OBJECTIVE: To evaluate the effect of chronic nicotine on contextual fear memory in rats. METHODS: Rats were subcutaneously injected saline or nicotine for 14 days continuously to induce nicotine dependence. Somatic signs of spontaneous nicotine withdrawal were assessed on day 1 and 14 after the last injection. Locomotor activity was tested 13 days after the last injection. Contextual fear conditioning task was run 14 days after the last injection, which included 3 phases: habituation, fear conditioning, and test. Percent freezing was used as an index for fear memory during the conditioning and test phases. Finally, footshock sensitivity test was conducted. RESULTS: Compared with the saline group, the global withdrawal scores significantly increased in the nicotine group when the somatic signs were assessed 1 day after the nicotine injection, while there was almost no difference in the 2 groups 14 days after the last injection. In the contextual task, the nicotine group showed a significant increase in the level of freezing response during the test phase but not in the conditioning phase. There was no significant difference in the locomotor activity and footshock sensitivity between the 2 groups. CONCLUSION Chronic nicotine enhances the contextual fear memory in rats. This effect is not attributed to the change of somatic signs, locomotor activity or footshock sensitivity.
Animals ; Brain ; drug effects ; Conditioning, Classical ; drug effects ; Electric Stimulation ; Fear ; drug effects ; Freezing Reaction, Cataleptic ; drug effects ; Learning ; drug effects ; Male ; Memory ; drug effects ; Nicotine ; pharmacology ; Nicotinic Agonists ; pharmacology ; Random Allocation ; Rats ; Rats, Sprague-Dawley