Nicotine blocks quinpirole-induced behavior in rats: psychiatric implications

Abstract 

Rationale and objectives: Because of known and imputed roles of dopaminergic and nicotinic cholinergic systems in a variety of neurological and neuropsychiatric disorders, combined neurochemical and behavioral methods assessments were made to study the intermodulatory roles of these neurochemical systems. Methods: Rats were treated daily during postnatal ontogeny with the dopamine D₂/D₃ agonist, quinpirole (QNP) HCl (1.0 mg/kg/day), for the first 3 weeks from birth. This priming process replicated previous findings of behavioral sensitization, manifested as hyperlocomotion, increased paw treading with jumping, and increased yawning. Results: All effects were partially or totally blocked by acute treatment with nicotine (0.3 mg/kg, i.p.). The effects of nicotine, in turn, were partially or totally blocked by the nicotinic antagonist, mecamylamine (1.0 mg/kg, i.p.). In concert with these behavioral actions, QNP-primed rats displayed greater binding of [³H]cytisine in midbrain and cerebellum and greater [¹²⁵I]α-bungarotoxin binding in hippocampus and striatum. Conclusions: Accordingly, these selective ligands for α₄β₂ and α₇ nicotinic receptors, respectively, demonstrate that nicotinic receptors are altered by dopamine D₂/D₃ agonist treatment of rats with primed dopamine receptors. We propose that nicotinic agonists may have a therapeutic benefit in behavioral disorders brought about by central dopaminergic imbalance.