Multifaceted purinergic regulation of stimulus-secretion coupling in the neurohypophysis.

The neurohypophysis is an original model of the CNS secretory system releasing vasopressin (AVP) and oxytocin (OXT), two neuropeptides hormones synthesized by the magnocellular neurons of the hypothalamus. Specific patterns of action potentials originating from cellular bodies of magnocellular neurons control the release of AVP and OT, but intra-neurohypophysis regulations do modulate the neuropeptides release. There is now good evidence for the effects of extracellular purines in the control of neurohypophysial secretion. This paper brings together evidence for the multiple, intricate actions of purines in the extracellular space of the neurohypophysis. It covers four main points. First, the activity-dependent release of endogenous ATP in the neurohypophysis. Second, the action of ATP on both neuronal and non-neuronal compartments of the neural lobe. Third, the termination of ATP positive feedback by ecto-nucleotidases. And finally the possible involvement of adenosine in the regulation of neurohypophysial secretion and glial plasticity. The data suggest that ATP and adenosine are physiological modulators of the release of neurohypophysial peptides by acting directly on nerve terminals and indirectly on neurohypophysial astrocytes. Since purinergic receptors are widespread in nervous and endocrine systems, the neurohypophysis appears as an useful model for studying the role of purines in the regulation of stimulus-secretion coupling and neuron-glia interactions. The feedback mechanisms found in the neurohypophysis could be ubiquitous, occurring throughout the central nervous system and in other secretory systems.