In gerbils, a dose of 30 µmol/kg po (12.64 µg/kg Ro 61-8048, compound 16) leads to inhibition of the cerebral enzyme which peaked after 2h (∼85% inhibition) and persisted for up to 8 h. Ro 61-8048 (0.1-100 μM) strongly reduces QUIN neo-formation, suggesting that, in vitro, kynurenine hydroxylase activity is required for QUIN neosynthesis.