The effect of a cholecystokinin agonist on masseter muscle activity in thecat

The CCKB agonist, pentagastrin, has been shown to induce anxiety in human s ubjects. Similarly, in the cat model, pentagastrin facilitates the expressi on of hypothalamically activated emotional behavior. Because hypothalamical ly mediated emotional behavior is also accompanied by increased EMG activit y in the jaw muscles, these experiments were designed to examine the combin ed effects of administration of pentagastrin with activation of hypothalami cally 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 establis hment of a stable threshold current for eliciting an emotional behavioral r esponse, the skin overlying the ipsilateral masseter muscle was shaved and cleaned with alcohol, and surface electrodes were attached. The EMG was rec orded, amplified, digitized, and stored in a microcomputer for analysis. Me an power frequencies (MPF) and latencies for behavior were calculated for b aseline prior to infusion of all drugs. Following this, the effects of intr avenous administration of pentagastrin and the CCKB antagonist LY288513 on the MPF were determined. The infusion of the CCKB agonist, entagastrin (0.7 7, 1.92, and 3.84 mug/kg), decreased MPF in a time-related manner. The effe cts of pentagastrin 1.92 mug/kg were blocked by the CCKB antagonist, LY2885 13 (6.54 mug/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.