The pre- and post-somatic segments of the human type I spiral ganglion neurons--structural and functional considerations related to cochlear implantation.
Bottom Line: These segments were found surrounded by non-myelinated Schwann cells (NMSCs) showing strong intracellular expression of laminin-β2/collagen IV.Their BMs express laminin-β2/collagen IV and reaches the BM of the sensory epithelium at the habenula perforata.We speculate that the NMSCs protect SGNs from further degeneration following dendrite loss.
Affiliation: Department of Surgical Sciences, Head and Neck Surgery, Section of Otolaryngology, Uppsala University Hospital, SE-751 85 Uppsala, Sweden; Department of Otolaryngology, Uppsala University Hospital, SE-751 85 Uppsala, Sweden. Electronic address: firstname.lastname@example.org.Show MeSH
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Mentions: Well preserved human SGNs were obtained and verified with LM, TEM and SEM (Figs. 1, 4 and 5A). Most type I SGNs were unmyelinated and lacked expression of MBP (Figs. 1 and 2A). Instead they were surrounded by SGCs whose extracellular surface was covered by a BM (Figs. 1 and 2A–C, E, F, 3). Their cell nuclei were often crescent-like. Many type I SGNs formed clusters and were jointly surrounded by SGCs and a distinct BM (Fig. 1). The continuous BM co-expressed the β2 isoform of laminin heterotrimeric complex and collagen type IV (Figs. 2 and 3). The BM surrounded the neurons from the spiral ganglion (SG) to the nerve entry in the sensory organ (habenula perforata) and stained positive for both markers (Fig. 2D). The BM also formed a thin sheet lining the short canal into the sensory organ (habenular canal) which coalesced with the BM of the sensory epithelium. The peripheral axons (or dendrites) lost their myelin sheath beneath the inferior canal opening of the habenula perforata (Fig. 2D). Dendrites and axons of the type I SGNs were bordered by MBP-positive, myelinating Schwann cells. The pre- and post-somal segments however, were mostly bordered by unmyelinated Schwann cells (MBP-negative). The non-myelinated zones varied considerably in length but could be up to 50 microns (Fig. 2A, E). Typically, as opposed to the SGCs, the NMSCs showed rich expression of intracellular laminin-β2 and collagen IV (Figs. 2E, F, and 3). This contrasted to the SGCs that showed no such expression. The NMSCs extended to the poles of the cell soma. Their cell nuclei were often round compared to the crescent shape of the SGCs nuclei.
Affiliation: Department of Surgical Sciences, Head and Neck Surgery, Section of Otolaryngology, Uppsala University Hospital, SE-751 85 Uppsala, Sweden; Department of Otolaryngology, Uppsala University Hospital, SE-751 85 Uppsala, Sweden. Electronic address: email@example.com.