-
Developmental NeuroscienceThe neuroscientist often divides the cellular world into neuronal and nonneuronal cells, setting the stage for emphasizing differences rather than similarities between... (Review)
Review
The neuroscientist often divides the cellular world into neuronal and nonneuronal cells, setting the stage for emphasizing differences rather than similarities between cell types. This review focuses on a common theme in cell biology: the sorting of newly-synthesized membrane proteins, their intracellular transport, and their delivery to distinct domains of the cell surface. At the subcellular level, membrane proteins in neurons pass through the cell body and enter the axon by a pathway reminiscent of that utilized in other cell types. At the molecular level, little is known of how sorting and delivery are directed in neurons, although details of such recognition mechanisms are emerging for many specific proteins in prokaryotic and eukaryotic cells. Analogies are drawn from these systems to propose how neuronal proteins destined for regions of axolemma and axon terminals are sorted from proteins destined for endomembranes, somal organelles, somal plasma membrane and dendrites, and delivered, via fast axonal transport, to their correct membrane domains.
Topics: Axonal Transport; Biological Transport; Cell Membrane; Forecasting; Golgi Apparatus; Nerve Tissue Proteins; Neurons; Time Factors
PubMed: 6199178
DOI: 10.1159/000112327 -
Biochemical and Biophysical Research... May 2005We have examined spinal motor neurons in Sprague-Dawley rats to further characterize a mechanoenzyme, myosin-Igamma (myr4), which is found in high concentration during...
We have examined spinal motor neurons in Sprague-Dawley rats to further characterize a mechanoenzyme, myosin-Igamma (myr4), which is found in high concentration during axon tract formation in neonates. We raised an antibody to myr4 and made riboprobes for in situ hybridization. Myr4 mRNA was abundant in spinal cord motor neurons (particularly during axon regrowth). Nerves undergoing Wallerian degeneration (from a crush 7 days earlier) showed anti-myr4 labeling of the axolemma and SER--after microtubules, neurofilaments, and F-actin had already been degraded--which is consistent with a described lipid-binding domain in the tail region of myosin-Is. Newly synthesized myr4 was carried in axons by the slow component (SC) of axonal transport at 1-8 mm/day, whereas, none was carried by the fast component (FC). We conclude that SC delivers myr4 to the cytoplasmic surfaces of stationary axonal membranes (SER and axolemma). This positioning would anchor the tail domain of myr4 and leave the catalytic head domain free to interact with F-actin.
Topics: Animals; Axonal Transport; Axons; Blotting, Western; Immunohistochemistry; In Situ Hybridization; Male; Motor Neurons; Myosin Type I; Protein Isoforms; Rats; Rats, Sprague-Dawley
PubMed: 15809075
DOI: 10.1016/j.bbrc.2005.02.187 -
Brain Research Jul 1977
Topics: Animals; Axons; Cell Membrane; Microscopy, Electron, Scanning; Rats; Schwann Cells; Sciatic Nerve
PubMed: 884515
DOI: 10.1016/0006-8993(77)90848-4 -
Journal of Neuroscience Research Mar 2004Pigment epithelium-derived factor (PEDF) is a multifunctional protein with known anti-angiogenic and trophic properties, capable of promoting the survival and growth of... (Comparative Study)
Comparative Study
Pigment epithelium-derived factor (PEDF) is a multifunctional protein with known anti-angiogenic and trophic properties, capable of promoting the survival and growth of Schwann cells (SC). Normal rat SCs and ganglioneuroma-derived human SCs secrete PEDF. The ability of normal SC to secrete a number of trophic factors is controlled by axonal contact. Normal human Schwann cells (HSC) and malignant peripheral nerve sheath tumors (MPNST) cell lines synthesize and secrete PEDF as determined by reverse transcription PCR analysis for PEDF mRNA, immunocytochemistry, and Western blot analysis for PEDF protein. Two MPNST cell lines secreted higher levels of PEDF than did HSC. A 90.3% decrease in PEDF mRNA and a 29.3% decrease in secreted PEDF were observed after treatment of HSC with axolemma-enriched fraction (AEF, 100 microg/ml), a neuronal membrane fraction of the axonal plasma membrane used with cultured SC to mimic axonal contact in vitro. PEDF levels remained unchanged, however, in MPNST-derived SC conditioned media under the same treatment paradigm. These results suggest that MPNST SC lose the ability to downregulate PEDF upon axonal contact, which is characteristic of HSC. The elevated PEDF levels expressed by MPNST cell lines may serve to promote their proliferation and survival.
Topics: Adult; Axons; Cell Membrane; Cells, Cultured; Down-Regulation; Eye Proteins; Gene Expression Regulation, Neoplastic; Humans; In Vitro Techniques; Nerve Growth Factor; Nerve Growth Factors; Nerve Sheath Neoplasms; Neurofibromatosis 1; Peripheral Nervous System Neoplasms; Proteins; RNA, Messenger; Reference Values; Schwann Cells; Serpins; Tumor Cells, Cultured; Up-Regulation
PubMed: 14991838
DOI: 10.1002/jnr.20002 -
The Journal of Membrane Biology Apr 1981Asymmetrical displacement currents are measured in the absence and in the presence of the lipophilic anion dipicrylamine (DPA) in the extracellular solution of nerve...
Asymmetrical displacement currents are measured in the absence and in the presence of the lipophilic anion dipicrylamine (DPA) in the extracellular solution of nerve fibers of the frog Rana esculenta. DPA (30 nM--3 microM) enhances the current by a component that has the properties expected for a translocation current of DPA ion across the lipid membrane. Analysis in terms of a single-barrier model yields the translocation rate constant (k), the total surface density of DPA absorbed to the membrane (Nt), and the equidistribution voltage (psi). The value of kappa of about 10(4) s-1 is similar to that for a solvent-free artificial bilayer formed by the Montal-Mueller method. The surface density Nt varies with the DPA concentration as it does in the artificial bilayer, but is about tenfold smaller at all concentrations. The DPA ions sense an intrinsic electric field that is offset by a transmembrane voltage between 0 and 30 mV (inside positive). The part of the axolemma probed by the DPA ion appears as a thin ( less than 2.5 nm), fluid bilayer of lipids. DPA ions seem, however, to be excluded from the major part of the axolemma as if this area is occupied by integral proteins or negative charges.
Topics: Animals; Biological Transport; Diphenylamine; Electric Conductivity; Ion Channels; Membrane Lipids; Membrane Proteins; Nerve Fibers, Myelinated; Neurilemma; Picrates; Rana esculenta
PubMed: 6264083
DOI: 10.1007/BF01875710 -
Cell Jan 2020The propagation of electrical impulses along axons is highly accelerated by the myelin sheath and produces saltating or "jumping" action potentials across internodes,...
The propagation of electrical impulses along axons is highly accelerated by the myelin sheath and produces saltating or "jumping" action potentials across internodes, from one node of Ranvier to the next. The underlying electrical circuit, as well as the existence and role of submyelin conduction in saltatory conduction remain, however, elusive. Here, we made patch-clamp and high-speed voltage-calibrated optical recordings of potentials across the nodal and internodal axolemma of myelinated neocortical pyramidal axons combined with electron microscopy and experimentally constrained cable modeling. Our results reveal a nanoscale yet conductive periaxonal space, incompletely sealed at the paranodes, which separates the potentials across the low-capacitance myelin sheath and internodal axolemma. The emerging double-cable model reproduces the recorded evolution of voltage waveforms across nodes and internodes, including rapid nodal potentials traveling in advance of attenuated waves in the internodal axolemma, revealing a mechanism for saltation across time and space.
Topics: Action Potentials; Animals; Axons; Male; Models, Neurological; Myelin Sheath; Nerve Fibers, Myelinated; Patch-Clamp Techniques; Pyramidal Cells; Ranvier's Nodes; Rats; Rats, Wistar
PubMed: 31883793
DOI: 10.1016/j.cell.2019.11.039 -
Proceedings of the Royal Society of... Feb 1988The density and diameter distributions of intramembranous particles (IMPs) within unmyelinated axolemma from rat cervical sympathetic trunk were examined with...
The density and diameter distributions of intramembranous particles (IMPs) within unmyelinated axolemma from rat cervical sympathetic trunk were examined with freeze-fracture electron microscopy. The axolemma displays a highly asymmetrical partitioning of IMPs with ca. 1200 IMPs microns-2 on P-faces and ca. 100 IMPs microns-2 on E-faces. Particle sizes (diameters) are unimodally distributed on both fracture faces, with a range from 2.4 nm to 15.6 nm. Approximately 16% of the particles on P-faces and 28% of particles on E-faces are of a large (greater than 9.6 nm) diameter. On both fracture faces, the IMPs appear to be randomly distributed; no aggregations of particles were observed. The results indicate that there are ca. 230 large IMPs microns-2 of unmyelinated axolemma from rat cervical sympathetic trunk. The density of these IMPs is similar to the density of saxitoxin binding sites on unmyelinated axolemma from rat cervical sympathetic trunk (Pellegrino et al. 1984 (Brain Res. 305, 357-360)), which suggests that many of the large diameter particles may be the morphological correlate of voltage-sensitive Na+ channels.
Topics: Animals; Axons; Cell Membrane; Freeze Fracturing; Ion Channels; Microscopy, Electron; Rats; Saxitoxin; Schwann Cells; Sodium; Sympathetic Nervous System
PubMed: 2451831
DOI: 10.1098/rspb.1988.0011 -
The Journal of General Physiology Sep 1966The penetration of (14)C-labeled erythritol, mannitol, and sucrose through the axolemma was determined in medium sized paired axons, one at rest and the other stimulated...
The penetration of (14)C-labeled erythritol, mannitol, and sucrose through the axolemma was determined in medium sized paired axons, one at rest and the other stimulated 25 times per sec. The resting permeabilities, in 10(-7) cm/sec, are erythritol, 2.9 +/- 0.3 (mean +/- SEM); mannitol, 2.3 +/- 0.4; and sucrose 0.9 +/- 0.1. In the stimulated axons they are: erythritol, 5.2 +/- 0.3; mannitol, 4.0 +/- 0.5; and sucrose, 1.8 +/- 0.3. Thus, the calculated permeabilities during activity (1 msec per impulse), in the same units, are: 100, 75, and 38, respectively. These changes in permeability are reversible. The effects of external potassium and sodium concentrations on erythritol penetration were also studied. At rest, erythritol penetration is independent of potassium and sodium concentrations. In the stimulated axons, erythritol penetration decreases when the extracellular sodium is diminished. Sodium influx (not the efflux) decreases during rest and activity when the extracellular sodium is diminished. The diminution during activity of erythritol and sodium entries in low sodium solutions may be related to a decrease of a drag effect of sodium ions on the nonelectrolyte molecules or to independent effects of the sodium concentration on sodium influx and the nonelectrolyte pathways. The axolemma discriminates among erythritol, mannitol, sucrose, and the different ionic species during rest and activity.
Topics: Alcohols; Animals; Axons; Carbon Isotopes; Cell Membrane; Cell Membrane Permeability; Erythritol; Mannitol; Mollusca; Neurons; Potassium; Sodium; Sucrose
PubMed: 5971032
DOI: 10.1085/jgp.50.1.43 -
Journal of Neuroscience Research Feb 1995The nature of the axon signal for the induction of proliferation and differentiation of peripheral glial cells is still unknown. Besides the existence of interactions...
The nature of the axon signal for the induction of proliferation and differentiation of peripheral glial cells is still unknown. Besides the existence of interactions among surface molecules the cellular responses can also be regulated by physicochemical parameters of the membrane. We have previously reported that planar axolemma monolayers coated on glass cover-slips at different defined surface molecular packing affected the Schwann cell (SC) morphology and their proliferative response (Calderon et al.: J Neurosci Res 34:206-218, 1993). In this paper we report that relative to SC cultured on uncoated coverslips, the level of expression of both glycoprotein Po and galactocerebroside (GC) (as revealed by immunofluorescence) was increased 2-4 times in SC cultured on axolemma monolayers with either high or low molecular packing. However, the cellular distribution of these antigens was profoundly influenced by the molecular packing density of the axolemma monolayer. SC cultured on an axolemma monolayer at high molecular packing showed preferential expression of Po at the SC surface whereas GC was concentrated intracellularly. On the other hand, SC grown on an axolemma monolayer at low molecular density GC showed preferential expression at the cell surface whereas Po was concentrated intracellularly.
Topics: Animals; Axons; Cell Count; Cells, Cultured; Fluorescence; Galactosylceramides; Glycoproteins; Immunohistochemistry; Rats; Schwann Cells
PubMed: 7745629
DOI: 10.1002/jnr.490400309 -
Journal of Neurotrauma Jul 1997Axons are particularly at risk in human diffuse head injury. Use of immunocytochemical labeling techniques has recently demonstrated that axonal injury (AI) and the... (Review)
Review
Axons are particularly at risk in human diffuse head injury. Use of immunocytochemical labeling techniques has recently demonstrated that axonal injury (AI) and the ensuing reactive axonal change is, probably, more widespread and occurs over a longer posttraumatic time in the injured brain than had previously been appreciated. But the characterization of morphologic or reactive changes occurring after nondisruptive AI has largely been defined from animal models. The comparability of AI in animal models to human diffuse AI (DAI) is discussed and the conclusion drawn that, although animal models allow the analysis of morphologic changes, the spatial distribution within the brain and the time course of reactive axonal change differs to some extent both between species and with the mode of brain injury. Thus, the majority of animal models do not reproduce exactly the extent and time course of AI that occurs in human DAI. Nonetheless, these studies provide good insight into reactive axonal change. In addition, there is developing in the literature considerable variance in the terminology applied to injured axons or nerve fibers. We explain our current understanding of a number of terms now present in the literature and suggest the adoption of a common terminology. Recent work has provided a consensus that reactive axonal change is linked to pertubation of the axolemma resulting in disruption of ionic homeostatic mechanisms within injured nerve fibers. But quantitative data for changes for different ion species is lacking and is required before a better definition of this homeostatic disruption may be provided. Recent studies of responses by the axonal cytoskeleton after nondisruptive AI have demonstrated loss of axonal microtubules over a period up to 24 h after injury. The biochemical mechanisms resulting in loss of microtubules are, hypothetically, mediated both by posttraumatic influx of calcium and activation of calmodulin. This loss results in focal accumulation of membranous organelles in parts of the length of damaged axons where the axonal diameter is greater than normal to form axonal swellings. We distinguish, on morphologic grounds, between axonal swellings and axonal bulbs. There is also a growing consensus regarding responses by neurofilaments after nondisruptive AI. Initially, and rapidly after injury, there is reduced spacing or compaction of neurofilaments. This compaction is stable over at least 6 h and results from the loss or collapse of neurofilament sidearms but retention of the filamentous form of the neurofilaments. We posit that sidearm loss may be mediated either through proteolysis of sidearms via activation of microM calpain or sidearm dephosphorylation via posttraumatic, altered interaction between protein phosphatases and kinase(s), or a combination of these two, after calcium influx, which occurs, at least in part, as a result of changes in the structure and functional state of the axolemma. Evidence for proteolysis of neurofilaments has been obtained recently in the optic nerve stretch injury model and is correlated with disruption of the axolemma. But the earliest posttraumatic interval at which this was obtained was 4 h. Clearly, therefore, no evidence has been obtained to support the hypothesis that there is rapid, posttraumatic proteolysis of the whole axonal cytoskeleton mediated by calpains. Rather, we hypothesize that such proteolysis occurs only when intra-axonal calcium levels allow activation of mM calpain and suggest that such proteolysis, resulting in the loss of the filamentous structure of neurofilaments occurs either when the amount of deformation of the axolemma is so great at the time of injury to result in primary axotomy or, more commonly, is a terminal degenerative change that results in secondary axotomy or disconnection some hours after injury.
Topics: Animals; Axons; Brain Injuries; Humans; Microscopy, Electron
PubMed: 9257661
DOI: 10.1089/neu.1997.14.419