Involvement of central 5-HT1A receptors in the reflex activation of pulmonary vagal motoneurones by inhaled capsaicin in anaesthetized cats.
1. The aim of the present experiments was to determine whether 5-HT1A 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-HT1A receptor ligands, 8-OH-DPAT (50 micrograms kg-1), buspirone (200 micrograms kg-1), WAY-100635 (100 micrograms kg-1), methiothepin (200 micrograms kg-1) and (-)-pindolol (100 micrograms kg-1) and the 5-HT2 receptor antagonist, cinanserin (200 micrograms kg-1), on the reflex bronchoconstriction evoked by inhaled capsaicin aerosol in alpha-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-HT1A 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-HT1A receptor agonist, 8-OH-DPAT (50 micrograms kg-1) given i.c., potentiated the capsaicin-evoked reflex bronchoconstriction, whereas buspirone (200 micrograms kg-1) i.c. had no effect. The 5-HT2 receptor antagonist, cinanserin (200 micrograms kg-1) also had no effect. 3. It is concluded that the reflex excitation of pulmonary vagal motoneurones by inhaled capsaicin in alpha-chloralose anaesthetized cats involves the activation of central 5-HT1A receptors.
Bootle
D J
DJ
Department of Pharmacology, Wellcome Research Laboratories, Kent.
Adcock
J J
JJ
Ramage
A G
AG
D000280:Administration, Inhalation; D000769:Anesthesia, Inhalation; D000818:Animals; D002211:Capsaicin / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002415:Cats; D008168:Lung / Q000294:innervation*; D008297:Male; D009046:Motor Neurons / Q000187:drug effects* / Q000502:physiology; D011985:Receptors, Serotonin / Q000502:physiology*; D044263:Receptors, Serotonin, 5-HT1; D012018:Reflex / Q000187:drug effects* / Q000502:physiology; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D014630:Vagus Nerve / Q000166:cytology / Q000187:drug effects / Q000502:physiology
D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D002211:Capsaicin