Transient early postnatal corticosterone treatment of rats leads to accelerated aquisition of a spatial radial maze task and morphological changes in the septohippocampal region

In the present study new-born rats were treated with corticosterone (CORT) between postnatal days 1 and 12. At the age of 16-20 weeks, these animals were tested for spatial learning capacity using an eight-arm radial maze. After behavioral testing, density of cholinergic fibers and sizes of the mossy fiber terminal fields in the hippocampus and number of cholinergic and GABAergic neurons in the septal area were quantified. In the radial arm maze CORT-treated animals initially showed better working memory performance than controls. However, control animals showed a significant improvement of spatial working memory in the last trials and reached similar working memory scores as compared to treated animals. At neither day of training differences in reference memory errors were found between groups. In the diagonal band of Broca, both numbers of cholinergic and GABAergic neurons were increased after corticosterone treatment. The fiber systems in hippocampus showed no significant differences between groups. In conclusion, early postnatal stress induced by CORT administration in neonatal rats results in mild, yet significant morphological and behavioral changes in later life.