Pain
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In order to determine which classes of spinal neurons are capable of mediating sympathetically maintained pain, recordings were made from single somatosensory neurons in spinal cords of anesthetized cats. Each neuron was functionally identified with mechanical stimuli, and its responses to electrical stimulation of the sympathetic trunk were recorded. Nearly half (45%) of the wide-dynamic-range (WDR) neurons tested were activated by sympathetic stimulation, but none of the high threshold (nociceptor-specific) neurons and only 17% of the low threshold neurons were activated. ⋯ Therefore, WDR neurons, rather than high threshold neurons, are most likely to mediate the spinal component of sympathetically maintained pain. These results provide supporting evidence for our previous hypothesis that sympathetically maintained pain is mediated by myelinated mechanoreceptors acting on sensitized WDR neurons. Our results also demonstrate that sympathetic activation of WDR neurons is mediated by an alpha-adrenergic mechanism in the skin.
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Pain responses (threshold, tolerance, and visual analog ratings) to the cold pressor task were studied in 46 normally menstruating dysmenorrheic and non-dysmenorrheic women during 2 phases of the menstrual cycle. Twenty-six women provided measurements during the follicular (days 8-14) and 20 during the luteal (days 15-21) phases of the menstrual cycle. A significantly lower pain threshold was obtained during the luteal as compared to the follicular phase. ⋯ Visual analog ratings were significantly lower in dysmenorrheic women during the follicular than the luteal phase. Also, these ratings were lower than those of non-dysmenorrheic women in the follicular phase. This finding may support an adaptation-levels model, in that dysmenorrheic women report less pain than do non-dysmenorrheic women because they compare cold pressor pain with internal menstrual pain.
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Psychophysical experiments were carried out on 7 human participants to determine the extent to which experimentally produced first or second pain is reduced by concomitant nociceptive stimulation of body regions remote from those at which test stimuli are presented. This form of pain reduction has been termed diffuse noxious inhibitory controls (DNIC). Test stimuli used to evoke first and second pain consisted of intense electrical pulses delivered to the ankle area by subepithelial electrodes. ⋯ All of these results closely parallel electrophysiological observations about DNIC in primates. Since the extent of reduction of first pain is relatively weak and the durations of all inhibitory effects are very brief, it is unlikely that DNIC subserves the functions of relieving pain or providing a mechanism of coding pain. The spatial and temporal pattern of DNIC indicates that it may be a phenomenon associated more with the organization and production of withdrawal reflexes than with the relief of pain or pain coding.
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This paper describes a new approach to the neurolytic block of the celiac plexus through the anterior abdominal wall using CT guidance. In 5 patients, CT guidance was used for needle placement and visualization of the spread of the injection. ⋯ No serious complications were observed. The anterior approach is simple and is useful in those patients with upper chronic abdominal pain scheduled for biopsy of the pancreas, and in those terminally ill patients who cannot tolerate the prone position.
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According to myogenic models that relate abnormal EMG patterns to the experience of pain, lumbar paravertebral muscle activity has been considered to play an important role in chronic low back pain. In the present study, 40 chronic low back pain patients and 40 matched non-patient controls were compared on lumbar paravertebral EMG during mechanically stabilized static and dynamic postures. ⋯ In addition, most patients did not show the flexion-relaxation response or the expected pattern of EMG responses during trunk rotation, most likely because of restricted range of motion and/or compensatory posturing. These findings provide support for the biomechanical model of chronic pain and indicate the need for further research pertaining to pain behavior and movement-related lumbar muscle activity.