European journal of pain : EJP
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The mechanism underlying discogenic low-back pain is unclear. It is difficult to explain this type of pain by the segmental innervation theory because the groin area is innervated by the genitofemoral or ilioinguinal nerves, which are the terminal branches of the L1 or L2 spinal nerves. Recently, some studies have indicated that sympathetic trunks are closely related to discogenic low-back pain. ⋯ We demonstrated that FG-labeled SP-ir neurons in L2 DRGs decreased when FG was applied to the ventral or dorsal portions of L5-6 discs. The results indicated that the L2 ramus communicans played an important role in the afferent pathway of both the ventral and dorsal portions of the L5-6 disc. Nociceptive information from the L5-6 disc may be transmitted mainly by L2 DRG neurons through the L2 ramus communicans.
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Mice lacking the serotonin-transporter (5-HTT-/- mice) develop reduced thermal hyperalgesia after nerve injury, concomitant with reduced serotonin (5-HT) levels in nervous tissue. Here we investigated pain behaviour in 5-HTT-/- mice compared to their wild type littermates after hind paw inflammation induced by complete Freund's adjuvant (CFA). We used standard tests for pain behaviour, high performance liquid chromatography for measurement of 5-HT, and immunohistochemistry of hind paw skin tissue and L5 dorsal root ganglia (DRG) to measure local inflammation and nerve injury. ⋯ Accordingly, a higher number of injured DRG neurons was identified by activating transcription factor 3 (ATF3) staining in 5-HTT-/- mice after CFA. We conclude that the phenotype of 5-HTT-/- mice leads to reduced inflammatory pain due to reduced tissue 5-HT levels and to greater peripheral nerve injury after inflammation. Human variants of the 5-HTT genotypes might be part of the factors determining the extent of nerve injury and hyperalgesia in inflammation.
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Loss of spinal inhibitory mechanisms is thought to contribute to the pathophysiology of abnormal pain states, including neuropathic pain. By using an evoked spinal field potential technique, the hypothesis was tested here that decreased spinal GABAergic control underlies poor response to morphine (MOR) that often accompanies neuropathic pain. Therefore, field potentials evoked by electrical peripheral nerve stimulation during spinal superfusion with MOR were recorded in rats rendered neuropathic by a spinal nerve ligation (SNL) procedure, and compared to responses recorded in naïve rats. ⋯ Two-way analysis of variance revealed no interaction of MOR with either CGP354348 (p = 0.42) or BIC (p = 0.14). Evidence is presented here that injury to the primary afferent system results in significant changes in the ability of spinal MOR to depress field potentials evoked by peripheral input. However, the present findings do not support a pathogenic role for decreased GABAergic inhibition in such changes.
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Randomized Controlled Trial
Effects of simultaneous dual-site TENS stimulation on experimental pain.
Transcutaneous electrical nerve stimulation (TENS) is commonly used for pain relief. However, little robust research exists regarding the combination of parameters required to provide effective doses. This study investigated the hypoalgesic effects of different parameter combinations, applied simultaneously at two sites (segmental and extrasegmental), on pressure pain threshold (PPT) in pain-free humans. ⋯ Those groups using high-intensity stimulation at the segmental stimulation sites showed significantly greater hypoalgesia than placebo (p < 0.025 in each case). The largest hypoalgesic effect was for simultaneous high-intensity stimulation at segmental and extrasegmental sites, using different frequencies. These results reaffirm that high-intensity stimulation (regardless of frequency) is of fundamental importance in effective dosage.
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Randomized Controlled Trial
A randomized controlled trial of exposure in vivo for patients with spinal pain reporting fear of work-related activities.
Pain-related fear is related to disability in persistent pain conditions. Exposure treatment has been reported to be of great benefit in replicated single case experiments. ⋯ Compared to a group receiving usual treatment and waiting for exposure, the exposure in vivo group demonstrated a significantly larger improvement on function. Overall exposure had moderate effects on function, fear and pain intensity. We conclude that exposure may be important in treatment, but is not recommended as a "stand alone" adjunct to usual treatment.