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The effects of intracerebroventricular administration of reduced metabolites of progesterone on locomotor activity and on exploration in the elevated plus-maze were assessed in adult female rats. Allopregnanolone (3 alpha-hydroxy-5 alpha-pregnan-20-one; 1.25, 5.0, and 10 micrograms) and pregnanolone (3 alpha-hydroxy-5 beta-pregnan-20-one; 2.5, 5.0, and 10 micrograms) elicited anxiolytic effects and, at the highest dose tested, allopregnanolone resulted in sedation. In contrast, the 3 beta-hydroxy-epimer of allopregnanolone was without effect in either behavioral paradigm. The anxiolytic response to pregnanolone was blocked by picrotoxin (0.75 mg/kg, i.p.), a dose that by itself did not affect behavior in the plus-maze. These data suggest that the anxiolytic effect of 3 alpha-hydroxy metabolites of progesterone is mediated by brain GABAA receptors in a stereospecific manner, and are in good agreement with the well-documented in vitro effects of these steroids as potent modulators of the GABAA receptor.
Bitran et al. (Tue,) studied this question.