Akieda-Asai S, Poleni PE, Date Y. Coinjection of CCK and leptin reduces food intake via increased CART/TRH and reduced AMPK phosphorylation in the hypothalamus. Am J Physiol Endocrinol Metab 306: E1284 -E1291, 2014. First published April 8, 2014 doi:10.1152/ajpendo.00664.2013.-CCK and leptin are anorectic hormones produced in the small intestine and white adipose tissue, respectively. Investigating how these hormones act together as an integrated anorectic signal is important for elucidating the mechanisms by which energy balance is maintained. We found here that coadministration of subthreshold CCK and leptin, which individually have no effect on feeding, dramatically reduced food intake in rats. Phosphorylation of AMP-activated protein kinase (AMPK) in the hypothalamus significantly decreased after coinjection of CCK and leptin. In addition, coadministration of these hormones significantly increased mRNA levels of anorectic cocaine-and amphetamineregulated transcript (CART) and thyrotropin-releasing hormone (TRH) in the hypothalamus. The interactive effect of CCK and leptin on food intake was abolished by intracerebroventricular preadministration of the AMPK activator AICAR or anti-CART/anti-TRH antibodies. These findings indicate that coinjection of CCK and leptin reduces food intake via reduced AMPK phosphorylation and increased CART/TRH in the hypothalamus. Furthermore, by using midbrain-transected rats, we investigated the role of the neural pathway from the hindbrain to the hypothalamus in the interaction of CCK and leptin to reduce food intake. Food intake reduction induced by coinjection of CCK and leptin was blocked in midbrain-transected rats. Therefore, the neural pathway from hindbrain to hypothalamus plays an important role in transmitting the anorectic signals provided by coinjection of CCK and leptin. Our findings give further insight into the mechanisms of feeding and energy balance. cholecystokinin; food intake; leptin; midbrain transection FOOD INTAKE IS FINELY REGULATED by a complicated interaction of many orexigenic and anorectic signals produced in the brain and peripheral tissues. To maintain energy balance, information on the metabolic state resulting from feeding-related factors must be transported efficiently to the brain. Leptin, an anorectic hormone produced by white adipose tissue, plays an important role in maintaining energy balance (47). Absence of leptin results in severe obesity in both rodents and humans (13,38). Leptin directly binds to its ObRb receptors, which are located mainly in the hypothalamus and hindbrain; it promotes energy expenditure by stimulating the Janus-activated kinase (JAK)-STAT3 signaling pathway (4). Leptin also inhibits AMP-activated protein kinase (AMPK) activity in the arcuate nucleus and paraventricular nucleus of the hypothalamus (33). Moreover, leptin administration enhances the anorectic response to satiety-signaling molecules such as bombesin (26) or amylin (52).CCK is a gastrointestinal hormone produced by I cells of the proximal small intestine ...