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

ABSTRACT

AIM: In the present study, we assessed the role of 5-hydroxytryptamine (5-HT) receptors (5-HT(1A), 5-HT(2) and 5-HT(7)) in the nucleus raphe magnus (NRM) on the ventilatory and thermoregulatory responses to hypoxia. METHODS: To this end, pulmonary ventilation (V(E)) and body temperature (T(b)) of male Wistar rats were measured in conscious rats, before and after a 0.1 microL microinjection of WAY-100635 (5-HT(1A) receptor antagonist, 3 microg 0.1 microL(-1), 56 mm), ketanserin (5-HT(2) receptor antagonist, 2 microg 0.1 microL(-1), 36 mm) and SB269970 (5-HT(7) receptor antagonist, 4 microg 0.1 microL(-1), 103 mm) into the NRM, followed by 60 min of severe hypoxia exposure (7% O(2)). RESULTS: Intra-NMR microinjection of vehicle (control rats) or 5-HT antagonists did not affect V(E) or T(b) during normoxic conditions. Exposure of rats to 7% O(2) 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. CONCLUSION: These data suggest that 5-HT acting on 5-HT(1A) receptors in the NRM increases the hypoxic ventilatory response.