Treatment of pregnant rats with cytosine arabinoside (ara-C, 50 mg/kg, i.p.)at 14 days of gestation severely impaired both prenatal and postnatal whole brain growth in their offspring, although the cerebellum was relatively less affected than whole brain. 2. Rats treated at 5 days of age with ara-C (250 mg/kg, i.p.) showed an impairment in growth of the cerebellum relative to the rest of the brain. 3. Adenine arabinoside (ara-A) treatment, either prenatally or postnatally, had negligible effect on brain growth, even at doses considerably higher than those of ara-C. 4. Adult rats, previously treated with ara-C (50 mg/kg, i.p.) at 14 days of gestation, showed an impairment in discrimination learning when tested in a water T-maze. 5. These results are discussed in relation to the proposed use of ara-C or ara-A as antiviral agents, particularly against intrauterine infection with cytomegalovirus.
