Intracerebral Release of Vasopressin and Oxytocin: New Aspects of the Old Concept of Neurosecretion

Abstract

The hypothalamic-neurohypophysial system belongs to the best investigated neurosecretory systems in the mammalian brain. The nonapeptides vasopressin and oxytocin are synthesized in the neurons of this system and are secreted either as hormones into the systemic circulation or as neuromodulators/neurotransmitters into the extracellular fluid of distinct brain areas. Recent findings of different lines of investigation provided new aspects in terms of stimuli, dynamics, mechanisms and consequences of the activation of the hypothalamic-neurohypophysial system and, consequently, the release of vasopressin and oxytocin into the different compartments. For instance, it is now evident that both nonapeptides are released not only from axon terminals but from virtually every part of the neuron’s surface. Depending upon the quality and intensity of a given stimulus, the release patterns from dendrites, perikarya, axons en passant, and axon terminals can be dissociated from each other and, thus, seem to be differentially controlled. These regulatory patterns of the hypothalamic-neurohypophysial system are likely to coordinate appropriate endocrine and behavioral responses of the organism to challenging situations. It is tempting to speculate whether the new aspects of neuroendocrine regulation discussed here can also be extended to other neurosecretory systems.