INTRODUCTION: Obesity is a global issue and a major metabolic disorder, leading to the development of serious diseases such as diabetes type 2 (DM2). Importantly, DM2 accounts for over 90 % of the diabetic cases in human. There are also sex‑specific differences in the development of obesity and DM2. The arcuate nucleus of the hypothalamus (ARC) is believed to be central to integration of peripheral and central anabolic and catabolic inputs and the maintenance of energy balance. Neuropeptide Y (NPY) neurons plays a role in the regulation of food intake and modulation of energy expenditure. In rat brain, NPY neurons are located in the ARC and send projections to numerous other hypothalamic regions. However, there is no data concerning the comparison of the role of diet-induced obesity and DM2 on these neurons in male and female rats. AIM(S): The aim of this project was to study the effects of obesity and DM2 on NPY-immunoreactivity in the ARC of the hypothalamus of male and female rats. METHOD(S): To induce obesity female and male Wistar rats were fed with a high fat diet (HFD). In order to mimic the DM2 condition, a subset of HFD animals were injected with streptozotocin (a toxin that destroys pancreatic cells). The control group received lab chow diet. Animals were sacrificed, perfused with paraformaldehyde, and blood and brains were collected for further analysis. Blood was used to assess the metabolic and hormonal status of the animals and brains were processed for immunohistochemistry. RESULTS: Analysis of metabolic and hormonal status confirmed induction of obesity and DM2 in animals. Preliminary data (n=3) indicate an increase in NPY‑immunostaining in the ARC of obese male and female rats compared to controls. Currently the remaining data are being analyzed. CONCLUSIONS: The preliminary data indicate that HFD-induced obesity may alter functions of NPY neurons in the ARC of male and female rats. FINANCIAL SUPPORT: Supported by OPUS NCN grant2015/17/B/NZ4/02021.