Intracellular calcium signalling in magnocellular neurones of the rat supraoptic nucleus: understanding the autoregulatory mechanisms

Oxytocin and vasopressin, released at the soma and dendrites of neurones, bind to specific autoreceptors and induce an increase in [Ca2+]1. In oxytocin cells, the increase results from a mobilisation of Ca2+from intracellular stores, whereas in vasopressin cells, it results mainly from an influx of Ca2+through voltage‐dependent channels. The response to vasopressin is coupled to phospholipase C and adenylyl‐cyclase pathways which are activated by V1(V1aand V1b)‐ and V2‐type receptors respectively. Measurements of [Ca2+]1in response to V1aand V2agonists and antagonists suggest the functional expression of these two types of receptors in vasopressin neurones. The intracellular mechanisms involved are similar to those observed for the action of the pituitary adenylyl‐cyclase‐activating peptide (PACAP). Isolated vasopressin neurones exhibit spontaneous [Ca2+]1oscillations and these are synchronised with phasic bursts of electrical activity. Vasopressin modulates these spontaneous [Ca2+]1oscillations in a manner that depends on the initial state of the neurone, and such varied effects of vasopressin may be related to those observed on the electrical activity of vasopressin neuronesin vivo.