Pain
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Injection of a dilute solution of formalin into a rat hindpaw produces a biphasic nociceptive response consisting of an early phase during the first 5 min after formalin injection and a later phase starting after 15 min and lasting for 40-50 min. The period between the two phases of nociceptive responding is generally considered to be a phase of inactivity. We compared the nociceptive behaviors produced by a single hindpaw injection of 50 microl of formalin with those produced by two formalin injections given 20 min apart. ⋯ As these data were obtained from pentobarbital-anesthetized, spinalized rats, the data suggest further that the two excitatory phases and the active inhibition are mediated by spinal mechanisms and that the inhibition is not under regulation of a GABAergic mechanism. The implication of the results is not only further evidence of physiological control mechanisms interacting to regulate pain, but they also indicate the overriding priority of intrinsic inhibitory mechanisms. This, in turn, suggests that the clinical management of pain may be enhanced by efforts to potentiate mechanisms of inhibition.
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Withdrawal reflex responses to graded von Frey filaments applied to the plantar surface of the paw were measured before and after bone hole damage in rats with either a dorsal column (DC) lesion or a sham DC lesion. Two methods were employed to produce models of osteotomy; a small hole was drilled through either the (1) tibia or (2) calcaneus (Houghton, A. K., Hewitt, E. and Westlund, K. ⋯ Nocifensive behavior, characterized by a lifting and guarding of the damaged limb, was also observed in animals with a hole through the calcaneus. In contrast, we found that interrupting the dorsal column pathway with a small mid-line lesion (1 week prior to the osteotomy) prevented the development of both the primary and secondary mechanical hyperalgesia and allodynia but not the guarding of the damaged limb. This study provides evidence that axons in the medial part of the dorsal column are involved in the development of mechanical hyperalgesia and allodynia after bone hole injury.
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Clinical Trial
Experimental human muscle pain and muscular hyperalgesia induced by combinations of serotonin and bradykinin.
In the present study, we assessed the muscle pain and possible development of muscular hyperalgesia to mechanical stimuli after two subsequent intramuscular infusions of serotonin (5-HT) and bradykinin (BKN). The pain intensity after the infusions was continuously scored on a visual analogue scale (VAS). The subjects drew the distribution of the pain areas on a map. ⋯ Cutaneous sensibility to mechanical stimuli and SPPTs were not affected by any of the combinations. The combinations of serotonin and bradykinin produce experimental muscle pain and muscular hyperalgesia to mechanical stimuli. Pre-treatment with serotonin may enhance the effect of bradykinin in the generation of muscle pain and muscular hyperalgesia in humans.
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Clinical Trial
Gender differences in associations between trauma history and adjustment among chronic pain patients.
This study examines the relationship between a trauma history and emotional functioning in response to a chronic pain condition. We broadened the traditional study of trauma in chronic pain from sexual and physical abuse to include a variety of traumatic events and experiences that occurred not only during childhood, but during adulthood as well. Seventy-three (51% female, 60% lower back) chronic pain patients were administered the Trauma History Questionnaire (Green, B. ⋯ Univariate tests showed that the interaction was significant only for emotional distress variables and not for pain severity and disability. Further, the multivariate effect of Trauma Group and the univariate effects for emotional distress variables were significant only among men. Results indicate that a substantial history of trauma may detrimentally impact a chronic pain patient's ability to manage their pain effectively, particularly among men.
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Patients who develop malignant infiltration of the psoas muscle and the lumbar plexus often experience a severe complex pain syndrome characterised by deep somatic pain, neuropathic pain and psoas spasm. Conventional analgesic regimes may not relieve these symptoms adequately. We describe the use of patient-controlled boluses of local anaesthetic via a psoas sheath catheter in this scenario. The recent availability of portable infusion pumps with the capability to deliver large volume boluses with long lockout times made this intervention possible and allowed the patient to be discharged home with effective relief of pain.