Axonal projections from Bötzinger expiratory neurons to contralateral ventral and dorsal respiratory groups in the cat

Summary We studied projection patterns of the augmenting expiratory neurons of the Bötzinger complex (BÖT) in the contralateral brainstem. Three experimental approaches were used: 1) electrophysiological analysis using antidromic microstimulation, and morphological analyses using 2) intraaxonal injection of HRP, and 3) application of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). Taken together, the three methods revealed morphological details of the axonal arborizations of the expiratory neurons in the BÖT and the ventral respiratory group (VRG). The majority of augmenting expiratory neurons of the BÖT had axonal collaterals in the contralateral brainstem. The stem axons to the contralateral side crossed the midline almost at the level of the cell somata. They descended dorsomedial to the ventral spinocerebellar tract and gave off collateral branches directed dorsomedially. Terminal boutons were distributed abundantly in the caudal part of the BÖT and in the more caudally situated VRG. Axon collaterals sometimes ran to the dorsal respiratory group (DRG) and distributed terminal boutons there. Together with the fact of extensive ipsilateral arborizations shown previously, the present results indicate that the augmenting expiratory neurons of the BÖT have wide bilateral influence on the BÖT, VRG, DRG, and spinal cord.Abbreviations VII facial nucleus - XII hypoglossal nucleus - AMB nucleus ambiguus - AP area postrema - CX external cuneate nucleus - D descending vestibular nucleus - DX dorsal-motor nucleus of the vagus - M medial vestibular nucleus - NTS nucleus of the solitary tract - R nucleus of Roller - S solitary tract - RFN retrofacial nucleusThis paper is dedicated to Professor Hajime Mannen on the occasion of his 65th birthdaySupported by grants-in-aid for Scientific Research nos. 60304044, 62570068, 62770043, and 63570027 from the Japan Ministry of Education, Science and Culture