Presynaptic GABAA receptors in vertebrate synapses

Area of Science:

• Neuroscience
• Neuropharmacology
• Synaptic Transmission

Background:

• Presynaptic gamma-aminobutyric acidA (GABAA) receptors were traditionally viewed as mediators of 'presynaptic inhibition' in the central nervous system (CNS).
• Emerging evidence suggests GABAA receptor activation can depolarize neurons and facilitate neurotransmitter release, contradicting the established inhibitory role.

Purpose of the Study:

• To investigate the role of GABAA receptors in synaptic transmission and neurotransmitter release.
• To clarify the contrasting roles of GABAA and GABAB receptors in neuronal excitability and signaling.

Main Methods:

• Utilized GABAA receptor agonists (e.g., isoguvacine) and GABAB receptor agonists (e.g., baclofen).
• Examined the effects on neurotransmitter release (e.g., substance P) and neuronal activity (e.g., EPSP, calcium currents).
• Investigated neuronal responses in central and peripheral tissues, including spinal cord and dorsal root ganglia (DRG).

Main Results:

• GABAA receptor activation depolarizes primary afferent neurons, facilitating the release of various neurotransmitters.
• Isoguvacine enhanced substance P release, while GABAB agonists produced antinociception.
• Baclofen (GABAB agonist) presynaptically inhibited dorsal horn neuron activity and substance P release by inhibiting calcium currents.

Conclusions:

• GABAA receptors likely mediate 'presynaptic facilitation' of transmitter release in the CNS.
• The findings challenge the long-held view of GABAA receptors solely mediating presynaptic inhibition.
• Differentiated roles of GABAA and GABAB receptors in modulating synaptic transmission and pain pathways were highlighted.