Neuropeptide Y (NPY), a 36-amino acid peptide, is widely expressed in the central and peripheral nervous system. NPY is involved in the regulation of several physiological processes, including energy balance, food intake, and nociception. Recently, we showed that activation of the NPY Y1 receptor is required for cutaneous neurogenic inflammation. Because neurogenic inflammation could participate in colitis, the aim of this study was to investigate the role of the NPY Y1 receptor in acute colitis using mice genetically deficient of NPY Y1 receptor. In addition, the Y1 receptor antagonist H409/22, was also investigated. Animals received 5% dextran sulfate sodium (DSS) in drinking water for 7 days. One group of animals also received the Y1 receptor antagonist, administered intraperitoneally twice daily. Disease activity was assessed daily for 7 days in all groups. DSS induced colitis in all animals resulting in weight loss, diarrhea, epithelial damage, crypt shortening, and inflammatory infiltration. However, clinical manifestation of the disease was markedly attenuated in Y1 null mutant mice as well as in mice receiving the Y1 antagonist. Histological analysis showed that tissue damage and ulceration were less severe in Y1-deficient animals. Consistent with the clinical and histological data, capsaicin-induced plasma extravasation was significantly reduced in the gut of Y1 null mutant animals compared with treated wild-type animals. These data indicate that NPY and Y1 receptor are involved in intestinal inflammation and suggest that inhibition of NPY Y1 receptor signaling may provide a novel therapeutic approach in the treatment of colonic inflammation. neurogenic inflammation; dextran sulfate sodium; in vivo animal models ULCERATIVE COLITIS AND CROHN'S disease constitute the two main forms of inflammatory bowel disease (IBD). This disease is characterized by a dysregulated immune response and chronic relapsing inflammation of the gastrointestinal (GI) tract, leading to diarrhea, hemoccult, abdominal pain, weight loss, and anemia.Despite intense research, the etiology of IBDs remains largely unknown. The development of IBD involves interactions among genetic, immunological, and environmental components (46). Other mediators implicated in the pathogenesis of colitis are neuropeptides released from enteric and sensory afferent neurons (37). These peptides have been shown to modulate different aspects of mucosal function, including blood flow and secretion, and may play a role in the recruitment of granulocytes and lymphocytes and in the modulation of mast cell activation (14,18).Stimulation and activation of capsaicin-sensitive sensory nerve endings produce an inflammatory response characterized by vasodilation and plasma extravasation (13). The inflammatory response is mediated by local release of sensory neuropeptides such as substance P (SP) and calcitonin gene-related peptide (CGRP) (25). The inflammatory response, termed neurogenic inflammation, is well described in many peripheral organs including the skin, ai...