Pain
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Comparative Study
Gender differences in pain ratings and pupil reactions to painful pressure stimuli.
In order to investigate gender differences in pain perception, the present study employed both a psychophysical and a psychophysiological measure. In experiment 1, 20 subjects rated the painfulness of 4 different levels of tonic pressure applied to their fingers using a verbally anchored categorization procedure. In general agreement with studies of pain threshold and tolerance, female subjects reported greater pain at high levels of stimulation, with no gender difference being evident at low pressure levels. ⋯ The pupil dilations seen during the last 10 sec of the 20-sec pressure application turned out to be a highly significant indicator of pain intensity. When female and male subjects were compared on this measure, a similar divergent pattern as in the psychophysical data emerged, with female subjects showing greater pupil dilations at high pressure levels only. The fact that gender differences in pain perception can be demonstrated using an autonomic indicator of pain that is beyond voluntary control suggests that these differences reflect low-level sensory and/or affective components of pain rather than attitudinal or response-bias factors.
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Primary C-fiber afferents can induce a state of increased excitability in spinal cord neurons amplifying their responsiveness to noxious and innocuous stimuli--the phenomenon of central sensitization. We have examined whether the hypersensitivity to low-intensity stimuli (mechanical allodynia) evoked by C-afferent conditioning inputs is NMDA receptor dependent. The enhancement by C-afferent conditioning stimuli of the normally low or absent cutaneous touch-evoked responses of posterior biceps femoris/semitendinosus flexor motoneurons in the decerebrate-spinal rat has been used as a model of touch-evoked allodynia. ⋯ Treatment with MK 801 some time after the conditioning input when the mechanical hypersensitivity is fully established, also reduced the increased touch-evoked responses. The reduction in threshold and the increase in touch responsiveness induced by cutaneous and muscle noxious C-fiber conditioning stimuli in the rat spinal cord are, therefore, both prevented and reversed by NMDA receptor antagonism. NMDA antagonists may be potentially useful, therefore, in treating postinjury pain hypersensitivity.