Activation of mesolimbic dopamine function by phencyclidine is enhanced by 5-HT2C/2B receptor antagonists:: neurochemical and behavioural studies

Administration of the non-competitive NMDA receptor antagonists phencyclidine (PCP) (0.6-5 mg/kg s.c.) and MK-801 (0.1-0.8 mg/kg s.c.) dose-dependently increased locomotor activity in the rat. Pre-treatment of rats with SE 221284 (0.1-1 mg/kg, i.p.) a 5-HT2C/2B receptor antagonist or SE 242084 (1 mg/kg, i.p.) a selective 5-HT2C receptor antagonist, doses shown to block mCPP induced hypolocomotion, significantly enhanced the hyperactivity induced by PCP or MK-801. Neither compound altered locomotor activity when administered alone. Furthermore, systemic administration of PCP (5 mg/kg s.c.) increased nucleus accumbens dopamine efflux in the rat to a maximum of approximately 220% of basal, 40-60 min after administration. pre-treatment with the 5-HT2C/2B receptor antagonist SE 221284 (1 mg/kg, i.p.) and the 5-HT2C receptor antagonist SE 242084 (1 mg/kg i.p.) failed to affect nucleus accumbens dopamine efflux per se but significantly enhanced the magnitude and duration of the increase induced by PCP. However, the time course of the neurochemical and behavioural effects were qualitatively and quantitatively different, suggesting the potential involvement of other neurotransmitter pathways. Nevertheless, the present results provide behavioural and neurochemical evidence which demonstrate that, in the absence of effects per se, blockade of 5-HT2C receptors enhanced the activation of mesolimbic dopamine neuronal function by the non-competitive NMDA receptor antagonists PCP and MK-801. (C) 2000 Elsevier Science Ltd. All rights reserved.