Cocaine- and amphetamine-regulated transcript (CART) located in the hypothalamus is well-known for its potent appetite-suppressing activity and its involvement in general energy homeostasis regulation. However, knowledge on the mechanisms underlying CART function remains limited. This study addresses the interaction and functional effects between CART and another key appetite-regulating neuropeptide, neuropeptide Y (NPY). In the hypothalamic arcuate nucleus, neuronal activities of CART and the orexigenic NPY are differentially regulated to induce antagonistic metabolic effects. Specifically, the arcuate NPY neuronal group exerts an inhibitory tone on CART-expressing neurons through intra-arcuate connections. To investigate the control of CART neuronal activity by the NPY system, a novel CART-cre knock-in mouse line was generated and crossed with our NPY-Y1 receptor (Y1-R) floxed line in order to selectively delete Y1-Rs in CART-expressing neurons. Preliminary data show that adult-onset Y1-R-deficiency in CART neurons leads to decreased body weight associated with suppressed food intake and adiposity, indicating that Y1-R signaling inhibits CART neurons and consequently modulates feeding behavior via this pathway.

Another underexplored aspect of CART function on the regulation of energy homeostasis is its effect on thermoregulation. To get more insight into this area we examined our novel CART knockout mouse model, at both room temperature (RT; 22˚C) and thermo-neutral condition (30˚C). Importantly, our results demonstrate that under thermo-neutral conditions, CART^-/- mice exhibited significantly higher adiposity compared to wild-type (WT) controls, independent of diet. Under thermo-neutral condition, CART^-/- mice also displayed a distinct phenotype with diminished food intake and body weight gain compared to WT, effects that were absent in RT environment. This indicates that the metabolic traits seen at regular RT-based experiments, where mild cold-induced stress is present, may represent the integrated effects of CART-deficiency on the interactive feeding and stress-related pathways. Collectively, our data suggest an indisputable role of CART in thermoregulation.