EFFECTS OF GABA AND ANXIOLYTICS ON THE SINGLE UNIT DISCHARGE OF SUPRACHIASMATIC NEURONS IN RAT HYPOTHALAMIC SLICES

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 GABAA and/or GABAB or GABA-BDZ receptor complex, respectively. © 1990.