Methamphetamine-induced behavioral effects and brain catecholamines following repeated administration of methamphetamine

Abstract

After mice were given methamphetamine (MA) at a dose of 25 mg/kg i.p. twice daily (9:00 a.m. and 5:00 p.m.) for 4 days, the behavioral effects and releases of brain catecholamines induced by MA were investigated. The behavioral effects which were estimated according to the rating system of Peachey et al. were a predominant increase in locomotor activity at 2.5 mg/kg MA, a predominant stereotyped behavior at 10 mg/kg MA and the mixed type at 5 mg/kg MA in the saline control. Following repeated administration of MA, the rating scores of each effect at 2.5 and 5 mg/kg MA were not significantly different from those of the saline control. At 10 mg/kg MA, the behavioral effects were of the mixed type. However, when locomotor activity was measured by Automex II 2SD, significant increases in locomotor activity were observed over 2 hr. Following repeated administration of MA, the brain NE level did not alter, while the brain DA level was significantly decreased. The increased accumulation of brain MHPG-S0i+ induced by MA was not significantly different from the saline control. The accumulation of HVA, however, did not alter at high doses of MA, which caused the increased accumulation of HVA in the saline control.