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

Abstract

Changes in extracellular Ca 2+ 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 μM) 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 μm away in the dendritic layer (stratum moleculare). The β-antagonist propranolol (1 μM) completely blocked the NE-induced enhancement of Ca 2+ signals in the dentate. In contrast to the dentate, NE did not enhance evoked Ca 2+ of K + concentration changes in the CA1 pyramidal cell layer. These results indicate that NE markedly enhanced both Ca 2+ and K + fluxes, probably by a β-receptor-mediated mechanism, in the dentate gyrus during high-frequency stimulation of a type able to elicit long-term potentition (LTP). These increases may underly the action of NE in modulating LTP in the dentate gyrus.