ANTAGONISM OF INTRACAUDATE CARBACHOL TREMOR BY LOCAL INJECTIONS OF CATECHOLAMINES

¹ Department of Neuropharmacology, Eastern Pennsylvania Psychiatric Institute, and Department of Pharmacology, Philadelphia College of Pharmacy and Science, Philadelphia, Pennsylvania

This study was structured to clarify two specific issues : to determine whether catecholamines can facilitate or inhibit tremor initiated by intracaudate injections of carbachol, and to test the hypothesis that a local neurohumoral balance in the caudate is an integral part of the tremor regulatory mechanisms. Injections of catecholamines into the caudate of unanesthetized chronic cats antagonized the involuntary movements induced by previously injected carbachol. The antitremor potencies of the catecholamines paralleled their order of adrenergic beta-receptor reactivity. Other adrenergic agents which act primarily on adrenergic alpha-receptors failed to antagonize the tremor. Local pretreatment with adrenergic beta-receptor blocking agents prevented antagonism of tremor by catecholamines; however, even at substantially larger doses, locally injected alpha-receptor blocking drugs were inactive. Intracaudate injections of agents which might be expected to change local vascular tone would not alter involuntary motor activity. These results, coupled with the finding that intracaudate injections of adenosine triphosphate also abolished tremor, suggest that antagonism of carbachol tremor by catecholamines is mediated by a " metabolic" effect on adrenergic beta-receptors in the caudate. Since intracaudate injections of cholinergic agents elicited tremor and subsequent administration of catecholamines abolished this involuntary motor activity, the conclusion that a caudate neurohumoral balance participates in tremor regulation appears justified.