Effects of amygdala lesions on body weight, conditioned taste aversion, and neophobia.

Female rats with posterodorsal amygdala (PDA), basolateral amygdala (BLA), or sham lesions were compared regarding ad libitum food intake, weight gain, consumption of a novel food, and acquisition of a conditioned taste aversion (CTA). While only the rats with PDA lesions evidenced substantial weight gains at 10 days after surgery eating standard lab chow (25-45 g more than the other groups), only the rats with BLA lesions demonstrated significant deficits in the CTA and neophobia paradigms. Rats with basolateral lesions, on average, took less than 30 s to begin drinking the novel sweetened condensed milk after pairing with illness while the other groups took approximately 15 min to begin drinking. Also, rats with basolateral lesions ate, on average, 5 g of the novel Froot Loops while the other groups ate approximately 2 g. It is concluded that the changes in food-motivated behavioral tests frequently observed in animals with amygdala lesions do not coexist with the hyperphagia and weight gain of animals with PDA lesions.

Sex differences in body weight gains following amygdaloid lesions in rats.

Lesions of the most posterodorsal aspects of the amygdala resulted in equal weight gains (mean = 58 g) in male and female rats during a 22-day observation period. However, the absolute weight gains in the first 5 days after lesions were greater in females (+41.4 g) than in males (+18.8 g), as were the longer-term gains relative to their respective control groups. In a second study with female rats, it was found that amygdaloid lesions had little effect on the estrous cycle and that ovariectomy resulted in additional excessive weight gains in both rats with sham lesions and those with amygdaloid lesions. The weight gains produced by amygdaloid lesions and ovariectomy were additive. It is concluded that there is a sex difference in weight gains after amygdaloid lesions, but that the lesion-induced obesity is independent of estrogen levels. Similarities to lesions of the ventromedial hypothalamus are noted, and an amygdaloid-ventromedial hypothalamic pathway for the regulation of feeding behavior is proposed.