Advantages of using recombinant measles viruses expressing a fluorescent reporter gene with vibratome slice technology in experimental measles neuropathogenesis

Aims: In this study of experimental measles neuropathogenesis, the utility of enhanced green fluorescent protein (EGFP) as a sensitive indicator of measles virus (MV) cell-to-cell spread in the central nervous system (CNS) has been assessed in vibratome-cut brain slices to demonstrate the degree and mechanism of viral spread in the rodent CNS. Methods: Recombinant MVs expressing EGFP were visualized at different levels in 200-μm vibratome-cut brain sections from infected animals by confocal scanning laser microscopy (CSLM). Comparison was made with 7-μm microtome sections, stained for the N protein of measles by immunocytochemistry (ICC). Results: The recombinant viruses were readily visualized in infected brain tissue, with no loss of neuropathogenicity. No difference was found in the sites of infection when MV infection was detected through EGFP fluorescence or by ICC. MV-infected cells were detected in the cerebral cortex, olfactory bulb and tract, hippocampus, thalamus, hypothalamus, ependyma and subventricular zone. However, the 200-μm vibratome-cut sections and confocal microscopy proved excellent for demonstrating virus distribution in neurites and for in-depth analysis of the extent of tract infection in the white matter of the cerebral hemispheres such as selective infection of the internal capsule and anterior commissure. Conclusions: The use of self-tracing recombinant MVs, viewed in thick vibratome-cut sections by CSLM, demonstrated that in experimental MV neuropathogenesis the infection is selective and spreads predominately by neurites using defined anatomical pathways.