Effect of docosahexaenoic acid on axonal damage after spinal cord injury

Rachael E. Ward, Wenlong Huang, John V. Priestley and Adina T. Michael-Titus. Neuroscience Centre, Institute of Cell & Molecular Science, Bart’s and the London, Queen Mary’s School of Medicine and Dentistry, University of London, 4 Newark Street, London E1 2AT.

We have shown that the omega-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) increases neuronal and oligodendrocyte survival in a rat compression model of spinal cord injury (King et al., 2006). As one of the major factors that contribute to the loss of neurological function following spinal cord injury is axonal pathology (Fehlings and Tator, 1995), in the present study we have focused on the effects of DHA on axonal and dendritic damage after compression injury. A laminectomy was performed in adult female Wistar rats (230-250 g) at thoracic level T12 and a 50 g weight was applied to the dorsal surface of the dura mater for 5 min. 30 minutes following compression, rats were intravenously given either saline or DHA (250 nmol/kg). After the DHA injection, one group of rats was placed on a DHA-enriched diet (400 mg/kg/day) whilst one group received normal chow. At least 5 animals were used per grou p. 1 or 6 weeks post-injury, animals were perfused intracardially with saline and 4% paraformaldehyde, under pentobarbital anaesthesia (60 mg/kg, intraperitoneal). The tissue was post-fixed and cryoprotected. 15 μm spinal cord sections were processed for immunohistofluorescence using the following primary antisera: β-amyloid precursor protein (β-APP) (1:500, Zymed), neurofilament-200 (NF-200) (1:2000, Sigma), SMI32 (non-phosphorylated neurofilament, 1:500, Sternberger Monoclonals Inc.), microtubule associated protein-2 (MAP-2) (1:500, Sigma) and myelin basic protein (MBP) (1:500, Roche). Data was expressed as means ± S.E.M. and analysed with one way ANOVA and post-hoc pairwise comparisons using the Bonferroni’s test. β-APP-positive axons were scarce in non-injured animals but prominent in the white matter tracts of saline-treated injured animals. At 1 week, in both groups of DHA-treated animals, β-APP-positive axon number in the dorsal columns was significantly reduced vs. saline-treated injured animals (saline 76±10, DHA injection 34±9, DHA injection and diet 33±11; p<0.05). By 6 weeks, β-APP immunoreactivity in the corticospinal tract and ventrolateral white matter was also significantly reduced vs. saline in both DHA-treated groups (p<0.05). The number of non-phosphorylated neurofilament-positive axons was reduced in injured animals compared to controls. At 1 week, this reduction was significantly reversed in the DHA injection group in the ventrolateral white matter (control 24±1, saline 11±1, DHA injection 19±3, DHA injection and diet 17±1; p<0.05). Similar results were seen in the ventral white matter. The effect of both DHA treatments on the reduction in the number of myelin rings and myelinated neurofilament-positive axons that occurs 1 week post-injury was heterogeneous and requires further evaluation. Neither DHA treatment protected against the injury-induced loss of dendritic MAP-2. In contrast, DHA injection and diet significantly prevented loss of cell body MAP-2 in the dorsal horn (saline -74%, DHA injection -44%, DHA injection and diet -27%; p<0.05) and ventral horn (p<0.05). These results indicate that DHA has major neuroprotective effects against the axonal and dendritic damage c aused by spinal cord injury.

Fehlings M.G. and Tator C.H. (1995). Ex p. Neurol.132: 220-228.
King V.R. et al., (2006). J. Neurosci. 26: 4672-80.

This work was supported by the Corporate Action Trust .