Pituitary peptide actions on early neuroendocrine organization

Ilya Glezer, Max Hamburgh, Gerard Louls-Jacques,Shari Barter and L. A. Mendoza, School of Biomedical Education & Dept. of Biology, City College of N. Y. and Hosp. Vargas Hypothyroidism was induced by feeding propylthiouracil to pregnant rats starting during the 2nd week of gestation and continued until weaning. Two main features of ultrastructural abnormalities were noted. I) Starting at birth till about 5 days of postnatal age the maturation of the rough endoplasmlc retlculum and of mitochondria was retarded, but by day i0 this difference had disappeared, and most neurons of experimental animals seemed to have caught up with the controls. 2) Starting on day I0 many developing neurons showed vacuolazation of cytoplasm accompanied by large osmophillc lysosomes filled with electron dense bodies presumably remnants of cell organelles. In addition many of the presynaptic endings were characterized by a rather dramatic paucity of synaptie vesicles. It is concluded that lack of thyroid hormone during neurogenesis seems to induce initially only transitory changes in the neuroblasts of the frontal cortex. These seem to be followedby more permanent cellular pathology which may reduce the population of the finally emerging neurons. The latter changes are more likely to be causally related to the mental retardation, a p e r m a n e n t feature of cretinism.