Different effects of vagotomy and atropine on hypothalamic stimulation-induced feeding

The effects of subdiaphragmatic vagotomy and atropine administration on thresholds for stimulation-induced feeding and self-stimulation were investigated in male rats. The animals first received permanent bipolar-stimulating electrode implants in the lateral hypothalamus. Once stable thresholds for stimulation-elicited feeding and self-stimulation were obtained, bilateral subdiaphragmatic vagotomies were performed (Experiment 1) or intraperitoneal injections of atropine sulfate were administered (Experiment 2). The first experiment indicated that vagotomy produces a marked disruption of stimulation-elicited feeding but does not interfere with either self-stimulation elicited from the same electrode or stimulation-induced gnawing obtained from comparable lateral hypothalamic sites. Additional observations suggest that a quantitative histological analysis of the vagal trunks can predict the degree of disruption of stimulus-elicited feeding and may provide a discriminating test for completeness of vagotomy. In the second experiment, production of an acute blockade of efferent vagal activity by an injection of atropine sulfate (8 mg/kg) 1 hr before testing had little effect on either feeding or self-stimulation. These results suggest that the vagus may play a significant role in the mediation of stimulation-induced feeding and that the effects of vagotomy on feeding cannot be reproduced by acute cholinergic blockade. The effects of surgical vagotomy on stimulation-induced feeding may reflect interruption of afferent mechanisms, elimination of atropine-refractory efferent systems, or disruption of feeding behavior caused by the sequelae of chronic vagal dysfunction.