Effects of nicotine on spontaneous and amphetamine-induced motor behaviors: The differences between nicotine tolerant and nontolerant rats

This study was designed to investigate the effect of nicotine on spontaneous and amphetamine (AMP)-induced motor activity in rats with or without tolerance to nicotine. Tolerance were induced by treating the rats with nicotine (0.3 mg/kg, S.C.) 2hr before receiving challenge doses. Motor activity including locomotion and stereotypy was monitored automatically by videocamera every 15 min for 90 min. The results indicated that: (1) Nicotine increased spontaneous locomotion at 0.15 or 0.3 mg/kg (S.C.) in naive rats and at 0.6 mg/kg in tolerant rats. Nicotine also slightly affected AMP-induced locomotion at 0.15, 0.3 or 0.6 mg/kg in both naive and tolerant rats, and (2) Nicotine increased spontaneous stereotypy at 0.3 or 0.6 mg/kg in naive rats only and showed no effect on AMP-induced stereotypy in either naive or tolerant rats. Comparing the results of spontaneous motor activity between naive and tolerant rats, it revealed behavioral desensitization in locomotion at low doses (0.15 or 0.3 mg/kg) and hyperlocomotion at higher dose (0.6 mg/kg), and revealed desensitization in stereotypy at 0.3 or 0.6 mg/kg. Moreover, nicotine had temporary (at 0-15 min interval) attenuating effect on AMP-induced locomotion in naive rats but showed a potentiating effect on AMP-induced locomotion in tolerant rats. The present results indicated that acute tolerance modified the action of nicotine in both spontaneous and AMP-induced locomotion, while stereotypy was changed only in the spontaneous one but not in the AMP-induced one. In other words, acute tolerance modified the effect of nicotine on locomotion-related dopaminergic system, and it affected the stereotypy-related dopaminergic system only in the spontaneous one but not in the AMP-induced one.