GABA

Question 1

How is GABA synthesised?

Answer 1

• Glutamate———> GABA.
  
  • via enzyme Glutamic acid decarboxylase(GAD).
• Only achieved via GABAergic neurons.

Question 2

• How does GABA get transported to vesicles?
• How is GABA removed from the synaptic cleft? and types of cells involved?
• What occurs when GABA is metabolized and how?

Answer 2

GABA to vesicles:

• Achieved via Vesicular GABA transporters(VGAT).

Removal of GABA from synaptic cleft:

• GAT1 and GAT2: present in neurons and astrocytes.
• GAT3: only present in astrocytes.

Metabolism of GABA:

• GABA——-> Glutamate + succinate:
  
  • via GABA aminotransferase(GABA-T).

Question 3

How is GABA metabolized and reused?

Name each cell within the steps involved?

Answer 3

• GABA——> Glutamate + succinate.
  
  • GABA aminotransferase( GABA-T).

Glutamate—-> Glutamine: within astrocytes.

• glutamine synthetase.

glutamine is released from astrocytes and converted to Glutamate in neurons, which can convert to GABA.

Question 4

State the function of GABA_A receptors?

Answer 4

• Ionotropic.
  
  • allows Cl^- to move outside to inside the cell.

Causing hyperpolarization and inhibition of the post-synaptic cell.

Question 5

Function of Muscimol?

Answer 5

• Agonist of GABA_A receptors.
  
  • causes hallucinogenic effects.
• Perception of objects are larger then they actually are.

Question 6

Function of Benzodiazepines(BDZ)?

• Requirement for BDZ to work?

Answer 6

• Bind to GABA_A receptor site, increasing the potency of GABA to open receptor channels.
  
  • However, can only open in the presence of GABA.
  • requires 3 alpha subunits, 1 beta subunit, and 1 gamma subunit.
• Promotes sedative, anti-anxiety and anticonvulsant behaviour.

Question 7

Characteristics of GABA_B receptors?

• Mechanism?

Agonist example and clinical use?

Answer 7

• Metabotropic.
• Require 2 different subunits to assemble membrane and work,

Mechanism:

• inhibit cAMP formation.
• K+ channel opening.

Agonist: Baclofen:

• anti-spastic agent, and a muscle relaxant.