2 ' 3 ' cyclic nucleotide 3 ' phosphodiesterase immunohistochemistry showsan impairment on myelin compaction in hypothyroid rats

The effects of hypothyroidism on oligodendroglial differentiation and myeli nation are for the first time studied by immunohistochemical localization o f an early oligodendroglial marker, the 2'3'cyclic nucleotide 3'phosphodies terase (E.C. 3.1.4.37-CNPase), in developing rats. Two groups received meth imazol; one during gestation (H) and another postnatally (PN). One H sub-gr oup received thyroxine after birth (T). We observed a delay in CNPase expre ssion followed by a decrease in the number of CNPase immunoreactive fibers in both H and PN groups. The T sub-group was not different from controls. F urthermore, the immunoreactive fibers, in mature hypothyroid animals, showe d a continuous pattern, of staining in contrast with a discontinuous one in controls. Myelinogenesis is a highly regulated timed event. CNPase links myelin relat ed proteins to the cytoskeleton also interacting with membrane lipids durin g extension and wrapping of the oligodendroglial process around the axon (e nsheathment phase). In mature myelinated fiber the CNPase is absent from co mpact myelin sheath, being located only in the inner and outer loops and in paranodal loops. Thus, our data suggest a disorder in myelin compaction an d point once more to the post-natal period as critical for the mechanisms t hat are thyroid hormone regulated in myelinogenesis. (C) 2000 ISDN. Publish ed by Elsevier Science Ltd. All rights reserved.