Age-related changes in susceptibility of rat brain slice cultures including hippocampus to encephalomyocarditis virus

Replication of the D variant of encephalomyocarditis virus (EMC-D) and its cytopathic effects were studied in the brain slice cultures including hippo campus (hippocampal slice) obtained from postnatal 1-, 4-, 7-, 14-, 28- and 56-day-old Fischer 344 rats. At 0, 12, 24, 36 and 48 h after infection, vi rus titres of the slices and culture media were assayed. Viral replication was observed in cultures from 1-to 28-day-old rats, and the highest titre w as recorded in the slice and culture medium from the youngest rat. The peak of virus titre decreased with age and no distinct viral replication was ob served in the cultures from 56-day-old rats. Light microscopy revealed that degenerative and necrotic changes appeared in the infected hippocampal sli ces from 1- to 28-day-old rats, and the changes became less prominent with age. In situ hybridization and indirect immunofluorescence staining showed that positive signals of viral RNA and antigen were prominent in younger ra ts and decreased with age. These results suggest that an age-related decrea se in the susceptibility of rat brain to EMC-D is less related to the matur ation of the immune system but possibly to that of the neurone.