Evidence for the involvement of d-aspartic acid in learning and memory of rat
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d-Aspartic acid (d-Asp) is an endogenous amino acid present in neuroendocrine systems. Here, we report evidence that d-Asp in the rat is involved in learning and memory processes. Oral administration of sodium d-aspartate (40 mM) for 12–16 days improved the rats’ cognitive capability to find a hidden platform in the Morris water maze system. Two sessions per day for three consecutive days were performed in two groups of 12 rats. One group was treated with Na-d-aspartate and the other with control. A significant increase in the cognitive effect was observed in the treated group compared to controls (two-way ANOVA with repeated measurements: F(2, 105) = 57.29; P value < 0.001). Five further sessions of repeated training, involving a change in platform location, also displayed a significant treatment effect [F(2, 84) = 27.62; P value < 0.001]. In the hippocampus of treated rats, d-Asp increased by about 2.7-fold compared to controls (82.5 ± 10.0 vs. the 30.6 ± 5.4 ng/g tissue; P < 0.0001). Moreover, 20 randomly selected rats possessing relatively high endogenous concentrations of d-Asp in the hippocampus were much faster in reaching the hidden platform, an event suggesting that their enhanced cognitive capability was functionally related to the high levels of d-Asp. The correlation coefficient calculated in the 20 rats was R = −0.916 with a df of 18; P < 0.001. In conclusion, this study provides corroborating evidence that d-aspartic acid plays an important role in the modulation of learning and memory.
Keywordsd-Aspartic acid Learning and memory Rat Hippocampus Brain Morris water maze system
We would like to thank Dr. Paola Merolla for editing the present manuscript and Dr. George Nwurim of the Animal Physiology and Evolution Laboratory, Stazione Zoologica Anton Dohrn, Napoli, Italy, for his enlightening suggestions.
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