Morphology of developing cerebral cortical synaptosomal fractions isolated from eu- and hypothyroid rats

Synaptosomal fractions isolated from the cerebrum of eu- and of hypothyroid rats during the neonatal period were analyzed by electron microscopy. This analysis revealed 3 main components: presynaptic endings, growth cones and unidentifiable structures that may be dendritic in origin. Since the size and the percentage of presynaptic endings were not altered by hypothyroidism but the size of the fraction in comparison to cerebrum weight was altered on postnatal day 14, it could be concluded that hypothyroidism results in a transient reduced synaptic density.