Recently, a new neuropeptide, named nesfatin-1, was discovered. It has been reported that nesfatin-1 inhibits food intake after injection into the third ventricle as well as intraperitoneal (ip) injection. Cholecystokinin (CCK) is well established to play a role in the regulation of food intake. The aim of the study was to examine whether CCK-8S injected ip modulates neuronal activity in nesfatin-1 immunoreactive (ir) neurons localized in the PVN and in the nucleus of the solitary tract (NTS). Additionally, tyrosine hydroxylase-immunoreactivity (TH-ir) in the PVN was determined to assess the distribution of TH-ir fibers in relation to nesfatin-1-ir. Non-fasted male Sprague-Dawley rats received 6 or 10 microg CCK-8S/kg or vehicle solution (0.15M NaCl; n=4 all groups) ip. The number of c-Fos-ir neurons was determined in the PVN, arcuate nucleus (ARC), and NTS. Double staining procedure for nesfatin-1 and c-Fos revealed that CCK-8S increased significantly and in a dose-dependent manner the number of c-Fos positive nesfatin-1-ir neurons in the PVN ( approximately 4-fold and approximately 7-fold) and NTS ( approximately 9-fold and approximately 26-fold). Triple staining in the PVN showed a dose-dependent neuronal activation of nesfatin-1 neurons that were colocalized with CRF and oxytocin. Double labeling against nesfatin-1 and TH revealed that nefatin-1-ir neurons were encircled in a network of TH-ir fibers in the PVN. No effect on the number of c-Fos-ir neurons was observed in the ARC. These results suggest that the effects of CCK on the HPA axis and on food intake may, at least in part, be mediated by nesfatin-1-ir neurons in the PVN.