Nicotine Enhance Reconsolidation Of Object Recognition Memory In Rats

Objectives: The formation of Long-term memory involves acquisition, consolidation,reconsolidation, retrieve, and many other aspects. Studies have shown that nicotine canenhance acquisition and consolidation of object recognition memory and so on. however, itremains unclear whether nicotine have effect on reconsolidation process of object recognitionmemory. Our study is based on the novel object recognition task of rats, then tested the effectof nicotine on reconsolidation of object recognition memory.Methods: In experiment1we tested whether nicotine treatment have influence on thereconsolidation of object recognition memory in rats. The novel object recognition taskbehavioral procedure involved four sessions: habituation (the first day and the second day),the sample phase (the third day), then the reactivation phase (the fourth day) and the choicephase (the fifth day). After the reactivation, rats were treated with either nicotine (0.1,0.2or0.4mg/kg) or saline by intraperitoneal injection immediately. The exploration time of thesample phase and the reactivation phase were recorded and analyzed, the recognition indexof the choice phase need to be calculated and analyzed. In experiment2, we examinedwhether nicotine treatment six hours after reactivation affect the reconsolidation of objectrecognition memory in rats, to clarify whether there is a time window for the impact ofnicotine on reconsolidation of object recognition memory. The novel object recognition taskbehavioral procedure was the same as the experiment1, the difference is that the rats receivedan injection of either nicotine or saline by intraperitoneal injection6hours after reactivation.The exploration time of the each phase were recorded and analyzed, then Calculate thediscrimination index of the choice phase. In experiment3, we examined whether nicotinehave effect on the consolidation of object recognition memory in rats while there were noreactivation. The novel object recognition task behavioral procedure was similar to theexperiment1, the difference is that there were no the reactivation phase, it just injected eithernicotine or saline to rats by intraperitoneal injection at the corresponding time of reactivation.The exploration time of the sample phase were recorded and analyzed, then Calculate therecognition index of the choice phase. In experiment4,we studied effects of nicotine on the spontaneous activity and anxiety level after it was treated48hours in rats. The rats receivedan intraperitoneal injection of either nicotine (0.1mg/kg) or saline, then48hours later weconducted the open field test for5minutes. The total distance of rat and the ratio of time inthe central zone to time in the peripheral zone was recorded and analyzed in the open fieldtest.Results：1. Experiment I: In the sample phase and the reactivation phase, the totalexploration time of objects was not significantly different between the groups treated withnicotine by different dose and the saline group. In the choice phase, the recognition Index ofthe0.1mg/kg dose nicotine group was significantly higher than the saline group; while0.2mg/kg and0.4mg/kg group had no significant differences on the recognition Indexcompare with the saline group.2. Experiment II: the nicotine group and the saline group hadno significant differences on the total exploration time of objects in the sample phase,reactivation phase, in the choice phase, it also have no significant differences between thenicotine group and the saline group.3. Experiment III: the recognition index between thenicotine group and the saline group rats were not significantly different in the sample phase,while the result of the choice phase is also have no significant difference.4. Experiment IV:there were no significant differences between nicotine group and saline group on thelocomotor activity and anxiety level48hours after drug treatment.Conclusion: Nicotine enhance reconsolidation process of object recognition memoryin rats, and this kind of enhancement not only depend on the reactivation experience but alsodepend on the limited time window after reactivation.