Prevention of adrenalectomy-induced brain growth stimulation by corticosterone treatment.

Previous research in our laboratory has shown that adrenalectomizing rats on day 11 postnatal leads to subsequent increases in brain weight, cellularity (measured in terms of DNA content), and myelination. The present study was designed to determine whether these effects are due to removal of circulating glucocorticoids. Male and female albino rats were adrenalectomized (ADX) on day 11 and then injected daily with either 7.0 mg/kg corticosterone in a steroid suspension vehicle or vehicle alone. A third group of animals was sham-operated (SHAM) and given daily vehicle injections. Subjects were sacrificed at 60 days of age for measurement of brain and body weights, cerebral DNA content, and the activity of 2',3'-cyclic nucleotide phosphodiesterase (CNP), a myelin marker enzyme. As expected from our earlier findings, brain weights and DNA and CNP levels were all significantly elevated in ADX-untreated rats compared to SHAMs. More importantly, all of these changes were completely prevented by chronic corticosterone administration. These results are consistent with previous reports that corticosterone treatment blocks increased brain growth in ADX weanling rats and support our hypothesis that the brain growth stimulating effects of day-11 adrenalectomy are likewise mediated by the removal of glucocorticoids. It appears that glucocorticoid hormones exert a tonic inhibition of at least some growth related processes in the brains of intact developing organisms.