The Kappa-Opioid Receptor (KOR) is a type of receptor in the brain that belongs to the opioid receptor family. It primarily binds to specific molecules called endorphins and enkephalins, which are natural pain-relieving substances produced by the body. KOR is involved in regulating pain, mood, and stress responses. Activation of KOR can lead to various effects, including analgesia (pain relief), sedation, and dysphoria (a state of unease). Unlike other opioid receptors, KOR activation does not typically produce euphoria, making it a target for research in developing new pain medications with fewer addictive properties.