Pain
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Clinical Trial
Mechanisms of spontaneous tension-type headaches: an analysis of tenderness, pain thresholds and EMG.
Pericranial muscle tenderness, EMG levels and thermal and mechanical pain thresholds were studied in 28 patients with tension-type headache and in 30 healthy controls. Each patient was studied during as well as outside a spontaneous episode of tension-type headache. Outside of headache, muscle tenderness and EMG levels were significantly increased compared to values in controls subjects, while mechanical and thermal pain thresholds were largely normal. ⋯ EMG levels were unchanged during headache. It is concluded that one of the primary sources of pain in tension-type headache may be a local and reversible sensitization of nociceptors in the pericranial muscles. In addition, a segmental central sensitization may contribute to the pain in frequent sufferers of tension-type headache.
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Nerve growth factor (NGF) is known to produce hyperalgesia as well as to stimulate synthesis of neuropeptides in dorsal root ganglia (DRG). In the present study, we wanted to determine the effects of local NGF administration and assess to which extent mast cell-dependent factors are mediating NGF responses. Rats received 1 daily unilateral intraplantar injection for 3 days. ⋯ We suggest therefore that NGF-induced local edema was caused by mast cell-derived vasoactive compounds which act together with afferent neuron-derived CGRP to increase vascular permeability. NGF-induced thermal hyperalgesia most likely was caused by an increased sensitivity of peripheral endings of capsaicin sensitive afferents. This effect of NGF was not mediated by products of the cyclooxygenase pathway, and was also observed in mast cell-depleted rats.
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Clinical Trial
Sensory-motor interactions of human experimental unilateral jaw muscle pain: a quantitative analysis.
Experimental muscle pain was elicited by bolus injection of 0.15 ml of 5% hypertonic saline into the human masseter muscle. The sensory experience was described using 10-cm visual analogue scales (VAS) and the McGill Pain Questionnaires (MPQ) on 10 subjects. Effects of pain on deliberately unilateral mastication were quantitatively assessed in 13 other male subjects using kinematic recordings of the mandible and jaw muscle electromyography (EMG). ⋯ Moreover, agonist EMG activity during pain was significantly lower in the ipsilateral masseter muscle (20.3 +/- 25.4%, P < 0.05) as compared to pre-pain root-mean-square (RMS) values. The observed sensory-motor interactions can be explained by a facilitatory effect of activity in nociceptive muscle afferents on inhibitory brain-stem interneurons during agonist action. Thus, generated movements have smaller amplitudes and they are slower which most likely represents a functional adaptation to experimental jaw muscle pain.
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Clinical Trial
The effects of isoflurane on repeated nociceptive stimuli (central temporal summation).
Central temporal summation of afferent nociceptive stimuli is involved in central hyperexcitability. This is assumed to be an important mechanism in the nociceptive system which is probably activated during surgery and trauma. The purpose of the present study was to investigate if isoflurane has a specific effect on central temporal summation in humans. ⋯ In contrast, 2-4-fold higher isoflurane concentrations (1.00-1.50 vol% end-tidal) that normally produce surgical anaesthesia were required to depress the nociceptive reflex to repetitive stimuli. This indicates that central temporal summation in the nociceptive system is a potent mechanism, and that isoflurane has a weak potency for depressing temporal summation in humans. As such isoflurane alone is not adequate for inhibiting surgically evoked hyperexcitability.