Evidence for GAP-43 within descending spinal axons in the North American opossum, Didelphis virginiana.
We have shown previously that GAP-43, a growth associated protein characteristically present in growing and regenerating axons, is relatively abundant in the spinal cord of adult opossums. In the present study, we combined the orthograde transport of the fluorescent marker Fluoro-Ruby with immunofluorescence for GAP-43 to determine if any of it is present within descending spinal axons. When Fluoro-Ruby was injected into the red nucleus and midbrain tegmentum, the medial pontine or medullary reticular formation, the medullary raphe or the lateral vestibular nucleus, axons were labeled in the expected areas of the spinal cord, but in most cases none showed evidence for GAP-43. In two of the four cases with rubral injections, however, a few labeled axons within the rubrospinal tract showed GAP-43 immunofluorescence, and in one case with an injection of the gigantocellular reticular nucleus and adjacent raphe, labeled axons within lamina IX immunostained for the protein. Since serotoninergic neurons are present within the gigantocellular reticular nucleus and adjacent raphe, and axons of the same phenotype are abundant within lamina IX, we asked whether serotoninergic axons contain GAP-43. When sections of the spinal cord were immunostained for both serotonin and GAP-43, many axons within lamina IX showed evidence for both substances. Such axons appeared to contact presumptive motoneurons. In cases with Fluoro-Ruby injections of the forelimb motor cortex, labeled axons were present within the pyramidal tract, and some of them showed evidence for GAP-43.
Zou
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XC
Department of Cell Biology, Neurobiology and Anatomy, The Ohio State University, College of Medicine, Columbus, USA.
Ho
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Wang
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Martin
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GF
D000818:Animals; D001369:Axons / Q000648:ultrastructure; D001931:Brain Mapping; D001933:Brain Stem / Q000033:anatomy & histology*; D019922:GAP-43 Protein; D006133:Growth Substances / Q000032:analysis*; D008562:Membrane Glycoproteins / Q000032:analysis*; D008856:Microscopy, Fluorescence; D009044:Motor Cortex / Q000033:anatomy & histology; D009419:Nerve Tissue Proteins / Q000032:analysis*; D009893:Opossums / Q000033:anatomy & histology*; D011712:Pyramidal Tracts / Q000033:anatomy & histology*; D011903:Raphe Nuclei / Q000033:anatomy & histology; D012012:Red Nucleus / Q000033:anatomy & histology; D012154:Reticular Formation / Q000033:anatomy & histology; D013116:Spinal Cord / Q000033:anatomy & histology*; D014726:Vestibular Nuclei / Q000033:anatomy & histology
D019922:GAP-43 Protein; D006133:Growth Substances; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins