RESPONSES OF PARABRACHIAL NUCLEUS NEURONS TO CHEMICAL-STIMULATION OF POSTERIOR TONGUE IN CHORDA TYMPANI-SECTIONED RATS

Responses of parabrachial nucleus (PEN) neurons (n = 43) to chemical s timulation of the posterior tongue were recorded in chorda tympani (CT )-sectioned rats and compared with those (n = 45) in CT-intact. The ch emical 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 dist illed water. These stimuli were applied to an area posterior to the in termolar eminence of the tongue. Neurons of CT-sectioned rats responsi ve to the chemical stimuli were located in more caudal areas of the PE N compared with those of CT-intact. Numbers of responses to the five s timuli and breadth of responsiveness to the four basics were not diffe rent between both groups of rats. However, average response magnitudes of the neurons in CT-sectioned rats were lower than those in CT-intac t. In both groups of rats, the response magnitudes to NaCl and HCl wer e larger than those to the other three stimuli, and responses to NaCl and those to HCl were highly correlated. It is suggested that glossoph aryngeal fibers responding strongly to acids and salts are likely to b e the main source of PBN responses from the posterior tongue. (C) 1997 Elsevier Science Ireland Ltd.