you, is below the thalamus. Well, here's the thalamus, the subthalamic nucleus is below it. And in the basal ganglia, there are lots of GABA-ergic neurons. So in order to understand the feedback loop that goes wrong in Parkinson's disease, we actually have to do lots of sine inversions. And sometimes it's really unclear how to do those sine inversions to make things even more challenging that striatum, which has these large neurons called the medium spiny neurons, has two types. In fact, there's two types of neurons, and these two projections were discovered by Malen DeLong, who wrote the chapter, I think it's chapter 43 in Candel. So there is the direct projection from the striatum back to the substantia nigroparse reticulata, which is not dopaminergic, but that feeds to the substantia nigroparse compacta, which is dopaminergic. And then there's an indirect, which has one more synapse. So the signs actually do change. But if you look carefully, this guy has a negative, let's see now, I hope I've got it right, this guy has negative to here, this guy is negative positive, positive, yeah, this guy is positive to here. So in fact, oh, but this is a change sign again. So this is a positive, and this is also a positive. So in both cases, the striatum feeds back in a positive way to the substantia nigroparse compacta. The two types of substantia nigranurans actually had different dopamine receptors on them. One is coupled to GI, the inhibitory G protein, and the other to GS, the stimulatory G protein. So even at the level of the substantia nigra, the dopaminergic projections to the striatum, we have lots of diversity. In the early stage of Parkinson's, people do lose individual dopaminergic neurons, but it may very well be that the remaining dopaminergic neurons sprout, increase their projections, so that the symptoms in early stages of losing Parkinson's disease are not so obvious. And there are various statements that neurologists like to say that Parkinson's does not become evident until people have lost 80% of their neurons. These days you can do a better diagnosis of early stage Parkinson's, so now people say that you begin to note Parkinson's when the patient has only lost 50% of his dopaminergic neurons. And again, as with Alzheimer's, there are inclusion bodies, there are deposits of poorly folded proteins in the cell. This one is called a Lewy body. I won't tell you who discovered the Lewy body. And they occur in dopaminergic neurons primarily, but they also occur in some other diseases. And so there is a disease called dementia with Lewy bodies. Parkinson's doesn't begin with a dementia. It begins as a movement disorder as the YouTube video demonstrated. But there are other signs in early adjuncts of Parkinson's disease. One of the most interesting is that typically 20 years before a patient manifests clinically obvious Parkinson's disease, that patient has constipation. Now I hasten to add to audiences my age that constipation is not a predictor of Parkinson's disease. Retrospectively you can see it, but lots of people have constipation and do not develop Parkinson's. And sure enough in the biopsy of the intestine there are Lewy bodies in the neurons of the intestinal wall and there are indeed dopaminergic neurons in the intestine and these dopaminergic neurons do seem to degenerate. But there is a famous neuroanonymous called Brock who looked at lots of brains and lots of places in the brain show Lewy bodies before dopaminergic neurons show Lewy bodies, particularly those with long axons, but the other places with long axons don't seem to show symptoms. Another dramatic effect in early stage Parkinson's is sleep disorders, especially rapid eye movement sleep or REM sleep. Also patients in early stage Parkinson's seem to have trouble smelling. Later stage Parkinson's patients clearly have in many cases depression and then in the latest stages of Parkinson's there is also some dementia many times. And so Parkinson's is by no means a pure loss of dopaminergic neurons. There is a degeneration which pervades eventually the entire brain. So genetics. There are about 16 genes associated with Parkinson's disease. Together they all account for perhaps 10% of Parkinson's disease. In some societies one or another of these diseases predominate. Typically the familial Parkinson's disease occurs a bit earlier. 30s to 50s. Sergei Bryn carries one of these mutations and he has been convincing 23 and the founder of Google. He has been convincing 23andMe, which is one of these genotyping companies to get lots of genotypes from Parkinson's patients. So there are various proteins involved that contribute to, that are very highly associated with Parkinson's. The pattern of inheritance is different. Autosomal dominant means that one copy of the gene will cause the disease. Autosomal recessive means that one needs to have two. And more is known about the early ones than the later ones. Certainly the most famous of the genes are alpha synuclein and parkin. Alpha synuclein is an intrinsically disordered protein that seems to be involved in membrane fusion among various organelles and probably in transmitter release in the membrane fusion associated with transmitter release. Parkin, entirely different function, it is an E3 ubiquitin ligase involved in clearing misfolded proteins or others marked for removable. So then there's LARC2, which is a kinase. LARC2 seems to be most apparent in Middle Eastern families. And so among the 10% of patients, for instance in Saudi Arabia, who have a familial Parkinson's, there's a surprisingly large number of LARC2 mutations. Any questions? So what is the pathophysiology of Parkinson's? Well, one has to say right off that most of the causes are unexplained. Dopamine-ergic neurons have this particular problem in that they make this transmitter, dopamine, with two adjacent hydroxyl groups. It is a catecholamine. This is a catechol, it's a catecholamine. And these can very easily be oxidized. And so the breakdown products of dopamine are undoubtedly a cause of Parkinson's disease. There are some very nice studies out of UCLA looking at inhabitants of the Central Valley of California and correlating increases in Parkinson's disease with the amount of pesticide spraying. And so it's thought that the pesticides become taken up into dopamine-ergic neurons and become toxic. Then there is of course the frozen addict story. This happened about 30 years ago in the Bay Area people started making a synthetic heroin using a bad formula. This was obviously illegal. This synthetic derivative of heroin was highly toxic, but was taken up by the dopamine transporter, which is expressed only in dopamine-ergic neurons and is the target for many drugs of abuse and of therapy including ADD medications. So this toxin taken up by the, this pro toxin taken up by the dopamine transporter was converted into a toxin in the dopamine-ergic neurons and killed virtually all of the dopamine-ergic neurons. Another death of dopamine-ergic neurons occurred during the worldwide encephalitis pandemic of 1918. And some of the people in this pandemic, pandemic means epidemic all over the world, had selective death presumably because of autoimmune reactions to their dopamine-ergic neurons. And when the late Oliver Sacks was still a medical student, he spent some time in a hospital, so this was in the late 60s, mid 60s in New York, found many patients who still had virtually complete paralysis due to this loss of dopamine-ergic neurons. And at the time, Eldopa was just beginning to be approved and his first book, Awakenings, was about the patients who transiently were remarkably benefited by Eldopa. Okay. So, alpha-synuclein with these mutations. So, what does it do? Oh, how embarrassing. We really do not know what alpha-synuclein does, but also for Alzheimer's, one of the earliest aggregation products may be the one that is most toxic in Parkinson's disease and the Lewy body may be a very late stage of that. One of the other early factors may be improper fission and fusion of mitochondria, and David Chan here at Caltech is one of the experts on that topic. Okay. So, what about these protein folding problems? I'm reproducing here a figure from Candel, but much larger so that you can see some of the topics. So, one of the neurodegenerative diseases is an expanded triplet repeat. We're not going to talk about that. Another is a missense mutation in a gene. We've seen these examples in Parkinson's and earlier today in Alzheimer's. ALS we are not going to discuss at all, just no time, but in general, it is thought that the protein that's made has an incorrect confirmation, and this incorrect confirmation persists and can't be cleared from the cell and may engage in incorrect protein-protein interactions or protein-nucleic acid interactions. In some cases, the cell can mount a defense bringing in chaperones, the unfolded protein response, the ubiquitin proteasome system. But in many cases, because this misfolded protein persists, it goes on for a long time, ultimately the misfolded protein begins to alter gene expression, alter mitochondrial function, alter synapses, begins to induce apoptosis and also causes inflammation. Axonal transport is a very delicate function of neurons, especially of neurons with long axons, and so this can easily be deranged, and so the picture in Candel shows in the late stages of a neurodegenerative disease obvious morphological changes and eventually cell death. We'll come back to this picture in a few minutes when we discuss nicotine. There are animal models for Parkinson's among the favorite animal models are mice treated with toxins, I think we will talk about that, but Drosophila that over-express various proteins that are associated with human Parkinson's disease are also fruitful and handy. There are a few dopamine-nergic neurons in Drosophila and when one over-expresses synuclein in these dopamine-nergic neurons, these dopamine-nergic neurons die preferentially. Other neurons do not, but the dopamine-nergic neurons do, and in fact these mice, sorry, these Drosophila have a kind of movement disorder. Normal Drosophila can climb very well, but Drosophila over-expressing certain synuclein mutants show a much poorer climbing ability, and Professor Bruce Hay here at Caltech has studied this along with Professor Yao at UCLA. Good. Ming-Gao, sorry. Okay, more models for Parkinson's disease, toxin-treated mice, rats, and monkeys, in which there are insults to these delicate dopamine-nergic neurons, mites with altered specific genes, even more reduced models, yeast that have synuclein mutations. The current emphasis on human embryonic stem cells and on induced pluripotent stem cells have given rise to the idea that you could do a disease in a dish. You could take a human neuron, a human stem cell, differentiate it to become a dopamine-nergic cell and ask the consequences of that, especially of a mutant, that you can either induce or find in a patient for the function of that cell. There are some technical issues associated with making embryonic stem cells. As we pointed out, there is the handlebar in the upper lip. These are two different types of dopamine-nergic neurons. The handlebars degenerate. The upper lip does not. The handlebars are the substantia nigra pars compacta. The upper lip is the ventral tegmental area, and we don't yet know how to differentiate neurons into the one or the other. Biomarkers. Again, there is probably the experienced neurologist. Carries the day. There is no blood test. The best indication of early stage Parkinson's is responsiveness to L-dopa. We'll talk about L-dopa in a while. Then there is also an imaging drug. It is a high-affinity dopamine transporter ligand. When dopamine-nergic neurons die, the dopamine transporter dies with them. There are lots of movement disorders, essential tremor, et cetera. A good neurologist can tell them apart, but imaging of dopamine-nergic neurons can also help. As usual, one gives a mealy-mouth statement about confirmatory tests, monitoring disease progression. That's probably a good use. Heterozygote advantage, non-known therapeutic approaches. The therapeutic approach that is most commonly used now is L-dopa. L-dopa is a precursor to dopamine. However, dopamine does not cross the blood-brain barrier. L-dopa does cross the blood-brain barrier. It is a Twitter ion. It's uncharged. Here, it's an amino acid. It permeates into the brain probably via a transporter in peripheral tissue. Now, there are also enzymes in tissue that will catabolize, will break down L-dopa. It's also used with a compound called carbidopa, which inhibits the d-carboxylase that would otherwise break down L-dopa before it gets to the brain. Sometimes people add a D2 receptor agonist. Remember, dopamine receptors are D1, D2. The D2 receptor has a rather higher affinity, so you can increase it with a D2 receptor agonist. We'll talk about dyskinesias in a moment. Obviously, L-dopa is effective only as long as you have dopamine-ergic neurons in the patient. These dopamine-ergic neurons can take up and secrete dopamine. When those dopamine-ergic neurons become too few, then the L-dopa starts not working very well. There are other reasons why L-dopa is not a great drug. There are side effects which are called dyskinesias, literally bad movements. They are very common in people who have used L-dopa for many years. In fact, most of the Parkinson's patients that one sees have the L-dopa-induced dyskinesias writhing in quick movements. You can see TV appearances of medicated Parkinson's patients who do that. Why and how L-dopa causes these dyskinesias is not known. I have a theory, but most people think of other reasons. Other effects of the L-dopa are poor sleep, hallucinations, in some cases psychotic symptoms, although that often comes from the D2 agonist. Very simple confusion. One of the remarkable aspects of this dyskinesias is that there is an on and off phenomenon. People go from having the dyskinesias to not having them during the course of the day. Really, they occur even after a person has stopped taking the L-dopa. This is really a mystery. Other drugs, monoamine oxidase inhibitors, maybe to stop production of toxin, muscarinic antagonists. These were actually the first drugs used for Parkinson's. A mantidine, which blocks NMDA receptors like memantine, maybe this reduces excited toxicity, mitochondrial stabilizers, and adenosine receptor antagonists. We don't understand how they work, but they seem to give a little bit of symptomatic relief. Deep brain stimulation for Parkinson's. I'm going to go over by about five minutes today. There's this feedback loop involving the positive and the negative projections in the basal ganglia. It has been thought for a while, let's interrupt the feedback loop. In fact, a favorite way to interrupt the feedback loop originally was to lesion one of the nuclei in the basal ganglia called the globus pallidus, parsexterna. Just destroy it. In order to make sure that people were lesioning correctly, they put electrodes on their wires that they were going to use to pass a lot of current, and recorded from neurons, and then stimulated those neurons to make sure that they were getting to the right place. And, lo and behold, it turned out, of course, that simply stimulating neurons in the right place, not lesioning neurons, also quieted down the tremors of Parkinson's disease. And so that's where deep brain stimulation came to the fore. It's been around now for almost 20 years, and it obviously involves an invasive surgery. You have to put wands with electrodes deep inside the brain. And so the question is, how does deep brain stimulation work? Does it work by activating neurons? By silencing them? And many people think that silencing is the answer because the stimulation frequencies that work are around 160 Hz, too frequent to silence neurons reliably, possibly enough to depolarize them, and therefore inactivate them. And the other possibility is that actually they're not working on the neurons themselves, but on the axons passing through. Deep brain stimulation is remarkably effective. I'm going to show you a video. Okay, thank you. That comes from a German clinic. Probably almost 20 years old. Okay, so they're all just starting the patient to open and close for this patient to have a deep brain stimulation. They've been turned off. Okay, now open it up. She can do that as well as she can. Okay, and with the other hand. Now the other hand, please. She can do that a little bit. Yeah, exactly. Okay, get up. What are we going to do? I don't know. I don't know. Okay. Okay, try to stand up again. Stimulator is there. It's got a magnetic switch, but it's locked. And now you're going to try to put it back here. It doesn't work. Not even if I hold it. It doesn't work either. Try it again. I already have it. Slowly with support from the neurologist, she is working. So now, a few moments. The neurologist is going to turn on the deep brain stimulation. Maybe you'll have to be a little bit more careful before you do that. The side is changing. So, don't tell me. I've got it. Then let's go back to bed. Slowly bringing her back to her chair. Okay. Now you're using the magnetic emulation. Can you do it, Markus? Yes. And then she's got bilateral stimulation. Now it's easier to do the same kind of stimulation. Open up as far as possible and back together. And go as fast as you can. But always open up completely. Always open up completely. And then with the left hand, please. Open up completely and close up again. And then with the right hand, open up completely and close up again. Always open up completely and close up again. Please put your arm in front of your chest. And stand up. And then come down. And then come down. Then you can go back to bed. So, the question is whether deep brain stimulation for Parkinson's actually delays degeneration? There are a couple of papers suggesting that it does. Professor Viviana Grosjean has said that it's a very important thing to do. And so, the question is whether deep brain stimulation for Parkinson's actually delays degeneration? There are a couple of papers suggesting that it does. Professor Viviana Gradi-Naro here at Caltech is very interested in that topic. And she also has one of the early papers, one of the very key papers on optogenetic stimulation as a substitute for deep brain stimulation in a mouse model for Parkinson's. Now, smokers get less Parkinson's disease. More precisely, in retrospective epidemiological studies, there's an inverse correlation between a person's history of smoking and his history of Parkinson's disease. More than 50 clinical studies show this over a period of 50 years. So, the question is, is this causality? Does tobacco use to protect against Parkinson's? Or is it inverse causality? Do Parkinson's patients use less tobacco? Now, remember that the handlebar moustache, there's the substantia nigra movement degenerates. And the DTA, the upper lip pleasure, both activated by nicotine. In humans, there's a little bit of a crossover between these two organs. And so, it's possible that the substantia nigra encodes some pleasure. So, when the substantia nigra degenerates, stops producing dopamine in response to nicotine, maybe patients stop smoking, they certainly do. Maybe that's enough to cause the inverse correlation, which has also been ascribed to causality. But animal models show that nicotine itself probably is part of the neuroprotective action because you can do lesions of rodents and monkeys, and nicotine protects. And this protection in a sort of a hokey paper, alpha-4 nicotinic receptor knockouts don't have this protection. So, we need additional data, and one of the best bodies of data are going to come eventually from studying the hundreds of millions of people in the world who take up vaping. And so, we will ask whether vapors get less Parkinson's disease. At least we'll know it's nicotine. How about using nicotine patches? Nicotine itself, and in fact, there is a clinical trial underway for Parkinson's patients given nicotine patches. I claim that clinical trial is poorly conceived. Nicotine itself is a very good addictive drug, but it's not a very good therapeutic drug because it affects lots of different nicotinic receptors and because many people can't tolerate nicotine. Drug companies know this. They're trying to make nicotine derivatives. So, what is the basis for nicotine's protection? How can it addict the upper lip but protect the handlebars? We have a paper impressing the Journal of Neuroscience suggesting that nicotine enhances the cellular defense pathway. Early on, so that cells are better able to protect themselves against certain misfolded proteins and never get into the apoptotic arms of the pathway. We'll see whether that pans out. Other therapeutic approaches, limiting neurotrophic hypothesis you may remember well. And so, the question is whether you can give neurons the right kind of growth factor to protect them and the right kind of growth factor is GDNF, GLEAL-derived neurotrophic factor. Unfortunately, trials with GDNF failed. They were tried at AMGEN first 25 years ago and they did not work. And so, then the question is what about gene therapy? To put in cells that release GDNF, there are some encouraging trials underway now. Let's see if that works. And then, there are other gene therapy approaches that actually convert the subthalamic nucleus, one of the excitatory nuclei, to be more negative, which ought to interrupt that feedback loop and those tremors. And those trials are underway now by using an adeno-associated virus to make these guys inhibitory. Lots of stories to tell. I can't be unfortunately at office hours today and I will not be here next week, but if you want to know more, email me. And have a good weekend and a happy Thanksgiving.