The pseudorabies virus (PRV) is a neurotropic herpesvirus, it is a pathogen of swine, causing Aujeszky's disease. PRV is a widely used model organism for studies in pathogenesis and molecular biology. This virus is also utilized as a neural circuit tracer. We have developed (1) a real-time RT-PCR method for the global analysis of PRV gene expression; (2) a novel calculation method to examine the relative expression ratios, and which is applicable for the analysis of gene expression in any genetic system that progressively changes in time; (3) PRV-based troponeon expressing transsynaptic tracers which label synaptically connected nerve cells; (4) transgenic viruses encoding differentially colored fluorescent proteins (FPs) and multiple colored FPs to differentiate the brain regions; (5) a method for a short-term culture of isolated cardiac muscle cells that retain their morphological and physiological integrity; (6) a PRV-based system for delivery of foreign genes to cardiomyocytes