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PubMed1985

Proteins transported in slow components a and b of axonal transport are distributed differently in the transverse plane of the axon.

The distribution of the proteins migrating with the slow components a (SCa) and b (SCb) of axonal transport were studied in cross-sections of axons with electron microscope autoradiography. Radiolabeled amino acids were injected into the hypoglossal nucleus of rabbits and after 15 d, the animals were killed. Hypoglossal nerves were processed either for SDS-polyacrylamide gel electrophoresis fluorography to identify and locate the two components of slow transport, or for quantitative electron microscope autoradiography. Proteins transported in SCa were found to be uniformly distributed within the cross-section of the axon. Labeled SCb proteins were also found throughout the axonal cross-section, but the subaxolemmal region of the axon contained 2.5 times more SCb radioactivity than any comparable area in the remainder of the axon.

Actins↗
PubMed1989

Differential axonal transport of isotubulins in the motor axons of the rat sciatic nerve.

The axonal transport of the diverse isotubulins in the motor axons of the rat sciatic nerve was studied by two-dimensional polyacrylamide gel electrophoresis after intraspinal injection of [35S]methionine. 3 wk after injection, the nerve segments carrying the labeled axonal proteins of the slow components a (SCa) and b (SCb) of axonal transport were homogenized in a cytoskeleton-stabilizing buffer and two distinct fractions, cytoskeletal (pellet, insoluble) and soluble (supernatant), were obtained by centrifugation. About two-thirds of the transported-labeled tubulin moved with SCa, the remainder with SCb. In both waves, tubulin was found to be associated mainly with the cytoskeletal fraction. The same isoforms of tubulin were transported with SCa and SCb; however, the level of a neuron-specific beta-tubulin subcomponent, termed beta', composed of two related isotubulins beta'1 and beta'2, was significantly greater in SCb than in SCa, relative to the other tubulin isoforms. In addition, certain specific isotubulins were unequally distributed between the cytoskeletal and the soluble fractions. In SCa as well as in SCb, alpha''-isotubulins were completely soluble in the motor axons. By contrast, alpha''' and beta'2-isotubulins, both posttranslationally modified isoforms, were always recovered in the cytoskeletal fraction and thus may represent isotubulins restricted to microtubule polymers. The different distribution of isotubulins suggests that a recruitment of tubulin isoforms, including specific posttranslational modifications of defined isoforms (such as, at least, phosphorylation of beta' and acetylation of alpha'), might be involved in the assembly of distinct subsets of axonal microtubules displaying differential properties of stability, velocity and perhaps of function.

Animals↗
PubMed2003

Restriction of axonal retraction and promotion of axonal regeneration by chronically injured neurons after intraspinal treatment with glial cell line-derived neurotrophic factor (GDNF).

The response of supraspinal neurons to acute or delayed treatment with GDNF following a spinal cord injury was examined. A cervical level 3 hemisection lesion cavity was created by tissue aspiration in adult, female rats. In one experiment gel foam saturated with GDNF was placed into the lesion cavity immediately after injury to determine if the extent of axonal retraction was affected by neurotrophic factor treatment. One week prior to sacrifice animals received a microinjection of biotinylated dextran amine (BDA) into the red nucleus and reticular formation to label descending spinal pathways by anterograde transport mechanisms. Animals were sacrificed 1 or 4 weeks after injury and treatment with GDNF. The terminal end of injured BDA-labeled rubrospinal and reticulospinal tract axons was identified and the distance from the lesion was measured. In comparison to PBS-treated animals, GDNF-treatment resulted in a significant decrease in the extent of axonal retraction of both rubrospinal and reticulospinal tract axons at 1 week after spinal cord injury for both tracts. At 4 weeks after injury the mean distance from the lesion was less than 240 microm following GDNF-treatment for both tracts, compared to over 480 microm following PBS-treatment. In the second experiment injured supraspinal neurons were labeled by retrograde transport of True Blue that had been placed into the lesion cavity. One month later scar tissue was removed from the cavity by aspiration to enlarge the cavity by approximately 500 microm in a rostral direction. GDNF-saturated gel foam was placed into the cavity for 60 min prior to apposition of an autologous peripheral nerve (PN) graft to the rostral cavity wall. One month later Nuclear Yellow was applied to the distal end of the PN graft and animals were sacrificed after 2 days. The number of supraspinal neurons containing both True Blue and Nuclear Yellow was counted as a measure of axonal regeneration by chronically injured neurons. There was a seven-fold increase in the number of regenerating neurons after GDNF-treatment, with the majority (65%) of dual-labeled neurons located within the reticular formation. These results indicate that GDNF has neuroprotective effects when provided acutely after injury and promotes axonal regeneration when provided in a chronic injury situation.

Animals↗
PubMed1990

Target selection by cortical axons: alternative mechanisms to establish axonal connections in the developing brain.

We have described our studies of the development of projections from layer 5 of the rat neocortex to subcortical targets in the midbrain and hindbrain. The major points are briefly summarized here. 1. Layer-5 neurons extend a primary axon out of cortex and along a spinally directed trajectory, bypassing all of their targets in the midbrain and hindbrain. These targets are later contacted exclusively by collaterals formed by a delayed interstitial branching of the primary axon, not by growth cone bifurcation. 2. Collateral branches only form at stereotypic positions, not randomly along the length of the axon. Thus, specific cues identify branch points, and the length of the primary axon well behind its growth cone responds to these cues. 3. Layer-5 neurons in diverse areas of cortex initially develop the same basic set of collateral branches, although they will permanently retain different subsets of the initial common set. Therefore, branch cues are recognized by layer-5 neurons independent of whether the collateral projection formed is functionally appropriate for the cortical region in which the neuron resides. 4. In vitro and in vivo evidence indicates that one of the major branches, which forms the corticopontine projection, is induced and directed into its target, the basilar pons, by a diffusible, target-derived, tropic signal. Thus, a chemotropic cue promotes recognition of the basilar pontine target by the primary layer-5 axons. 5. In this system, then, target selection is not the responsibility of the growth cone of the primary axon.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Axonal transport of polyamines in intact and regenerating axons of the rat sciatic nerve.

The axonal transport of putrescine or its polyamine derivatives spermidine or spermine is a subject of some debate. We investigated this question by injecting [3H]putrescine into the lumbar spinal cord of the rat and measuring the accumulation of radioactivity central to ligatures placed on intact and regenerating sciatic nerves. In normal nerves, approximately twice as much radioactivity built up proximal to these ligatures 2 or 3 days after injection than at more distal ligatures used to control for accumulation of radioactivity which might be due to tissue damage alone. In regenerating nerves the amount of radioactivity accumulating at the ligature was approximately five times that at the distal ligature and two to three times greater than in intact nerves. The identity of the radioactivity in regenerating nerves, determined on an amino acid analyzer, was found to be primarily spermidine and an unknown compound that migrated as a frontal elution peak. Autoradiographic analysis showed that the radioactivity was largely confined to axons, but a significant amount of the silver grains was associated with Schwann cells and myelin sheaths surrounding labeled axons in both intact and regenerating nerves. The data indicate that polyamine derivatives of putrescine are transported axonally in rat sciatic nerves, and some of this transported material accumulates in Schwann cells surrounding the labeled axons. These processes are apparently augmented during regeneration of the injured axons.

Animals↗
PubMed1982

Nerve impulse blockage in squid axons by n-alkanes: the effect of axon diameter.

1. The anaesthetic effects of aqueous solutions of the n-alkanes pentane to nonane on the propagated action potential of squid axons have been investigated for a range of axon diameters. 2. By the use of small axons (approx. 200 microns diameter) to minimize effects due to long diffusion times and alkane depletion it was found that n-pentane and n-hexane caused a rapid reversible inhibition of the impulse, while higher homologues had progressively less effect, n-nonane being apparently inert. 3. The rate of action potential decline due to the n-alkanes was found to be strongly dependent on axon diameter. For n-hexane, n-heptane and n-octane the rate of decline was inversely proportional to the square of the axon diameter. 4. The mechanisms which may underly the increased sensitivity of small axons to impulse blockade by n-alkanes are discussed. A quantitative comparison is made between the effects of n-hexane, n-heptane and n-octane on the action potential. It is argued that this supports the idea of a real decline in anaesthetic potency on ascending the homologous series, rather than an effect due to long diffusion times and solution depletion.

Action Potentials↗
PubMed1991

Ultrastructure of axons in stereotaxically placed ibotenic acid-induced lesions of the hippocampus in the adult rat. Evidence for demyelination and degeneration of dispersed axons of passage.

The fate of axons in lesions following stereotaxic injections of ibotenic acid into the rat hippocampus was studied on the ultrastructural level. Myelinated and unmyelinated axons were examined in the, presumably, axon sparing lesions induced by circumscribed in vivo injections of ibotenic acid. In lesions placed in the dentate gyrus or parts of the Ammon's horn a considerable amount of dispersed myelinated axons of passage were affected, showing a characteristic pattern of demyelination and suggesting the involvement of oligodendroglia processes. However, the structural integrity of unmyelinated axons of passage, studied with the example of the mossy fiber system, was completely unaffected after exposure to ibotenic acid. Thus, at least in the hippocampus, in situ injections of ibotenic acid cannot be looked upon as being completely axon sparing as frequently proposed.

Animals↗
PubMed1988

Experimental diabetic neuropathy: similar changes of slow axonal transport and axonal size in different animal models.

Analysis of slow axonal transport in sciatic and primary visual systems of BB rats with spontaneous diabetes of 2.5-3.5 months duration revealed a delay in transport of the neurofilament (NF) subunits, tubulin, actin, and the 60, 52, and 30 kDa polypeptides in both systems. The polypeptides examined were not affected uniformly. Rather, the transport of the 60, 52, and 30 kDa polypeptides and the rapidly moving component of tubulin, all constituents of the slow component b (SCb) of axonal transport, appeared to be more severely delayed than the transport of polypeptide constituents of the slow component a (SCa), such as NF and the slow-moving tubulin. Transport was not impaired in diabetic BB rats maintained normoglycemic with optimal doses of insulin. A 52 kDa polypeptide constituent of SCb was identified as neuron-specific enolase, and the 30 and 60 kDa polypeptides are likely to be aldolase and pyruvate kinase; all 3 are glycolytic enzymes. Morphometric analysis revealed that the cross-sectional area of sciatic axons was increased proximally at the level of the motor roots and decreased distally at the level of the tibial nerve. The changes in slow transport and caliber observed in central and peripheral axonal systems of diabetic BB rats are virtually identical to those previously described in rats with streptozotocin-induced diabetes, another model of insulin-dependent diabetes. In both models, the alterations of axonal caliber are likely to be secondary to the impairment of axonal transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Paths of axons in the visual system of perciform fish and implications of these paths for rules governing axonal growth.

The optic nerve of many perciform fish is ribbon-shaped, and axons from ganglion cells in specific parts of the retina are consistently found in specific places in this ribbon. I utilized this organization to fill selected groups of axons with horseradish peroxidase. I then traced these groups of axons through the nerve and across the tectum to their terminal arbors. The paths of the axons suggest that axons use a number of different mechanisms to guide them to their correct terminal sites. At some points they appear simply to grow along the surface created by earlier axons, but at other points they seem to be using cues more complex than simple mechanical guidance. In addition, I have demonstrated that for every anulus of ganglion cells on the retina there is an anulus of terminal arbors on the tectum. With time the terminals in a given anulus must move caudally to keep the retinotopic map centered on the tectum while the tectum continues growing nonsymmetrically . I have shown both that the anuli of terminals do remain roughly centered on the tectum and that the predicted pattern of terminal movement is visible on the tecta of perciform fish.

Animals↗
PubMed2001

Induction and axonal localization of epithelial/epidermal fatty acid-binding protein in retinal ganglion cells are associated with axon development and regeneration.

Epithelial/epidermal fatty acid-binding protein (E-FABP) is induced in peripheral neurons during nerve regeneration and is found at high levels in central neurons during neuronal migration and development. Furthermore, E-FABP expression is required for normal neurite outgrowth in PC12 cells treated with nerve growth factor (NGF). The present study examined whether E-FABP plays a role in retinal ganglion cell (RGC) differentiation and axon growth. Rat retinal tissues from embryonic (E) and postnatal (P) development through adulthood were examined using immunocytochemical labeling with E-FABP and growth-associated protein 43 (GAP-43) antibodies. E-FABP colocalized with GAP-43 at E14 through P10. At E14, E-FABP immunoreactivity was confined to the somas of GAP-43-positive cells in the ganglion cell layer, but it was localized to their axons by E15. The axons in the optic nerve were GAP-43-positive and E-FABP-negative on E15, but the two proteins were colocalized by E18. Retinal cultures at E15 confirmed that E-FABP and GAP-43 colocalize in RGCs. Postnatally, labeling was present between P1 and P10 but decreased at older ages and was minimally present or absent in adult animals. Western immunoblotting revealed that at E18, P1, and P10 E-FABP levels were at least fourfold greater than those in the adult. By P15, protein levels were only twofold greater, with adult levels reached by P31. Furthermore, E-FABP could be reinduced during axon regeneration. Dissociated P15 retinal cells cultured in the presence of brain-derived neurotrophic factor, ciliary neurotrophic factor, and basic fibroblast growth factor exhibited sixfold more GAP-43 and E-FABP double-positive RGCs (cell body and axons) than controls. Moreover, all GAP-43-immunoreactive RGCs were also positive for E-FABP. Taken together, these results indicate the following: 1) E-FABP is expressed in RGCs as they reached the ganglion cell layer and 2) E-FABP plays a functional role in the elaboration of RGC axons in both development and regeneration.

Aging↗
PubMed2003

The morphogen sonic hedgehog is an axonal chemoattractant that collaborates with netrin-1 in midline axon guidance.

Developing axons are guided to their targets by attractive and repulsive guidance cues. In the embryonic spinal cord, the floor plate chemoattractant Netrin-1 is required to guide commissural neuron axons to the midline. However, genetic evidence suggests that other chemoattractant(s) are also involved. We show that the morphogen Sonic hedgehog (Shh) can mimic the additional chemoattractant activity of the floor plate in vitro and can act directly as a chemoattractant on isolated axons. Cyclopamine-mediated inhibition of the Shh signaling mediator Smoothened (Smo) or conditional inactivation of Smo in commissural neurons indicate that Smo activity is important for the additional chemoattractant activity of the floor plate in vitro and for the normal projection of commissural axons to the floor plate in vivo. These results provide evidence that Shh, acting via Smo, is a midline-derived chemoattractant for commissural axons and show that a morphogen can also act as an axonal chemoattractant.

Animals↗
PubMed1999

Intra-axonal overloading of calcium ion in rat diffuse axonal injury and therapeutic effect of calcium antagonist.

OBJECTIVE: Exploring the intra-axonal overloading of calcium ion (Ca(2+)) in brain diffuse axonal injury (DAI) and the therapeutic effect of calcium antagonist(Nimotop) on DAI. METHODS: Fourteen SD rats were divided into injury group, treatment group and control group. The DAI model of rats was produced by using a head-instant-axial-rotation device. Tissues from the medulla oblongata of rats were taken 2-24 h post-injury and processed for electron microscopic observation by a cytochemical technique for calcium ion. RESULTS: In the injured rats there was evidence of local disruption of myelin sheath,lucent spaces between myelin sheath lamellae, separation of axolemma from the inner layer of myelin sheath, peripheral accumulation of organellae, intra-axonal formation of vacuoles and reduction of mitochondria. A large number of fine calcium deposits were seen on the affected myelin sheath. The severity of the myelin sheath lesion was related positively to the number of calcium deposits on it. In the later post-injury period the coarse calcium particles appeared within the damaged axon. Neuronal somas and microvascular endotheliums showed a lot of vacuoles and some fine calcium deposits. Many microvilli formed on the luminal aspect of endothelium. In the treatment group myelin sheath tended to be injured locally, and axoplasmic mitochondria were nearly normal in number, structure, and distribution. Few calcium deposits were found in axons. Vacuolization was obviously reduced in neuronal soma and endothelium. CONCLUSIONS: In DAI there exists an intra-axonal overloading of calcium ion, which is a key factor to the occurrence and development of DAI. Early use of Nimotop can alleviate DAI.

Journal Article↗
PubMed1994

Axonal transport of type III intermediate filament protein peripherin in intact and regenerating motor axons of the rat sciatic nerve.

Slow axonal transport of peripherin has been studied in the motor axons of both intact and regenerating rat sciatic nerves 7 days post-crush. The studies were done by two-dimensional gel electrophoresis after intraspinal injection of 35S-methionine. In the first experiment, the sciatic nerves were removed 3 weeks after the radiolabeling pulse and cut into 6 mm segments. Each nerve segment was submitted to two-dimensional gel electrophoresis and analyzed by an original procedure which allowed us to study the distribution along the nerve of the radioactivity associated with several proteins of the cytoskeleton, especially the intermediate filament proteins, peripherin, and the low molecular mass neurofilament protein, NF-L. Peripherin was transported at two main rates: 66% of the total radiolabeled peripherin moved at 1.42 mm/day and the remainder moved at 2.28 mm/day. The radioactivity associated with NF-L exhibited a similar pattern. In the second experiment, similar intraspinal injections were made 7 days after a unilateral crush of the sciatic nerve. Regenerating nerves exhibited a clear SCa wave. However, in contrast to the intact nerves, the SCb wave could not be precisely defined in the regenerating nerves. Thus, the changes in the amount of transported proteins were analyzed in the SCa wave only. Autoradiograms of 2D-PAGE revealed that in the regenerating axons, the quantity of transported peripherin in SCa was increased by 3.5-fold. In contrast, the quantity of transported NF-L was decreased by 1.6-fold. The regenerating motor axons conveyed significantly greater (approximately twofold) amounts of labeled tubulins and actin than did intact motor axons. Our results suggest that peripherin, although mainly conveyed by SCa, plays a role during the elongation process in addition to actin and tubulin.

Animals↗
PubMed1999

Intra-axonal continuous measurement of lidocaine concentration and pH in squid giant axon.

PURPOSE: To measure the dynamic penetration process of lidocaine, lidocaine concentration (Ci) and pH (pHi) in squid giant axon, and to determine the times and Ci of disappearance and reappearance of action potentials (AP). METHODS: Lidocaine solutions adjusted to four different pHs (pH = 5.5, 6.8, 7.8 and 9.0) were externally administered to the axon and Ci and pHi were measured using lidocaine and pH microsensors. The times and Ci when the AP just disappeared and reappeared were recorded. In addition, for comparison with Ci, the lidocaine content in the whole axon (Cw) was measured with high-performance liquid chromatography (HPLC). RESULTS: The Ci (charged plus uncharged) was 1.5 times greater than the uncharged form of administered lidocaine. The changes in pHi depended on the increase in Ci. The AP disappeared only after administration of high pH lidocaine solutions (pH = 7.8, 9.0) and reappeared by washing out the solution in the chamber. Nerve block occurred more rapidly at pH 9.0 than at pH 7.8, and the time after washing out the lidocaine was longer at pH 9.0 than at pH 7.8. The mean Ci and charged lidocaine concentration in the axoplasm, when the AP disappeared or reappeared, were lower at pH 9.0 than at pH 7.8 (P < 0.05). CONCLUSION: Uncharged lidocaine penetrates the axon membrane to the axoplasm where it changes to the charged form and is concentrated in the axon membrane and axoplasm. External application of uncharged lidocaine plays a role in modulating nerve conduction.

Action Potentials↗
PubMed1986

Axonal transport and the movement of 45Ca inside the giant axon of squid.

45Ca was microinjected directly into the giant axon of squid, and the radioisotope profile along the axon was determined after 2-12 h. Our results indicated that the intracellular Ca ions at the axon, unlike those at the cell body, were not axonally transported at a fast rate. The implication of this finding on the involvement of Ca in the axonal transport system is discussed.

Animals↗
PubMed1988

Relationships between axonal diameter, soma size, and axonal conduction velocity of HRP-filled, pyramidal tract cells of awake cats.

Relationships between axonal diameter, soma size, and axonal conduction velocity were examined in intracellularly recorded pyramidal tract (PT) cells of conscious cats using pressure injection of horseradish peroxidase. Positive linear correlations were found between axonal conduction velocities and axonal diameters as well as between axonal conduction velocities and soma sizes. All PT cells had somata located in layer V. Slow PT cells had high densities of dendritic spines in layer III; however, so did some fast PT cells, making this morphologic feature unacceptable for distinguishing between slow and fast conducting PT neurons.

Animals↗
PubMed1985

Comparison of the effects of sciatic nerve crush or resection on the proteins of fast axonal transport in rat dorsal root ganglion cell axons.

Proteins of fast axonal transport in rat sciatic nerve axons were separated and characterized by SDS-polyacrylamide gel electrophoresis and fluorography, after injection of L-[35S]methionine into the dorsal root ganglion. The effects of crushing or resecting the sciatic nerve on the relative labeling of specific polypeptide bands were compared. Initially, both types of axon injury produced the same response, but after 3 weeks there was a partial return to normal composition in crushed nerves. In resected nerves, the changes characteristic of axon injury persisted beyond 7 weeks. Behavioral testing showed that crushed nerves reinnervated foot skin, whereas no reinnervation was detected after resection. We conclude that in sensory neurons, as in several other neuronal types, the restoration in normal composition of fast-transported protein after axon injury depends on reinnervation of target tissues. This aspect of the cell body reaction to injury seems to be regulated by a retrograde trophic interaction with the target.

Animals↗
PubMed1992

Axonal transport of class II and III beta-tubulin: evidence that the slow component wave represents the movement of only a small fraction of the tubulin in mature motor axons.

Pulse-labeling studies demonstrate that tubulin synthesized in the neuron cell body (soma) moves somatofugally within the axon (at a rate of several millimeters per day) as a well-defined wave corresponding to the slow component of axonal transport. A major goal of the present study was to determine what proportion of the tubulin in mature motor axons is transported in this wave. Lumbar motor neurons in 9-wk-old rats were labeled by injecting [35S]methionine into the spinal cord 2 wk after motor axons were injured (axotomized) by crushing the sciatic nerve. Immunoprecipitation with mAbs which recognize either class II or III beta-tubulin were used to analyze the distributions of radioactivity in these isotypes in intact and axotomized motor fibers 5 d after labeling. We found that both isotypes were associated with the slow component wave, and that the leading edge of this wave was enriched in the class III isotype. Axotomy resulted in significant increases in the labeling and transport rates of both isotypes. Immunohistochemical examination of peripheral nerve fibers demonstrated that nearly all of the class II and III beta-tubulin in nerve fibers is located within axons. Although the amounts of radioactivity per millimeter of nerve in class II and III beta-tubulin were significantly greater in axotomized than in control nerves (with increases of +160% and +58%, respectively), immunoassay revealed no differences in the amounts of these isotypes in axotomized and control motor fibers. We consider several explanations for this paradox; these include the possibility that the total tubulin content is relatively insensitive to changes in the amount of tubulin transported in the slow component wave because this wave represents the movement of only a small fraction of the tubulin in these motor fibers.

Amino Acid Sequence↗