Effects of castration and sex steroid treatment on the motor copulatory pattern of the rat

The effect of castration and sex steroid (testosterone propionate, TP or estradiol benzoate, EB) treatment on the motor copulatory pattern was studied by an accelerometric technique in 14 male Wistar rats. This technique allows precise measurements of the following parameters: (a) duration of mounts (M), intromissions (I) and ejaculations (E); (b) thrusting frequency, and (c) amplitude of pelvic movements. Analysis of the signals generated during M, I or E, allows clear differentiation among the three behavioral patterns. Castration abolished sexual activity in most of our rats. The motor copulatory pattern was analyzed in four castrated rats, which continued to display sexual behavior for some time after castration. Castration did not alter thrusting frequency nor vigor of mounting. Duration of M, but not that of I or E, was prolonged by castration. TP (5 mg/day) restored sexual behavior to precastration levels in all 6 TP-treated rats. The motor copulatory pattern of the TP-treated rats was similar to that of intact rats. EB treatment (5 μg or 50 μg/day) induced mounting in 6 out of 7 subjects, but only two rats ejaculated once. EB failed to restore M duration to precastration levels and increased the frequency of pelvic thrusting above control values. Present results suggest that estrogen in large dosages exerts subtle effects on the motor copulatory pattern of the rat.