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The pre-Bötzinger complex and phase-spanning neurons in the adult rat
Respiratory Researchvolume 2, Article number: P4 (2001)
Recent in vitro studies indicate that neurons in the pre-Bötzinger (pre-Bot) complex of neonatal rats play an essential role in respiratory rhythm generation. In the adult rat, however, the location and physiology of pre-Bot neurons is less clearly understood. The present study aims to investigate the firing patterns of neurons that are located between Bötzinger and rVRG area, and the precise location of this transition zone in relation to other medullary nuclei. Sprague-Dawley rats (weighted between 400–550 g) were anaesthetised with 72 mg/kg sodium pentobarbitone and 0.4 mg/kg atropine (i.p.), and paralysed with 1 mg/kg pancuronium dibromide (i.v.), followed by additional doses as required. Extracellular recordings were made from 302 respiratory units located between 0 and 1.6 mm caudal to the facial nucleus and ventral to the nucleus ambiguus. As expected, expiratory units were mostly recorded from the rostral medulla (80%, 125/157) and inspiratory units were concentrated in the more caudal area (80%, 36/45). However, we report here that, between the Bötzinger expiratory and rVRG inspiratory units, there exists a transition zone containing a mixture of phase-spanning units (41%, 41/100) as well as inspiratory (37%) and expiratory units (22%). The phase-spanning units are active across the expiratory-inspiratory phase, or vice versa. The rostrocaudal extension of this transition zone is about 400 μm, with the caudal end at the level of the caudal pole of the ambigual compact formation. Our preliminary data suggest that this transition zone could be the locus of pre-Bot neurons in the adult rat.