Histochemical localization of aspartate aminotransferase activity in the hippocampal formation and in peripheral ganglia of the rat with special reference to the glutamate transmitter metabolism.

The regional distribution and cellular localization of aspartate aminotransferase (AspAT), an glutamate/aspartate metabolizing enzyme, was studied in the hippocampal formation, in dorsal root ganglia, and in superior cervical ganglia during the postnatal development of the rat. In the dendritic layers of the hippocampal formation the enzyme activity was found to be very low in newborns, increased markedly from the second week of life and reached adult levels during the postweaning period. These results coincide with parameters of the maturation of glutamatergic structures in this brain region. The staining intensity of AspAT in the peripheral ganglia, in which glutamate/aspartate inputs do not obviously occur, did not display any evident differences during the postnatal development. The increase of AspAT activity parallel to the maturation of glutamatergic/aspartatergic mechanisms suggest that the enzyme studied is involved in glutamate/aspartate neurotransmitter metabolism.