Involvement of central 5‐HT_1A receptors in the reflex activation of pulmonary vagal motoneurones by inhaled capsaicin in anaesthetized cats

Abstract

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.

Modulation of reflexly evoked vagal bradycardias by central 5‐HT1A receptors in anaesthetized rabbits

“…and i.c. application of WAY‐100635 has already been reported for the upper‐airway evoked bradycardia in anaesthetized rabbits (Dando et al ., 1998) and the reflex‐evoked bronchoconstriction in anaesthetized cats and guinea‐pigs (Bootle et al .,1996; 1998). Thus, 5‐HT 1A receptors appear to play a physiological role in the reflex activation of cardiac vagal preganglionic neurones by cardiopulmonary afferents in rats (Bogle et al ., 1990), cats (Wang & Ramage, 2001) and rabbits (present study; Dando et al ., 1998).…”

Evidence for the involvement of central 5‐HT7 receptors in the micturition reflex in anaesthetized female rats

“…Central 5‐hydroxytryptamine (5‐HT) containing neurones, via activation of 5‐HT 1A receptors, play an important role in the reflex control of parasympathetic outflow to the heart in rats ( Bogle et al , 1990 ), rabbits ( Futuro‐Neto et al , 1993 ; Dando et al , 1998 ; Skinner et al , 2002 ) and cats (Wang & Ramage, 2001), to the airways in cats ( Bootle et al , 1996 ) and guinea‐pigs ( Bootle et al , 1998 ) and to the bladder in rats ( Lecci et al , 1992 ; Testa et al , 1999 ; Conley et al , 2001 ; Kakizaki et al , 2001 ; Pehrson et al , 2002 ). Even though stimulation of other 5‐HT receptors, 5‐HT 1B/1D ( Dando et al , 1998 ) and 5‐HT 2C receptors (Steers & De Groat, 1989), can effect reflex activation of parasympathetic outflow, these receptors do not seem to play a physiological role in these reflexes.…”

Central 5‐HT7receptors are critical for reflex activation of cardiac vagal drive in anaesthetized rats

“…Central 5‐hydroxytryptamine (5‐HT)‐containing neurones make an important contribution to the reflex activation of parasympathetic outflow in a number of species (Ramage, 2001; Jordan, 2005). Blockade of 5‐HT 1A receptors within the CNS attenuates reflex parasympathetic outflow to the heart in rats (Bogle et al 1990), rabbits (Futuro‐Neto et al 1993; Dando et al 1998; Skinner et al 2002) and cats (Wang & Ramage, 2001), to the airways in cats (Bootle et al 1996) and guinea pigs (Bootle et al 1998), and to the bladder in rats (Conley et al 2001). Recently, blockade of supraspinal but not spinal 5‐HT 7 receptors has been shown to attenuate the micturition reflex (i.e.…”