Kappa Opioid System Involvement in Mood and Anxiety Disorders

Abstract

Current interest in opioid drugs is directed mostly on morphine-like drugs that activate the μ opioid peptide (MOP) system and induce euphoria and, potentially, addiction. Less attention has been paid to the κ opioid peptide (KOP) system, likely because drugs that activate the KOP system have low abuse potential. Indeed, activation of the KOP system often is reported to have effects on brain and behavior that are opposite to MOP activation. The literature suggests that dynorphin and its κ receptor are, indeed, unique among the opioids. That uniqueness has generated interest in our laboratory. We have taken a different approach to understanding the KOP system. Rather than focusing on drug abuse, we have adopted mood and anxiety as a model for investigation of the KOP system. The assumption is that clarification of the underlying mechanisms and behavioral outcomes of κ agonists and antagonists will help inform the KOP system for other situations, including drug use and abuse. This review will highlight the basis for our fascination with KOP and the κ receptor.