Neuroleptic-induced acute dyskinesias in rhesus monkeys

Rhesus monkeys, previously subjected to twice-weekly injections of various neuroleptics, subsequently respond to acute IM injections of haloperidol with marked bucco-lingual and whole body movement disturbances consisting of mouth opening, protrusion, retraction or curling of the tongue together with writhing movements of the neck, trunk and/or limbs. These phenomena, which closely resemble the acute dyskinetic or dystonic reactions described in patients at the beginning of neuroleptic treatment, were also observed after acute IM injections of other neuroleptics such as fluphenazine, metoclopramide, oxiperomide, sulpiride, sultopride and tiapride. No dyskinesias were observed after chlorpromazine, chlordiazepoxide, clozapine, RMI81582 or thioridazine at doses which otherwise had marked behavioural effects. The dyskinesias induced by haloperidol could be suppressed by prior treatment with the anti-cholinergic scopolamine. These observations, which correlate well with clinical findings, suggest that neuroleptic induced acute dyskinesias in the Rhesus monkey might be a useful model for predicting the liability of new anti-psychotics for inducing acute dyskinetic reactions in man.