TREMULOUS CHARACTERISTICS OF THE VACUOUS JAW MOVEMENTS INDUCED BY PILOCARPINE AND VENTROLATERAL STRIATAL DOPAMINE DEPLETIONS

Vacuous jaw movements induced by the muscarinic agonist pilocarpine an d striatal dopamine depletions were examined using a slow motion video tape system. With this procedure, rats were videotaped in a Plexiglas tube so that the profile of the head region could be seen. Vacuous jaw movements were analyzed by examining the tape at 1/6 normal speed. An observer recorded each jaw movement using a computer, and the compute r program re-calculated the temporal characteristics of jaw movement r esponses back to normal speed. The interresponse time was recorded for each jaw movement, and each jaw movement interresponse time was assig ned to a 50 ms wide time bin. Thus, the distribution of interresponse times could be used to analyze the temporal characteristics of jaw mov ement responses. In the first experiment, rats were administered salin e vehicle, 1.0 mg/kg and 2.0 mg/kg pilocarpine. The rats were videotap ed 10-15 min after injection, and the data were analyzed as described above. Pilocarpine induced very high levels of vacuous jaw movements, and the vast majority of all movements occurred in ''bursts'' with int erresponse times of 1.0 s or less. Analysis of the interresponse time distributions showed that most of the jaw movements were within the 15 0-350 ms range. The modal jam movement interresponse time was in the 1 50-200 ms range, which corresponds to a local frequency of 5-6.66 Hz. In the second experiment, the neurotoxic agent 6-hydroxydopamine was i njected directly into the ventrolateral striatum in order to produce a local dopamine depletion. The dopamine-depleted rats were observed fo r jaw movements 7 days after surgery. The overall lever of jaw movemen t activity resulting from dopamine depletion was much lower than that produced by pilocarpine. There was a significant inverse correlation b etween ventrolateral striatal dopamine levels and total number of vacu ous jaw movements. Videotape analysis indicated that the temporal char acteristics of jaw movements induced by dopamine depletions were simil ar to those shown with pilocarpine. These experiments indicate that va cuous jaw movements induced by pilocarpine and striatal dopamine deple tion occur in a frequency range similar to that shown in parkinsonian tremor. (C) 1997 Elsevier Science Inc.