Pain
-
The present study examined the effect of peripheral administration of the excitatory amino acid (EAA) glutamate on the intensity of perceived pain and pressure pain thresholds (PPTs) in healthy young women (n=17) and men (n=18). Two injections separated by 25 min of 0.2 ml, 1.0M glutamate into the masseter muscle produced significantly higher scores of pain on 0-10 cm visual analogue scales (VAS) in women than in men (analysis of variance, ANOVA: P<0.001). There was no significant difference between the VAS scores for the first and the second injections in either men or women. ⋯ The reduction of PPTs in the masseter muscle following administration of glutamate in a concentration of 1.0M may reflect allodynia to mechanical stimuli. This process of sensitization was not gender-dependent. The present results suggest that injection of 1.0M glutamate into the masseter muscle may provide a useful experimental method to test sensitization and efficacy of peripheral EAA receptor antagonists in human subjects.
-
Comparative Study
A dissociative change in the efficacy of supraspinal versus spinal morphine in the neuropathic rat.
The efficacy of spinally versus supraspinally administered morphine was studied in rats with a spinal nerve ligation-induced neuropathy. Behavioural assessment indicated that the effect of intrathecally administered morphine on pain-related responses was attenuated when compared with unoperated controls. The decreased efficacy of spinal morphine was associated with neuropathic symptoms, since sham ligation or nerve ligation without accompanying tactile allodynia did not lead to spinal inefficacy of morphine. ⋯ The inhibitory effect of spinally and systemically administered morphine on WDR neuron responses was attenuated whereas that induced by morphine in the PAG was enhanced in neuropathic animals. The results indicate that in spinal nerve ligation-induced neuropathy the efficacy of spinal morphine is decreased whereas that of supraspinal morphine is increased. Descending influence from brainstem-spinal pathways, involving NMDA receptors in the rostroventromedial medulla, may contribute to the selective reduction in tactile antiallodynic efficacy of spinal morphine.
-
Randomized Controlled Trial Comparative Study Clinical Trial
Cold allodynia and hyperalgesia in neuropathic pain: the effect of N-methyl-D-aspartate (NMDA) receptor antagonist ketamine--a double-blind, cross-over comparison with alfentanil and placebo.
Cold allodynia and hyperalgesia are frequent clinical findings in patients with neuropathic pain. While there have been several clinical studies showing the involvement of central sensitization mechanisms and N-methyl-D-aspartate (NMDA) receptor activation in mechanical allodynia/hyperalgesia and ongoing pain, the mechanisms of thermal allodynia and hyperalgesia have received less attention. The aim of the present study was to examine the effect of the NMDA-receptor antagonist ketamine on thermal allodynia/hyperalgesia, ongoing pain and mechanical allodynia/hyperalgesia in patients with neuropathic pain (11 patients with post-traumatic neuralgia and one patient with post-herpetic neuralgia). ⋯ Significant and marked reductions of hyperalgesia to cold (visual analogue score at threshold value) were seen following both alfentanil (4.5 before, 1.4 after, median value) and ketamine (6.8 before, 0.4 after, median value). Alfentanil and ketamine also significantly reduced ongoing pain and mechanical hyperalgesia. It is concluded that NMDA-receptor mediated central sensitization is involved in cold hyperalgesia, but since CPDT remained unaltered, it is likely that other mechanisms are present.
-
Comparative Study Clinical Trial Controlled Clinical Trial
Effects on muscle pain by intramuscular injection of granisetron in patients with fibromyalgia.
We have previously reported that the level of 5-HT in the masseter muscle is increased in patients with fibromyalgia as compared with healthy subjects and that high intramuscular level of 5-HT is associated with muscle pain. We have also reported that injection of the 5-HT(3) receptor antagonist granisetron (GRA) into the masseter muscle of healthy subjects reduced pain induced by 5-HT and abolished allodynia/hyperalgesia. The aim of this study was to investigate whether GRA can influence pain and allodynia/hyperalgesia of the masseter muscle in patients with fibromyalgia. ⋯ Eight of the patients responded to the GRA injection by an increase of PPT during the experimental period that differed from saline. They also showed a tendency to a lower increase of pain intensity after injection of GRA when compared to saline. In conclusion, the results of this study do not prove that injection of the 5-HT(3)-antagonist GRA into the masseter muscle influences local pain and allodynia/hyperalgesia in patients with fibromyalgia.
-
Comparative Study Clinical Trial
Gender differences in pressure pain threshold in healthy humans.
AIMS OF INVESTIGATION: To quantify the magnitude of putative gender differences in experimental pressure pain threshold (PPT), and to establish the relevance of repeated measurements to any such differences. ⋯ Healthy females exhibited significantly lower mean PPTs in the first dorsal interosseous muscle than males, which was maintained for fourteen repeated measures within a 1 h period. This difference is likely to be above clinically relevant levels of change, and it has clear implications for the use of different gender subjects in laboratory based experimental designs utilising PPT as an outcome measure.