Radioimmunoassay of brain tissue and cell nuclear corticosterone

A combined cell fractionation-radioimmunoassay procedure is described to measure tissue and cell nuclear levels of corticosterone (CORT) in rat brain in intact animals in morning, afternoon, and following ether stress as well as in adrenalectomized animals with and without replacement therapy. Tissue and nuclear CORT are, as expected, higher in afternoon than in morning and still higher after stress. Replacement of CORT by a subcutaneous pellet and by single injection of 100 μg CORT give tissue and nuclear levels in the afternoon range. Measurement of cell nuclear CORT in brain regions reveals a pattern in intact rats very similar to that seen in ADX rats given CORT replacement, with highest CORT concentrations in hippocampus. In ADX rats comparison of cell nuclear CORT levels by radioimmunoassay with levels obtained by scintillation counting after [³H]-CORT gives further validation of the radioimmunoassay procedure.