Effects of GABA and anxiolytics on the single unit discharge of suprachiasmatic neurons in rat hypothalamic slices

Abstract

The effects of gamma-aminobutyric acid (GABA), muscimol, baclofen and the anxiolytics; diazepam (DZP), flurazepam (FZP) and zopiclone on single-unit neural activities in the suprachiasmatic nucleus (SCN) were investigated using the rat hypothalamic slice preparation. Exposure of the slice to GABA 10 −4 M produced inhibitory responses in 65% of the 49 SCN neurons examined. The threshold concentration of GABA ranged from 10 −6 to 10 −f4 M. Neurons responsive to GABA were not found to be restricted to a subdivision of the SCN, but were diffusely distributed throughout the nucleus. DZP, FZP and zopiclone produced responses similar to those of GABA. The inhibitory effects of GABA (10 −5 M) were potentiated by coadministration of DZP (10 −5 M). Muscimol and baclofen (10 −7 M to 10 −4 M) also inhibited SCN neuronal activity in a dose-dependent manner. Bicuculline (10 −5 M–10 −4 M) scarcely affected the baclofen-induced inhibition ( 1 6 ) but strongly antagonized the effects of muscimol ( 6 6 ), GABA ( 6 8 ) and DZP ( 4 5 ). These results suggest that the receptors mediating the inhibitory effects of GABA and anxiolytics within the SCN may be GABA A and/or GABA B or GABA-BDZ receptor complex, respectively.