MIXTURE IN THE DISTRIBUTION OF HALOPERIDOL-INDUCED ORAL DYSKINESIAS IN THE RAT SUPPORTS AN ANIMAL-MODEL OF TARDIVE-DYSKINESIA

Spontaneous adventitious oral movements which are produced in rats by very chronic (6- month) neuroleptic treatment have some phenomenologic and pharmacologic characteristics in common with tardive dyskinesia i n humans. However, since not all of the features match, this putative model has been questioned and further support is warranted. Data from several laboratories support dichotomizing these neuroleptic-induced r at oral movements into ''low'' or ''not TD-like'' movements and ''high '' or ''TD-like'' movements, similar to the division of neuroleptic-in duced involuntary movements in humans. Here, we have used mixture anal ysis to test this proposal statistically in 185 haloperidol-treated an d 127 water-treated animals. Rats from several different studies were grouped together to form these two cohorts. The haloperidol dose, rout e of administration, rating technique; and balanced experimental group s were held constant across all experiments. Results show that two dis tinct groups of rat movements are induced by very chronic haloperidol treatment (1.5 mg/kg per day). The ''low'' vacuous chewing movement (V CM) group of rats had an average of 3.6 VCMs/5 min, and the ''high'' V CM group had an average of 16.1 VCMs/5 min; the conrol group, with a m edian VCM rate of 2.0 VCMs/5 min, demonstrated a single distribution. These data suggest that rats, like humans, dichotomize into two groups either expressing or not expressing ''high'' VCM dyskinesias with ver y chronic haloperidol treatment.