β-galactosidase expressing recombinant pseudorabies virus for light and electron microscopic study of transneuronally labeled CNS neurons

A β-galactosidase expressing pseudorabies virus (Bartha strain) was constructed, injected into the adrenal gland of rats, and subsequently shown to transneuronally label the CNS autonomic neurons that project to sye sympathoadrenal preganglionic neurons. Virally infected neurons were visualized with a one-step histochemical reaction using the Bluo-Gal substrate (halogenated indolyl-β-d-galactoside) for the localization of β-galactosidase activity. In some infected neurons, a Golgi-like staining of the primary and sometimes secondary dendrites could be obtained. For electron microscopic studies, the Bluo-Gal substrate produces an electron-dense reaction product that is easily identified at both low and high magnification. This virus may be useful for the study of the cell architecture and synaptic organization of transneuronally labeled neurons of functionally defined neural circuits. These results also demonstrate that it is possible to deliver foreign genes into specific chains of neurons in the mammalian CNS by means of the retrograde transneuronal viral labeling method.