No Change in Spontaneous Behavior of Rats after Acute Oral Doses of Aspartame, Phenylalanine, and Tyrosine

Abstract

No Change in Spontaneous Behavior of Rats after Acute Oral Doses of Aspartame, Phenylalanine and Tyrosine. MULLENIX, P. J., TASSINARI, M. S., SCHUNIOR, A., AND KERNAN, W. J. (1991). Fundam. Appl. Toxicol. 16, 495–505. Spontaneous behavior subsequent to acute oral administration of high doses of aspartame, phenylalanine, or tyrosine was analyzed using a computer pattern recognition system. Sprague-Dawley male rats (250–300 g) were dosed orally with aspartame (500 or 1000 mg/kg), phenylalanine (281 or 562 mg/kg), or tyrosine (309 or 618 mg/kg), and their behavior was analyzed 1 hr after dosing. The computer pattern recognition system recorded and classified 13 different behavioral acts performed by the animals during the first 15-min exploration of a novel environment. Three measures that provide independent information concerning motor output from the central nervous system were taken: the number of behavioral initiations, total time, and time structure. These results were compared with the effects induced by d-amphetamine. Plasma concentrations of phenylalanine and tyrosine were determined from blood samples taken immediately after behavioral examination. Data analysis revealed that these doses of aspartame, phenylalanine, and tyrosine did not induce any significant changes in spontaneous behavior. Unlike low doses of amphetamine and despite high plasma concentrations of phenylalanine and tyrosine, no behavioral alteration was detected by the computer pattern recognition system. Absence of behavioral changes in this study using an objective analysis of behavior raises questions concerning the relationship between amino acid precursor loading and purported anecdotal changes in behavior following aspartame administration.