The relationship between adrenal steroids and enrichment-induced brain growth.

The question of whether brain growth brought about by environmental enrichment is mediated by the adrenal cortex has not been answered. Accordingly, young male rats were either adrenalectomized (ADX) and infused with a constant maintenance dose of corticosterone (2 mg.kg-1.day-1) or sham-operated and implanted with a blank infusion device. Half of each surgical group was maintained in either impoverished (IC) or enriched conditions (EC). After 30 days, changes in forebrain growth and thickness of various cortical and subcortical regions were determined for each group. Enrichment and ADX independently increased forebrain weight and thickened cortical tissue at about the same anatomical sites. However, combined treatments were additive, not interactive. EC-induced brain growth is mimicked but not mediated by adrenalectomy.