Selective excitatory amino acid uptake in glutamatergic nerve terminals and in glia in the rat striatum: quantitative electron microscopic immunocytochemistry of exogenous (D)-aspartate and endogenous glutamate and GABA.
To characterize glutamate/aspartate uptake activity in various cellular and subcellular elements in the striatum, rat striatal slices were exposed to 10 and 50 mu M exogenous (D)-aspartate. After fixation with glutaraldehyde/formaldehyde the distribution of (D)-aspartate was analysed by postembedding immunocytochemistry and the ultrastructural distribution was compared with the distributions of endogenous glutamate and GABA. Light microscopically, (D)-aspartate-like immunoreactivity was localized in conspicuous dots along very weakly labelled dendritic profiles and neuron cell bodies. At the electron microscope level gold particles signalling (D)-aspartate occurred at highest density in nerve terminals making asymmetrical contacts with postsynaptic spines (i.e. resembling synapses of cortical afferents). Astrocytic processes also contained gold particles, but at a lower density than nerve endings. In contrast, dendritic spines were only weakly (D)-aspartate-positive. The difference in labelling at 10 and 50 mu M (D)-aspartate was consistent with 'high-affinity' uptake. Neighbouring sections processed with other antibodies showed that the D-aspartate labelling. Occurred in nerve terminals strongly immunoreactive for glutamate, rather than in terminals very weakly glutamate-immunopositive or in nerve endings immunoreactive for GABA. Glutamate labelling of perfusion-fixed striatum confirmed that terminals forming asymmetrical synaptic contacts with spines were enriched with gold particles, suggesting that these terminals use glutamate as a transmitter. This study demonstrates that high-affinity uptake sites for excitatory amino acids in the striatum are most strongly expressed on presumed glutamatergic nerve terminals and on astrocytes.
Gundersen
V
V
Anatomical Institute, University of Oslo, Norway.
Ottersen
O P
OP
Storm-Mathisen
J
J
D000818:Animals; D001224:Aspartic Acid / Q000493:pharmacokinetics*; D003342:Corpus Striatum / Q000378:metabolism* / Q000648:ultrastructure; D018846:Excitatory Amino Acids / Q000493:pharmacokinetics*; D005404:Fixatives; D005971:Glutamates / Q000378:metabolism*; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D009411:Nerve Endings / Q000378:metabolism* / Q000648:ultrastructure; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018846:Excitatory Amino Acids; D005404:Fixatives; D005971:Glutamates; D001224:Aspartic Acid; D005680:gamma-Aminobutyric Acid