Evaporative cooling in the rat: Effects of hypothalamic lesions and chorda tympani damage

Abstract

Previous studies have demonstrated the importance of saliva spreading for evaporative cooling by rats in the heat. In particular, submaxillary–sublingual salivary gland function must be unimpaired for the rat to regulate its body temperature at ambient temperatures above 38 °C. The present study investigated some of the neural components of this thermoregulatory effector system. Bilateral destruction of the chorda tympani, the parasympathetic innervation of the submaxillary–sublingual glands, severely impaired the rat's tolerance of high ambient temperatures. Rats with bilateral electrolytic lesions in the anterior or lateral hypothalamus, placed without chorda tympani damage, also showed pronounced deficits in salivary evaporative water loss and impaired thermal tolerances during heat stress. Other heat loss mechanisms, such as peripheral vasodilatation, may also have been disrupted. These results support previous reports of thermoregulatory deficits in rats following hypothalamic lesions.