[Quantitative ultrastructural study of the perikaryon of the Purkinje cell and of the adjacent area in normal and hypothyroid rats aged 21 days].

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.