Elsevier

Neuroscience Letters

Volume 69, Issue 2, 29 August 1986, Pages 137-142
Neuroscience Letters

Laminar profiles of the changes in extracellular calcium concentration induced by repetitive stimulation and excitatory amino acids in the rat dentate gyrus

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Abstract

Changes in extracellular free calcium concentration ([Ca2+]o) were measured with ion-selective microelectrodes in the dentate gyrus of the rat hippocampal slice preparation. Repetitive stimulation (20 Hz 10 s) of the perforant path or mossy fibers, or alternatively, iontophoresis of the excitatory amino acids N-methyl-d-aspartate (NMDA) or quisqualate (Quis) elicited decreases in [Ca2+]o (ΔCa2+) which were unequally distributed along the axis of the granule cells. Laminar profiles of the [Ca2+]o changes revealed marked differences between stimulus- and amino acid-induced responses. The ΔCa2+ induced by either anti- or orthodromic stimulation were relatively small (<0.15 mM) and were found to be maximal at the cell body layer (stratum granulosum). In contrast, the excitatory amino acids NMDA and Quis evoked large ΔCa2+ (>1.2 mM) which were maximal at dendritic sites, 100 μm away from the cell body layer in the inner stratum moleculare. The effect of NMDA was reversibly blocked by 2-amino-5-phosphonovaleric acid without antagonism of the synaptic responses or the stimulus-induced changes in [Ca2+]o. Therefore, under normal conditions, NMDA receptors appear not to participate in synaptically induced ΔCa2+ in the dentate gyrus.

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This research was supported by DFG Grant SFB220-B3 to U.H.; I.M. is recipient of MRC Canada and I.W. William Postdoctoral Fellowships.

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