Food and water intake in rats after transections of fibers en passage in the tegmentum

A 145 micron diameter wire knife was used to transect fibers en passage in ventral, medial, and dorsal aspects of the tegmentum. Data from 74 rats with bilaterally symmetric cuts indicate that the interruption of fibers which course through the central region of the tegmentum result in hyperdipsia. Three distinct syndromes were observed: (a) extreme hyperdipsia beginning on the first or second day after surgery and persisting for 4–6 days; (b) a smaller increase in water intake beginning on the first or second day after surgery and persisting for the duration of the experiment; and (c) normal or subnormal water intake for several days after surgery followed by a sharp increase which persisted for 4–6 days. Cuts through the dorsolateral tegmentum consistently produced hyperphagia in male rats maintained on a dry pellet diet. The magnitude of the effects was comparable to that seen in male rats after ventromedial hypothalamic (VMH) lesions. These cuts, as well as others which did not result in hyperphagia, abolished the normal feeding responses to 2-deoxy-D-glucose (2-DG) without affecting the feeding response to insulin. Some of our cuts produced significant overeating but no commensurate weight gain, suggesting that metabolic disturbances may have occurred. Knife cuts of comparable size through the ventral third of the tegmentum, the pons, or the ventral aspects of the central grey, failed to affect either food or water intake reliably. Histological evidence of minimal direct damage to cellular components of the region of the behaviorally effective cuts and their extensive rostro-caudal distribution indicate that direct damage to perikarya of tegmental neurons probably is not responsible for the effects of the cuts.