Introduction: Despite the ongoing increase in the prevalence of obesity, there are few licensed anti-obesity medications, and these therapies have limited efficacy and significant side effects. Therefore, new treatments are being developed, including 11-βhydroxysteroid dehydrogenase type1 (11βHSD1) inhibitors. In vivo, the enzyme 11-βhydroxysteroid dehydrogenase type1 (11βHSD1), converts the inactive glucocorticoid, 11-dehydrocorticosterone, to its active form (corticosterone). Tissue-specific 11βHSD1 has been reported to be important in the development of obesity. 11βHSD1 is expressed in the arcuate nucleus (ARC), a major hypothalamic centre which regulates energy homeostasis. We investigated the effect of modulation of intra-ARC 11βHSD1 expression on appetite and body weight in rodents. Methods: Experiments were performed using adult male Wistar rats fed a standard chow diet. In the overexpression experiment, recombinant adeno-associated virus (rAAV) encoding 11βHSD1 (rAAV-S11βHSD1) was injected bilaterally into the ARC of 12 rats and rAAV expressing green fluorescent protein (rAAV-GFP) was injected bilaterally into the ARC of 12 control rats. In the underexpression experiment, rAAV encoding small interfering RNA to 11βHSD1 (rAAV-si11βHSD1) was injected bilaterally into the ARC of 12 rats and rAAV-GFP injected into the ARC of 12 control rats. Starting 1 week post-surgery, body weight and food intake were measured three times a week for 10 weeks. At the end of the experiments, tissues and plasma were collected for gene expression and hormone analysis. Results and Conclusions: Compared to controls, ARC 11βHSD1 overexpression increased ARC corticosterone levels (iARC-S11βHSD1 243±34pg/mg vs iARC-GFP 89±39pg/mg, p