Pain
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We examined whether continual constant-rate infusion of lidocaine would provide analgesia during the initial post-injury phase in the chronic constriction injury model of neuropathic pain. Male Sprague-Dawley rats were divided into control and ligated groups and infused with saline or lidocaine (0.15, 0.33, 0.67, and 1.3mg/kg/h) via subcutaneously implanted Alzet((R)) osmotic minipumps. Thermal withdrawal latencies were obtained prior (Day 0) and 3 days after loose sciatic ligation and pump implantation surgery. ⋯ Average plasma lidocaine concentrations were 0.11, 0.36, and 0.45microg/ml for animals receiving 0.33, 0.67 and 1.3mg/kg/h of lidocaine, respectively. These results suggest that continual systemic infusion of lidocaine prevents or reverses the development of neuropathic pain following chronic constriction injury. These results add to the increasing body of evidence supporting the therapeutic value of preemptive and post-operative lidocaine administration for the relief of neuropathic pain.
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Activation of adenosine A1 receptors by endogenous adenosine or synthetic agonists produces anti-nociception in animal models of acute pain and also reduces hypersensitivity in models of inflammatory and nerve-injury pain. Allosteric adenosine modulators facilitate adenosine agonist binding to the A1 receptor. The purpose of the current study was to examine the effect, mechanisms of action, and interaction with noradrenergic systems of intrathecal (i.t.) or oral administration of the allosteric adenosine modulator T62 in a rat model of neuropathic pain. ⋯ Anti-dopamine hydroxylase (DH)-saporin treatment reduce spinal norepinephrine content by 97%, accompanied by an almost complete loss of DH immunoreactive axons in the spinal dorsal horn and neurons in the locus coeruleus. The effect of T62 was completely lost in animals treated with anti-DH-saporin. These data support the hypothesis that activation of the A1 receptor by the allosteric modulator, T62, produces anti-nociception via spinal noradrenergic activation.
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The efficacy of psychological treatments emphasising a self-management approach to chronic pain has been demonstrated by substantial empirical research. Nevertheless, high drop-out and relapse rates and low or unsuccessful engagement in self-management pain rehabilitation programs have prompted the suggestion that people vary in their readiness to adopt a self-management approach to their pain. The Pain Stages of Change Questionnaire (PSOCQ) was developed to assess a patient's readiness to adopt a self-management approach to their chronic pain. ⋯ Principal component analysis supported a two-factor structure: 'Contemplation' and 'Engagement'. Subsequent analyses revealed that the PSEQ was a better predictor of treatment outcome than the PSOCQ scales. Discussion centres upon the utility of the PSOCQ in a clinical pain setting in light of the above findings, and a need for further research.
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Treatment of pain in newborns is associated with problematic drug side effects. Previous studies demonstrate that an intraoral infusion of sucrose and other sweet components of mother's milk are effective in alleviating pain in infant rats and humans. These findings are of considerable significance, as sweet tastants are used in pain and stress management in a number of clinical procedures performed in human infants. ⋯ Taken together, these results indicate that intraoral sucrose alleviates transient pain in response to thermal and mechanical stimuli, and also effectively reduces inflammatory hyperalgesia and allodynia. Sucrose-induced analgesia is age-dependent and limited to the pre-weaning period in rats. The age-dependency of sucrose-induced analgesia and its differential maturation for the fore- and hindpaw may be due to developmental changes in endogenous analgesic mechanisms and developmental modulation of the interaction between gustatory and pain modulatory pathways.
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Comparative Study
Gender differences in temporal summation of mechanically evoked pain.
Several studies indicate that females are more sensitive to experimentally induced pain than males. Moreover, it was recently shown that temporal summation of heat pain is greater in females than males, suggesting that central processing of nociceptive input may be upregulated in women. Temporal summation of pain has been examined principally using thermal or electrical stimuli. ⋯ Temporal summation occurred across all ISIs, but shorter ISIs (1-3 s) elicited significantly greater temporal summation than longer ISIs (4-6 s). Finally, although higher pain ratings were obtained when the ten consecutive stimuli were applied on the same versus different skin areas, the degree of temporal summation was not significantly different. These findings indicate that temporal summation of mechanically evoked pain is higher in females compared to males, is stimulation frequency dependent and is centrally mediated.