Neuropharmacology exam 1

7 types of Neurotransmitters

Acetylcholine, Glutamate, GABA, Glycine, Catecholamines, Serotonin, Histamine

Neuropharmacology

study of how drugs affect the nervous system

Drug

any chemical that has an effect on the body or brain

Why do we take drugs?

Variety of reasons (recreation, energy, treating illnesses, etc)

Limit of the nervous system

Drugs taken orally circulate throughout the entire body and can’t target a specific area

Why are opioid overdoses common?

People with chronic pain take opioids to relieve pain and eventually build tolerance, so they take a higher dose which causes respiratory depression and can be fatal

Historical uses for drugs

Medicinal, spiritual, recreational

Phenothiazine

First drug created to treat the nervous system (psychiatric disorders) in 1899, made from methylene blue

Chloropromazine

First discovered antipsychotic drug (1950s)

Pyramidal neurons

contains apical and basal dendrites

Pluripotent/Multipolar

Most common type of neuron

Purkinje neuron

Characterized by large “tree” of dendrites above the soma

How are neurons unique from other cells?

Cellular structures (dendrites, axons), mechanisms of signaling, patterns of neuronal connectivity, relationship of signaling to different behaviors, plasticity

Action potential

1. Resting potential (maintained by high K+ conductance)

2. EPSPs depolarize cell until it reaches threshold (-40 mV)

3. At -40 mV, voltage-gated Na+ channels open and sodium flows into the cell

4. Sodium continues entering the cell until it reaches equilibrium potential (+50 mV)

5. Voltage-gates sodium channels close and voltage-gated potassium channels open

6. Potassium flows out of the cell until it reaches its equilibrium potential (-100 mV)

7. Voltage-gated potassium channels close and cell returns to resting membrane potential

8. Refractory period in which another AP cannot be generated

Where are voltage-gated Na+ and K+ channels found?

Axon hillock and nodes of Ranvier

Resting membrane potential

Influenced by Na+/K+ pump to maintain ion concentration gradients, electrostatic force, and potassium leak channels

Threshold

Sum of EPSPs and IPSPs reach -40mV to cause an action potential

Absolute refractory period

Voltage-gated Na+ channels are inactivated, so action potentials can occur

Relative refractory period

Membrane potential is lower than resting potential, requires high excitation for AP to occur

Voltage-gated Na+ channels

Made up of 10 genes for alpha subunits, each channel is made up of alpha subunits and auxiliary subunits, contains 24 transmembrane segments (4th segment is positively charged and pushes out when Na+ is present)

Na+ channel blockers

Tetrodotoxin (TTX), Saxitoxin, Lidocaine, Antiepileptics

Tetrodotoxin (TTX)

Puffer fish toxin, blocks the pore of sodium channels

Scorpion toxin

Blocks the S4 segment of sodium channels to inhibit inactivation

Lidocaine

Local anesthetic, blocks inside of sodium channel

Batrachotoxin

Poison dart frog toxin, blocks S4 segment of sodium channel causing persistent activation

Where are most voltage-gated Ca++ channels found?

Axon terminus

High vs Low Voltage Activated Ca++ channels

High-voltage: expressed at axon terminus because positively charged ions flow towards axon terminal

Low voltage: expressed in dendrites, contribute to EPSPs

Calmodulin

Protein that binds calcium to form protein complex

Voltage-gated K+ channels

Made up of 48 genes in 16 subfamilies, each channel is made up of 4 subunits, 12 types

K_ATP currents

Gated by intracellular ATP, ATP closes K_ATP channels so decreased ATP levels keeps cells hyperpolarized

Opening K_V channels _________________ excitability of cell

decreases

K_V7 (KCNQ) currents

Generates M-currents due to inhibition following activation of muscarinic Ach receptors, when open channels contribute to repolarization of AP or decreasing frequency of APs

Two pore (2P) domain K+ channels

Potassium leak channels, modulated by stretch, temperature, acidosis, lipids, and anesthetics

Primary Erythromelalgia

Inflammation in extremities caused by mutation in SCN9A (gene encoding for Na+ channel alpha subunit)

Types of synaptic transmission

Electrical and Chemical

Electrical transmission

Direct connection between two neurons, signal is bidirectional

Gap junctions

Made up of 2 hemichannels called connexons, each connexon is comprised of 6 connexin proteins

Chemical transmission

Converts electrical signal into chemical signal back into an electrical signal at the synapse, most common type of transmission, unidirectional, allows for differential effects in signaling

3 components of a synapse

Presynaptic neuron containing proteins required for neurotransmitter release, Postsynaptic neuron containing receptors for neurotransmitters, and synaptic cleft

Neurotransmitter

Chemical substances synthesized and released by the presynaptic neuron responding to electrical stimulation, packaged into vesicles for release

Exocytosis

Releases neurotransmitters from vesicles by fusing vesicle with the membrane due to Ca++ influx at axon terminal

Clathrin

Protein that coats vesicles during exocytosis via adapter protein 2 (AP-2), bound to synaptotagmin

Dynamin

Protein that pinches off budding vesicles to be recycled in the presynaptic neuron

Small molecule neurotransmitters

Made and packaged in advance in the rough ER and golgi, travels across axon slowly, enzymes bind with precursor molecules to form neurotransmitters to be released (small clear vesicles)

Peptide neurotransmitters

Synthesized on demand, fast axonal transport already in vesicles (large dense vesicles)

Vesicle loading

Protons are pumped into the vesicle through ATPase proton pump, and neurotransmitter enters vesicle in exchange for protons

Vesicle pH

Acidic

Presynaptic terminal

Contains high density of VG Ca++ channels, contains proteins that participate in transmitter release (synaptotagmin, SNARES)

Synaptotagmin

Calcium sensor, contains 2 calcium binding domains that each bind 2 calciums (binds 4 calciums total)

SNAREs

Proteins that allow for vesicles to fuse to the membrane, V-SNARE binds with T-SNARE to facilitate exocytosis

T-SNARE proteins

Binds to V-SNAREs and membrane (SNAP-25 and syntaxin)

V-SNARE protein

Binds to vesicle and T-SNAREs (synaptobrevin) - vesicle-associated membrane protein (VAMP)

Synaptobrevin is a _____-SNARE

V

Syntaxin is a _____-SNARE

T

SNAP-25 is a _____-SNARE

T

Synaptic delay

Caused by delay of opening Ca++ channels relative to action potential

Botulinum Toxin (Botox)

Drug that blocks vesicle from fusing with the membrane by targeting SNAP-25 and synaptobrevin, has local distribution, stops neurotransmitter release

3 ways transmitter function can terminate

1. Transmitter can diffuse away from the synapse

2. Enzymatic degredation

3. Reuptake

Neurotransmitter degrading enzymes

Monoamine oxidase (MAO) - breaks down serotonin, norepinephrine, and dopamine

Catechol-o-methyltransferase - breaks down NE and dopamine

Acetylcholinesterase - breaks down Ach

Peptidases - breaks down peptide transmitters

Endogenous

Made in the body

Exogenous

Delivered to the body

Receptor

Protein that interacts with a molecule to cause a cellular effect

Agonist

Drug that binds to a receptor and activates it

Antagonist

Drug that binds to a receptor and inactivates it

Drugs are ______ acids/bases

Weak - do not fully ionize

Law of Mass Action

Higher concentration of products pushes reaction back to reactants

Why are most drugs weak acids?

Because they are taken orally so they get absorbed by stomach acid and the build-up of protons pushes drug back to de-ionized form so they can enter the bloodstream

pKa

pH which a drug is balanced between its charged and uncharged form

Blood Brain Barrier

Protects brain from harmful substances, formed by tight junctions, vessels surrounded by pericyte and astrocytes

Signal transduction mechanisms

Ion channels, G-protein coupled receptors, Enzyme-linked receptors, nuclear receptors

2 main receptor types

Ionotropic and Metabotropic

Ionotropic receptors

When ligand binds to receptor, ion channel opens and either positively charged or negatively charged ions enter the cell to cause IPSPs or EPSPs (immediate effect)

Metabotropic receptors/G-Protein coupled receptors (GPCRs)

Made of 7 transmembrane segments, activation leads to different cascade pathways (slow effect)

GPCR cycle

1. Receptor and G-protein are inactive

2. Ligand binds receptor, recruiting G-protein

3. GTP displaces GDP on G-protein

4. GTP-bound subunit dissociates from b-y subunit

5. Subunits perform their functions

6. a subunit hydrolyzes GTP to GDP inactivating the subunit

7. a subunit and b-y subunit rejoin

Types of G-alpha subunits

Alpha-i, alpha-q, alpha-s

Alpha-i subunit

Inhibits cAMP production, ion channels, phosphodiesterases, and phospholipases

Alpha-q subunit

Activates PLC-B, DAG, Ca++, and PKC

Alpha-s subunit

Increases cAMP production

Cholera toxin

Activates Gs proteins by blocking GTPase activity

Perussis toxin

Prevents Gi proteins from coupling with receptors

Seconds messengers

Calcium, cyclic nucelotides, phospholipase C, arachidonic acid (AA)

Calcium (second messenger)

Influx through channels or release from intracellular stores

Cyclic nucleotides

cAMP or cGMP are formed by adenylyl or guanylyl cyclase

Phospholipase C

Breaks down phosphatidylinositol into IP3 and DAG

Arachidonic Acid (AA) metabolites

Phospholipase A2 cleaves AA out of membrane

Effectors downstream of Ca++

Calmodulin, CaMK, Protein Kinase C, MEK, Phosphoinositide kinase 3 (PI3K)

Calmodulin

Protein that binds Ca++, activates calcium-calmodulin dependent protein kinase (CaMK), calcineurin, MAPK, phosphodiesterase, histone deacetylases

CaMK

consists of N-terminal catalytic domain, regulatory domain, association domain

Protein kinase C

Phosphorylates many proteins

MEK

Mitogen activated protein kinase (MAPK)/extracellular signal-related kinase

Phosphoinositide kinase 3 (PI3K)

Phosphorylates PDK1 which phosphorylates protein kinase B

cAMP

Activates protein kinase A (PKA) which phosphorylates cAMP response element binding protein (CREB)

cGMP

Generated by guanylyl cyclase and most commonly activated by nitric oxide (NO), regulates ion channels, smooth muscle, visual transduction and activated protein kinase G (PKG)

Breakdown of cAMP and cGMP

Phosphodiesterases (at least 10)

Phospholipase C (PLC)

Catalyzes breakdown of phosphatidylinositol into IP3 and DAG, most commonly activated by Gq proteins, specifically b-y subunits

IP3

Opens calcium channel on ER

DAG

Binds to calcium to activate PKC

Arachidonic acid metabolites

AA is cleaved out of membrane by phospholipase A2 (activated by Ca++), AA is converted by cycloosygenase 1 and 2 (COX1 and 2) into prostaglandins (PGE2, PGD2, PDF2)

Enzyme-linked receptors

Cytokine receptors, Tyrosine kinase receptors, Serine/threonine kinase receptors

Cytokine receptor ligands

Interleukins, interferons, tumor necrosis factor