The relationship between motor effects in rats following acute and chronic haloperidol treatment.

Tardive dyskinesia (TD) is a serious and sometimes irreversible side-effect to long-term neuroleptic treatment. In order to find predictors for development of TD, it would be of interest to known whether susceptibility to develop acute side-effects increases the risk of TD development. The study investigated in female Sprague-Dawley rats the relationship between haloperidol-induced acute motor effects, assessed by means of the grid test and the open field test, and the chronic motor effect assessed as vacuous chewing movements (VCM). The doses of haloperidol were 1.2, 2.4 and 4.8 mg/kg IP in the acute experiments and haloperidol decanoate 38 mg/kg per 4 weeks IM in the chronic experiment. The VCM obtained at different timepoints during the 24 weeks of chronic treatment were highly correlated. However, no correlation was found between the motor effects in the acute and the chronic experiments. The study does not indicate any connection between susceptibility to acute side-effects on neuroleptics and later development of TD.