How Does Pain Influence Opioid Craving?

To assess the factors that influence opioid misuse in the context of chronic pain, investigators used a rodent model. Pain was induced by a noxious substance injected into the paw, and drug craving was measured by the amount of bar pressing to obtain morphine.

Animals with or without chronic pain exhibited similar seeking of morphine in doses analogous to those used in human pain. During morphine withdrawal, when bar pressing released saline instead of morphine, this behavior was extinguished in pain-free animals; however, it persisted in chronic-pain subjects, even though evidence of physical pain remitted. In animals with chronic pain, continued morphine craving was associated with up-regulation of the GluA1 subunit of the glutamate AMPA r…