Role of the Bötzinger complex in fastigial nucleus-mediated respiratory responses.

We have reported that the phrenic neurogram (PN) is modulated by stimulation of the fastigial nucleus (FN) of the cerebellum. The present study was undertaken to search for brainstem site(s) involved in the FN efferent pathway to modulate phrenic nerve activities. Experiments were performed on 35 anesthetized, paralyzed, and ventilated cats, using the PN as the index of the respiratory motor output. Results showed that bilateral electrolytic lesions of the red nucleus (RN), the paramedian reticular nucleus (PRN), or the pontine respiratory group (PRG) had little effect on the ability of FN stimulation to modulate the respiratory output. However, the modulation was abolished by bilateral electrolytic lesions of the Bötzinger complex (BötC). Further studies showed that bilateral chemical inactivation of BötC neurons produced by topical microinjection of kainic acid or cobalt chloride failed to abolish the modulation. We concluded that fibers of passage, not synapses or cell bodies in the BötC, were involved in the modulatory effect of FN stimulation on the PN. The RN, PRN, and PRG appear not to be important in the neural circuitry responsible for the FN modulation of the phrenic activity.