Objective To study the effects of 90 d butyl 2, 4-dichlorophenoxyacetate (2, 4-D b.e.) exposure on learning and memory behavior and levels of amino acid neurotransmitters in rats' pallium and hippocampi．
Methods A total of 40 healthy 30-day-old Wistar male rats (SPF grade) were divided into four groups at random: control group (corn oil:distilled water=1:1) and 2, 4-D b.e. low, middle, and high dose experimental groups (at doses of 6, 18, and 36 mg/kg, representing 1/100 LD50, 3/100 LD50, and 6/100 LD50 respectively), 10 in each group. Administration by gavage was performed 5 times a week for 90 d. After 4, 8, and 13 weeks, Morris water maze test was used to evaluate the learning and memory abilities of rats. At the end of the study, the animals were decapitated to determine the contents of glutamate, asparaginic acid, gamma amino butyric acid, and glycine in pallium and hippocampi by high performance liquid chromatography.
Results After 13 weeks, the results of Morris water maze demonstrated that the mean escape latency increased with higher concentrations of 2, 4-D b.e. (P<0.05) in a dose-effect manner (r=0.961 1,P<0.01). With the concentration of 2, 4-D b.e. increasing, in pallium the level of glutamate showed a rising tendency (P<0.05), the level of gamma amino butyric acid showed a falling tendency (P<0.05), both in a dose-effect relationship (r=0.942 5,r=-0.887 2, bothP<0.01); and the content of asparaginic acid in the high dose group was significantly elevated (P<0.05). In hippocampi the contents of both glutamate and asparaginic acid showed an increasing tendency (P<0.05), whereas the content of gamma amino butyric acid showed a falling tendency (P<0.05), all displaying a dose-effect relationship (r=0.970 1,r=0.886 6,r=-0.916 2, all P<0.01).
Conclusion Sub-chronic 2, 4-D b.e. exposure could affect the learning and memory ability and the levels of ammo acid neurotransmitters in brain tissues of rats.
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