Am. J. Respir. Crit. Care Med., Vol 149, No. 1, Jan 1994, 261-263.
Capsaicin desensitization inhibits swallowing reflex in guinea pigs
Y Jin, K Sekizawa, T Fukushima, M Morikawa, H Nakazawa and H Sasaki
Department of Geriatric Medicine, Tohoku University School of Medicine, Sendai, Japan.
To determine whether capsaicin-sensitive sensory nerves are involved in the
swallowing reflex, we examined swallowing reflex in terms of the number of
swallows elicited by injections of three different volumes (0.2, 0.4, and
0.6 ml) of distilled water, into the pharynx through a catheter in
anesthetized guinea pigs pretreated with and without systemic capsaicin.
The number of swallows was counted by submental electromyographic activity
and visual observation of characteristic laryngeal movement. Injections of
distilled water caused a volume- dependent increase in the number of
swallows in animals treated with and without capsaicin. Capsaicin treatment
significantly decreased the number of swallows elicited by all volumes of
distilled water (p < 0.01). Exogenously administered substance P (SP)
caused a dose- dependent increase in the number of swallows in all volumes
but calcitonin gene-related peptide and acetylcholine were without effect.
FK 888 (10(-5) M; 1 ml), a specific inhibitor of NK1 receptor, reduced the
number of swallows elicited by distilled water to a similar degree as
capsaicin treatment. Pharyngeal application of lidocaine (4%; 1 ml) also
inhibited distilled water-induced swallowing. These results suggest that
nonmyelinated C-fibers regulate the swallowing reflex through the release
of SP in response to stimulation.
