Reactivity to aversive stimuli as a function of alterations in body weight in normal and gonadectomized female rats

Two studies compared the quinine aversion and shock thresholds of intact and gonadectomized female rats. Using food deprivation to modify body weight, the first study measured the reactivity of gonadectomized and intact rats at the same weight level and compared their behavior to a food deprived, but heavier, gonadectomized group. While maintained at the same weight levels, no differences in either shock thresholds or quinine aversion were found between gonadectomized and intact animals. The heavier gonadectomized group showed decreased reactivity on both measures. The second study manipulated body weight with gonadal hormones. Estrogen and the combination of estrogen and progesterone maintained the body weight of gonadectomized rats at the level of the intact control group. During this period the reactivity of both estrogen injected groups was not different from the control group. Progesterone had no effect on weight gain and the progesterone injected group did not differ in reactivity from an oil injected gonadectomized group. Both the progesterone and oil injected gonadectomized groups were heavier and showed less reactivity to both shock and quinine. These results were interpreted as direct support for previous work suggesting that the effects of alterations in gonadal hormones are mediated by the weight changes attendant on hormone level changes and are not direct effects of gonadal hormones, themselves.