Differential effects of morphine on pain and temperature perception in human volunteers.

Electrophysiological and behavioral evidence suggests that morphine may have a differential effect on nociceptive and thermal pathways. In this study, we explored the perceptual consequences of these differential actions by examining the effect of a low morphine dose (0.08 mg/kg) on pain and temperature sensations arising from cutaneous thermal stimuli. In a double-blind placebo-controled study, we compared the perceived temperature intensity and perceived pain intensity and unpleasantness of noxious and innocuous heat and cold applied to the face of human subjects, with and without low doses of systemic morphine. The results showed that morphine modified pain-related sensations. In contrast, perceived thermal intensity of both noxious and innocuous heat or cold stimuli was unchanged by low-dose morphine administration. These findings suggest that low doses of morphine have a differential effect on pain and temperature sensations arising from the same stimulus, and thus that these sensations could be subserved by different neuronal populations. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.