Salivary secretion and grooming behaviour during heat exposure in freely moving rats.

1. At neutral (24 degrees C) and at hot (40 degrees C) ambient temperatures (Ta) salivary secretion from the submandibular gland of freely moving rats was recorded, together with simultaneous observation of saliva-spreading behaviour (grooming). 2. At a Ta of 24 degrees C, basal salivary flow was less than 2 microliters/min. When rats were first placed in the experimental chamber, brief grooming bouts often occurred. Transient secretion at more than 10 microliters/min was associated with this grooming, and the rate of salivary flow was positively correlated with the duration of grooming activity. 3. At a Ta of 40 degrees C, grooming appeared frequently and salivary secretion at more than 20 microliters/min continued even between grooming bouts. Threshold rectal temperatures (Tre) for thermally induced grooming (38.2 +/- 0.2 degrees C) and for salivary secretion (38.2 +/- 0.1 degrees C) were similar, and for eleven of sixteen rats the two thresholds coincided. 4. At the threshold Tre both the rate of salivary secretion and the duration of grooming increased in a stepwise fashion. Above the threshold, there was no correlation between the duration of grooming and the rate of salivary flow. 5. Thermally induced salivary secretion and grooming behaviour appear to be controlled by independent mechanisms.