Effect of Thyroxine and Cortisol on Brain Catecholamines in Neonatal Rats

Abstract

There is strong evidence for an important role for both thyroxine and corticosterone as coordinators of maturational events. The role of thyroxine in the postnatal maturation of mammalian brain is well known (1). The influence of thyroid status or glucocorticoids on the maturation of the Autonomic Nervous System, particularly the Catecholamine System, has also been studied (2), and both thyroxine and glucocorticoids apparently accelerate the development of sympathetic neuronal interconnections in the short term. However, central biogenic amines are also regulated by steroids and thyroid hormones (3). Because adrenergic activity in the periphery is governed trans-synaptically by suprasegmental mechanisms in the central nervous system, it is important to determine the exact role of these monoamines in adrenomedullary maturation and the possible influence of hormonal status on these central mechanisms. The rat is the species of choice for these studies because innervation of the adrenal medulla develops after birth. Thus, the sympatho-adrenomedullary reflex evoked by insulin-induced hypoglycemia is absent in the neonate and must await the development of splanchnic innervation toward the end of first postnatal week (4). In young rats adrenal CA release has thus been used as a marker for the development of functional innervation.