PT4 (6) Neurotransmission (Meng)

4. Activation of Receptors

1. Ionotropic - ligand bind, open ion channel -Several ion channels open -Cation channel, allow positive charge in DIRECT EFFECT QUICK ACTION -Increase permeability to Cl FAST!!! -Ca enters into neuron, LONG TERM CHANGES 2. Metabotropic - Slower onset -Modify action of other proteins -G protein Alpha and Beta-gamma subunits split apart -GPCR - Amplification of your signal -Long lasting effects

3. Neurotransmitter Release

1. NT release is Ca dependent 2.Ca influx into cell, induce SNARE - grab vesicles to bring to membrane 3. Causes merge with membrane and spill out synaptic cleft 4. SNARE - grab vesicles and pull into membrane

Hyperkalemia

depolarize cell Extracellular K across membrane Depolarize enough -> reach threshold -> cell fire Acute = depolarize Chronic = conduction block

CNS Synpase (vs NMJ)

-Nicotinic (EPSP, Ionotropic)/Muscarinic (IPSP, Metabotropic) Receptors -Uses ACh -Cholinergic neurons produce and release ACh -EPSP depolarization (nicotinic/ionotropic) -IPSP (muscarinic/metabotropic GPCR)

NMJ (vs CNS Synapse)

-Nicotinic receptors -ACh released from Motor neurons -Ap 6x threshold

(?) Muscarinic Receptors (second messenger systems)

-beta-gamma subunit causes opening of K channel -Affecting conductance of K in membrane -HYPERPOLARIZES MEMBRANE -Make IPSP by opening K channels -Slow HEART RATE through muscarinic receptors, inhibitory effect

4.Activation of Receptors AMPLIFICATION

1 NT binds to 1 receptor -1 receptor bumps into many G proteins -Each G protein activates adenylyl cyclase -Activates Protein Kinase A -Phosphorylation of many proteins

Synaptic Transmission

1) NTs 2) Receptors 3) Simple neural circuits and their modification (plasticity)

1. Neurotransmitter *Synthesis*

1. Amino Acids: Glutamate (hyperalgesia), GABA (allodynia) 2. Amines: ACh, Norepi 3. Peptides Glutamate is converted into GABA Amines start from amino acids Dopamine and Epi made from Tyrosine Peptides start as proteins then cleaved

5. Neurotransmitter INACTIVATION

1. Diffusion 2. Degradation 3. Re-uptake 4. Desensitization

GABA excitatory inhibitory

1. GABA binds GABA A, cell permeable to Cl, =increase Cl conductance 11.5 to 1 out to in -65 8 to 1 out to in -40 GABA bind receptor GABA A membrane potential low to activate Na channels, opening channels = EPSP

QUESTION - you discovered a new disease that you believe is caused by too much activation of muscarinic receptors in the brain. Develop treatment.

1. What is the NT (endogenous agonist) that bind to muscarinic receptor = Ach 2. Describe 2 ways you can interfere with NT at muscarinic receptor = degrade, muscarinic receptor antagonist, block synthesis (get rid of precursor), block release 3. Drug binds muscarinic receptor. Unsure if it is agonist or antagonist. How determine? = Agonist: Mimics the effect of another known agonist or produce identical physic response - give known antagonist and block the effect Antagonist = giving an antagonist to heart, getting increase in HR, got to be agonist there working on receptor, antagonizing agonist -Block effect

Glutamate

1.Glutamate causes Ca to go in 2.Put + in cell, closer to AP 3. Ca Na in 4. Hits AMPA, just Na 5. -65 to -30 6.NMDA activated -30 7.NMDA with Mg on, comes off and NMDA opens 8.Ca through NMDA triggers AMPA to get plugged into membrane, more AMPA receptors 9. AMPA receptors triggered by glutamate 10. Enough EPSP fire without NMDA, pavlov conditioning neurons to fire more easily 11. leads to sensitization

K/Cl symporter

1.Neg inside, K+ wants to go out 2. Cl- is attacked to following K positive charge, wants to move out 3. Due to Ca entering cell, down regulation of symporter lose concentration gradient of Cl Increase permeability of Cl can make harder to excite neuron neuron downreg symporter depolarized EPSP inhibitory to excitatory increase ion Cl change concentration of Cl lost concentration gradient Cl leaves cell

Application of NT Principles

1.Pain transmission 2. Central sensitization (allodynia and hyperalgesia) 3. Plasticity 4. Descending modulation (opiates/cannabinoids)

Sensitization How does glutamate release from primary afferent neurons lead to influx of Ca in dorsal horn nociceptive neurons?

1.Repeated, high frequency of nociceptors can produce long-term changes in spinal cord dorsal horn that are Ca dependent

K/Cl symporter

GABA A receptor are ligand gated Cl channel. effect on membrane potential depends on intracell Cl concentration. When GABA A receptor open, Vm pulled toward Cl- equilibrium potential. Low supporters, results in high Cl in, and more depolarized Activation of GABA A depolarizes cell

Referred Pain

dermatome same nerve root MI and arm pain somatic and visceral pain fibers converge on second order neurons both used, brain can't figure out which organ pain visceral firing so much collaborates with somatic - amplification of signal

Spinothalamic Pathway B.Pain and Temp

dorsal horn of spinal cord

Rubbing Pain Gate Control Pain Theory

A-beta fibers myelinated get preference Rubbing = A-beta Perceive pressure not pain C-fiber ignored Interneuron releases GABA triggered by A-beta that down regulates/inhibits C-fiber

Dorsal Column-Medial Lemniscal Pathway A. Fine Discrimination Touch

A beta pathway - Pathway for sensation -Ipsolateral pathwya -Dorsal horn of spinal cord -Motor reflexes -Dorsal region

Distinguish between postsynaptic inhibition and presynaptic inhibition and provide examples of each.

A. Receptor activation - now I'm freestyling here but let's go with Myasthenia gravis for this one. So basically that destroys all the AChR's and pretty much prevents enough ACh from even binding to cause an effect. B. Reuptake/degradation - well this one was harder lol but I guess think of AChEI (acetylcholinesterase inhibitors) such as pyridostigmine or neostigmine for treatment of Myasthenia gravis. So this will prevent the degradation/reuptake of acetylcholine from the cleft allowing for more acetylcholine for a longer period of time in the cleft which will hopefully allow for more to bind to the AChR that are still functioning. Presynaptic inhibition -- screwing with synthesis, storage or release of neurotransmitters C. Synthesis- think Parkinson's disease right. So here we have a malfunctioning Tyrosine hydroxylase (which is the rate limiting step of dopamine synthesis) so we are not producing Dopamine to release from the presynaptic membrane D. Storage - think of Reserpine (which is a HTN medication) so this blocks storage of norepi and dopamine which means that you can't release those as a neurotransmitter ultimately lowering your BP. this shit has a lot of side effects so I'd probably pick a different HTN medication but I mean you do you. E. Release - so here let's think of BOTOX. That crap works magic for wrinkles which Jack (not me other one) highly recommends in his future career as a dermatologist. So this stuff is gonna go into the neuron and cleave the SNARES ultimately preventing release of the neurotransmitter in the cleft. Side fact... Cool thing is this stuff doesn't cross the BBB so our brain is saved from the toxin.

Catecholaine Re-Uptake (AMINES)

Amino acids have robust re-uptake Drugs that affect re-uptake SSRI: 1. Increase serotonin in synapse 2. Ways to extinguish the signal -Produces response in presynaptic terminal -Reduces transmission -Negative feedback line Only muscarinic in brain?

Opiate and Cannabinoid Analgeisa

high stress, don't feel pain until later -Stress induced analgesia -Placebo analgesia endogeonous opioid release Cannabinoid release pain Opioid to treat pain = affect opioid receptors. Presynaptic mechanism of inhibition Increase activity of RVM rostral ventral medulla neurons

GABA

main inhibitory NT Cl conductance goes up GABA B: K hyperpolarize

Allodynia

normally noxious pain is now painful - down regulation of K/Cl symporters piezo 2 a-beta fiber

Current = (voltage)(conductance) I = V*g

open channels = increase conductance No current = no driving force High conductance zero current zero membrane potential on channels for Cl No concentration gradient = no net movement of charge

Allosteric Modulators

Benzodiazepine - prolongs opening of Cl channels, enhancing effect of GABA Barbiturate Ethanol Effect permeability of Cl by binding away from GABA binding site

Glutamate: Excitatory Amino Acid

used by primary afferent neurons, brain IONOTROPIC receptors, produce EPSP Brain uses Glutamate to excite other neurons. Bind, changes permeability to ions, that produces excitation EPSP, excitatory NT named for agonists that bind

Driving force

what happens when channels open Driving force = |Vm - Eion| * g g= conductance

Equilibrium Potential

what membrane would be if selectively permeable to that one ion

Botox

Botox - cleave SNARE inhibit NT Ach release, doesn't cross BBB, muscle spasticity, migraine Botulinum toxin -Cleaves SNARE proteins -Inhibit release of NT -inject into muscle region, affect release of ACh -Botox doesn't cross BBB

Central Sensitization Dorsal Horn Spinal Cord C fibers A-beta fibers

C fibers - unmyelinated A-beta fibers - light touch, highly myelinated use Glutamate as NT -Constant activation of C fibers -Constant glutamate -Get long term changes, plasticity -Increase synaptic strength - GET EXAGGERATED RESPONSE! *Outcome could be Hyperalgesia C-fiber exaggerated response = hyperalgesia Slight Rubbing, depolarize and activate - mechanism for allodynia A-beta fiber, release GABA from interneuron, helps pain

Study

CHEMICAL NT IN BRAIN not just electrical*** IPSP hyper polarization proves chemical synapses Excitatory or nothing on off Chemicals - on off way off inhibited

GABA flipping, becomes excitatory Cl/K Symporter

Cl/K supporter breaks when injured Cl inside cell HIGHER THAN NORMAL GABA hits Cl channels, Cl doesn't want to come in Cl/K leave cell* through symporter Normally Cl in Cl gradient high inside and outside Channel open, Cl doesn't flow in, might leave a little No hyperpolarization, DEPOLARIZES!! *GABA is inhibitory unless symporter messed up* Cl normally higher out than in K leaves cell

2. Neurotransmitter *Storage*

Synaptic Vesicles - have transporters in membrane to bring in NT -Uses glutamate transporters to bring in glutamate and concentrate in vesicles To affect neurotransmission, affect Transporter molecules and vesicles Synthesis of amines in axon terminal alter NT through altering storage

GABAa Receptor = Ionotropic GABAb Receptor - Metabotropic

Conditioning = Increase in Synaptic Strength 1. Ca++ through NMDA channels, 2. to increase # AMPA receptors in synapse 3. (Salivation just from bell) When GABA binds to GABAb, increases K conductance

Voltage dependent NMDA channels***

Synaptic strength: same input = greater response upreg AMPA 1.Glutamate binds and Mg kicked off 2.Increases conductance of ions including Ca 3. Ca can make long changes in neurons 4.

Sensitization How does down regulation of Cl transporters cause GABA to switch from inhibition to excitation/how can opening Cl channel cause depolarization

Down regulation of Cl transporters in spinal cord dorsal horn can lead to GABA-induced excitation of nociceptive neurons

Opiate and Cannabinoid Analgesia

Descending modulation Rostral Ventral Medulla (RVM) High stress -> don't feel pain until later Stress induced Analgesia Placebo analgesia Endogenous opioid release Cannabinoid release pain, increase activity RVM neurons

Parkinson's (clinical example)

Dopamine Synthesis Tyrosine Hydroxylase - Rate Limiting Step for Dopamine Synthesis L-Dopa: precursor pro-drug, converted to Dopamine in neurons with enzyme to make Dopamine Substantia Nigra dying, give L-Dopa the precursor for Dopamine

QUESITON: Binding of Glutamate to AMPA receptor causes increase in permeability to Na+ and K+. What response would you expect upon AMPA activation?

EPSP Depolarization when channels open, K+ and Na+ increase conductance K/Cl Symporter -65 to -40

However, influx of Ca++ into the cell through the DHPR is not needed for the initiation of Ca++ release from the SR. Indeed, skeletal muscle is able to contract in the absence of extracellular Ca++

Instead, release of Ca++ from the terminal cisternae of the SR is thought to result from a conformational change in the DHPR as the action potential passes down the T tubule, and this conformational change in the DHPR, by means of a protein-protein interaction, opens the RyR and releases Ca++ into the myoplasm.

Effect of increasing K+ conductance on membrane potential

Hyperpolarize membrane make IPSP opening K channel get slowing of heart rate through muscarinic

Ionotropic Muscarinic

In ionotropic you will see ACH binding the two alpha subunits on a nicotinic receptor on the skeletal muscles leading to a net increase of sodium into the cell and causing a depolarization/AP FAST In metabotropic, you will see ACH triggering a muscarinic receptor on the heart, leading to potassium channel activation by the beta gamma subunit, hyperpolarizing the cell and decreasing heart rate Takes time..needs to amplify

Chemical Synapse

MAJORITY*** With NT More modulation

Cation Channel: Na/K Conductance

NMDA receptor - Increase Na and K, also Ca -Mg++ plugged channel AMPA increase conductance to Na and K

Cannabinoids - Breaking the rules

NT released as soon as synthesized, not stored Ca influx active response in presynaptic Rules 1. Synthesis and storage in presynaptic neuron 2. Released by presynaptic axon terminal 3. Produces response in postsynaptic cell

QUESTION: Binding of GABA to GABAa, causes opening of Cl channels, causing

Neuron to become less excitable Membrane potential depolarized

1 transmitter, many targets

Nicotinic receptor - Curare (antagonist) block receptor + Nicotine (agonist) - activate receptor Muscarinic -Atropine (antagonist) +Muscarine (agonist) Agonist - activate receptor Antagonist - block receptor

Electrical Synapse

No NT FAST! - no diffusion involved Less modulation Na depolarizes post synaptic

GABA causing Hyperalgesia Allodynia

Normal - GABA inhibit, low Cl concentration in cell GABA A receptor activated by GABA released from interneurons results in Cl- influx and neuron hyperpolarization Pain from dysfunction of inhibitory networks Inhibitory interneurons bad - GABA decreased, Accumulation of Cl in neuron GABA A receptor activation results in reduced hyper polarization, and even depolarization (excitation) Hyperalgesia allodynia

Reserpine

Old drug, first drug to control high blood pressure, treat psychosis Reduces storage of Norepi and Dopamine -Norepinephrine (storage reduced) -Trying to reduce levels of dopamine in neurons -Monoamine transporter for norepinephrine and dopamine bring in NT to vesicle

Opioid Agonists for pain treatment

Peptides made by brain (Endogenous opioids) GPCR hyper polarize cell Have diff selectivities *OPIOID = GPCR* HYPERPOLARIZEs cell (postsynaptic action) Inhibit transmitter release (presynaptic action)

Synaptic Transmission 5 things Important treatment that affect NT transmission: Affect Weekly #5

Presynaptic neuron action, before synapse: 1. Synthesis (drugs that affect synthesis) 2. Storage (drugs that affect storage of NTs) 3. Release (of NTs is Ca dependent) a. Voltage-gated Ca++ channels b. Influx of Ca causes release of NT Postsynaptic Neuron Action: 4. Receptors (post synaptic action, agonists or antagonists) 5. Signal termination (degradation of NT, re-uptake, diffusion) (Treatments that affect NS)

Referred Pain

Structures from dame dermatome - use same NERVE ROOT. For heart attack get referred pain to Left arm because developed from same embryonic segment Convergence-Projection Theory. Somatic and visceral pain fibers converge on same 2nd order neurons within the ipsilateral dorsal horn. This signal is then sent to thalamus and then the somatosensory cortex where the brain does its thing. Somatic nociceptive fiber in normal do not activate these second order neurons but when there is prolonged visceral stimulus they will start using somatic fiber endings to propagate and now second order neurons are being stimulated by both viscera and somatic pathway and brain can't figure out if stimulus was coming from organ or area that developed with same neuron as organ 1.Brain misinterprets pain signal 2.C3,4,5 keeps the diaphragm alive, carries these nerve roots 3.Phrenic nerve irritated 4.Brain thinks pain fibers from dermatomes - shoulder fine 5.Heart attacks - phrenic 6.Thinks pain from dermatomal distirbution 7.Referred pain = organ pain 8. Heart or diaphragm irritate nerve 9.Diaphragm right heart left

presynaptic inhibition and postsynaptic inhibition

Synthesis - *Parkinson's*, malfunctioning *Tyrosine hydroxylase* (rate limiting step of dopamine synthesis) not producing dopamine to release from presynaptic membrane Storage - *Reserpine*, *blocks storage of norepi and dopamine*, can't release those as NT and lower your BP HTN medication Release - *BOTOX, goes into neuron and cleaves SNARE* preventing release of NT in cleft, doesn't cross BBB Receptor - Myasthenia graves destroys Ach receptors prevents Ach binding Reuptake - AchE inhibitor - pyridostigmine or neostigmine treat MG, prevent degradation reuptake of ach, allowing longer in cleft, and allow binding to receptors still there

The Equilibrium Potential for an Ion Depends on:

THE CONCENTRATION OF THAT ION INSIDE AND OUTSIDE OF THE CELL! Not permeability of membrane Nernst Equation

Referred Pain Summary

Visceral nerve is firing so much that is collaborates with somatic nerve endings near second order neurons and allows amplification of signal to brain saying HEY WE'RE NOT OKAY HERE but brain says IDK WHAT'S GOING ON idk if you organ or nociceptive free endings from skin

Central Sensitization Hyperalgesia Allodynia

What: central sensitization = exaggerated response to stimuli Where: C fibers, Dorsal horn of spinal cord Why: increase in synaptic strength due to increased AMPA receptors How: nociceptive input → APs firing in c-fiber → pre-synaptic release of glutamate (and/or substance P) stimulates post-synaptic AMPA receptors (and NMDA activation also contributes to this) → increases conductance of Na+ and K+ (and Ca++ w/NMDA) and permeability also increases → so with increased conductance and permeability you have a driving force for EPSPs -> the constant depolarization of C-fibers will eventually increase synaptic strength (with AMPA up-regulation) and lead to central sensitization

GAD Glutamic Acid Decarboxylase

converts Glutamate to GABA -Convert Glutamate into inhibitory GABA Use GABA as NT

SNARE

grab vesicles and pull to membrane Ca induces SNARE

glutamate and GABA. excitatory versus inhibitory ionotropic receptor regulation of neuronal

• Glutamate is an excitatory NT • GABA is an inhibitory NT Glutamate 1. Glutamate binds to AMPA receptor, opens Na+ channels 2. Na+ influx into cell causes depolarization 3. Mg+ is kicked off of NMDA receptor and NMDA opens, causes influx of Ca++ into cell 4. Ca++ binds to PKC, leads to gene transcription of AMPA receptors 5. Resulting in up-regulation of AMPA receptors 6. Now when glutamate binds, you get an enhanced response to due the increase in AMPA receptors -> Central Sensitization Hyperalgesia and Allodynia GABA (is usually inhibitory, but when the K/Cl symporter is damaged GABA becomes excitatory) 1. GABA binds to ionotropic GABA receptor 2. Binding causes Downregulation of K/Cl symporters in membrane 3. Resulting in increased Cl conductance, Cl goes out 4. Chloride equilibrium potential becomes More positive 5. Becomes more positive and easier to fire -> Central Sensitization Hyperalgesia and Allodynia