1 The aim of the present experiments was to determine whether 5-HTIA receptors play a role in the control of the reflex activation of pulmonary vagal motoneurones. This was carried out by investigating the effects of intracisternal injections (i.c.) of the 5-HTIA receptor ligands, 8-OH-DPAT (50 ,ug kg-'), buspirone (200 ug kg-'), WAY-100635 (100 Mg kg-'), methiothepin (200 Mg kg-') and (-)-pindolol (100 Mg kg-') and the 5-HT2 receptor antagonist, cinanserin (200 ug kg-'), on the reflex bronchoconstriction evoked by inhaled capsaicin aerosol in a-chloralose anaesthetized, neuromuscularly blocked and artificially ventilated cats. Recordings were made of heart rate, blood pressure and upper tracheal pressure.2 Central application of all the 5-HTIA receptor antagonists (methiothepin, WAY-100635 and (-)-pindolol) attenuated the reflex bronchoconstriction in the upper trachea. However, the same dose of WAY-100635 given i.v. had no effect on this reflex bronchoconstriction. The 5-HTlA receptor agonist, 8-OH-DPAT (50 Mg kg-') given i.c., potentiated the capsaicin-evoked reflex bronchoconstriction, whereas buspirone (200 Mg kg-') i.c. had no effect. The 5-HT2 receptor antagonist, cinanserin (200 Mg kg-') also had no effect. 3 It is concluded that the reflex excitation of pulmonary vagal motoneurones by inhaled capsaicin in achloralose anaesthetized cats involves the activation of central 5-HTIA receptors.
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