Regional patterns of brain growth during the first three weeks following early adrenalectomy

Day 11 adrenalectomized (ADX) and sham-operated control rats were compared with respect to overall and regional brain growth and DNA content at 1, 2, and 3 weeks postsurgery. Possible treatment effects on the rate of postnatal cell loss were also assessed by injecting the animals with ³H-thymidine on day 2 postnatal (9 days prior to surgery) and subsequently measuring the amount of radiolabelled DNA remaining in various brain regions at each time point. Adrenalectomy led to reliable increases in cerebral cortex and midbrain-diencephalon weights within 1 week postsurgery, whereas cerebellum, hippocampus, and overall brain weights were not significantly elevated until 1 or 2 weeks later. The effects of adrenalectomy on tissue DNA content were likewise regionally dependent. According to the ³H-thymidine results, there was no significant influence of adrenalectomy on the loss of previously labelled DNA. In conclusion, the timing of brain growth acceleration following adrenal removal is regionally specific, with the most rapid effects occurring in the cortex and midbrain-diencephalon. Furthermore, adrenalectomy-induced increases in brain cell number appear to depend primarily on increased cellular genesis (as previously demonstrated) rather than decreased cell death.