Source Paper
SR Bodnoff, AG Humphreys, JC Lehman, DM Diamond, GM Rose et al.
Journal of Neuroscience • 1995
Prolonged treatment with stress levels of corticosterone has been reported to produce changes in the hippocampus. In the experiments reported here, we examined for functional and morphological consequences of this treatment. First, young adult or mid-aged male Long-Evans rats were treated for either 1 or 3 months with corticosterone, at a dose sufficient to mimic the elevated hormone levels observed following exposure to mild stress. Two weeks following the termination of treatment, the animals were tested in the Morris water maze to assess spatial learning. No behavioral deficits were observed after 1 month of treatment. A 3 month treatment period also had no effect in young rats, but produced a learning impairment in the mid-aged rats. We then examined whether the effect of elevated corticosterone in mid-aged animals could be produced by a physiological stressor. Mid-aged rats were maintained for 6 months under conditions of low or high social stress. Six months of exposure to high social stress produced significant spatial learning impairments in the Morris water maze. These effects were absent in high social stress animals that had been previously adrenalectomized (with low-level corticosterone replacement), suggesting that elevated glucocorticoid levels mediate the effects of stress on spatial memory in older animals. In a final experiment, mid-aged rats were treated with corticosterone at levels that mimicked those naturally occurring at the diurnal peak (medium-B: 12–17 micrograms/dl) or in response to stress (high-B: 25–32 micrograms/dl). Only rats exposed to high levels of corticosterone demonstrated impaired performance in the Morris water maze.(ABSTRACT TRUNCATED AT 250 WORDS)
Objective: Assess spatial learning and memory in rats following corticosterone treatment or social stress exposure using the Morris water maze
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Young adult or mid-aged male Long-Evans rats treated with corticosterone for 1 month at a dose sufficient to mimic elevated hormone levels observed following mild stress
Note: No behavioral deficits were observed after this treatment period
“young adult or mid-aged male Long-Evans rats were treated for either 1 or 3 months with corticosterone, at a dose sufficient to mimic the elevated hormone levels”
Young adult or mid-aged male Long-Evans rats treated with corticosterone for 3 months at a dose sufficient to mimic elevated hormone levels observed following mild stress
Note: Had no effect in young rats but produced learning impairment in mid-aged rats
“A 3 month treatment period also had no effect in young rats, but produced a learning impairment in the mid-aged rats”
Two weeks following the termination of corticosterone treatment before behavioral testing
Note: Allows for washout period before Morris water maze testing
“Two weeks following the termination of treatment, the animals were tested in the Morris water maze”
Animals tested in the Morris water maze to assess spatial learning following corticosterone treatment
Note: Testing occurred 2 weeks after treatment termination
“Two weeks following the termination of treatment, the animals were tested in the Morris water maze to assess spatial learning”
Mid-aged rats maintained under conditions of low or high social stress to examine whether effects of elevated corticosterone could be produced by physiological stressor
Note: High social stress produced significant spatial learning impairments
“Mid-aged rats were maintained for 6 months under conditions of low or high social stress. Six months of exposure to high social stress produced significant spatial learning impairments”
High social stress animals tested in Morris water maze to assess spatial learning
Note: Testing performed after 6 months of social stress exposure
“Six months of exposure to high social stress produced significant spatial learning impairments in the Morris water maze”
High social stress animals previously adrenalectomized with low-level corticosterone replacement to test whether elevated glucocorticoid levels mediate stress effects
Note: Effects of high social stress were absent in adrenalectomized animals with low-level corticosterone replacement
“high social stress animals that had been previously adrenalectomized (with low-level corticosterone replacement), suggesting that elevated glucocorticoid levels mediate the effects of stress”
Mid-aged rats treated with corticosterone at medium-B levels (12-17 micrograms/dl) mimicking naturally occurring diurnal peak
Note: No impaired performance in Morris water maze at medium-B levels
“mid-aged rats were treated with corticosterone at levels that mimicked those naturally occurring at the diurnal peak (medium-B: 12–17 micrograms/dl)”
Mid-aged rats treated with corticosterone at high-B levels (25-32 micrograms/dl) mimicking stress-induced hormone levels
Note: Only rats exposed to high levels of corticosterone demonstrated impaired performance
“or in response to stress (high-B: 25–32 micrograms/dl). Only rats exposed to high levels of corticosterone demonstrated impaired performance in the Morris water maze”
Animals tested in Morris water maze following treatment with different corticosterone dose levels
Note: Performance impairment only observed at high-B corticosterone levels
“Only rats exposed to high levels of corticosterone demonstrated impaired performance in the Morris water maze”
Some animals were adrenalectomized with low-level corticosterone replacement in social stress experiments
Evidence-Based
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