European journal of pain : EJP
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The effects of gentle mechanical skin stimulation on reflex discharges in cardiac sympathetic nerve evoked by somatic afferent stimulation were studied in anesthetized rats. Mass discharges were recorded from cardiac sympathetic efferent nerve while somatocardiac sympathetic A- and C-reflexes were elicited by single electrical stimuli to myelinated A- and unmyelinated C-afferent fibers of the tibial nerve. Continuous touch was applied to inner thigh skin with a force of 0.12 N for 10 min periods by a soft elastomer "brush" (1.1cm in diameter with 417 microcones). ⋯ We recorded unitary afferent activity from thigh branches of the saphenous nerve and found fibers excited by touch were low-threshold mechanoreceptive Abeta, Adelta and C fibers that have rapidly or slowly adapting properties. In all units tested, average discharge rates during touch period were less than 4 Hz. The results suggest that touch-induced excitation of low threshold cutaneous mechanoreceptive fibers inhibits nociceptive transmission conveyed by C-primary-afferents, via the release of both opioid and non-opioid inhibitory mediators.
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Randomized Controlled Trial
Driving plasticity in the motor cortex in recurrent low back pain.
The sensory and motor systems can reorganise following injury and learning of new motor skills. Recently we observed adaptive changes in motor cortical organisation in patients with recurrent low back pain (LBP), which are linked to altered motor coordination. Although changes in motor coordination can be trained and are associated with improved symptoms and function, it remains unclear whether these training-induced changes are related to reorganisation of the motor cortex. ⋯ Changes were not observed following unskilled walking exercise. This is the first observation that motor training can reverse reorganisation of neuronal networks of the motor cortex in people with recurrent pain. The observed relationship between cortical reorganisation and changes in motor coordination following motor training provides unique insight into potential mechanisms that underlie recovery.
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The precise mechanism by which gonadal hormones influence pain perception is still obscure. However, no studies have examined experimental pain responses at supra-physiological hormone levels. This study explored the influence of pharmacological estradiol (E2) levels on the stability of pain perception obtained via quantitative sensory testing. ⋯ Mixed model repeated measures ANOVA indicated that participants who over-responded to the ovarian stimulation session (E2 > 10,500 pmol/l) showed significant enhanced pain responses under this condition (p=0.004). No correlations between progesterone, LH and experimental pain perception were found in any of the study sessions. Although pain perceptions at different E2 levels remained constant, the enhancement of pain scoring at supra-physiological E2 levels, underscore the possible role of sex hormones in pain modulation and experience.
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The novel analgesic tapentadol combines mu-opioid receptor agonism and noradrenaline reuptake inhibition in a single molecule and shows potent analgesia in various rodent models of pain. We analyzed the contribution of opioid and monoaminergic mechanisms to the activity of tapentadol in rat models of nociceptive and neuropathic pain. Antinociceptive efficacy was inferred from tail withdrawal latencies of experimentally naive rats using a tail flick test. ⋯ Ritanserin did not affect antinociceptive or antihypersensitive ED(50) values of tapentadol. Activation of both mu-opioid receptors and alpha2-adrenoceptors contribute to the analgesic effects of tapentadol. The relative contribution is, however, dependent on the particular pain indication, as mu-opioid receptor agonism predominantly mediates tapentadol's antinociceptive effects, whereas noradrenaline reuptake inhibition predominantly mediates its antihypersensitive effects.