ABSTRACT
This chapter describes the evidence for glutamate as a neurotransmitter in brain. The acidic amino acids, aspartate and glutamate, are probably quantitatively the most important excitatory transmitters in the central nervous system. The main difficulty in studying the role of glutamate as a transmitter or, even more, to identify the transmitter pool of glutamate is the widespread role of glutamate in brain metabolism. The hippocampal formation is phylogenetically an old part of the cerebral cortex. It is a laminar structure where the different fiber connections are organized in a well-defined pattern. The area dentata is the major entrance of fibers to the hippocampus. The mossy fibers show a specific labeling with d-aspartate or l-glutamate at the electron microscopic level. Most fibers in the descending fornix originate from the pyramidal cells of the subiculum. The corticostriatal pathway therefore satisfies all the four criteria for glutamate as a neurotransmitter. This region has become important for studying different aspects of transmitter glutamate.
