The kappa opioid receptor, (also known as OP2, KOP, KOR), is a member of the opioid family ofG-protein-coupled receptors that also includes mu, delta and NOP receptors. Three variants of the receptordesignated kappa1, kappa2, and kappa3 have been characterized. However only one cDNA clone has beenidentified, hence these receptor subtypes are likely to arise from interaction of one kappa-opioid receptorprotein with other membrane associated proteins. kappa Opioid receptors are located predominantly in thecerebral cortex, nucleus accumbens, claustrum and hypothalamus and have been implicated in the regulation ofnociception, diuresis, feeding and neuroendocrine secretions. Dynorphins A and B and alpha-neoendorphinappear to be the endogenous ligands.