Developing Hypothalamus in Differentiation of Neurosecretory Neurons and in Establishment of Pathways for Neurohormone Transport

Abstract

Publisher Summary This chapter discusses the data obtained from the differentiation of neurosecretory (NS) neurons producing classic adenohypophysiotropic (AHT) neurohormones during ontogenesis. The chapter focuses on the differentiation of tanycytes and on the development of portal capillaries as they are responsible for the transfer of neurohormones from the hypothalamus to the hypophysial portal circulation and, finally, to the adenohypophysis. NS neurons produce not only classic peptide and monomine neurohormones but also substances identical to adenohypophysial and gut hormone immunological properties. Hypothalamic catecholamines, mainly dopamine, and to a lesser extent, noradrenaline have been widely implicated in the neuroendocrine regulation in adult mammals. Dopamine—either as a neurohormone or a neurotransmitter and neuromodulator—provides an inhibiting influence on the secretion of luteinizing hormone-releasing hormone (LHRH), somatostatin, thyrotropin-releasing hormone (TRH), prolactin, α-melanocyte-stimulating hormone, and β-endorphin. The sprouting of NS axons to the median eminence (ME) is one of the most important characteristics of the differentiation of NS neurons. NS axons—either abutting the primary portal plexus or penetrating to the third ventricle—provide pathways for neurohormone transfer to the hypophysial portal circulation and the CSF, respectively.