Expression of adrenal steroid receptors by newly born cells and pyknotic cells in the dentate gyrus of the postnatal rat.

Neurogenesis and cell survival in the postnatal rat dentate gyrus are regulated by adrenal steroids. Increases in the circulating levels of glucocorticoids and mineralocorticoids result in decreased cell birth and increased cell survival in the dentate gyrus during the first postnatal week. It is presently unknown whether the effects of these hormones on cell birth and survival are direct or indirect. The expression of adrenal steroid receptors by dentate gyrus neuroblasts and pyknotic cells would support the contention that adrenal steroids directly affect neurogenesis and cell death. To determine whether or not this is the case, immunohistochemistry for the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR) was combined with short-survival [(3)H]thymidine autoradiography in rat pups during the first postnatal week. Light microscopic analysis revealed immunoreactivity for both GRs and MRs in the dentate gyrus. Approximately 50% of all pyknotic cells showed GR-like immunoreactivity, whereas no examples of MR-immunoreactive pyknotic cells were detected. In addition, some [(3)H]thymidine-labeled cells were immunoreactive for GRs (approximately 10%) but no [(3)H]thymidine-labeled MR-immunoreactive cells were observed. The relatively high percentage of pyknotic cells that were GR-immunoreactive suggests that adrenal steroids influence cell survival directly through GRs. In contrast, the relatively low percentage of [(3)H]thymidine-labeled cells expressing GRs indicates that adrenal steroids influence cell birth indirectly through an as yet unidentified mechanism.