NICOTINE-INDUCED SENSITIZATION TO AMBULATORY STIMULANT EFFECT PRODUCED BY DAILY ADMINISTRATION INTO THE VENTRAL TEGMENTAL AREA AND THE NUCLEUS-ACCUMBENS IN RATS

Bilateral injections of nicotine (30-mu-g/side) into the ventral tegmental area (VTA) and the nucleus accumbens (NACC) increased the ambulatory activity in rats. Moreover, daily injections of nicotine (10, 20 and 30-mu-g/side) into the VTA and the NACC for 6 successive days produced sensitization to the ambulatory stimulant effect of nicotine. Sensitization produced by daily injections of nicotine (20-mu-g/side) into both the sites was maintained for withdrawal periods of 10 days. Mecamylamine (2 mg/kg, i.p.), SCH23390 (0.05 mg/kg, i.p.) and spiperone (0.1 mg/kg, i.p.) antagonized nicotine-induced sensitization to the ambulatory stimulant effect produced by daily injections into the VTA. These results suggest that nicotine-induced sensitization to the ambulatory stimulant effect involves the stimulation of the mesolimbic dopaminergic pathway through the nicotinic acetylcholine receptor (nAChR) in the VTA and the NACC.