CAPSAICIN-SENSITIVE AREA IN THE VENTRAL SURFACE OF THE RAT MEDULLA

In acute experiments on nembutal-urethan-anesthetized rats, structures selectively sensitive to capsaicin were found near the ventral surfac e of the medulla at the exit of hypoglossal nerve roots. Microinjectio n of 5-50 nl 0.01% capsaicin to the rostral region of the capsaicin-se nsitive area mostly activated; respiration, arterial pressure and hear t rate (HR) while that to the caudal region inhibited arterial pressur e and HR. In chronic experiments on rats, injection of 25 nl 1% capsai cin to the caudal capsaicin-sensitive area led to a decrease in arteri al pressure by 35-45% and in HR by 10-15% within a week after operatio n. Arterial pressure and HR virtually reached the control level and th e rostral and caudal ventral medulla showed asymmetric distribution of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d)-posi tive cells by the end of the 2nd week. It is suggested that nitric oxi de may be involved in the mechanisms of neurochemical rearrangements i n the brainstem after application of capsaicin to the caudal ventrolat eral medulla (CVLM).