NEUR 402 Exam 1

autonomic system

made up of sympathetic and parasympathetic systems that have generally opposing actions

* ex: sympathetic → increased HR

parasympathetic → decreased HR

ionotropic receptors

protein that contains within it an ion channel

* direct gating
* fast actions
* last only milliseconds
* mediate rapid behaviors

metabotropic

protein that acts through a separate G protein

* 3 types of muscle: skeletal smooth, and cardiac
* indirect gating
* slow actions
* long-lasting effects (seconds to minutes)
* modulate behaviors

6 classes of Neurotransmitters

ACh, Biogenic Amines, AAs, Neuropeptides, Purine, Gases

acetylcholine (ACh)

makes HR slower

Biogenic Amines (Monoamines)

dopamine, (DA), norepinephrine (NE), epinephrine (E), serotonin (5-HT), and histamine

AAs

glutamate, gamma-amine butyric acid (GABA), and glycine

Neuropeptides

substance P and two enkephalins

Purine

ATP, adenosine

Gases

NO

5 criteria for determining whether compound is *Endogenous* Transmitter at specific synapse

1. synthesized in the neuron → neuron can make transmitter
2. present in the presynaptic terminal and released (amts sufficient to exert an action) → has to store and release it
3. mimics action of the endogenously released transmitter exactly -→ have to put in a level reasonable to what a nerve produces (has to make muscle contract)
4. mechanisms exists for terminating its action → has to be able to terminate transmitter


1. when specific antagonists are administered, they produce the same actions on the exogenously administered compound as on neurally released transmitters (sweat gland is exception)

five steps in natural history of neurotransmitter

1. synthesis
2. storage
3. release
4. postsynaptic action (receptors)
5. inactivation

ACh biochemistry and pharmacology

* synthesized from acetylene CoA and choline via choline acetylene transferase
* acts on both nicotinic (all inotropic and cause depolarization) and muscarinic (all metabotropic) receptors
* subtypes of both receptors exist
* nicotinic receptor stimulation leads to depolarization/excitation and muscarinic receptors lead to either excitation (ex: salivation) or inhibition (ex: cardiac muscle)
* cholinergic transmission is terminated by the catabolism of ACh via enzyme acetylcholinesterase (AChE)
* AChE inhibitors prolong ACh action → lead to depolarization block → inhibitors differ in how tightly they bind to AChE enzyme
* choline is a product of AChE action and is selectively taken back up into cholinergic nerve terminal and reutilized to make more ACh

nicotinic receptors

based on selective agonist nicotine and selective antagonist curare

muscarinic receptors

based on selective agonist muscarine and selective antagonists atropine

catecholamines

all contain catechol (benzene with two adjacent hydroxyl) → NE, Epi, Dopamine

pathway for biosynthesis of catecholamines

tyrosine → L-dopa → dopamine → NE → E

* hydrozylated, decarboxylated, hydroxylated, methylated

what does rate-limiting step mean

TH (tyrosine hydroxylate) is rate limiting enzyme for catecholamine biosynthesis

* if you want to speed up catecholamine biosynthesis speed up the rate-limiting step (TH)

dopamine function?

* dopamine levels were measured in the brain and shown that dopamine functions as transmitter within striatum
* cell bodies of dopaminergic endings in striatum are found in substantial nigra → cells called that due to high content of melanin
* tract called nigrostriatal tract
* Parkinson’s = low levels of dopamine in substantial nigra and striatum and TH
* L-Dopa restores catecholamines in system
* “bench to bedside” → speed of the dopamine findings not shown in other diseases (Alzheimer’s)

dopaminergic neurons express:

TH, I-AAAD

noradrenergic neurons express:

TH, I-AAAD, DBH

adrenergic neurons express:

TH, I-AAAD, DBH, PNMT

CNS noradrenergic system

locus coeruleus → bluish in humans

reuptake transporters for NE and choline

* NE is inactivated when taken back up
* AChE is active in the synaptic cleft → degrades ACh and gets choline reuptake → choline gets added to acetate to make ACh again

what are the consequences of blocking NE or choline uptake

* NE uptake → cause more NE in the synaptic cleft → cause increased alertness, raised HR, etc.
* choline uptake → no more choline to synthesize the NE → less NE or none in synaptic cleft → can cause to be left with with memory loss and muscle disorders

Neuropharmacology of catecholamines

* 3 catecholamines: DA, NE, E
* which catecholamine a neuron releases depends on which of the biosynthetic enzymes in pathway it expresses
* catecholines is terminated by being taken back up into the terminals they are released from
* catecholamine degradation *occurs intracellularly* rather than in synaptic cleft
* in the PNS, NE is the transmitter of sympathetic post ganglionic neurons

serotonin biosynthesis

* pathway is through Raphe nuclei

histamine biosynthesis

comes from histidine → histamine using enzyme histidine decarboxylase

glutamic acid

excitatory

GABA

inhibitory

* decarboxylation from glutamic acid

Glycine

inhibitory

AA transmitters

* glutamate is excitatory and only stored in synaptic vesicles in glutaminergic neurons
* GABA is inhibitory and synthesized from glutamate by glutamate decarboxylase
* Glycine is release at 50% of inhibitory synapses

peptidergic neurons

* MANY neuropeptides are thought to function as neurotransmitters
* LHRH is one → luteinizing hormone releasing hormone
* different families of neuropeptides
* neuropeptide synthesis occurs in neuronal cell bodies based on mRNA
* neuropeptide transmission terminated by diffusion

NO synthesis

from arginine

3 methods used for inactivation of neurotransmitters

hehe

late slow epsp

LHRH → present in sympathetic ganglion and nothing to do with leutinizing hormone

cotransmission

the release of more than one neurotransmitter from a single nerve terminal

* nonlocal neurons → projection neurons

neuromodulator

interacts with other molecules to modulate the effect of a neurotransmitter by enhancing or inhibiting its activity → ex: increasing binding with GABA

* E and NE are neuromodulators and regulate GABA and Glutamate

excitatory synapses

* postsynaptic depolarization
* Na+, Ca2+
* glutamate, ACh, serotonin, ATP

inhibitory synapses

* postsynaptic hyperpolarization
* Cl-, K+
* GABA, glycine

K+ conc and reversal pot

* more K+ intracellular
* K+ will want to leave the cell → creates a more negative charge inside cell
* reversal potential = -90

Na+ conc and reversal pot

* more Na+ extracellular
* Na will want to come into the cell → creates a more positive charge inside cell
* reversal potential = +60 mV

Cl- conc and reversal pot

* more Cl extracellular
* Cl will want to come into the cell → creates a more negative charge inside cell
* reversal potential = -70 mV

Ca2+ conc and reversal pot

* more Ca extracellular
* Ca will want to come into the cell → creates a more positive charge inside cell
* reversal potential = +100 mV

AMPA

* both AMPA and Kainate
* gated by glutamate
* permeable to Na and K
* excitatory or depolarizing
* reversal potential of \~0 mV
* depolarize = makes more excitable
* AMPAR -- GluA1-4
* agonists: AMPA, glutamate
* antagonists: *CNQX, NBQX, DNQX*
* when AMPA current goes up (+30) → pushes ions outside (K)
* when AMPA current goes down (-30) → pushes ions inside (Na)

NMDA

* blocked by Mg2+
* core agonists Gly needs to be there
* permeable to Na, K, *and* Ca
* NMDAR -- GluN1, GluN2A-D, GluN3
* agonists: glutamate, aspartate, NMDA
* antagonists: *D-APV (D-AP5)*, MK-801, Ketamine, Phencyclidine

Ca and NMDA

* Ca makes this special → important 2nd messenger → rise of intracellular Ca can activate calcium-calmodulin-dependent protein kinase II (CaMKII) → leads to long-term potentiation (LTP)
* high levels of intracellular Ca = toxic to postsynaptic neurons = glutamate excitotoxicity

NMDA and Mg

* AMPA → depolarize → Mg gets pushed away from NMDA → NMDA activated
* AMPA receptors undergo fast, sub-millisecond activation by glutamate → depolarization of the postsynaptic membrane → relief of magnesium block of NMDA receptors → rapid desensitization and deactivation on a millisecond time scale

NMDA and EPSC

* EPSC = excitatory postsynaptic current
* NMDA doesn’t contribute much to EPSC at hyper polarized membrane potentials
* can tell with the APV test → APV is an antagonist for NMDAs
* without APV you have a delays response but with APV you have a very fast response → depolarization
* Hyperpolarization → faster response with APV than without

kinetics of inotropic glutamate receptors

* AMPA/Kainate-EPSC is faster than NMDA EPSC

NMDA and synaptic plasticity processes

* NMDA receptors act as *coincidence detectors* during synaptic plasticity processes
* NMDA require Glutamate and requires postsynaptic depolarization activity to release to Mg → LTP
* presynaptic activity = glutamate release
* postsynaptic activity = depolarization → relieve Mg in NMDA

AMPA and NMDA with PSD (excitatory)

* PSD = postsynaptic density
* group of proteins at PSD that tether AMPA and NMDA
* TARP = transmembrane AMPAR Regulatory Protein
* regulates AMPA
* PSD-95 can influence AMPA through TARP and then NMDA indirectly through Mg release

GABAa receptors

* ligand-gated Cl channels
* mediates fast GABA transmission
* reversal potential = -60 mV for inotropic GABA receptor
* GABA a → ionotropic and GABA b → metabotropic

Glutamate receptors

* reversal potential = 0 mV (AMPA-like) for inotropic glutamate receptor

pharmacology of GABAa receptors

* antagonists: bicuculline, SR95531 (gabazine), Picrotoxin
* agonists: muscimol → activates GABA and diffuse and inhibits it → used to see role of GABA so temporary and reversible
* enhancers: benzodiazepines, barbiturates, anesthesia
* GABAA RECEPTOR IMPORTANT DRUG TARGET
* used for epilepsy
* GABA B slow compared to GABA A → B activated by GABA and permeable to K

synaptic second messanger sys

* cAMP sys: NE → beta-adrenergic receptor →transducer: Gs with primary effector adenylyl cyclase → cAMP to cAMP dependent protein kinase
* phosphoinositol sys: ACh → type 1 muscarinic ACh receptor → Gq and PLC beta → IP3 to Ca release and DAG to PKC
* direct G protein-gating: ACh → type 2 muscarinic ACh receptor → Gbetagamma → G protein-gated K channel (GIRK)

synaptic actions with same neurotransmitter

* fast inotropic and slow metabotropic synaptic actions mediated by same neurotransmitter
* M-type K+ channel → normally makes cell less excitable and bonded to PIP2 → in the muscarinic ACh type 1 recenptor → when PIP2 breaks off into DAG and IP3 → M-type K channel closes

DREADDs

* modify gene for GPCR of the M4 muscarinic receptor for ACh by modifying the motif (AA sequence) essential for ACh binding and engineer a like-minded receptor specifically meant for an inert ligand (CNO = clozapine-N-oxide) that will only turn on the modified receptor (no other such as ACh can cause a signaling cascade)
* used to study signaling and GPCR functions specific to the receptor without any other factors interfering other systems

synapse formation progression

neural stem cells (NSCs) → neurogenesis to become neurons → axon growth and pathfinding to become axons AND dendritic morphogenesis to become dendrites → both axons and dendrites go towards synapse formation which does signal transduction

neurotransmitter

any of several chemical substances ( E or ACh) that *transmit nerve impulses* across a synapse to postsynaptic element as another nerve, muscle, or gland

* time and spatialness is tightly controlled by neural signaling and regulates the signal transduction happening

ionotropic GLURs

NMDA, Kainate, AMPA

metabotropic GLURs

Group I → Gq

Group II → Gi/Go

Group III → Gi/Go

* the IP3 pathway

GABA B receptors

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* GABA B is either pre or postsynaptic


* GTP dependent G protein in GABAb receptor alpha subunit inhibits adenylyl cyclase and beta gamma subunit either inhibits Ca voltage-gated channel in pre synapse (inhibiting an excitatory response) OR activates GIRK channel for efflux K ions out of cell (causes an inhibitory response)

Earl Sutherland Jr

discovered cAMP

Martin Rodbell and Alfred G. Gilman

discovered G-proteins

cAMP activation of PKA

* cAMP releases catalytic domains on PKA that go downstream of signal transduction and phosphorylates proteins that do things
* if there is a long activation period → proteolysis and catalytic domains just out there without getting inactivated → causes disease

Edwin G. Krebs and Edmond H. Fischer

discovery of kinases and phosphotases

GPCR Ca Release

* PIP2 broken to DAG and IP3 by phospholipase C → DAG activates PKC and IP3 activates Ca Channel on ER that release Ca from ER to cytoplasm → signals Ca store-operated channels to let more Ca in to replenish depleted storage as Ca released from ER goes to PKC and then phosphorylation of substrates

cellular Ca homeostasis

* extracelular Ca greater than city Ca which is less than ER lumen Ca
* too high of Ca = toxicity of cell and keeps NMDA open too long and neuron will die
* SERCA takes Ca from store-operated Ca channels that bring in Ca from extracellular to replenish Ca in ER lumen when IP3 Ca channel opens and lets Ca out of ER lumen

STIM1-Orai1 Complex

* STIM1 → distributed throughout ER in resting cell and has EF hand motif to bind to Ca to see Ca level for conformational change
* when Ca in ER lumen is sufficiently high → EF hand site will be occupied by Ca and it will be in resting confirmation
* if STIM 1 detects Ca depletion → Ca will leave EF hand site (conformational change) → move laterally in ER and accumulate near plasma membrane → signals Orai1 to activate Ca influx to replenish ER lumen Ca levels

regulators of Ca conc

* ligand-gated iron channels: nAChR, NMDA
* voltage-gated Fe channels: Ca channels
* GPCRs: Gq → PLC → IP3
* Orai1 channels with STIM1
* extracellular: about 2mM Ca, ER is 0.6-0.8
* cross talk of mito and ER Ca signaling to keep homeostasis of Ca levels intracellularly

what does Ca neuronal signaling do?

* intracellular Ca binds to Ca binding proteins, channels and enzymes ( goes to annexing, Ca channels, K channels, PKC, etc.) and Calmodulin (NMDA receptor, CaM kinases, adenylyl cyclase, etc.) that go and do a variety of things

techniques to study Ca signalling

* organic Ca indicator dyes (in vitro not in vivo)
* GECIs (GCaMP series) = single polypeptide chain of fluorescent protein and Ca binding motif (in vitro and in vivo)
* single wavelengths and FRET-based ratiometric
* sensitive to Ca level

neuronal Ca sensor (NCS) proteins

* recoverin
* Guanylylcyclase activation protein (GCAP)
* visinin-like protein
* neurocalcin
* hippocalcin

techniques to study glutamate signalling

* classical pharmacological approaches can’t address this alone → molecular and functional diversity of GluR and distribution to multiple locations makes it hard to understand individual GluR contribution to neuronal signaling
* genetic approaches → high molecular and cellular specificity → but slow mode of action, in-reversibility, and compensatory mechanisms
* optical techniques → provide spatial and temporal resolution
* photo-caging, inactivation and switching → light to control activation at specific location and time

techniques to study GPCR signaling

* biosensors → imaging for a time and see effect in nucleus on genes

basic signaling properties

* from surface to nucleus
* there is a convergence and divergence of signalling
* synergy and differential regulation of adenylyl cyclase
* ALWAYS A BALANCE → inactivation and activation pathway of everything!!!
* cross talk → regulation done for homeostasis

receptor potentials

membrane potential response elicited in a sensory neuron by a sensory stimulus

synaptic potentials

membrane potential response elicited in a postsynaptic cel resulting from synaptic input from a presynaptic cell

AP

regenerative membrane potential response elicited in excitable cells, either spontaneous or in response to an input

what triggers AP generation

receptor and synaptic potentials

intrinsic electrical properties of excitable cells depend on three things

* plasma membrane
* active ion transporters
* ion channels

plasma membrane intrinsic electric property

* serves as boundary that separates intracellular and extracellular
* permits establishment of differences in chemical composition → basis for *chemical* driving force that influence passive solute movement through channels
* permits separation of charge between intra and extracellular → basis for *chemical* driving force influencing passive ion movement through channels
* mimic capacitor that can *store charge →* source of an electric field inside membrane → produces electric force on ions that encounter channel pore and elicit driving force from higher energy state to lower → ions go through change in energy as well moving between regions of different voltage

membrane potential

= difference in electric potential between intra and extracellular solutions = charge on membrane capacitor / membrane capacitance = electric field x membrane thickness

* extracellular solution taken as 0 for reference potential by convention

active ion transporters intrinsic electrical property

* use metabolically-derived energy to transport ions in an energetically uphill direction → supports non equilibrium distribution of ions → used to generate rapid transport through ion channels (ex: opening sensitive to stimulation)
* Na/K ATPase important transporter from standpoint of fast electrical signaling in excitable cells → establishes and maintains diffs in conc of intra and extracellular ions

ion channels intrinsic electrical property

* provide main pathway for ions to flow “passively” across biological membranes → energetically downhill direction
* regulated channel activity is used by cells to control flow of ions for generating electrical and chemical signals
* *active export* maintains a *low* intracellular solute conc → creates a driving force for *passive influx* through gated channels
* *active import* maintains a *high* intracellular conc → creates a driving force for *passive efflux* through gated channels
* Na/K ATPase maintains driving force → favors Na influx and K efflux through voltage-gated channels
* two functional properties of ion channels:
* permeation = ion movement through open channels
* determinants of ion permeation through channels
* ion size
* relative E of dehydration of ion in solution vs. within pore
* strength of ion binding to intra-pore ion binding sites
* gating = processes that control when channel is open or closed
* larger channel population you have = less noise and fluctuation you get → mean macroscopic current has smaller SD cuz so many of them makes randomness more identical

what does driving force depend on

* differences in ion conc and diffs in electrical potential across plasma membrane

flux

amount of substance passing through unit area in unit time (in direction of flow)

* = conductance x driving force
* ion movement = flow of charge = a flux

Fick’s 1st Law of Diffusion

* solute flux ( x Faraday’s constant (F) = current) at certain position and time is proportional to derivative of conc with respect to position at that time
* J = solute flux = moles/cm2/s
* D = diffusion coefficient = cm2/s
* solute flows from higher to lower conc
* diffusion coefficient is of the solute in particular solvent used
* if diffusing species is charged, net diffusion is accompanied by an electric current (i)
* z = ion valence
* zF = charged carried by one mole of solute

drift velocity depends on magnitude of E and ion mobility and constitutes a current

* given drift velocity (Vdrift) → there is ionic flux (Jelectro)
* Jelectro is product of ion conc (c) and Vdrift
* flux leads to current

electrodiffusion of ions in bulk solution

* the fluxes resulting from diffusion and the electrical force *add*
* Jtotal = Jdiff + Jelectro

Nernst-Planck electrodiffusion equation

* describes current through pores based on properties of the pore interior
* hard to apply this theory to ion movement through a channel and bulk ion concs and volts because the determinants of current magnitude inside channel pore are largely unknown and are only subject to indirect control by defining the composition of external solutions
* three things come from this: Nernst potential, modified ohm’s law, and GHK theory

Nernst potential

* conditions for zero net ion flux through a pore
* current is zero when voltage intra and extracellular has unique value that depends on concentration extra/conc intra of bulk solutions
* symmetrical solutions in cation-selective pore
* when Vm = 0, equal movements of flux from inside to out and out to in so everyone 0
* when Vm>0 → positive charges congregate to inside of plasma membrane and bigger cation flux from in to out than out to in
* both Vm and Vm-Ek (electrochemical driving force) increase
* net current from in to out
* when Vm

modified ohms law

* describes current as a function of Vm and yion (unitary conductance)
* assumes current is in steady state

what is the voltage for the total current through a channel equal to zero (Volt = Vrev)

* channel permeable to one ion species
* Vrev = Nernst pot for permeant ion
* channel permeable to multiple ion species
* Vrev depends on conc and permeation properties of all permeant ions
* Vrev is then the weighted average of equilibrium potentials of permeant ions where the weighting factors are the fractional conductances of the channel for the respective ions

main determinants for Vrev

* equilibrium potentials for permeant ions which depend on ratios of external and internal ion conc
* fractional conductance of channel to permeant ions

GHK (Goldman, Hodgkin, katz) constant field Theory

* describes current as a function of conc in, conc out, Vm and Ppore
* assumes current is a steady state and E is constant
* way current goes through ion channel varies through diff volts
* ex: resting potential for membrane containing two pops of leak channels (K and Na) with macroscopic conductances

Vrest

* volt at resting potential
* for cell with multiple types of leak channels is weighted average of reversal potentials for various channel types → each reflecting on ion selectivity properties of the respective channels with weighting factors representing fractional conductances imparted to membrane by the each channel pop

membrane potential dynamics

* Vm is proportional to membrane charge
* Vm(t) = Q(t)/Cm (membrane capacitance)
* time rate of change of Vm is proportional to net current
* sign convention for current → inward current is (-)
* Vrest is a stable equilibrium

passive responses

* when passive ion channels are present → allows for cell to go back to a net current of 0 and to its initial state volt instead of going to a voltage and staying there