Studies on the Morphological Changes of Neurons in Dorsal Root Ganglion and Spinal Dorsal Horn of the Rat with an Experimental Peripheral Neuropathy

Lee, Won Taek; Son, Min Gyun; Jung, Gyung Seung; Lee, Hong Suk; Park, Gyung Ah

Abstract

Animal models for human chronic pain syndromes were developed and widely used for pain research. One of thsese neuropathic pain model by Kim and Chung[1992] has many advantages for operation and pain elicitation. We have examined the c-fos protein, substance P, CGRP immunoreactivity in dorsal root ganglia and dorsal horn in this neuropathic model. About 50 Sprague-Dawley rats were used for this study. L5 and L6 spinal nerve were ligated tightly to produce neuropathic pain model. After 2, 4, 8, 16, 24 hours and 1 week of surgery, rats were anesthesized and sacrificed by perfusion through the left ventricle with saline followed by 0.1M phosphate buffer[pH 7.4] containing 3% paraformaldehyde, 3% glutaraldehyde, and 0.1% picric acid. After confirmation of the roots transected by the surgery, the L5 and L6 dorsal root ganglion and spinal cord were removed and processed for immunohistochemistry. All tissue sections were immunohistochemically stained for substance P, CGRP and c-fos by using the peroxidase-antiperoxidase[PAP] method. Count the number of immunostained substance P and CGRP dorsal root ganglion cells and c-fos immunoreactive dorsal horn cells and analyzed statistically with Mann-Whitney U test. The results are as follows. 1. The number of c-fos protein immunoreactive neurons in the superficial layer of dorsal horn were increased markedly at 2 hours after operation, gradually decreased to normal level 1 week after operation. 2. The number of c-fos protein immunoreactive neurons in the deep layer of dorsal horn were gradually increased to the peak 24 hours after operation, decreased to normal level 1 week after operation. 3. The number of substance P and CGRP immunoreactive L5 and L6 dorsal root ganglion neurons were decreased markedly at 1 week after pain model operation. In conclusion, after neuropathic pain model operation, c-fos protein were immediately expressed in the superficial layer of spinal dorsal horn, thereafter c-fos protein in the deep layer of spinal dorsal horn were expressed. CGRP and substance P immunoreactive neurons were decreased markedly 1 week after neuropathic pain model operation.