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The neuroexcitant effects of aspartame: an investigation using kindling

Memorial University of Newfoundland
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A great deal of controversial evidence has arisen regarding the artificial sweetener Aspartame (NutraSweet). This dipeptide is composed of two amino acids that have been shown to have detrimental effects on brain/behavior function (Olney and Ho, 1970; Nyhan, 1984; Wurtman, 1983B). Aspartame ingestion causes a significant increase in brain phenylalanine and tyrosine, and a decrease in brain tryptophan (Wurtman, 1983), which may change brain excitability (Racine and Coscina, 1979; Cadell, Harlow and Waisman, 1962). The purpose of the present study was to determine if aspartame consumption for a one week period changed brain excitability by reducing after-discharge thresholds as measured by the kindling technique. Animals were stereotactically implanted with one bipolar electrode in Area CA3 of the Hippocampus. After-discharges were obtained for all animals (Day 0). The groups were: Group 0, animals that consumed water, Group 200, animals that consumed 200mg/kg of aspartame in water, and Group 800, animals that consumed 800mg/kg of aspartame, in water. After-discharge thresholds were obtained on Days 1 and 7 of liquid consumption. The mass kindling procedure began on the day following the end of the period of aspartame consumption. All animals were stimulated two or three times a day with the inter-stimulus interval being at least four hours. This was continued until three Stage-5 seizures were obtained. A generalized seizure triggering threshold (GST) was then obtained. The results show that there were no significant differences between food consumption, liquid consumption, weight gain or after-discharge thresholds between the groups. After-discharge thresholds were significantly different over days. A Newman-Kuels analysis comparing after-discharge thresholds for days showed Day0 > Day 1 > Day 7, and the ADT for Day 7 > GST. This was an expected finding since after-discharge thresholds do decrease with repeated stimulations (Racine, 1972A). However, brain excitability is not altered by aspartame consumption using the procedure employed in this study, nor was there any difference found in brain amino acid levels. Future studies should include a more detailed analysis on long-term aspartame consumption. -- Key Words: Aspartame (APM); Kindling; Epilepsy; Phenylalanine (PHE); Aspartic Acid (ASP); Tyrosine (TYR); Tryptophan (TRP); Serotonin (5-HT); After-discharge Threshold (ADT); After-discharge (AD); Generalized Triggering Seizure Threshold (GST); Glutamate (GLU); Seizure.

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