Estrous cycle and sex differences in performance on anxiety tasks coincide with increases in hippocampal progesterone and 3alpha,5alpha-THP

Pharmacol Biochem Behav. 2000 Nov;67(3):587-96. doi: 10.1016/s0091-3057(00)00392-0.


Sex differences and estrous cycle variations in anxiolytic-like behaviors and progestin concentrations were examined. Proestrous (n=22), estrous (n=19), diestrous (n=20), and male (n=18) Long-Evans rats were tested in horizontal crossing, open field, elevated plus-maze, emergence, holeboard, social interaction, tailflick, pawlick, and defensive burying tasks. Concentrations of plasma and hippocampal progesterone and 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) were measured by radioimmunoassay in behaviorally tested (proestrus n=11, estrus n=8, diestrus n=9, male n=7) and yoked non-tested rats (proestrus n=11, estrus n=8, diestrus n=10, male n=8). Proestrous females exhibited more anxiolytic-like behavior than all other groups on the elevated plus-maze, social interaction, and defensive burying tasks. Proestrous females had significantly shorter latencies to emerge from a cylinder than did estrous and diestrous females, but not males. Proestrous and estrous females entered significantly more peripheral and total squares in a brightly-lit open field than did males. While proestrous females had a tendency to make more beam breaks than did males in the horizontal crossing task, there were no differences between groups on the holeboard task. There was a tendency for proestrous females to have longer tailflick latencies than diestrous and male rats; however, on the pawlick task there were no differences among the groups. Plasma and central progesterone and 3alpha,5alpha-THP of tested and non-tested rats were not different. Proestrous females had significantly higher plasma and hippocampal progesterone and 3alpha,5alpha-THP levels than all other groups. These data demonstrate that proestrous increases in anxiolytic-like behavior coincide with elevated circulating and hippocampal progestin concentrations.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Anxiety / metabolism*
  • Behavior, Animal / physiology
  • Desoxycorticosterone / analogs & derivatives*
  • Desoxycorticosterone / metabolism*
  • Estrus / metabolism*
  • Female
  • Hippocampus / metabolism*
  • Male
  • Progesterone / metabolism*
  • Rats
  • Rats, Long-Evans
  • Sex Factors


  • Desoxycorticosterone
  • tetrahydrodeoxycorticosterone
  • Progesterone