King. Combination unilateral amygdaloid and ventromedial hypothalamic lesions: evidence for a feeding pathway. Am J Physiol Regul Integr Comp Physiol 288: R702-R707, 2005; doi:10.1152/ajpregu.00460.2004.-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. ventromedial hypothalamus; amygdala; stria terminalis; feeding behavior; body weight LESIONS OF THE MOST POSTERODORSAL part of the amygdala result in hyperphagia and excessive weight gain in rats (42). Female rats with bilateral lesions typically gain 50 -80 g in 20 days, and gains of as much as 100 g in 20 days have been observed (15,16,18,20,21). The obesity syndrome resembles that which follows lesions of the ventromedial hypothalamus (VMH) in many respects. For example, the weight gains are greater in female rats than in male rats (23), and the animals are hyperinsulinemic even when food restricted (16) and do not respond appropriately to caloric challenges (24).Excessive weight gains have been produced with small lesions limited exclusively to the posterodorsal medial amygdaloid nucleus and the intra-amygdaloid bed nucleus of the stria terminalis (42). Examination of anterograde degeneration by the amino-cupric silver method in the brains of rats given unilateral posterodorsal amygdala (PDA) lesions revealed a dense pattern of degenerating terminals in areas that have previously been shown to be involved in various aspects of feeding behavior and/or body weight regulation (17). Particularly dense staining was observed in the VMH ipsilateral to the PDA lesion, but not in the contralateral VMH. There was little to no staining in the paraventricular hypothalamic nucleus.The pattern of anterograde degeneration observed after unilateral PDA lesions suggests an ipsilateral pathway mediating feeding behavior and body weight regulation. The major pathway between the PDA and VMH is the stria terminalis (5, 6, 39), and after unilateral PDA lesions there is dense degeneration in the dorsal component and medial part of the ventral componen...

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