Termination of Neurotransmitter Action

Overview

• Objective: Proper neuronal communication requires the termination of neurotransmitter action.
• Processes Involved:
  • Transport: Physically removes neurotransmitter from the synaptic cleft.
  • Degradation: Breaks down the neurotransmitter molecule via enzyme activity.

Acetylcholine (ACh)

• Termination Process:
  • Enzyme: Acetylcholinesterase
  • Action: Degrades acetylcholine into choline and acetate.
  • Choline is transported back to the presynaptic terminal for new ACh synthesis.

Glutamate

• Termination Mechanisms:
  1. Reuptake into the presynaptic terminal.
  2. Transport into glial cells using sodium co-transporters.
• Glial Cell Processing:
  • Converted into glutamine by glutamine synthetase.
  • Glutamine is transported back to the presynaptic terminal for future synthesis.

GABA and Glycine

• Termination Process:
  • Reuptake into presynaptic terminal or transport to glial cells.
  • Uses sodium electrochemical gradient for transport.
  • Can be repackaged in synaptic vesicles or broken down in glial cells.

Dopamine

• Termination Process:
  • Reuptake into presynaptic terminal via dopamine transporter.
  • Inside the cell:
    • Degraded by monoamine oxidase (MAO) or catechol-o-methyltransferase (COMT).
    • Or repackaged into vesicles.

Norepinephrine

• Termination Process:
  • Similar to dopamine:
    • Reuptake via norepinephrine transporter.
    • Degraded by MAO or COMT, or repackaged.

Serotonin

• Termination Process:
  • Reuptake via serotonin transporter.
  • Degradation strictly by monoamine oxidase (MAO).
• Difference: Only MAO is used for degradation, unlike catecholamines.