The caudal nucleus tractus solitarii (NTS) is the main central station of
cough-related afferents and a strategic site for the modulation of the
cough reflex. The similarities between the characteristics of central processing of nociceptive and
cough-related inputs led us to hypothesize that
galanin, a neuropeptide implicated in the control of
pain, could also be involved in the regulation of the
cough reflex at the level of the NTS, where
galanin receptors have been found. We investigated the effects of
galanin and
galnon, a nonpeptide agonist at
galanin receptors, on
cough responses to mechanical and chemical (
citric acid) stimulation of the tracheobronchial tree. Drugs were microinjected (30-50 nl) into the caudal NTS of
pentobarbital sodium-anesthetized, spontaneously breathing rabbits.
Galnon antitussive effects on
cough responses to the mechanical stimulation of the airway mucosa via a custom-built device were also investigated. Bilateral microinjections of 1 mM
galanin markedly decreased
cough number, peak abdominal activity, and increased
cough-related total cycle duration. Bilateral microinjections of 1 mM
galnon induced mild depressant effects on
cough, whereas bilateral microinjections of 10 mM
galnon caused marked
antitussive effects consistent with those produced by
galanin.
Galnon effects were confirmed by using the
cough-inducing device. The results indicate that
galanin receptors play a role in the inhibitory control of the
cough reflex at the level of the caudal NTS and provide hints for the development of novel
antitussive strategies.