Viral labelling of synaptically connected neurons.

A method has recently been developed to study the neuroanatomical connections in the brain by trans-synaptic tract-tracing via neurotropic viruses. Neurotrop viruses injected into a peripheral organ or directly into the central nervous system are transported axonally. Viruses are expressed in the infected neurons and they are transferred through synapses to reach other neurons. Many research studies illustrate by immunocytochemical detection of the viral proteins that the trans-synaptically interconnected neurons can be visualized, in addition, their neurochemical character can be identified. Thus, viruses could serve as a self-amplifying specific markers of connected neurons along hierarchial chains of functionally related circuits. Herein, we reviewed the methodology of the neuroanatomical studies obtained with a member of a-herpes viruses, the pseudorabies virus, frequently used in tracer studies in rats.