5-HT6 receptor antagonism potentiates the behavioral and neurochemical effects of amphetamine but not cocaine

The localization of serotonin 5-HT6 receptors in limbic and motor brain regions, and the high affinity of these receptors for several antipsychotic agents, suggest that they may be involved in motor activity, reward-related behaviors, and psychotic disorders. The present study characterized the effects of a novel 5-HT6 receptor antagonist, SB 258510A, on psychostimulant-induced motor activity, self-administration, and increases in extracellular dopamine in the nucleus accumbens and frontal cortex of male Wistar rats. The locomotor-activating effects of amphetamine (1 mg/kg) were dose-dependently enhanced by pretreatment with SB 258510A (3, 10 mg/kg). Similarly, amphetamine self-administration was dose-dependently altered by SB 258510A in a manner indicative of enhanced reinforcing effects of amphetamine on both fixed and progressive ratio schedules or reinforcement. SB 258510A treatment had no effect on either cocaine-induced locomotor activity or cocaine self-administration. Dual-probe in vivo microdialysis revealed that pretreatment with 3 mg/kg SB 258510A potentiated an amphetamine-induced increase in extracellular dopamine more robustly in the frontal cortex than in the nucleus accumbens. These data indicate that activation of 5-HT6 receptors may regulate behaviors related to amphetamine but not cocaine, and point to the frontal cortex as a possible site of action for these effects. (C) 2002 Elsevier Science Ltd. All rights reserved.