Spinal nerve lesion induces upregulation of constitutive isoform of heme oxygenase in the spinal cord - An immunohistochemical investigation in the rat

The influence of carbon monoxide (CO) on chronic spinal nerve lesion induce d spinal cord neurodegeneration was examined using immunohistochemical expr ession of the constitutive isoform of its synthesising enzyme, hemeoxygenas e-2 (HO-2) in a rat model. Spinal nerve lesion at L-5 and L-6 level was pro duced according to the Chung model of neuropathic pain and rats were allowe d to survive for 8 weeks. Sham operated rats, in which the spinal nerves we re exposed but not ligated, served as controls. Ligation of spinal nerves i n rats resulted in an upregulation of HO-2 expression which was most pronou nced in the ipsilateral gray matter of the spinal cord compared to the cont ralateral side. In these rats, morphological investigations showed distorte d neurons, membrane disruption, synaptic damage and myelin vesiculation. Sh am operated rats did not show an upregulation of HO-2 expression and the st ructural changes in the spinal cord were absent. These observations strongl y suggest that spinal nerve lesion is associated with an increased producti on of CO which is somehow contributing to the neurodegenerative changes in the spinal cord, not reported earlier.