Effect of thiopental on hippocampal GABA receptors in rat brain

The effect of thiopental on rat brain hippocampal GABA receptors was studied in slice preparations and membrane fractions. In slice preparations, thiopental at a concentration of 10(?5) M enhanced the GABA (1?5 x 10(?4)M) inhibition of the field potentials evoked in pyramidal neurons by stratum radiatum stimulation. In hippocampal slices obtained from chronically barbital-administered (100 mg/kg, b.i.d., 10 days) rats, less enhancement of thiopental on GABA inhibition of the field potentials was observed. In binding experiments, two components of specific [(3)H]GABA binding to membrane fractions were observed. While thiopental was without effect on high-affinity sites, [(3)H]GABA binding with low affinity was enhanced by 80% in the presence of 10(?5) M thiopental. The results are discussed in relation to the phenomena underlying chronic barbiturate administration.