Modulation of glutamate transport and receptor binding by glutamate receptor antagonists in EAE rat brain.

Grzegorz Sulkowski,Lidia Strużyńska,Elżbieta Salińska,Beata Dąbrowska-Bouta,Valentin Ceña

doi:10.1371/journal.pone.0113954

Grzegorz Sulkowski, Lidia Strużyńska + Show 3 more

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https://doi.org/10.1371/journal.pone.0113954

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Abstract

The etiology of multiple sclerosis (MS) is currently unknown. However, one potential mechanism involved in the disease may be excitotoxicity. The elevation of glutamate in cerebrospinal fluid, as well as changes in the expression of glutamate receptors (iGluRs and mGluRs) and excitatory amino acid transporters (EAATs), have been observed in the brains of MS patients and animals subjected to experimental autoimmune encephalomyelitis (EAE), which is the predominant animal model used to investigate the pathophysiology of MS. In the present paper, the effects of glutamatergic receptor antagonists, including amantadine, memantine, LY 367583, and MPEP, on glutamate transport, the expression of mRNA of glutamate transporters (EAATs), the kinetic parameters of ligand binding to N-methyl-D-aspartate (NMDA) receptors, and the morphology of nerve endings in EAE rat brains were investigated. The extracellular level of glutamate in the brain is primarily regulated by astrocytic glutamate transporter 1 (GLT-1) and glutamate-aspartate transporter (GLAST). Excess glutamate is taken up from the synaptic space and metabolized by astrocytes. Thus, the extracellular level of glutamate decreases, which protects neurons from excitotoxicity. Our investigations showed changes in the expression of EAAT mRNA, glutamate transport (uptake and release) by synaptosomal and glial plasmalemmal vesicle fractions, and ligand binding to NMDA receptors; these effects were partially reversed after the treatment of EAE rats with the NMDA antagonists amantadine and memantine. The antagonists of group I metabotropic glutamate receptors (mGluRs), including LY 367385 and MPEP, did not exert any effect on the examined parameters. These results suggest that disturbances in these mechanisms may play a role in the processes associated with glutamate excitotoxicity and the progressive brain damage in EAE.

Highlights

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disease of the CNS
The current study demonstrated changes in glutamate transport and the expression of mRNA for specific glutamate transporters (GluTs), alterations in MK-801 ligand binding to specific NMDA receptors, and ultrastructural disturbances in nerve endings during the clinical course of EAE
The results reported in the present work indicate that the expression of mRNA for the tested glutamate transporter 1 (GLT-1), glutamate-aspartate transporter (GLAST), and EAAC1 increased in the forebrain of the EAE rats during the acute phase of the disease (12 d.p.i.)

Summary

Introduction

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disease of the CNS. The characteristic features of the disease include demyelinating areas in the white matter of the spinal cord and brain, which lead to disturbances in nerve transmission [1,2]. The process of inflammation is accompanied by increased levels of soluble inflammatory cytokines and enhanced levels of glutamate and excitotoxicity. These mechanisms have been proposed as major determinants of the neurodegeneration observed in MS and its animal model EAE [1,3,4,5]. Correlations between altered glutamate homeostasis, cell death, axonal damage, and disturbances in glutamatergic neurotransmission have been identified during MS/EAE pathology [7,8,9]

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