Certain neurotropic viruses can invade the nervous system of their hosts and spread in
chains of synaptically connected neurons. Consequently, it is possible to identify entire
hierarchically connected circuits within an animal. In this review, we discuss the use of
neurotropic herpesviruses as neuronal tract tracers. Although a variety of tract tracing
viruses are available, each with its own unique infection characteristics, we focus on the
widespread use of attenuated strains of pseudorabies virus (PRV), a swine herpesvirus with …