Psychopharmacology

Question 1

Differentiate asymmetric and symmetric synapses.

Answer 1

Asymmetric: Excitatory; features a prominent postsynaptic density.
Symmetric: Inhibitory; features a less prominent postsynaptic density.

Question 2

What is an ionotropic receptor?

Answer 2

• Ligand-gated ion channels
• Fast, direct effects on membrane potential
• Cause immediate depolarisation or hyperpolarisation
• E.g., AMPA, NMDA (glutamate); GABA-A

Question 3

What is a metabotropic receptor?

Answer 3

• G-protein-coupled receptors (GPCRs)
• Indirect, slower effects via second messengers
• Modulate gene expression, plasticity, excitability
• E.g., GABA-B, dopamine D1–D5, muscarinic ACh

Question 4

What are the three subunits of G-proteins?

Answer 4

Alpha (α), Beta (β), and Gamma (γ) subunits.

Question 5

What do Gs-coupled receptors do?

Answer 5

• Activate adenylyl cyclase → ↑ cAMP
• Enhances plasticity, gene expression, and excitability
• Promotes depolarisation
• Example: Dopamine D1 receptors

Question 6

What do Gi-coupled receptors do?

Answer 6

• Inhibit adenylyl cyclase → ↓ cAMP
• Open K⁺ channels → hyperpolarisation
• Reduces plasticity and neuronal firing
• Example: Dopamine D2 receptors

Question 7

What are the main types of glutamate receptors and their functions?

Answer 7

AMPA (ionotropic):
* Opens with glutamate binding
* Allows Na⁺ influx → fast EPSPs
NMDA (ionotropic):
* Requires glutamate, glycine, and depolarisation to remove Mg²⁺ block
* Allows Na⁺ and Ca²⁺ influx → promotes plasticity and learning
* Highly gated to prevent excitotoxicity
mGlu (metabotropic):
* Activates G-proteins
* Increases plasticity and excitability

Question 8

What are the main types of GABA receptors and their functions?

Answer 8

GABA-A (ionotropic):
* Opens Cl⁻ channels → hyperpolarisation
* Fast inhibitory effect
GABA-B (metabotropic):
* Activates K⁺ channels via G-proteins
* Slower, prolonged inhibition

Question 9

How do agonists affect neurotransmitter systems?

Answer 9

Enhance neurotransmitter action
* Mimic neurotransmitters (e.g., L-DOPA, MDMA)
* Block reuptake (e.g., SSRIs, cocaine)
* Inhibit degradation (e.g., MAOIs)

Question 10

How do antagonists affect neurotransmitter systems?

Answer 10

Block neurotransmitter action
* Bind receptors without activating them
* E.g., naloxone (opioid), ketamine (NMDA), antipsychotics (D2), propranolol (β-adrenergic)

Question 11

How does ketamine act on NMDA receptors?

Answer 11

• NMDA antagonist
• Blocks the channel (mimics Mg²⁺ plug) even when glutamate and glycine are bound
• Preferentially targets NMDA receptors on inhibitory interneurons → increased excitation at low doses

Question 12

What is D-cycloserine (DCS) and how does it affect NMDA receptors?

Answer 12

• Partial agonist at the glycine site of NMDA receptors
• Enhances likelihood of receptor opening
• Promotes plasticity and learning
• Used experimentally to enhance extinction learning

Question 13

How do benzodiazepines affect GABA-A receptors?

Answer 13

• Positive allosteric modulators
• Bind to specific α subunits
• Enhance GABA’s inhibitory effect by increasing Cl⁻ influx

Question 14

How do hypnotics (e.g., barbiturates) affect GABA-A receptors?

Answer 14

• Positive allosteric modulators.
• Bind to α1 subunits of GABA-A receptors
• Enhance duration of Cl⁻ influx → hyperpolarisation
• Induces enhanced and prolonged inhibition

Question 15

What is optogenetics and how does it work?

Answer 15

• Uses light-activated ion channels
• Light triggers immediate activation or inhibition of targeted neurons
• Enables precise control of neural activity during behaviour

Question 16

What is chemogenetics and how does it work?

Answer 16

• Uses engineered GPCRs (DREADDs) activated by synthetic ligand (CNO)
• Modulates neuronal excitability via second messengers
• Allows selective, reversible control of specific neural circuits