Rabies as a transneuronal tracer of circuits in the central nervous system.

The ability of selected neurotropic viruses to move transneuronally in the central nervous system makes them particularly well suited for use as tracers in experimental neuroanatomy. Recently, techniques have been developed for using rabies virus as a transneuronal tracer. Several features of rabies infection make the virus particularly useful for this purpose. We examined transneuronal transport of rabies in the central nervous system of primates after intracortical and intramuscular injections. Rabies was transported in a time-dependent manner to infect synaptically-connected chains of neurons. Transport occurred exclusively in the retrograde direction. At the survival times we used, rabies infection was restricted to neurons and did not cause cell lysis. There are several methodological and safety issues that must be considered when designing studies that use rabies as a transneuronal tracer. When appropriate protocols and laboratory practices have been established, transneuronal transport of rabies can be a safe and efficient tool for revealing the organization of multi-synaptic circuits in the central nervous system.