Changes in stimulus reactivity following gonadectomy in male and female rats of different ages

Three studies compared the quinine aversion and shock thresholds of intact and gonadectomized male and female rats. The first two studies used rats gonadectomized at 50 days of age. The last study used rats gonadectomized at 100 days of age. Half of the animals in each study were tested shortly after surgery prior to the development of within-sex differences in body weight. All animals were tested 9–10 weeks after surgery when weight differences attributable to gonadectomy were evident. Prior to the development of weight differences, no reliable differences in either quinine aversion or shock thresholds were found. After weight differences had developed, the heavier group (within a given sex) was less responsive to both shock (higher thresholds) and quinine (decreased suppression). This weight-behavior relationship existed regardless of the age at which the rat was gonadectomized. It was suggested that these behavioral changes might not be a direct function of gonadectomy in view of the correlation between weight change and behavior change.