Lithium's effects on muscarinic receptor binding parameters: a relationship to therapeutic efficacy?

Variables confounding efforts to interpret data on lithium's effects in laboratory animals in vivo and from in vitro muscarinic receptor binding studies are discussed. After accounting for the effects of these variables, the author concludes that it is of theoretical interest and heuristic value to hypothesize that lithium renders cholinergic systems more stable or less perturbable in the face of mono-aminergic overdrive. Thus lithium may diminish the propensity of cholinergic systems to undergo up-regulation and supersensitization consequent to exogenous and endogenous events apt to induce these changes. Lithium's antidepressant, antimanic, and anticycling efficacy may depend on its cholinotropic properties. The potential significance of lithium's cholinergic effects is highlighted by findings that seizures and verapamil induce similar cholinotropic effects. The author hypothesizes that with further investigation anticycling agents will come to be regarded as unique among psychotropics by virtue of their effects on cholinergic-monoaminergic interactions and mechanisms.