Adrenalectomy in the developing rat: does it cause reduced or increased brain myelination?

We have previously demonstrated increased myelination in adult rats that were adrenalectomized (ADX) neonatally. However, Preston and McMorris (1984) recently reported reduced myelination at Day 21 or 22 in day 14 ADX animals. The present experiment attempted to replicate Preston and McMorris' study to determine whether early adrenalectomy might be producing a transient hypomyelination prior to the hypermyelination observed at later time points. We were unable to duplicate the exact protocol of Preston and McMorris (which involved weaning at Day 18 with administration of saline and glucose drinking solutions) because of 100% mortality of our ADX rats by Day 20. However, using our standard mineralocorticoid replacement therapy which allowed the animals to remain with their mothers, all of the ADX rats survived, and we were able to assess myelination in these animals by means of standard biochemical methods. All measures showed absolutely no reduction in myelination in ADX rats compared with sham-operated controls. The discrepancy between the present results and those of Preston and McMorris are attributed, at least in part, to the early weaning procedure used by these investigators.