Inhibition of Cerebellar Dendrite Development in Neonatal Thyroid Deficiency

Inhibition of cerebellar dendrite development in neonatal thyroid deficiency Thyroid hormone deficiency was induced in neonatal rats by propylthiouracil. Serum thyroxine levels were assayed and thyroid tissue was examined to assess the clinical condition. At 8, 14, 20, 30 and 42 days after birth, age‐matched controls and hypothyroid animals were killed by perfusion. Nissl stains, Golgi preparations, and electron microscopy were done on the cortex of Lobules IX and X of the developing cerebellum. Measurements of the molecular layer revealed that at 8 days, controls are slightly but significantly wider, but at 20 days the difference is much greater and remains so even at 42 days. Golgi studies show deceleration and distortion of development of the Purkinje cell dendritic tree in the abnormal rats. Spine counts of the spiny branchlets on these dendrites show the same incidence per linear micrometer as the age‐matched controls, but linear measurements of the branchlets show that the deficient animals have shorter branchlets and regions where spines are absent. Electron microscopy shows that if a spine does develop, it appears similar in control and hypothyroid animals at comparable ages. The effect of the abnormal Purkinje cell dendritic arborization on synaptogenesis in the molecular layer is discussed.