Cholecystokinin tetrapeptide (CCK-4 Trp-Met-Asp-Phe-NH2; also PTK7) is a peptide fragment derived from the larger peptide hormone cholecystokinin. Unlike cholecystokin which has a variety of roles in the gastrointenstinal system as well as central nervous system effects CCK-4 acts primarily in the brain as an anxiogenic although it does retain some GI effects but not as much as CCK-8 or the full length polypeptide CCK-58.
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