HYPOTHALAMIC REGULATION OF FEMALE SEXUAL BEHAVIOUR; ESTABLISHMENT OF BEHAVIOURAL OESTRUS IN SPAYED GUINEA-PIGS FOLLOWING HYPOTHALAMIC LESIONS

Summary. Individual characteristics of sexual behaviour were empirically determined for twenty-seven spayed female guinea-pigs given three standardized tests after injection with 0·0034 mg of oestradiol benzoate and, 36 hr later, 0·4 mg of progesterone. Following this preoperative series of tests, hypothalamic lesions were produced electrolytically at different loci with various parameters of current duration and intensity. Alterations in the patterns of sexual behaviour displayed on three postoperative tests with identical hormonal treatments were evaluated statistically for each individual. Posteroventral hypothalamic lesions involving mammillary and premammillary structures were not associated with significant behavioural changes (N equals 4). Mid-ventral lesions were associated with alterations in response patterns in all but two animals. The behavioural changes were not correlated with size of lesions. Nine females with complete behavioural losses failed to display any signs of receptivity postoperatively. Ten showed statistically significant but incomplete losses in one or more of the components comprising the pattern of sexual behaviour, and two females displayed behavioural oestrus postoperatively in the absence of exogenous hormone. Lesions in females with behavioural oestrus appear to be more anterior and possibly more medial than those which eliminate sexual behaviour. Uteri of behavioural-oestrous females were atrophic suggesting that no oestrogen was provided by endogenous sources. The results suggest that mechanisms for both the facilitation and inhibition of female sexual behaviour exist within the hypothalamus. Moreover, hypothalamic regulation of reproductive behaviour is quantitative in nature, not 'all-or-none', and a range of partial deficits in behaviour can be observed after hypothalamic damage.