Leptin transiently antagonizes ghrelin and long-lastingly orexin in regulation of Ca2+ signaling in neuropeptide Y neurons of the arcuate nucleus

Figure 2 Leptin suppresses ghrelin-induced and orexin-induced [Ca²⁺]_i increases via different signaling pathways in NPY neurons. A-G: Effects of inhibitors for signaling molecules on the leptin action against ghrelin and orexin. Preincubation for 1 h with 50 μmol/L LY294002, an inhibitor for PI3-kinase, interfered with leptin action to suppress [Ca²⁺]_i responses to ghrelin (A), but not orexin (B). Preincubation for 1 h with 100 nmol/L wortmannin, another PI3-kinase inhibitor, little affected the leptin suppression of orexin-induced [Ca²⁺]_i increases (C). Preincubation for 30 min with 10 μmol/L milrinone, a PDE3 inhibitor, blocked the leptin action to suppress [Ca²⁺]_i responses to ghrelin (D), but not orexin (E). Preincubation for 30 min with 10 μmol/L U0126, an inhibitor for MAP-kinase, little affected the leptin action to suppress orexin-induced [Ca²⁺]_i increases (F). Preincubation for 30 min with a STAT3 inhibitor peptide at 500 μmol/L, did not significantly alter the leptin suppression of orexin-induced [Ca²⁺]_i increases (G). H: The number of neurons whose [Ca²⁺]_i responses to ghrelin or orexin were suppressed by leptin in the presence of inhibitors is expressed by percentage. The numbers above the bars indicate the number of neurons inhibited by leptin over that responded to ghrelin or orexin-A. I: Reduction of amplitudes of [Ca²⁺]_i responses to ghrelin or orexin-A by leptin is expressed by percentage. ^aP < 0.05, ^bP < 0.01 vs control. The data regarding ghrelin in H and I were in part taken from our previous paper[17].