Raphe modulation of the pre-Bötzinger complex respiratory bursts in in vitro medullary half-slice preparations of neonatal mice
Spontaneous respiratory bursts which begin in the pre-Bötzinger complex were recorded from the hypoglossal (XIIth) nerve rootlets of in vitro slices prepared from newborn mice. First, we examined the respiratory bursts before and after a midline or para-midline transection which spared the caudal raphe nuclei: the raphe obscurus and raphe pallidus. After a midline transection, the respiratory bursts in both half-slices were desynchronized and had slightly decreased amplitudes and frequencies. After a para-midline transection, the bursts continued with similar frequencies in the half slice containing the raphe obscurus and raphe pallidus. Second, to analyze the effects of modulation by the raphe obscurus and raphe pallidus, a dorsal or ventral midline lesion was used to damage either the raphe obscurus or raphe pallidus. After a dorsal lesion, the synchronized respiratory bursts persisted with slightly decreased frequencies. In contrast, after a ventral lesion, the bursts were almost completely abolished, but recovered significantly after the addition of 5-HT. The present results demonstrated that the pre-Bötzinger complex on each side of the medulla can independently generate rhythmic respiratory activity. It is suggested that the 5-HT released from the ventral part of the raphe nuclei (predominantly the raphe pallidus) plays a critical role in sustaining rhythmic respiratory bursts.