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The Journal of Neurophysiology Vol. 85 No. 6 June 2001, pp. 2446-2454
Copyright ©2001 by the American Physiological Society
Faculty of Dentistry, The University of Toronto, Toronto, Ontario M5G 1G6, Canada
Cairns, Brian E.,
Barry J. Sessle, and
James W. Hu.
Characteristics of Glutamate-Evoked Temporomandibular Joint
Afferent Activity in the Rat. J. Neurophysiol. 85: 2446-2454, 2001. Injection of glutamate into the rat
temporomandibular joint (TMJ) capsule can reflexly induce a prolonged
increase in the electromyographic (EMG) activity of the jaw muscles,
however, the characteristics of TMJ afferents activated by glutamate
have not been investigated. In the present study, we examined the
effect of glutamate injection into the TMJ capsule on jaw muscle EMG activity and the extracellularly recorded activity of single trigeminal afferents that had receptive fields in the TMJ tissue and
antidromically identified projections to the brain stem subnucleus
caudalis (Vc) in rats of both sexes. Glutamate (0.05-1.0 M, 10 µl)
injection into the TMJ capsule evoked EMG activity in a dose-related
manner; however, at concentrations of 0.5 and 1.0 M, glutamate-evoked digastric muscle responses were greater in female than in male rats. In
experiments where jaw muscle EMG and afferent activity were recorded
simultaneously, glutamate (0.5 M, 10 µl) injection into the TMJ
capsule evoked activity in the jaw muscles as well as in 27 (26 A
and 1 C-fiber afferent) of 34 trigeminal afferents that could be
activated by blunt mechanical stimulation of the TMJ tissue. In these
experiments, glutamate-evoked jaw muscle activity was significantly
increased for 6 min after the glutamate injection, whereas afferent
activity was significantly increased only during the first minute after
the glutamate injection. The glutamate-evoked afferent activity was
inversely related to conduction velocity and, in afferents with
conduction velocities <10 m/s, was significantly greater in female
(n = 6) than in male (n = 10) rats.
These results suggest that glutamate excites putative nociceptive
afferents within the TMJ to a greater degree in female than in male
rats. This sex-related difference in afferent discharge may, in part,
underlie sex-related differences in glutamate-evoked jaw muscle EMG activity.
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