Respiratory actions of vanilloid receptor agonists in the nucleus of the solitary tract: Comparison of resiniferatoxin with non-pungent agents and anandamide

Abstract

1 Activation of vanilloid receptors on sensory nerve terminals in the commissural nucleus of the solitary tract (cNTS) of rats with capsaicin, produces respiratory slowing. In this study, we used microinjection techniques employing pungent and non-pungent vanilloids to further characterize vanilloid receptors in the cNTS. 2 Microinjection of the pungent vanilloid, resiniferatoxin (RTX), into the cNTS of urethane-anaesthetized rats, dose-dependently reduced respiratory rate without affecting tidal volume. RTX was 20 fold more potent at slowing respiration (∼ED 50, 100 pmol) than capsaicin (∼ED 50, 2 nmol). Doses of RTX greater than 100 pmol caused either irregular (dyspnoeic) breathing or ter..