Effect of l-phenylalanine on central nervous system elements in tissue culture.

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Abstract
Tissue cultures of cerebral cortex from newborn puppies were used as experimental models for testing the effects of L-phenylalanine on central nervous system elements. In an attempt to duplicate the pathological condition occurring in the brains of patients with phenylketonuria L-phenylalanine was introduced into the cultures in these concentrations as follows: 25 mg/100 ml, 50 mg/100 ml and 100 mg/100 ml. Until the 53rd day, when the material was exhausted, random samples from each group were assayed for enzyme activity and sudanophilia and compared with controls. Control and experimental cultures were also evaluated in areas where proliferation and maturation of neuroectodermal system had occurred and in areas where fibroblastic activity was predominent. Results indicate that the neuron is the target prone to damage in phenylketonuria. Neuronal damage which may be reversible in the early stages, eliminates, at least temporarily an essential element for myelin formation. In the brains of patients with phenylketonuria, therefore, retardation of myelinization is regarded secondary to neuronal damage. Pathological changes were observed in the neurons and observed seizures were considered as being precipitated by neuronal damage. The lowest concentration of L-phenylalanine did not interfere with cell differentiation while the highest concentration was toxic, producing cell destruction. The intermediate concentration produced neuronal damage suggesting the perikaryon zone as the target area. Although the number of differentiated neuroectodermal cells, especially the parenchymal elements, was lower in the presence of high concentrations of L-phenylalanine, some of the cells did succeed in attaining morphological differentiation in the absence of any evidence of my elinization.

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