European journal of pain : EJP
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The tricyclic antidepressant imipramine has shown analgesic effect in human clinical and experimental pain studies. The aim of the present study was to test the effect of imipramine on a pure short-term nociceptive stimulus with pin-prick pain quality. In a randomized, placebo-controlled, double-blind, crossover study, the hypoalgesic effect of a single oral dose of 100 mg imipramine was investigated in 10 healthy volunteers. ⋯ This study demonstrates the important fact that a drug may show clear analgesic effect in some experimental pain models while it is without effect in other models; e.g. imipramine is known to affect pain tolerance and summation thresholds. Pre-clinical tests of potentially analgesic drugs should therefore be based on different pain-stimulation modalities. Copyright 1998 European Federation of Chapters of the International Association for the Study of Pain.
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The formalin test is a well-established model for assessing nociceptive processes and analgesic drug effects. Previous studies have provided statistical validation of optimal procedures for conducting and scoring the rat formalin test. In the mouse model, formalin concentration has been subjected to validation studies. ⋯ Multiple regression analyses defined the optimal second-phase formalin response in outbred, Swiss-Webster mice as 15-35 min post formalin injection, and revealed that the second-phase response is best characterized by the cumulative time spent biting/licking the injected paw. Finally, paw physiological measures provided convergent evidence of nociceptive and antinociceptive processes in the mouse formalin test. Copyright 1998European Federation of Chapters of the International Association for the Study of Pain.
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This study found that in lightly-anesthetized rats a unilateral micro-injection of glutamate (200 mm, 0.5 µl) into the thalamic nucleus submedius (Sm) markedly depressed the radiant heat-evoked tail flick (TF) reflex. After injection, the mean TFL increased 25.6+/-6.5% (n=24) of the baseline at 5 min, up to a peak value (48.4+/-7.2%) at 20 min, and recovered to the baseline level at 60 min. This inhibitory effect was dose-related and repeatable over a time interval of 1.0-1.5 h in the same animal. ⋯ These results confirmed our previous findings that electrical stimulation of Sm depressed the rat TF reflex and that this inhibitory effect was blocked by electrolytic lesion of the VLO or PAG. Therefore, the present study provides further support for the hypothesis that Sm plays an important role in modulation of nociception, and that its effects are mediated by the VLO-PAG pathway, leading to activation of the brainstem descending inhibitory system and depression of the nociceptive inputs at the spinal cord level. Copyright 1998 European Federation of Chapters of the International Association for the Study of Pain.
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Low back pain patients (n=142) on sick leave for at least 8 weeks were given a multi-modal cognitive behavioural treatment program (MMCBT) that lasted for 4 weeks. Before treatment, all patients were tested with a comprehensive test battery. The outcome at 12-month follow-up was predictable from the pretest, but only when combining medical and psychological data. ⋯ Non-returners in the control group lacked energy, trained less regularly, worked in occupations that gave an almost constant load on the back, and did not expect to be back to work in the course of a couple of weeks. It seems to be important to develop further diagnostic tools to identify those who might benefit from extensive or specific treatments. Copyright 1998 European Federation of Chapters of the International Association for the Study of Pain.
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To elucidate neurophysiological mechanisms of persistent pain induced by tissue injury, the present study was designed to investigate the effects of s.c. bee venom injection on responses of the dorsal horn nociceptive neurons and those of behavior in anesthetized and awake cats, respectively. A parallel comparative study was also performed to compare the effects of s.c. bee venom and formalin injections on neuronal responses by using an extracellular single-unit recording technique. The present results showed that s.c. bee venom injection into the peripheral cutaneous receptive field resulted in a protracted, tonic monophase of increase in spike responses of wide-dynamic-range (WDR) neurons for more than 1 h, while injection of the same volume of vehicle did not have such an effect. ⋯ Comparative studies showed that the duration and frequency of the bee venom-induced neuronal responses were comparable to those induced by s.c. formalin; however, responses of WDR neurons to mechanical stimuli applied to the injection site of the two chemical agents were quite different. Bee venom produced a significant enhancement of mechanical responses of WDR neurons, while, on the contrary, formalin produced a desensitization of sensory receptors in the injection site, suggesting that the two tonic pain models may have different underlying mechanisms. Copyright 1998 European Federation of Chapters of the International Association for the Study of Pain.