Pain
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Attentional disruption has been demonstrated using laboratory-induced pain, but has not been reliably established in everyday pain conditions. This study is the first to examine the effect of everyday acute headache on attention. Seventy-five frequent headache sufferers completed a flanker task, n-back task, attentional switching task, and dual task. ⋯ Headache did not, however, alter performance on the dual task, or the size of the attentional switching effect or result in a flanker effect. It must therefore be emphasised that headache pain appears to impair general task performance, irrespective of task complexity, rather than specific attentional mechanisms. Headache pain has an effect on the core cognitive components necessary for the successful completion of tasks, and in particular those involving the updating of the cognitive system.
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In patients with complex regional pain syndrome (CRPS) type 1, processing of static tactile stimuli is impaired, whereas more complex sensory integration functions appear preserved. This study investigated higher order multisensory integration of body-relevant stimuli using the rubber hand illusion in CRPS patients. Subjective self-reports and skin conductance responses to watching the rubber hand being harmed were compared among CRPS patients (N=24), patients with upper limb pain of other origin (N=21, clinical control group), and healthy subjects (N=24). ⋯ However, patients with CRPS of the right hand reported significantly stronger neglect-like symptoms and significantly lower illusion strength of the affected hand than patients with CRPS of the left hand. The weaker illusion of CRPS patients with strong neglect-like symptoms on the affected hand supports the role of top-down processes modulating body ownership. Moreover, the intact ability to perceive illusory ownership confirms the notion that, despite impaired processing of proprioceptive or tactile input, higher order multisensory integration is unaffected in CRPS.
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Pontospinal noradrenergic neurons form part of an endogenous analgesic system that suppresses acute pain, but there is conflicting evidence about its role in neuropathic pain. We investigated the chronology of descending noradrenergic control during the development of a neuropathic pain phenotype in rats following tibial nerve transection (TNT). A lumbar intrathecal cannula was implanted at the time of nerve injury allowing administration of selective α-adrenoceptor (α-AR) antagonists to sequentially assay their effects upon the expression of allodynia and hyperalgesia. ⋯ Contralateral thermal hyperalgesia was also reversibly uncovered by yohimbine administration in a contact heat ramp paradigm in anaesthetised TNT rats. Following TNT there is an engagement of inhibitory α2-AR-mediated noradrenergic tone which completely masks contralateral and transiently suppresses the development of ipsilateral sensitization. This endogenous analgesic system plays a key role in shaping the spatial and temporal expression of the neuropathic pain phenotype after nerve injury.
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Pain and sensitization are major issues in patients with osteoarthritis both before and after total knee arthroplasty (TKA) and revision TKA (re-TKA). The aim of this study was to assess sensitization in patients with and without chronic pain after re-TKAs. Twenty patients with chronic knee pain and 20 patients without pain after re-TKA participated. ⋯ Additionally, significant correlations between knee pain intensity and cuff PPTs, temporal summation, and CPM and between total duration of knee pain and temporal summation were found (P<.05). This study demonstrated widespread sensitization in patients with pain after re-TKA and highlighted the importance of ongoing nociceptive input for the chronification process. This has important implications for future revisions, and precautions should be taken if patients have widespread sensitization.
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Cannabinoid agonists such as Δ(9)-tetrahydrocannabinol (THC) are more potent and/or efficacious antinociceptive agents in female than male rats using acute pain models. We tested the hypothesis that THC is more effective in females than males using a model of longer-lasting, inflammatory pain. THC's anti-allodynic, anti-hyperalgesic, and anti-edema effects were examined 1, 3, and 7 days after injection of complete Freund's adjuvant (CFA) into the hind paw. ⋯ THC's anti-edema effect in males. This study suggests that cannabinoids may be better at reducing edema in males while being more effective against inflammatory pain in females. Furthermore, sex differences in THC's peripheral effects against inflammatory pain may be a result of activation of both types of cannabinoid receptors in females, in contrast to predominantly CB1 receptors in males.