Exam 3 Neurobiology

Describe the steps of the synaptic vesicle cycle

Put simply: budding, loading with neurotransmitter, storage in synapsins, docking via SNARE complexes, priming, fusion, and recycling via dynamin and fission

How does calcium induce vesicle fusion and neurotransmitter exocytosis?

Calcium binding to synaptotagmin initiates the fusion of the vesicle and presynaptic membranes.

Explain how NT are loaded/transported into the vesicles

Neurotransmitters are loaded into vesicles using a proton gradient created by the vacuolar H+-ATPase, which powers an H+/NT antiport (EX: VGLUT)

What is a vesicular transporter? Do all NTs have the same transporter?

A vesicular transporter is a membrane protein on the surface of a synaptic vesicle that moves neurotransmitters (NTs) into the vesicle using the proton gradient. Each NT has a different transporter

What protein is responsible for vesicle recycling after fusion to the PM?

Clathrin assembles into a coat on the cytoplasmic side of the plasma membrane, helping the membrane bend inward to form a budding vesicle. This clathrin coat shapes and stabilizes the developing vesicle, ensuring efficient recycling of synaptic membrane. Dynamin (GTPase enzyme) wraps around the narrow neck of the budding vesicle performing fission.

What is the role of Dynamin in the vesicle recycling process?

Dynamin uses GTP to pinch off clathrin-coated vesicles from the plasma membrane, completing vesicle fission during recycling.

Botulinum Toxin impairs what part of the vesicle cycle? What protein does BoTox “eat

away at”?

impairs the vesicle fusion step by destroying the SNARE complex so the vesicle cannot fuse with the membrane

What defines a Neurotransmitter?

NTs must be: present/stored in the presynaptic neuron, released during synaptic activity, and bind postsynaptic receptors

Define Myasthenia Gravis; how does it affect the nmj?

an autoimmune disease that produces antibodies against nicotinic Ach receptors at the NMJ which creates much smaller end plate potentials leading to muscle weakness and fatigue

Where is dopamine produced, what is it produced from, and what metabolizes it?

Produced in the substantia nigra and ventral tegmental area from dopa via dopa decarboxylase. it is metabolized by monoamine oxidase (MAO) and catechol-O-methyltransferase

List pathologies and drugs associated with dopamine

parkinsons is classified as degenerating neurons in the substantia nigra. Cocaine inhibits DAT for reuptake which increases the time that dopamine is in the synapse

Where is norepinephrine produced, what is it produced from, and what does it regulate?

Produced in the locus coeruleus from dopamine via dopamine b-hydroxylase and regulates cardiovascular and respiratory blood vessels

Where is epinephrine produced, what is it produced from, and what does it regulate?

Produced in relatively low levels in the CNS from norepinephrine via phenylethanolamine-N-methyltransferase and regulates cardiovascular and respiratory functions

Where is serotonin produced, what is it produced from, and what does it regulate?

Synthesized in the raphe nucleus from tryptophan initially by tryptophan-5-hydroxylase and regulates sleep and eating

What can make a NT unconventional?

they are not stored in vesicles, not always released from the presynaptic terminal, and are often involved in retrograde signaling

Define ionotropic receptors

Ionotropic receptors are ligand gated ion channels that open directly when a neurotransmitter binds, allowing ions to flow and rapidly change the membrane potential.

Define metabotropic receptors

Metabotropic receptors are gpcrs that trigger intracellular signaling cascades indirectly affecting ion channels or cellular activity, slow and longer lasting

Define fast vs slow synaptic transmission

Fast synaptic transmission occurs when neurotransmitters bind to ionotropic receptors, causing immediate ion flow and rapid changes in membrane potential (milliseconds).

Slow synaptic transmission happens through metabotropic receptors that activate G-proteins and second messengers, leading to slower, longer-lasting effects on the neuron (seconds to minutes).

What are the 3 essential components of GPCRs?

GPCR for reception, G-protein for signaling, and the effector or target

What is a G-Protein?

G proteins have an alpha and beta gamma subunit. When a ligand binds, GTP replaces GDP on the α subunit, causing it to dissociate from the βγ complex.

The α and βγ subunits then activate different effectors, and the α subunit’s GTPase activity ends the signal by hydrolyzing GTP to GDP.

Define the structure of metabotropic NT receptors

Metabotropic neurotransmitter receptors (GPCRs) have seven transmembrane domains with an extracellular NH₂ terminus and intracellular COOH terminus.

Their intracellular loops (C2, C3) and COOH tail bind and activate specific G-proteins, and they make up a superfamily of over 1,000 receptors.

What are the functions of M 1,3,5 vs M2,4?

M1,3,5: Gaq CNS and PNS, mostly affects smooth muscle contraction in glands. M2,4 : Gai CNS and PNS, slows heart rate by decreasing cAMP, Gby binds inward rectifiers to increase potassium permeability at your SA node

Compare mGluRs vs iGluRs

mGluRs mediate long term effects and participate in long term plasticity. iGluRs mediate most of the short term plasticity or initiate long term effects

Where are GABAb receptors found, and what type of receptor are they?

they are metabotropic receptors found in the CNS and autonomic centers; they regulate action potential frequency and are mostly inhibitory.

What G-protein do GABAb receptors couple to, and what is their effect on ions?

receptors couple to Gai; they open potassium channels and block calcium channels, leading to hyperpolarization

What G-proteins are coupled with the three families of adrenergic (epinephrine/norepinephrine) receptors?

a1 receptors with Gaq, a2 receptors with Gai, b receptors with Gas.

Where are neuropeptide receptors located relative to release sites, and what type are they?

All neuropeptide receptors are metabotropic and can act far from their release sites because they function at low concentrations.

What are the major classes and G-protein couplings for opioid and cannabinoid receptors?

Opioid receptors: coupled to Gαi and Gαq (modulate Ca²⁺ and K⁺ channels for analgesia).
Cannabinoid receptors: CB1 and CB2, both coupled to Gαi.

What are the different brain regions in which cannabinoid receptors are located and what function do they have in each region?

CB1 receptors are abundant in the hippocampus, basal ganglia, cerebellum, and prefrontal cortex. They inhibit neurotransmitter release by reducing calcium influx. CB2 receptors are mainly in microglia and immune cells, where they regulate inflammation and neuroimmune signaling.

Describe the properties of endocannabinoids.

Endocannabinoids are lipid based retrograde messengers. They are synthesized on demand in the postsynaptic neuron, not stored in vesicles, and diffuse back to presynaptic CB1 receptors to reduce neurotransmitter release.

How is nitric oxide synthesized, and how is its synthesis regulated?

Nitric oxide is made from arginine by nitric oxide synthase. NO synthesis is regulated by calcium levels

Nitric oxide is mostly studied in what type of signaling pathway and why?

NO acts as a retrograde signaling molecule. It diffuses from the postsynaptic neuron to the presynaptic terminal, where it modulates neurotransmitter release. Because it’s a gas that diffuses freely, it’s ideal for short-distance, activity-dependent modulation involved in processes like long-term potentiation (LTP).

What are EPSPs and IPSPs, and how do they differ from action potentials?

EPSPs and IPSPs are graded local changes in membrane potential caused by ligand-gated ion channels. EPSPs depolarize, IPSPs hyperpolarize. Unlike action potentials, they are not all-or-none and do not propagate, but instead summate to influence AP generation.

What is the reversal potential of the synapse dependent on?

The reversal potential depends on the type of ion channels at the synapse and the ions they pass. The direction of current flow is determined by the difference between membrane potential and the equilibrium potential

When is a postsynaptic potential considered excitatory or inhibitory?

A postsynaptic potential is excitatory when the reversal potential is above the action potential threshold, It is inhibitory when the reversal potential is below threshold

If inputs are considered excitatory or inhibitory, what determines this?

The receptor type and ion selectivity. Glutamate receptors are excitatory, GABA and glycine receptors are inhibitory

The dendritic shape and synaptic connectivity determines what?

determines how inputs are summated, affecting whether the neuron reaches threshold for firing.

Do synapses contain one type of receptor or multiple types?

Synapses often contain multiple receptor types, including both ionotropic and metabotropic which allows neurons to integrate rapid and long-term signaling for precise control of synaptic strength.

What are the 4 types of receptors and how do the gating kinetics differ?

ionotropic receptors open ion channels directly when a neurotransmitter binds; Enzyme-linked receptors are activated by growth factors and initiate signaling cascades; GPCRs activate G-proteins that trigger second messenger cascades. intracellular receptors bind lipid-soluble ligands such as steroid hormones or estrogen, which cross the cell membrane and directly influence gene transcription

Explain the difference between synaptic and paracrine signaling.

Synaptic signaling involves the release of neurotransmitters into a synaptic cleft, fast and localized. Paracrine signaling occurs when neurotransmitters diffuse through the extracellular space to affect nearby neurons more broadly, slow and widespread

Describe the membrane delaminated pathway

the gby subunit acts directly on nearby ion channels within the membrane, creating fast and localized changes

Describe the diffusible second messenger pathway

the diffusible second messenger pathway relies on the Galpha subunit to activate enzymes such as adenylyl cyclase or phospholipase C, which then produce second messengers like cAMP, IP3, or DAG. This indirect signaling is slower but allows for greater amplification and longer-lasting cellular effects.

Explain how GPCRs enable amplification in the signaling cascade.

GPCRs enable amplification because one activated receptor can activate many G-proteins, and each G-protein can in turn activate multiple effector enzymes, such as adenylyl cyclase. These enzymes then generate large amounts of second messengers like cAMP, which activate many downstream kinases.

What is the classic membrane-delimited pathway?

the betagamma subunit of metabotropic receptors opens GIRK resulting in potassium efflux and hyperpolarizing the membrane to reduce excitability

What are GIRK channels and how do they play a role in the membrane-delimited pathway?

GIRK channels open in response to the binding of beta subunits released from activated GPCRs. When these channels open, potassium ions flow out of the cell, causing hyperpolarization. This hyperpolarization reduces the cell’s excitability and, in the heart, helps slow the rate of contraction.

Explain how scientists can test for a membrane-delimited pathway.

using patch clamping they can test whether a GPCR and an ion channel are directly coupled If acetylcholine is applied to the bath and there is no change in GIRK channel activity, but activity increases when acetylcholine is placed directly in the recording pipette, it indicates that the receptor and channel are physically close within the same patch of membrane.

Explain the different ways in which metabotropic receptors can modulate synaptic transmission.

Metabotropic receptors are extremely diverse. Presynaptically, they can alter channel activity to regulate how much neurotransmitter is released. Postsynaptically, they can modulate the function or number of ionotropic receptors modifying the neuron’s overall excitability.

What do cAMP and cGMP target? how are they removed?

cAMP and cGMP activate protein kinases A and G (PKA and PKG), and are broken down by phosphodiesterases

What does IP3 target? how is it removed?

IP3 binds to receptors on the endoplasmic reticulum to release calcium and is deactivated by phosphatases

What does DAG target? how is it removed?

DAG remains in the membrane, where it activates protein kinase C (PKC) before being metabolized. Calcium serves as a universal messenger that activates kinases such as CaMKII and PKC and is removed from the cytoplasm by calcium pumps, sodium-calcium exchangers, and reuptake into the endoplasmic reticulum and mitochondria.

What proteins are involved in increasing calcium to the cytoplasm and removing calcium?

Calcium enters the cytoplasm through voltage-gated calcium channels, ligand-gated calcium channels, and receptors such as IP3 and ryanodine receptors. To remove calcium, the cell uses sodium-calcium exchangers, plasma membrane calcium ATPases and can store calcium in mitochondria

List some examples of Protein Kinases and describe their general function.

Important protein kinases include CaMKII, PKA, PKC, and MAPK. These enzymes phosphorylate target proteins, altering their activity, localization, or function. They regulate synaptic strength, AMPA receptor trafficking, and long term changes in plasticity and learning

List some examples of Protein phosphatases and describe their general function.

Examples of protein phosphatases include PP1, PP2A, and calcineurin. These enzymes remove phosphate groups, often acting to reverse the effects of kinases. They are crucial for resetting signaling pathways and regulating AMPA receptor signaling

Explain how the GPCR cascade can affect gene transcription.

The GPCR cascade can lead to PKA entering the nucleus and phosphorylating transcription factors that bind to DNA

Define synaptic facilitation

a temporary increase in neurotransmitter release caused by the buildup of residual calcium in the presynaptic terminal during rapid, repeated stimulation

Define synaptic depression

a reduction in neurotransmitter release during sustained activity, caused by vesicle depletion or reduced vesicle mobility

Define post tetanic potentiation

Post-tetanic potentiation is a short term increase in neurotransmitter release following high frequency stimulation, resulting from enhanced calcium entry and increased vesicle release probability.

What is a silent synapse?

a silent synapse is one that contains NMDA receptors but no AMPA receptors, making it functionally inactive at resting potential until AMPA receptors are inserted during development or plasticity.

What is the timescale for short-term plasticity?

Short term plasticity operates on a timescale of seconds to minutes from temporary biomechanical changes

Describe how Eric Kandel used the sea slug to examine synaptic plasticity, habituation, and sensitization.

Eric Kandel used the sea slug Aplysia by examining its gill withdrawal reflex. When the siphon was repeatedly touched, the reflex response weakened, demonstrating habituation due to reduced neurotransmitter release. However, when paired with an electric shock, the response became stronger, showing sensitization.

Habituation is due to what factors?

Habituation occurs because of a decrease in neurotransmitter release from the presynaptic sensory neuron. Short term it is due to lack of neurotransmitter availability but overtime synaptic connections can be lost

Describe the mechanism of short-term sensitization.

Short-term sensitization occurs when serotonin released from modulatory interneurons binds to GPCRs on the presynaptic sensory neuron. This activates adenylyl cyclase, increasing cAMP levels and activating protein kinase A (PKA). PKA then phosphorylates and inhibits potassium channels while enhancing calcium channel activity, leading to prolonged depolarization and greater calcium influx. The increased calcium triggers more glutamate release, strengthening the postsynaptic response for several minutes.