Detection of herpes simplex virus mRNA in latently infected trigeminal ganglion neurons by in situ hybridization

Latent infection of the trigeminal ganglion with herpes simplex virus type 2 (HSV‐2) was studied in guinea pigs by in situ DNA hybridization. Frozen ganglion sections from animals killed during the period of latent virus infection were studied under nondenaturing conditions. Some sections were treated with deoxyribonuclease (DNase) or ribonuclease (RNase) before incubation with HSV DNA probes. HSV probes consisted of viral DNA nick translated and labeled in vitro with tritiated nucleotides. Bacteriophage lambda DNA, similarly prepared, was used as a control probe. The lamba probe was negative in all situations, including HSV‐2‐infected monolayer cells in cell culture. HSV‐2 probes produced heavy label and, therefore, evidence of hybridization with HSV‐2‐infected monolayer cells. When HSV‐2 probes were incubated with latently infected ganglion sections, hybridization was detected in 71% of guinea pigs and 46% of ganglia. Label was seen only in neurons, and in positive ganglia 0.3 to 5% of neurons were labeled. The amount of label was markedly decreased by pretreatment of ganglion sections with RNase but not DNase, indicating that the DNA probes hybridized to HSV messenger RNA in the latently infected ganglia.