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, b ind to specific autoreceptors and induce an increase in [Ca2+](i). In oxyto cin cells, the increase results from a mobilisation of Ca2+ from intracellu lar 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 activate d by V-1 (V-1a and V-1b)- and V-2-type receptors respectively. Measurements of [Ca2+](i) in response to V-1a and V-2 agonists and antagonists suggest the functional expression of these two types of receptors in vasopressin ne urones. 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+](i) oscillations and these are synchronised with phasic bursts of electrical activity. Vaso pressin modulates these spontaneous [Ca2+](i) oscillations in a manner that depends on the initial state of the neurone, and such varied effects of va sopressin may be related to those observed on the electrical activity of va sopressin neurones in vivo.