Abstract
We have previously demonstrated that the medullary raphe nuclei played important roles in respiratory control in cats. Electrical stimulation of the medullary raphe complex [raphe magnus (RM), raphe pallidus (RP) and raphe obscurus (RO)] exerts different effects on respiration. The present study aimed to clarify the effects of raphe stimulation on respiration in rats, and to identify the putative neurotransmitters (GABA and serotonin (5-HT)) involved, using electrophysiological and immunohistochemical methods. Experiments were performed on adult Wistar rats anesthetized with ketamine and xylazine. Train pulse stimulation (100 Hz, 100 pulses, 10-30 μA) was applied at the raphe nucleus regions. Electrical stimulation of RM depressed respiratory movements measured by means of abdominal pneumograph, while stimulation of RP facilitated inspiratory movements. Stimulation of RO evoked mixed (inhibitory and facilitatory) effects depending on stimulus sites and intensities. After microinjection of Texas red into phrenic motor nucleus regions of the C4-5 segments, some neurons in the RM, RP and RO were retrogradely labeled. 5-HT positive neurons were observed predominantly in RP and sparsely in RM, while GAD positive neurons were predominantly observed in RM. The results suggest that RM inhibits respiration thorough a GABAergic system, while RP facilitates respiration through a serotonergic system. [Jpn J Physiol 54 Suppl:S110 (2004)]
