Hypothalamic CART and serum leptin levels are reduced in the anorectic (anx/anx) mouse.

Cocaine- and amphetamine-regulated transcript (CART) is expressed in the hypothalamus, and putative peptides encoded by CART potently inhibit feeding when administered centrally. CART is strongly down-regulated in the lateral hypothalamic area and the arcuate nucleus in animal models of obesity with disrupted leptin signaling. Here we have used in situ hybridization and immunohistochemistry to study CART expression in mice homozygous for the anorexia (anx) mutation which are characterized by a much reduced food intake and premature death. anx/anx mice had significantly decreased levels of CART mRNA label and peptide-immunoreactive cell bodies and fibers in the arcuate nucleus and a lower number of detectable CART-expressing cells in the dorsomedial hypothalamic nucleus/lateral hypothalamic area. Moreover, serum leptin levels were significantly lower in anx/anx mice compared to normal littermates, most likely due to the prominent depletion of body fat in these animals. The decrease in the anorexigenic agents leptin and CART, may reflect a compensatory down-regulation in response to the energy-deprived state of anx/anx mice. Alternatively, the reduced arcuate CART expression may be a consequence of a molecular defect in the arcuate nucleus of these animals.