Synaptic GABAA receptor clustering without the γ2 subunit.

Area of Science:

• Neuroscience
• Molecular Biology
• Synaptic Plasticity

Background:

• Postsynaptic GABAA receptors (GABAARs) are critical for neuronal function, but the role of the gamma2 subunit in their synaptic clustering is debated.
• Synaptic currents persist in neurons lacking the gamma2 subunit, suggesting alternative mechanisms for GABAAR localization.

Purpose of the Study:

• To investigate the role of the gamma2 subunit in synaptic GABAAR enrichment.
• To identify alternative GABAAR subunits responsible for synaptic clustering in the absence of gamma2.

Main Methods:

• Spatially and temporally controlled deletion of the gamma2 subunit using Cre-expressing viral vectors in GABAARγ2(77I)lox mice.
• Whole-cell recordings to analyze miniature inhibitory postsynaptic currents (IPSCs).
• Freeze-fracture replica immunogold labeling and pharmacological experiments to identify GABAAR subunits and their function.

Main Results:

• Miniature IPSCs in neurons lacking gamma2 subunits showed prolonged decay times but unchanged amplitudes and rise times.
• Alpha1 and beta3 GABAAR subunits were found at perisomatic synapses in cells lacking the gamma2 subunit.
• Pharmacological analysis indicated that alpha1beta3gamma3 GABAARs, not other combinations, mediated the slowly decaying IPSCs.

Conclusions:

• The gamma2 subunit is not strictly essential for the synaptic enrichment of GABAARs.
• The gamma3 subunit is a likely candidate for mediating GABAAR clustering at synapses in the absence of the gamma2 subunit.
• Alternative GABAAR subunit compositions can support synaptic function.