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C‐fiber (Remak) bundles contain both isolectin B4‐binding and calcitonin gene‐related peptide‐positive axons
Author(s) -
Murinson Beth Brianna,
Hoffman Paul Ned,
Banihashemi Michael Reza,
Meyer Richard Arthur,
Griffin John Wesley
Publication year - 2005
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.20506
Subject(s) - axon , biology , calcitonin gene related peptide , dorsal root ganglion , immunogold labelling , colocalization , neuroscience , wheat germ agglutinin , anatomy , neuropeptide , microbiology and biotechnology , spinal cord , biochemistry , ultrastructure , receptor , lectin
Unmyelinated nerve fibers (Remak bundles) in the rodent sciatic nerve typically contain multiple axons. This study asked whether C‐fiber bundles contain axons arising from more than one type of neuron. Most small neurons of the lumbar dorsal root ganglion (DRG) are either glial cell line‐derived neurotrophic factor dependent or nerve growth factor dependent, binding either isolectin B4 (IB4) or antibodies to calcitonin gene‐related peptide (CGRP), respectively. Injection of IB4‐conjugated horseradish peroxidase into a lumbar DRG resulted in intense labeling of IB4 axons, with very low background. Visualized by confocal fluorescence, IB4‐binding and CGRP‐positive nerve fibers orginating from different DRG neurons came together and remained closely parallel over long distances, suggesting that these two types of axon occupy the same Remak bundle. With double‐labeling immunogold electron microscopy (EM), we confirmed that IB4 and CGRP axons were distinct and were found together in single Remak bundles. Previous studies indicate that some DRG neurons express both CGRP and IB4 binding. To ensure that our immunogold results were not a consequence of coexpression, we studied large populations of unmyelinated axons by using quantitative single‐label EM. Tetramethylbenzidine, a chromogen with strong intrinsic signal amplification of IB4‐horseradish peroxidase, labeled as many as 52% of unmyelinated axons in the dorsal root. Concomitantly, 97% of the Remak bundles with more than one axon contained at least one IB4‐labeled axon. Probabilistic modeling using binomial distribution functions rejected the hypothesis that IB4 axons segregate into IB4‐specific bundles ( P < 0.00001). We conclude that most Remak bundle Schwann cells simultaneously support diverse axon types with different growth factor dependences. J. Comp. Neurol. 484:392–402, 2005. © 2005 Wiley‐Liss, Inc.