The anxiolytic and anticonvulsant effects of benzodiazepines, barbiturates, ethanol and neuroactive steroids are mediated by selective interactions with γ-aminobutyric acidA (GABAA) receptors. Chronic ethanol exposure decreases the sensitivity of GABAA receptors to benzodiazepines, barbiturates and ethanol. Ethanol withdrawing rats are cross-tolerant to the anticonvulsant effects of benzodiazepines as shown by a 16% decrease in the anticonvulsant efficacy of diazepam compared to controls. In contrast, ethanol withdrawing rats are sensitized to the anticonvulsant effects of the neuroactive steroid 3α-hydroxy-5α-pregnan-20-one (3α,5α-THP), exhibiting a 46% increase in the anticonvulsant effect against bicuculline-induced seizures compared to control rats. This effect may involve a change in the sensitivity of GABAA receptors to 3α,5α-THP because potentiation of GABAA receptor mediated chloride uptake into cerebral cortical synaptoneurosomes is enhanced by 3α,5α-THP up to 50% in ethanol withdrawing rats compared to controls. 3α,21-dihydroxy-5α-pregnan-20-one (THDOC) potentiation of GABAA receptor-mediated chloride uptake is also enhanced during ethanol withdrawal. Moreover, the plasma levels of 3α,5α-THP and progesterone did not differ in ethanol withdrawing rats compared to controls. These alterations in neurosteroid sensitivity were also accompanied by selective alterations in cortical GABAA receptor subunit mRNA levels. Levels for the α1 and α4 subunit showed only slight alterations during withdrawal whereas we had previously observed a significant decrease in α1 and a significant increase in α4 mRNA levels in ethanol dependent (not withdrawing) animals. β2, β3 and γ1 mRNA levels significantly increased during ethanol withdrawal. Taken together, these results suggest that ethanol withdrawal produces alterations in GABAA receptors that sensitize rats to the pharmacological effects of neuroactive steroids, Because ethanol-dependent or withdrawing rats are tolerant to the intoxicating, anxiolytic and anticonvulsant effects of ethanol and cross-tolerant to many effects of benzodiazepines and barbiturates, sensitization to the effects of neuroactive steroids could have significant therapeutic potential.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - Aug 1996|
ASJC Scopus subject areas
- Molecular Medicine