Postnatal development of 11β‐hydroxysteroid dehydrogenase type 1 in the rat hippocampus

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Abstract
Glucocorticoids (GCs) have important actions in the hippocampus of the brain, where their access to glucocorticoid receptor (GR) is increased by 11β‐hydroxysteroid dehydrogenase type 1 (11β‐HSD1). 11β‐HSD1 converts biologically inactive 11‐dehydrocorticosterone into active corticosterone. However, the postnatal development of 11β‐HSD1 in the hippocampus is not properly understood. In this study, the postnatal distribution and development of 11β‐HSD1 in the hippocampus of the rat brain was studied with immunohistochemistry and Western blot analysis. Results showed that abundant 11β‐HSD1 immunoreactive substance (ir‐11β‐HSD1) was present in the hippocampus. There were homogeneous distributions of 11β‐HSD1 in the hippocampal CA1, CA2, CA3, CA4 regions and the dentate gyrus at postnatal days 1, 3, and 7. Interestingly, the developmental distribution of GR in the hippocampus followed the same pattern as 11β‐HSD1. Western blot analysis demonstrated that a higher level of expression of 11β‐HSD1 in the hippocampus was found in the first 2 weeks of life. The expressions of 11β‐HSD1 started to drop to adult levels at about postnatal day 15 both in the hippocampus and in other brain areas. These results suggest that the higher expression of 11β‐HSD1 in the neonatal hippocampus may be important for the maturation of the central nervous system mediated by GCs through GR.