Postnatal development of corticosteroid receptor immunoreactivity in the rat hippocampus

Postnatal changes in corticosteroid receptor immunoreactivity in the rat hippocampus were examined using an antiserum against a fusion protein containing an N-terminal peptide of the Type I receptor, and a monoclonal antibody against the rat liver Type II-receptor. Age-related regional differences were observed. In the pyramidal cell layer of Ammon's horn, and granule cell layer of the dentate gyrus (DG), the percentage of Type I receptor immunoreactive (Type I-ir) and Type II receptor immunoreactive (Type II-ir) cells was high perinatally, declined sharply by postnatal day 10 (P10), and showed a variable increase to adult levels subsequently. The pyramidal cells of CA1-CA2, subiculum and DG showed a selective increase in Type II-ir in late postnatal life into adulthood, while most other regions showed higher Type I-ir in both early and late postnatal life, suggesting different roles for these receptors during development. Type II-ir was predominantly nuclear in most neurons, except for a transient appearance of cytoplasmic Type II-ir in neurons of the stratum oriens and molecular layers of Ammon's horn and dentate gyrus of P20-P30. Type I-ir was diffusely nuclear and cytoplasmic at all developmental ages. This is suggestive of differential genomic and extragenomic roles for these receptors during postnatal development of the hippocampus.