Pain
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The reproducibility of both the conscious experience of pain and the reproducibility of psychophysical assessments of pain remain critical, yet poorly characterized factors in pain research and treatment. To assess the reproducibility of both the pain experience and two methods of pain assessment, 15 subjects evaluated experimental heat pain during four weekly sessions. In each session, both brief (5s) and prolonged (90s) heat stimuli were utilized to determine effects of stimulus duration on reproducibility. ⋯ However, the VAS was significantly more sensitive to small differences in perceived pain intensity and pain unpleasantness, and did not exhibit some of the order effects present with the VDS. Taken together, these results indicate that the reproducibility of psychophysical ratings of pain can be maximized: (1) by averaging responses to multiple, brief stimuli; (2) by providing subjects with a training period distinct from the study period; and (3) by ensuring that interpretation of scale parameters remains constant over time. Thus, although the experiences of both experimental and clinical pain are highly variable, pain assessment procedures can be structured to minimize session-to-session variability.
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Cutaneous laser stimulation activates predominantly the A-delta and C mechano-heat nociceptors. Applied to the perioral region, low intensity CO(2)-laser pulses evoke reproducible trigeminal cortical evoked potentials (LEPs). High intensity CO(2)-laser stimuli induce a reflex response in the contracted jaw-closing muscle, the so-called laser silent period (LSP). ⋯ In all experiments experimental tonic pain decreased the subjective ratings of the perioral laser stimulation (P< 0.001). Experimental tonic pain, either from muscle or from skin, induced bilateral inhibitory effects on the trigeminal laser evoked potentials and brainstem reflex responses and on the subjective ratings of the laser pulses. These effects could be mediated through the activation of segmental and suprasegmental inhibitory systems that may function interdependently.
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Little research has examined the role of patient cognitive and behavioral responses, including catastrophizing, in adjustment to chronic pain associated with spinal cord injury (SCI). The objective of this study was to examine the associations of catastrophizing and specific pain coping strategies with pain intensity, psychological distress, and pain-related disability among individuals with chronic pain and SCI, after controlling for important demographic and SCI-related variables that might affect outcomes. Participants in this study were 174 community residents with SCI and chronic pain who completed a mailed questionnaire that included the SF-36 Mental Health scale, Coping Strategies Questionnaire, and Graded Chronic Pain Scale. ⋯ The coping and catastrophizing scales accounted for an additional 30% of the variance in psychological distress (P<0.001) and 11% of the variance in pain-related disability (P<0.001), after controlling for pain intensity and demographic and SCI variables. Catastrophizing, but not any other single pain coping strategy, was consistently strongly and independently associated with the outcome measures. Potentially, the assessment and treatment of catastrophizing may reduce psychological distress and pain-related disability among individuals with chronic pain and SCI.
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Although activation of alpha(2)-adrenoceptors is known to play an important role in mediating antinociception, the contribution of various alpha(2)-adrenoceptor subtypes in modulating trigeminal nociception remains unknown since subtype specific agonists and antagonists are not available. The present study investigated the functional role of alpha(2)-adrenoceptor subtypes in modulating the N-methyl-D-aspartate-induced nociceptive behavior in the medullary dorsal horn by using antisense oligodeoxynucleotides to selectively knock-down the receptor subtypes. Microinjection of N-methyl-D-aspartate (2 nmol in 10 microl) through a cannula implanted dorsal to the medullary dorsal horn produced a total of 164.9+/-8.8 scratches in the facial region (n=14), and the scratching behavior lasted for 77.8+/-5.2s (n=14). ⋯ Antisense treatment reduced alpha(2A) and alpha(2C) receptor immunoreactivity in the medullary dorsal horn compared to the sense and the vehicle-treated animals. Quantitative image analysis revealed a significant decrease in pixel intensity following the antisense treatment. These results indicate that activation of alpha(2A) adrenoceptor plays an important role in mediating the antinociceptive effect of clonidine in the medullary dorsal horn in the rat.
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Clinicians tend to assign greater weight to non-verbal expression than to patients' self-report when judging the location and severity of pain. Judgments can misrepresent the actual experience because patients can successfully alter their pain expressions. The present research provides a basis for discriminating genuine and deceptive pain expressions by expanding detailed accounts of facial expressions to include previously unexamined variables, including study of temporal patterns and contiguity of facial actions as well as the occurrence of specific deception cues. ⋯ Findings confirmed the difficulty of discriminating the facial expressions, but indicated that faked pain expressions show a greater number of pain-related and non-pain-related actions, have a longer peak intensity and overall duration, and the facial actions observed tend to be less temporally contiguous than are those in genuine pain expressions. The differences between masked pain and neutral expressions were subtle, with a greater frequency of mouth opening and residual eyebrow movement in masked pain expressions. Thus, there is an empirical basis for discriminating genuine and deceptive facial displays.