Week 1: PAIN 1. Why is pain important? - Pain sends your body signals that something is happening that it needs to avoid in order to stay safe. It functions as an essential survival mechanism to keep us out of harm’s way and avoid future situations where we may be put in danger. - Creating aversive behaviors to things that are dangerous is an evolutionarily protective mechanism 2. What happens in your body when you get injured? - Tissues leak intracellular contents when you sustain an injury, and this serves as a signal to activate inflammatory responses. Signals include potassium, histamine, and acetylcholine - Bradykinin is a key polypeptide that is released in response to injury and activates inflammatory mechanisms like vasodilation for increased blood flow 3. What happens in your brain when you get injured? What are nociceptors and how do they work? - Primary afferent nociceptors located on peripheral nerve endings are the first to be activated, and they have many different channels that can be activated in order to initiate an action potential - Heat from TRPV1 is a possible activator, but so is bradykinin or ATP. Any of these receptors being activated can initiate an action potential - The threshold of nociceptors is higher than for touch neurons- the stimulation from lukewarm water would not be enough to cause a pain sensation - You can sense that heat is involved, but as more hheat is added the TRPV1 receptors would cause an action potential to give a pain message in addition to the heat recognition 4. What are the different features/aspects of inflammation? - Heat because blood is warm and there is increased blood flow to areas of injury - Redness since capillary permeability is decreased and there is more blood near the surface - Swelling- histamines cause capillaries to be leaky - Pain- signals that cause pain/activation of nociceptors - An injury like a burn may produce an area that is very sensitive after the injury occurs. This can cause allodynia in the area, where previously non painful stimuli produce a pain response due to increased sensitization (receptors may be phosphorylated to produce an action potential more easily. - If this continues for an extended period of time this can be known as neuropathycontinued sensitization long after an injury 5. What are the different types of peripheral nerve fibers and how do they transmit information differently? - A fibers, myelinated and fast transmission - Delta: activates two different cell types and is responsible for the sensation of a sharp pain - Beta: also fast transmission, but only responsible for touch sensation - C fiber: unmyelinated so slower transmission, secondary activation and responsible for aching sensations - These fibers are packaged and located in the dorsal horn of the spinal cord 6. What role does the somatosensory cortex play in pain perception? How does the homunculus model demonstrate this? - The somatosensory cortex maps our body for us. The homunculus model shows us the areas that are highly sensitive (like our lips and hands) and areas that are less sensitive, like our back and calves. More brain area is devoted to these larger areas and this is proportionally represented in the model to give a better picture of what areas our body prioritizes for sensitivity to touch and pain perception. 7. Describe the ascending and descending pathways of pain perception. - The ascending pathway takes information from the part of the body that an injury has occurred (primary afferent nociceptors), to the dorsal root ganglion that synapses to the dorsal horn of the spinal cord. This information is the transmitted up into the brain, where different tracts provide various pieces of information - Projection to the intralaminar thalamic nucleus and VPL contribute to emotional response - Projections to the somatosensory cortex tells us where in the body the injury occurred - The descending pathway takes this information back down from the brain to produce a behavior. - The descending pathway has inhibitory projections to the spinal cord so it can reduce the perception of pain so that the body’s main focus can be getting away from danger. This is an evolutionary mechanism for safety and survival. 8. What is the mechanism behind fever? - Fever is a response that originates in the hypothalamus. Ligands that are a result of pain and injury are carried up to the brain and bind to inhibit the normal thermoregulation that occurs in the brain. PGE2 G proteins in the median preoptic nucleus of the hypothalamus causes the removal of inhibition of the paraventricular nucleus and the dorsomedial nucleus. The PVN and the DMH are now activated and can tell the body to retain more heat, thus causing fever. Case 1 1. What is the mechanism of action of Tylenol? - Drug name: acetaminophen - Safe at low doses and safe for children to use - Blocks prostaglandin production (made from arachidonic acid) by inhibition of cyclooxygenase 1 and 2 - Metabolite of acetaminophen acts on TRPV1/cannabinoid receptors in the brain - Works as a fever reducer by acting in the hypothalamus 2. What is the mechanism of action of Lyrica? - Generic name: pregabalin - Calcium channel antagonist that binds alpha-2-delta subunits to decrease glutamate in synapses - Also increases EAAT activity - Activates potassium channels to increase hyperpolarization of the cell 3. What is the mechanism of action of Vicodin? - Generic name: hydrocodone/acetaminophen - Targets opioid receptors (specifically mu receptors) as an agonist- activation them blocks ascending pain signals - Acetaminophen has same action on COX enzymes 4. What is the mechanism of action of Advil? - Generic name: ibuprofen - Similarly to Tylenol, Advil inhibits COX 1 and COX 2 to inhibit prostaglandin synthesis from arachidonic acid. - Ibuprofen works throughout the body and so can reduce inflammation as well as pain, whereas acetaminophen only works in the brain to reduce pain Week 2: GLUTAMATE 1. Be able to draw a pre and postsynaptic neuron and synapse. - Glutamate is a very wide reaching neurotransmitter and is produced/used all over the brain. Many of the projections between pre and postsynaptic neurons are very long - Used for point to point communication - - Most of the receptors that it hits are excitatory, so glutamate could be considered an excitatory neurotransmitter, but sometimes it has inhibitory effects depending on which receptor type it interacts with Tripartite synapses are commonly seen- a third cell aside from the pre and postsynaptic cells called astrocytes helps to terminate responses by reuptake of neurotransmitters 2. Know the differences between ionotropic and metabotropic (G) receptors. - Ionotropic receptors are activated by a ligand (neurotransmitter) that binds. The conformation of the ion channel changes to allow the flow of ions through its pore. - GPCRs are also activated by the binding of a ligand/neurotransmitter, but have a different effect. In the unbound state, the alpha, beta, and gamma subunits all associate loosely with each other and the alpha subunit is bound to GDP. When the ligand binds, alpha subunit loses its connection with GDP and binds GTP instead. GTP binding causes the gamma and beta subunits to dissociate from the alpha and each are able to move to activate or inhibit an effector protein. In the final step, the ligand dissociates and GTPase degrades GTP back to GDP, causing the beta, gamma, and alpha subunits to reassociate and go back to the beginning of the process. 3. Explain the glutamate synapse: neurotransmitter production, packaging and release, types of receptors on the postsynaptic neuron, and effect of the neurotransmitter. - The neurotransmitter glutamate is a product of the Krebs cycle and can also be made from the amino acid glutamine (converted to glutamate by glutaminase) - Glutamate is packaged into vesicles by VGLUT transporters - opening of voltage gated calcium channels due to an action potential leads to fusion of the vesicle with the presynaptic membrane with the help of SNARE proteins. - The glutamate is now in the synaptic cleft and can interact with the postsynaptic receptors- ionotropic and metabotropic - Ionotropic receptors - AMPA: quick response to glutamate, allows Na+ in - NMDA: medium speed and allows Na+ and Ca++ in when the Mg2+ plug is removed - Kainate: slower to react, lets in Na+ - Metabotropic receptors - mGLURI: bound to Gq to create an excitatory response through the activation of phospholipase C effector protein and increases second messenger response - mGLURII,III: bound to Gi/o and located presynaptically as well as post. Activation of these receptors and the Gi/o G protein inhibits the activity of adenylyl cyclase - - Presence of mGLURII,III receptors on the presynaptic membrane works as an autoregulator to control glutamate release Glutamate is taken back up from the synapse by excitatory amino acid transporters (EAAT) that pull glutamate into the astrocyte cell. Inside the cell glutamate is converted back into glutamine where SN1 transporters put it back out where it can be taken back into the presynaptic cell. At this point the glutamine is ready to be converted back to glutamate, packaged into vesicles, and start the process over again 4. How does glutamate contribute to long term potentiation? - We know that environmental information changes synapses to form memories, particularly in the hippocampus - When glutamate activates AMPA and NMDA receptors, calcium and sodium ions flow into the postsynaptic cell - The calcium that enters is able to activate CaMKII (calmodulin kinase II) - CaMKII interacts with the nucleus to activate genes and initiate transcription factors that will work to make a new synapse (new dendritic spines to create more connectivity) - Additionally, CamKII causes AMPA receptors to be added to the surface of the postsynaptic cell, so it is easier to depolarize the cell and create an action potential. - The AMPA receptors are also phosphorylated, which changes their conformation to make them stay open for longer and again, it is easier for the neuron to reach the threshold for action potential. Case 2 1. What did we learn from our cognitive enhancement case? How do we upregulate or increase long term potentiation? What are the possible detrimental effects of excessive glutamate? - Our initial drug thought was making it easier to remove the Mg2+ plug from NMDA receptors, because this would allow calcium to flow into the cell with a smaller amount of excitement and create LTP pathways faster - We found out that creating cognitive enhancement drugs is not as easy as potentiating the mechanism of LTP and that excessive glutamate in the cells can actually cause excitotoxicity and very detrimental effects on neurons - Excess glutamate can actually trigger cell death/apoptosis Week 3: GABA 1. How is GABA created? What are its precursors? - A precursor of GABA is made naturally through the Krebs cycle- alpha-ketoglutarate which is acted on by GABA-T enzyme to make glutamate, which is then converted to GABA by GAD. 2. What are the differences between GABA-A and GABA-B receptors? What are the subtypes of each of these? - GABA-A receptors are ionotropic, and GABAB receptors are metabotropic - GABA-A receptors are pentameric and there are many different types of subunits that make up the receptor. These confer specificity and change their function- how fast they open, how long they stay open for, ect - Both are inhibitory receptors, and there are no subtypes! - GABA-A allows chloride ions to flow into the postsynaptic cell, depolarizing it so it is very difficult for it to fire. - GABA-B- activation of the beta-gamma subunit causes potassium channels to open to ions flow out- this leads to further depolarization of the cell - GABA-B receptors can also be located on excitatory cells that produce glutamate in order to turn them down - GABAB receptors activation causes the inhibition of adenylyl cyclase 3. What are the effects of presynaptic GABA-B receptors? - GABA-B receptors are able to serve as autoregulators, they inhibit the presynaptic cell from releasing too much GABA. This is part of the molecular fulcrum that works to balance mainly glutamate and GABA to keep the system in equilibrium and not provide too much sedation or anxiety 4. Be able to describe the GABA synapse. - GABA is created through the metabolic pathway described in 1. The neurotransmitter is then packaged into vesicles by the V-GAT transporter. - A similar mechanism for fusion and release exists for GABA as for glutamate- calcium entering the cell causes the vesicle to fuse with the membrane and release the NT across the synaptic cleft. - GABA interacts with GABA-A and GABA-B receptors on the postsynaptic membrane - Transporters both on the presynaptic neuron and the astrocyte take GABA back up from the synapse, where it is able to be recycled and repackaged into vesicles to begin the process again 5. What kind of drugs interact with GABA receptors? - Drugs generally have an effect on the GABA-A receptors and tend to bind as agonists - Benzodiazepines: Binding is generally allosteric- GABA is still needed in order for the receptors to be activated - - Causes channels to open more frequently so that hyperpolarization is more intense Barbiturates: does not require the presence of GABA, and so is more dangerous - Increased amount of time that the channels are open for Case 3 1. How does alcohol affect the body? - Generally, alcohol affects the GABA receptors in the brain 2. Review the brain areas that are affected by ethanol uptake and what action they impact. - Effects on balance occur in the cerebellum, alcohol specifically affects Purkinje cells that are needed for motor coordination - Disrupted GABA-A receptor transmission because ethanol increases the release of GABA - Sedation occurs generally with ethanol consumption because it is an overall CNS depression - GABA receptors are more active and cause stronger inhibition within the central nervous system - The perception that alcohol makes you feel warmer is not necessarily true, it actually decreases you core body temperature - Ethanol affects hypothalamus GABA receptors to make it less good at keeping homeostasis of temperature - Motor incoordination, similarly to balance, is also caused by Purkinje cells that have enhanced GABA release when ethanol is consumed - Reduced input from Purkinje cells means less coordinated output from cerebellar nuclei so motor commands from this area are more imprecise and poorly timed - Slurred speech from motor cortex inhibition- less able to make the actual sounds and mouth movements needed to generate proper speech. - Respiratory depression: receptors in the medulla oblongata and pons brain regions decreases excitation and so response to increased CO2 is diminished - Vomiting: area postrema- alcohol activates this area because of gastrointestinal irritation sense through afferent connections and above a specific BAC - Disinhibition: increased presence of dopamine in the prefrontal cortex leads to decreases perception of social cues and decreased behavioral control Week 4: SEROTONIN/DOPAMINE 1. What are some of the functions that are regulated by dopamine? - Dopamine functions as more of a modulatory neurotransmitter than glutamate and GABA, so instead of an on/off it has levels Needed for biological functions like sleeping and waking up, arousal, attention, and vigilance Dopamine and serotonin are both monoamines. They are made in certain brain regions but then can be sent out to perform their function elsewhere, compared to glutamate which is made all over the brain. 2. What are the key areas that dopamine is found in the brain? Why is the VTA a particularly important brain area to consider? - Substantia nigra pars compacta: learning and movement - Neuronal death in this region leads to Parkinson’s disease - Ventral tegmental area - Covers many different regions (hippocampus, amygdala, cingulate cortex) - The VTA fires when you receive a reward, but also fires in advance of getting a reward (prediction)- this creates the sensation of craving/wanting - Role of emotional memory and cognitive control of behavior - The reward pathways make the VTA (and projections to the nucleus accumbens) very important to consider, especially when thinking about the effects of drug use and other things that can become “addictive” - Median forebrain bundle as the key connection between the VTA and the NA. - arcuate nucleus 3. What are the precursors to dopamine creation? - Tyrosine is the amino acid precursor to dopamine, with L-DOPA as another intermediate 4. What are the types and functions of dopamine receptors? - Dopamine only acts on metabotropic receptors - D1,5 is linked to a Gs protein and is an excitatory receptor - Activated adenylyl cyclase, which activates cAMP and many other second messengers - D2,3,4 are linked to Gi/o proteins and are inhibitory receptors - Inhibits adenylyl cyclase so cAMP cannot be activated and causes potassium channels to open so ions flow out and lead to hyperpolarization of the cell 5. Be able to explain the dopamine synapse. - Dopamine neurotransmitters are loaded into vesicles by VMAT transporters - When calcium flows into the cell, vesicles fuse with the presynaptic membrane to be released into the synaptic cleft - - Dopamine binds to the receptors located on the postsynaptic membrane, and either inhibitory or excitatory responses ensue Many different ways to take dopamine out of the synapse are present - Dopamine transporters (DAT) are on the presynaptic membrane to reuptake DA neurotransmitters so they do not stay in the synapse too long (cocaine blocks these so dopamine is present in the synapse for longer) - Sensitivity is maintained through - Monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) converts DA to homovanillic acid so it cannot continue to act within the synapse D2 receptors are also located on the presynaptic membrane to serve as autoreceptors. The beta-gamma subunit inhibits voltage-gated calcium channels from opening and causing vesicles to fuse and release NT. alpha subunits activate the potassium channels so ions flow out of the cell and hyperpolarizes the presynaptic neuron, making it harder for it to reach an action potential. - DAT activity is increased so that reuptake occurs faster - D2 alpha subunits also inhibit adenylyl cyclase in the presynaptic cell. This prevents downstream effects, like the phosphorylation of tyrosine that is needed to create dopamine, from occurring. The actual creation and packaging of dopamine is disrupted so there are less of the actual neurotransmitters being released if the neuron is even able to fire 6. What is the function of the Raphe nucleus? - In the Raphe nucleus, not all of the cells are responsible for making serotonin. They are distributed throughout this brain region. - Projections dorsally to the rest of the central nervous system - Projections caudally to the medulla and spinal cord - Huge brain area but only some cells actually make serotonin- this diffuseness makes it hard to study - We know that disturbances to serotonin affects sleep, arousal, attention, feeding, and processing of sensory information 7. What is the precursor to serotonin? - Tryptophan is the precursor to 5-HT - Monoamine oxidase also breaks down serotonin, similarly to dopamine 8. Be able to explain the 5-HT synapse. Case 4 - - - - Study design: Comparison of the Reinforcing and Anxiogenic Effects of IV Cocaine and Cocaethylene - Gave rats doses of both cocaine and cocaethylene when they reached a goal box and examined behavior for running speed - Cocaethylene rats ran faster to get the goal box and had fewer retreatsshows that cocaethylene by itself is a very powerful motivator and also that it has anxiolytic effects compared to cocaine Study design: Comparison of Reinforcing Effects of Cocaethylene and Cocaine in Monkeys - Self administration of either cocaine or cocaethylene through implanted catheter - Fixed ratio of food being given, but progressive ratio of the drug - How much effort are they willing to give to get the drug over the food that they know how much work they have to do to get? Study design: Cocaine and Cocaethylene: Effects on Extracellular Dopamine in the Primate - Surgically placed cannulae into the caudate nucleus region of the brain - IV injection of either cocaine or cocaethylene - Measure the amount of dopamine release that occurred with the drugs Study design: Comparison of IV Cocaethylene and Cocaine in Humans - Human volunteers who were already users of cocaine - Measured physiological measures before and during drug injection, like HR, BP, cardiac rhythm - Also used visual analog scales to rate how good the drug “felt” - Procedure was double blind- neither the researcher or the participant knew whether they were given cocaine or cocaethylene - Were also asked to guess the identity of the medication- at higher doses they were better able to differentiate that they had not been given cocaine
