Nucleus raphe obscurus modulates hypoglossal output of neonatal rat in vitro transverse brain stem slices

Respiratory Neuroscience Laboratory, Departments of Physiology and Anaesthesia, University of Toronto, Toronto, Ontario, Canada M5S 1A8 Nucleus raphé obscurus (NRo) modulates hypoglossal (XII) nerve motor output in the in vitro transverse brain stem slice of neonatal rats (1-5 days old); chemical ablation of NRo and its focal CO 2 acidification modulated the bursting rhythm of XII nerves. We microinjected a 4.5 mM solution of kainic acid into the NRo to disrupt cellular activity and observed that XII nerve activity was temporarily abolished ( n = 10). We also microinjected CO 2 -acidified (pH = 6.00 ± 0.01) artificial cerebrospinal fluid (aCSF) into the NRo ( n = 6), the pre-Bötzinger complex (PBC) ( n = 6), as well as a control region in the lateral tegmental field equidistant to NRo, PBC, and the XII motor nuclei ( n = 12). CO 2 acidification of the control region had no effect on XII motor output. CO 2 acidification of the NRo significantly ( P