Aspartate and glutamate as synaptic transmitters of parallel visual cortical pathways

Push-pull cannulae were inserted into both medial and lateral banks of the suprasylvian sulcus and used for local perfusion with artificial extracellular fluid (aECF). Electrical stimulations of regions of cortex projecting to the lateral suprasylvian area (LSA) were accompanied by enhanced levels of release of excitatory amino acids. Electrical stimulation of the area 17/18 border evoked a greater release of aspartate relative to glutamate in the medial bank of the LSA (posteromedial lateral suprasylvian: PMLS), of glutamate over aspartate in the lateral bank (posterolateral lateral suprasylvian: PLLS) while in the fundus, both were released equally or glutamate levels were slightly elevated over those of aspartate. These data support and extend the earlier proposition (Hicks and Guedes 1983) that an excitatory amino acid mediates synaptic transmission within visual cortico-cortical pathways.