Ontogeny of type I and type II corticosteroid receptors in the rat hippocampus

The ontogeny of the corticoid receptors in the rat hippocampus was examined by in vitro [3H]corticosterone (CORT) binding to soluble molecules in the cytosol, using the selective Type II glucocorticoid agonist, RU 28362, to discriminate between Type I and Type II receptor sites. Type I receptors were undetectable until 8 days after birth. From this age on, the receptor showed adult characteristics for both the binding capacity (Bmax) and affinity (Kd). The Type II receptor concentration increased gradually over the observed period; however, at 3 weeks of age concentrations were still only about 65% those found in adults. The binding affinity of Type II to CORT was high during the first week of life but decreased thereafter towards adult value. These data thus suggest clear distinctions in the developmental patterns of Type I and Type II receptors for corticosteroids in the rat.