Role of superior laryngeal nerve and Fos staining following dehydration and rehydration in the rat.

Immunohistochemistry for Fos was used to determine the role of the superior laryngeal nerve in conscious rats following water deprivation and rehydration. Adult male rats were subjected to either unilateral superior laryngeal nerve section (SLNX) or sham surgery. Two weeks later rats from each surgical group were water deprived for 48 h or water deprived for 46 h and given access to water for 2 h prior to perfusion. Controls were allowed ad libitum access to water. Brains were processed for Fos using a commercially available antibody. Changes in plasma osmolality and hematocrit were not significantly different between SLNX and sham following any of the treatments. Water intake in rats was not significantly affected by SLNX. In the supraoptic nucleus (SON) of sham rats, water deprivation significantly increased Fos staining while water intake following dehydration prevented this increase. Water deprivation significantly increased Fos staining in the SON of SLNX rats. Following water intake after 46 h water deprivation in SLNX rats, Fos staining in the ipsilateral SON was significantly greater than the contralateral SON and significantly lower than 48 h water deprivation. In the nucleus of the solitary tract (NTS) of sham rats, both water deprivation and water intake produced significant increases in Fos staining bilaterally compared to euhydrated controls. In SLNX rats, water deprivation significantly increased Fos in both ipsilateral and contralateral NTS that was not different from sham rats. SLNX significantly decreased Fos staining in the ipsilateral NTS of rats given access to water after dehydration compared to the corresponding sham treated rats. Fos staining was not affected in the contralateral NTS of SLNX rats given access to water after dehydration. This suggests that the superior laryngeal nerve contributes to changes in Fos staining in the NTS and SON following water intake in dehydrated rats.