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TOLERANCE AND SENSITIZATION TO WEEKLY NICOTINE EXPOSURES ON THE MOTOR ACTIVITY OF RATS.
Citation:
MacPhail, R C., J D. Farmer, AND H A. Tilson. TOLERANCE AND SENSITIZATION TO WEEKLY NICOTINE EXPOSURES ON THE MOTOR ACTIVITY OF RATS. Presented at Society of Toxicology, Philadelphia, PA, March 19-23, 2000.
Description:
Motor activity was examined in adult female Long-Evans rats in a photocell device during daily (M-F) 30-min sessions. Following adaptation to the testing routine the rats were divided into six groups of eight that were designated to receive either nothing (non-injected control), saline vehicle, or 0.3, 0.6, 1.2 or 1.8 mg/kg nicotine, s.c. (in 1 ml/kg) five-min prior to a session. Nicotine (or vehicle) was administered at weekly intervals for four weeks. Initially, nicotine produced either no effect on horizontal activity or a decrease (30%) at the highest dose, but a substantial dose-related decrease in vertical activity. Weekly dosing produced tolerance to nicotine's effect on vertical activity, and increases (ca. 100%) in horizontal activity at all doses. Baseline activity levels determined throughout the period of weekly dosing did not differ between dose groups. Alterations in motor activity due to weekly nicotine were still obtained after three weeks without nicotine. Finally, when all rats received 0.3 mg/kg, prior controls (non-injected, vehicle-injected) displayed the same effect of nicotine obtained initially in the 0.3-mg/kg group, which differed from that obtained in all prior nicotine dose groups. Systematic changes in the behavioral effects of insecticidal nicotinic agonists may therefore occur with episodic (weekly) exposures.
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