Elsevier

Brain Research

Volume 738, Issue 1, 28 October 1996, Pages 109-120
Brain Research

Research report
Comparison of effects induced by toxic applications of kainate and glutamate and by glucose deprivation on area CA1 of rat hippocampal slices

https://doi.org/10.1016/0006-8993(96)00766-4Get rights and content

Abstract

Baseline and stimulus-induced changes in [Ca2+]o and [K+]o as well as field potentials (fp's) were studied during application of the excitatory amino acids kainate or glutamate, or during glucose deprivation in area CA1 and CA3 of rat hippocampal slices. Bath application of kainate in concentrations of 1, 2, 5, 8 and 10 mM induced a sudden rapid fall of [Ca2+]o in area CA1, associated with a negative shift of the slow fp. Kainate induced disappearance of stratum radiatum (SR) as well as alveus stimulation-evoked postsynaptic fp's, with partial recovery after application of up to 2 mM kainate, but no recovery after 5 mM kainate. Only afferent volleys and repetitive SR stimulation-induced decreases of [Ca2+]o recovered after 5 mM kainate. Similar observations were made with glutamate. Only when glutamate was applied with 20 mM, irreversible disappearance of postsynaptic fp's was noted. Glucose deprivation for 60–90 min led to an initial slow decline of [Ca2+]o in area CA1 and CA3, associated with increases in [K+]o, but no significant changes in the fp baseline. Before reaching the lowest level in [Ca2+]o, stimulation of afferent and efferent fibres in area CA1 and CA3 evoked epileptiform discharges. After reaching the lowest level in [Ca2+]o, all postsynaptic potential components were irreversibly abolished, sparing afferent volleys and SR stimulation-induced decreases in [Ca2+]o. The application of the glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 30 μM) and l-2-amino-5-phosphonovalerate (2APV, 30 μM) during glucose deprivation did not prevent irreversible loss of alveus and SR stimulation-induced postsynaptic signals. These findings suggest that glutamate release during glucose deprivation is not the main factor of acute cell damage.

Introduction

Reduction of glucose supply to the brain can lead to neuronal death, which is thought to be caused by release of excitatory amino acids such as glutamate 21, 24. Glutamate increases the intracellular Ca2+ concentration and mediates destructive processes resulting in neuronal cell death [8]. We have previously shown that glucose deprivation leads to decreases in extracellular calcium concentration ([Ca2+]o) and subsequently to loss of neuronal function [1]. Measurements with ion sensitive/field potential recording electrodes revealed that, after prolonged glucose deprivation, stimulation of the alveus no longer induced ionic changes or field potential (fp) responses in area CA1 of rat hippocampal slices. In this condition stimulation of the Schaffer collateral and commissural (SCC) fibres in stratum radiatum (SR) still induced afferent fibre volleys, which are the equivalent of action potentials in presynaptic fibres, and also small decreases in [Ca2+]o, without any components in fp responses however, which could be ascribed to postsynaptic activation. We concluded that these small [Ca2+]o decreases likely represent presynaptic Ca2+-uptake [1].

In the present study we describe the glucose deprivation-induced decreases in [Ca2+]o and associated fp shifts in more detail, the compare them to similar effects of high doses of glutamate and kainate. We were particularly interested comparing the decreases in [Ca2+]o and changes in fp's induced by toxic concentrations of kainate or glutamate to those induced by glucose deprivation. We also wanted to know whether, after kainate or glutamate application, presynaptic fibres survive the immediate neurotoxic effects. Moreover, we have examined which effects glutamate receptor antagonists exert on decreases in [Ca2+]o during glucose deprivation, and what effects such treatments have on functional recovery of synaptic potentials.

Section snippets

Materials and methods

The experiments were performed on more than 160 transverse rat hippocampal slices. The slices were obtained from adult Wistar rats of both sexes (180–200 g) decapitated under deep ether anesthesia. Transverse hippocampal slices (350 μm) were prepared as described previously [22]and transferred into an interface chamber, where they were continuously perfused with oxygenated (95% O2/5% CO2), prewarmed (36 ± 1°C) artificial cerebrospinal fluid (ACSF) containing (in mM): NaCl 124, KCl 3, CaCl2 1.6,

Results

SR stimulation resulted in typical transient fp responses in area CA1 (Fig. 1B). In SR the stimulus artefact was followed by a first negative deflection, which corresponds to the summed action potential in afferent fibres. This afferent volley was followed by the excitatory field potential (EPSP), which could be superimposed by a positive or negative population spike generated in hippocampal pyramidal cells. In SP the afferent volley was not always visible. Stimulation of the alveus caused a

Discussion

As previously reported by others [9]prolonged glucose deprivation caused irreversible loss of postsynaptic components, which we interpret as indicators of neuronal loss. Such loss was shown in four ways: (1) stimulation of SR no longer induced postsynaptic potentials; (2) increase in [K+]o and decreases in [Ca2+]o induced by stimulation of the SR were strongly reduced; (3) alvear stimulation no longer elicited fp responses; and (4) repetitive stimulation of the alveus failed to provoke any

Acknowledgements

This research was supported by a grant from the SFB 507 and BMFT. We are indebted to M. Bullmann and A. Düerkop for excellent technical assistance. We thank M. Pfeiffer for critical reading of prior versions of the manuscript.

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