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The role of attentional mechanisms and endogenous opioids in the influence of anxiety on acute pain sensation was investigated. Forty-five spider phobics received mildly painful electrical stimulation. The opioid antagonist naltrexone or placebo was administered between subjects to examine an analgesia due to anxiety-induced endorphinergic activity, while anxiety and focus of attention were manipulated within subjects. In accordance with previous research, pain ratings and skin conductance responses (SCRs) were not influenced by anxiety when focus of attention was controlled for. Attention towards pain led to an increase in subjective pain as opposed to distraction from pain. SCRs, however, were increased in the distraction conditions, probably due to heightened unexpectedness. Further, both high and low anxiety resulted in an analgesia compared to the pretest in the placebo condition, which was reversed by a low dose of naltrexone, but not by a high dose. Apart from possible agonist properties of high doses of naltrexone, this effect suggests an opioid-induced analgesia. It remains to be demonstrated whether this was due to endogenous opioids released during high anxiety.
Janssen et al. (Thu,) studied this question.