Glutamic acid as a putative transmitter of the interhemispheric corticocortical connections in the rat

The effect of hemidecortication on the endogenous levels of amino acids in medial, sulcal, and dorsal frontal cortex as well as in parietal, temporal, and occipital cortex of the rat was investigated. Under aseptic conditions, the right cerebral cortex was aspirated by suction. Then, 21 days later, the content of glutamic acid, aspartic acid, gamma-aminobutyric acid, glycine, serine, threonine, and alanine was analyzed in six areas of the intact contralateral cortex using GLC. The results demonstrated a specific decrease in the endogenous levels of glutamic acid in both parietal and temporal cortex after hemidecortication of the contralateral side. This finding suggests that glutamic acid may serve as a neurotransmitter for some of the interhemispheric corticoparietal and corticotemporal fibers. In a follow-up experiment, the effect of a frontal lesion on the endogenous levels of the same amino acids in the striatum was also examined. In this case, the glutamic acid content exhibited a decrease of 31% relative to the control value. This observation confirms the earlier finding of a glutamate-containing pathway from the frontal cortex to the striatum.