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Hibbard EA, Sengelaub DR. Intraneural Topography of Rat Sciatic Axons: Implications for Polyethylene Glycol Fusion Peripheral Nerve Repair. Front Cell Neurosci 2022; 16:852933. [PMID: 35431811 PMCID: PMC9005634 DOI: 10.3389/fncel.2022.852933] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 02/11/2022] [Indexed: 11/13/2022] Open
Abstract
Peripheral nerve injuries are the most common type of nerve trauma. We have been working with a novel repair technique using a plasmalemmal fusogen, polyethylene glycol (PEG), to re-fuse the membranes of severed axons. PEG-fusion repair allows for immediate re-innervation of distal targets, prevents axonal degeneration, and improves behavioral recovery. PEG-fusion of severed axons is non-specific, and we have previously reported that following injury and PEG-fusion misconnections between spinal motoneurons and their distal targets were present. Surprisingly, appropriately paired proximal and distal motor axons were observed in all PEG-fused animals. We hypothesized that a topographic organization of axons contributing to the sciatic nerve could explain the incidence of appropriate connections. We traced the course of specific axon populations contributing to the sciatic nerve in young adult male and female rats. Following intraneural injection of Fast Blue into the tibial branch, labeled axons were confined to a discrete location throughout the course of the nerve. Following intramuscular injection of cholera toxin-conjugated horseradish peroxidase into the anterior tibialis, labeled axons were confined to a smaller but still discrete location throughout the nerve. In both cases, the relative locations of labeled axons were consistent bilaterally within animals, as well as across animals and sexes. Thus, the relatively consistent location of specific axon populations could allow for realignment of appropriate populations of axons, and enhanced behavioral recovery seen in PEG-fused animals. Knowing the organization of axons within the sciatic nerve promotes accurate territory realignment during repair, therefore aiding in recovery outcomes.
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Ghergherehchi CL, Hibbard EA, Mikesh M, Bittner GD, Sengelaub DR. Behavioral recovery and spinal motoneuron remodeling after polyethylene glycol fusion repair of singly cut and ablated sciatic nerves. PLoS One 2019; 14:e0223443. [PMID: 31584985 PMCID: PMC6777790 DOI: 10.1371/journal.pone.0223443] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Accepted: 09/20/2019] [Indexed: 11/22/2022] Open
Abstract
Polyethylene glycol repair (PEG-fusion) of severed sciatic axons restores their axoplasmic and membrane continuity, prevents Wallerian degeneration, maintains muscle fiber innervation, and greatly improves recovery of voluntary behaviors. We examined alterations in spinal connectivity and motoneuron dendritic morphology as one potential mechanism for improved behavioral function after PEG-fusion. At 2–112 days after a single-cut or allograft PEG-fusion repair of transected or ablated sciatic nerves, the number, size, location, and morphology of motoneurons projecting to the tibialis anterior muscle were assessed by retrograde labeling. For both lesion types, labeled motoneurons were found in the appropriate original spinal segment, but also in inappropriate segments, indicating mis-pairings of proximal-distal segments of PEG-fused motor axons. Although the number and somal size of motoneurons was unaffected, dendritic distributions were altered, indicating that PEG-fusion preserves spinal motoneurons but reorganizes their connectivity. This spinal reorganization may contribute to the remarkable behavioral recovery seen after PEG-fusion repair.
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Affiliation(s)
- Cameron L. Ghergherehchi
- Department of Molecular Biosciences, University of Texas at Austin, Austin, Texas, United States of America
| | - Emily A. Hibbard
- Department of Psychological and Brain Sciences, Indiana University, Bloomington, Indiana, United States of America
| | - Michelle Mikesh
- Department of Neuroscience, University of Texas at Austin, Austin, Texas, United States of America
| | - George D. Bittner
- Department of Neuroscience, University of Texas at Austin, Austin, Texas, United States of America
| | - Dale R. Sengelaub
- Department of Psychological and Brain Sciences, Indiana University, Bloomington, Indiana, United States of America
- * E-mail:
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Gonzalez Porras MA, Durfee P, Giambini S, Sieck GC, Brinker CJ, Mantilla CB. Uptake and intracellular fate of cholera toxin subunit b-modified mesoporous silica nanoparticle-supported lipid bilayers (aka protocells) in motoneurons. NANOMEDICINE-NANOTECHNOLOGY BIOLOGY AND MEDICINE 2018; 14:661-672. [PMID: 29339186 DOI: 10.1016/j.nano.2018.01.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Revised: 11/30/2017] [Accepted: 01/02/2018] [Indexed: 02/02/2023]
Abstract
Cholera toxin B (CTB) modified mesoporous silica nanoparticle supported lipid bilayers (CTB-protocells) are a promising, customizable approach for targeting therapeutic cargo to motoneurons. In the present study, the endocytic mechanism and intracellular fate of CTB-protocells in motoneurons were examined to provide information for the development of therapeutic application and cargo delivery. Pharmacological inhibitors elucidated CTB-protocells endocytosis to be dependent on the integrity of lipid rafts and macropinocytosis. Using immunofluorescence techniques, live confocal and transmission electron microscopy, CTB-protocells were primarily found in the cytosol, membrane lipid domains and Golgi. There was no difference in the amount of motoneuron activity dependent uptake of CTB-protocells in neuromuscular junctions, consistent with clathrin activation at the axon terminals during low frequency activity. In conclusion, CTB-protocells uptake is mediated principally by lipid rafts and macropinocytosis. Once internalized, CTB-protocells escape lysosomal degradation, and engage biological pathways that are not readily accessible by untargeted delivery methods.
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Affiliation(s)
- Maria A Gonzalez Porras
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, MN, United States
| | - Paul Durfee
- Center for Micro-Engineered Materials, University of New, Mexico
| | - Sebastian Giambini
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, MN, United States
| | - Gary C Sieck
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, MN, United States; Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States
| | - C Jeffrey Brinker
- Center for Micro-Engineered Materials, University of New, Mexico; Department of Chemical and Biological Engineering University of New, Mexico; Department of Molecular Genetics and Microbiology University of New, Mexico; Self-Assembled Materials Department, Sandia National Laboratories, Albuquerque, New, Mexico
| | - Carlos B Mantilla
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, MN, United States; Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, United States.
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A novel approach for targeted delivery to motoneurons using cholera toxin-B modified protocells. J Neurosci Methods 2016; 273:160-174. [PMID: 27641118 DOI: 10.1016/j.jneumeth.2016.09.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Revised: 09/12/2016] [Accepted: 09/13/2016] [Indexed: 12/18/2022]
Abstract
BACKGROUND Trophic interactions between muscle fibers and motoneurons at the neuromuscular junction (NMJ) play a critical role in determining motor function throughout development, ageing, injury, or disease. Treatment of neuromuscular disorders is hindered by the inability to selectively target motoneurons with pharmacological and genetic interventions. NEW METHOD We describe a novel delivery system to motoneurons using mesoporous silica nanoparticles encapsulated within a lipid bilayer (protocells) and modified with the atoxic subunit B of the cholera toxin (CTB) that binds to gangliosides present on neuronal membranes. RESULTS CTB modified protocells showed significantly greater motoneuron uptake compared to unmodified protocells after 24h of treatment (60% vs. 15%, respectively). CTB-protocells showed specific uptake by motoneurons compared to muscle cells and demonstrated cargo release of a surrogate drug. Protocells showed a lack of cytotoxicity and unimpaired cellular proliferation. In isolated diaphragm muscle-phrenic nerve preparations, preferential axon terminal uptake of CTB-modified protocells was observed compared to uptake in surrounding muscle tissue. A larger proportion of axon terminals displayed uptake following treatment with CTB-protocells compared to unmodified protocells (40% vs. 6%, respectively). COMPARISON WITH EXISTING METHOD(S) Current motoneuron targeting strategies lack the functionality to load and deliver multiple cargos. CTB-protocells capitalizes on the advantages of liposomes and mesoporous silica nanoparticles allowing a large loading capacity and cargo release. The ability of CTB-protocells to target motoneurons at the NMJ confers a great advantage over existing methods. CONCLUSIONS CTB-protocells constitute a viable targeted motoneuron delivery system for drugs and genes facilitating various therapies for neuromuscular diseases.
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Rogers ML, Smith KS, Matusica D, Fenech M, Hoffman L, Rush RA, Voelcker NH. Non-viral gene therapy that targets motor neurons in vivo. Front Mol Neurosci 2014; 7:80. [PMID: 25352776 PMCID: PMC4196515 DOI: 10.3389/fnmol.2014.00080] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Accepted: 09/18/2014] [Indexed: 12/11/2022] Open
Abstract
A major challenge in neurological gene therapy is safe delivery of transgenes to sufficient cell numbers from the circulation or periphery. This is particularly difficult for diseases involving spinal cord motor neurons such as amyotrophic lateral sclerosis (ALS). We have examined the feasibility of non-viral gene delivery to spinal motor neurons from intraperitoneal injections of plasmids carried by “immunogene” nanoparticles targeted for axonal retrograde transport using antibodies. PEGylated polyethylenimine (PEI-PEG12) as DNA carrier was conjugated to an antibody (MLR2) to the neurotrophin receptor p75 (p75NTR). We used a plasmid (pVIVO2) designed for in vivo gene delivery that produces minimal immune responses, has improved nuclear entry into post mitotic cells and also expresses green fluorescent protein (GFP). MLR2-PEI-PEG12 carried pVIVO2 and was specific for mouse motor neurons in mixed cultures containing astrocytes. While only 8% of motor neurons expressed GFP 72 h post transfection in vitro, when the immunogene was given intraperitonealy to neonatal C57BL/6J mice, GFP specific motor neuron expression was observed in 25.4% of lumbar, 18.3% of thoracic and 17.0% of cervical motor neurons, 72 h post transfection. PEI-PEG12 carrying pVIVO2 by itself did not transfect motor neurons in vivo, demonstrating the need for specificity via the p75NTR antibody MLR2. This is the first time that specific transfection of spinal motor neurons has been achieved from peripheral delivery of plasmid DNA as part of a non-viral gene delivery agent. These results stress the specificity and feasibility of immunogene delivery targeted for p75NTR expressing motor neurons, but suggests that further improvements are required to increase the transfection efficiency of motor neurons in vivo.
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Affiliation(s)
- Mary-Louise Rogers
- Department of Human Physiology, Centre for Neuroscience, Flinders University Adelaide, SA, Australia
| | - Kevin S Smith
- Department of Human Physiology, Centre for Neuroscience, Flinders University Adelaide, SA, Australia
| | - Dusan Matusica
- Department of Anatomy and Histology, Centre for Neuroscience, Flinders University Adelaide, SA, Australia
| | - Matthew Fenech
- Department of Human Physiology, Centre for Neuroscience, Flinders University Adelaide, SA, Australia
| | - Lee Hoffman
- Department of Chemistry and Biochemistry, South Dakota State University Brookings, SD, USA
| | - Robert A Rush
- Department of Human Physiology, Centre for Neuroscience, Flinders University Adelaide, SA, Australia
| | - Nicolas H Voelcker
- Australian Research Council Centre of Excellence in Convergent Bio-Nano Science and Technology, Mawson Institute, University of South Australia Adelaide, SA, Australia
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Chunfeng G, Xiaozhou L, Gang W, Jing J, Chao J, Josine TL. Expression of Cholera Toxin B–Lumbrokinase Fusion Protein in Pichia pastoris—The Use of Transmucosal Carriers in the Delivery of Therapeutic Proteins to Protect Rats Against Thrombosis. Appl Biochem Biotechnol 2012; 169:636-50. [DOI: 10.1007/s12010-012-0004-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Accepted: 11/30/2012] [Indexed: 11/28/2022]
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Abstract
Anti-GM1 antibodies are present in some patients with autoimmune neurological disorders. These antibodies are most frequently associated with acute immune neuropathy called Guillain-Barré syndrome (GBS). Some clinical studies associate the presence of these antibodies with poor recovery in GBS. The patients with incomplete recovery have failure of nerve repair, particularly axon regeneration. Our previous work indicates that monoclonal antibodies can inhibit axon regeneration by engaging cell surface gangliosides (Lehmann et al., 2007). We asked whether passive transfer of human anti-GM1 antibodies from patients with GBS modulate axon regeneration in an animal model. Human anti-GM1 antibodies were compared with other GM1 ligands, cholera toxin B subunit and a monoclonal anti-GM1 antibody. Our results show that patient derived anti-GM1 antibodies and cholera toxin beta subunit impair axon regeneration/repair after PNS injury in mice. Comparative studies indicated that the antibody/ligand-mediated inhibition of axon regeneration is dependent on antibody/ligand characteristics such as affinity-avidity and fine specificity. These data indicate that circulating immune effectors such as human autoantibodies, which are exogenous to the nervous system, can modulate axon regeneration/nerve repair in autoimmune neurological disorders such as GBS.
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Persson S, Havton LA. Retrogradely transported fluorogold accumulates in lysosomes of neurons and is detectable ultrastructurally using post-embedding immuno-gold methods. J Neurosci Methods 2009; 184:42-7. [PMID: 19631688 DOI: 10.1016/j.jneumeth.2009.07.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2009] [Revised: 07/14/2009] [Accepted: 07/15/2009] [Indexed: 01/10/2023]
Abstract
For ultrastructural studies, it is of great interest to be able to combine anatomical tracer techniques with sensitive immunohistochemical methods. Fluorogold (FG) is a fluorescent and retrogradely transported anatomical tracer, which is commonly used to label neurons in the brain and spinal cord for light microscopic studies. We here describe a method for detecting FG-labeled somata in the electron microscope using a high resolution post-embedding immuno-gold method. For this purpose, spinal motoneurons were retrogradely labeled by an intraperitoneal injection of FG in the adult rat. The rats were intravascularly perfused with a fixative solution containing 2% paraformaldehyde and 1-2% glutaraldehyde. Vibratome sections of spinal cord tissues were cryo-protected in glycerol, freeze substituted in methanol containing uranyl acetate, and embedded in the Lowicryl HM20 resin at low temperatures. Electron microscopic analysis demonstrated atypical lysosome-like structures in the cytoplasm of FG-labeled motoneurons. Subsequent post-embedding immuno-gold labeling demonstrated prominent accumulation of FG in numerous lysosomes but not in other organelles or cytoplasmic compartments of the labeled neurons. The protocol is versatile and allows for combining anatomical tracing of neurons with, e.g., neuro-transmitter studies in the electron microscope. We suggest that the described method for sensitive detection of FG in the spinal cord may also have broad applicability to other areas of the central nervous system.
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Affiliation(s)
- Stefan Persson
- Department of Neurology, David Geffen School of Medicine at UCLA, Neuroscience Research Building, 635 Charles E. Young Drive South, Los Angeles, CA 90095, United States
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Wu R, Wang H, Xia X, Zhou H, Liu C, Castro M, Xu Z. Nerve injection of viral vectors efficiently transfers transgenes into motor neurons and delivers RNAi therapy against ALS. Antioxid Redox Signal 2009; 11:1523-34. [PMID: 19344276 PMCID: PMC2842583 DOI: 10.1089/ars.2009.2618] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
RNA interference (RNAi) mediates sequence-specific gene silencing, which can be harnessed to silencing disease-causing genes for therapy. Particularly suitable diseases are those caused by dominant, gain-of-function type of gene mutations. In these diseases, the mutant gene generates a mutant protein or RNA product, which possesses toxic properties that harm cells. By silencing the mutant gene, the toxicity can be lessened because the amount of the toxic product is lowered in cells. In this report, we tested RNAi therapy in a mouse model for amyotrophic lateral sclerosis (ALS), which causes motor neuron degeneration, paralysis, and death. We used a transgenic model that overexpresses mutant Cu, Zn superoxide dismutase (SOD1G93A), which causes ALS by a gained toxic property. We delivered RNAi using recombinant adenovirus (RAd) and adeno-associated virus serotype 2 (AAV2). We compared the efficiency of RNAi delivery between injecting the viral vectors into muscle and into nerve, and found that nerve injetion is more efficient in delivering RNAi to motor neurons. Based on this data, we conducted therapeutic trials in the mouse model and found that nerve injection of RAd, but not AAV2, at the disease onset had a modest therapeutic efficacy. These results highlight the potential and the challenges in delivering RNAi therapy by gene therapy.
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Affiliation(s)
- Rui Wu
- Department of Biochemistry, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA
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Tseng LP, Liang HJ, Deng MC, Lee KM, Pan RN, Yang JC, Huang YY, Liu DZ. The influence of liposomal adjuvant on intranasal vaccination of chickens against Newcastle disease. Vet J 2009; 185:204-10. [PMID: 19570697 DOI: 10.1016/j.tvjl.2009.05.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2008] [Revised: 02/15/2009] [Accepted: 05/25/2009] [Indexed: 11/17/2022]
Abstract
The adjuvant effect of liposomes formulated with three phospholipids including phosphatidylcholine-liposomes (PC-Lip), phosphatidylserine-liposomes (PS-Lip), and stearylamine-liposomes (SA-Lip) was compared with virus alone using inactivated Newcastle disease virus (NDV) as a model antigen. The difference in adjuvanticity was evaluated using the haemagglutination-inhibition (HI) test, enzyme-linked immunosorbent assay, and a challenge study following intranasal inoculation of specific pathogen-free chickens. After two inoculations, a liposomal vaccine consisting of NDV in PC-Lip resulted in a significant increase in HI titre, up to 32-fold higher than a vaccine containing virus alone and 320-fold higher than a vaccine containing NDV in SA-Lip. PC-Lip also elicited a significant mucosal secretary immunoglobulin A response (P<0.05) in tracheal lavages and a serum IgG response (P<0.05). In response to viral challenge, all control animals died, whereas 90% of animals which received PC-Lip survived. The results suggest that PC-Lip may be suitable as an adjuvant for mucosal vaccination against NDV in chickens.
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Affiliation(s)
- Li-Ping Tseng
- Graduate Institute of Biomedical Engineering, College of Engineering, College of Medicine, National Taiwan University, Taipei, Taiwan
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Limaye A, Koya V, Samsam M, Daniell H. Receptor-mediated oral delivery of a bioencapsulated green fluorescent protein expressed in transgenic chloroplasts into the mouse circulatory system. FASEB J 2006; 20:959-61. [PMID: 16603603 PMCID: PMC3481851 DOI: 10.1096/fj.05-5134fje] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Oral delivery of biopharmaceutical proteins expressed in plant cells should reduce their cost of production, purification, processing, cold storage, transportation, and delivery. However, poor intestinal absorption of intact proteins is a major challenge. To overcome this limitation, we investigate here the concept of receptor-mediated oral delivery of chloroplast-expressed foreign proteins. Therefore, the transmucosal carrier cholera toxin B-subunit and green fluorescent protein (CTB-GFP), separated by a furin cleavage site, was expressed via the tobacco chloroplast genome. Polymerase chain reaction (PCR) and Southern blot analyses confirmed site-specific transgene integration and homoplasmy. Immunoblot analysis and ELISA confirmed expression of monomeric and pentameric forms of CTB-GFP, up to 21.3% of total soluble proteins. An in vitro furin cleavage assay confirmed integrity of the engineered furin cleavage site, and a GM1 binding assay confirmed the functionality of CTB-GFP pentamers. Following oral administration of CTB-GFP expressing leaf material to mice, GFP was observed in the mice intestinal mucosa, liver, and spleen in fluorescence and immunohistochemical studies, while CTB remained in the intestinal cell. This report of receptor-mediated oral delivery of a foreign protein into the circulatory system opens the door for low-cost production and delivery of human therapeutic proteins.
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Affiliation(s)
| | | | - Mohtashem Samsam
- Department of Molecular Biology and Microbiology, University of Central Florida, Biomolecular Science, Orlando, Florida, USA
| | - Henry Daniell
- Department of Molecular Biology and Microbiology, University of Central Florida, Biomolecular Science, Orlando, Florida, USA
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Havton LA, Broman J. Systemic administration of cholera toxin B subunit conjugated to horseradish peroxidase in the adult rat labels preganglionic autonomic neurons, motoneurons, and select primary afferents for light and electron microscopic studies. J Neurosci Methods 2005; 149:101-9. [PMID: 16054225 DOI: 10.1016/j.jneumeth.2005.03.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2005] [Revised: 03/12/2005] [Accepted: 03/22/2005] [Indexed: 11/16/2022]
Abstract
Retrograde and transganglionic labeling techniques are commonly used to visualize subsets of neurons and sensory afferent projections in the nervous system. These methods commonly require anesthesia and surgical methods. However, some tracers can also be administered systemically in awake animals, thus reducing risks associated with anesthesia and surgery and allowing for labeling of neuronal populations that are difficult to label with local tracer injections. Here, we demonstrate in the adult rat that intraperitoneal administration of cholera toxin subunit B conjugated to horseradish peroxidase labels preganglionic autonomic neurons, motoneurons, and the terminal projections of select primary afferents for both light and electron microscopic studies. We demonstrate also that this method can be combined with post-embedding immunogold labeling to detect amino acid transmitters in synaptic boutons.
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Affiliation(s)
- Leif A Havton
- Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095-1769, USA.
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von Bartheld CS. Axonal transport and neuronal transcytosis of trophic factors, tracers, and pathogens. ACTA ACUST UNITED AC 2003; 58:295-314. [PMID: 14704960 DOI: 10.1002/neu.10315] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Neurons can specifically internalize macromolecules, such as trophic factors, lectins, toxins, and other pathogens. Upon internalization in terminals, proteins can move retrogradely along axons, or, upon internalization at somatodendritic domains, they can move into an anterograde axonal transport pathway. Release of internalized proteins from neurons after either retrograde or anterograde axonal transport results in transcytosis and trafficking of proteins across multiple synapses. Recent studies of binding properties of several such proteins suggest that pathogens and lectins may utilize existing transport machineries designed for trafficking of trophic factors. Specific pathways may protect trophic factors, pathogens, and toxins from degradation after internalization and may target the trophic or pathogenic cargo for transcytosis after either retrograde or anterograde transport along axons. Elucidating the molecular mechanisms of sorting steps and transport pathways will further our understanding of trophic signaling and could be relevant for an understanding and possible treatment of neurological diseases such as rabies, Alzheimer's disease, and prion encephalopathies. At present, our knowledge is remarkably sparse about the types of receptors used by pathogens for trafficking, the signals that sort trophins or pathogens into recycling or degradation pathways, and the mechanisms that regulate their release from somatodendritic domains or axon terminals. This review intends to draw attention to potential convergences and parallels in trafficking of trophic and pathogenic proteins. It discusses axonal transport/trafficking mechanisms that may help to understand and eventually treat neurological diseases by targeted drug delivery.
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Affiliation(s)
- Christopher S von Bartheld
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557, USA.
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