Early adrenalectomy increases myelin content of the rat brain

Rats were adrenalectomized (ADX) or sham-operated (SHAM) on the 11th day of life and killed on days 35-36, 63, or 151-153 for the isolation of cerebral myelin from each animal. Despite having lower overall body weights, ADX rats had heavier cerebra than SHAM control rats at all ages. Mean cerebral weight increases were 10.0% at day 35-36, 15.3% at day 63, and 16.7% at day 151-153. Recovered myelin dry weights were even more elevated in the ADX rats, but only at day 63 (41.7% increase) and 151-153 (42.1% increase). At both of these ages, there was a clear linear relationship between cerebral wet weights and the amount of myelin recovered from the cerebra. Analysis of the day-63 myelin samples showed no group differences in total cholesterol or protein concentration or in the specific activity of the myelin marker enzyme 2':3'-cyclic-nucleotide 3'-phosphodiesterase (CNP). However, myelin isolated from the ADX rats appeared to be deficient in both galactolipid and phospholipid. Optic nerve myelination was assessed in all animals by measuring CNP activity in homogenates prepared from this tissue. No difference between ADX and SHAM rats was observed at any age. These results indicate that early adrenalectomy stimulates myelin deposition in the rat brain as part of a more general, long-lasting enhancement of brain growth. Myelin from the brains of ADX animals may be slightly abnormal in its lipid composition. Finally, the optic nerve data may mean that myelination is not affected equally in all areas of the CNS by the loss of adrenal glands.