Examining The Impact Of Opioid Withdrawal On Pain Processing: The Influence Of Social Isolation Stress

The use of opioids as a traditional treatment for acute and chronic pain has been severely hindered by the addictive nature of these substances and the pain relief they provide. Clinical reports suggest that opioid addicts are hypersensitive to pain during abstinence, and this effect may persist for months afterward. Examinations of nociceptive processing during opioid withdrawal in rodents have produced mixed results, with little evidence of decreased thresholds or latencies to noxious stimuli. To date, no studies have explicitly evaluated pain affect during the withdrawal period. Therefore, the purpose of the current study was evaluate both sensory and affective pain processing in response to opioid withdrawal as well as the impact of social isolation stress on these measures. Sensory pain processing was examined during the seven-day morphine dosing period and over a five day period following abstinence. Pain affect was evaluated during the withdrawal period, following the induction of an experimental inflammatory condition. The doses of morphine selected produced robust analgesia and a reliable withdrawal syndrome. The results demonstrated no changes in sensory pain processing in response to morphine or social isolation during the withdrawal period, but differential effects of morphine and social isolation on pain affect on the first and second days of withdrawal. Group-housed subjects in morphine withdrawal demonstrated increased pain affect relative to saline-dosed subjects, but only on the first day of testing. Socially isolated subjects demonstrated decreased pain affect in comparison to group-housed subjects on the first and second day only, and no difference between socially isolated morphine- and saline-dosed subjects were present. The current study provides evidence of altered emotional pain processing during withdrawal, which could contribute to the development of novel treatments for opioid addicts with underlying chronic pain conditions.