Cobalt accumulation in neurons expressing ionotropic excitatory amino acid receptors in young rat spinal cord: Morphology and distribution

István Nagy, Clifford J. Woolf, Andy Dray, László Urbán

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Excitatory amino acids (EAA) acting on N‐methyl‐D‐aspartate (NMDA), α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA) and kainate receptors play an important role in synaptic transmission in the spinal cord. Quantitative autordiography and physiological experiments suggest that NMDA receptors are localized mainly in lamina II while kainate and AMPA receptors are found on both dorsal and ventral horn neurons. However the cell types expressing EAA receptors and their laminar distribution is not known. We have used a cobalt uptake mentod to study the morphology and distribution of spinal cord neurons expressing AMPA, kainate, or NMDA excitatory amino acid receptors in the lumbar enlargement of the rat spinal cord. The technique involved superfusion of hemisected spinal cords of 14 day‐old rat pups in vitro with excitatory amino acid receptor ligands in the presence of CoCl2. Cobalt has been shown to enter cells through ligand‐gated ion channels in place of Ca2+. Cells which accumulated cobalt ions following activation by ionotropic excitatory amino acid receptors were visualised histochemically. The cobalt uptake generated receptors‐specific labeling of cells, as the NMDA receptor antagonist D‐(−)‐2‐amino‐(5)‐phosphonovaleric acid (D‐AP‐5) (20 μM) blocked the NMDA, but not kainte‐inducced cobalt uptake. The kainate‐induced cobalt labeling was reduced by the non‐selective excitatory amino acid receptor antagonist kynurenic acid (4 mM). Passive opening of the voltage‐gated Ca2+ ‐channel by KCI (50 mM) did not result in colbalt uptake, indicating that cobalt enters cells through ligand‐gated Ca2+ ‐channels. AMPA (500 μM), kainate (500 μM), or NMDA (500 μM) each induced cobalt uptake with characteristic patterns and distributions of neuronal staining. Overall, kainate induced cobalt uptake in the greatest number of neuronal perikarya while NMDA‐induced uptake was the lowest. AMPA and kainate, but not NMDA superfusion, resulted in cobalt labeling of glial cells. Our result show that the cobalt uptake technique is a useful way to study the morphology and distribution of cells expressing receptors with ligand‐gated Ca2+ channels. © 1994 Wiley‐Liss, Inc.

Original languageEnglish
Pages (from-to)321-335
Number of pages15
JournalJournal of Comparative Neurology
Issue number3
Publication statusPublished - Jun 15 1994


  • AMPA receptor
  • NMDA receptor
  • cobalt uptake
  • kainate receptor

ASJC Scopus subject areas

  • Neuroscience(all)

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