Progesterone facilitates exploration, affective and social behaviors among wildtype, but not 5α-reductase Type 1 mutant, mice

• Progestins enhanced behavior only in mice that had increased brain 3α,5α-THP.
• 3α,5α-THP to WT and 5α-RKO mice enhanced exploration, anti-anxiety and social behavior.
• MPA did not alter behavior or brain 3α,5α-THP levels of WT or 5α-RKO mice.
• Progestins’ 5α-reduction is required for exploration, affect and prosocial behavior.
• Brain targets of 3α,5α-THP may be the hippocampus and prefrontal cortex.

Progesterone (P4) facilitates exploration, anxiety and social behaviors in estrogen (E2)-primed mice. Some of these effects may be due to actions of its 5α-reduced metabolite, 5α-pregnan-3α-ol-20-one (3α,5α-THP). In order to address the role of P4 and its metabolite, 3α,5α-THP, a mouse model was utilized. We hypothesized that if P4's metabolism to 3α,5α-THP is essential to facilitate exploratory, anti-anxiety and social behaviors of mice, then wildtype, but not 5α-reductase knockout (5α-RKO), mice will have greater expression of these behaviors. Experiment 1: Mice were ovariectomized (ovx), E2-primed and administered P4 (0, 125, 250, or 500 μg) subcutaneously and then tested 4 h later in a battery of tasks: open field, elevated plus maze, and social interaction. Experiment 2: Ovx, E2-primed mice were administered P4 (4 mg/kg), 3α,5α-THP (4 mg/kg), medroxyprogesterone acetate (MPA, which does not convert to 3α,5α-THP; 4 mg/kg), or vehicle subcutaneously and tested 4 h later. There was a dose-dependent effect of P4 to wildtype, but not 5α-RKO, mice. Neither wildtype, nor 5α-RKO, mice had increased exploration, anti-anxiety or pro-social behavior with MPA administration. Progesterone only exerted effects on anti-anxiety behavior, and increased 3α,5α-THP in the prefrontal cortex and hippocampus, when administered to wildtype mice. 3α,5α-THP to both WT and 5α-RKO mice increased exploration, anti-anxiety and social interaction and 3α,5α-THP levels in the hippocampus and prefrontal cortex. Thus, metabolism of P4 by the 5α-reductase enzyme may be essential for enhancement of these behaviors.