Central cholinergic mechanisms in electrical self-stimulation and in drug-induced tremor in rats.

Oxotremorine, a specific stimulant of central muscarinic acetylcholine receptors, inhibited lateral hypothalamic self-stimulation at a dose-level less than one-tenth of that necessary to produce body tremor. Tremor induced by oxotremorine (0.5 mg/kg) was inhibited by pretreatment with hyoscine (scopolamine) (0.3 mg/kg) or propranolol (20 mg/kg) but not by methylhyoscine (0.3 mg/kg) or apomorphine (0.3 mg/kg). Inhibition of self-stimulation by oxotremorine (.03 mg/kg) was prevented by hyoscine (0.3 mg/kg) but not by any other of the drugs tested and thus constitutes a uniquely specific in vivo model for assessing central antimuscarinic activity. The results confirm the presence of centrally situated ACh receptors eleciting tremor and inhibiting self-stimulation but provide no evidence of an effect on tremor by central adrenergic beta-receptors.