Glucocorticoid modulation of specific protein metabolism in hippocampal slices maintained in vitro

Transverse slices of hippocampus, the primary neural target of the glucocorticoids, were prepared from adult male Sprague-Dawley rats and maintained in vitro at 32–34 °C in a balanced salt medium. The incorporation of [3H]leucine into TCA-precipitable proteins during a 1 h incubation in the presence or absence of 10−9 M corticosterone was determined. In addition, the incorporation of labeled amino acid into specific proteins was evaluated by fractioning proteins from nuclear, microsomal, and cytosol subcellular fractions on SDS-polyacrylamide gels. In further experiments, slices of neocortex, a brain region which shows considerably less hormone binding, were co-incubated with hippocampal slices and subjected to identical treatments and analyses. Hormone treatment neither increased nor decreased the incorporation of [3H]leucine into acid-precipitable proteins in either hippocampal or cortical slices. However, analysis of SDS-polyacrylamide gels revealed that incubation of hippocampal slices in 10−9 M corticosterone for 1 h consistently (18/20 experiments) and significantly (t = 4.21; df = 19; P < 0.001) increased amino acid incorporation into at least one soluble cytoplasmic protein by an average of 12% over controls. The affected protein(s) has an apparent molecular weight of approximately 54,000 daltons. Glucocorticoid treatment did not detectably alter the metabolism of any cortical proteins. These results provide the first evidence that steroid hormones may regulate the synthesis or degradation of specific proteins in their central as well as their peripheral target organs.