Hippocampal glutamate receptors.

For years, the hippocampus has been the privileged domain of anatomists and electrophysiologists for investigating various neurobiological processes. The present review deals with recent work which shows that this structure is also well suited to study the role of glutamate as a neurotransmitter and more particularly the characteristics of glutamate receptors and their possible involvement in hippocampal function. After a brief description of the main anatomical features of the hippocampus, we attempt a critical evaluation of the electrophysiological studies of hippocampal glutamate receptors. We then describe the properties of Na-independent 3H-glutamate binding sites in hippocampal membranes, and discuss the possibility that these binding sites are related to postsynaptic glutamate receptors. Finally we show that these binding sites are extremely labile and that hippocampal membranes possess various mechanisms which regulate their number. In particular we develop the idea that the calcium-stimulation of 3H-glutamate binding in hippocampal membranes may be the mechanism by which electrical activity regulates the number of glutamate receptors at hippocampal synapses and thus induces long-lasting changes in synaptic transmission.