Effects Of Advanced Maternal Age On Development And Ability Of Learning And Memory In Offspring Rats

With the development of social and economic pressures, people gradually change the attitude of marriage and childbearing, so that elderly fertility is increasingly. Especially in 2016 the implementation of the two-child policy, can be expected in the next few years will show a peak of elderly fertility. Currently, the exact impact on the elderly fertility of offspring growth and development is inconclusive. Some epidemiological evidence suggested the negative effect of advanced maternal age, which is associated with higher risk of offspring suffering from Down syndrome, mental disorders and other diseases. However, other epidemiological studies have also put forward different views. There is correlation between advanced maternal age and offspring’s neural development and int elligence. In order to explore the possible impact of advanced maternal age on development and the ability of learning and memory in offspring. We recorded the development indicators of offspring during development. We examined and compared memory and learning ability of offspring rats by Morris water maze. Using HE staining and Nissl staining, we also observed the morphological changes in the hippocampus.Objective1. To investigate the effect of advanced maternal age on reproductive outcome.2. To investigate the effect of advanced maternal age on birth weight and some development index of offspring.3. To explore the effect of advanced maternal age on the ability of learning and memory in offspring.4. To investigate the effect of advanced maternal age on the morphological change in hippocampal.Methods1. Experimental animals and group: Sprague–Dawley rats were bought from laboratory animal center of Zhengzhou University. Six 3-month-old and seven 12-month-old female Sprague–Dawley rats were individually housed with a randomly selected 3-month-old male SD rat. Take out the male rat from the cage when the female was pregnant. Then the female rats continue feed to the offspring born. Record pairing-to-birth days, litter size and sex of pups within the first 24 h after parturition. The offspring divided into two groups: control group, advanced age pregnancy group.2. Reproductive ability: Record and compare pairing-to-birth days, litter size and sex of pups.3. Development indicators: Measure and compare the weight(born after 1,3,7,14,21,28 day) and development indicators(ears opening, teething, eyes opening)of the two groups on different days.4. Morris water maze test: The two groups of offspring were feed to 2 months. Morris water maze were used for place navigation test and Spatial probe test in the two groups.5. Morphological observation of hippocampal tissue: The brain tissue of the two groups were removed when the Morris water maze finished. Then placed in 4% paraformaldehyde and paraffin embedded, continuous coronal sections, and HE staining and Nissl staining, observed the morphological characteristics of the hippocampal tissue.6. Statistical analysis: Using SPSS17.0 statistical software for data analysis. ANOVA for repeated measures design information were used for weight change, escape latency and swimming distance of the two groups. Difference in reproductive ability, development indicators, the target area residence time and the number of crossing the platform were tested using t test. The inspection level taking α=0.05.Results1. Reproductive ability : The pairing-to-birth days of 3-months-age rats were 23.17±0.82 d, the 12-month-age rats were 30.93±2.41 d, the pairing-to-birth days of the 12-month-age rats were significantly longer than the 3-months-age rats(P<0.01).The litter size of 3-months-age rats were 13.00±2.61, the 12-month-age rats were 4.86±1.35, The litter size at birth in the 12-month-age rats were significantly less than 3-months-age rats(P<0.01).No statistically significant different in percentage of male pups at birth between the control group and advanced age pregnancy group(P>0.05).2. Development indicators: Both of the two groups heavier than the day before. Compared with the control group, the advanced age pregnancy group have no statistically significant different in weight(P>0.05).Ear opening of the control group were 3.57±0.31 d, the advanced age pregnancy group were 3.66±0.29 d. Teething of the control group were 8.22±0.57 d, the advanced age pregnancy group were 8.43±0.59 d. Eyes opening of the control group were 15.90±0.97 d, the advanced age pregnancy group were 16.18±0.55 d.No statistically significant different in ear opening, teething, and eyes opening between the two groups.3. Morris water maze test: The day before Morris water maze, measuring the body weight of the two groups, and the results show that the two groups have no significantly different(P>0.05).Place navigation test: after 6 days of training, the escape latency and the path length of the two groups gradually shorten. But everyday’s escape latency of the advanced age pregnancy group was longer than the control group(P<0.01).The path length of the advanced age pregnancy group is significant longer than the control group at first three days(P<0.05). And have no statistically significant at the last three days(P>0.05).Spatial probe test: the target area residence time of the control group were 38.95±1.68%, the advanced age pregnancy group were 28.54±2.41%. The number of crossing the platform of the control group were 3.57±0.32, the advanced age pregnancy group were 1.74±0.27. The target area residence time and the number of crossing the platform of the advanced age pregnancy group were significant less than the control group(P<0.05).4. Morphological observation of hippocampal tissue: HE staining showed that hippocampal formation of the two groups are clear, the structures of granulose cells and pyramidal cell are intact. The cells are arranged densely and neatly., the outline is clearly visible. The nucleus are large and round and in the middle, the cell membrane is intact, intercellular tight around without edema. There are no significant difference between the two groups.The Nissl staining showed the pyramidal cells of hippocampal CA1, CA3 of the control groups are clear and arranged in neat rows close. The cells are cone-shaped and spherical. The nucleus are large and round. In cytoplasm can see the deep blue Nissl body. There are no significant difference between the two groups.Conclusion1. Advanced maternal age has a negative effect on reproductive performance.2. Advanced maternal age has no significant effect on birth weight, some physiologic index and the structure of the hippocampus in offspring.3. Advanced maternal age can cause decreased ability of learning and memory in offspring, the mechanism also needs to be further explored.