Central respiratory control of A5 and A6 pontine noradrenergic neurons.

Sympathetic nerve discharge (SND), phrenic nerve discharge (PND), and unit activity of locus ceruleus (LC) and of putative A5 noradrenergic cells were recorded in vagotomized rats anesthetized with urethan. SND was activated by stimulation of carotid chemoreceptors with hypoxia (N2 inhalation, 5-15 s or 12% O2 inhalation, 2-5 min) and displayed a prominent central respiratory modulation during the hypoxic challenge (postinspiratory pattern). LC cells were also activated by peripheral chemoreceptor stimulation. The discharge of most LC units (28 of 31) exhibited central respiratory modulation. 15 LC units had a postinspiratory pattern and 11 had an inspiratory one. Putative A5 cells were also excited by hypoxia and also displayed a clear central respiratory modulation (mostly postinspiratory pattern). These experiments indicate that 1) the firing rate of most pontine noradrenergic cells is increased by peripheral chemoreceptor stimulation, and 2) pontine noradrenergic neurons receive afferent information of a respiratory nature, possibly from their ventrolateral medullary inputs.