Entorhinal kindling permanently enhances Ca²⁺-dependent L-glutamate release in regio inferior of rat hippocampus

Rats were kindled to two consecutive class 5 seizures by once-daily entorhinal electrical stimulation. After one stimulus-free month, in vitro Ca²⁺-dependent, K⁺-stimulated endogenous amino acid release was measured in regio superior, regio inferior and dentate gyrus of the hippocampal formation. Ca²⁺-dependent l-glutamate release was robust in all 3 regions of controls and greatest in dentate gyrus; release of GABA and l-aspartate were significant in regio superior and dentate gyrus. l-Glutamate release was significantly enhanced in ipsilateral regio inferior of kindled hippocampus and tended to be greater contralaterally. This pattern was not seen in regio superior or dentate gyrus. These studies, in concert with others, suggest that Ca²⁺-dependent l-glutamate release in hippocampus is augmented by entorhinal kindling and that this enhanced release may be primarily from presynaptic granule cell mossy fiber projections.