Chronic ethanol administration alters the modulatory effect of 5α- pregnan-3α-ol-20-one on the binding characteristics of various radioligands of GABA(A) receptors

In this study, we investigated the modulatory effect of 5α-pregnan- 3α-ol-20-one, a neurosteroid, on the binding characteristics of [³H]flunitrazepam (2 nM), [³H]muscimol (5 nM), and 4 nM [³⁵S]t- butylbicyclophosphorothionate (TBPS) in cerebral cortex, cerebellum, and hippocampus of control, ethanol-dependent, and ethanol-withdrawn rats. 5α- Pregnan-3α-ol-20-one potentiated the binding of [³H]flunitrazepam and [³H]muscimol in all the rat brain regions investigated in this study. There was a significant increase in the maximal potentiation of [³H]flunitrazepam as well as [³H]muscimol binding (E(max)) in the ethanol-dependent rat cerebellum as compared to control group (p < 0.025). Furthermore, 5α- pregnan-3α-ol-20-one elicited a biphasic response, i.e., it potentiated the binding of [³⁵S]TBPS at lower concentrations (≤ 100 nM) and inhibited the binding at higher concentrations (> 100 nM). There was a significant higher inhibition of [³⁵S]TBPS binding (-E(max)) by 5α-pregnan-3α-ol-20-one in the hippocampus of ethanol-dependent as well as ethanolwithdrawn rats (p < 0.025). These observations suggest that the neurosteroid binding site associated with the γ-aminobutyric acid(A) (GABA(A)) receptors in cerebellum and hippocampus plays an important role during ethanol-dependence and ethanol-withdrawal, and some of the changes following ethanol dependence and its withdrawal may be mediated through the neurosteroid binding site.