Influence of age at inoculation on avian oncornavirus-induced brain tumor incidence, tumor morphology, and postinoculation survival in F344 rats.

Intracranial neoplasms were induced by intracerebral inoculation of a standardized, cell-free inoculum of the Bratislava-77 strain of avian sarcoma virus in F344 rats at 1, 9,97 to 99, and 528 days of age. Deaths from diseases that occur spontaneously in aged F344 rats complicated assessment of tumor incidence in rats inoculated at 528 days; 20 of 30 rats inoculated at this age developed brain tumors. All rats inoculated at age 1 day (47 rats), at age 9 days (37 rats), and at 97 to 99 days of age (41 rats) developed brain tumors. The incidence of animals developing tumors was 100% in these three groups, but the incidence of multiple tumors declined with increasing age at inoculation. The mean and variance of postinoculation survival increased from 83.8 +/- 21.5 days for rats inoculated at 1 day of age to 284.6 +/- 151.5 days for rats inoculated at 97 to 99 days of age. Poorly differentiated astrocytomas and astrocytomas of mixed morphology were common among rats inoculated as neonates. Solitary, pilocytic astrocytomas were the most common tumors among rats inoculated as adults.