| Abstract No.: | B-E2161 |
| Country: | Canada |
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| Title: | DECREASED HIPPOCAMPAL NEUROGENESIS AND INCREASED SPATIAL LOCATION MEMORY AFTER ADOLESCENT SOCIAL STRESS IN FEMALES. |
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| Authors/Affiliations: | 1 Catherine Thomas; 1 Bobbi Jo Loewi; 1 Iva Z Mathews; 1 Cheryl M McCormick*;
1 Brock University, St. Catharines, ON, Canada
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| Content: | OBJECTIVES: Prolonged exposure to stressors is known to alter hippocampal structure and physiology and have sex-specific effects on spatial memory. Chronic stress is associated with decreased proliferation and/or survival of new neurons in the dentate gyrus. However, the effect of stress in adolescence, a time of higher rates of neurogenesis than in adulthood, is unknown. We have shown previously that social instability stress in adolescent females (SS: daily 1 h isolation followed by change of cage partner for 16 days from day 45 – 16 of age) alters hypothalamic-pituitary function, increases the locomotor-activating effects of amphetamine, and increases depressive behaviour. Many of the effects of SS persist into adulthood.
MATERIALS AND METHODS: Females underwent the SS procedure or were not stressed (CTL) on days 30-45 of age (n = 20 / group). Half of each group received 5 injections of bromodeoxyuridine (BrdU) spread across days 43-45 of age. All underwent object recognition (OR) and spatial location (SL) memory testing on days 46-48 of age. Both tests involved a 3 min exposure to two objects placed in different corners in a test arena. After a 4 h interval, either a new object replaced one of the previously seen objects (OR), or one of the two original objects was moved to a different corner of the area (SL) test. Difference in time spent investigating the novel versus the familiar was used as the index of memory. Rats were perfused on day 49 of age, and after 34 h in 30% sucrose and 4% paraformaldehyde, coronal sections throughout the hippocampus were processed for immunohistochemical labeling of cells containing BrdU. RESULTS: SS and CTL females did not differ in amount of time spent investigating objects during the pretest for either the OR or SL tasks. For OR after 4 h, groups differed on the basis of injection (p = 0.03), such that only those that had not been injected with BrdU spent more time investigating the novel object than the familiar, but SS and CTL did not differ. For SL after 4 h, SS spent more time investigating the object in the new location than in the familiar (p = 0.03), and CTL spent the same time with both. CTL had more BrdU-labeled cells than SS in the dentate gyrus (p = 0.007). CONCLUSION: As for chronic stress in adult females, social stress in adolescence improved performance on the SL test, for which there is a stronger link to the integrity of the hippocampus than there is for the OR test. The results also indicate a strong effect of social stress on neurogenesis in adolescence. However, whether the decrease reflects a reduction in proliferation during the social stress period or a reduction in survival over the days and testing that followed remains to be determined, as does the extent to which there is any relationship between the effect of social stress in adolescence on hippocampal neurogenesis and its effect on spatial location memory. |
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