In patients who experience unilateral chronic pain, abnormal sensory perception at the non-painful side has been reported. Contralateral sensory changes in these patients have been given little attention, possibly because they are regarded as clinically irrelevant. Still, bilateral sensory changes in these patients could become clinically relevant if they challenge the correct identification of their sensory dysfunction in terms of hyperalgesia and allodynia. Therefore, we have used the standardized quantitative sensory testing (QST) protocol of the German Research Network on Neuropathic Pain (DFNS) to investigate somatosensory function at the painful side and the corresponding non-painful side in unilateral neuropathic pain patients using gender- and age-matched healthy volunteers as a reference cohort. Sensory abnormalities were observed across all QST parameters at the painful side, but also, to a lesser extent, at the contralateral, non-painful side. Similar relative distributions regarding sensory loss/gain for non-nociceptive and nociceptive stimuli were found for both sides. Once a sensory abnormality for a QST parameter at the affected side was observed, the prevalence of an abnormality for the same parameter at the non-affected side was as high as 57% (for Pressure Pain Threshold). Our results show that bilateral sensory dysfunction in patients with unilateral neuropathic pain is more rule than exception. Therefore, this phenomenon should be taken into account for appropriate diagnostic evaluation in clinical practice. This is particularly true for mechanical stimuli where the 95% Confidence Interval for the prevalence of sensory abnormalities at the non-painful side ranges between 33% and 50%.

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.

A midline dorsal column (DC) 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 DC lesion for the relief of pancreatitis pain in awake rats. Homecage activity was measured in rats with pancreatitis or sham surgery. Pancreatitis was induced by infusion of glycodeoxycholic acid (10 mM) into the pancreas and intraperitoneal injection of caerulian (72 microg). Homecage activity was also measured in rats with pancreatitis after either a DC lesion of the C1 level of the spinal cord or a sham DC lesion. A significant reduction in rearing behavior was observed in rats with pancreatitis when compared to sham animals. DC lesions reversed this reduction in rearing activity. This study suggests that the DCs are involved in transmitting nociceptive signals from the pancreas to the brain.

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