Andrew J Mcgeehan1, Patricia H Janak, M Foster Olive. 1. Department of Neurology, Ernest Gallo Clinic and Research Center, University of California at San Francisco, 5858 Horton Street, Suite 200, Emeryville, CA 94608, USA.
Abstract
RATIONALE: Recent evidence suggests that, in addition to ascending monoaminergic systems, glutamate systems also play a role in psychostimulant-induced locomotor activity. The present study was conducted to examine the effects of the selective type-5 metabotropic glutamate receptor (mGluR5) antagonist 6-methyl-2-(phenylethynyl)pyridine (MPEP) on the acute locomotor stimulant effects of cocaine, D-amphetamine, and the dopamine reuptake inhibitor GBR12909. METHODS: Male DBA/2J mice were treated with saline or MPEP (1, 5, 20 or 30 mg/kg i.p.) 10 min prior to the administration of cocaine (15 mg/kg or 30 mg/kg i.p.), D-amphetamine (3 mg/kg or 5 mg/kg i.p.) or GBR12909 (10 mg/kg or 20 mg/kg i.p.). Locomotor activity was then monitored in an open-field environment for 30 min. The effects of MPEP alone (1, 5, 20 and 30 mg/kg i.p.) on locomotor activity were also examined. RESULTS: MPEP dose dependently inhibited the acute locomotor stimulant effects of cocaine, D-amphetamine, and the 10-mg/kg dose of GBR12909. However, MPEP had no effect on the locomotor stimulant effects of the higher (20 mg/kg) dose of GBR12909. When tested alone, MPEP increased locomotor activity at doses of 5 mg/kg and 20 mg/kg. CONCLUSIONS: Our data suggest that mGluR5 receptors not only mediate spontaneous locomotor activity in DBA/2J mice but also the acute locomotor stimulant effects of cocaine, D-amphetamine and lower doses of GBR12909. However, the fact that MPEP did not attenuate the locomotor stimulant effects of the high (20 mg/kg) dose of GBR12909 suggests complex interactions between metabotropic glutamate receptors, dopamine transporters and possibly other monoamines in the regulation of psychostimulant-induced locomotor activity.
RATIONALE: Recent evidence suggests that, in addition to ascending monoaminergic systems, glutamate systems also play a role in psychostimulant-induced locomotor activity. The present study was conducted to examine the effects of the selective type-5 metabotropic glutamate receptor (mGluR5) antagonist 6-methyl-2-(phenylethynyl)pyridine (MPEP) on the acute locomotor stimulant effects of cocaine, D-amphetamine, and the dopamine reuptake inhibitor GBR12909. METHODS: Male DBA/2J mice were treated with saline or MPEP (1, 5, 20 or 30 mg/kg i.p.) 10 min prior to the administration of cocaine (15 mg/kg or 30 mg/kg i.p.), D-amphetamine (3 mg/kg or 5 mg/kg i.p.) or GBR12909 (10 mg/kg or 20 mg/kg i.p.). Locomotor activity was then monitored in an open-field environment for 30 min. The effects of MPEP alone (1, 5, 20 and 30 mg/kg i.p.) on locomotor activity were also examined. RESULTS:MPEP dose dependently inhibited the acute locomotor stimulant effects of cocaine, D-amphetamine, and the 10-mg/kg dose of GBR12909. However, MPEP had no effect on the locomotor stimulant effects of the higher (20 mg/kg) dose of GBR12909. When tested alone, MPEP increased locomotor activity at doses of 5 mg/kg and 20 mg/kg. CONCLUSIONS: Our data suggest that mGluR5 receptors not only mediate spontaneous locomotor activity in DBA/2J mice but also the acute locomotor stimulant effects of cocaine, D-amphetamine and lower doses of GBR12909. However, the fact that MPEP did not attenuate the locomotor stimulant effects of the high (20 mg/kg) dose of GBR12909 suggests complex interactions between metabotropic glutamate receptors, dopamine transporters and possibly other monoamines in the regulation of psychostimulant-induced locomotor activity.
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