Vesicular glutamate transporters in the spinal cord, with special reference to sensory primary afferent synapses

J Comp Neurol. 2004 May 3;472(3):257-80. doi: 10.1002/cne.20012.

Abstract

Spinal cord sensory synapses are glutamatergic, but previous studies have found a great diversity in synaptic vesicle structure and have suggested additional neurotransmitters. The identification of several vesicular glutamate transporters (VGLUTs) similarly revealed an unexpected molecular diversity among glutamate-containing terminals. Therefore, we quantitatively investigated VGLUT1 and VGLUT2 content in the central synapses of spinal sensory afferents by using confocal and electron microscopy immunocytochemistry. VGLUT1 localization (most abundant in LIII/LIV and medial LV) is consistent with an origin from cutaneous and muscle mechanoreceptors. Accordingly, most VGLUT1 immunoreactivity disappeared after rhizotomy and colocalized with markers of cutaneous (SSEA4) and muscle (parvalbumin) mechanoreceptors. With postembedding colloidal gold, intense VGLUT1 immunoreactivity was found in 88-95% (depending on the antibody used) of C(II) dorsal horn glomerular terminals and in large ventral horn synapses receiving axoaxonic contacts. VGLUT1 partially colocalized with CGRP in some large dense-core vesicles (LDCVs). However, immunostaining in neuropeptidergic afferents was inconsistent between VGLUT1 antibodies and rather weak with light microscopy. VGLUT2 immunoreactivity was widespread in all spinal cord laminae, with higher intensities in LII and lateral LV, complementing VGLUT1 distribution. VGLUT2 immunoreactivity did not change after rhizotomy, suggesting a preferential intrinsic origin. However, weak VGLUT2 immunoreactivity was detectable in primary sensory nociceptors expressing lectin (GSA-IB4) binding and in 83-90% of C(I) glomerular terminals in LII. Additional weak VGLUT2 immunoreactivity was found over the small clear vesicles of LDCV-containing afferents and in 50-60% of C(II) terminals in LIII. These results indicate a diversity of VGLUT isoform combinations expressed in different spinal primary afferents.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Afferent Pathways / cytology
  • Afferent Pathways / metabolism*
  • Afferent Pathways / ultrastructure
  • Animals
  • Animals, Newborn
  • Anterior Horn Cells / metabolism
  • Anterior Horn Cells / ultrastructure
  • Calcitonin Gene-Related Peptide / metabolism
  • Carrier Proteins / metabolism*
  • Carrier Proteins / ultrastructure
  • Cell Count / methods
  • Fluorescent Antibody Technique / methods
  • Glycoproteins / metabolism
  • Glycosphingolipids / metabolism
  • Immunohistochemistry / methods
  • Lectins / metabolism
  • Membrane Transport Proteins*
  • Microscopy, Confocal / methods
  • Microscopy, Immunoelectron / methods
  • Parvalbumins / metabolism
  • Phosphopyruvate Hydratase / metabolism
  • Presynaptic Terminals / classification
  • Presynaptic Terminals / metabolism
  • Presynaptic Terminals / ultrastructure
  • Rats
  • Rats, Sprague-Dawley
  • Rhizotomy / methods
  • Secretory Vesicles / metabolism
  • Secretory Vesicles / ultrastructure
  • Spinal Cord / growth & development
  • Spinal Cord / metabolism*
  • Spinal Cord / ultrastructure
  • Stage-Specific Embryonic Antigens
  • Synapses / metabolism*
  • Synapses / ultrastructure
  • Vesicular Glutamate Transport Protein 1
  • Vesicular Glutamate Transport Protein 2
  • Vesicular Transport Proteins*

Substances

  • Carrier Proteins
  • Glycoproteins
  • Glycosphingolipids
  • Lectins
  • Membrane Transport Proteins
  • Parvalbumins
  • Slc17a6 protein, rat
  • Slc17a7 protein, rat
  • Stage-Specific Embryonic Antigens
  • Vesicular Glutamate Transport Protein 1
  • Vesicular Glutamate Transport Protein 2
  • Vesicular Transport Proteins
  • isolectin B4-binding glycoprotein, rat
  • stage-specific embryonic antigen-4
  • Phosphopyruvate Hydratase
  • Calcitonin Gene-Related Peptide