Combination unilateral amygdaloid and ventromedial hypothalamic lesions: evidence for a feeding pathway.

Previous studies have reported hyperphagia and obesity in female rats with bilateral lesions of the most posterodorsal part of the amygdala. In rats with unilateral posterodorsal amygdaloid lesions, a dense pattern of anterograde degeneration appears in the ipsilateral ventromedial hypothalamus, but not the contralateral nucleus. In the present study, female rats with unilateral ventromedial hypothalamic lesions or sham lesions were given either sham lesions or unilateral lesions of the posterodorsal amygdala (PDA) 20 days later. Unilateral lesions of the ventromedial hypothalamus resulted in hyperphagia and excessive weight gain. Subsequent amygdaloid lesions that were contralateral to the initial hypothalamic lesions resulted in hyperphagia and additional excessive weight gains, but amygdaloid lesions ipsilateral to the initial hypothalamic lesions did not. It is concluded that the effects of the two lesions on body weight are not additive and that the PDA and ventromedial hypothalamus are part of the same ipsilateral pathway regulating feeding behavior and body weight regulation.