Winding and twisting like a labyrinth, the brain consists of an elaborate network of passages through which information flows at high speeds, rapidly generating thoughts, emotions, and physical responses. Much of this information is relayed by chemical messengers, or neurotransmitters — like dopamine and serotonin.
Although fine-tuned and evolved for complex processing, the brain and its neurotransmitters are vulnerable to hijacking by chemical substances, including opioid drugs such as oxycodone, psychostimulants such as cocaine, and alcohol. Chronic use of any of these substances enhances the activity of a molecule known as the kappa opioid receptor (KOR), which is active in the brain’s reward circuitry. KOR activation produces dysphoria and an inability to feel pleasure. Its enhanced activity following chronic drug or alcohol use plays a crucial role in substance abuse.
KORs have been known to exist in certain brain regions, particularly those involved in pain processing, reward, and stress responses,