年龄增长对大鼠操作行为的影响

Age dependent operant behavior changes in wistar rats

目的研究年龄增长对大鼠操作行为学习和记忆的影响。方法用电脑控制的测定箱对１０只雄性近交系Ｗｉｓｔａｒ大鼠于其月龄为４、１０、１９个月时分别进行了操作行为测定。测定其活动期和非活动期高频度差别强化率（ＤＲＨ）和低频度差别强化率（ＤＲＬ），最后进行了６天获得性学习曲线测定。结果在３次实验中，大鼠的学习成绩在第２次实验（１０月龄成年鼠）的所有程序中都比其在第１次实验时（４月龄青年鼠）提高（Ｐ＜０．０５）；在第３次实验（１９月龄老年鼠）时却表现了不同的结果：ＤＲＨ程序的成绩比前２次测定都提高，而ＤＲＬ程序则比第２次降低（Ｐ＜０．０５）。其活动期和非活动期分辨学习的成绩及获得性学习曲线亦呈现相同趋势。结论大鼠的长时记忆随年龄增长有不同的变化，１０月龄鼠能很快回忆起先前学习过的所有操作行为程序，而１９月龄老年鼠只能回忆起相对简单的操作行为程序，对较为复杂的ＤＲＬ程序则容易遗忘。

Objective To study the effects of aging on operant learning and retention in rats. Methods Ten male inbred Wistar rats were studied at three age points (4,10,and 19 months old). Operant test performance was tested in simultaneously operated computer controlled lever boxes. The automated, nocturnal (16∶00 07∶00) test sessions lasted 15 hours with alternation ON (30 min) and OFF (60 min) periods. Food reward was available only during the ON periods and made contingent to the requirements of two different schedules of positive reinforcement: differential reinforcement of high rate (DRH) and differential reinforcement of low rate (DRL). Each test was presented in 3 consecutive steps with incrementally increased learning demand: DRH 2/1, DRH 4/2,DRH 8/4 respectively. DRL 1/8,DRL 1/16,DRL 1/32. In addtion, the DRH 8/4 and the DRL 1/32 was repeated 6 times to obtain the acquisition performance. Replicates of this test sequence were run in the same subjects (ss) after an interval of 6 and again of 9 months. Results It showed that the performance of all ss had improved in the second test run, when the rats were 10 months old ( P <0 05). However, the third test run in the 19 months old rats revealed a difference due to the test procedure: again, performance in the DRH tests was even better than that obtained in the first and second test runs. However the results of the third DRL tests were significantly worse than in previous run. Also, the analysis of ON OFF discrimination ability and of the acquisition performance in both test sets, DRH and DRL, showed a similar trend. Conclusions Apparently,10 months old rats could easily retrieve all previously trained conditioned performances. To the contrary, 19 months old ss were found to be able to retrieve only rather simple conditioning patterns and demonstrated deficits for the more complex requitrments of the DRL procedure.