Pain
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Comparative Study
Effects of systemic carbamazepine and gabapentin on spinal neuronal responses in spinal nerve ligated rats.
There are few pharmacological studies of central neuronal measures in animal models of neuropathic pain. In the present study we have compared the effects of two anticonvulsants, carbamazepine and gabapentin, on spinal neuronal responses of nerve injured rats (selective ligation of spinal nerves L5 and L6, SNL) and sham-operated rats. The development and maintenance of cooling and mechanical allodynia of the lesioned hindlimb of SNL rats was followed with behavioural indices. ⋯ The peripheral nerve dysfunction reveals an effect of carbamazepine which is maintained throughout the observation period, validating this experimental approach. Gabapentin, a novel treatment for neuropathic pain states, also reduced neuronal responses, but the actions of the drug were not dependent on nerve injury. Further studies at the spinal level may shed light on the physiology and pharmacology of the aberrant processes associated with neuropathic pain.
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Case Reports
Epileptic seizure associated with intracerebroventricular and intrathecal morphine bolus.
We report on two patients with morphine-related seizures associated with either intrathecal or intracerebroventricular administration. Both patients had a history of malignant tumor and both experienced the seizures following bolus application of morphine, while even higher dosages were well tolerated when continuously infused. ⋯ Initiation of intrathecal morphine therapy and bolus application should be performed carefully and only when constant monitoring is provided for at least 12 h. Animal data and possible mechanisms for morphine-related seizures are discussed.
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A cold plate apparatus was designed to test the responses of unrestrained rats to low temperature stimulation of the plantar aspect of the paw. At plate temperatures of 10 degrees C and 5 degrees C, rats with either chronic constriction injury (CCI) of the sciatic nerve or complete Freund's adjuvant (CFA) induced inflammation of the hindpaw displayed a stereotyped behavior. Brisk lifts of the treated hindpaw were recorded, while no evidence of other nociceptive behaviors could be discerned. ⋯ At 60 days, neither morphine nor naltrexone affected cold-induced paw lifting in CFA rats, suggesting that the neuronal circuit mediating cold hyperalgesia in these animals had become opiate insensitive. In conclusion, the cold plate was found to be a reliable method for detecting abnormal nociceptive behavior even at long intervals after nerve or inflammatory injuries, when responses to other nociceptive stimuli have returned to near normal. The results of pharmacological studies suggest that cold hyperalgesia is in part a consequence of altered sensory processing in the periphery, and that it can be independently modulated by opiate and adrenergic systems.
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Recent studies into the common complaint of chronic neck pain have focused on its anatomical origin, identifying especially the cervical zygapophysial joints. However the pathophysiology of chronic neck pain remains poorly understood. In this psychophysical study, responses to electrocutaneous stimulation in subjects with chronic neck pain were examined. ⋯ There was a small difference in detection threshold between the two groups: both pain threshold and pain tolerance were significantly lower in the pain group compared with pain free controls. These findings define hyperalgesia psychophysically and, taken together with the absence of tissue damage at the sites of testing. suggest that these painful cervical regions may be examples of secondary hyperalgesia which, in turn, implies central sensitisation of nociceptive pathways. These results are compatible with studies which identify potential anatomical origins of chronic neck pain but provide evidence that central sensitisation may be the relevant mechanism of pain production.
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The proportion of people 65 years of age and older who report musculoskeletal pain and physical disability is high. The main objective of this study was to determine whether physical disability was associated with the presence of musculoskeletal pain in a sample of senior citizens. Self-administered questionnaires were sent to a sample of 1306 community-dwelling senior citizens in London, Ontario, Canada between August and October 1995. ⋯ Logistic regression analysis, without controlling for potential confounding variables, revealed that those who reported having musculoskeletal pain were seven times more likely to have some difficulty performing three or more activities listed in the questionnaire (OR = 6.91 95% CI 4.92-9.69). When significant confounding variables were controlled in the analysis, seniors who reported musculoskeletal pain were still three times more likely to have some difficulty with three or more activities (OR = 2.93, 95% CI 1.96-4.38). Although no causal relationship can be inferred, thorough pain assessment and pain management may be important in the maintenance of independent living for adults 65 years of age or older.