Given the distinct and even opposing roles of DOR, κ-opioid receptor (KOR), and μ-opioid receptor (MOR) in modulating animal behaviors, such as response of locomotion, level of anxiety, depressive-like behavior or alcohol intake in different opioid receptor knockout mice (Kieffer and Gavériaux-Ruff, 2002), the overlap between the distribution of opioid receptors and the location of amyloid plaques in AD patients led us to postulate a possible role of these three opioid receptors in the pathology of AD. This evidence concerns the gene OPRM1 and Alzheimer disease.