Examination of GABAergic and dopaminergic compounds in the acquisition of nicotine-conditioned hyperactivity in rats.

In rats, a distinct environment repeatedly paired with nicotine (0.421 mg/kg base, s.c.) comes to evoke an increase in activity in the absence of any drug. This hyperactivity indicates a Pavlovian-conditioned association between the environment and nicotine. We investigated whether a dopamine D(1) receptor antagonist (SCH-23390), a D(2)/D(3) antagonist (eticlopride) or a GABA(B) agonist (baclofen) would prevent the acquisition of nicotine-conditioned hyperactivity. In saline-pretreated rats, acute nicotine suppressed activity during the conditioning phase (i.e. environment-nicotine pairings); chronic nicotine stimulated activity. Pretreatment with SCH-23390 (0.01 mg/kg, i.p.) attenuated the activating effects of nicotine without affecting controls. Eticlopride (0.03-0.07 mg/kg, i.p.) and baclofen (0.625 and 1.25 mg/kg, i.p.) did not affect nicotine-induced activity in a selective manner. Regardless of the pretreatment drug, rats acquired the environment-nicotine association as indexed in a drug-free test. The inability of SCH-23390 to block the acquisition of nicotine-conditioned locomotor activity is notable because in past research SCH-23390 blocked expression of the learned association. Copyright 2002 S. Karger AG, Basel