Amygdala-lesion obesity: what is the role of the various amygdaloid nuclei?

Anatomic descriptions of amygdaloid lesions resulting in hyperphagia and obesity in rats, cats, and dogs have been inconsistent and often contradictory, frequently resulting in failures to replicate. The present study attempted to reconcile these differences by examining common areas of overlap among differently placed lesions in female rats. Small bilateral lesions of the most posterodorsal aspects of the amygdala resulted in substantial weight gains (mean = 45.4 g/10 days). The smallest lesions caused damage limited to the posterodorsal medial amygdaloid nucleus and the bed nucleus of the stria terminalis and were directly in the area where axons are collecting to form the stria terminalis. Larger lesions that extensively damaged the central and/or anterodorsal medial amygdaloid nuclei sometimes resulted in excess weight gains, as did very large lesions of the basolateral nuclei, but substantial weight gains occurred only when the lesions extended (unilaterally or bilaterally) into the posterodorsal amygdala. Examination of previously published brain sections indicated that the hyperphagia and obesity that have been observed after widely differing lesion placements in cats and dogs were also the result of damage to a common area of overlap (i.e., the bed nucleus and/or stria terminalis). In rats, the critical area producing weight gain has extensive reciprocal relations with the medial hypothalamus.