Voluntary ethanol consumption reduces GABAergic neuroactive steroid (3α,5α)3-hydroxypregnan-20-one (3α,5α-THP) in the amygdala of the cynomolgus monkey

Neuroactive steroids such as (3 alpha,5 alpha)3-hydroxypregnan-20-one (3 alpha,5 alpha-THP, allopregnanolone) enhance the gamma-aminobutyric acid (GABA)-ergic effects of ethanol and modulate excessive drinking in rodents. Moreover, chronic ethanol consumption reduces 3 alpha,5 alpha-THP levels in human plasma, rat hippocampus and mouse limbic regions. We explored the relationship between 3 alpha,5 alpha-THP levels in limbic brain areas and voluntary ethanol consumption in the cynomolgus monkey following daily self-administration of ethanol for 12 months and further examined the relationship to hypothalamic-pituitary-adrenal (HPA) axis function prior to ethanol exposure. Monkeys were subjected to scheduled induction of ethanol consumption followed by free access to ethanol or water for 22 h/day over 12 months. Immunohistochemistry was performed using an anti-3 alpha,5 alpha-THP antibody. Prolonged voluntary drinking resulted in individual differences in ethanol consumption that ranged from 1.2 to 4.2g/kg/day over 12 months. Prolonged ethanol consumption reduced cellular 3 alpha,5 alpha-THP immunoreactivity by 13 +/- 2 percent (P<0.05) in the lateral amygdala and 17 +/- 2 percent (P<0.05) in the basolateral amygdala. The effect of ethanol was most pronounced in heavy drinkers that consumed 3 g/kg20 percent of days. Consequently, 3 alpha,5 alpha-THP immunoreactivity in both the lateral and basolateral amygdala was inversely correlated with average daily ethanol intake (Spearman r=-0.87 and -0.72, respectively, P<0.05). However, no effect of ethanol and no correlation between drinking and 3 alpha,5 alpha-THP immunoreactivity were observed in the basomedial amygdala. 3 alpha,5 alpha-THP immunoreactivity following ethanol exposure was also correlated with HPA axis function prior to ethanol exposure. These data indicate that voluntary ethanol drinking reduces amygdala levels of 3 alpha,5 alpha-THP in non-human primates and that amygdala 3 alpha,5 alpha-THP levels may be linked to HPA axis function.