Background
The GABAergic neuroactive steroid (3α,5α)-3-hydroxy-pregnan-20-one (3α,5α-THP, allopregnanolone) enhances GABAergic activity and produces subjective effects similar to ethanol. The effect of chronic alcohol exposure on 3α,5α-THP concentrations has been studied in mouse, rat, and monkey limbic brain areas. Chronic ethanol exposure produced divergent brain region and cell specific changes in 3α,5α-THP concentrations in animal studies. However, 3α,5α-THP levels in similar human brain regions have never been examined in individuals diagnosed with alcohol use disorder (AUD). Therefore, we used immunohistochemistry to examine 3α,5α-THP levels in the ventral tegmental area (VTA), substantia nigra pars medialis (SNM), and amygdala of human postmortem brains of patients diagnosed with AUD compared to social drinkers. The effects of sex and liver disease on 3α,5α-THP concentrations were examined in the aforementioned brain regions.
Methods
Human postmortem brains of AUD patients and age-matched controls were obtained from the New South Wales Brain Tissue Resource Center. Immunohistochemistry was performed using anti-3α,5α-THP antibody on formalin fixed and paraffin embedded brain sections to detect cellular 3α,5α-THP levels. Immunoreactivity was analyzed by pixel density/mm2 for the comparison between AUD patients and controls.
Results
3α,5α-THP immunoreactivity was increased by 23.2±9% in the VTA of AUD patients compared to age matched controls (p= 0.014). Moreover, a 29.6±10% increase in 3α,5α-THP immunoreactivity was observed in the SNM of male AUD patients compared to male controls (p<0.01), but not in female subjects. 3α,5α-THP immunoreactivity in the VTA and SNM regions did not differ between non-cirrhotic and cirrhotic AUD patients. A sex difference in 3α,5α-THP immunoreactivity (female 51±18% greater than male) was observed among control subjects in the SNM, but no other brain region. 3α,5α-THP immunoreactivity in the basolateral and lateral amygdala were negatively correlated with the length of the tissue fixation time as well as the age of the subjects, precluding assessment of the effect of AUD.
Conclusions
Cellular 3α,5α-THP levels in VTA are increased in human AUD patients, an effect that is likely independent of sex and liver disease. The differences between animal models and human studies should be factored into the interpretation of the physiological significance of elevated 3α,5α-THP levels in humans.