Articles: hyperalgesia.
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Rats in which the sciatic nerve is partially transected develop hyperalgesia which is relieved by sympathectomy. We carried out experiments using this model of experimental peripheral neuropathy to examine the peripheral mechanisms underlying sympathetically maintained pain. Subcutaneous injection of noradrenaline (NA) into the affected paw exacerbated the hyperalgesia but had no effect in control animals. ⋯ Following a chemical sympathectomy, hyperalgesia was eliminated and injection of NA into the hyperalgesic paw had no effect on pain thresholds. We concluded that NA exacerbates hyperalgesia in this experimental model by acting on alpha 2-adrenoreceptors which are located on post-ganglionic sympathetic terminals. Our results are consistent with the proposal (Levine et al. 1986) that activation of these adrenoreceptors brings about an increased release of prostaglandins which sensitises nociceptors.
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This study analyzed hypersensitization in sensory systems after mechanical irritation of the dorsal root ganglion. ⋯ This experimental model reliably produced a disorder resembling an acute phase sciatica and should help further advance the understanding of pathomechanisms of spinal pain after irritation of the dorsal root ganglion in humans.
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In 40 rats anaesthetized with enflurane, we identified convergent dorsal horn neurones responding to both noxious (pinch) and innocuous (brush) mechanical stimulation of their receptive fields on the tail. We recorded extracellular activity before and during ischaemia of the receptive fields, as well as during subsequent reperfusion. Two NSAIDs, indomethacin and diclofenac sodium, or saline were applied locally to the spinal cord before the induction of ischaemia. ⋯ The neurones became hypersensitive to both pinch and brush during reperfusion of their receptive field, and receptive field size increased. Application of indomethacin and diclofenac sodium to the spinal cord abolished both the hypersensitivity and the increase in receptive field size. Our results indicate that spinal cord prostanoid synthesis facilitates the enhanced excitability of dorsal horn convergent neurones to both noxious and innocuous mechanical stimuli during reperfusion of their receptive fields, but does not affect the neurones' responses to receptive field ischaemia, nor their responses to mechanical stimuli in the absence of a conditioning stimulus.
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Acta neuropathologica · Jan 1995
Neurotransmitters in the spinal cord dorsal horn in a model of painful neuropathy and in nerve crush.
We tested the hypothesis that neurochemical changes in the spinal cord dorsal horn associated with neuropathic pain states differ from those seen in association with non-painful neuropathies. Immunohistochemistry was performed on spinal cord sections from rats with a chronic constriction injury (CCI), which develop hyperalgesia, and from animals with a nerve crush injury, which do not develop hyperalgesia or other signs of a painful syndrome. Immunohistochemistry was quantified by computer-assisted densitometry. ⋯ Met-enkephalin (Met-enk) immunoreactivity was increased in CCI and unchanged in crush. Although SP and CGRP are involved in pain transmission, we conclude that their decrease in immunoreactivity is not specific for the CCI model, but rather a more general event in nerve de- and regeneration. The increase in immunoreactivity for the opioid peptide Met-ink, however, was only seen in the late phase of CCI, and may be specific for conditions associated with neuropathic pain and its resolution.
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Reversible functional joint disorders (joint blockages, somatic dysfunction) of the intervertebral and rib joints can be treated using manual therapy, which improves the related segmental changes in both the dorsal and the ventral area [pseudoradicular syndrome, hyperalgesia zone (HAZ)]. This phenomenon is triggered by a decrease in the heightened nociceptor irritation in the joint capsule and in the surrounding tissues. ⋯ From our results we conclude that blocking of the peripheral nociceptors, rather than of the peripheral nerve bundles, is of primary significance for the effective treatment of anterior thoracalgia.