Foreign genes have been successfully transferred and expressed in experimental animal brains using adenoviral vectors. However, it is not fully understood whether adenovirus-mediated gene transfer causes stressful or cytotoxic injury in brain. A replication-defective adenoviral vector containing the Escherichia coli lacZ gene (AdCMVnLacZ) was directly injected into right hippocampus and lateral ventricle of normal gerbil brains. Temporal and spatial profiles of the expression of lacZ gene products, DNA fragmentation detected by terminal deoxynucleotidyl d-UTP nick end labeling (TUNEL) staining, and heat shock protein 72 (HSP72) immunoreactivity were examined until 21 days after the injection. In the ventricle, lacZ gene was immediately and strongly expressed at 8 hr after the injection of AdCMVnLacZ, with a peak at 1-3 days, and disappeared by 21 days. Although a small number of choroid plexus cells were TUNEL positive at 3 and 7 days, no HSP72 immunostaining was observed in the ventricle. Small-to-moderate expression of lacZ gene was found in the needle route from 8 hr to 3 days after the injection, and a small number of TUNEL-positive cells were detected at the needle track at 1-3 days. In the hippocampus, lacZ gene was markedly expressed around the dentate gyrus (DG) at 8 hr to 3 days with a peak at 1 day. Large number of TUNEL or moderate-to-dense HSP70 staining cells were also detected in the same area. CA1 neuronal cells just adjacent to the needle route showed TUNEL positivity at 1 to 3 days. However, the TUNEL staining was not associated with lacZ gene expression. The majority of lacZ-expressing cells were discriminated from the TUNEL-positive cells, whereas some were double-positive with HSP72 staining in DG. Cellular loss was observed in the CA1 layer around the needle route. An apoptotic change was morphologically observed in the marginal region of the DG at 1-3 days and in the ventricle at 3-7 days. In the sham control group, TUNEL-positive or HSP72-staining cells were only detected around the needle track including CA1 cells adjacent to the needle route. These data suggest that adenoviral gene transfer may induce direct traumatic injury in the CA1 sector near the needle route, indirect apoptotic cell loss in the DG and ventricle, and stressful effect on the dentate granule cells in association with adenovirus infection in normal gerbil brain.