Nicotine increases cytosolic Ca2+ in vasopressin neurons.

Strong immunoreactivity for neuronal nicotinic acetylcholine receptor alpha4 subunit was detected in neurons of the supraoptic nucleus (SON). At the ultrastructural level, immunoreactivity for alpha4 was detected in the post-synaptic membranes as well as in the cytoplasmic matrices in the magnocellular neurons. Nicotine (1-10 microM) increased cytosolic Ca2+ concentrations ([Ca2+]i) in isolated arginine-vasopressin (AVP)-containing neurons in the rat SON. Nicotine (10 microM) was less potent in increasing [Ca2+]i in AVP-containing neurons than noradrenaline (1 microM), a known neurotransmitter in the SON. The nicotine-induced [Ca2+]i increase in AVP-containing neurons was markedly reduced when pre-treated with a protein kinase A (PKA) blocker, H89 (40 microM). These findings suggest that nicotine, a known neurotransmitter in the SON, activates AVP-containing neurons via nicotinic acetylcholine receptor which is linked to stimulation of cAMP-PKA-regulated Ca2+ signaling pathway.