Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
-
We recently showed that C-tactile fibres (CTs) in human hairy skin (anterior leg) mediate crossover between innocuous touch and noxious touch, i.e. mechanical allodynia. Although there is no evidence for existence of a phenotypically identical class of CTs in human glabrous skin, the 'qualia' of affective stimuli are comparable across skin types. In 42 healthy subjects, muscle pain was induced by infusing hypertonic saline (5 %) into flexor carpi ulnaris muscle. ⋯ Furthermore, brushing produced a near-identical expression of C-fibre-mediated allodynia. Prior to induction and upon cessation of muscle pain, vibration and brushing were reported as non-painful. Based on these results, we postulate that a functional homologue of the CTs (hairy skin) mediates allodynia in human glabrous skin.
-
Studies of humans, monkeys and rodents have implicated combined gray and white matter damage as important for development of chronic pain following spinal cord injury (SCI). Below-level chronic pain and hyperalgesia following injury to the spinal white matter, including the spinothalamic tract (STT), can be enhanced by excitotoxic influences within the gray matter at the site of SCI. Also, excitotoxic injury of thoracic gray matter without interruption of the STT results in below-level heat hyperalgesia. ⋯ Skin temperature recordings revealed enhanced sympathetic activation by nociceptive heat stimulation following spinal QUIS injury. However, increased sympathetic activation with peripheral vasoconstriction should enhance cold aversion, in contrast to the observed increase in heat aversion. Thus, peripheral sympathetic vasoconstriction can be ruled out as a mechanism for heat hyperalgesia following excitotoxic gray matter injury.