exceeds that of control viruses 2 4 u00d7 10 12 ml by od which carry neither cre nor a loxp site to determine the efficiency of viral rearrangement in vivo and whether such rearrangement is dependent on the presence of ligand ad102 7 virus 4 u00d7 10 pfu mouse as determined by optical density were injected via tail vein into rag 2 mice that were pretreated with vehicle alone or 110 u03bcg day of tamoxifen for 7 days as follows rag 2 mice were injected with either pbs mock or 4 u00d7 10 11 adenovirus particles as determined by od 260 of type a virus ad102 7 via the tail vein at various times after injection animals were sacrificed and the liver tissues were removed and frozen rapidly on dry ice to visualize gfp expression in animal tissues mice were anaesthetized and perfused with 4 paraformaldehyde containing 0 2 glutaraldehyde intracardially kafri et al natl genet 17 314 317 1997 and the liver tissues were removed and fixed overnight at room temperature in the perfusion buffer containing 30 sucrose the fixed tissues were sectioned serially and observed under confocal scanning laser microscopy in experiments evaluating the responses of ligand regulated recombinase mice were injected either with vehicle vegetable oil alone or with 110 u03bcg day of tamoxifen for 7 days prior to adenoviral injection liver tissues from these animals were harvested at 2 5 hours post injection the earliest time point taken after injection and hirt dna from approximately 250 mg of frozen hepatic tissue was.