Axonal Cytoskeletal Changes After Nondisruptive Axonal Injury. II. Intermediate Sized Axons (original) (raw)
Related papers
Axonal cytoskeletal changes after non-disruptive axonal injury
Journal of Neurocytology, 1997
In animal models of human diffuse axonal injury, axonal swellings leading to secondary axotomy occur between 2 and 6 h after injury. But, analysis of cytoskeletal changes associated with secondary axotomy has not been undertaken. We have carried out a quantitative analysis of cytoskeletal changes in a model of diffuse axonal injury 4 h after stretch-injury to adult guinea-pig optic nerves. The major site of axonal damage was the middle portion of the nerve. There was a statistically significant increase in the proportion of small axons with a diameter of 0.5 μm and smaller in which there was compaction of neurofilaments. Axons with a diameter greater than 2.0 μm demonstrated an increased spacing between cytoskeletal elements throughout the length of the nerve. However, in the middle segment of the nerve these larger axons demonstrated two different types of response. Either, where periaxonal spaces occurred, there was a reduction in axonal calibre, compaction of neurofilaments but no change in their number, and a loss of microtubules. Or, where intramyelinic spaces occurred there was an increased spacing between neurofilaments and microtubules with a significant loss in the number of both. Longitudinal sections showed foci of compaction of neurofilaments interspersed between regions where axonal structure was apparently normal. Neurofilament compaction was correlated with disruption of the axolemma at these foci present some hours after injury. We suggest that the time course of these axonal cytoskeletal changes after stretch-injury to central axons is shorter than those changes documented to occur during Wallerian degeneration.
Post-Acute Alterations in the Axonal Cytoskeleton after Traumatic Axonal Injury
Journal of Neurotrauma, 2003
In the present study we tested the hypothesis that there are, in addition, ultrastructural pathological changes up to 1 week after injury. TAI was induced in the adult guinea pig optic nerve of nine animals. Three animals were killed at either 4 h, 24 h, or 7 days (d) after injury. Quantitative analysis of the number or proportion of axons within 0.5-mm-wide bins showed an increase in the number of axons with a diameter of less than 0.5 mm at 4 h, 24 h, and 7 d, the presence of lucent axons at 24 h and 7 d and that the highest number of injured axons occurred about half way along the length of the nerve. A spectrum of pathological changes occurred in injured fibers-pathology of mitochondria; dissociation of myelin lamellae but little damage to the axon; loss of linear register of the axonal cytoskeleton; differential responses between microtubules (MT) and neurofilaments (NF) in different sizes of axon; two different sites of compaction of NF; loss of both NF (with an increase in their spacing) and MT (with a reduction in their spacing); replacement of the axoplasm by a flocculent precipitate; and an increased length of the nodal gap. These provide the first ultrastructural evidence for Wallerian degeneration of nerve fibers in an animal model of TAI.
Influences of the Glial Environment on the Elongation of Axons After Injury
SUMMARY Tissue transplantation methods, previously used to study neural develop- ment, myelination and inherited disorders of myelin can be applied also to the investigation of repair and regeneration in the mammalian CNS. The elon- gation of axons from injured peripheral nerve or CNS has been studied in adult mice and rats by observing the growth of axons into PNS or CNS tissue grafts. Following spinal cord injury and also after transplantation of optic nerves into the PNS there is axonal sprouting but these neuronal processes fail to elongate more than a few mm into the surrounding glia. On the other hand if segments of a peripheral nerve are grafted into the transected spinal cord, axons arising from spinal neurons and dorsal root ganglia become associated with the transplanted Schwann cells and elongate along the graft, approxi- mately 1 cm. Recently the elongation of axons from spinal and medullary neurones was studied using a new experimental model which employed PNS grafts as...
Changes in Neurofilament and Microtubule Distribution following Focal Axon Compression
PLOS ONE, 2015
Although a number of cytoskeletal derangements have been described in the setting of traumatic axonal injury (TAI), little is known of early structural changes that may serve to initiate a cascade of further axonal degeneration. Recent work by the authors has examined conformational changes in cytoskeletal constituents of neuronal axons undergoing traumatic axonal injury (TAI) following focal compression through confocal imaging data taken in vitro and in situ. The present study uses electron microscopy to understand and quantify in vitro alterations in the ultrastructural composition of microtubules and neurofilaments within neuronal axons of rats following focal compression. Standard transmission electron microscopy processing methods are used to identify microtubules, while neurofilament identification is performed using antibody labeling through gold nanoparticles. The number, density, and spacing of microtubules and neurofilaments are quantified for specimens in sham Control and Crushed groups with fixation at <1min following load. Our results indicate that the axon caliber dependency known to exist for microtubule and neurofilament metrics extends to axons undergoing TAI, with the exception of neurofilament spacing, which appears to remain constant across all Crushed axon diameters. Confidence interval comparisons between Control and Crushed cytoskeletal measures suggests early changes in the neurofilament spatial distributions within axons undergoing TAI may precede microtubule changes in response to applied loads. This may serve as a trigger for further secondary damage to the axon, representing a key insight into the temporal aspects of cytoskeletal degeneration at the component level, and suggests the rapid removal of neurofilament sidearms as one possible mechanism.
Temporal Profiles of Cytoskeletal Protein Loss following Traumatic Axonal Injury in Mice
Neurochemical Research, 2007
To examine the time course and relative extent of proteolysis of neurofilament and tubulin proteins after traumatic axonal injury (TAI), anesthetized mice were subjected to optic nerve stretch injury. Immunohistochemistry confirmed neurofilament accumulation within axonal swellings at 4, 24, and 72 h postinjury (n = 4 injured and 2 sham per time point). Immunoblotting of optic nerve homogenates (n = 5 injured and 1 sham at 0.5, 4, 24 or 72 h) revealed calpain-mediated spectrin proteolytic fragments after injury. Protein levels for NF68 progressively decreased from 0.5 h to 24 h postinjury, while NF200 and alpha-tubulin levels decreased acutely (0.5-4 h), with a secondary decline at 72 h postinjury. These data demonstrate that diffusely distributed TAI is associated not only with a localized accumulation of neurofilament proteins, but also significant decreases in total cytoskeletal protein levels which may be mediated, in part, by calpains. Protection of the axonal cytoskeleton represents a potential therapeutic target for axonal damage associated with injury or neurodegenerative diseases.
Journal of Experimental Biology
Tissue transplantation methods, previously used to study neural development, myelination and inherited disorders of myelin can be applied also to the investigation of repair and regeneration in the mammalian CNS. The elongation of axons from injured peripheral nerve of CNS has been studied in adult mice and rats by observing the growth of axons into PNS or CNS tissue grafts. Following spinal cord injury and also after transplantation of optic nerves into the PNS there is axonal sprouting but these neuronal processes fail to elongate more than a few mm into the surrounding glia. On the other hand if segments of a peripheral nerve are grafted into the transected spinal cord, axons arising from spinal neurons and dorsal root ganglia become associated with the transplanted Schwann cells and elongate along the graft, approximately 1 cm. Recently the elongation of axons from spinal and medullary neurones was studied using a new experimental model which employed PNS grafts as 'bridges&...
Acta Neuropathologica, 2006
By means of a new head-injury apparatus, a 0.75-mm-deep depression was produced momentarily at a predetermined site of the rat calvaria. This immediately evoked ultrastructural (neurofilament) compaction in many myelinated axon segments in layers IV and V of the neocortex under the impact site. The affected axon segments run quasi-parallel to the brain surface in a diffuse distribution among normal axons. Other kinds of damage to the brain tissue were insignificant; the conditions were therefore favorable for investigation of the fate of the compacted axons. Quantitative analysis of the findings on groups of ten rats that were sacrificed either immediately after the head injury or following a 1 day or a 1 week survival period showed that around 50% of the compacted axons recovered in 1 day, and a further less than 10% did so in 1 week. Electron microscopy revealed that the non-recovering compacted axons underwent a sequence of degenerative morphological changes including homogenization, fragmentation and resorption of the fragments. However, the myelin sheaths around these degenerating axons remained apparently unchanged even in the long-surviving rats, and hardly any phagocytotic cells were encountered. On the other hand, many such myelin sheaths contained axolemma-bound, normal-looking axoplasm besides the above morphological signs of axon-degeneration. It is concluded that the non-recovering compacted axons undergo an uncommon (non-Wallerian) kind of degeneration, which is mostly reversible.
Experimental Neurology, 2001
Traumatic axonal injury (TAI) contributes to morbidity and mortality following traumatic brain injury (TBI). Single-label immunocytochemical studies employing antibodies to neurofilament compaction (NFC), RM014, and antibodies to APP, a marker of impaired axonal transport (AxT), have shown that TAI involves both NFC and disruption of AxT. Although it may be hypothesized that both events occur within the same injured axon, this has not been confirmed. To determine the relationship between NFC and impaired AxT, dual-label immunofluorescence was employed. To compare and contrast specific changes associated with these two markers of TAI, single-label electron microscopy was also used. Rats were subjected to an impact acceleration injury (30 min-6 h survival), and their brains were prepared for duallabel immunofluorescence and single-label electron microscopy. APP and RM014 were consistently found in two distinct classes of TAI. One, which showed only RM014 immunoreactivity, was thin and elongate, was sometimes vacuolated, and revealed little progressive change over time. The second was distinguished by focal axonal swellings containing APP immunoreactivity alone in small-caliber axons or in combination with RM014 immunoreactivity in large-caliber axons. These swellings were localized to either nodal or internodal loci and underwent progressive swelling over time, ultimately leading to secondary axotomy. Ultrastructural examination of these two classes of TAI revealed NFC together with mitochondrial dilation without organelle pooling in the RM014 singlelabeled axons. However, the APP single-labeled smallcaliber axons and APP/RM014 dual-labeled large-caliber axons revealed a progressive accumulation of organelles associated with increased axonal swelling over time. In contrast to previous thought, it now appears that NFC may occur independent of impaired AxT in TAI. This finding underscores the complexity of TAI, suggesting the need for multiple immunocytochemical approaches to fully assess the overall axonal response to TBI.
Intra-axonal calcium changes after axotomy in wild-type and slow Wallerian degeneration axons
Neuroscience
Calcium accumulation induces the breakdown of cytoskeleton and axonal fragmentation in the late stages of Wallerian degeneration. In the early stages there is no evidence for any long-lasting, extensive increase in intra-axonal calcium but there does appear to be some redistribution. We hypothesized that changes in calcium distribution could have an early regulatory role in axonal degeneration in addition to the late executionary role of calcium. Schmidt-Lanterman clefts (SLCs), which allow exchange of metabolites and ions between the periaxonal and extracellular space, are likely to have an increased role when axon segments are separated from the cell body, so we used the oxalate-pyroantimonate method to study calcium at SLCs in distal stumps of transected wild-type and slow Wallerian degeneration (Wld(S)) mutant sciatic nerves, in which Wallerian degeneration is greatly delayed. In wild-type nerves most SLCs show a step gradient of calcium distribution, which is lost at around 20%...