Chapter 8 Glial cells in the hypothalamo-neurohypophysial system: key elements of the regulation of neuronal electrical and secretory activity

Abstract

This chapter discusses the present knowledge of the role of glial cells in the regulation of neuronal activity in the Hypothalamo-Neurohypophysial System (HNS) and the general organization of the system, as the specific anatomical relationships between glia and neurons are directly correlated to the functional properties of the system. The HNS consists of two neuronal populations that synthesize the neurohormones vasopressin (VP) or oxytocin (OT). The cell bodies of these magnocellular neurons are mainly localized in the hypothalamic supraoptic (SON) and paraventrieular nuclei (PVN), although many of them can also be found as accessory groups of neurons scattered between the two nuclei. Three main pieces of evidence provide the basis of the present understanding of the physiological implication of glial cells in the control of neuroendocrine function in the HNS. The HNS is well known for the activity dependent plasticity of the morphological relationships between neurons and glial cells. This mainly results in long-term changes in the functional properties of the neuronal network, by modifying the well-established functions of glial cells, such as regulation of ionic composition or uptake of neurotransmitters, and by regulating other less classical neuron–glia interactions just as those involving release of neuroactive substances by glial cells.