Effects of glutamate uptake blockers on stimulus-induced field potentials in rat entorhinal cortex in vitro

L-Glutamic acid (Glu) is a key excitatory transmitter in the central nervous system. Excessive amounts of Glu are highly toxic to neurons and particularly the entorhinal cortex (EC) exhibits a remarkable loss of cells in the superficial layers in acute brain injury. The accumulation of Glu is limited by a family of high-affinity Glu transporters. Using extracellular potential recordings in rat brain slices we tested whether application of the Glu uptake blockers dihydrokainate and L-trans-pyrrolidine-2,4-dicarboxylate (L-trans-2,4-PDC) affect stimulus-induced field potentials (FPs) in superficial layer III and deep layer V of the medial EC. We found that a high concentration (400 microM) of the uptake blockers significantly reduces stimulus-induced FPs in both layers. At lower concentration (200 microM), only dihydrokainate is efficient. The data show that Glu uptake is involved in the control of extracellular Glu levels during synaptic excitation of layers III and V of the medial EC.