title: The expression of vesicular glutamate transporters VGLUT1 and VGLUT2 in neurochemically defined axonal populations in the rat spinal cord with emphasis on the dorsal horn.
abstract: Two vesicular glutamate transporters, VGLUT1 and VGLUT2, have recently been identified, and it has been reported that they are expressed by largely nonoverlapping populations of glutamatergic neurons in the brain. We have used immunocytochemistry with antibodies against both transporters, together with markers for various populations of spinal neurons, in an attempt to identify glutamatergic interneurons in the dorsal horn of the mid-lumbar spinal cord of the rat. The great majority (94-100%) of nonprimary axonal boutons that contained somatostatin, substance P or neurotensin, as well as 85% of those that contained enkephalin, were VGLUT2-immunoreactive, which suggests that most dorsal horn neurons that synthesize these peptides are glutamatergic. In support of this, we found that most somatostatin- and enkephalin-containing boutons (including somatostatin-immunoreactive boutons that lacked calcitonin gene-related peptide and were therefore probably derived from local interneurons) formed synapses at which AMPA receptors were present. We also investigated VGLUT expression in central terminals of primary afferents. Myelinated afferents were identified with cholera toxin B subunit; most of those in lamina I were VGLUT2-immunoreactive, whereas all those in deeper laminae were VGLUT1-immunoreactive, and some (in laminae III-VI) appeared to contain both transporters. However, peptidergic primary afferents that contained substance P or somatostatin (most of which are unmyelinated), as well as nonpeptidergic C fibres (identified with Bandeiraea simplicifolia isolectin B4) showed low levels of VGLUT2-immunoreactivity, or were not immunoreactive with either VGLUT antibody. As all primary afferents are thought to be glutamatergic, this raises the possibility that unmyelinated afferents, most of which are nociceptors, express a different vesicular glutamate transporter.
authors.affiliation: Spinal Cord Group, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK. a.toss@bio.gla.ac.uk
authors.forename: A J
authors.initials: AJ
authors.lastname: Todd
authors.forename: D I
authors.initials: DI
authors.lastname: Hughes
authors.forename: E
authors.initials: E
authors.lastname: Polgár
authors.forename: G G
authors.initials: GG
authors.lastname: Nagy
authors.forename: M
authors.initials: M
authors.lastname: Mackie
authors.forename: O P
authors.initials: OP
authors.lastname: Ottersen
authors.forename: D J
authors.initials: DJ
authors.lastname: Maxwell
mesh_terms: D000276:Adjuvants, Immunologic / Q000032:analysis; D000344:Afferent Pathways / Q000737:chemistry*; D000818:Animals; D001369:Axons / Q000737:chemistry*; D002352:Carrier Proteins / Q000032:analysis*; D002772:Cholera Toxin / Q000032:analysis; D004745:Enkephalins / Q000032:analysis; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D007395:Interneurons / Q000737:chemistry; D008161:Lumbosacral Region; D008297:Male; D026901:Membrane Transport Proteins; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D009496:Neurotensin / Q000032:analysis; D020671:Posterior Horn Cells / Q000737:chemistry*; D017729:Presynaptic Terminals / Q000737:chemistry; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000032:analysis / Q000648:ultrastructure; D013004:Somatostatin / Q000032:analysis; D013116:Spinal Cord / Q000737:chemistry*; D013373:Substance P / Q000032:analysis; D013569:Synapses / Q000648:ultrastructure; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins
chemical_list: D000276:Adjuvants, Immunologic; D002352:Carrier Proteins; D004745:Enkephalins; D026901:Membrane Transport Proteins; D018091:Receptors, AMPA; C493475:Slc17a6 protein, rat; C493466:Slc17a7 protein, rat; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins; D013373:Substance P; D009496:Neurotensin; D013004:Somatostatin; D002772:Cholera Toxin