Research on the change of cyclin-dependent kinase 5 in hippocampus CA1 after conditioned fear extinction

Abstract

Objective To investigate the change of cyclin-dependent kinase 5(CDK5)during 1 week after conditioned fear extinction.Methods Forty-two male adult SD rats were randomly divided into native group,extinction control group and 24h extinction group.Extinction retention test and immunohistochemistry of CDK5 of hippocampus were done at 1st,3rd,7th day after fear extinction.The numbers of CDK5 positive cell in hippocam-pus CAI was measured by computer analytic system.Results (1)Extinction retention scores were increasedgradually in extinction group compared with native group(75.60±2.51)%,the scores of extinction control group was decreased at 1st day(15.62±10.28)% and 3th day(20.58±7.79)% after extinction(P＜0.01);24h extinction group(71.04±11.65)% were better than extinction control group(35.48±12.37)at 7th day after extinction(P＜0.01).(2)The number of CDK5 positive cell was increased significantly in 24h extinction group (24.94±5.20;32.25±6.14;33.28±6.56)compared with native group(75.60±2.51;P＜0.01).In 24h extinction group the number was increased significantly at 3rd day(P＜0.01)and 7th day(P＜0.05)compared with extinction control group(25.09±4.83;26.70±4.57),and decreased at 1st day compared to 3rd day(P＜0.05)and 7th day(P＜0.01).Conclusion From 1st to 7th day after extinction,CDK5 may contribute to the retention of fear extinction in hippocampal CA1. Key words: Fear extinction; Hippocampus; Cyclin-dependent kinase 5(CDK5)