Neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one modulates electrophysiological and behavioral actions of ethanol - PubMed (original) (raw)

Neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one modulates electrophysiological and behavioral actions of ethanol

M J VanDoren et al. J Neurosci. 2000.

Abstract

Neuroactive steroids are synthesized de novo in brain, yet their physiological significance remains elusive. We provide biochemical, electrophysiological, and behavioral evidence that several specific actions of alcohol (ethanol) are mediated by the neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP; allopregnanolone). Systemic alcohol administration elevates 3alpha, 5alpha-THP levels in the cerebral cortex to pharmacologically relevant concentrations. The elevation of 3alpha,5alpha-THP is dose- and time-dependent. Furthermore, there is a significant correlation between 3alpha,5alpha-THP levels in cerebral cortex and the hypnotic effect of ethanol. Blockade of de novo biosynthesis of 5alpha-reduced steroids using the 5alpha-reductase inhibitor finasteride prevents several effects of ethanol. Pretreatment with finasteride causes no changes in baseline bicuculline-induced seizure threshold but reverses the anticonvulsant effect of ethanol. Finasteride pretreatment also reverses ethanol inhibition of spontaneous neural activity in medial septal/diagonal band of Broca neurons while having no direct effect on spontaneous firing rates. Thus, elevation of 3alpha,5alpha-THP levels by acute ethanol administration represents a novel mechanism of ethanol action as well as an important modulatory role for neurosteroids in the CNS.

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Figures

Fig. 1.

Cerebral cortical 3α,5α-THP levels are elevated after acute, systemic ethanol administration.A, Cerebral cortical 3α,5α-THP levels exhibit a biphasic response to increasing ethanol concentrations. Ethanol increased 3α,5α-THP levels to pharmacologically active concentrations at doses between 1.35 and 4.0 gm/kg (*p < 0.0001, ANOVA; p < 0.05, Dunnett's post hoc) measured 60 min after ethanol administration. Data represent mean ± SEM of duplicate determinations in 6–10 rats per dose from two independent experiments. Further analysis of trend shows a significant match to a quadratic equation (F(1,32) = 17.49;p < 0.05) using random samples of five rats per dose. B, Cerebral cortical 3α,5α-THP levels peak between 40 and 80 min after an injection of ethanol (2 gm/kg, i.p.) followed by a gradual decrease. Data shown are the mean ± SEM of a representative experiment repeated twice with similar results (n = 6/time point; *p < 0.05 Dunnett's post hoc).

Fig. 2.

Elevations in cerebral cortical 3α,5α-THP are related to the hypnotic effect of ethanol. Alcohol (3.5 gm/kg, i.p.) was administered to male rats. The duration of the loss of righting reflex (sleep time) was correlated (r = 0.59;p < 0.0001; n = 37) with cerebral cortical 3α,5α-THP levels measured after awakening.

Fig. 3.

Anticonvulsant effect of ethanol on bicuculline seizure threshold is reversed by finasteride pretreatment.A, Ethanol (2 gm/kg, i.p.) increases bicuculline-induced seizure threshold at 40 min, but not 10 min, after administration (two-way ANOVA, effect of drug, F = 5.96,p < 0.02; Tukey's multiple comparison, *p < 0.02; n = 11–13).B, Finasteride pretreatment selectively reverses (ANOVA,F = 5.476, p < 0.01; Tukey's multiple comparison, †p < 0.05;n = 9–11) the ethanol-induced increase of seizure threshold.

Fig. 4.

Finasteride pretreatment prevents ethanol-induced inhibition of spontaneous neural activity in MS/DB neurons.A, Systemic ethanol injection (1.5 gm/kg, i.p.) reduced spontaneous neural activity by a maximum of 38.00 ± 1.52%, 20–40 min after injection. Finasteride pretreatment reversed the inhibition of spontaneously active MS/DB neurons produced by systemic ethanol administration (p < 0.0001, two-way ANOVA with repeated measures; main effect of finasteride,F(2,152) = 34.77). Complete blockade of ethanol inhibition was observed between 16 and 25 min after the ethanol injection at both doses of finasteride. However, only the high dose of finasteride completely blocked ethanol inhibition throughout the recording session. Inset is a representative oscilloscope trace of medial septum/diagonal band of Broca neuron.B, Baseline firing rate (5 min before ethanol); *p < 0.05; †p < 0.07.B, A grand mean of ethanol-induced inhibition for each neuron was calculated by collapsing the data across the 12, 5 min time bins. Acute ethanol administration inhibited the spontaneous activity of MS/DB neurons compared to preinjection baseline (paired_t_ test, T = 3.12; *p < 0.05). Pretreatment with 25 mg/kg finasteride did not alter the effect of ethanol on spontaneous firing rate. However, pretreatment with 50 mg/kg finasteride completely prevented ethanol-induced inhibition of spontaneous MS/DB neural activity (one-way ANOVA, F(2,13) = 5.45,p < 0.02; Tukey's post hoc test,q = 4.593, †p < 0.05).C, Representative MS/DB neural traces from an animal treated with ethanol only and an animal treated with ethanol + 50 mg/kg finasteride. Each neuron was recorded for 60 min after a 1.5 gm/kg ethanol injection (vertical arrow). The neural trace preceding the vertical arrow is the baseline recording session. Note, ethanol injection resulted in an ∼32% inhibition in the MS/DB neuron from the control rat, whereas the ethanol-induced inhibition was completely blocked by pretreatment with 50 mg/kg finasteride.

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Neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one modulates electrophysiological and behavioral actions of ethanol - PubMed (original) (raw)