Articles: hyperalgesia.
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The termination of an unpleasant or painful somatic condition can produce a rewarding sense of relief, even if the stimulus that causes the termination is itself unpleasant or painful under normal circumstances. We aimed to identify central neural mechanisms of pain relief from capsaicin-elicited heat-hyperalgesia by administering cold stimuli. We hypothesized that cooling might facilitate endogenous descending inhibitory mechanisms. ⋯ When neural responses to the 0 degrees C-stimulus were compared between the untreated and capsaicin-treated skin condition there were stronger BOLD-responses in prefrontal cortex (PFC) and periaqueductal grey (PAG) which correlated with increasing perceived pleasantness (VAS). Based on a connectivity analysis which identified cold-dependent contributions of PFC activity with PAG in heat-hyperalgesia we propose that cold-induced pain relief partly results from activation of endogenous descending inhibition of nociception. The data illustrate that perception of nociceptive input may largely be determined by competing aversive-appetitive motivational states.
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Surgical trauma can affect spinal neuronal excitability, but there have been no studies of the effects of surgical cutaneous injury on central nociceptive processing of deep afferent inputs evoked by noxious stimuli such as capsaicin. Thus our aim was to test the effect of surgical cutaneous incision in influencing central sensitization induced by capsaicin injection into the temporomandibular joint (TMJ). The activity of single nociceptive neurons activated by noxious mechanical stimulation of the TMJ was recorded in the trigeminal subnucleus caudalis/upper cervical cord of halothane-anesthetized rats. ⋯ Incision itself induced a barrage of neuronal spikes and excitability increases reflecting central sensitization (cutaneous RF expansion, cutaneous MAT reduction) in most neurons tested whereas lidocaine pretreatment significantly attenuated the barrage and central sensitization. Capsaicin injection into the TMJ induced cutaneous RF expansion, cutaneous MAT reduction and TMJ MAT reduction following lidocaine pretreatment of the cutaneous incision site whereas capsaicin injection following incision alone not only failed to induce further central sensitization but also decreased the existing incision-induced central sensitization (no cutaneous RF expansion, increased cutaneous MAT and TMJ MAT) in most neurons tested. These findings suggest that central sensitization induced by capsaicin alone or by cutaneous incision alone can readily occur in TMJ-responsive nociceptive neurons and that following incision-induced excitability increases, capsaicin may result in a temporary suppression of nociceptive neuronal changes reflecting central sensitization.
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Controlled Clinical Trial
Oral opioid use alters DNIC but not cold pain perception in patients with chronic pain - new perspective of opioid-induced hyperalgesia.
Opioids can elicit unexpected changes in pain sensitivity, known as opioid-induced hyperalgesia (OIH). The aim of this study was to explore whether OIH exists in patients with chronic pain treated with oral opioids (OP) versus non-opioid (NOP) analgesics. The sensitivity to cold pain and the magnitude of diffuse noxious inhibitory control (DNIC) were evaluated in 73 OP and 37 NOP treated patients. ⋯ A regression analysis showed that opioid dosage and treatment duration had a significant negative effect on the magnitude of DNIC in OP treated men (beta=-2.175, p=0.036 and beta=-2.061, p=0.047, respectively). In conclusion, oral opioids usage for the treatment of chronic pain does not result in abnormal sensitivity to cold pain, but seems to alter pain modulation. The use of 'advanced' psychophysics tests such as evaluation of DNIC can help understanding the phenomenon of OIH.
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Previous studies have shown that peripheral nerve injury in rats induces increased expression of the voltage gated calcium channel (VGCC) alpha-2-delta-1 subunit (Ca v alpha2 delta1) in spinal dorsal horn and sensory neurons in dorsal root ganglia (DRG) that correlates to established neuropathic pain states. To determine if injury discharges trigger Ca v alpha2 delta1 induction that contributes to neuropathic pain initiation, we examined allodynia onset and Ca v alpha2 delta1 levels in DRG and spinal dorsal horn of spinal nerve ligated rats after blocking injury induced neural activity with a local brief application of lidocaine on spinal nerves before the ligation. The lidocaine pretreatment blocked ligation-induced discharges in a dose-dependent manner. ⋯ In addition, preemptive intrathecal Ca v alpha2 delta1 antisense treatments blocked concurrently injury-induced allodynia onset and Ca v alpha2 delta1 upregulation in dorsal spinal cord. These findings indicate that injury induced discharges regulate Ca v alpha2 delta1 expression in the spinal dorsal horn that is critical for neuropathic allodynia initiation. Thus, preemptive blockade of injury-induced neural activity or Ca v alpha2 delta1 upregulation may be a beneficial option in neuropathic pain management.
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Arthritis and rheumatism · Oct 2008
Impact of nervous system hyperalgesia on pain, disability, and quality of life in patients with knee osteoarthritis: a controlled analysis.
Refractory, disabling pain associated with knee osteoarthritis (OA) is usually treated with total knee replacement. However, pain in these patients might be associated with central nervous sensitization rather than peripheral inflammation and injury. We evaluated the presence of hyperalgesia in patients scheduled for a total knee replacement due to knee osteoarthritis with refractory pain, and we assessed the impact of pressure pain threshold measurements (PPT) on pain, disability, and quality of life of these patients. ⋯ Patients with pain due to osteoarthritis who were scheduled for total knee replacement showed hyperalgesia of nervous system origin that negatively impacted pain, knee functional capacity, and most aspects of quality of life.