Cholecystokinin (CCK) is a peptide originally discovered in the gastrointestinal tract (Ivy and Oldberg 1928), but also found in high density in the mammalian CNS (Vanderhaeghen et al. 1975). This peptide, initially characterized as a 33 amino acid sequence, is present in a variety of biologically active molecular forms (Rehfeld and Nielsen 1995) derived from a 115 amino acid precursor molecule. The CCK fragments are involved in numerous physiological functions such as feeding behaviour, central respiratory control and cardiovascular tonus, vigilance states, memory processes, nociception, emotional and motivational responses. The C-terminal octapeptide fragment CCK8, constitutes one of the major neuropeptides in the brain, and binds with nanomolar affinities with two different receptors, designated CCK1 (CCKa) and CCK2 (CCKe/gastrin) receptors. The N-terminus of these heptahelical receptors is located extracellularly and the C-terminal domain is often anchored in the plasma membrane by means of a cysteine bearing a fatty acid.
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