The traditional pain pathway for the transmission of information from the dorsal horn of the spinal cord to the brain is via the anterolateral quadrant white matter of the spinal cord. Based on lesion and tracing studies, tracts located within these sites include the spinothalamic, spi-noreticular, spinomesencephalic, and spinohypothalamic tracts. This area is clearly important for cutaneous pain sensation because lesions of the anterolateral spinal white matter lead to pinprick analgesia in contralateral der-matomes below the level of the lesion. However, recently researchers have demonstrated that surgical lesions of the dorsal midline of the spinal cord have profound effects on visceral pain-related responses in humans, primates, and rodents. Specifically, a punctate thoracic midline mye-lotomy in humans has been demonstrated to relieve cancer-related pelvic and abdominal pain.20,2122,23,24,25 Similar lesions in nonhuman primates reduce the activity of thalamic neurons evoked by colorectal distension26 and in rats, similar lesions reduce or abolish thalamic neuronal responses and/or behavioral responses to colorectal distension,27, 28 duodenal distension,29 pancreatic stimu-lation,30 and hypersensitivity following lower extremity osteotomy.31 Not all ascending information related to the viscera travels by this midline route: dorsal midline lesions abolished visceral inputs to the nucleus gracilis of the medulla,32 but did not affect inputs to the ventrolateral medulla.28 Spinal neurons with viscero-somatic convergence and axonal extensions into the dorsal columns have been demonstrated for primates33 and rats.20,32 In rats, acute inflammation of the colon, produced by the topical application of mustard oil, resulted in increased responses of these postsynaptic dorsal column neurons to colorectal distension.34 Using that model, Palacek and Willis35 demonstrated that the dorsal midline pathway may be necessary for the augmentation of reflex responses that occur secondary to visceral inflammation, but not for the basal reflex responses.
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Are Headaches Taking Your Life Hostage and Preventing You From Living to Your Fullest Potential? Are you tired of being given the run around by doctors who tell you that your headaches or migraines are psychological or that they have no cause that can be treated? Are you sick of calling in sick because you woke up with a headache so bad that you can barely think or see straight?