Temporal Regulation of GABA Receptor Subunit Expression: Role in Synaptic and Extrasynaptic Communication in the Suprachiasmatic Nucleus.

Recent molecular studies suggest that the expression levels of δ and γ2 GABA receptor (GABAR) subunits regulate the balance between synaptic and extrasynaptic GABA neurotransmission in multiple brain regions. We investigated the expression of GABAδ and GABAγ2 and the functional significance of a change in balance between these subunits in a robust local GABA network contained within the suprachiasmatic nucleus of the hypothalamus (SCN). Muscimol, which can activate both synaptic and extrasynaptic GABARs, injected into the SCN during the day phase advanced the circadian pacemaker, whereas injection of the extrasynaptic GABA superagonist 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP) had no effect on circadian phase.