Changes in behavior and spinal cord dorsal horn CGRP following chronic compression of DRG in rats / 中华麻醉学杂志

ABSTRACT

Objective To develop a reliable and reproducible modei of hyperalgesia arising from chronic compression of dorsal root ganglion (DRG) and investigate the contribution of spinal cord dorsal horn calcitonin gene-related peptide (CGRP) to the clinical manifestation of sciatica.Methods Sixty healthy Wistar rats of either sex weighing 200-300 g were randomly divided into three groups group A control ( n = 12) ; group B sham operation (n = 24) and group C chronic compression of DRG ( n = 24) . In group B and C the animals were anesthetized with intraperitoneal 1.25% thiopental sodium (50mg?kg-1) . The animals were then placed in prone position and the left L4 and L5 intervertebral foramina were exposed. In group C a 4 mm long 1-0 chromic catgut was inserted into the intervertebral foramen. Motor function of the hind limbs was assessed by gait disturbance scores (GDS) , and paw-withdrawal threshold (PWT) was measured with modified Randall algometer 3, 5, 7, 10, 14, 17, 21 and 28 days after operation. In group B and C 12 animals were decapitated on the 5th and 28th days after operation respectively and lumbar section of spinal cord was removed for determination of dorsal horn CGRP content (by radio-immunoassay) and microscopic examination of DRG. Results In chronic compression group (C) significant hyperalgesia occurred after operation and reached a peak one week after operation then gradually decreased but didn't return to normai on the 28th day, while in sham operation group (B) postoperative hyperalgesia quickly decreased and returned to normai on the 7th day. In group C dorsal horn CGRP content on the compressed side significantly increased on the 5th and 28th day after operation as compared with that on the contralateral side in the sham operation and control group. Microscopic examination of DRG showed significant edema of endoneurium and neurons which persisted on the 28th day but significantly attenuated. Conclusion This animal model reliably produces a disorder resembling low back pain. It is easy to perform less traumatic and produces significant hyperalgesia. The dorsal horn CGRP content on the compressed side significantly increases, which is consistent with chronic pain.