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PubMed1980

Lack of glia-axon transfer of proteins in the normal optic system of goldfish.

An ultrastructural autoradiographic study of the goldfish optic tectum was carried out to determine whether proteins synthesized in glial cells are transferred into adjacent optic axons. Goldfish were injected intracranially over the optic tecta with [3H]leucine and fixed by perfusion 30 min, 4 and 24 h later. All unincorporated precursors were removed by repeated washings with fixatives, and tissue slices from the optic tecta were embedded and processed for electrom microscopy autoradiography (EMA). The densities of the silver grains were determined over optic axons and their myelin sheaths. The densities over the axons were lower than those over the myelin sheaths at all time intervals. The density of the intraaxonal grains, in absolute terms as well as relative to that of the myelin, was highest in the 4 h experiment. Analysis of the distribution of the grain densities over the myelin sheath and over concentric axonal compartments was carried out at this time interval to determine whether the grain density over the axon represented intraaxonal [3H]proteins or was only the result of grains 'scattered' from [3H]proteins located in the surrounding myelin sheaths. When the experimental distribution of the grain densities over the axon was compared with the theoretical distribution expected over the axon if only the myelin sheaths were labeled, no significant difference was found. This indicates that the silver grains present in the axons were scattered from the adjacent myelin sheath and did not represent intraaxonal radioactivity. It is therefore concluded that in our system there is not a quantitatively significant transfer of proteins between glial cells and adjacent axons.

Animals↗
PubMed1991

Lysosomal activity at nodes of Ranvier in dorsal column and dorsal root axons of the cat after injection of horseradish peroxidase in the dorsal column nuclei.

The occurrence of acid phosphatase (AcPase)-positive bodies, i.e. lysosomes, in dorsal column and dorsal root axons of the spinal cord segments C8 and L7 in adult cats was analyzed by light and electron cytochemical methods after injection of horseradish peroxidase (HRP) in the dorsal column nuclei. Axonal lysosomes were, with few exceptions, concentrated at the nodes of Ranvier. We found no changes in nodal occurrence and distribution of lysosomes in axons of the HRP-injected sides, as compared to axons of the uninjected sides or of animals not exposed to HRP. Axonal lysosomes were very rare in the dorsal columns, where the frequency of nodes containing light microscopically detectable AcPase-positive bodies was 0-5% at the HRP-injected sides, 0-6% at the contralateral sides, and 0-3% in control animals. The corresponding values in the cervical and lumbar dorsal roots were 6-23%, 9-20%, 10-12% and 19-37%, 21-40%, 26-43%, respectively. In view of our recent observations in alpha-motor neurons, the results point at a noteworthy difference in local degradative ability between dorsal column axons and alpha-motor axons, the latter being able to accumulate intramuscularly injected and retrogradely transported HRP at their PNS nodes of Ranvier for 48-60 h, during which period the axoplasmic AcPase activity/concentration increases at some nodes. Such a degradative activity, which could protect the motor neurons by restricting axoplasmic transport of exogenous materials imbibed by their axon terminals outside the CNS, may not be of the same significance for neurons, e.g. dorsal root ganglion neurons, the axon terminals of which are located within the CNS.

Acid Phosphatase↗
PubMed1989

Early posttranslational modifications of the three neurofilament subunits in mouse retinal ganglion cells: neuronal sites and time course in relation to subunit polymerization and axonal transport.

We have characterized stages in the posttranslational processing of the three neurofilament subunits, High (NF-H), Middle (NF-M), and Low (NF-L), in retinal ganglion cells in vivo during the interval between synthesis in cell bodies within the retina and appearance of these polypeptides in axons at the level of the optic nerve (optic axons). Neurofilament proteins pulse-labeled by injecting mice intravitreally with [35S]methionine or [32P]orthophosphate, were isolated from Triton-soluble and Triton-insoluble fractions of the retina or optic axons by immunoprecipitation or immunoaffinity chromatography. Within 2 h after [35S]methionine injection, the retina contained neurofilament-immunoreactive radiolabeled proteins with apparent molecular weights of 160, 139, and 70 kDa, which co-migrated with subunits of axonal neurofilaments that were dephosphorylated in vitro with alkaline phosphatase. The two larger polypeptides were not labeled with [32P]orthophosphate, indicating that they were relatively unmodified forms of NF-H and NF-M. About 75% of the subunits were Triton-insoluble by 2 h after isotope injection, and this percentage increased to 98% by 6 h. Labeled neurofilament polypeptides appeared in optic axons as early as 2 h after injection. These subunits exhibited apparent molecular weights of 160, 139, and 70 kDa and were Triton-insoluble. The time of appearance of fully modified polypeptide forms differed for each subunit (2 h for NF-L, 6-18 h for NF-M, 18-24 h for NF-H) and was preceded by the transient appearance of intermediate forms. The modified radiolabeled subunits in optic axons 3 days after synthesis were heavily labeled with [32P]orthophosphate and exhibited the same apparent molecular weights as subunits of axonal neurofilaments (70 kDa, 145 and 140 kDa, and 195-210 kDa, respectively). Whole mounts of retina immunostained with monoclonal antibodies against NF-H in different states of phosphorylation demonstrated a transition from non-phosphorylated neurofilaments to predominantly phosphorylated ones within a region of the axon between 200 and 1000 microns downstream from the cell body. These experiments demonstrate that the addition of most phosphate groups to NF-M and NF-H takes place within a proximal region of the axon. The rapid appearance of modified forms of NF-L after synthesis may imply that processing of this subunit occurs at least partly in the cell body. The presence of a substantial pool of Triton-insoluble, unmodified subunits early after synthesis indicates that the heaviest incorporation of phosphate occurs after neurofilament proteins are polymerized.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2004

Calcium overloading in traumatic axonal injury by lateral head rotation: a morphological evidence in rat model.

The study investigated morphologically axonal calcium overloading and its relationship with axonal structural changes. Twelve SD rats were divided into an injury and a sham group. The rat model of traumatic axonal injury (TAI) by lateral head rotation was produced. The oxalate-pyroantimonate technique for calcium localization was used to process the rat's medulla oblongata tissues with thin sections observed electron-microscopically for axonal structure and calcium precipitates on it. The axonal damage in medulla oblongata appeared at 2 h post-injury, gradually became diffuse and severe, and continued to exist at 24 hours. At 2 hours, calcium precipitates were deposited on separated lamellae and axolemma, but were rarely distributed in the axoplasm. At 6 hours, calcium precipitates occurred on separated lamellae and axolemma in much higher density, but on axoplasm in extremely small amounts. Some axons, though lacking structural changes of the myelin sheath, sequestered plenty of calcium deposits on their swollen mitochondria. At 24 hours, damaged axons presented with much more severe lamellae separation and calcium deposits. Axonal calcium overloading developed in rat TAI model using lateral head rotation. This was significantly related to structural damage in the axons. These findings suggest the feasibility of using calcium antagonists in cope the management of human DAI in its very early stage.

Animals↗
PubMed1997

Three-dimensional morphology and distribution of pallidal axons projecting to both the lateral region of the thalamus and the central complex in primates.

This study presents a three-dimensional analysis of pallido-thalamic axons and axonal endings in the monkey (Macaca mulatta and M. irus). Injections of the anterograde tracer biocytin were made in the dorsal, associative region of the medial pallidum. Numerous axonal endings were observed within the pallidal territory of the lateral region of the thalamus and the central complex. Individual axons were reconstructed from serial sections and traced in three dimensions. Two axons made a collateral branch in the ventral part of the lateral region and ended in the central complex. In the pallidal territory of the lateral region, axons divided several times before ending in different parts of the territory in a 'bunch', a characteristic dense terminal arborization. Axonal endings in the central complex were differently organized. Our data show that associative medial pallidal information is distributed throughout the pallidal territory of the lateral region and the pars media of the central complex by means of individual axons with numerous branches and axonal endings specific to each of the two targets.

Animals↗
PubMedDate not supplied

Protein synthesis in axons and its possible functions.

Proteins synthesized in neuronal cell bodies are transported along axons by fast and slow axonal transport. Cytoskeletal proteins and cytosolic proteins that travel by slow axonal transport could take years to reach the terminals of meter-long axons, and it is difficult to see how proteins could last long enough to make this journey. How then are proteins supplied to the distal regions of long axons? Evidence has accumulated indicating that axons contain specific mRNAs and ribosomes and can synthesize cytoskeletal proteins and some other proteins. This review considers the direct evidence that proteins can be synthesized in axons and considers the possible functional significance of axonal protein synthesis. It remains unclear whether local protein synthesis could supply the cytoskeletal proteins and other slow-transported proteins required for the maintenance, plasticity, and regeneration of long axons.

Animals↗
PubMed1990

Turnover of fluorescently labelled tubulin and actin in the axon.

The cytoskeleton has an important role in the generation and maintenance of the structure of the axon. Microtubules, neurofilaments and actin, together with various kinds of associated proteins, form highly organized dynamic cytoskeletal structures. Because tubulin and actin molecules are essential cytoskeletal components and are transported down the axon, it is important to understand their dynamic behaviour within the axon. Although previous pulse-labelling studies have indicated that the axonal cytoskeleton is a static complex travelling down the axon, this view has been challenged by the results of several recent experiments. We have now addressed this question by analysing the recovery of fluorescence after photobleaching fluorescent analogues of tubulin and actin in the axons of cultured neurons. We did not observe movement or spreading of bleached zones along the axon, both in neurons injected with fluorescein-labelled tubulin and actin. All bleached zones recovered their fluorescence gradually, however, indicating that microtubules and actin filaments are not static polymers moving forward within the axon, but are dynamic structures that continue to assemble along the length of the axon.

Actins↗
PubMed1990

Synthesis, axonal transport, and turnover of the high molecular weight microtubule-associated protein MAP 1A in mouse retinal ganglion cells: tubulin and MAP 1A display distinct transport kinetics.

Microtubule-associated proteins (MAPs) in neurons establish functional associations with microtubules, sometimes at considerable distances from their site of synthesis. In this study we identified MAP 1A in mouse retinal ganglion cells and characterized for the first time its in vivo dynamics in relation to axonally transported tubulin. A soluble 340-kD polypeptide was strongly radiolabeled in ganglion cells after intravitreal injection of [35S]methionine or [3H]proline. This polypeptide was identified as MAP 1A on the basis of its co-migration on SDS gels with MAP 1A from brain microtubules; its co-assembly with microtubules in the presence of taxol or during cycles of assembly-disassembly; and its cross-reaction with well-characterized antibodies against MAP 1A in immunoblotting and immunoprecipitation assays. Glial cells of the optic nerve synthesized considerably less MAP 1A than neurons. The axoplasmic transport of MAP 1A differed from that of tubulin. Using two separate methods, we observed that MAP 1A advanced along optic axons at a rate of 1.0-1.2 mm/d, a rate typical of the Group IV (SCb) phase of transport, while tubulin moved 0.1-0.2 mm/d, a group V (SCa) transport rate. At least 13% of the newly synthesized MAP 1A entering optic axons was incorporated uniformly along axons into stationary axonal structures. The half-residence time of stationary MAP 1A in axons (55-60 d) was 4.6 times longer than that of MAP 1A moving in Group IV, indicating that at least 44% of the total MAP 1A in axons is stationary. These results demonstrate that cytoskeletal proteins that become functionally associated with each other in axons may be delivered to these sites at different transport rates. Stable associations between axonal constituents moving at different velocities could develop when these elements leave the transport vector and incorporate into the stationary cytoskeleton.

Animals↗
PubMed1982

Cross-linker system between neurofilaments, microtubules, and membranous organelles in frog axons revealed by the quick-freeze, deep-etching method.

The elaborate cross-connections among membranous organelles (MO), microtubules (MT), and neurofilaments (NF) were demonstrated in unifixed axons by the quick-freeze, deep-etch, and rotary-shadowing method. They were categorized into three groups: NF-associated cross-linker, MT-associated cross-bridges, and long cross-links in the subaxolemmal space. Other methods were also employed to make sure that the observed cross-connections in the unfixed axons were not a result of artifactual condensation or precipitation of soluble components or salt during deep-etching. Axolemma were permeablized either chemically (0.1% saponin) or physically (gentle homogenization), to allow egress of their soluble components from the axon; or else the axons were washed with distilled water after fixation. After physical rupture of the axolemma or saponin treatment, most of the MO remained intact. MT were stabilized by adding taxol in the incubation medium. Axons prepared by these methods contained many longitudinally oriented NF connected to each other by numerous fine cross-linkers (4-6 nm in diameter, 20-50 nm in length). Two specialized regions were apparent within the axons: one composed of fascicles of MT linked with each other by fine cross-bridges; the other was in the subaxolemmal space and consisted of actinlike filaments and a network of long cross-links (50-150 nm) which connected axolemma and actinlike filaments with NF and MT. F-actin was localized to the subaxolemmal space by the nitrobenzooxadiazol phallacidin method. MO were located mainly in these two specialized regions and were intimately associated with MT via fine short (10-20 nm in length) cross-bridges. Cross-links from NF to MO and MT were also common. All these cross-connections were observed after chemical extraction or physical rupture of the axon; however, these procedures removed granular materials which were attached to the filaments in the fresh unextracted axons. The cross-connections were also found in the axons washed with distilled water after fixation. I conclude that the cross- connections are real structures while the granular material is composed of soluble material, probably protein in nature.

Actins↗
PubMed1982

Redistribution of proteins of fast axonal transport following administration of beta,beta'-iminodipropionitrile: a quantitative autoradiographic study.

Beta,beta'-iminodipropionitrile (IDPN) produces a rearrangement of axoplasmic organelles with displacement of microtubules, smooth endoplasmic reticulum, and mitochondria toward the center and of neurofilaments toward the periphery of the axon, whereas the rate of the fast component of axonal transport is unchanged. Separation of microtubules and neurofilaments makes the IDPN axons an excellent model for study of the role of these two organelles in axonal transport. The cross-sectional distribution of [3H]-labeled proteins moving with the front of the fast transport was analyzed by quantitative electron microscopic autoradiography in sciatic nerves of IDPN-treated and control rats, 6 h after injection of a 1:1 mixture of [3H]-proline and [3H]-lysine into lumbar ventral horns. In IDPN axons most of the transported [3H] proteins were located in the central region with microtubules, smooth endoplasmic reticulum and mitochondria, whereas few or none were in the periphery with neurofilaments. In control axons the [3H]-labeled proteins were uniformly distributed within the axoplasm. It is concluded that in fast axonal transport: (a) neurofilaments play no primary role; (b) the normal architecture of the axonal cytoskeleton and the normal cross-sectional distribution of transported materials are not indispensable for the maintenance of a normal rate of transport. The present findings are consistent with the models of fast transport that envision microtubules as the key organelles in providing directionality and propulsive force to the fast component of axonal transport.

Animals↗
PubMed1980

The axonal pathology in chronic IDPN intoxication.

Neurofilamentous axonal swellings occur in a number of degenerative and toxic disorders of the nervous system. In one of these, experimental intoxication with beta, beta'-iminodiproprionitrile (IDPN), accumulation of neurofilaments has been shown to result from a defect in slow axonal transport. The consequence of this functional abnormality is a series of changes in axonal morphology: Neurofilaments accumulate in the proximal axon; the proximal axon becomes swollen; the distal axon loses volume (axonal atrophy). These studies indicate that axonal atrophy occurs secondary to an impairment of slow axonal transport and suggest that a similar abnormality may underlie the pathological changes in certain other degenerative and toxic diseases of the nervous system.

Animals↗
PubMed1980

Fast axonal transport of foreign transmitters in an identified serotonergic neurone of Aplysia californica.

1. Radioactively labelled compounds, several of which are neurotransmitters, were injected with pressure into the soma of the serotonergic giant cerebral neurone (g.c.n.) of Aplysia californica. The compounds injected were [3H]dopamine, [3H]DL-octopamine, [3H]histamine, [3H]gamma-aminobutyric acid and [3H]choline. 2. Substantial amounts of radioactivity appeared in the axons of the g.c.n. with all of the injected compounds. Except for [3H]choline, the amounts were similar to the amount appearing when [3H]serotonin is injected. 3. The biogenic amines, [3H]dopamine, DL-[3H]octopamine and [3H]histamine, all moved in the axon at velocities similar to that of [3H]serotonin. In contrast, the radioactivity in axons of cells injected with [3H]gamma-aminobutyric acid and [3H]choline moved much more slowly. In addition, the shapes of the spatial distributions of radioactivity in the axons of cells injected with the biogenic amines resembled that obtained when [3H]serotonin is injected. This distribution is characteristic of fast axonal transport. The spatial distributions of radioactivity in the axons of cells injected with [3H]gamma-aminobutyric acid and [3H]choline were markedly different. We thus conclude that [3H]dopamine, DL-[3H]octopamine and [3H]histamine move by fast axonal transport, whereas the radioactivity in the axons of cells injected with [3H]gamma-aminobutyric acid and [3H]choline does not. 4. Injection of large amounts of dopamine and octopamine reduced the export into the axon of [3H]serotonin injected into the same cell. Large amounts of choline did not reduce export of [3H]serotonin. We conclude that the biogenic amines compete with serotonin for the vesicular storage site and that they move by fast transport because they are sequestered by the serotonergic storage vesicle. 5. The specificity of uptake into the storage vesicle as assayed with this in vivo system is similar to the specificity of uptake into aminergic vesicles as previously studied in vitro.

Animals↗
PubMed1996

Morphology of individual axons in crossed corticorubral projections in developing cats and effects of partial denervation.

Ordered neuronal connections in mature brains are thought to be sculpted from initially diffuse projections by elimination of inappropriate projections and strengthening of appropriate ones. Although evidence suggests that neuronal activity plays a role in these processes, the mechanism behind the modification of neuronal connections remains obscure. To gain insight into the mechanisms of axonal elimination and projection strengthening, we examined the morphology of individual axons that were to be eliminated as well as the consequences of partial denervation. While corticorubral projections in adult cats are thought to be uncrossed, early in postnatal development and after early unilateral lesions to the sensorimotor cortex, however, a significant amount of crossed corticorubral projections occurs. We examined the morphology of individual corticorubral axons in fetal cats and kittens from embryonic day 59 to postnatal day 48 and those that had received early unilateral lesions to the cortex, by serial reconstruction of Phaseolus-vulgaris-leucoagglutinin- or biocytin-labeled axons. For about 2 weeks during pre- and postnatal development, crossed axons remained simple in morphology, with few branches. Thereafter, they showed an increase in branch number, but then began to show fewer branches again. Axons and their collaterals were found in nonrestricted areas of the red nucleus (RN) throughout the period of observation, indicating that axons can sit at an inappropriate target for weeks but fail to ramify. In contrast, crossed corticorubral axons in kittens with cortical lesions showed terminal-arbor-like structures in the RN region that are in mirror symmetry to topographically appropriate areas in the ipsilateral RN, although some showed simple morphology without arbors. These complicated forms of morphology of individual axons during development and after partial denervation may not be explained by a simple activity-dependent mechanism.

Animals↗
PubMed1995

Evidence of constriction of optic nerve axons at the lamina cribrosa in the normotensive eye in humans and other mammals.

The ultrastructure of optic nerve axons was examined in several mammals (human, cat, rat, sheep, ox, pig, guinea pig, rabbit). Human material was obtained from normotensive, glaucoma-free eyes and from eyes with a history of glaucoma and raised intra-ocular pressure (IOP). We describe accumulations of organelles (principally mitochondria) in optic nerve axons where they traverse the lamina cribrosa. Accumulations were most prominent in unmyelinated lengths of axons close to lamellae of the lamina cribrosa. Comparable accumulations were not apparent in axons in the retina or optic nerve, suggesting that axoplasmic flow is constricted at the lamina cribrosa. Accumulations were observed both centrally and peripherally to the lamellae, suggesting that flow is constricted in both ortho- and anterograde directions. Accumulations of organelles were more marked in unmyelinated axons than in adjacent, myelinated axons. In the rabbit, in which most axons are myelinated as they traverse the optic nerve head, organelle accumulations were observed only in a sparse population of unmyelinated axons. In human eyes with a history of raised IOP and glaucoma, the accumulations were abnormally large and frequent and in many axons showed dense-body and fibrillar changes not seen in normotensive eyes. It is suggested that chronic, partial constriction of axoplasmic flow is present at the lamina cribrosa of normotensive eyes in a wide range of mammals, including humans, that the constriction results from the pressure gradient across the lamina cribrosa and that the constriction may be a factor in the many cases of primary glaucoma in which IOP is not raised.

Adult↗
PubMed1993

Spinal cord transection in adult rats: effects of local infusion of nerve growth factor on the corticospinal tract axons.

The spinal cord of adult female rats was completely transected at the T8 level. Nerve growth factor (NGF) was administered at the lesion site via indwelling, implanted, osmotic minipumps. Purified NGF was supplied at doses of 100, 200, and 500 micrograms during a 30-day period. Control rats were treated with saline. At the end of the treatment, the proximal stump of corticospinal tract axons in the spinal cord was labeled with anterograde transported horseradish peroxidase (HRP) injected into the sensorimotor cortex. In control rats, the corticospinal tract axons ended abruptly, proximal to the zone of maximal damage. Sterile swellings developed at the axon tips, and no labeled axonal sprouts were apparent. On the contrary, in NGF-treated animals, the leading front of the corticospinal tract axons showed a trend of approaching the zone of maximal damage following abnormal paths through the dorsal-injured white matter. Axonal sprouts were seen more proximally, traveling toward the transection site in aberrantly located dorsal paths, completely outside the normal position of the corticospinal tract. NGF seems to partly restore the pattern of the regenerative behavior of the severed corticospinal tract axons after spinal cord transection in newborn rats, i.e., the induction of axonal sprouting in aberrantly located dorsal paths. An automated image analysis of the HRP reaction field close to the transection site demonstrated that the density of HRP-labeled axons in the corticospinal tract was significantly higher in the NGF-treated rats than in the control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

Traumatic axonal injury induces calcium influx modulated by tetrodotoxin-sensitive sodium channels.

Diffuse axonal injury (DAI) is one of the most common and important pathologies resulting from the mechanical deformation of the brain during trauma. It has been hypothesized that calcium influx into axons plays a major role in the pathophysiology of DAI. However, there is little direct evidence to support this hypothesis, and mechanisms of potential calcium entry have not been explored. In the present study, we used an in vitro model of axonal stretch injury to evaluate the extent and modulation of calcium entry after trauma. Using a calcium-sensitive dye, we observed a dramatic increase in intra-axonal calcium levels immediately after injury. Axonal injury in a calcium-free extracellular solution resulted in no change in calcium concentration, suggesting an extracellular source for the increased post-traumatic calcium levels. We also found that the post-traumatic change in intra-axonal calcium was completely abolished by the application of the sodium channel blocker tetrodotoxin or by replacement of sodium with N-methyl-d-glucamine. In addition, application of the voltage-gated calcium channel (VGCC) blocker omega-conotoxin MVIIC attenuated the post-traumatic increase in calcium. Furthermore, blockade of the Na(+)-Ca(2+) exchanger with bepridil modestly reduced the calcium influx after injury. In contrast to previously proposed mechanisms of calcium entry after axonal trauma, we found no evidence of calcium entry through mechanically produced pores (mechanoporation). Rather, our results suggest that traumatic deformation of axons induces abnormal sodium influx through mechanically sensitive Na(+) channels, which subsequently triggers an increase in intra-axonal calcium via the opening of VGCCs and reversal of the Na(+)-Ca(2+) exchanger.

Axons↗
PubMed1989

Changes in cytoskeletal gene expression affect the composition of regenerating axonal sprouts elaborated by dorsal root ganglion neurons in vivo.

The effect of a change in neurofilament (NF) and tubulin gene expression on the elongation of axonal sprouts by adult rat sensory neurons was examined. Distal sciatic nerve crush axotomy was used to initiate changes in cytoskeletal gene expression in lumbar dorsal root ganglion (DRG) neurons. In situ hybridization of DRG neurons with 35S-labeled cDNA probes revealed a significant reduction in the level of mRNAs for the low-molecular weight-NF protein and a significant increase in the level of beta tubulin mRNAs by 2 weeks after axotomy. A novel modification of the axonal transport paradigm was used to examine the biochemical composition of the regenerating axons formed by primed and unprimed DRG neurons. Primed neurons (which had sustained a crush axotomy of the distal sciatic nerve 2 weeks earlier) and unprimed (normal) neurons were labeled by microinjection of 35S-methionine and then stimulated to regenerate axons by a crush located very close to the DRG. In this paradigm, axonal sprouts that formed after the proximal crush axotomy incorporated radiolabeled, slow axonally transported proteins as they elongated. Fluorographs of SDS-PAGE revealed that the regenerating axonal sprouts of primed DRG cells incorporated and conveyed significantly less labeled NF protein than did the regenerating axons of unprimed DRG neurons. Electron microscopy revealed that the regenerating axonal sprouts of primed DRG cells contained numerous microtubules but very few identifiable NFs compared with the regenerating sprouts of unprimed DRG neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Optic nerve axons and acquired alterations in the appearance of the optic disc.

The pathophysiologic events in optic nerve axons have recently been recognized as crucial to an understanding of clinically significant acquired alterations in the ophthalmoscopic appearance of the optic disc. Stasis and related abnormalities of axonal transport appear to explain most aspects of optic nerve head swelling, including optic disc drusen and retinal cottonwool spots. Loss of axoplasm and axonal death can be invoked to interpret optic disc pallor, thinning and narrowing of rim tissue, changes in the size and outline of the optic cup, laminar dots, atrophy of the retinal nerve fiber layer, and acquired demyelination and myelination of the retinal nerve fiber layer. It is speculated that the axons may also play a role in the mechanical support of the lamina cribrosa in resisting the pressure gradient across the pars scleralis of the optic nerve head. Axons and their associated glial cells may be involved in those cases where "reversibility" of cupping of the optic disc has been reported. The structure, physiology, and experimental pathologic findings of the optic nerve head have been reviewed. Many aspects concerning the final anatomic appearance of the optic nerve head have been explained. However, many questions remain concerning the intermediate mechanisms by which increased intracranial pressure retards the various components of axonal transport in papilledema and by which increased IOP causes axonal loss in glaucoma. Investigation of the molecular biology of axonal constituents and their responses to abnormalities in their physical and chemical milieu could extend our understanding of the events that result from mechanical compression and local ischemia. Moreover, we have identified a need to further explore the role of axons in the pathophysiology of optic disc cupping.

Animals↗