Modification of the tremorigenic activity of physostigmine

Drugs which reduce central catecholamine activity increased the tremorigenic action physostigmine (0.25 mg/kg) in the rat. The potentiation of physostigmine tremor induced by these neuroleptic drugs was quantitated measuring the ratio of post- to prephysostigmine motor activity; this ratio may be useful index of catecholamine/cholinergic balance. Of the compounds tested, chlorpromazine HC1 (15 mg/kg) and reserpine (10 mg/kg) had the greatest potentiating effect on the tremor-producing action of physostigmine. LDOPA (500 mg/kg) reduced the tremor induced by physostigmine in rats pre-treated with reserpine, but not in rats pre-treated with chlorpromazine.