Ontogeny of receptors for thyrotropin-releasing hormone in the rat brain.

Developmental changes in the thyrotropin-releasing hormone (TRH) receptor concentrations of hypothalamic and certain extrahypothalamic structures in the rat were evaluated from 2 days after birth until sexual maturity. The maturational pattern of TRH receptors in hypothalamus, striatum and amygdala follow that of the pituitary and all show the same kinetic properties. The developmental pattern also coincides with that of other components of the hypothalamic-pituitary-thyroid axis. In all tissues, the concentration of receptors increased in early life to reach a maximum between 10 and 30 days of age and then decreased gradually to adult values. Development of TRH receptors reflected changes in the number of receptor sites but not in binding affinity, which remained constant and suggests that the TRH receptor is identical in all 4 tissues studied. These results indicate the parallel development of pituitary and central nervous system TRH receptors.