Chronic administration of typical, but not atypical neuroleptics induce persisting alterations in rest-activity cycles in rats.

The behavior of rats administered chronic neuroleptics was observed using an extremely sensitive, computerized device which detected any cage movements, thereby continuously monitoring even very small levels of activity. In the first experiment, it was found that normal rats have a strong rest-activity rhythm with a cycle length of 60-70 min, whereas rats which have been chronically administered either haloperidol (HAL) or fluphenazine (FLU) decanoate for 20 months show a distinct lengthening of this cycle and that this effect persists long after cessation of drug injections. In a second experiment, it was further observed that these lengthened rest-activity cycles also occur when HAL is administered chronically either via osmotic minipumps or in the drinking water, but not following the chronic administration of two atypical neuroleptics (clozapine and raclopride). These findings suggest a useful new technique for the study of side-effects of neuroleptics in rats.