Thyroid hormone receptors of developing chick brain are predominantly in the neurons

Abstract

The relative concentration of the triiodothyronine (T₃) receptors in the neuronal and glial nuclei of developing chick brain have been studied. Scatchard analysis indicate that the number of T₃ binding sites in the neuronal nuclei increases from 400 to 1600 sites/nucleus between 7-11 day of embryonic development without any concomitant change in the level of glial nuclear receptors (130-200 sites/nucleus). Both sites are of high affinity (K_a=1-3×10⁹ M⁻¹) at all ages examined. The abundance of the T₃-receptors in the neuronal nuclei and the close coincidence of the period of rise in the level of these receptors in these nuclei (7-11 day) with that of maximal neuronal growth and synaptogenesis (7-13 day) suggest that the neurons are the primary site of action of T₃ in the developing brain.