Effect of lithium on the physostigmine-induced behavioral syndrome and plasma cyclic GMP

Physostigmine has been reported to induce a syndrome of psychomotor retardation and in some cases a depressive syndrome. We attempted to investigate a possible mode of action of lithium's proven prophylactic value in depression by assessing the effect of pre-treatment with lithium on this physostigmine-induced behavioral response. A marked physostigmine response was observed in 5 lithium-treated, euthymic manic-depressive subjects as well as in 5 lithium-free, normal controls, with no diminution in the lithium-treated subjects. Plasma cyclic GMP, a possible product of cholinergic receptor activity, also showed no differential response in lithium-treated and lithium-free subjects.