| There is a wealth of research on the effects of stress on learning and memory. The principle that has emerged is that the stress hormone, glucocorticosteroid (GS), damages the hippocampus and, consequently, disrupts forms of memory that rely heavily on normal hippocampal function. In particular, spatial memory seems most vulnerable, and non-spatial and emotional memories are less vulnerable to stress and GS. In contrast, the role of another steroid hormone, estrogen, in learning and memory is presumed to be facilitory. Estrogen (E2) administered to ovariectomized females is thought to improve both spatial and non-spatial memories.; This experiment examined the interaction of GS and E2 by comparing different types of memory during chronic administration of either or both steroid hormones. Forty adult female rats were ovariectomized and assigned to one of four treatment groups: vehicle, GS-only, E2-only or GS+E2. Three cognitive tasks, the spatial holeboard, object recognition, and social memory tasks, were used to assess different aspects of learning and memory. Animals were sacrificed at the end of behavioral testing for measurement of physiological markers of HPA activity including adrenal, pituitary and thymus weights. Plasma levels of GS and E2 were also measured.; On the spatial holeboard, the GS-only group performed worse than the other groups. Between and within group comparisons suggested that the GS-only group displayed learning impairments. E2-only and GS+E2 groups performed similarly to controls on the holeboard. Analyses of object recognition indicated that the two GS-treated groups performed worse than vehicle controls. E2-only animals performed similarly to vehicles on object recognition. No group differences were found on social memory, however, within groups comparisons demonstrated that both GS-treated groups experienced worse memory of a conspecific. Adrenal glands were heavier for both GS-treated groups, and pituitary weights were heavier for both E2-treated groups. Plasma levels of GS were highest in the GS-only group, and E2 levels were highest in the E2-treated groups.; The GS-treated groups showed impaired spatial and non-spatial memories that were attenuated by co-administration of E2. Implications are that chronic GS will lead to impaired memory and co-administered E2 performs a neuroprotective function against these eventual debilitations. |
