Etude ultrastructurale quantitative du pericaryon de la cellule de Purkinje et de son environnement chez le rat normal et hypothyro�dien ag�s de 21 jours

Abstract

The effects of neonatal hypothyroidism on synaptic organization, glial surrounding and cytoplasmic structures of the Purkinje cell perikaryon of the 21 days old rat were studied by electron microscopy. Hypothyroidism decreases the size of the perikaryon but does not change the nucleo-cytoplasmic ratio of the cell. At 21 days the axonal endings that make synapse on the Purkinje cell perikaryon, already show the adult morphological features and hypothyroidism does not change these. The general synaptic density on the Purkinje perikaryon is not significantly altered, but the cells of hypothyroid animals still recieve 1/3 of their axo-somatic synapses on somatic spines, whereas euthyroid animals have practically no synapses on somatic spines. Hypothyroidism leads the disappearance of the synchronism which normally exists between the translocation or resorption of the Purkinje cell somatic spines and the establishment of the basket cell synapses. The basket cell axons of the normal animals form synapses only on the smooth surfaces of the Purkinje cell perikaryon while they also establish it on the somatic spines of the hypothyroid animals. The density of the axon terminals of basket cells is decreased, while that of the endings of Purkinje cell axon collaterals and of climbing fibers are increased. Hypothyroidism produces an increase in the size of the glial sheath around the Purkinje perikaryon. It does not alter the proportion of the cytoplasmic area occupied by mitochondria, but in thyroid deficiency there is an increase in the numbers of mitochondria which are reduced in average size. The Golgi apparatus is only slightly affected. Thyroid defiency does not alter the density of the cytoplasmic agreggates of free ribosomes but there is a decrease in density of the ergastoplasm and a disorganization of the Nissl bodies.

Age-dependent changes in the specificity of tRNA methyltransferases in the cerebellum of the icteric and nonicteric Gunn rat

“…The sudden drop in cerebellar weight was not attributed to the higher than normal cerebellar bilirubin levels, but instead appeared to correlate with the decrease in cerebellar thymidine kinase activity (14,27) which occurs as early as 6 days postnatally. It is noteworthy that Dainat and Rebi6re (28) found precursor incorporation into RNA and DNA of the cerebellum of the Wistar rat to be maximal at 6 and close to minimal at 21 days, a time when cerebellar development also nears completion (13,29) and when homologous cerebellar tRNA methylation (examined in the Sprague-Dawley rat) is significantly different from its 6 day levels (8,9).…”

Membrane Enzyme Development in Nerve Ending Mitochondria during Neonatal Hypothyroidism

“…Although early studies suggested that pro pylthiouracil may have a neurotoxic effect in adult brain [56], recent examination of pro pylthiouracil-induced neonatal hypothyroi dism has shown that most effects are reversed by concurrent thyroid hormone treatment [8,29,39],…”

Correction of the biochemical effects of neonatal hypothyroidism by daily low doses of thyroxine. Comparative effects of hyperthyroidism and these corrections

“…In hypothyroid young rats, administration of 0.5 or 1.0 pg/day of thyroxine for a week, before the 28th postnatal day, partially adjusted the abnormalities in synaptogenesis of the molecular layer (Rebikre & Dainat 1976a). On the other hand, administration of 2 or 4 ,&day of thyroxine for a week before the 14th postnatal day, restored Purkinje cells development and the rate of disappearance of the cerebellar granular layer (Legrand 1967b).…”