Neuropeptide Y increases intracellular calcium in rat pinealocytes

The pineal gland is mainly innervated by sympathetic fibres containing noradrenaline (NA) and neuropeptide Y (NPY). NA released at night stimulates melatonin synthesis via a beta1-adrenergic-induced increase in cyclic adenosine monophosphate (cAMP) concentration potentiated by an alpha1-adrenergic-induced increase in Ca2+ concentration. We previously showed that NPY acted on presynaptic Y2 receptors inhibiting NA release and on postsynaptic Y1 receptors stimulating melatonin synthesis. Here we used Fura-2 imaging to assess the effect of NPY on the intracellular Ca2+ concentration, [Ca2+]i, in cultured rat pineal cells. In 84% of cells, on average, 10 nM NPY induced a progressive rise of [Ca2+]i from its basal value of 102+/-3 nM to a plateau of 180+/-6 nM (n = 467 cells), which lasted the time of NPY application. This effect of NPY appeared dependent on extracellular Ca2+.