AV3V LESIONS REDUCE SALIVATION AND THERMAL TOLERANCE.

Abstract

The anteroventral third ventricular region (AV3V) of the brain is important in the regulation of body fluid balance. Lesions of this area impair tail dilation, water intake, vasopressin release and salivation in response to various stimuli. PURPOSE: To determine the influence of the AV3V region on salivation and thermal tolerance during a heat stress. METHODS: AV3V and sham lesions were generated in 12 (6 per group) male Sprague-Dawley rats (300–400g). During the following 3 weeks rats were weaned back onto water and accustomed to handling and the experimental environment. Each rat was exposed to a heat stress of 37°C for 2 hours. Peritoneal temperature (Tc) was measured every 2 minutes using a radiotelemeter system. Relative differences in salivation between the groups was determined using the “spit-print” technique. All animals survived the heating protocol and were sacrificed 24 hours later and the extent of the lesion determined. A successful AV3V lesion was defined as ablation of the organum vasculosum of the lamina terminalis and the median preoptic nucleus and variable amounts of damage to the periventricular preoptic and medial preoptic nuclei. RESULTS: There was no difference between sham and AV3V Tc at the start of the experiment. AV3V rats Tc rose to significantly higher levels than that of shams during the 2 hour heat stress (41.5°C ± 0.52 vs 38.4°C ± 0.26, P < 0.01). AV3V rats also lost significantly less body weight (3.3% ± 0.49 vs 6.3% ± 0.16, P < 0.01) and this was reflected in a reduced “saliva positive” area on the spit prints (15.3% ± 3.47 vs 36.8% ± 4.56, P < 0.05). CONCLUSIONS: These data suggest that salivation is stimulated in response to a heat stress by excitatory inputs mediated through the AV3V region. It is hypothesized that these stimuli may be both humoral (e.g.angiotensin II) and neural (e.g. temperature sensitive neurons in the MnPO) in origin. Supported by a grant from the American College of Sports Medicine Research Foundation.