This study was designed to compare the effects of several neuroactive steroids with varying patterns of modulation of γ-aminobutyric acid (GABA)A and NMDA receptors on operant self-administration of ethanol or water. Once stable responding for 10% (w/v) ethanol was achieved, separate test sessions were conducted in which male Wistar rats were allowed to self-administer ethanol or water following pre-treatment with vehicle or one of the following neuroactive steroids: (3β,5β)-3-hydroxypregnan-20-one (epipregnanolone; 5, 10, 20 mg/kg; n = 12), (3α,5β)-20-oxo-pregnane- 3-carboxylic acid (PCA; 10, 20, 30 mg/kg n = 10), (3α,5β)-3- hydroxypregnan-20-one hemisuccinate (pregnanolone hemisuccinate; 5, 10, 20 mg/kg; n = 12) and (3α,5α)-3-hydroxyandrostan-17-one hemisuccinate (androsterone hemisuccinate; 5, 10, 20 mg/kg; n = 11). The effect of the 3β-epimer of PCA, (3β,5β)-20-oxo-pregnane-3-carboxylic acid (10, 20, 30 mg/kg; n = 9), on ethanol self-administration was also examined. The compounds were administered using a Latin-square design 45 min prior to the weekly test sessions. The effects of the 30 mg/kg dose of the steroidal hemisuccinates on ethanol intake were also examined 5 min after administration of these drugs. Both epipregnanolone and PCA attenuated ethanol self-administration. However, neither of the hemisuccinate compounds significantly altered this behavior. The steroidal hemisuccinates (30 mg/kg; n = 7) were also tested 5 min before behavior testing and had no effect on ethanol intake 5 min after administration. The 3β-epimer of PCA also failed to alter ethanol intake. None of the test compounds altered water intake. In electrophysiological studies, the effects of PCA and androsterone hemisuccinate on evoked GABAA receptor-mediated inhibitory postsynaptic currents (GABAA-IPSCs) was examined in brain slices of the amygdala. PCA had a stimulatory effect at concentrations of 5 and 25 μM. Androsterone hemisuccinate had no agonist activity. The ability of epipregnanolone and PCA to alter ethanol intake appears to be related to different inhibitory actions of these compounds on either GABAA or NMDA receptors, respectively. Thus, dual modulation of these systems by selected neuroactive steroids may offer potential for modifying the reinforcing effects of alcohol.
- Neuroactive steroid