Neurotransmitter Receptors II: Metabotropic
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Questions and Answers

What is the primary result of Gbg-mediated inhibition of voltage-dependent calcium channels (VDCCs)?

  • Binding of calcium to synaptotagmin
  • Decrease in neurotransmitter release (correct)
  • Increase in neurotransmitter release
  • Activation of SNARE complex

What component is directly interacted with by the inhibiting mechanism that affects the SNARE complex?

  • GIRK channels
  • Syntaxin (correct)
  • Calcium channels
  • Synaptotagmin

How does the activation of VDCCs affect synaptic transmission?

  • It facilitates vesicle fusion (correct)
  • It prevents exocytosis
  • It decreases calcium influx
  • It inhibits SNARE protein interactions

What is one of the consequences of inhibiting the SNARE complex in presynaptic GPCR modulation?

<p>Impeded membrane fusion (C)</p> Signup and view all the answers

Which ion's influx is primarily responsible for triggering exocytosis at presynaptic terminals?

<p>Calcium (A)</p> Signup and view all the answers

Which of the following receptors is NOT classified as a metabotropic receptor?

<p>GABAA receptors (C)</p> Signup and view all the answers

What is a key function of metabotropic receptors in contrast to ionotropic receptors?

<p>They modulate synaptic behaviors. (D)</p> Signup and view all the answers

What key function do GIRK channels have in the context of GPCR modulation?

<p>Regulate potassium permeability (C)</p> Signup and view all the answers

Which aspect of the exocytotic machinery is directly influenced by Gbg?

<p>SNARE complex assembly (C)</p> Signup and view all the answers

Which of the following is a presynaptic effector mechanism associated with GPCR activation?

<p>Inhibition of neurotransmitter release (D)</p> Signup and view all the answers

What mechanism does presynaptic GPCRs utilize to modulate neurotransmitter release?

<p>Inhibition of exocytotic machinery (C)</p> Signup and view all the answers

Which GPCR type is primarily associated with the actions of glutamate?

<p>mGluRs (A)</p> Signup and view all the answers

What happens during GPCR desensitization?

<p>Decreased responsiveness to receptor stimulation (C)</p> Signup and view all the answers

Which of the following mechanisms is responsible for the modulation of synaptic transmission by GPCRs?

<p>Initiating second messenger cascades (D)</p> Signup and view all the answers

What is a common feature of both mAChRs and adrenergic receptors?

<p>Both act via G protein-coupled signaling. (A)</p> Signup and view all the answers

Which receptor type is involved in the modulation of anxiety and mood through GABA signaling?

<p>GABABRs (B)</p> Signup and view all the answers

What role does Gbg play in relation to GIRK channels?

<p>It opens GIRK channels. (D)</p> Signup and view all the answers

In what direction do GIRK channels primarily pass current?

<p>Outward direction is preferred. (D)</p> Signup and view all the answers

What effect does GIRK activation have on the membrane potential?

<p>Hyperpolarizes the membrane. (C)</p> Signup and view all the answers

What is the consequence of PKA-mediated closure of K+ channels on postsynaptic excitability?

<p>Decreases K+ efflux and leads to depolarization. (B)</p> Signup and view all the answers

How does prolonged GPCR activity modify synaptic transmission?

<p>By changing transcription and chromatin structure. (D)</p> Signup and view all the answers

Which type of channel does PKA primarily affect to alter postsynaptic excitability?

<p>S-type K+ channels. (A)</p> Signup and view all the answers

What is the physiological outcome of GIRK channel activation?

<p>Induction of membrane hyperpolarization. (C)</p> Signup and view all the answers

During the GPCR activation process, what happens at the postsynaptic level regarding K+ channels?

<p>They can close, which decreases K+ efflux. (A)</p> Signup and view all the answers

What is the primary structural difference between metabotropic glutamate receptors (mGluRs) and most other GPCRs?

<p>mGluRs are functional dimers. (B)</p> Signup and view all the answers

Which of the following GPCR types is primarily involved in memory formation?

<p>mGluRs (D)</p> Signup and view all the answers

What does the activation of CREB primarily enhance?

<p>Transcription of genes related to memory. (A)</p> Signup and view all the answers

In the context of GPCRs, which action would likely NOT involve presynaptic mechanisms?

<p>Regulation of ion channel opening. (D)</p> Signup and view all the answers

Which type of receptor primarily contributes to the processes of presynaptic and postsynaptic signaling in the nervous system?

<p>Metabotropic receptors (D)</p> Signup and view all the answers

Which of the following statements about GPCR desensitization is false?

<p>Desensitization is an irreversible process. (D)</p> Signup and view all the answers

What is a primary function of G proteins in GPCR signaling?

<p>They facilitate effector mechanisms. (C)</p> Signup and view all the answers

Which GPCR type is known for its involvement in the modulation of mood and emotion?

<p>Serotonin receptors (B)</p> Signup and view all the answers

What distinguishes D1-like receptors from D2-like receptors regarding their effect on adenylyl cyclase (AC)?

<p>D1-like receptors activate AC through Gs, whereas D2-like receptors inhibit AC through Gi/o. (D)</p> Signup and view all the answers

Which of the following locations is NOT associated with D1-like receptors?

<p>Hippocampus (HPC) (A)</p> Signup and view all the answers

Which G protein is associated with the D2 receptor subtypes?

<p>Gi/o (C)</p> Signup and view all the answers

Which effect is associated with D2-like receptors?

<p>Inhibition of adenylyl cyclase (AC). (C)</p> Signup and view all the answers

What type of receptors are 5-HT1AR and 5-HT4R classified as?

<p>Metabotropic serotonin receptors (B)</p> Signup and view all the answers

Which of the following mGluRs is primarily localized in postsynaptic terminals?

<p>mGluR1 (B)</p> Signup and view all the answers

What is a primary function of D1-like receptors within the brain's frontal cortex?

<p>Increasing levels of cyclic AMP (cAMP). (B)</p> Signup and view all the answers

What characterizes the behavior of presynaptic versus postsynaptic serotonin receptors?

<p>Both groups can exist in presynaptic terminals but serve different functions. (B)</p> Signup and view all the answers

What is the role of β-arrestin in homologous desensitization?

<p>It prevents Gs coupling to GPCRs. (C)</p> Signup and view all the answers

Which type of desensitization does not require ligand binding?

<p>Heterologous desensitization (A)</p> Signup and view all the answers

What effect does GRK-mediated phosphorylation have on GPCR function?

<p>It facilitates β-arrestin binding. (A)</p> Signup and view all the answers

What is one consequence of short-term desensitization of GPCRs?

<p>Uncoupling of GPCR from G proteins (A)</p> Signup and view all the answers

In what manner does homologous desensitization primarily occur?

<p>Via GRK-induced phosphorylation and subsequent β-arrestin binding (C)</p> Signup and view all the answers

Which of the following best describes the mechanism of heterologous desensitization?

<p>Non-ligand-dependent phosphorylation of GPCRs (D)</p> Signup and view all the answers

Which intracellular component is primarily responsible for the phosphorylation of GPCRs during desensitization?

<p>GPCR kinase (GRK) (B)</p> Signup and view all the answers

Which of the following statements correctly differentiates between homologous and heterologous desensitization?

<p>Homologous desensitization is induced by GRK activity on ligand-bound receptors. (D)</p> Signup and view all the answers

Flashcards

Metabotropic receptors

These receptors indirectly regulate ion channels by activating second messenger cascades.

GPCRs

G-protein coupled receptors; a large family of receptors that use G proteins as intermediaries.

GPCR Activation

Binding of a neurotransmitter activates a GPCR, triggering a cascade of events within the cell

Effector Mechanisms

These mechanisms describe how activated GPCRs influence synaptic transmission.

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mGluRs

Metabotropic glutamate receptors. A type of GPCR.

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mAChR

Muscarinic acetylcholine receptors; GPCRs that respond to acetylcholine.

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GPCR Desensitization

Mechanisms and processes within the cell that reduce the ability of GPCRs to respond to further stimulation.

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Ionotropic receptors

These receptors rapidly open ion channels in response to neurotransmitters.

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GIRK channel activation

G protein subunits directly interact with GIRK channels, causing them to open, leading to hyperpolarization of the membrane due to potassium efflux.

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Inward rectifier channels

Channels that allow ion movement more easily in one direction (inward) compared to the other (outward).

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VDCC Inhibition

Gbg protein reduces voltage-dependent calcium channel activity, lowering calcium influx.

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CREB Activation

Process triggered by PKA (protein kinase A) leading to memory formation.

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Potassium efflux

Potassium ions flowing out of the cell.

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Hyperpolarization

Membrane potential becomes more negative.

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SNARE Complex Inhibition

Gbg protein interferes with SNARE complex proteins (syntaxin, SNAP-25, VAMP/synaptobrevin) preventing vesicle fusion and neurotransmitter release.

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mGluR Structure

Metabotropic glutamate receptors (mGluRs) exist in dimers in the plasma membrane, needing 2 glutamate molecules for maximal effect

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Neurotransmitter Release

Action potential causes calcium influx via VDCCs, which interacts with synaptotagmin, causing neurotransmitter vesicle release.

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PKA-mediated K+ channel closure

PKA enzyme phosphorylates K+ channels, causing them to close, decreasing K+ efflux, and leading to depolarization.

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GPCR Activation

Neurotransmitter binding to G-protein coupled receptors starts a signaling cascade.

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Serotonin-sensitive K+ channels

Type of potassium channels that are responsive to serotonin.

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GPCR Function: Presynaptic Effects

Activated G protein coupled receptors (GPCRs) affect synaptic transmission at the presynaptic terminal.

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Gbg Protein

A protein subunit related to G protein that mediates presynaptic GPCR signaling, affecting neurotransmitter release.

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GPCR modulation of synaptic transmission

G protein-coupled receptors (GPCRs) can affect how signals are passed between nerve cells by indirectly opening or closing ion channels or influencing other cellular processes.

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GPCR Function: Postsynaptic Effects

Activated G protein coupled receptors (GPCRs) affect synaptic transmission at the postsynaptic terminal.

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Synaptotagmin

A protein that binds calcium and triggers vesicle fusion with the membrane for neurotransmitter release.

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Long-term synaptic modulation

Changes in synaptic strength persisting for extended periods.

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Exocytosis

The process where a vesicle releases its contents by fusing with the cell surface.

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Ionotropic vs. Metabotropic

Ionotropic receptors open channels directly, while Metabotropic receptors use a second messenger pathway.

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G Protein Coupled Receptors (GPCRs)

A large family of receptors that use G proteins as intermediaries for intracellular signaling.

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SNARE complex

A group of proteins that play a vital role in the fusion, or "zippering", of vesicles and the cell membrane.

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Effector Mechanisms

Actions that describe how activated GPCRs influence signaling pathways and synaptic transmission.

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Presynaptic GPCRs

G protein-coupled receptors located on the presynaptic neuron that modulate synaptic transmission.

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D1-like Receptors

Dopamine receptors that activate adenylyl cyclase (AC) via Gs protein.

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D2-like Receptors

Dopamine receptors that inhibit adenylyl cyclase (AC) via Gi/Go proteins.

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5-HT receptors

Serotonin receptors mostly at post-synaptic terminals, some are also presynaptic.

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GPCRs

G-protein Coupled Receptors are a large class of cell surface receptors

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G-proteins

Intracellular signaling proteins linked to GPCRs

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Adenylyl cyclase (AC)

An intracellular enzyme that converts ATP to cyclic AMP (cAMP).

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Presynaptic Terminals

Areas of nerve axons that release neurotransmitters

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Postsynaptic Terminals

Area of nerve cells receiving neurotransmitters

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GPCR Desensitization: Heterologous

Desensitization of GPCRs without any direct ligand binding. PKA and PKC phosphorylate the GPCR, affecting its ability to interact with G proteins.

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GPCR Desensitization: Homologous

Desensitization of GPCRs with ligand binding. GRKs phosphorylate the GPCR, enabling β-arrestin binding and uncoupling of the GPCR from the G protein.

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Short-term GPCR desensitization

GPCRs quickly reduce their response to continued stimulation. This process often involves phosphorylation, interaction with β-arrestins, and uncoupling from G proteins.

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GRKs (G protein-coupled receptor kinases)

Enzymes that phosphorylate GPCRs, leading to their desensitization.

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β-arrestin

A protein that binds to phosphorylated GPCRs, preventing them from interacting with G proteins and potentially initiating internalization.

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GPCR Internalization

The process of removing a GPCR from the cell membrane.

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Ligand-bound GPCR Desensitization

A desensitization process that occurs when a ligand is bound to the receptor. This is characterized by GRK-mediated and β-arrestin coupling, leading to the receptor's inactivation/internalization.

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PKA and PKC

Protein kinases that phosphorylate GPCRs leading to changes and often desensitization. Often involved in heterologous desensitization.

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Study Notes

Neurotransmitter Receptors II: Metabotropic Receptors

  • Metabotropic receptors are a type of neurotransmitter receptor
  • These receptors are a complex system

The Life Cycle of Neurotransmission

  • Synthesis (steps 1-2)
  • Storage (step 3)
  • Release (from lecture 4)
  • Receptor Binding (steps 4-5)
  • Inactivation (steps 6-9)

Overview of lonotropic vs. Metabotropic Actions

  • GPCR General Structure
  • GPCR Activation and Action
  • Binding to G-proteins
  • Effector Mechanisms: Presynaptic
  • Effector Mechanisms: Postsynaptic
  • GPCR Types and Specific Mechanisms
    • mGluRs
    • mAChRs
    • GABABRs
  • Dopamine and Serotonin Receptors
  • GPCR Desensitization
  • Overview

Ionotropic Receptors

  • These receptors mediate behaviors
  • Metabotropic receptors modulate behaviors
  • Nicotinic acetylcholine (ACh) receptors
  • γ -aminobutyric acid (GABA) and Glycine receptors
  • α- and β-adrenergic receptors
  • Muscarinic ACh receptors
  • GABAB receptors
  • Subset of glutamate and serotonin receptors
  • Dopamine receptors
  • Receptors for neuropeptides, odorant receptors, rhodopsin
  • AMPA/Kainate and NMDA receptors

How does the Activation of these Second Messenger Cascades Impact Synaptic Transmission?

  • Table 11-1 shows a comparison of Synaptic Excitation.
  • Ion channels involved, effects on conductance/potential, time course, type of synaptic action, second messengers are all included

Metabotropic Receptors Regulate a Variety of Channel Types

  • Resting channels
  • Voltage-gated channels (action potential, Ca2+ influx for neurotransmitter release)
  • Ligand-gated channels

A Shared Logic of GPCR Activation

  • Neurotransmitter (first messenger)
  • Receptor
  • Transducer
  • Primary effector
  • Second messenger
  • Secondary effector

Common G protein Effector Targets

  • cAMP system- including norepinephrine, acetylcholine, and B-adrenergic and muscarinic receptors
  • Phosphoinositol system- including norepinephrine, acetylcholine, and B-adrenergic and muscarinic receptors
  • Direct G protein-gating

Ligand-Induced GPCR Conformational Changes Activate G Proteins

  • Agonist binding stabilizes the active conformation and shifts the equilibrium
  • Antagonist binding blocks activation (through negative or neutral antagonism)

General Mechanisms of GPCR Modulation of Synaptic Transmission

  • Presynaptic GPCRs: Neurotransmitter Release
    • Gs
    • Phosphorylation of proteins involved in vesicle recruitment, docking, and fusion

GPCR Desensitization

  • Heterologous desensitization (no ligand binding necessary)
  • Homologous desensitization (ligand bound)
  • ẞ-arrestin binding enhances rate of GPCR internalization

Overview

  • Ligand-induced conformational changes in GPCRs facilitate interaction with heterotrimeric G-proteins
  • GPCR internalization and degradation or recycling are followed by attenuation of effector signaling

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Lecture 6 Outline | Neurotransmitter Receptors | PDF

Description

Dive into the complex world of metabotropic receptors and their role in neurotransmission. This quiz covers receptor binding, GPCR mechanisms, and the life cycle of neurotransmission. Understand how these receptors differ from ionotropic receptors and their impact on behavior.

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