Pain
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Comparative Study Clinical Trial
Age-related differences in the time course of capsaicin-induced hyperalgesia.
The effect of age on hyperalgesia, one of the most common signs of injury, has not been previously examined in humans. A psychophysical study was conducted in 10 young (26.9+/-4.6 years) and 10 older (79. 0+/-5.7 years) healthy volunteers to investigate the effect of age on the development of hyperalgesia induced by topical application of capsaicin (0.1 ml, 5 mg/ml). The capsaicin patch (diameter 2 cm) was applied for 1 h. ⋯ We conclude that, given the same intensity of noxious stimulation, older adults display a similar magnitude of hyperalgesia as younger persons. However, once initiated, punctate hyperalgesia appears to resolve more slowly in older people. This finding may indicate age differences in the plasticity of spinal cord neurons following an acute injury.
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Clinical Trial
Do beliefs, coping, and catastrophizing independently predict functioning in patients with chronic pain?
Physical and psychosocial disability in patients with chronic pain have been shown to be associated with patients' pain-related beliefs, tendency to catastrophize, and pain coping strategy use. However, little is known about whether beliefs, catastrophizing, and coping strategies are independently associated with patient adjustment. Identification of specific beliefs, cognitive responses, and coping strategies strongly and independently associated with physical and psychosocial functioning would suggest the importance of targeting those variables for modification in treatment. ⋯ Belief scores significantly and independently predicted both physical disability and depression, after controlling for age, sex, pain intensity, catastrophizing, and coping. Coping scores significantly and independently predicted physical disability, but not depression, whereas catastrophizing independently predicted depression, but not physical disability. These findings suggest the importance of targeting specific pain-related beliefs and coping strategies, as well as catastrophizing, for modification in the treatment of patients with chronic pain.
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The omega-conopeptide, ziconotide, is an N-type calcium-channel blocker that has been shown to produce antinociception in animals using formalin and hot-plate tests. Initial reports of intrathecal administration of ziconotide in cancer and AIDS patients whose pain was unrelieved with opioids demonstrated analgesic efficacy. Although adverse effects were reported, these appeared to be easily managed through dose reduction or symptomatic treatment. This clinical report describes the experiences of three patients with serious adverse effects associated with intrathecal ziconotide.
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A total of 68 neurons were recorded from the ventro-postero-lateral nucleus of thalamus (VPL) in rats with a unilateral chronic constriction injury (CCI) of the sciatic nerve (n=20), sham operation (n=24) and naive rats (n=24), and effects of the lesion of dorsal column (DC) pathway [DC lesion or DC+gracile nucleus lesions] on VPL nucleus neuronal activities were studied. In the VPL nucleus contralateral to the CCI (receiving input from the injured nerve), response latencies of low threshold mechanoreceptive (LTM) and wide dynamic range (WDR) neurons to electrical stimulation of the sciatic nerve were significantly longer than that in the contralateral VPL nucleus receiving input from the sham-operated side (P<0.05). In contrast, response latencies of LTM and WDR neurons to DC stimulation were not different between the sham operated and CCI sides (0.05). ⋯ The decrease in noxious stimulus-evoked responses of WDR neurons in the VPL nucleus contralateral to the CCI side after DC and DC+gracile nucleus lesions was greater than that in the VPL nucleus contralateral to the sham operated side and naive animals. These results indicated that DC and DC+gracile nucleus lesions produced selective and stronger effect on noxious responses of VPL nucleus WDR neurons receiving input from the site of nerve injury. The findings suggest that the gracile nucleus-thalamic pathway conveys, or modulates, nociceptive information to the VPL nucleus following peripheral nerve injury, resulting in an increase in VPL nucleus response to noxious stimuli that contributes to the development of mechanical hyperalgesia.
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The rostral ventromedial medulla (RVM) is critical for the modulation of dorsal horn nociceptive transmission. Three classes of RVM neurons (ON, OFF, and NEUTRAL) have been described that have distinct responses to noxious stimuli and mu opioid receptor (MOR) agonists. The present study in barbiturate anesthetized rats investigated the effects of the delta 2 opioid receptor (DOR2) agonist, [D-Ala2]deltorphin II (DELT), microinfused into the RVM on the tail flick reflex and activity of RVM neurons. ⋯ The activity of NEUTRAL cells was not affected. The antinociceptive effects and corresponding changes in ON and OFF cell activity produced by DELT were antagonized by the DOR2 antagonist, naltriben methanesulfonate, administered at the same site. These DOR2 mediated effects on noxious stimulation-evoked changes in RVM neuronal activity are similar to those reported for MOR agonists and suggest that both DOR2 and MOR produce analgesia through activation of OFF cells.