[Chronological change in abnormal behavior produced by long-term methamphetamine administration in the rat].

Rats received once daily injections of methamphetamine (MAP; 4 mg/kg/day) intraperitoneally, at most 100 times. Enhanced ambulatory activity by MAP reduced during the long-term administration of MAP. The mean rating score of MAP-induced abnormal behavior, including locomotion, stereotyped behavior, motor inhibition and the response to acoustic stimulation, increased until 56th injection of MAP. But after that, the score tended to decrease mainly because the injected MAP failed to keep the movement of rats reduced under acoustic stimulation. Neither the time course of these rating score nor the decrease in [3H] spiperone binding sites, examined after the injection of MAP 100 times, seemed to develop along with the repeated MAP administration. Thus, the changes in both behavior and [3H] spiperone binding sites produced by repeated MAP would not necessarily indicate the symptoms of MAP-induced psychosis in man, because the susceptibility to psychosis in man increases along with the time of MAP injection. It is presumed that the animal model of psychosis produced by administration of MAP is important not as a model of psychotic symptoms, but as a model of increased susceptibility to psychosis induced by MAP.