The Meal Patterns of the Oestrous Cycle and Their Motivational Significance

Food intake was monitored continuously throughout the oestrous cycle of the rat by operant methods. On the night of oestrus the size of meals eaten was reduced and the average intermeal interval was shorter; and even after meals of the same size, oestrous animals returned to eat again more quickly than dioestrous animals. These results suggest that the way in which ovarian oestrogens reduce food intake is by intensifying processes responsible for the short-term satiation of hunger without affecting the motivational processes responsible for its arousal. Signs of motivational arousal at oestrus could thus be the result of a self-imposed nutritional deprivation, rather than a direct effect of ovarian hormones on sexual receptivity.