Phenylalanine and phenylacetate adversely affect developing mammalian brain neurons.

Myelin alteration is thought to be the primary pathologic characteristic of phenylketonuria. Clinical symptoms and histologic changes in brain suggest that neuronal insult also may be important. We evaluated the effects of chronic exposure of phenylalanine (0.6 mM) and phenylacetate (0.6 mM) on immature mammalian cortical neuronal cultures. Observations after exposure suggested neuronal drop out. 125I-tetanus toxin binding, choline acetyltransferase activity, high-affinity 3H-GABA uptake, and glutamic acid decarboxylase activity decreased in the presence of either metabolite. Neither substance was a more potent cause of adverse effects. Chronic exposure to either phenylalanine or phenylacetate had a detrimental effect on cultured cortical neurons, both cholinergic and GABAergic.