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RELATIONSHIP OF PHENYLALANINE TO SEIZURE THRESHOLD DURING MATURATION

—The effect on seizure threshold of the acute intraperitoneal administration of dl‐phenylalanine in varying doses to the albino rat at different ages was investigated. Seizure threshold was measured by the technique using the volatile convulsant, hexafluorodiethylether. The alterations in seizure threshold associated with administration of the amino acid were correlated with blood and brain levels of phenylalanine and tyrosine. In 3‐ to 4‐week‐old albino rats the reduction in seizure threshold was directly related to the amount of phenylalanine administered. The effect was detected at 30 min after injection and had returned to control levels by 2 hr after administration of 20 or 40 mg of Dl‐phenylalanine and by 3 hr following the injection of 80 mg. There was a decreasing susceptibility to reduction in seizure threshold associated with phenylalanine administration with increasing age of the animals. The time course of reduction in seizure threshold in the youngest animals was temporally related more to the rise and fall of concentrations of phenylalanine in brain than to plasma levels of phenylalanine. The seizure threshold in 10‐week‐old animals was not reduced in spite of comparable elevation of blood and brain phenylalanine to the levels effective in 3‐ to 4‐week‐old animals. The results have been discussed in relation to previous studies on chronic, oral administration of phenylalanine to the rat and to possible mechanisms of action.