gms | German Medical Science

Objective: This work aimed to investigate the efficacy among some experimental lesions in the spinal cord on inducing a chronic painful state in rats.

Method: Twenty Sprague-Dawley rats weighting 200 – 300g were randomly divided into 4 experimental groups: sham (S), Longitudinal dorsal section (LDS), spinal cord hemisection (SCH), and dorsal hemisection (DH). All rats but in sham underwent a laminectomy and spinal cord lesion. Prior to surgery and up to 3 months thereafter, mechanical and thermal thresholds were determined using automatized von Frey filament and hot plate tests. Three months after surgery, animals were sacrificed and the thoracic segment of the spinal cord was removed for determination of the lesion extension and immunohistochemical characterization (neurofilament-200 and GABA). All animal procedures were approved by the Ethical Committee at our institution.

Results: Among the lesions investigated, SCH was the most effective on inducing chronic pain (p<0.05). Thermal thresholds reduced from 100% to 65% on the relevant side within the first week (p<0.05). Mechanical thresholds, on the other hand, reduced to a higher degree from 100 to 60% on the relevant side (p<0.05). In the other groups, no statistical significant difference could be observed. Histologically, a drastic reduction on the number of NF-200 and GABA-positive cells were seen in the SCH group.

Conclusions: Our results show that spinal cord hemisection seems to be a more adequate model to assess chronic myelopathic pain in rats, as compared to other SC lesions. Furthermore, lesions restricted to the thick myelinated fibers in the dorsal columns were not sufficient to generate pain, what may indicate a relative importance of the anterolateral pain system over the dorsal columns.