Norepinephrine enhances stimulus-evoked calcium and potassium concentration changes in dentate granule cell layer

Changes in extracellular Ca2+ and K+ concentrations were measured in the dentate gyrus with ion-selective/reference electrodes during high-frequency perforant path stimulation. Bath application of norepinephrine (NE, 50 microM) markedly enhanced both evoked decreases in extracellular calcium and increases in extracellular potassium concentration. These effects of NE were observed in the granule cell layer (stratum granulosum), but not 200 microns away in the dendritic layer (stratum moleculare). The beta-antagonist propranolol (1 microM) completely blocked the NE-induced enhancement of Ca2+ signals in the dentate. In contrast to the dentate, NE did not enhance evoked Ca2+ of K+ concentration changes in the CA1 pyramidal cell layer. These results indicate that NE markedly enhanced both Ca2+ and K+ fluxes, probably by a beta-receptor-mediated mechanism, in the dentate gyrus during high-frequency stimulation of a type able to elicit long-term potentiation (LTP). These increases may underly the action of NE in modulating LTP in the dentate gyrus.