The transneuronal labeling properties of three genetically engineered forms of the Bartha strain of pseudorabies virus (PRV) were studied in the ocular sympathetic pathway of rats. Bartha PRV mutants in which expression of the viral glycoprotein gI (homologous to gE of herpes simplex virus type 1, HSV-1) was restored (Bartha gI+) or which express a wildtype form of glycoprotein gIII (homologous to gC of HSV-1 and referred here as Bartha gIIIKa) were analyzed. In addition, a Bartha PRV mutant (Bartha beta-gal) containing the lacZ gene encoding E. coli beta-galactosidase inserted into the gX gene (homologous to gG of HSV-1) was also studied. These were compared to the parental strain--Bartha PRV. The pattern of transneuronal labeling in the intermediolateral cell column was studied 4 days after 5 microliters of different concentrations of viral stocks were injected into the anterior chamber of the eye. The optimal infectious dose required to produce the maximal number of cases with specific transneuronal labeling of sympathetic preganglionic neurons was determined and these were as follows: Bartha PRV = 10(7.5) pfu/ml, Bartha beta-galactosidase = 10(6.5) pfu/ml, Bartha gIIIKa = 10(5) pfu/ml, Bartha gI+ = 10(4) pfu/ml. An inverse relationship between specificity and infectivity rate was observed. Bartha beta-gal produced the greatest number of cases with specific labeling (76%); Bartha gI+ produced the lowest level (10%) and thus, this virus is not useful for transneuronal labeling studies. Bartha gIIIKa labeled more sympathetic preganglionic neurons (second-order neurons) than Bartha beta-gal or Bartha PRV. Bartha gIIIKa and Bartha beta-gal viruses labeled more interneurons (third-order) than the standard Bartha PRV.(ABSTRACT TRUNCATED AT 250 WORDS)