Effect Of Ketamine Administered Repeatedly On The Ability Of Learning And Memory As Well As Apoptotic Neurocytes In Hippocampus In Aged Mice

0bjective: To investigate effect of ketamine administered repeatedly on the ability of learning and memory as well as apoptotic neurocytes in hippocampus in aged mice.Method: Twenty-four 12-month-old mice were randomly divided into 3 groups(n=8,each):control group(A) which was administered normal saline 0.5ml ip,chloral hydrate group(B)which was given 10%chloral hydrate 300mg. kg^-1 ip and followed with 100 mg. kg^-1 when necessary, ketamine group(C) which was given 5% ketamine 100 mg. kg^-1 ip then followed with ketamine 100mg.kg^-1.h^-1 for 6 hours. Drugs mentioned above were injected one time a day for 7 days. Learning and memory ability of each mouse was detected with MORRIS water maze system after 7-day treatments. At the end of testing in the MORRIS water maze system, mice were killed and both sides of hippocampus were taken, the right side hippocampal tissues were prepared for detecting the ultramicrostructure changes and apoptotic neurocytes under transmission electron microscope, the left side hippocampal tissues were made into paraffin sections, then to locate the apoptotic cells using Tunel. SPSS 13.0 was applied to analyze the numbers of apoptotic nerve cells in hippocampus in each groups and the changes of the learning and memory in MORRIS water maze testing.Results: 1.Ethology detection:①mean escapelatency (MEL):During 4 days training, MEL values of mice in three groups decreased gradually, but the degree of alteration in three groups were not the same. In group C ,the value of MEL decreased from 54.83±7.35S to 47.50±6.76s, in group A from 56.99±5.42s to 29.44±4.95s and in group B from 53.48±6.88s to 28.21±8.78s.The differences of the MEL values among three groups were not significant in the first day and the second day (P>0.05), however, the differences became obvious in the third and fourth day (P<0.05). Compared with that in group A or group B, the MEL value in group C was significantly lower (P<0.05), but the difference was not significant between group A and group B(P>0.05).②Spatial probe test: The average times of passing the safe zone was 4.00±2.83 in group A,3.50±1.77 in group B and 1.13±1.13 in group C; The travelling distance in the third quadrant, where the safe platform located in originally, was 2752.30±794.41mm in group A ,2624.13±905.36mm in group B and 1479.58±747.47mm in group C; and the travelling time in the third quadrant was 21.23±7.72s in group A ,20.85±6.75s in group B and 10.86±5.01s in group C. Statistic analysis showed that there was obviously difference between group C and group A (P<0.05),or group C and group B(P<0.05).But no significant difference between group A and group B(P>0.05).2. TUNEL: The result of TUNEL showed that the numbers of apoptotic cells in hippocampus CA1 region were 5.84±3.45 in group A,7.19±4.02 in group B and 18.66±8.61 in group C under light microscope with 200 times amplification. ANOVA analysis showed the differences in apoptotic cells were significant among the three groups(P<0.05). By LSD analysis, the apoptotic cells in group C were obviously more than that in group A or group B(P<0.05),but no significant difference between group A and group B(p>0.05). 3.Transmission electron microscope detection: By transmission electron microscope, it could be found in group C that the volume of cells became diminutive, the nuclear membrane was unclear, the chromatin concentrated to conglobation, the chromatin gathered to the wall of the caryotheca and apoptotic body could be found clearly in the cellular nucleus, the cytoplasm became disintegration, the mitochondrion swelled and cavitated. While in group A and group B, the organelles of neurocytes in hippocampus were found clearly, such as apparato reticulares, rough endoplasmic reticulum, mitochondrion and so on, the cellular nucleus were big, the euchromatin and chromatospherite were clear.Conclusion: Without the influences of other factors, the administration of ketamine alone to the aged mice could induced neurons apoptosis in the hippocampus and damaged the ability of the learning and memory.