The orexin receptor 1 (OX1R) in the rostral medullary raphe contributes to the hypercapnic chemoreflex in wakefulness, during the active period of the diurnal cycle

It has been shown that orexin plays an important role in the hypercapnic chemoreflex during wakefulness, and OX1Rs in the retrotrapezoid nucleus (RTN) participate in this mechanism. We hypothesized that OX1R in the rostral medullary raphe (MR) also contributes to the hypercapnic chemoreflex. We studied the effects on ventilation in air and in 7% CO2 of focal antagonism of OX1R in the rostral MR by microdialysis of SB-334867 in rats during wakefulness and NREM sleep, under dark and light periods. During wakefulness in the dark period, but not in the light period, SB-334867 caused a 16% reduction of the hyperventilation induced by 7% CO2 compared with vehicle. There was no significant effect in sleep. The basal ventilation, body temperature and V˙O2 were not affected. No effect was observed in a separate group of animals which had the microdialysis probe misplaced (peri-raphe). We conclude that OX1R in the rostral medullary raphe contribute to the hypercapnic chemoreflex in wakefulness, during the dark period in rats.