Elsevier

Neuroscience

Volume 85, Issue 4, August 1998, Pages 1183-1193
Neuroscience

Regional and cellular expression of glial (GLT1) and neuronal (EAAC1) glutamate transporter proteins in ovine fetal brain

https://doi.org/10.1016/S0306-4522(97)00673-8Get rights and content
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Abstract

Glutamate transport is a primary mechanism for regulating extracellular levels of glutamate which can have either neurotrophic or neurotoxic effects in the developing brain, depending on its concentration. Using immunoblotting and immunocytochemistry, we tested the hypotheses that expression of neuronal and glial glutamate transporter proteins was regionally and temporally regulated in the developing ovine brain and that expression of the glial isoform early in development was not cell-type specific. Immunoblots for the neuronal glutamate transporter EAAC1 revealed a major band of immunoreactivity at 69,000 mol. wt, whereas glial glutamate transporter-1 (GLT1) immunoreactivity was observed as 73,000 and 146,000 mol. wt proteins. EAAC1 and GLT1 are regulated differently during development, with EAAC1 immunoreactivity being most abundant at 60 and 71 days completed gestation (term=145 days) and dissipating thereafter, while GLT1 immunoreactivity was most abundant at 136 days gestation. By immunocytochemistry EAAC1 expression is neuronal throughout gestation with intense labelling of dendrites within the telencephalon evident at 60 days. Neuropil, neuronal cell bodies and processes are EAAC1-immunoreactive throughout gestation with no evidence of astrocytic or oligodendroglial immunoreactivity. In contrast, GLT1 is expressed by neuronal and non-neuronal cell types during midgestation with astrocyte selectivity developing by 136 days. During midgestation, GLT1 is transiently expressed in neurons of the subplate, cranial nerve nuclei, basal ganglia, and cerebellar cortex.

The major finding of this study, that GLT1 is transiently expressed in various neuronal populations at midgestation demonstrates that the cell-type specificity of the GLT1 phenotype is developmentally regulated and depends on brain maturity.

Keywords

glutamate transport
excitotoxicity
brain development
corticogenesis
neuronal maturation

Abbreviations

DAB
diaminobenzidine
EAAC1
neuronal glutamate transporter
EDTA
ethylenediaminetetra-acetate
EGTA
ethyleneglycolbis(aminoethylether)tetra-acetate
GFAP
glial fibrillary acidic protein
GLT1
glial glutamate transporter-1
MAP2
microtubule-associated protein 2
PAP
peroxidase-antiperoxidase
TBS
Tris-buffered saline
TX
Triton X-100

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