The Journal of Neuroscience, February 1, 2003, 23(3):978
Suppression of Central Taste Transmission by Oral Capsaicin
Christopher T.
Simons1, 2,
Yves
Boucher3, and
E.
Carstens1
1 Section of Neurobiology, Physiology, and Behavior and
2 Department of Food Science and Technology, University of
California, Davis, Davis, California 95616, and
3 Laboratorie de Physiologie de la Manducation,
Université Paris 7, 75231 Paris, France
Because intraoral capsaicin is reported to reduce the perceived
intensity of certain taste qualities, we investigated whether it
affects the central processing of gustatory information. The responses
of gustatory neurons in the nucleus tractus solitarius (NTS) to tastant
stimuli were recorded before and after lingual application of capsaicin
in anesthetized rats. Thirty-four NTS units were characterized as
responding best to sucrose (0.3 M), NaCl (0.1 M), citric acid (0.03 M), monosodium glutamate
(0.2 M), or quinine (0.001 M). During lingual
application of 330 µM capsaicin for 7 min, the firing
rate increased for five units and decreased for four units; the
remainder were unaffected. Immediately after capsaicin, responses to
each tastant were in nearly all cases depressed (mean, 61.5% of
control), followed by recovery in most cases. NTS tastant-evoked unit
responses were unaffected by lingual application of vehicle (5%
ethanol). Capsaicin elicited an equivalent reduction (to 64.5%) in
tastant-evoked responses of nine additional NTS units recorded in rats
with bilateral trigeminal ganglionectomy, arguing against a
trigeminally mediated central effect. Furthermore, capsaicin elicited a
puncate pattern of plasma extravasation in the tongue that matched the
distribution of fungiform papillae. These results support a peripheral
site of capsaicin suppression of taste possibly via direct or indirect
effects on taste transduction or taste receptor cell excitability. The
depressant effect of capsaicin on gustatory transmission might underlie
its ability to reduce the perceived intensity of some taste qualities.
Key words:
capsaicin; rat; gustatory; nucleus of the solitary
tract; trigeminal; taste; irritation
Copyright © 2003 Society for Neuroscience 0270-6474/03/233978-08$05.00/0
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