慢性尼古丁处理增强大鼠场景性恐惧记忆的研究

目的：检测慢性尼古丁处理对大鼠场景性恐惧记忆的影响。方法：以递增剂量法连续皮下注射尼古丁14 d建立尼古丁依赖模型，并随机将大鼠分为尼古丁组和生理盐水对照组。在戒断后第1天和第14 天进行戒断症状评估；在第13天行自发活动检测；第14天进行场景性恐惧条件化训练，训练分为习惯化、条件化与检测三阶段，以大鼠僵直时间作为评价恐惧记忆指标。检测完成后，进行足底电击敏感性测试。结果：在戒断后第1天，尼古丁组大鼠戒断症状明显强于生理盐水组，而在第14天2组之间无明显差异。在场景性恐惧条件化任务中，2组大鼠在条件化阶段其僵直时间百分比无明显差异；在检测阶段，尼古丁组大鼠僵直时间百分比明显高于生理盐水组。此外，2组大鼠自发活动与足底电击敏感性无明显组间差异。结论：慢性尼古丁处理增强大鼠场景性恐惧记忆，该效应并非由戒断症状、自发活动或足底电击敏感性改变所引起。

Chronic nicotine enhances contextual fear memory in rats

ObjectiveTo evaluate the effect of chronic nicotine on contextual fear memory in rats. MethodsRats 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. ResultsCompared 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. ConclusionChronic nicotine enhances the contextual fear memory in rats. This effect is not attributed to the change of somatic signs, locomotor activity or footshock sensitivity.