Morphology of Vasopressin and Oxytocin Neurones and Their Central and Vascular Projections

Vasopressin and oxytocin projections may be involved in the regulation of autonomic activity, and the paraventricular nuclei (PVN) sends vasopressin and oxytocin projections to various autonomic centers in the brainstem and spinal cord. This chapter discusses the immunohistochemical studies on the distribution, morphology, and projections of neurons producing classical neurohypophysial peptides and presents evidence that neurons in this system may produce additional peptides. Vasopressin and oxytocin are associated with a family of low molecular weight proteins, the neurophysins, also present in the extracts of the neurohypophysis. Vasopressin and oxytocin are present in fibres throughout the mammalian central nervous system. In target areas, fibres surround and contact neurons and in some cases these contacts have been identified as synaptic. In a number of these areas, vasopressin and oxytocin have been shown to alter the electrical or biochemical activity of neurons, and may be involved in various centrally regulated functions. There is evidence that both vasopressin and oxytocin can alter the electrical activity of neurons in various parts of the central nervous system, where fibres containing these peptides are present. Thus these peptides, which were originally characterized as the circulating hormones released from the neurohypophysis, may have an additional important role in influencing the activity of central neurons through direct projections to these neurons.