Weight gain induced by an energy-dense diet is hypothesized to arise in part from defects in the neuronal response to circulating adiposity negative feedback signals, such as insulin. Peripheral tissue insulin resistance involves cellular inflammatory responses thought to be invoked by excess lipid. We sought to determine if similar signaling pathways are activated in the brain of rats fed a high-fat (HF) diet, and whether these effects depend upon excess calorie intake. We compared plasma hormones and glucose tolerance, behavioral and neuronal responses to intracerebroventricular (icv) insulin, hypothalamic long- chain acyl-CoA content and inflammatory markers in HF and low-fat (LF) fed rats, and determined the role of increased energy intake in the hypothalamic and metabolic effects of HF feeding. We also determined the effect of icv infusion of palmitate on hypothalamic insulin signaling and whether icv infusion of an inhibitor of IKK, affects intake of either a LF or HF diet. The ability of icv insulin to reduce food intake or activate hypothalamic signal transduction was attenuated in HF fed rats, as previously reported (6). This effect was accompanied by both hypothalamic accumulation of long-chain fatty acyl-CoAs and activation of inflammatory signaling. CNS insulin resistance and inflammation were observed after either icv palmitate infusion or HF feeding, and the effect of HF feeding was not dependent on excess calorie intake. Lastly, we observed that central IKK inhibition lowered food intake in rats fed a HF diet, but not a LF diet, and that this effect is associated with increased hypothalamic insulin sensitivity. These data support a model in which dietary fat induces CNS insulin resistance by raising hypothalamic content of long-chain acyl-CoAs and triggering local inflammatory responses. Since this results in a failure to constrain food intake appropriately, it may play a role in diet induced obesity (DIO) pathogenesis.