Fastigial nucleus-mediated respiratory responses depend on the medullary gigantocellular nucleus

Electrical stimulation of the rostral fastigial nucleus (FNr) alters respir ation via activation of local neurons. We hypothesized that this FNr-mediat ed respiratory response was dependent on the integrity of the nucleus gigan tocellularis of the medulla (NGC). Electrical stimulation of the FNr in 15 anesthetized and tracheotomized spontaneously breathing rats significantly altered ventilation by 35.2 +/- 11.0% (P < 0.01) with the major effect bein g excitatory (78%). This respiratory response did not significantly differ from control after lesions of the NGC via bilateral microinjection of kaini c or ibotenic acid (4.5 +/- 1.9%; P > 0.05) but persisted in sham controls. Eight other rats, in which horseradish peroxidase (HRP) solution was previ ously microinjected into the left NGC, served as non-stimulation controls o r were exposed to either 15-min repeated electrical stimulation of the righ t FNr or hypercapnia for 90 min. Histochemical and immunocytochemical data showed that the right FNr contained clustered HRP-labeled neurons, most of which were double labeled with c-Fos immunoreactivity in both electrically and CO2-stimulated rats. We conclude that the NGC receives monosynaptic FNr inputs and is required for fully expressing FNr-mediated respiratory respo nses.