THE PRE-BOTZINGER COMPLEX AND PHASE-SPANNING NEURONS IN THE ADULT-RAT

To characterise respiratory neurons in the pre-Botzinger complex of ad ult rats, extracellular recordings were made from 302 respiratory neur ons in the ventral respiratory group of sodium pentobarbitone anaesthe tised adult rats, Neurons were located 0 to 1.6 mm caudal to the facia l nucleus, and ventral to the nucleus ambiguus. The pre-Botzinger comp lex comprised expiratory neurons (22%, 22/100), inspiratory neurons (3 7%, 37/100) and phase-spanning neurons (41%, 41/100). In contrast, 80% (125/157) of Botzinger neurons were expiratory, and 80% (36/45) of ro stral ventral respiratory group neurons were inspiratory. Rostrocaudal ly, the pre-Botzinger complex extended about 400 mu m, starting at the caudal pole of the nucleus ambiguus compact formation, The pre-Botzin ger complex was also characterised by a predominance of propriobulbar neurons (81%, 13/16). Furthermore, 68% (33/48) of expiratory-inspirato ry neurons found were located within the pre-Botzinger complex. The va riety of neuronal subtypes in the pre-Botzinger complex, including man y firing during the expiratory-inspiratory transition is consistent wi th the hypothesis that this nucleus plays a key role in respiratory rh ythm generation in the adult rat. (C) 1998 Published by Elsevier Scien ce B.V. All rights reserved.