title: Distribution of transmembrane AMPA receptor regulatory protein (TARP) isoforms in the rat spinal cord.
abstract: The transmembrane α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor regulatory proteins (TARPs) are a family of auxiliary AMPA receptor subunits that differentially modulate trafficking and many functional properties of the receptor. To investigate which TARP isoforms may be involved in AMPA receptor-mediated spinal synaptic transmission, we have mapped the localization of five of the known TARP isoforms, namely γ-2 (also known as stargazin), γ-3, γ-4, γ-7 and γ-8, in the rat spinal cord. Immunoblotting showed expression of all isoforms in the spinal cord to varying degrees. At the light microscopic level, immunoperoxidase labeling of γ-4, γ-7 and γ-8 was found throughout spinal gray matter. In white matter, γ-4 and γ-7 immunolabeling was observed in astrocytic processes and in mature oligodendrocytes. In pepsin-treated spinal cord, γ-7 often colocalized with GluA2 immunopositive puncta in the deep dorsal horn as well as in the ventral horn, but not in the superficial dorsal horn. Postembedding immunogold labeling was further used to assess the synaptic localization of γ-2, γ-7 and γ-8 in the dorsal horn. Synaptic immunogold labeling of γ-2 was sparse throughout the dorsal horn, with some primary afferent synapses weakly labeled, whereas relatively strong γ-7 immunogold labeling was found at deep dorsal horn synapses, including at synapses formed by low-threshold mechanosensitive primary afferent terminals. Prominent immunogold labeling of γ-8 was frequently detected at synapses established by primary afferent fibers. The spinal localization patterns of TARP isoforms reported here suggest that AMPA receptors at spinal synaptic populations and in glial cells may exhibit different functional characteristics owing to differences in auxiliary subunit composition.
authors.affiliation: Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden; Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden. Electronic address: max.larsson@ki.se.
authors.forename: M
authors.initials: M
authors.lastname: Larsson
authors.affiliation: Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: N
authors.initials: N
authors.lastname: Agalave
authors.affiliation: Department of Anatomy, Hokkaido University School of Medicine, Sapporo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Watanabe
authors.affiliation: Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: C I
authors.initials: CI
authors.lastname: Svensson
mesh_terms: D000818:Animals; D000906:Antibodies; D015220:Calcium Channels / Q000032:analysis / Q000276:immunology; D008297:Male; D008565:Membrane Proteins / Q000032:analysis*; D020671:Posterior Horn Cells / Q000378:metabolism* / Q000648:ultrastructure; D020033:Protein Isoforms / Q000032:analysis; D021122:Protein Subunits / Q000032:analysis* / Q000276:immunology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000032:analysis* / Q000276:immunology
chemical_list: D000906:Antibodies; C491911:Cacng2 protein, rat; C522274:Cacng4 protein, rat; C532435:Cacng7 protein, rat; D015220:Calcium Channels; D008565:Membrane Proteins; D020033:Protein Isoforms; D021122:Protein Subunits; D018091:Receptors, AMPA; C588152:cacng8 protein, rat
keywords: astrocyte; dorsal horn; electron microscopy; glutamate receptor; synaptic transmission; ventral horn