Spatial and temporal patterns of transneuronal labeling in CNS neurons after injection of pseudorabies virus into the sciatic nerve of adult rats.
The distribution of labeled neurons in the brain and spinal cord was studied after injecting the Bartha strain of pseudorabies virus (PRV) into the sciatic nerve to provide a baseline for studying neural circuitry after spinal cord injury (SCI) and regeneration. Following a single injection of viral particles into the left sciatic nerve, PRV labeling was found in the spinal cord at 2 days post-injection (p.i.). Increasing complexity in viral labeling from the spinal cord to supraspinal regions became apparent with increasing survival time. In brain regions, several neuronal groups that regulate sympathetic outflow, such as the rostroventrolateral medulla, the lateral paragigantocellular nuclei, and the A5 cells, were densely labeled. However, relatively sparse labeling was noticed in the lateral vestibular nuclei, the red nucleus and the motor cortex whose spinal projections regulate somatic motor function, although those areas were abundantly labeled with Fast blue (FB) in a double-labeling experiment in which FB was co-injected into the lumbar cord. The pattern of viral labeling became more complex beyond 5 days p.i. when increased numbers of cell groups were labeled with PRV but not FB. In addition, some infected neurons started to lyse, as evidenced by a decrease in viral labeling at 7 days p.i. Thus, the 5th day post-viral injection would appear to be an appropriate survival time to obtain maximal labeling with acceptable specificity. We suggest that transneuronal labeling using PRV should be appropriate for studying multi-neural circuitry after SCI and regeneration.