Responses of parabrachial nucleus neurons to chemical stimulation of posterior tongue in chorda tympani-sectioned rats.

Responses of parabrachial nucleus (PBN) neurons (n = 43) to chemical stimulation of the posterior tongue were recorded in chorda tympani (CT)-sectioned rats and compared with those (n = 45) in CT-intact. The chemical stimuli used were 0.5 M sucrose, 0.5 M sodium chloride (NaCl), 0.03 M hydrochloric acid (HCl), 0.01 M quinine hydrochloride, and distilled water. These stimuli were applied to an area posterior to the intermolar eminence of the tongue. Neurons of CT-sectioned rats responsive to the chemical stimuli were located in more caudal areas of the PBN compared with those of CT-intact. Numbers of responses to the five stimuli and breadth of responsiveness to the four basics were not different between both groups of rats. However, average response magnitudes of the neurons in CT-sectioned rats were lower than those in CT-intact. In both groups of rats, the response magnitudes to NaCl and HCl were larger than those to the other three stimuli, and responses to NaCl and those to HCl were highly correlated. It is suggested that glossopharyngeal fibers responding strongly to acids and salts are likely to be the main source of PBN responses from the posterior tongue.