DEPRESSANT EFFECTS ON INSPIRATORY AND EXPIRATORY ACTIVITY PRODUCED BYCHEMICAL ACTIVATION OF BOTZINGER COMPLEX NEURONS IN THE RABBIT

The respiratory role of the Botzinger complex (Bot. c.) was investigat ed in alpha-chloralose-urethane or pentobarbitone anesthetized rabbits by means of microinjections of DL-homocysteic acid (DLH). The animals were either spontaneously breathing or vagotomized, paralysed and art ificially ventilated. Both phrenic and abdominal activities were monit ored; extracellular recordings from medullary respiration-related neur ons were performed. Unilateral microinjections (5-30 nl) of DLH (160 m M) into the Bot. c., at sites where intense expiratory activity with a n augmenting discharge pattern was encountered, provoked mild or moder ate depressant effects on inspiratory activity characterized by decrea ses in frequency as well as in peak amplitude and rate of rise of phre nic nerve discharge. Stronger depressant effects up to complete apnea were consistently obtained in response to bilateral microinjections. C oncomitant depressant effects on the activity of both expiratory moton eurons and expiration-related (ER) neurons of the caudal ventral respi ratory group (cVRG) were observed. At variance with previous findings in the cat, the results indicate that chemical activation of Bot. c. a ugmenting ER neurons may exert inhibitory influences not only on inspi ratory activity, but also on cVRG ER neurons and, hence, on expiratory motoneurons. The functional role of the Bot. c. in the control of res piration deserves further investigations; present findings suggest tha t the rabbit may profitably be used for such a purpose.