Kappa-opioid receptors are a type of protein found in the brain and other parts of the body. They belong to the opioid receptor family and are activated by specific substances, including natural peptides like dynorphins and synthetic drugs. These receptors play a role in pain regulation, mood, and stress responses. When activated, kappa-opioid receptors can produce effects such as pain relief and sedation, but they may also lead to dysphoria or unpleasant feelings. Research into these receptors is important for developing new treatments for pain and mood disorders while minimizing side effects associated with other opioid receptors, like mu-opioid receptors.