AIM: To explore the mechanism for interactions of leptin with ghrelin and orexin in the arcuate nucleus (ARC) activating neuropeptide Y (NPY) neurons during physiological regulation of feeding. METHODS: Single neurons from ARC of adult rats with matured feeding function were isolated. [Ca2+]i was measured to monitore their activities. The time course of leptin effects on ghrelin-induced versus orexin-induced [Ca2+]i increases in NPY neurons was studied. RESULTS: Administration of ghrelin or orexin-A at 10-10 mol/L increased cytosolic Ca2+ concentration ([Ca2+]i) in NPY neurons isolated from the ARC of adult rats. Upon administration of leptin at 10-14-10-12 mol/L, ghrelin-induced [Ca2+]i increases were initially (< 10 min) inhibited but later restored, exhibiting a transient pattern of inhibition. In contrast, orexin-induced [Ca2+]i increases were inhibited by leptin in a longlasting manner. Furthermore, a prior administration of leptin inhibited orexin action but not ghrelin action to increase [Ca2+]i. CONCLUSION: Leptin counteracted ghrelin effects transiently and orexin effects long-lastingly in NPY neurons. The transient property with which leptin counteracts ghrelin action in NPY neurons may allow the fasting-associated increase in ghrelin levels to activate NPY neurons in the presence of physiological leptin and to stimulate feeding. AIM: To explore the mechanism for interactions of leptin with ghrelin and orexin in the arcuate nucleus (ARC) activating neuropeptide Y (NPY) neurons during physiological regulation of feeding. METHODS: Single neurons from ARC of adult rats with matured feeding function were isolated. [Ca2 +] i was measured to monitore their activities. The time course of leptin effects on ghrelin-induced versus orexin-induced [Ca2 +] i increases in NPY neurons was studied. RESULTS: Administration of ghrelin or orexin-A at 10-10 mol / L increased cytosolic Ca2 + concentration ([Ca2 +] i) in NPY neurons isolated from the ARC of adult rats. Upon administration of leptin at 10-14-10-12 mol / L, ghrelin-induced [Ca2 +] i increases were initially ( <10 min) inhibited but later restored, exhibiting a transient pattern of inhibition. In contrast, orexin-induced [Ca2 +] i increases have inhibited by leptin in a longlasting manner. Furthermore, a prior administration of leptin inhibited orexin action but not ghrelin action to increase [Ca2 +] i. CONCLUSION: Leptin counteracted ghrelin effects transiently and orexin effects long-lastingly in NPY neurons. The transient property with which leptin counteracts ghrelin action in NPY neurons may allow the fasting-associated increase in ghrelin levels to activate NPY neurons in the presence of physiological leptin and to stimulate feeding.