5-HT₁A, but not 5-HT₂ and 5-HT₇, receptors in the nucleus raphe magnus modulate hypoxia-induced hyperpnoea

In the present study, we assessed the role of 5-hydroxytryptamine (5-HT) receptors (5-HT₁A, 5-HT₂ and 5-HT₇) in the nucleus raphe magnus (NRM) on the ventilatory and thermoregulatory responses to hypoxia. To this end, pulmonary ventilation (VE) and body temperature (Tb) of male Wistar rats were measured in conscious rats, before and after a 0.1 μL microinjection of WAY-100635 (5-HT₁A receptor antagonist, 3 μg 0.1μL⁻¹, 56 m m), ketanserin (5-HT₂ receptor antagonist, 2 μg 0.1μL⁻¹, 36 m m) and SB269970 (5-HT₇ receptor antagonist, 4 μg 0.1 μL⁻¹, 103 m m) into the NRM, followed by 60 min of severe hypoxia exposure (7% O₂). Intra-NMR microinjection of vehicle (control rats) or 5-HT antagonists did not affect VE or Tb during normoxic conditions. Exposure of rats to 7% O₂ evoked a typical hypoxia-induced anapyrexia after vehicle microinjections, which was not affected by microinjection of WAY-100635, SB269970 or ketanserin. The hypoxia-induced hyperpnoea was not affected by SB269970 and ketanserin intra-NMR. However, the treatment with WAY-100635 intra-NRM attenuated the hypoxia-induced hyperpnoea. These data suggest that 5-HT acting on 5-HT₁A receptors in the NRM increases the hypoxic ventilatory response.