Catatonic behavior induced by haloperidol, increased by retesting and elicited without drug in rats.

The catatonogenic action of haloperidol in rats was assessed through different experimental procedures. In the first experiment the animals were injected intraperitoneally with haloperidol, 0.4-4.0 mg/kg, and then divided into two subgroups. The first group was tested for catatonic behavior from 20 min up to 4 h after the injection, while the second was only tested throughout the last 3- to 4-hour period. In the second experiment, animals received, either 0.2 or 0.6 mg haloperidol/kg 3 times at 15-day intervals, and were tested for catatonic behavior from 20 to 240 min after the injection. 15 days after the last drug session, the same animals were injected with distilled water and then tested for catatonia. The results showed that retesting drastically influenced the amount of catatonic behavior and that, when under no drug, the rats still displayed catatonia. The data suggest a learning component of this behavior.