Different patterns of respiratory and cardiovascular responses elicited bychemical stimulation of dorsal medulla in the rat

dRespiratory and cardiovascular responses to microinjections (10 nl) of L-g lutamate (10 mM) into the dorsal medulla were studied in spontaneously brea thing urethane-anesthetized, adult male Wistar rats. A total of 10 patterns of respiratory and cardiovascular responses were observed: (1) hypotension alone; (2) hypotension and bradycardia; (3) hypotension and apnea; (4) hyp otension, bradycardia, and apnea; (5) apnea alone; (6) hypotension and fast and shallow breathing; (7) hypotension, bradycardia, and fast and shallow breathing; (8) fast and shallow breathing alone; (9) sighs; and (10) increa se in BP and HR accompanied with fast and shallow breathing. The sites from which a combination of hypotension, bradycardia, and apnea was elicited, o ccupied a region in the medial subnucleus of nucleus tractus solitarius (nT S), the reticular formation just ventral to it, and the dorsal motor nucleu s of vagus. The sites from which hypotension alone or a combination of hypo tension and apnea were elicited occupied the margins of the medial subnucle us of nTS. The sites from which apnea alone was elicited were located in th e ventrolateral part of nTS and the reticular formation just ventral to it. In the commissural subnucleus of nTS, the responses comparable to those el icited by peripheral chemoreceptor stimulation (i.e., increase in BP, HR, a nd respiratory rate) were located in a midline region just caudal to the ca lamus scriptorius, the sites from which sighs were elicited were located sl ightly lateral and deeper, the sites from which fast and shallow breathing were elicited were located in the dorsal portion, slightly lateral to the m idline. These results are expected to prove useful in studies in which micr oinjection technique is used to identify transmitters/receptors involved in mediating respiratory and cardiovascular reflex responses. (C) 2000 Elsevi er Science B.V. AU rights reserved.