Leptin suppresses ghrelin- and orexin-induced [Ca²⁺]i increases in neuropeptide Y neurons in the rat arcuate nucleus.

Abstract

Neuropeptide Y (NPY) neurons in the hypothalamic arcuate nucleus (ARC) are the site of convergence of central and peripheral feeding regulating signals and play an important role for feeding stimulation. In this study, we investigated how leptin, ghrelin and orexin signals are integrated in NPY neurons. We isolated single neurons from the ARC of rats and measured the cytosolic Ca²⁺ concentration ([Ca²⁺]i) with fura-2 fluorescence imaging. To identify NPY neurons, we did immunocytochemical staining after [Ca²⁺]i measurements. Leptin infusion suppressed ghrelin- and orexin-induced [Ca²⁺]i increases in single NPY neurons, and the suppression was temporal for ghrelin-induced [Ca²⁺]i increases. Because our previous research showed that [Ca²⁺]i increases induced by ghrelin were suppressed by a PKA inhibitor and those by orexin were suppressed by a PKC inhibitor in NPY neurons, we investigated whether leptin could suppress the [Ca²⁺]i increases induced by adenylyl cyclase activator and PKC activator. Leptin suppressed both forskolin- and TPA-induced [Ca²⁺]i increases, while those induced by a high concentration of KCl were not affected. These results demonstrate that leptin suppresses the ghrelin-and orexin-induced [Ca²⁺]i increases at least partly by counteracting the cAMP-PKA and PKC signaling, respectively, but not by direct inhibition of Ca²⁺ channels. These interactions in NPY neurons may play an important role in integrating metabolic, nutritional and central signals of the body and thereby producing an appropriate feeding-controlling output. [Jpn J Physiol 54 Suppl:S220 (2004)]