Changes of hippocampal beta-alanine and citrulline levels are paralleling early and late phase of retrieval in the Morris Water Maze
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Although a series of amino acids (AA) have been associated with spatial memory formation, there is limited information on concentrations of beta-alanine and citrulline in rodent brains. Given the importance of AA metabolism in cognitive functions it was the aim of the study to determine hippocampal levels of beta-alanine and citrulline in rats during two different phases of memory retrieval in a spatial memory paradigm. Ten rats were used per group and the first group was trained and sacrificed five min, the second six hours following retrieval in the Morris Water Maze (MWM) and the third and fourth group were untrained, yoked controls. Hippocampi were taken and free AA were determined using a well-established HPLC protocol. Beta-alanine and citrulline levels were higher in trained rat hippocampi, during both, early and late phase of memory retrieval. Taurine, methionine, cysteine, lysine and ornithine levels were higher in yoked rats at the late phase while tyrosine was higher in yoked rats during the early phase. There were no significant correlations between time spent in the target quadrant and any of the AA levels. Herein, an AA pattern, different between yoked and trained animals at early and late phase of memory retrieval is shown, indicating probable involvement of different AA pathways in animals trained and untrained in the MWM. The results may be useful for the interpretation of previous studies and the design of future experiments to identify amino acids as possible targets for modulating spatial memory.
author list (cited authors)
Sase, A., Dahanayaka, S., Höger, H., Wu, G., & Lubec, G.