Nicotine-induced grooming: a possible dopaminergic and/or cholinergic mechanism

The ability of nicotine, to induce grooming in rats was studied, Grooming w as induced by i.p. injection of different doses (0.0675-0.5 mg/kg) of nicot ine to rats. The effect was dose-dependent. However, the response was decre ased with increasing doses of the drug from 0.25-0.5 mg/kg. Administration of the dopamine (DA) D-1/D-2 receptor agonist apomorphine (0.025-5 mg/kg, i .p.) also caused grooming in a dose-dependent manner. High doses of apomorp hine (0.1-0.5 mg/kg, i.p.) also induced a lower degree of response. Combina tion of a low dose of nicotine (0.0675 mg/kg) with different doses of apomo rphine did not show any interaction. However, there was an interaction betw een a high dose of nicotine and apomorphine. Thus, combination of a higher dose of nicotine (0.125 mg/kg) with apomorphine, reduced apomorphine-induce d grooming. The muscarinic receptor antagonist atropine (5 and 10 mg/kg), peripheral ni cotinic receptor antagonist hexamethonium (5 and 10 mg/kg), central nicotin ic receptor antagonist mecamylamine (I and 3 mg/kg) and D-1 DA receptor ant agonist SCH23390 (0.05 and 0.1 mg/kg) all decreased the response to nicotin e. Atropine, mecamylamine and SCH23390 by themselves reduced spontaneous gr ooming. It is concluded that nicotine elicits grooming indirectly through a possible D-1 dopaminergic mechanism. However, muscarinic and nicotinic cho linergic mechanism(s) may be involved.