Pain
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Promising recent developments in the therapeutic value of neuropeptide antagonists have generated renewed importance in understanding the functional role of neuropeptides in nociception and inflammation. To explore this relationship we examined behavioral changes and primary afferent neuronal plasticity following deep tissue inflammation. One hour following craniofacial muscle inflammation ipsilateral as well as contralateral head withdrawal thresholds and ipsi- and contralateral hindpaw withdrawal thresholds were lowered and remained reduced for 28 days. ⋯ Local injection of CGRP antagonist directly into the masseter muscle prior to CFA produced similar, but less pronounced, effects. These findings indicate that unilateral craniofacial muscle inflammation produces mechanical allodynia at distant sites and upregulates CGRP and SP in primary afferent neurons innervating deep tissues. These data further implicate CGRP and SP in deep tissue nociceptive mechanisms and suggest that peptide antagonists may have therapeutic potential for musculoskeletal pain.
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Low back pain (LBP) is a common symptom among adults but little is known about its persistence over time in defined populations. The aim of this study was to examine the persistence of LBP among a cohort of industrial employees studied in four successive surveys during a total of 28 years. Cross-tabulations and logistic regression was used to estimate the interdependence of LBP occurrence at the surveys. ⋯ The odds ratio of local LBP at the 5-, 10-, or 28-year follow-up for those with such pain at baseline vs. not were 6.0 (95% CI 4.3-8.3), 4.7 (3.3-6.6) and 4.0 (2.6-6.3), adjusted for age, gender and occupational class. The respective figures for radiating LBP were 8.5 (5.7-12.5), 6.7 (4.4-10.1) and 2.3 (1.5-3.6). We conclude that LBP is commonly recurrent.
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Transcutaneous electrical nerve stimulation (TENS) reduces pain through central mechanisms involving spinal cord and brainstem sites. Since TENS acts through central mechanisms, we hypothesized that TENS will reduce chronic bilateral hyperalgesia produced by unilateral inflammation when applied either ipsilateral or contralateral to the site of muscle inflammation. Sprague-Dawley rats were injected with carrageenan in the left gastrocnemius muscle belly. ⋯ Either low or high frequency TENS applied to the gastrocnemius muscle ipsilateral to the site of inflammation significantly reversed mechanical hyperalgesia, both ipsilateral and contralateral to the site of inflammation. Low or high frequency TENS applied to the gastrocnemius muscle contralateral to the site of inflammation also significantly reduced mechanical hyperalgesia, both ipsilateral and contralateral to the site of inflammation. Since ipsilateral or contralateral TENS treatments were effective in reducing chronic bilateral hyperalgesia in this animal model, we suggest that TENS act through modulating descending influences from supraspinal sites such as rostral ventromedial medulla (RVM).
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Randomized Controlled Trial
Chronobiological characteristics of painful diabetic neuropathy and postherpetic neuralgia: diurnal pain variation and effects of analgesic therapy.
Clinical impressions suggest that neuropathic pain is often worse at night and significantly impairs sleep. However, the temporal pattern of neuropathic pain during waking hours has not been clearly characterized. Using clinical trial data, we have evaluated the diurnal variation of pain intensity before and during analgesic treatment in patients with diabetic neuropathy (DN) and postherpetic neuralgia (PHN). ⋯ Neuropathic pain intensity progressively increases throughout the day and this temporal profile appears to be unaffected by treatment with gabapentin and/or morphine. Advancing our understanding of the chronobiology of neuropathic pain may shed new light on various neurohormonal and neurophysiologic influences and lead to the identification of novel therapeutic targets. Furthermore, recognizing diurnal pain patterns may guide treatment strategies such as the targeted timing of analgesic therapies.
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Randomized Controlled Trial
The effects of noxious heat, auditory stimulation, a cognitive task, and time on task on pain perception and performance accuracy in healthy volunteers: a new experimental model.
The effects of cognitive and competing sensory processing tasks on pain perception and as a function of time are only partially understood. To study these effects, we compared the simultaneous effects of noxious heat stimulation (HS), auditory stimulation (AS) (sinusoidally modulated speech-like signal, SMSLS), and a cognitive task (CT) (rate change detection of the SMSLS) on pain perception and task performance over repeated experimental runs. Sixty healthy paid volunteers were randomly assigned to four groups, one exposed to AS while performing the CT, one to HS (46 degrees C/6 min), one to AS and HS, and one to AS and HS while performing the CT. ⋯ Neither pain rating, nor rate of errors on the CT varied significantly across runs. These findings point to a significant influence of competing passive sensory processing on pain perception, with the cognitive task not necessarily adding to the perception of pain. Advantages and shortcomings of the present experimental model for future pain studies are discussed.