Pharmacological characteristics of GABAA responses in postnatal suprachiasmatic neurons in culture.

The suprachiasmatic nucleus (SCN) is considered to be an endogenous circadian pacemaker. Previous studies have suggested functional roles of gamma-aminobutyric acid (GABA) in the control of circadian rhythms. In this study, the responses to applied GABA in cultured SCN neurons dissociated from postnatal rat hypothalamus were investigated using whole-cell voltage-clamp techniques. GABA and muscimol induced a large current response (EC50 values 5.3 and 1.6 microM, respectively), which was blocked by the GABAA antagonist bicuculline. This current response was also blocked by Zn2+ (0.5-50 microM) in a concentration-dependent manner, but was not potentiated by diazepam (10 microM) or ethanol (21 mM). These characteristics seem to correspond to those of GABAA receptors that lack gamma-type subunits.