Articles: hyperalgesia.
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Chronic pain, lymphoedema, post-irradiation neuropathy and other symptoms are reported in as many as 75% of women following breast cancer treatment. This study examined pain and sensory abnormalities in women following breast cancer surgery. Sensory tests were carried out on operated and contralateral sides in 15 women with spontaneous pain and sensory abnormalities and 11 pain-free women. ⋯ Pinprick-evoked pain was correlated to spontaneous pain but not to flux. Spontaneous pain was not correlated to flux. Sensitization seems to be a feature in breast cancer-operated women with pain, but not in pain-free women.
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Complete or partial spinal section at T(8) has been shown to block tactile allodynia but not thermal hyperalgesia following L(5)/L(6) spinal nerve ligation (SNL), suggesting the supraspinal integration of allodynia in neuropathic pain. In the present study, the possibility of mediation of nerve injury-associated pain through tonic activity of descending nociceptive facilitation arising from the rostroventromedial medulla (RVM) was investigated. Specifically, the actions of brainstem cholecystokinin and the possible importance of sustained afferent input from injured nerve fibers were determined using pharmacological and physiological approaches in rats with SNL. ⋯ These results suggest that changes in supraspinal processing are likely to contribute to the observed poor efficacy of opioids in clinical states of neuropathic pain. These data also indicate that the activation of descending nociceptive facilitatory pathways is important in the maintenance of neuropathic pain, appears to be dependent on CCK release, and may be driven from sustained afferent input from injured nerves to brainstem sites. Collectively, these data support the hypothesis that abnormal tonic activity of descending facilitation mechanisms may underlie chronic pain from peripheral nerve injury.
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Reg Anesth Pain Med · Sep 2000
Randomized Controlled Trial Clinical TrialEffect of oral mexiletine on capsaicin-induced allodynia and hyperalgesia: a double-blind, placebo-controlled, crossover study.
Mexiletine is a sodium channel blocker that has been used for the treatment of a variety of neuropathic pain syndromes. A recent double-blinded placebo-controlled study concluded that it was ineffective in the treatment of allodynia associated with neuropathic pain. However, this study failed to achieve adequate plasma levels of mexiletine. This was a study in healthy volunteers that sought to push the drug to dose-limiting side effects and then evaluate the effects on human experimental pain. ⋯ Mexiletine has minimal effects on human experimental pain. It is severely limited by side effects and tolerable doses seem to be void of effects on normal neurosensation and facilitated pain induced by capsaicin and thermal heat pulses.
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Moxonidine, a novel imidazoline-alpha2-adrenergic receptor-selective analgesic, was recently identified as antinociceptive but has yet to be evaluated in neuropathic pain models. alpha2-adrenergic receptor-selective analgesics, and high-efficacy opioids, effectively inhibit neuropathic pain behaviors in rodents. In contrast, morphine potency and efficacy decreases in states of neuropathic pain, both in rodents and in humans, but may be restored or enhanced by coadministration of morphine with alpha2-adrenergic receptor-selective analgesics. The current experiments extend the evaluation of opioid-coadjuvant interactions in neuropathic subjects by testing the respective antihyperalgesic interactions of moxonidine and clonidine with morphine in a test of mechanical hyperalgesia. ⋯ Moxonidine and clonidine both synergize with morphine to inhibit paw withdrawal from nociceptive mechanical stimuli in nerve-injured mice.
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Neuroscience letters · Aug 2000
Morphine and gabapentin decrease mechanical hyperalgesia and escape/avoidance behavior in a rat model of neuropathic pain.
A behavioral test paradigm that measures the aversive quality of stimulus-evoked pain in an animal model of neuropathic pain (L5 ligation) was tested for sensitivity to (1) different forces (476 and 202 mN) and frequencies (once every 15 or 30 s) of mechanical stimulation to the hyperalgesic paw and (2) different doses of the common antinociceptive compounds morphine (1 and 10 mg/kg) and gabapentin (30 and 90 mg/kg). Compared to non-ligated controls, the greater force (476 mN) and frequency (every 15 s) of mechanical stimulation of the hyperalgesic paw was associated with the greatest degree of escape/avoidance behavior. ⋯ The antinociceptive and antiaversive effects were found at doses that did not produce evidence of decreased motor activity. It is concluded that the behavioral test paradigm used to measure the aversiveness of stimulus-evoked nociceptive behavior is sensitive to different degrees of evoked pain and traditional analgesic compounds.