Journal of Dental Research, Vol 79, 1823-1828, Copyright © 2000 by International & American Associations for Dental Research Online Journals
The effect of a cholecystokinin agonist on masseter muscle activity in the cat
P. Sitthisomwong, S. Weiner, L. Levin, S. Reisman and A. Siegel
Department of Prosthodontics, Faculty of Dentistry, Mahidol University, Bangkok, Thailand.
The CCK(B) agonist, pentagastrin, has been shown to induce anxiety in human
subjects. Similarly, in the cat model, pentagastrin facilitates the
expression of hypothalamically activated emotional behavior. Because
hypothalamically mediated emotional behavior is also accompanied by
increased EMG activity in the jaw muscles, these experiments were designed
to examine the combined effects of administration of pentagastrin with
activation of hypothalamically mediated emotional behavior upon jaw muscle
EMG activity. Electrodes were carefully lowered through previously placed
guide tubes overlying the hypothalamus until a behavioral site was
identified. Following the establishment of a stable threshold current for
eliciting an emotional behavioral response, the skin overlying the
ipsilateral masseter muscle was shaved and cleaned with alcohol, and
surface electrodes were attached. The EMG was recorded, amplified,
digitized, and stored in a microcomputer for analysis. Mean power
frequencies (MPF) and latencies for behavior were calculated for baseline
prior to infusion of all drugs. Following this, the effects of intravenous
administration of pentagastrin and the CCK(B) antagonist LY288513 on the
MPF were determined. The infusion of the CCK(B) agonist, pentagastrin
(0.77, 1.92, and 3.84 microg/kg), decreased MPF in a time-related manner.
The effects of pentagastrin 1.92 microg/kg were blocked by the CCK(B)
antagonist, LY288513 (6.54 microg/kg). In addition, the infusion of
LY288513 alone increased MPF. These results are surprising in that
pentagastrin's anxiogenic properties would appear to make it likely to
facilitate motor activity, not suppress it.
