Xm. Yu et al., EFFECTS OF INFLAMMATORY IRRITANT APPLICATION TO THE RAT TEMPOROMANDIBULAR-JOINT ON JAW AND NECK MUSCLE-ACTIVITY, Pain, 60(2), 1995, pp. 143-149
An electromyographic (EMG) study was carried out in 40 anaesthetized r
ats to determine if the activity of jaw and neck muscles could be infl
uenced by injection of the small-fibre excitant and inflammatory irrit
ant mustard oil into the region of the temporomandibular joint (TMJ).
Injection of a vehicle (mineral oil, 20 mu l) did not produce any sign
ificant change in EMG activity. In contrast, injection of mustard oil
(20 mu l, 20%) evoked increases in EMG activity in the jaw muscles but
not in the neck muscles. The increased EMG activity evoked by mustard
oil was reflected in 1 or 2 phases of increased activity. The early E
MG increase occurred soon after the mustard oil injection (mean latenc
y +/-SD: 3.5 +/- 2.3 sec), peaked within 1 min, and then subsided (mea
n duration: 7.5 +/- 5.2 min). The later EMG increase occurred at 14.6
+/- 10.0 min after the mustard oil injection and lasted 14.3 +/- 12.3
min. These excitatory effects of mustard oil on the EMG activity of ja
w muscles appear to have a reflex basis since they could be abolished
by pre-administration of local anaesthetic into the TMJ region. These
results document that TMJ injection of mustard oil results in a sustai
ned and reversible activation of jaw muscles that may be related to th
e reported clinical occurrence of increased muscle activity associated
with trauma to the TMJ.