Do nociceptive signals from the pancreas travel in the dorsal column?
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A midline dorsal column lesion has been shown to be an effective surgical treatment for the relief of pelvic visceral pain in patients. The aim of this study was to examine the effectiveness of a dorsal column lesion upon: (i) increased electrophysiological responses of neurons in the ventral posterolateral thalamic nucleus in anesthetized rats evoked by the application of bradykinin to the surface of the pancreas, and (ii) pain-related behaviors observed after pancreatic infusion with bradykinin. In rats anesthetized with pentobarbital, recordings from individual thalamic neurons were made using tungsten electrodes. Brief application of bradykinin (10 microg/ml) to the surface of the pancreas resulted in an increased firing rate in approximately 20% of neurons recorded. A dorsal column lesion or intrathecal administration of morphine greatly reduced the excitatory effects of pancreatic bradykinin application on thalamic neurons. In a separate group of rats, bradykinin was infused into the pancreas through a previously implanted catheter resulting in a decrease in exploratory behavior and an increase in other pain-related behaviors, e.g. licking of the abdomen. A dorsal column lesion made prior (1 week) to the bradykinin infusion reduced the decrease in exploratory behavior but did not return exploratory behavior to control levels. In conclusion, nociceptive information relayed to the thalamus about the pancreas is transmitted from the spinal cord through the dorsal columns, possibly by the post-synaptic dorsal column pathway. However, the dorsal column pathway may not be the sole route for relaying information about noxious stimulation of the pancreas, particularly that impacting complex behavioral responses.