Variable mounting levels in the female rat: The influence of experience and acute effects of testosterone

Ovariectomized female rats were tested for mounting behaviour along 4 different procedures in order to investigate which factors may contribute to the variability of this behaviour observed in different experiments. Mounting behaviour was facilitated by repeated testing (group A). Estradiol-benzoate, when given for a short period of time (group B), induced a dramatic and long-lasting increase in mounting in females which were repeatedly tested according to the procedure of group A. Prolonged adaptation to the test environment (group C) did not facilitate mounting in repeatedly tested females. The 3 procedures used did not reduce inter-individual variability. Highly significant, positive, inter-test correlation coefficients indicated that relative individual differences in mounting remained highly stable throughout testing. Facilitatory effects of testosterone propionate (TP, 500 μg, injected once 48 h prior to testing) on mounting behaviour appeared to stimulate existing behavioural tendencies, rather than activating new patterns of behaviour: TP facilitated mounting in groups A and B, but not in group C. Neither did TP facilitate mounting in a group which had been left sexually naive (group D) until the time of TP-injection. It is concluded that highly stable inter-individual differences in mounting behaviour are present in the adult female rat. Differences in sensitivity for gonadal hormones are not likely to underly these individual differences.