Pathology of the Spinal Cord of C57BL/6J Mice Infected with Rabies Virus (CVS-11 Strain)

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Fixed rabies viruses (CVS-11 strain) were inoculated intramuscularly to C57BL/6J mice, and the pathomorphological changes of the spinal cord including dorsal root spinal ganglion cells were investigated. At 4 days postinoculation (PI), viral antigens were first detected in the spinal neurons and dorsal root spinal ganglion cells without producing morphological changes. At 5 days PI, mild infiltration of lymphocytes was observed around the central canal, small blood vessels and leptomeninges. Cells positive to anti-Iba1 and anti-GFAP antibodies increased significantly from 3 to 5 days PI, respectively. Microglia changed their morphological forms to be ramified or amoeboid, and astroglia extended their cytoplasm from the leptomeninges to the parenchyma. At 7 days PI, apoptotic cells were found in the spinal cord and dorsal root spinal ganglion using TUNEL. We confirmed that most of T lymphocytes and a minority of microglial cells underwent apoptosis, using a combination of TUNEL and immunostaining with antibodies to viral phosphoprotein, CD3, Iba1 and GFAP. On the other hand, astroglial cells and virus-infected nerve cells were negative against TUNEL and cleaved caspase-3 antibody. These findings indicate that T lymphocytes and microglial cells died by apoptosis, whereas virus-infected nerve cells died by necrosis. This was accompanied by increased numbers and morphological changes of glial cells associated with the pathogenesis of CVS-11 in the C57BL/6J mouse.