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  • Title: Habituation to test procedure modulates the involvement of dopamine D2- but not D1-receptors in ethanol-induced locomotor stimulation in mice.
    Author: Pastor R, Miquel M, Aragon CM.
    Journal: Psychopharmacology (Berl); 2005 Nov; 182(3):436-46. PubMed ID: 16133139.
    Abstract:
    RATIONALE: Novelty associated with behavioral testing has been shown to enhance psychostimulant- and morphine-induced locomotor stimulation. Evidence has demonstrated that novelty increases dopamine (DA) activity, and habituation to a novel environment reduces such activation. However, it is not clear whether novelty modulates ethanol-induced behavioral stimulation and whether DA plays a role in this effect. OBJECTIVES: The present work sought to demonstrate a role of habituation to test procedure as a factor that could modulate the involvement of DA in ethanol-induced locomotor stimulation. METHODS: Non-habituated (NH) and habituated (H) Swiss mice pretreated with DA D1- (SCH23390; 0-0.045 mg/kg) or D2-receptor (sulpiride; 0-50 mg/kg) antagonists were tested for ethanol (0-2.5 g/kg)-induced locomotor stimulation. Experiments with amphetamine (0-4 mg/kg), morphine (0-5 mg/kg) and caffeine (0-15 mg/kg)were designed to compare their results to those obtained with ethanol. The effect of the non-selective opioid receptor antagonist naltrexone (0-1.5 mg/kg) was also tested on ethanol-induced locomotor stimulation. RESULTS: NH and H animals did not differ in their locomotor response to ethanol or caffeine; however, amphetamine- and morphine-induced stimulation was greater in NH than in H mice. SCH23390 only reduced ethanol-induced stimulation at doses that also reduced spontaneous activity in both NH and H mice. Sulpiride decreased ethanol-stimulated behavior only in the NH condition. Habituation did not modify the effect of sulpiride on amphetamine-, morphine- or caffeine-induced activation. Naltrexone (0-1.5 mg/kg) reduced ethanol-induced stimulation regardless of habituation. CONCLUSIONS: The present data suggest that the participation of DA D2-receptors in ethanol-induced behavioral stimulation requires the presence of novelty. Results also support the involvement of neurotransmitter systems other than DA (i.e., endogenous opioid system) as important substrates mediating ethanol-induced locomotor activation.
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