Cholinergic imbalance hypotheses of psychoses and movement disorders: strategies for evaluation.

It has been proposed that the etiologies of tardive dyskinesia and Huntington's chorea and of some forms of schizophrenia and the affective disorders involve a cholinergic imbalance with respect to a second neurotransmitter. This relative over- or underactivity of the cholinergic system could result from altered synthesis, storage, release, degradation, or reuptake or from a variety of receptor interactions. Under these hypotheses, clinical symptoms would reflect both the brain region in which the imbalance occurs and the neurotransmitter with which acetylcholine is interacting. Effective treatments could involve the correction of this hypothetical imbalance by changing the relative availability of either one or both of the neurotransmitters. Both precursor loading with choline or dimethylaminoethanol and cholinesterase inhibition may be useful in evaluating the effects of increased cholinergic activity in these disease states; the relative merits of these strategies are discussed.