MEDULLARY PATHWAYS OF CARDIOVASCULAR-RESPONSES TO 5-HT2 AND 5-HT3 RECEPTOR STIMULATION IN THE RAT NUCLEUS-TRACTUS-SOLITARIUS

As previously found for the baroreceptor reflex. microinjection of kyn urenic acid (KYN, 2 nmol), a glutamate receptor antagonist, into the c audal ventrolateral medulla (CVL) blocked the hypotension and bradycar dia elicited by microinjections of a 5-HT2 receptor agonist, 2,5-dimet hoxy-4-iodoampheramine (DOI.0.5 pmol) into the nucleus tractus solitar ius (NTS). In addition, as previously observed with the sympathetic ch emoreflex response, microinjections of KYN into the RVL blocked the in crease in blood pressure elicited by microinjections of 1-m-(chlorophe nyl)-biguanide (1200 pmol), a 5-HT3 receptor agonist, into the NTS. Th ese results suggest that medullary pathways involved in the responses to 5-HT2 and 5-HT3 receptor stimulation in the NTS are similar to thos e that mediate the baroceptor and chemoreceptor reflex responses, resp ectively.