Supersensitivity on methamphetamine effects of rats after chronic pretreatment of haloperidol

The present investigation examined methamphetamine-induced stereotypy and hypermotility after withdrawal from chronic haloperidol. Haloperidol was administered intraperitoneally to male rats of Wistar strain (150-160gr) daily (a dose of 0.5mg or 2.5mg) or every two days (a dose of lmg/kg or 5mg/kg) for 14 days. All “measurements were taken during the 60 min period following methamphetamine (3mg/kg or 10mg/kg i.p.) on every rat 4 days or 8 days after withdrawal from chronic haloperidol or saline injections. Stereotyped licking and biting (especially the former activity) were shown in every haloperidol-pretreated group given methamphetamine (3mg/kg), but not in saline-pretreated rats given methamphetamine with a same dose. Stereotyped biting activity was manifested in many cases of haloperidol-pretreated rats given methamphetamine (10mg/kg), while the licking activity was shown in saline-pretreated rats given methamphetamine at the same dose. Methamphetamine (3mg/kg) induced hypermotility; especially, horizontal movement and stereotyped locomotion were potentiated partially in haloperidol (2.5mg/kg) -pretreated rats only. These results suggested that the supersensitivity after withdrawal from chronic haloperidol treatment was manifested clearly by an enhanced stereotypy in response to doses of methamphetamine, but not markedly by locomotor activity.