Pain
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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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Headaches can be evoked by activation of meningeal nociceptors, but an involvement of pericranial tissues is debated. We aimed to examine a possible extracranial innervation by meningeal afferents in the rat. For in vivo neuronal tracing, dextran amines were applied to the periosteum underlying the temporal muscle. ⋯ Noxious stimulation of the temporal muscle caused CGRP release from the dura mater and elevated meningeal blood flow. Collaterals of meningeal nerve fibers project through the skull, forming functional connections between extra- and intracranial tissues. This finding offers a new explanation of how noxious stimulation of pericranial tissues can directly influence meningeal nociception associated with headache generation and why manual therapies of pericranial muscles may be useful in headaches.
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Fibromyalgia (FM), characterized by chronic widespread pain, is known to be associated with heightened responses to painful stimuli and atypical resting-state functional connectivity among pain-related regions of the brain. Previous studies of FM using resting-state functional magnetic resonance imaging (rs-fMRI) have focused on intrinsic functional connectivity, which maps the spatial distribution of temporal correlations among spontaneous low-frequency fluctuation in functional MRI (fMRI) resting-state data. In the current study, using rs-fMRI data in the frequency domain, we investigated the possible alteration of power spectral density (PSD) of low-frequency fluctuation in brain regions associated with central pain processing in patients with FM. rsfMRI data were obtained from 19 patients with FM and 20 age-matched healthy female control subjects. ⋯ According to the results, patients with FM exhibited significantly increased frequency power in the primary somatosensory cortex (S1), supplementary motor area (SMA), dorsolateral prefrontal cortex, and amygdala. In patients with FM, the increase in PSD did not show an association with depression or anxiety. Therefore, our findings of atypical increased frequency power during the resting state in pain-related brain regions may implicate the enhanced resting-state baseline neural activity in several brain regions associated with pain processing in FM.
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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.