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Expression and localization of insulin receptor in rat dorsal root ganglion and spinal cord

Authors

  • Kazuhiro Sugimoto,

    1. Departments of Pathology 1 and Neurology,2Morris Hood Jr Comprehensive Diabetes Center,3
      Wayne State University School of Medicine, Detroit, Michigan
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    • *

      Current address: 3rd Department of Internal Medicine, Hirosaki University School of Medicine, 5-Zaifu-cho, Hirosaki, Japan, 036-8562

  • 1 3 Yuichi Murakawa,

    1. Departments of Pathology 1 and Neurology,2Morris Hood Jr Comprehensive Diabetes Center,3
      Wayne State University School of Medicine, Detroit, Michigan
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  • and 1 3 Anders A. F. Sima 1 2 3

    1. Departments of Pathology 1 and Neurology,2Morris Hood Jr Comprehensive Diabetes Center,3
      Wayne State University School of Medicine, Detroit, Michigan
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Address correspondence to: Dr. A.A.F. Sima, Department of Pathology, Wayne State University School of Medicine, 540 E Canfield Ave., Detroit, MI, 48201, USA. Tel.: 313-577-1150; Fax: 313-577-0057; E-mail: asima@med.wayne.edu

Abstract

Abstract  The expression and localization of the insulin receptor (IR) was examined in rat dorsal root ganglia (DRG) and spinal cord using Western blotting, in situ hybridization and immunocytochemistry. Western blotting showed that the molecular weight of the IR β subunit was higher in PNS than that found in CNS. Both IR mRNA and protein expressions were highest in small-sized sensory DRG neurons and myelinated sensory root fibers expressed higher levels of IR protein than myelinated anterior root fibers. In the spinal cord, IR immunoreactive neurons were present in lateral lamina V and in lamina X, suggesting the presence of IR in nociceptive pathways. Electronmicroscopy of DRGs revealed a polarized localization of the IR in abaxonal Schwann cell membranes, outer mesaxons in close vicinity to tight junctions of both myelinating and non-myelinating Schwann cells and to plasma membranes of sensory neurons. From these findings, we speculate that insulin may play a role in sensory fibers involved in nociceptive function often perturbed in diabetic neuropathy. The high expression of IR localizing to tight junctions of dorsal root mesaxons of DRGs may suggest a regulatory role on barrier functions compensating for the lack of a blood–nerve barrier in dorsal root ganglia. This is consistent with the colocalization of IR with tight junctions of the paranodal barrier and endoneurial endothelial cells in peripheral nerve.

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