Sex Differences in Ethanol's Anxiolytic Effect and Chronic Ethanol Withdrawal Severity in Mice with a Null Mutation of the 5α-Reductase Type 1 Gene

Abstract

Manipulation of endogenous levels of the GABAergic neurosteroid allopregnanolone alters sensitivity to some effects of ethanol. Chronic ethanol withdrawal decreases activity and expression of 5α-reductase-1, an important enzyme in allopregnanolone biosynthesis encoded by the 5α-reductase-1 gene (Srd5a1). The present studies examined the impact of Srd5a1 deletion in male and female mice on several acute effects of ethanol and on chronic ethanol withdrawal severity. Genotype and sex did not differentially alter ethanol-induced hypothermia, ataxia, hypnosis, or metabolism, but ethanol withdrawal was significantly lower in female versus male mice. On the elevated plus maze, deletion of the Srd5a1 gene significantly decreased ethanol's effect on total entries versus wildtype (WT) mice and significantly decreased ethanol's anxiolytic effect in female knockout (KO) versus WT mice. The limited sex differences in the ability of Srd5a1 genotype to modulate select ethanol effects may reflect an interaction between developmental compensations to deletion of the Srd5a1 gene with sex hormones and levels of endogenous neurosteroids.

FIGURE 1

The effect of acute ethanol (2 g/kg) on elevated plus maze behavior in male and female Srd5a1 knockout (KO) and wildtype (WT) mice. Deletion of the Srd5a1 gene significantly decreased ethanol’s anxiolytic effect, measured by percent (%) open arm entries in female KO versus WT mice (A), and decreased ethanol’s effect on total entries, an index of activity, in KO versus WT mice (B). Values are mean ± SEM for the number of animals in parentheses. ⁺p<0.10, **p<0.01 versus respective saline group

FIGURE 2

Sensitivity to ethanol’s ataxic (2 g/kg) effect (A) and hypothermic (3 g/kg) effect (B) in male and female Srd5a1 knockout (KO) and wildtype (WT) mice. (A) The ethanol-induced decrease in rotarod performance at 30 min did not differ significantly in KO versus WT mice. (B) While body temperature was higher in female versus male mice, the ethanol-induced decrease in body temperature did not differ in KO versus WT mice. Depicted are the mean ± SEM for the number of animals in parentheses.

FIGURE 3

Ethanol’s hypnotic (3.6 g/kg) effect did not differ in male and female Srd5a1 knockout (KO) and wildtype (WT) mice, measured by loss of righting reflex (LORR) duration (A) and blood ethanol concentration at return of righting reflex; BEC at RORR (B). Shown are mean ± SEM for the number of animals in parentheses. ⁺p<0.10 versus males

FIGURE 4

Srd5a1 genotype and sex did not significantly alter ethanol metabolism following an acute 2 g/kg injection (A) or an acute 4 g/kg injection (B). Values represent the mean ± SEM for the number of animals in parentheses.

FIGURE 5

Effect of systemic ethanol injection (2 g/kg) on plasma corticosterone (CORT) levels (A), and plasma allopregnanolone (ALLO) levels (B) in male and female Srd5a1 knockout (KO) and wildtype (WT) mice. Separate groups of mice were injected with ethanol or saline and euthanized 30 min later. Values are the mean ± SEM, and group sizes are provided in parentheses. ⁺p<0.10, ***p<0.001 versus respective saline group

FIGURE 6

Chronic ethanol withdrawal severity, measured by hourly handling-induced convulsion (HIC) scores (A & B) and area under the curve (AUC 25) (C), in male and female Srd5a1 knockout (KO) and wildtype (WT) mice. Baseline HIC scores (not shown) did not differ in male and female KO and WT mice. While 72 hrs of ethanol vapor exposure significantly increased HIC scores and AUC 25, these measures of chronic withdrawal severity were significantly lower in female versus male mice. Values represent the mean ± SEM for the number of animals in parentheses.