Behavioral deficit in phenylketonuric rats: role of aromatic acid metabolites of phenylalanine.

To investigate the relationship between the biochemical and behavioral deficits in phenylketonuria (PKU), we treated rats from Postnatal Days 2 through 21 with p-chlorophenylalanine plus L-phenylalanine to simulate PKU or with one of the following aromatic acid metabolites of phenylalanine phenylacetate, phenylpyruvate, phenyllactate, and mandelate. Behavioral tests were begun at about 9 weeks of age. Differences between experimental and control animals were found only in the water maze and in the open field. In the former, PKU rats required significantly more trials to reach criterion than controls. None of the single metabolite-treated groups exhibited a similar learning deficit. In the open field, PKU and mandelate-treated rats were hypoactive compared with controls, whereas phenylacetate- and phenylpyruvate-treated rats wee hyperactive. These results demonstrate a lack of congruence between morphological and behavioral effects of treatment, suggesting that performance deficits in PKU rats may be due to interactive effects of 2 or more metabolites.