Pain
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The respective roles of the ventral posterior complex (VP) and of the more recently described VMpo (posterior part of the ventral medial nucleus) as thalamic relays for pain and temperature pathways have recently been the subject of controversy. Data we obtained in one patient after a limited left thalamic infarct bring some new insights into this debate. This patient presented sudden right-sided hypesthesia for both lemniscal (touch, vibration, joint position) and spinothalamic (pain and temperature) modalities. ⋯ Neurophysiological studies showed a marked reduction (67%) of cortical responses depending on dorsal column-lemniscal transmission, while spinothalamic-specific, CO2-laser induced cortical responses were only moderately attenuated (33%). Our results show that the VP is definitely involved in thermo-algesic transmission in man, and that its selective lesion can lead to central pain. However, results also suggest that much of the spino-thalamo-cortical volley elicited by painful heat stimuli does not transit through VP, supporting the hypothesis that a non-VP locus lying more posteriorly in the human thalamus is important for thermo-algesic transmission.
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Comparative Study
Activation of p38 MAPK in primary afferent neurons by noxious stimulation and its involvement in the development of thermal hyperalgesia.
Alterations in the intracellular signal transduction pathway in primary afferents may contribute to pain hypersensitivity. We demonstrated that very rapid phosphorylation of p38 mitogen-activated protein kinase occurred in dorsal root ganglion (DRG) neurons that were participating in the transmission of noxious signals. Capsaicin injection induced phosphorylated-p38 (p-p38) in small-to-medium diameter sensory neurons with a peak at 2 min after capsaicin injection. ⋯ Intrathecal administration of the p38 inhibitor, FR167653, reversed the thermal hyperalgesia produced by the capsaicin injection. Inhibition of p38 activation was confirmed by the decrease in the number of p-p38-IR neurons in the DRG following capsaicin injection. Taken together, these findings suggest that the activation of p38 pathways in primary afferents by noxious stimulation in vivo may be, at least in part, correlated with functional activity, and further, involved in the development of thermal hyperalgesia.
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Cavernous hemangiomas (cavernomas) of the spinal cord are rare congenital malformations that comprise less than 5% of all intramedullary lesions. Despite this rarity, we describe the third case of central neuropathic itch associated with intramedullary cavernoma. Since fewer than 10 cases of central spinal itch from all causes have been published, this concurrence suggests the possibility of a specific association. ⋯ Such rats develop unilateral dermatomal hyperalgesia and self-injurious scratching and biting (autotomy). Although this pathological grooming is currently interpreted as a response to chronic pain, we propose that it more likely models scratching provoked by central neuropathic itch, as seen in our patient and others. Study of quisqualate-injected rats may provide leads towards new treatments for neuropathic itch.