Cholinergic stimulation of the ventrolateral striatum elicits mouth movements in rats: pharmacological and regional specificity

Cholinomimetic drugs are known to induce changes in perioral behavior in rodents, characterized primarily by "purposeless" chewing movements, but little is known about their central sites of action. Using observational methods, the effects of direct microinfusion of a mixture of physostigmine and acetylcholine (PS/Ach, 0, 0.5, 2.5, 5.0 micrograms of each in 0.5 microliter saline) into the ventrolateral striatum (VLS) were assessed. Cholinergic stimulation of this region produced a dose-dependent induction of mouth movements, characterized by chewing movements, jaw opening and closing, tongue protrusions and jaw tremors. These movements were not directed toward any stimulus. In some rats, cholinergic stimulation of the VLS also induced stereotyped self-biting, although this effect was less prominent and of shorter duration. Induction of mouth movements by cholinergic stimulation of the VLS was blocked by prior administration of atropine, either systemically (50 mg/kg) or directly into the VLS (10 micrograms). Systemic administration of methylatropine (50 mg/kg) did not block the mouth movements. Pretreatment with haloperidol (2.5 micrograms into VLS) had no effect on PS/Ach-induced mouth movements. Infusion of PS/Ach (0, 2.5, 5.0 micrograms) into the dorsolateral or ventromedial striatum did not produce significant changes in oral behavior, although the level of mouth movements was somewhat higher at the medial site. The three sites studied were also differentiated with respect to spontaneous motor behaviors (locomotion and rearing) following direct cholinergic stimulation. These findings are considered as further evidence for the role of the ventrolateral striatum in oral motor behavior.