The induction of intracranial neoplasms following the intracerebral inoculation of avian sarcoma virus (ASV) in neonatal mammals is well established. The present study demonstrates the susceptibility of adult rats and compares the incidence and morphology of tumors induced by a uniform inoculum of the Bratislava-77 strain of ASV in adult, neonatal, and fetal Fischer 344 rats. Post-inoculation mortality varied significantly between groups inoculated at 1, 10 and 100 days and was most precipitous in perinatally inoculated rats. Percentage of tumor induction declined from 100% among rats inoculated at 1 day of age to 50% among rats inoculated at 100 days of age. The mean number of tumors/animal was inversely proportional to the logarithm of the age at inoculation. A large majority of tumors in each group were glial; the remainder were mesenchymal and mixed glial and mesenchymal. Neuroglial tumors included: mixed gliomas with oligodendroglial and astrocytic elements; and gemistocytic, pilocytic, fibrillary, anaplastic and protoplasmic astrocytomas. Tumors induced in perinates were more heterogeneous in histological pattern while tumors induced in perinates were more heterogeneous in histological pattern while tumors induced in older animals tended to be purely astrocytic and of uniform cell type. Mesenchymal tumors occurred primarily in the meninges and were common among animals inoculated perinatally but were rare among animals inoculated as adults. No neuronal tumors were encountered even among rats inoculated as early as 16 days of gestation.

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