Regional distribution of D-amino acids in the rat brain

Regional distribution of D-amino acids in the rat brain was studied by highly sensitive HPLC analytical method. The method includes fluorogenic derivatization of each amino acid, isolation of each amino acid by reverse-phase HPLC, followed by enantiomeric separation with a chiral stationary phase. D-Amino acid contents were determined in the cerebrum, cerebellum, hippocampus, medulla oblongata. pituitary gland and pineal gland. A remarkably high concentration of D-aspartate was found in the pineal gland (approx. 3,5micromol/g wet tissue) and a smaller amount was found in the pituitary gland (approx. 80nmol/g). D-Alanine was present exclusively in the pituitary gland (approx. 26nmol/g), whereas minute levels of D-leucine were found in the pineal gland (approx. 3.4nmol/g) and the hippocampus (approx. 1.6nmol/g). D-Serine was detected in various regions except for the cerebellum and medulla oblongata. No other D-amino acids were found by this method. In addition, we developed polyclonal anti-D-aspartate antibody, with which we immunolocalized D-aspartate within the pineal gland. D-Aspartate was present in the cytoplasm of pinealocyte, the predominant cell type in the gland. D-Aspartate immunoreactivity was more evident in the distal region than in the proximal region of the gland. The pinealocytes in the distal region are presumably involved in the synthesis and secretion of the pineal hormone, melatonin, suggesting that D-aspartate may have correlation with melatonin secretion.