Measuring Pain Avoidance-Like Behavior in Drug-Dependent Rats.

In contrast to their analgesic properties, excessive use of either opioids or alcohol produces a paradoxical emergence of heightened pain sensitivity to noxious stimuli, termed hyperalgesia, which may promote increased use of opioids or alcohol drinking to manage worsening pain symptoms. Hyperalgesia has traditionally been measured in rodents via reflex-based assays, including the von Frey method. To better model the motivational and affective dimensions of pain in a state of opioid/alcohol dependence and withdrawal, this unit describes the use of a non-reflex-based method for measuring pain avoidance-like behavior in dependent rats. In the mechanical conflict-avoidance task, rats run across probes of varying heights to avoid a bright aversive light and to reach a dark goal chamber. A longer latency to exit onto the nociceptive probes reflects increased pain avoidance-like behavior during withdrawal. Mechanical conflict-avoidance testing can be repeated to provide both baseline assessment of pain avoidance behavior and pain avoidance measures after the induction of dependence.