Thermally induced salivary secretion in anesthetized rats

Effect of thermal stimulation on salivary secretion was examined in urethane anesthetized (i.p., 1.0 g/kg) rats. First, rectal temperature (T_re) was maintained at various levels by warming the whole trunk with a heating blanket. Copious salivary secretion occurred when T_re reached a threshold value above 40°C, which is considerably higher than the threshold for tail vasodilation. Local warming of the scrotum, face, or hypothalamus also elicited salivary secretion, but only if T_re was in a limited range just below the threshold temperature at which T_re alone would induce salivary secretion. The higher the T_re within that limited range, the lower the temperature of the site locally warmed at which salivary secretion began. Changes in temperature of the abdomen, not including the scrotum, modulated the salivary secretion elicited by scrotal warming. Hypothalamic and scrotal temperatures interacted with each other to affect salivary secretion. Temperature signals from both core and periphery thus appear to be integrated in bringing about salivary secretion. Thermally induced salivary secretion may function as a basis for saliva spreading behavior observed in rats in a hot environment.