Effect of age on synthesis of the GABAergic steroids 5-alpha-pregnane-3,20-dione and 5-alpha-pregnane-3-alpha-ol-20-one in rat cortex in vitro

Interaction between allopregnanolone and pregnenolone sulfate in modulating GABA-mediated synaptic currents in neurons from the rat medial preoptic nucleus

The two neurosteroids 3alpha-hydroxy-5alpha-pregnane-20-one (allopregnanolone; AlloP) and pregnenolone sulfate (PregS) affect neuronal GABA(A) receptors differently. While AlloP mainly potentiates the currents through GABA(A) receptors, PregS reduces such currents. The present study aimed at clarifying the interaction of AlloP and PregS at GABA(A) receptors in neurons from the medial preoptic nucleus of male rat. AlloP has previously been shown to dramatically prolong GABA-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) in these neurons. Here, by recording sIPSCs under voltage-clamp conditions with the perforated-patch technique, it was shown that PregS by itself did not significantly affect the amplitude or time course of such currents. However, PregS, in a concentration-dependent manner, reduced the AlloP-evoked prolongation of sIPSC decay when the two neurosteroids were applied together. In contrast to sIPSC amplitude and time course, sIPSC frequency was significantly reduced by 10 microM PregS alone. Further, although 1.0 microM AlloP alone induced a clear increase in sIPSC frequency, the frequency was not significantly different from control when 1.0 microM AlloP was applied in combination with 10 microM PregS. In addition to the effects on sIPSC parameters, PregS reduced the baseline current evoked by 1.0 microM AlloP in the absence of GABA application or synaptic activity. PregS by itself did not significantly affect the baseline current. The main effects of AlloP and PregS on the sIPSC time course were mimicked by a simplified model with AlloP assumed to reduce the rate of GABA unbinding from the receptor and PregS assumed to increase the rate of desensitization.

Finasteride inhibits the progesterone-induced spike-wave discharges in a genetic model of absence epilepsy

Previously, it was found that progesterone aggravates spike-wave discharges (SWD) in WAG/Rij rats in a nongenomic way. In order to elucidate whether the regulatory effect of progesterone depends on its conversion to allopregnanolone, the effect of finasteride, a 5alpha-reductase inhibitor, on progesterone-induced increase in SWD was studied in the same model for absence epilepsy. Progesterone (10 and 20 mg/kg ip) dose-dependently increased the number of SWD (by 54% and 97%, respectively) during the first hour postinjection. Pretreatment of rats with finasteride (50 mg/kg sc) blocked the progesterone-induced enhancement of SWD. Finasteride alone had no effect on the number of SWD, up to 24 h following its administration. It is concluded that finasteride blocked the progesterone-induced increase in SWD, which indicates that this action of progesterone is mediated by its neuroactive metabolite allopregnanolone.