Neuroleptic-induced acute dyskinesias in squirrel monkeys: Correlation with propensity to cause extrapyramidal side effects

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Abstract
In squirrel monkeys that had undergone repeated treatment with haloperidol at intervals of 7–14 days, subsequent acute administration of haloperidol induced dystonia and dyskinesias. This acute effect of haloperidol was dose-related and occurred at the same doses that impaired Sidman avoidance performance. Chlorpromazine, fluphenazine, metoclopramide, tetrabenazine, and Su-23397, all of which have been associated with extrapyramidal side effects, reliably elicited dyskinesias in these monkeys. Dyskinesias were less marked after thioridazine and absent after clozapine, corresponding to the reported lower incidence of extrapyramidal side effects in the clinic. The non-neuroleptics, baclofen, and diazepam, failed to elicit dyskinesias. In contrast to the dyskinetic syndrome, the incidence of catalepsy or tremor did not accurately predict propensity to elicit extrapyramidal symptomatology. The acute dyskinetic syndrome in squirrel monkeys may therefore serve as an animal model for predicting the ability of antipsychotics to cause extrapyramidal dysfunction, and may yield insight into the mechanisms of these drug-induced motor disorders.