Glutamate as a transmitter of the hippocampal commissural system

In rabbits, after unilateral hippocampus extirpation, glutamate level decreased in the contralateral hippocampal fields CA1, CA3 and area dentata. No change in aspartate content was observed. A detailed analysis of glutamate level in single layers of the dentate area revealed that, after removal of the contralateral hippocampus, glutamate content decreased in those layers receiving normally a dense input of commissural terminals. If, however, deafferented layers border innervation zones of other glutamergic systems, such as of the entorhinal perforant path, their glutamate concentration will normalize after longer survival times. It is concluded that glutamergic fibers of different origin proliferate into the decommissurated areas. As a reflection of this activity, glutamate level rises in those layers where the sprouting originates.