Overexpression of MAP2 and NF-H Associated with Dendritic Pathology in the Spinal Cord of Mice Infected with Rabies Virus

Abstract

Rabies is a viral infection that targets the nervous system, specifically neurons. The clinical manifestations of the disease are dramatic and their outcome fatal; paradoxically, conventional histopathological descriptions reveal only subtle changes in the affected nervous tissue. Some researchers have considered that the pathophysiology of rabies is based more on biochemical changes than on structural alterations, as is the case with some psychiatric diseases. However, we believe that it has been necessary to resort to other methods that allow us to analyze the effect of the infection on neurons. The Golgi technique is the gold standard for studying the morphology of all the components of a neuron and the cytoskeletal proteins are the structural support of dendrites and axons. We have previously shown, in the mouse cerebral cortex and now with this work in spinal cord, that rabies virus generates remarkable alterations in the morphological pattern of the neurons and that this effect is associated with the increase in the expression of two cytoskeletal proteins (MAP2 and NF-H). It is necessary to deepen the investigation of the pathogenesis of rabies in order to find therapeutic alternatives to a disease to which the World Health Organization classifies as a neglected disease.

Keywords: Golgi–Cox; MAP2; NF-H; dendrite pathology; immunohistochemistry; rabies virus; spinal cord.

Figure 1

Rabies immunoreactivity in the spinal cord of mice. (A,C) Infected mouse. (A) Note the presence of rabies antigens in all the cells of the cervical spinal cord (10×). (C) Neurons in the ventral horn are marked as positive for rabies. The distribution of viral antigens throughout the cytoplasm illustrates the cellular morphology (40×). (B,D) Control mouse. Note non-immunoreactivity and non-labeling of viral antigens. (B) (10×) and (D) (40×).

Figure 2

Immunoreactivity of Microtubule-Associated Protein (MAP2) in the mouse spinal cord. (A,C) Control mouse. (A) There is notable immunoreactivity of the soma and neuropil in all of the laminae of the ventral horn. (C) At higher magnification, heavy staining is evident in the cytoplasm (perikaryon) but not in the nuclei. (B,D) Infected mouse. Infection with rabies virus increased immunoreactivity to MAP2 in the neurons and neuropil of the spinal cord (Panoramic images (A,B) are at 10× magnification. (C,D) are at 40×).

Figure 3

Immunoreactivity to heavy neurofilamets (NF-H) in the mouse spinal cord. (A,C) Control mouse. (A) The panoramic image reveals diffuse staining in the gray matter. (B) At higher magnification, notable immunostaining is evident in the perikaryon (but not the nucleus) and the neural processes. (B,D) Infected mouse. Infection with rabies virus resulted in increased immunoreactivity to NF-H in neurons and neuropil in the spinal cord. Note the greater number of processes in the infected animal (D) in comparison to the control (C) (Panoramic images (A,B) are at 10× magnification. (C,D) are at 40×).

Figure 4

Golgi–Cox staining in samples from the control and infected groups. (A,C) Control mouse. Soma and a dense dendritic net are observed in the ventral horn of the spinal cord. Panel C highlights a motor neuron in the center of the image. (B,D) Infected mouse. Infection with rabies virus resulted in a notable decrease in the number and length of the dendrites of each of the neurons. This is reflected in a lower-density dendritic net. (Panoramic images (A,B) are at 5× magnification. (C,D) are at 40×).