Different expression of membrane-bound and cytosolic hippocampal steroid receptor complexes during spatial training in young male rats.

Brain steroid receptors are involved in mediating stress responses and cognitive processes throughfast non-genomic signaling of membrane-bound receptors or through the slower genomic actions of cytosolic receptors. Although the contribution of these different pathways in the formation and maintenance of memories has been widely discussed, little is known about the regulation of membrane versus cytosolic receptors during a learning task. Besides the relatively well studied corticosterone-binding glucocorticoid (GR) and mineralocorticoid (MR) receptors, sex steroid hormone receptors, such as the androgen and estrogen (ERα and ERβ) receptors, have also been shown to be involved in the regulation of stress and cognition. Moreover, the latter receptors are known to be functional in both sexes. Therefore, we studied the expression of hippocampal receptors in both cellular fractions during spatial learning in male rats. Membrane and cytosolic GR were shown to be downregulated after memory acquisition and unaffected after consolidation, whereas membrane MR was upregulated after both learning phases and unaffected in the cytosol. Cytosolic ERα was downregulated after both phases and unaffected in the membrane. The remaining receptors were not regulated. The data suggest a specific role of MR and ERα during training as fast and slow mediators, respectively.