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Changes in Response Properties and Receptive Fields of Spinal Dorsal Horn Neurons after Spinal Cord Injury in the Rat


, : Changes in Response Properties and Receptive Fields of Spinal Dorsal Horn Neurons after Spinal Cord Injury in the Rat. Anesthesiology Abstracts of Scientific Papers Annual Meeting ( ): Abstract No A-1371

Introduction: Spinal cord injury (SCI) results in a devastating loss of motor and sensory functions below the level of the lesion. Once spinal shock has subsided, there are various degrees of motor function recovery and chronic central pain syndrome,which is characterized as spontaneous pain and hyperalgesia /allodynia, develops in the majority of SCI patients. Little is known about the mechanisms of the central pain following SCI, and the pain has remained refractory to clinical treatments. In order to gain a better understanding of the mechanisms of the pain, we investigated changes in neuronal activity of spinal dorsal horn neurons in the rat following SCI. Methods: Male Sprague-Dawley rats were hemisectioned in the right spinal cord at the level of Th 12 according to a previously described method (1). At 10 to 14 days after the hemisectioning of the spinal cord, when spontaneous pain and mechanical hyperalgesia/allodynia had fully developed, the lumbar spinal cord (L3-4) was exposed by a laminectomy of the Th 13 vertebrae. A single neuronal activity was isolated in wide-dynamic-range (WDR) and high-threshold (HT) neurons of the dorsal horn of the spinal cord under isoflurane anesthesia (0.8%). After determination of the low- and high- receptive fields (RFs), spontaneous activity (SPONT) of the neurons were recorded. Low-intensity mechanical stimuli, such as brushing (BRUSH) using a paint brush and punctate stimuli using a 3.6-g von Frey hair (VF), were applied in the center of the RF, and the responses to the stimuli were recorded. Responses to high-intensity stimuli using a tungsten tip (calibrated force of 35 g, TUN) and an arterial clip (a force of 250 g/mm2, PINCH) were then recorded. Results: The firing rates of spontaneous activity and evoked responses to innocuous as well as noxious stimuli were significantly greater in WDR neurons obtained from SCI animals than in those from sham-operated rats, as is shown in Table1.In HT neurons, the firing rates of evoked responses to PINCH were 4.6+-0.5 and 69.2+-34.3 (/second, means +- SD) in sham-operated and SCI animals, respectively. The low- and high-threshold RF sizes in WDR neurons were significantly greater in the SCI rats (10.2+-4.0 vs.17.4+-5.4 cm2,means+-SD) than in the sham-operated rats (2.9+-1.2 vs. 6.2+-1.9cm2). Conclusions: The results suggest that SCI results in increases in spontaneous activity and evoked responses to innocuous as well as noxious stimuli for WDR neurons. In HT neurons, evoked response to noxious stimuli may increase following SCI. It is likely that these changes in response properties in spinal dorsal horn neurons contribute to the development of behavioral central pain syndrome in SCI patients. Anesthesiology 2002; 96: A1371 Journal Symposium: Mechanism-Based Diagnosis and Therapy of Chronic Pain (9:00 AM-12:30 PM).

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