ABSTRACT
After intramuscular (m. tibialis anterior) injection of three different algogenic substances, the pain intensity was continuously scored on a visual analogue scale (VAS) in eight volunteers. The subject drew the distribution of the local and referred pain areas on a map. Four times within the first hour after injection, the pressure pain-thresholds (PPTs) and supra pressure-pain thresholds were assessed at the injection point, 2 cm distal from the injection site, at the arm, and at the contralateral leg. Measurements were done before and after injection of 0.5 ml of the algogenic substance [bradykinin (BKN), serotonin (5-HT), substance P (SP)], and isotonic saline as control. Cutaneous sensitivity to mechanical stimuli was assessed with a Von Frey hair at the same location as PPT determinations.The pain intensity (VAS-peak) after BKN (2, 4, and 10 nmol) and 5-HT (2, 4, and 20 nmol) was significantly higher (p< 0.05) than after SP (0.2, 0.4, and 0.8 nmol) and isotonic saline. The VAS-peak after infusions of hypertonic saline was significantly higher (p< 0.05) compared with VAS-peaks after all other substances. A significantly larger (p< 0.05) local pain area was found after BKN compared with isotonic saline. After injections of hypertonic saline, the offsets of evoked pain were significantly longer (p< 0.05) and the local and referred pain areas were significantly larger (p< 0.05) compared with all other substances. There was no dose-response relation between the pain intensity and the different doses of BKN, 5-HT, and SP. PPTs and skin sensitivity were not affected by any of the injections.We conclude that under the present experimental conditions, BKN and 5-HT can produce low levels of muscle pain after intramuscular injection. In the used concentrations, however, BKN, 5-HT, and SP did not generate cutaneous or muscular hyperalgesia. Copyright 1999 European Federation of Chapters of the International Association for the Study of Pain.
ABSTRACT
Positron emission tomography (PET) and accumulation of H(2)(15)O as a marker of neuronal activity were used to create maps of cerebral blood-flow changes evoked by painful heat stimulation in 10 subjects. Two levels of painful tonic and phasic heat stimuli were applied with use of a newly developed contact heat thermode on the volar surface of the dominant (right) arm. The subjects participated in two separate PET sessions. Maps reflecting low and high levels of painful tonic heat were obtained in the first session, and low and high levels of painful phasic heat in the second session. The subjects scored their peak pain intensity and unpleasantness on 10-cm visual analogue scales. For each subject, PET images were aligned to nuclear magnetic resonance (NMR) images and remapped into the standardized co-ordinate system of Talairach. After normalization of the PET volumes, subtraction images were formed voxel-by-voxel and converted to a t-statistic volume. The perceived pain intensity and unpleasantness were identical with painful tonic and phasic heat stimulation. Directed searches revealed significant blood-flow increases in the contralateral primary sensorimotor cortex (MI/SI), SII, insular cortex and cingulate cortex when the low tonic heat map was subtracted from the high. A similar, but not identical, pain-processing network was observed for the maps representing the subtraction of low and high phasic heat. In this subtraction, the blood-flow increases in MSI/SI did not reach statistical significance, and significant blood flow decreases were found in the contralateral middle temporal gyrus. Finally, the location of the activation site in the cingulate cortex was different from that observed during tonic heat pain. This study has provided more evidence for the existence of a common pain-processing network engaged during the perception of different levels of toxic and phasic heat pain. Copyright 1998 European Federation of Chapters of the International Association for the Study of Pain.
