Previous work has shown that cholinomimetic drugs induce "vacuous" or 
non-directed jaw movements in rats. In the present study, five experiments were 
conducted to provide a pharmacological, anatomical and behavioral 
characterization of tacrine-induced vacuous jaw movements. In the first 
experiment, tacrine produced vacuous chewing in a dose-related manner in a range 
of 1.25 mg/kg to 1.0 mg/kg. This effect was reduced, also in a dose-related 
manner, by the co-administration of the muscarinic antagonist scopolamine in a 
range of 0.125 to 1.0 mg/kg, but not by N-methylscopolamine. The fourth 
experiment examined the effect of scopolamine (2.5 to 10.0 micrograms) injected 
into the ventrolateral striatum on vacuous jaw movements induced by 5.0 mg/kg 
tacrine. Intrastriatal injections of scopolamine completely blocked 
tacrine-induced jaw movements. The fifth experiment utilized a slow-motion 
videotaping system to analyze the temporal characteristics of vacuous chewing 
induced by 5.0 mg/kg tacrine. The vast majority of the movements occurred in 
rapid "bursts," and analysis of interresponse times (i.e., the time between each 
jaw movement) showed that most of the jaw movements occurred within a local 
frequency range of 3 to 7 Hz. Thus, tacrine-induced jaw movements are reduced by 
antimuscarinic treatment, and most of these movements occur in the parkinsonian 
tremor frequency range. Tremulous jaw movements induced by tacrine in rats 
appear to share some characteristics with Parkinsonian tremor.