In this brief review, the function of the excitatory amino acids glutamate and aspartate as neurotransmitters in the nervous system and the vertebrate retina is analyzed. These compounds induce a whole range of cellular responses, due to the presence of distinct types of receptors in postsynaptic cells, showing differences in structure as well as signal transduction mechanisms such as ligand-gating of ion channels or activation of second messenger cascades. The characteristics of these receptors are described in the light of molecular biology studies, and their distribution in neurons and glia from the retina is also documented. Attention is drawn to the recent finding of glial cell excitability in response to neurotransmitters, which opens a new line of cell communication within the nervous system
