Articles: hyperalgesia.
-
Am. J. Med. Genet. B Neuropsychiatr. Genet. · Aug 2003
Association between human mu-opioid receptor gene polymorphism, pain tolerance, and opioid addiction.
Central to both pain responses and opioid addiction is activity at the micro -opioid receptor. To explore the role of the micro -opioid receptor gene (OPRM) in human pain tolerance and opioid addiction, we examined the relationships among OPRM genotype and experimental pain tolerance in opioid addicts in methadone treatment (n = 50) and healthy normal controls (n = 59). Pain phenotype (pain tolerant vs. pain intolerant) was operationalized as tolerance to a standardized noxious stimulus (either thermal or mechanical), and dichotomized based on distribution. ⋯ Although the established relationship between the phenotypes of opioid addiction and pain intolerance was validated (P = 0.02), genotype differed neither between addict-affected vs. control, nor pain tolerant vs. intolerant subjects. The variant A118G was absent in all individuals and the C17T polymorphism appeared in only three African-American individuals (two addicts and one control). The absence of this polymorphism, the small sample size and the heterogeneous ethnic backgrounds of participants in the pilot study allow only tentative conclusions based on the results, thus the role of the opioid receptor in pain and opioid reward response remains uncertain.
-
Randomized Controlled Trial Comparative Study Clinical Trial
Different lipid profiles as constituencies of liquid formula diets do not influence pain perception and the efficacy of opioids in a human model of acute pain and hyperalgesia.
Nutritional support and pain control by medication are often used concomitantly, but interactions are hardly investigated. A randomised, double-blind, cross-over study in ten right-handed volunteers was performed evaluating the influence of cholecystokinin (CCK)-excretion on the perception of pain in a standardised model. CCK-excretion was induced by a liquid formula diet with either long- or medium-chain triglycerides (LCT, MCT). ⋯ In a second series of experiments, alfentanil (4.1+/-0.5 mg) was administered for 90 min using target-controlled infusions and measurements were performed as stated above. Oral administration of LCT as well as MCT may lead to different CCK blood levels, but we found no evidence for CCK-induced effects on pain sensation, touch-evoked allodynia, secondary hyperalgesia or morphine-induced anti-nociception in humans. In our studies, liquid formula diets did not influence acute pain perception or the efficacy of opioids in a human model of pain.
-
Comparative Study
Intramuscular injection of tumor necrosis factor-alpha induces muscle hyperalgesia in rats.
The role of proinflammatory cytokines in neuropathic and inflammatory pain is well established. Recent studies suggest that cytokines such as tumor necrosis factor-alpha (TNF) may also be involved in the development of muscle pain. To investigate the pathophysiology of intramuscular TNF, exogenous TNF (0.1-10 microg), formalin (9%) or vehicle was injected into the gastrocnemius or biceps brachii muscles of rats. ⋯ TNF and formalin evoked intramuscular upregulation of CGRP and NGF, whereas PGE2 was increased exclusively after TNF injection. These findings allow us to speculate that endogenous TNF may play a role in the development of muscle hyperalgesia. Targeting proinflammatory cytokines might be beneficial for the treatment of musculoskeletal pain syndromes.
-
Comparative Study
Unilateral carrageenan injection into muscle or joint induces chronic bilateral hyperalgesia in rats.
Chronic musculoskeletal pain is a major clinical problem and there is a general lack of animal models to study this condition. Carrageenan is commonly used to produce short-lasting acute inflammation and hyperalgesia in animal models. However, the potential of carrageenan to produce chronic, long-lasting hyperalgesia has not been evaluated. ⋯ At 1 week, the inflammation converted to primarily a macrophage response with scattered mast cells. The data suggest that animals injected with 1 or 3% carrageenan in the knee joint or gastrocnemius muscle could be used as models of acute inflammation through 24 h and chronic inflammation after 1 week. Furthermore, 3% carrageenan injected into deep tissues produces hyperalgesia that spreads to the contralateral side, at the same time period as the inflammation transforms from acute to chronic.
-
Developmental differences in short- and long-term responses to pain, especially surgical pain, have received minimal attention. The purpose of the present study was to examine postoperative responses in rats of developmental ages paralleling the infant to young adult human. ⋯ The more rapid recovery of the younger animals from the mechanical allodynia but not thermal hypersensitivity after surgery suggests the presence of developmental differences in modulation of A-fiber sensitization after surgery. However, the lack of age difference in recovery of thermal hypersensitivity after surgery suggests that sensitization of C-fiber input has a similar time course of resolution of pain over the ages studied in this model. The neural bases for these developmental differences are under study and may lead to a better understanding of pain during development and altered approaches to treatment of postoperative pain in neonates and infants.