碩士 / 臺灣大學 / 生理學研究所 / 98 / Early life experience appears to have long-lasting influences on an organism’s physiological functions and behavior. Neonatal maternal separation (MS) has been used to model long-term changes in neurochemical responses and behavior associated with exposure to early-life stress. Many studies have shown that neonatal MS changes the behavior and physiological responses to stress, and the spatial memory and learning ability in adulthood. The duration of MS is a critical factor of these effects. Although stress induces different physiological and behavioral responses between males and females, male rats were used as subjects in most of these studies. In addition, whether neonatal MS leads to sex differences in abovementioned behaviors remains unclear in post-weaning rats. In the present study, we used both male and female Long-Evans rats on postnatal 22-24 days which have been through different duration of MS to reveal the effects of MS on anxiety responses, spatial memory and learning and cell proliferation.
Neonatal pups were divided into three groups: control, MS 15 minutes (MS-15) and MS 180 minutes (MS-180). Infant rats were deprived of maternal contact between the 4th and the 21st postnatal days. Elevated plus maze was used to investigate the anxiety-like behavior on 22nd postnatal day. MS-15 female rats showed significantly lower anxiety-like behavior. We also collected the blood to measure the basal levels of coritocosterone and weighed the adrenal glands. Our results showed that MS-15 and MS-180 female rats reduced the basal levels of corticosterone and the percentage of adrenal gland/body weight. MS-15 male rats reduced the percentage of adrenal gland/body weight and both MS-15 and MS-180 male rats had lower basal level of corticosterone than control male rats. The duration on target quadrant of Morris water maze was used to investigate the spatial memory and learning ability. MS-180 female rats stay longer on the target quadrant than control and MS-15 female rats, while MS-15 male spend more time on the target quadrant than control and MS-180 male rats. To investigate the cell proliferation in granule cell layer (GCL), 5-bromo-2''-deoxyuridine (BrdU) was given at a dose of 100 mg/kg to rats by intraperitoneal injection and the animals were perfused two hours later. The immunohistochemistry of BrdU was conducted to examine cell proliferation in the hippocampus dentate gyrus. Our results showed that there is no significant difference in cell proliferation in GCL between all groups.
In summary, both MS-15 and MS-180 groups reduced the basal levels of corticosterone. In female rats, MS 15 minutes and MS 180 minutes reduced the percentage of adrenal weight/body weight. In male rats, only MS 15 minutes had the same effect. Moreover, MS 15 minutes reduced the anxiety-like behavior in female rats, and improved the spatial memory and learning ability in male rats. On the other hand, MS 180 minutes improved the spatial memory and learning ability in female rats. These results indicated that neonatal short-term and long-term MS induced different effects on post-weaning rats, and gender-difference may involve in the effects.
| Identifer | oai:union.ndltd.org:TW/098NTU05116001 |
| Date | January 2010 |
| Creators | Yi-Sian Wu, 吳以嫻 |
| Contributors | 蔡元奮 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 60 |
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