[Neuronal dentritic morphology alterations in the cerebral cortex of rabies-infected mice: a Golgi study]

The neurological signs of rabies are very dramatic. Nevertheless, the infected brain manifests only very subtle histological changes.

The neuronal morphology in the cerebral cortex of rabies-infected mice was examined by means the Golgi technique for detection of neuropathy.

Two groups of mice were inoculated with rabies-one with street virus isolated from an infected dog and the second with fixed CVS (challenge virus standard) virus. At the terminal phase of illness, the animals were sacrificed and fixed for histological staining by perfusion with paraformaldehyde. Next, the brains were treated by the Golgi technique and coronal sections were obtained. Neurons enclosed within 1 mm2 frames of the frontal cortex sections were counted and the sizes of the cellular bodies were measured. Photographs of several depth levels from the sections were obtained.

Cortical pyramidal neurons showed distinctive morphological alterations in the soma and dendrites (including loss of dendritic spines) in 12.9% of cells from intracerebral infected-mice with street virus; in 8.2% of neurons from intramuscular infected-mice with street virus, and in 31.8% of neurons from mice injected intramusculary with fixed virus. In addition, the number of neurons impregnated by the Golgi technique in infected brains was considerably lower than in the non-infected samples.

Rabies virus can induce structural neuron damage. The infection also appears to induce tissue changes that interfere with the chemical mechanisms of the Golgi silver impregnation method.