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The Journal of Neuroscience, September 24, 2008, 28(39):9692-9701; doi:10.1523/JNEUROSCI.1551-08.2008

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Cellular/Molecular
Numbers, Densities, and Colocalization of AMPA- and NMDA-Type Glutamate Receptors at Individual Synapses in the Superficial Spinal Dorsal Horn of Rats

Miklós Antal,^1 * Yugo Fukazawa,^4 * Mária Eördögh,¹ Dóra Muszil,¹ Elek Molnár,² Makoto Itakura,³ Masami Takahashi,³ and Ryuichi Shigemoto⁴

¹Department of Anatomy, Histology, and Embryology, Faculty of Medicine, Medical and Health Science Center, University of Debrecen, H-4012 Debrecen, Hungary, ²Medical Research Council, Centre for Synaptic Plasticity, Department of Anatomy, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom, ³Department of Biochemistry, Kitasato University School of Medicine, Sagamihara, Kanagawa 228-8555, Japan, and ⁴Division of Cerebral Structures, National Institutes for Physiological Sciences, Myodaiji, Okazaki 444-8787, Japan

Correspondence should be addressed to Miklós Antal, Department of Anatomy, Histology, and Embryology, Faculty of Medicine, Medical and Health Science Center, University of Debrecen, Nagyerdei krt 98, H-4012 Debrecen, Hungary. Email: antal{at}chondron.anat.dote.hu

Ionotropic glutamate receptors play important roles in spinal processing of nociceptive sensory signals and induction of central sensitization in chronic pain. Here we applied highly sensitive freeze-fracture replica labeling to laminae I–II of the spinal dorsal horn of rats and investigated the numbers, densities, and colocalization of AMPA- and NMDA-type glutamate receptors at individual postsynaptic membrane specializations with a high resolution. All glutamatergic postsynaptic membranes in laminae I–II expressed AMPA receptors, and most of them (96%) were also immunoreactive for the NR1 subunit of NMDA receptors. The numbers of gold particles for AMPA and NMDA receptors at individual postsynaptic membranes showed a linear correlation with the size of postsynaptic membrane specializations and varied in the range of 8–214 and 5–232 with median values of 37 and 28, whereas their densities varied in the range of 325–3365/µm² and 102–2263/µm² with median values of 1115/µm² and 777/µm², respectively. Virtually all (99%) glutamatergic postsynaptic membranes expressed GluR2, and most of them (87%) were also immunoreactive for GluR1. The numbers of gold particles for pan-AMPA, NR1, and GluR2 subunits showed a linear correlation with the size of postsynaptic surface areas. Concerning GluR1, there may be two populations of synapses with high and low GluR1 densities. In synapses larger than 0.1 µm², GluR1 subunits were recovered in very low numbers. Differential expression of GluR1 and GluR2 subunits suggests regulation of AMPA receptor subunit composition by presynaptic mechanism.

Key words: ionotropic glutamate receptors; NR1; GluR1; GluR2; molecular anatomy; postsynaptic active zones; SDS-FRL

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Received Dec. 19, 2007; revised Aug. 15, 2008; accepted Aug. 19, 2008.

Correspondence should be addressed to Miklós Antal, Department of Anatomy, Histology, and Embryology, Faculty of Medicine, Medical and Health Science Center, University of Debrecen, Nagyerdei krt 98, H-4012 Debrecen, Hungary. Email: antal{at}chondron.anat.dote.hu

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				T. Yasaka, D. I. Hughes, E. Polgar, G. G. Nagy, M. Watanabe, J. S. Riddell, and A. J. Todd Evidence against AMPA Receptor-Lacking Glutamatergic Synapses in the Superficial Dorsal Horn of the Rat Spinal Cord J. Neurosci., October 21, 2009; 29(42): 13401 - 13409. [Abstract] [Full Text] [PDF]

				Y. Shinohara, H. Hirase, M. Watanabe, M. Itakura, M. Takahashi, and R. Shigemoto Left-right asymmetry of the hippocampal synapses with differential subunit allocation of glutamate receptors PNAS, December 9, 2008; 105(49): 19498 - 19503. [Abstract] [Full Text] [PDF]

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