CENTRAL CHROMATOLYSIS AND THE AXON REACTION: A REAPPRAISAL

Mild heat stress induces hormetic effects in protecting the primary culture of mouse prefrontal cerebrocortical neurons from neuropathological alterations

Hormesis is a dose response phenomenon of cells and organisms to various types of stressors. Mild stress stimulates prosurvival pathways and makes the cells adaptive to stressful conditions. It is a widely used fundamental dose-response phenomenon in many biomedical and toxicological sciences, radiation biology, health science etc. Mild heat stress is an easily applicable hormetic agent that exerts consistent results. In the present investigations mouse cerebrocortical prefrontal neurons from E17 mouse embryos were grown in the laboratory on poly-L-lysine coated glass cover slips. The cells from the mild heat stressed group were subjected to a hyperthermic stress of 38 °C for 30 min every alternate day (i.e. mild heat stress was repeated after 48 h) up to the sixth day. After completion of twenty four hours of the final i.e. third exposure of the mild heat stress, the neurons were fixed for the cytochemical studies of neurofibrillary tangles, senile plaques, lipofuscin granules and Nissl substance. There was highly significant decrease in the neuropathological alterations (viz. deposition of Neurofibrillary tangles, deposition of senile plaques, accumulation of Lipofuscin granules) in the neurons from the mild heat stressed group as compared to control. Moreover, the Nissl substance was significantly preserved in the mild heat stressed group as compared to control. The results indicate that the applied mild heat stress (38 °C for 30 min) exerts beneficial effects on the prefrontal cerebrocortical neurons by slowing down the neuropathological alterations, suggesting the hormetic effect of the mild heat stress.

Chromatolysis: Do injured axons regenerate poorly when ribonucleases attack rough endoplasmic reticulum, ribosomes and RNA?

After axonal injury, chromatolysis (fragmentation of Nissl substance) can occur in the soma. Electron microscopy shows that chromatolysis involves fission of the rough endoplasmic reticulum. In CNS neurons (which do not regenerate axons back to their original targets) or in motor neurons or dorsal root ganglion neurons denied axon regeneration (e.g., by transection and ligation), chromatolysis is often accompanied by degranulation (loss of ribosomes from rough endoplasmic reticulum), disaggregation of polyribosomes and degradation of monoribosomes into dust‐like particles. Ribosomes and rough endoplasmic reticulum may also be degraded in autophagic vacuoles by ribophagy and reticulophagy, respectively. In other words, chromatolysis is disruption of parts of the protein synthesis infrastructure. Whereas some neurons may show transient or no chromatolysis, severely injured neurons can remain chromatolytic and never again synthesize normal levels of protein; some may atrophy or die. Ribonuclease(s) might cause the following features of chromatolysis: fragmentation and degranulation of rough endoplasmic reticulum, disaggregation of polyribosomes and degradation of monoribosomes. For example, ribonucleases in the EndoU/PP11 family can modify rough endoplasmic reticulum; many ribonucleases can degrade mRNA causing polyribosomes to unchain and disperse, and they can disassemble monoribosomes; Ribonuclease 5 can control rRNA synthesis and degrade tRNA; Ribonuclease T2 can degrade ribosomes, endoplasmic reticulum and RNA within autophagic vacuoles; and Ribonuclease IRE1α acts as a stress sensor within the endoplasmic reticulum. Regeneration might be improved after axonal injury by protecting the protein synthesis machinery from catabolism; targeting ribonucleases using inhibitors can enhance neurite outgrowth and could be a profitable strategy in vivo. © 2018 Wiley Periodicals, Inc. Develop Neurobiol, 2018

The biochemical pathways of central nervous system neural degeneration in niacin deficiency

Neural degeneration is a very complicated process. In spite of all the advancements in the molecular chemistry, there are many unknown aspects of the phenomena of neurodegeneration which need to be put together. It is a common sequela of the conditions of niacin deficiency. Neural degeneration in Pellagra manifests as chromatolysis mainly in pyramidal followed by other neurons and glial cells. However, there is a gross lack of understanding of biochemical mechanisms of neurodegeneration in niacin deficiency states. Because of the necessity of niacin or its amide derivative NAD in a number of biochemical pathways, it is understandable that several of these pathways may be involved in the common outcome of neural degeneration. Here, we highlight five pathways that could be involved in the neuraldegeneration for which evidence has accumulated through several studies. These pathways are: 1) the tryptophan-kyneurenic acid pathway, 2) the mitochondrial ATP generation related pathways, 3) the poly (ADP-ibose) polymerase (PARP) pathway, 4) the BDNF-TRKB Axis abnormalities, 5) the genetic influences of niacin deficiency.

A quantitative evaluation of gross versus histologic neuroma formation in a rabbit forelimb amputation model: potential implications for the operative treatment and study of neuromas

Background

Surgical treatment of neuromas involves excision of neuromas proximally to the level of grossly "normal" fascicles; however, proximal changes at the axonal level may have both functional and therapeutic implications with regard to amputated nerves. In order to better understand the retrograde "zone of injury" that occurs after nerve transection, we investigated the gross and histologic changes in transected nerves using a rabbit forelimb amputation model.

Methods

Four New Zealand White rabbits underwent a forelimb amputation with transection and preservation of the median, radial, and ulnar nerves. After 8 weeks, serial sections of the amputated nerves were then obtained in a distal-to-proximal direction toward the brachial plexus. Quantitative histomorphometric analysis was performed on all nerve specimens.

Results

All nerves demonstrated statistically significant increases in nerve cross-sectional area between treatment and control limbs at the distal nerve end, but these differences were not observed 10 mm more proximal to the neuroma bulb. At the axonal level, an increased number of myelinated fibers were seen at the distal end of all amputated nerves. The number of myelinated fibers progressively decreased in proximal sections, normalizing at 15 mm proximally, or the level of the brachial plexus. The cross-sectional area of myelinated fibers was significantly decreased in all sections of the treatment nerves, indicating that atrophic axonal changes proceed proximally at least to the level of the brachial plexus.

Conclusions

Morphologic changes at the axonal level extend beyond the region of gross neuroma formation in a distal-to-proximal fashion after nerve transection. This discrepancy between gross and histologic neuromas signifies the need for improved standardization among neuroma models, while also providing a fresh perspective on how we should view neuromas during peripheral nerve surgery.

Motor neuron involvement in experimental lumbar nerve root compression: a light and electron microscopic study

STUDY DESIGN

The aim of this study is to investigate changes in lumbar motor neurons induced by mechanical nerve root compression using an in vivo model. This study is to investigate the changes of lumbar motor neuron induced by mechanical nerve root compression using in vivo model.

OBJECTIVES

The effect of axonal flow disturbance induced by nerve root compression was determined in lumbar motor neuron.

SUMMARY OF BACKGROUND DATA

The lumbar motor neuron should not be overlooked when considering the mechanism of weakness, so it is important to understand the morphologic and functional changes that occur in motor neurons of the spinal cord as a result of nerve root compression. However, few studies have looked at changes of neurons within the caused by disturbance of axonal flow, the axon reaction, chromatolysis, and cell death as a result of mechanical compression of the ventral root.

METHODS

In mongrel dogs, the seventh lumbar nerve root was compressed for 1 week, or 3 weeks using a clip. Morphologic changes of the motor neurons secondary to the axon reaction were examined by light and electron microscopy.

RESULTS

Light and electron microscopy showed central chromatolysis of motor neurons in the lumbar cord from 1 week after the start of compression. After 3 weeks, some neurons undergoing apoptosis were seen in the ventral horn.

CONCLUSION

It is important to be aware that, in patients with nerve root compression due to lumbar disc herniation or lumbar canal stenosis, dysfunction is not confined to degeneration at the site of compression but also extends to the motor neurons within the lumbar cord as a result of the axon reaction. Patients with weakness of lower leg should therefore be fully informed of the fact that these symptoms will not resolve immediately after surgery.

Nicotinic acetylcholine receptor subtypes in the rat sympathetic ganglion: pharmacological characterization, subcellular distribution and effect of pre- and postganglionic nerve crush

Nicotinic acetylcholine receptors (nAChRs) mediate fast synaptic transmission in autonomic ganglia, which innervate and control the activity of most visceral organs. By combining ultrastructural, immunocytochemical, and pharmacological analyses, we characterized the nAChR subtypes in the rat superior cervical ganglion (SCG) and the effect of pre- and postganglionic nerve crush on their number in the ganglion and their distribution at the intraganglionic synapses. Binding with radioactive nicotinic ligands, immunoprecipitation, and immunolocalization experiments revealed the presence of different nAChR subtypes: those containing the alpha3 subunit associated with beta4 and/or beta2 subunits that bind 3H-Epibatidine with high affinity, and those containing the alpha7 subunit that bind 125I-alphaBungarotoxin. After postganglionic nerve crush, the number of nicotinic receptors and immunopositive intraganglionic synapses for each nAChR subunit strongly decreased. Both the number of nAChRs and immunoreactivity recovered 26 days after injury, when regenerating postganglionic fibers had reinnervated the peripheral target organs, as shown by the restoration of tyrosine hydroxylase immunoreactivity in the iris. This observation and the lack of any effect of preganglionic nerve crush on the number of nicotinic receptors suggest that the peripheral targets affect the organization of intraganglionic synapses in adult SCG.

Cellular GDNF delivery promotes growth of motor and dorsal column sensory axons after partial and complete spinal cord transections and induces remyelination

Glial cell line-derived neurotrophic factor (GDNF) is the prototypical member of a growth factor family that signals via the cognate receptors ret and GDNF-receptor alpha-1. The latter receptors are expressed on a variety of neurons that project into the spinal cord, including supraspinal neurons, dorsal root ganglia, and local neurons. Although effects of GDNF on neuronal survival in the brain have previously been reported, GDNF effects on injured axons of the adult spinal cord have not been investigated. Using an ex vivo gene delivery approach that provides both trophic support and a cellular substrate for axonal growth, we implanted primary fibroblasts genetically modified to secrete GDNF into complete and partial mid-thoracic spinal cord transection sites. Compared to recipients of control grafts expressing a reporter gene, GDNF-expressing grafts promoted significant regeneration of several spinal systems, including dorsal column sensory, regionally projecting propriospinal, and local motor axons. Local GDNF expression also induced Schwann cell migration to the lesion site, leading to remyelination of regenerating axons. Thus, GDNF exerts tropic effects on adult spinal axons and Schwann cells that contribute to axon growth after injury.

Rapid subcellular redistribution of Bax precedes caspase-3 and endonuclease activation during excitotoxic neuronal apoptosis in rat brain

Neuronal apoptosis is induced prominently in the newborn rodent brain by glutamate receptor excitotoxicity and related insults, including trauma and hypoxia-ischemia. However, the molecular mechanisms of this neurodegeneration are unclear. We tested the hypothesis that changes in the subcellular distribution of the proapoptotic protein Bax precede the activation of downstream apoptosis-effector mechanisms such as caspase-3 cleavage and endonuclease activation during the progression of excitotoxic neuronal apoptosis in the striatum of newborn rat. Kainic acid (4 nmol) was injected into striatum of anesthetized 7-day-old rats, and the animals were killed at 2, 6, 12, and 24 h postinsult. Controls were age-matched, vehicle-injected, or naive rats. Counts of ultrastructurally confirmed striatal neuron apoptosis in brain sections were highest at 24 h. Striatal tissue was microdissected and fractionated into cytosolic, mitochondrial-, and nuclear-enriched compartments. Immunoblots showed that Bax translocates from the cytosol fraction to the mitochondrial fraction, with maximal translocation by 2 h in the absence of changes in mitochondrial accumulation. Cleaved caspase-3 levels increase progressively in both cytosolic and mitochondrial fractions between 6 and 24 h. Cleaved caspase-3 accumulates in apoptotic striatal neurons as shown by immunolocalization. Internucleosomal fragmentation of DNA coincides with caspase-3 cleavage. We conclude that rapid translocation of Bax to mitochondria precedes caspase-3 and endonuclease activation during excitotoxic neuronal apoptosis in newborn rat brain and that initiation of this death cascade occurs within 2 h after glutamate receptor activation.

Neuronal response to physical injury and its relationship to the pathology of Alzheimer's disease

1. Central nerve cells undergo a stereotyped regenerative response following physical injury. 2. This reaction involves adaptive changes within the axon and cell body of origin, directed at sprouting and synaptogenesis. 3. Intimately associated with the regenerative response are specific alterations to cytoskeletal proteins, including the neurofilament (NF) triplet. 4. The morphological and neurochemical alterations to NF within axons following injury are reminiscent of plaque-associated dystrophic neurites (DN) in early Alzheimer's disease (AD). 5. Associated changes in perikaryal NF resemble Alzheimer neurofibrillary tangle pathology, while growth-associated sprouting markers are localized to the abnormal neurites of AD. 6. The present review postulates that beta-amyloid plaques in AD cause physical damage to local nerve cell processes and it is the chronic stimulation of the stereotyped response to injury that results in the end-stage pathology and neurodegeneration associated with AD.

Ultrastructural and quantitative motoneuronal changes after ventral root avulsion favor early surgical repair

This study assesses qualitative and quantitative morphological changes that occur in motoneurons after ventral root avulsion. The motoneuronal perikaryal changes in the ventral horn of the cat's C7 cord segment were studied after survival times of 2, 8, 14, 30, 60 and 90 days. Generally, large motoneurons showed a light type of reaction, and the small ones either light or dark. In addition, neurons with a normal ultrastructural appearance were found. These latter are considered to be in a 'steady state', which may be associated with regenerative potency. All these types of neuron reactions were present at all survival times, but the number of cells marked by a specific reaction depends on the time of survival. Qualitative and quantitative evidence is given for cell death in 36% of the motoneuronal population between 2 and 14 days after avulsion. This reduction primarily concerns large, presumably alpha motoneurons with the light type reaction. Small, presumably gamma motoneurons become seriously affected after 14 days. These findings suggest that early surgical repair may have the better chances for clinical recovery.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Occipital cortex ablation in adult rat causes retrograde neuronal death in the lateral geniculate nucleus that resembles apoptosis

The mechanisms of retrograde neurodegeneration following axotomy and target deprivation in the adult central nervous system remain poorly understood. We used a unilateral occipital cortex ablation model in adult rats to test the hypothesis that retrograde neurodegeneration in the dorsal lateral geniculate nucleus resembles apoptosis. Using the retrograde tracer Fluorogold, combined with nuclear dyes or the terminal transferase-mediated deoxyuridine triphosphate-biotin nick end labeling method for detecting nuclear DNA fragmentation, apoptotic geniculocortical projection neurons were identified at approximately. six to seven days postlesion. Degeneration of dorsal lateral geniculate neurons was characterized by aberrant accumulation of perikaryal non-phosphorylated neurofilaments and, ultrastructurally, by early vacuolation and subsequent swelling of dendrites. Ultrastructural alterations in the perikaryon of dying dorsal lateral geniculate neurons included the classic chromatolytic response, with redistribution of the rough endoplasmic reticulum and dispersion of free ribosomes followed by fragmentation of the rough endoplasmic reticulum, as well as dilatation and vesiculation of the Golgi, and accumulation of intact mitochondria. Subcellular alterations evolved into classic apoptotic changes, including progressive cytoplasmic and nuclear condensation with chromatin compaction into uniformly large round clumps, while the morphological integrity of mitochondria was preserved until late in the progression of neuronal death. Cytoplasmic and then nuclear fragments budded into the surrounding neuropil and were engulfed by oligodendrocytes. We conclude that the retrograde neurodegeneration of geniculocortical neurons in adult brain results in neuronal death which has a phenotype that closely resembles apoptosis. The morphological changes that occur during this process progress from chromatolysis through consecutive stages associated with apoptosis.

Neurodegeneration in excitotoxicity, global cerebral ischemia, and target deprivation: A perspective on the contributions of apoptosis and necrosis

In the human brain and spinal cord, neurons degenerate after acute insults (e.g., stroke, cardiac arrest, trauma) and during progressive, adult-onset diseases [e.g., amyotrophic lateral sclerosis, Alzheimer's disease]. Glutamate receptor-mediated excitotoxicity has been implicated in all of these neurological conditions. Nevertheless, effective approaches to prevent or limit neuronal damage in these disorders remain elusive, primarily because of an incomplete understanding of the mechanisms of neuronal death in in vivo settings. Therefore, animal models of neurodegeneration are crucial for improving our understanding of the mechanisms of neuronal death. In this review, we evaluate experimental data on the general characteristics of cell death and, in particular, neuronal death in the central nervous system (CNS) following injury. We focus on the ongoing controversy of the contributions of apoptosis and necrosis in neurodegeneration and summarize new data from this laboratory on the classification of neuronal death using a variety of animal models of neurodegeneration in the immature or adult brain following excitotoxic injury, global cerebral ischemia, and axotomy/target deprivation. In these different models of brain injury, we determined whether the process of neuronal death has uniformly similar morphological characteristics or whether the features of neurodegeneration induced by different insults are distinct. We classified neurodegeneration in each of these models with respect to whether it resembles apoptosis, necrosis, or an intermediate form of cell death falling along an apoptosis-necrosis continuum. We found that N-methyl-D-aspartate (NMDA) receptor- and non-NMDA receptor-mediated excitotoxic injury results in neurodegeneration along an apoptosis-necrosis continuum, in which neuronal death (appearing as apoptotic, necrotic, or intermediate between the two extremes) is influenced by the degree of brain maturity and the subtype of glutamate receptor that is stimulated. Global cerebral ischemia produces neuronal death that has commonalities with excitotoxicity and target deprivation. Degeneration of selectively vulnerable populations of neurons after ischemia is morphologically nonapoptotic and is indistinguishable from NMDA receptor-mediated excitotoxic death of mature neurons. However, prominent apoptotic cell death occurs following global ischemia in neuronal groups that are interconnected with selectively vulnerable populations of neurons and also in nonneuronal cells. This apoptotic neuronal death is similar to some forms of retrograde neuronal apoptosis that occur following target deprivation. We conclude that cell death in the CNS following injury can coexist as apoptosis, necrosis, and hybrid forms along an apoptosis-necrosis continuum. These different forms of cell death have varying contributions to the neuropathology resulting from excitotoxicity, cerebral ischemia, and target deprivation/axotomy. Degeneration of different populations of cells (neurons and nonneuronal cells) may be mediated by distinct or common causal mechanisms that can temporally overlap and perhaps differ mechanistically in the rate of progression of cell death.

Regeneration of dorsal column axons after spinal cord injury in young rats

In contrast to previous reports denying the occurrence of axonal regeneration of the dorsal column (DC) projections, here we demonstrate for the first time that marked regeneration occurs spontaneously after transection in infant rats. Transection was made sharply so as to produce edema-free lesions without subsequent formation of either scars or cysts. Transganglionic labeling of axons revealed that regenerated axons ascended in the normal tract in a manner similar to normal projections as a tightly-packed fasciculus and terminated densely in the nucleus gracilis. The present study indicates that failure of regeneration of DC axons is due to neither intrinsic deficiency of regrowth potential nor globally-inhospitable axonal environment but rather the local conditions of the lesion site.

The cellular mechanism underlying neuronal degeneration in glaucoma: parallels with Alzheimer's disease

Evidence is presented that the characteristic pattern of neuronal degeneration associated with glaucoma is due to a combination of the persistent physical damage to axons at the level of the lamina cribrosa and the associated neuronal reaction to this kind of trauma. The class of neuronal cytoskeletal proteins known as the neurofilament triplet are crucially involved in the reaction to physical damage and the selective localization of these proteins to larger retinal ganglion cells may underlie their susceptibility to eventual degeneration. The appearance of glaucoma-like neuronal pathology in Alzheimer's disease may follow the reaction of neurofilament-containing retinal ganglion neurons to persistent damage to their axons by beta-amyloid plaque formation in subcortical visual centers.

Central infusions of brain-derived neurotrophic factor and neurotrophin-4/5, but not nerve growth factor and neurotrophin-3, prevent loss of the cholinergic phenotype in injured adult motor neurons

Neurotrophic factors are molecules that prevent neuronal degeneration and regulate neuronal phenotype during either development or adulthood. Relatively little is known about the comparative responsiveness of injured adult central nervous system motor neurons to various neurotrophic factors. In the present study we examined the effects of four members of the neurotrophin family on injured adult motor neurons. Nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 or neurotrophin-4/5 were infused intracerebroventricularly into adult rats following transection of the motor hypoglossal nerve. Two weeks after axotomy, brain-derived neurotrophic factor and neurotrophin-4/5 completely prevented the loss of the cholinergic phenotype in hypoglossal motor neurons (97 +/- 11% and 99 +/- 5%, respectively) as assessed by choline acetyltransferase immunolabeling. In contrast, nerve growth factor and neurotrophin-3 exerted no protective effect. The low-affinity p75 neurotrophin receptor, capable of binding all four neurotrophins, was re-expressed in injured hypoglossal neurons; the majority of injured hypoglossal neurons also express trkB receptors but not trkA or trkC receptors. Thus, injury-induced responses to neurotrophins in adult motor neurons are mediated by trk receptors and their agonists, but may or may not also require low-affinity p75 neurotrophin receptors. Intracerebroventricular infusions of trkB agonists may be a useful means of targeting multiple and distantly separated populations of motor neurons for neurotrophic factor therapy.

Maintaining the neuronal phenotype after injury in the adult CNS. Neurotrophic factors, axonal growth substrates, and gene therapy

Multiple genetic and epigenetic events determine neuronal phenotype during nervous system development. After the mature mammalian neuronal phenotype has been determined it is usually static for the remainder of life, unless an injury or degenerative event occurs. Injured neurons may suffer one of three potential fates: death, persistent atrophy, or recovery. The ability of an injured adult neuron to recover from injury in adulthood may be determined by events that also influence neuronal phenotype during development, including expression of growth-related genes and responsiveness to survival and growth signals in the environment. The latter signals include neurotrophic factors and substrate molecules that promote neurite growth. Several adult CNS regions exhibit neurotrophic-factor responsiveness, including the basal forebrain, entorhinal cortex, hippocampus, thalamus, brainstem, and spinal cord. The specificity of neurotrophic-factor responsiveness in these regions parallels patterns observed during development. In addition, neurons of several CNS regions extend neurites after injury when presented with growth-promoting substrates. When both neurotrophic factors and growth-promoting substrates are provided to adult rats that have undergone bilateral fimbria-fornix lesions, then partial morphological and behavioral recovery can be induced. Gene therapy is one useful tool for providing these substances. Thus, the mature CNS remains robustly responsive to signals that shape nervous system development, and is highly plastic when stimulated by appropriate cues.

Axonal regeneration into chronically denervated distal stump. 1. Electron microscope studies

In this study, we have analyzed the ability of axons to regenerate into chronically denervated peripheral nerve. As an experimental rat model, the proximal end of a newly transected rat tibial nerve was sutured into chronically denervated (3 months up to 16 months) common peroneal nerve. Samples for morphological studies were collected 3 and 6 weeks after anastomosis of the tibial and common peroneal nerves. Our results showing a distinct organization of the endoneurial matrix in the chronically denervated distal stumps conformed with those from previous studies. Long cytoplasmic processes of endoneurial fibroblasts in close contact with collagen fibrils (with a diameter of 50-60 nm) surrounded areas of thin collagen fibrils (with a diameter of 25-30 nm). Remnants of Schwann cell columns (i.e., bands of Büngner) were situated in areas of thin collagen fibrils. After 12 months of denervation the majority of the Schwann cells columns were replaced by thin collagen fibrils. Successful axonal regeneration was noted in distal stumps that had been denervated for 14 and even 16 months. However, axonal regeneration diminished with prolonged denervation. The regenerating axons grew through the areas of thin collagen fibrils. The maturation and thickening of the regenerated axonal sprouts resulted in a decrease in areas of thin collagen fibrils. These results suggest that a chronically denervated nerve stump has the capacity to meet regenerating axons even after 16 months of denervation, although the progressive atrophy of Schwann cell columns impairs the likelihood of good axonal regeneration. The areas of thin collagen fibrils may act as a 'plastic' bed for successful axonal regeneration, and a study of these fibrils may provide further insight into the role of the extracellular matrix during peripheral nerve regeneration.

Increased expression of phosphotyrosine after axotomy in the dorsal motor nucleus of the vagus nerve and the hypoglossal nucleus

To investigate the role of tyrosine kinase underlying glial cell proliferation after axotomy, the localization of phosphotyrosine was studied immunohistochemically in the dorsal motor nucleus of the vagus nerve and the hypoglossal nucleus after nerve transection in adult rats. An anti-phosphotyrosine antibody weakly stained the cytoplasm of the neurons and some glial cells on the control side of both nuclei, while preferentially staining the plasma membrane of perineuronal microglial cells and neurons weakly on the severed side 2 days after axotomy and intensely between 3 and 7 days. Some of the microglial cells reacted positively with both anti-bromodeoxyuridine and anti-phosphotyrosine antibodies, suggesting that tyrosine kinase is involved in microglial cell proliferation. Proliferation of numerous microglial cells was observed in the severed nuclei between 2 and 4 days after axotomy, while only a few were detected on days 5 and 7. These findings suggest that tyrosine kinase is involved in not only the proliferation of perineuronal microglial cells but also in some retrograde neuronal reactions such as differentiation and regeneration.

Axotomy-induced changes in cytochrome oxidase activity in the cat trochlear nucleus

Following a unilateral section of the trochlear nerve, the effects of axotomy on cytochrome oxidase levels in the trochlear nucleus were studied. Cytochrome oxidase levels in the axotomized nucleus were significantly lower than in the control nucleus. The maximal decrease was observed at 2 weeks. Following partial restoration during weeks 3 and 4, cytochrome oxidase levels stabilized at levels only slightly below normal. Since a significant number of trochlear motoneurons die following axotomy, the restoration of cytochrome oxidase levels close to normal suggests that the surviving neurons may compensate for an increased load with a permanent increase in oxidative metabolism.

Ultrastructure of gamma-motoneurons after temporary or permanent interruption of peripheral target contact

The paradigm of nerve crush, vs. nerve transection and ligation, was used to examine the effects of temporary or permanent interruption of peripheral target contact on the ultrastructure of cat thoracic gamma-motoneurons. The normal, highly ordered ultrastructure of Nissl bodies was lost 8 days after axotomy. Nissl bodies remained disorganised up to 305 days after nerve transection and ligation. In contrast, normal ultrastructural orderliness was restored for many of the Nissl bodies of gamma-motoneurons 64 days following nerve crush. A decrease in the area of the Golgi apparatus was found 64 days following both nerve crush and nerve transection with ligation. Other organelles were unaltered.

Different stability of neurofilaments for trypsin treatment after axotomy in the dorsal motor nucleus of the vagal nerve and the hypoglossal nucleus

In an attempt to obtain information about changes of neurofilaments in motor neurons after axotomy, we immuno-histochemically investigated the accumulated neurofilaments in the dorsal motor nucleus of the vagal nerve, which shows nerve cell loss and degenerative changes after axotomy, and in the hypoglossal nucleus, which shows regenerative changes. Affected neurons in the hypoglossal nucleus showed intensified immunoreactivities for neurofilament antibodies phosphorylated at the carboxy-terminal, and these reactions disappeared with trypsin treatment. Accumulated neurofilaments in the neuronal perikarya in the dorsal motor nucleus of the vagal nerve and axons in brain stem also showed intensified immunoreactivities for the same antibodies, and these reactions remained positive after trypsin treatment. Anti-ubiquitin antibody preferentially stained accumulated neurofilaments in the affected vagal neurons, while no reaction was found in the affected hypoglossal neurons. Phosphorylated neurofilaments in hypoglossal neurons are vulnerable to trypsin treatment probably because of the blocking of polymerization or the disassembly of neurofilaments due to amino-terminal phosphorylation. In vagal neurons, the deteriorated amino-terminal phosphorylation or hyperphosphorylation at the carboxy-terminal seems to cause the cross-linkage and polymerization of neurofilaments, and densely packed polymerized neurofilaments probably fail in axonal transport resulting in nerve cell degeneration and death in the dorsal motor nucleus.

Vibration exposure and conditioning lesion effect in nerves: an experimental study in rats

The effects of controlled vibrations of defined frequency (80 Hz), acceleration (32 m/s2 root mean square), and duration (5 hours daily, 2 or 5 days) induced to the hind limb of rats on the regeneration potential in the sciatic nerve after a test crush lesion were determined. Exposure to vibration induced a marked and significant increase in outgrowth length of axons from the crush injury as evaluated after 3 and 6 days with the pinch reflex test. This effect was still observed 1 month but not 3 months after exposure to vibration. Even such a short duration of vibration exposure as 2 days induced an increased length of outgrowth. Such a conditioning effect may be due to local changes in the environment of the axons or to changes in the nerve cell bodies in the dorsal root ganglion. The results indicate that an alarm reaction exists in the nerve at a time point where no structural changes are observed in the nerve. By inducing such a conditioning lesion to nerve tissue, vibration represents a trauma corresponding to a crush lesion or transection of the nerve.

Cytophotometric analysis of magnocellular azure B-RNA and Feulgen-DNA following chronic GABA infusion into the nucleus basalis of rats

This investigation was undertaken to examine possible cytopathic effects of GABA infusion on nucleus basalis (NBM) magnocellular neurons. Sixty-three male Long-Evans rats received unilateral, intra-NBM infusions of either GABA100 (100 micrograms/microliters/h), GABA10 (10 micrograms/microliters/h), or ultrafiltered saline (1 microliter/h) for a period of 24 hours. Rats from each of these groups were sacrificed at either 24 hours, 48 hours or 8 days following initiation of infusions. The sham operated hemisphere of each rat served as a control for the infused hemisphere. After stoichiometric azure B-RNA and Feulgen-DNA staining of brain sections, scanning-integrating microdensitometry was used to quantify GABA-induced alterations in these well established indices of neuronal toxicity. These results provide evidence that the neurotoxic effects of 24 hours of 100 micrograms/microliters-h GABA infusion are manifested within 48 hours post-initiation of infusions. Although 24 hours of 10 micrograms/microliters-h GABA infusion suppressed NBM neuronal metabolism, the lower magnitude and duration of this effect signified an impending recovery. GABA infusion resulted in little if any NBM neuronal chromatin template impairment (i.e., reduced Feulgen-DNA reactivity), irrespective of the dosage employed and the delay prior to sacrifice.

Facial nerve transection causes expansion of myelin autoreactive T cells in regional lymph nodes and T cell homing to the facial nucleus

Nervous tissue expression of immunological signal and recognition molecules, as well as lymphoid tissue immune responses after facial nerve trauma was studied in male rats of the Lewis and Brown Norway (BN) strains. In both rat strains nerve transection caused within four days the appearance of IFN-gamma-like immunoreactivity in the cytoplasm of axotomized motor neurons and an induction of MHC class I and II, and CD4 molecules on surrounding glial cells to a similar extent. T lymphocytes also infiltrated the facial nuclei ipsilateral to the axotomy in all animals. The number of autoreactive T cells in superficial cervical lymph nodes, which in response to whole myelin or peptides of myelin basic protein (MBP) secreted IFN-gamma increased markedly after axotomy. This response was more conspicuous in Lewis rats, which are susceptible to experimental allergic encephalomyelitis (EAE), than in BN rats, which are EAE resistant. A proportion of the axotomized Lewis rats also developed widespread perivascular infiltration of mononuclear cells in the CNS, reminiscent of EAE. Hypothetically, a strong expansion of myelin autoreactive IFN-gamma producing T cells secondary to nerve trauma may have immunopathological consequences in genetically predisposed individuals. It is also possible that myelin reactive T cells, whether recruited to the lesioned nerve, could have impact on macrophage function during Wallerian degeneration in the distal stump.

Sleep deprivation-induced neuronal damage may be due to nicotinic acid depletion

Prolonged sleep deprivation induces chromatolysis of central nervous system neurons. This unusual form of neuronal damage is curiously similar to the neuronal damage seen in pellagra. It is proposed that the neuronal damage of prolonged sleep deprivation is a consequence of nicotinic acid depletion.

The central representation area of the radial nerve in the goat, studied by the axon reaction

The central representation area of the radial nerve has been investigated in the goat, using the axon reaction. The retrograde changes after a two or six weeks survival time have been used to study both its position and architecture. Reconstructions have been made using a computer assisted approach. In the goat the central representation area of the radial nerve is situated in the dorsolateral part of the lateral motoneuronal cell group, extending from caudal C6 to caudal T1. It begins very small in C6, enlarges through C7, reaches its maximal diameter in C8, from where it gradually decreases to end in caudal T1. The contribution of the C6 segment to the central representation area of the radial nerve in the goat is in agreement with findings in some other species but it contrasts with the macroscopic origin of the radial nerve in ruminants. It is suggested that this finding, together with the statistically significant reduction in the number of alpha motoneurons at the C6 level in calves affected with Arthrogryposis Multiplex Congenita (AMC) in the forelimbs, may prove an at least partial involvement of the radial nerve in the pathogenesis of this disease, which is also suggested by clinical symptoms.

Basal forebrain cell loss following fimbria/fornix transection

Following fimbria/fornix transection, cells in the medial septum appear to undergo retrograde degeneration as shown by Nissl and acetylcholine esterase (AChE) staining. Recent studies using immunocytochemical techniques have also demonstrated loss of choline acetyltransferase (ChAT) and nerve growth factor receptor (NGFr) labeling of neurons in this region. Whether the apparent loss of ChAT- and NGFr-positive neurons is the result of the actual death of these neurons, or is instead a loss of ChAT enzyme or NGFr expression below levels detectable by immunocytochemical methods, remains an unresolved issue. In order to address this question, rhodamine-labeled fluorescent latex microspheres were injected into the hippocampus where they retrogradely transported to the cell bodies of the medial septum. Five days later these animals received either unilateral or bilateral fimbria/fornix lesions and were allowed to survive an additional 4 weeks. Compared to unlesioned control animals, unilaterally lesioned animals showed a 91% loss of fluorescently labeled cells and bilaterally lesioned animals showed a 93% loss. The inability to detect the fluorescent microspheres in the medial septum suggests that the majority of medial septal cells die after fimbria/fornix transection. ChAT and NGFr immunohistochemical staining were also performed. Cells stained for ChAT were reduced in number by 92% in animals with unilateral lesions and by 75% in animals with bilateral lesions, while NGFr-stained cells were reduced in number by 75% in animals with unilateral lesions and by 68% in animals with bilateral lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Strategy and timing of peripheral nerve surgery

The authors review the latest theories of peripheral nerve regeneration and repair. They present their research on nerve regeneration including the alterations in the mother cell body, and in the distal part of the axon, and the time required to reach the best production of amino acids for cytoskeleton reconstruction. Other research of particular interest which is presented regards the chemotactic arrangement of motor and sensory axons inside a vein. This research has shown that the axons are able to find their way to the appropriate (sensory or motor) distal endoneural tubes. Adoption phenomena are also presented. The discussion of surgery includes the type (suture, glueing, grafts, tubulization) and the time of surgical repair. Timing and repair strategies are related to the site of the lesion (which can require that a greater or smaller amount of cytoskeleton be reconstructed), the type of the injury, the state of surrounding tissues, the age of the patients, injuries to muscles, tendons, bones, vessels and skin. A scheme of strategy is proposed.

Local enhancement of major histocompatibility complex (MHC) class I and II expression and cell infiltration in experimental allergic encephalomyelitis around axotomized motor neurons

The effect of unilateral peripheral nerve lesions on the inflammatory response of experimental allergic encephalomyelitis (EAE) in rat central nervous system (CNS) was studied. Immunostaining for major histocompatibility complex (MHC) antigens and T-cell subsets demonstrated that MHC class I expression was markedly enhanced in as well as around axotomized motor neurons and that MHC class II expression was induced on several cells, probably microglial cells, in close proximity to the axotomized motor neurons. There was also a pronounced increase in interleukin 2 receptor-positive lymphocytes as well as T-cells and the T-cell subsets on the injured as compared to the non-injured contralateral side. These effects were present particularly in the initial phase of EAE and persisted for several weeks. The results suggest that neurons may communicate immunoregulatory signals to their microenvironment and that retrograde axonal signals from the distant periphery may alter the immune response locally within the CNS.

Morphological and physiological properties of neurons after long-term axonal regeneration: observations on chronic and delayed sequelae of peripheral nerve injury

Axonal regeneration has been the focus of extensive investigation of mechanisms which mediate structural and functional recovery after injury to mammalian peripheral nerves and has proven to be a valuable model for development and plasticity in the nervous system. Although details of the acute morphological and physiological responses to nerve injury are well-described, less information is available to nerve injury are well-described, less information is available about long-term alterations which persist or develop after regenerated axons have established connections with their targets. The present paper briefly discusses the mammalian neuron's initial response to peripheral nerve injury and subsequent events which occur during regeneration. Morphological and physiological alterations observed in neurons after long-term axonal regeneration are described and are considered in the context of their potential implications for clinical recovery after nerve injury, as well as their potential contribution to the appearance of delayed neurological dysfunction. Selective responses to neuronal injury during development and in different fiber populations are discussed.

Organelle changes in cat thoracic alpha- and gamma-motoneurons following axotomy

Horseradish peroxidase was used as a retrograde marker to identify the cell bodies of cat thoracic alpha- and gamma-motoneurons 8 days following axotomy. A quantitative ultrastructural comparison revealed changes in Nissl bodies, the Golgi apparatus, mitochondria and lysosomes for axotomised alpha-motoneurons, while axotomised gamma-motoneurons only showed changes in Nissl bodies and nuclear pores.

Neurofilament phosphorylation in neuronal perikarya following axotomy: a study of rat spinal cord with ventral and dorsal root transection

Rat spinal cord was stained by indirect immunofluorescence with 11 neurofilament monoclonal antibodies that recognize phosphorylated epitopes. All monoclonals were axon-specific in this location. The large motoneurons containing bundles of neurofilaments did not stain and the pattern remained unchanged after transection of the sciatic nerve in the thigh. With nine monoclonals, stained motoneurons were observed in the ventral horns 3 days, 5 days, 1 week, and 2 weeks after transection of the ventral roots close to the spinal cord. The abnormal motoneurons were typically scattered among normal (i.e., nonstained) cells. Even in animals showing the most severe reaction, the whole motoneuron population at the site of rhizotomy was not affected, stained and nonstained perikarya often coexisting side by side. Stained motoneurons were no longer observed 3 weeks after ventral root transection. Changes in neuronal immunoreactivity were also observed after dorsal root transection. However, a different population was affected, i.e., middle-sized neurons in dorsal horns and at the base of ventral horns. With two monoclonals (A9 and D21), cell bodies remained negative following all operations. It is concluded that axotomy in proximity of the cell body may induce certain neurofilament phosphorylation events in motor neuron perikarya, whereas other phosphorylation events remain confined to the axons under these experimental conditions. The absence of changes after transection of the sciatic nerve in the thigh suggests that neurofilament phosphorylation is a reaction to cell injury rather than a cellular event related to nerve regeneration.

Ultrastructure of axotomized alpha and gamma motoneurons in the cat thoracic spinal cord

Using horseradish peroxidase as a retrograde marker, the ultrastructural response of alpha and gamma motoneuronal cell bodies in the cat thoracic spinal cord has been compared 1-8 days following intercostal nerve transection and ligation. By light microscopy, reduction of Nissl body size, together with nuclear and nucleolar alterations were seen in alpha motoneurons 4-8 days following axotomy, but not at any stage in axotomized gamma motoneurons. In the electron microscope, disorganization of Nissl body ultrastructure was seen in both alpha and gamma motoneurons 2 days following axotomy. Only in alpha motoneurons, however, did these disorganized Nissl bodies subsequently fragment into smaller pieces. Both alpha and gamma motoneurons lost synapses following axotomy, but the proportional loss from gamma motoneurons was two-fold greater than that from alpha motoneurons. Loss of synaptic terminals with flattened synaptic vesicles was two-fold higher than that of synaptic terminals with round synaptic vesicles from axotomized gamma motoneurons, whereas axotomized alpha motoneurons lost both types of synaptic terminal equally.

Reorganization of neuronal connections following CNS trauma: principles and experimental paradigms

The present review summarizes how the nervous system responds to trauma. The goal is to provide an introduction to the problems, techniques, experimental paradigms, current issues, and future promise. The review is especially designed for basic scientists and clinicians who are not currently involved in research on CNS reorganization, and for students just entering the field. The review characterizes the secondary degenerative events that occur after trauma, and the types of growth that commonly occur. A standard terminology is set forth with criteria for differentiating between related phenomena. Experimental methods are described that can be used documenting reorganization of circuitry. The principles that determine whether a given process will or will not occur are summarized, and some of the factors that may regulate the nature and extent of growth are considered. Research strategies are outlined that have been used to evaluate whether reorganization of circuitry is functionally significant. Finally, future directions in research and clinical application are discussed, focusing especially on the efforts to facilitate regeneration, and the work on transplants of CNS tissue to facilitate growth of surviving connections, and to replace tissue destroyed by trauma.

Axonal sprouting after botulinum toxin does not elicit a histological axon reaction

In an attempt to determine which elements of the axon reaction are essential for early axonal outgrowth, axonal sprouting was induced with botulinum toxin (BoTx) and the nerve cell body changes compared with those accompanying axonal growth after nerve trauma. Anterior horn cells of mice were examined histologically at times ranging from 3 days to 3 weeks after either BoTx hindlimb injection or sciatic nerve crush. After sciatic nerve crush there was dispersion of Nissl substance, increase in cell body size, and an increase in neurofilament protein staining. None of these changes were found after BoTx-induced terminal axonal sprouting, suggesting that these morphological features of the axon reaction are not essential for early axonal outgrowth.

Attempts to prevent equine post neurectomy neuroma formation through retrograde transport of two neurotoxins, doxorubicin and ricin

Digital neurectomies, performed to relieve pain and lameness, are often complicated postoperatively by formation of painful neuromas. In this study attempts were made to deliver lethal doses of neurotoxin to the cell bodies of the transected digital nerve fibres via long-distance retrograde axon transport and, thereby, prevent the regenerative changes that lead to neuroma formation. After applying doxorubicin in various ways to the digital nerve stumps of ponies, degenerating or necrotic neurones appeared only sporadically in the spinal ganglia. Although doxorubicin was largely ineffective in retrograde destruction of cell bodies, when absorbed in pledgets on the stumps it exerted a sustained action which prevented Schwann cell proliferation and axon sprouting. Ricin, in contrast to doxorubicin, was effective in retrograde destruction of sensory neurons. Many affected neurons were devoid of polysomes but packed with mitochondria; others had advanced to various stages in cytolysis. Despite its effectiveness, ricin cannot be recommended because of its extreme toxicity. The clinical use of retrograde transport in equine neurectomy will probably depend on future development of hybrid toxins with high neural specificity and low systemic toxicity.

Morphological changes in spinal motor neurons giving rise to long-term regenerated sciatic nerve axons

Morphological properties of rat spinal motor neurons were examined 14-16 months following unilateral sciatic nerve crush and compared to the properties observed in neurons contralateral to injury and in cord segments from age-matched control rats. Regenerated and control motor neurons were identified by retrograde labelling with HRP applied to sciatic nerves distal to the site of crush or at a comparable location in control nerves. Many of the experimental motor neurons were enlarged and had thickened dendritic processess compared to the finer dendrites seen in control cells. Mean cell area ipsilateral to the crush lesions was larger than mean control cell area (P-value less than 0.001) despite representation of all control cell areas in the regenerated population. These data suggest that persistent or continued morphological abnormalities occur in mammalian motor neurons following simple sciatic crush injury when examined at extended times beyond the period of axonal regeneration and clinical recovery.

Axotomy induces MHC class I antigen expression on rat nerve cells

Immunomorphological staining demonstrates that class I major histocompatibility complex (MHC)-coded antigen expression can be selectively induced on otherwise class I-negative rat nerve cells by peripheral axotomy. Induction of class I as well as class II antigen expression was simultaneously seen on non-neural cells in the immediate vicinity of the injured nerve cells. As nerve regeneration after axotomy includes growth of new nerve cell processes and formation of new nerve cell contacts, the present findings raise the question of a role for MHC-coded molecules in cell-cell interactions during nerve cell growth.

Response of septal cholinergic neurons to axotomy

In the present study we employed quantitative morphometric techniques to assay the response of septal cholinergic neurons following unilateral transection of the fimbria/fornix and supracallosal stria. Analysis of 50-micron-thick tissue sections with a Quantimet 920 image analysis system demonstrated a reduction in ChAT immunoreactivity as early as 1 day following denervation. This decrease was associated with a drop in the number of labeled cells ipsilateral to the lesion and a decrease in the area of cholinergic perikarya on the lesioned and nonlesioned side of the septum. The response at 1 day, however, was transient, and at 4 days the number of labeled neurons was not significantly different from controls. By 8 days we observed a dramatic reduction in the number and size of ChAT-positive cells ipsilateral to the lesion and a reduction in the size of cholinergic perikarya on the contralateral (i.e., nonlesioned) side. These values persisted throughout the remainder of the study. To assess more completely the morphologic response of neurons to axotomy than can be determined in 50-micron-thick tissue sections, we embedded the adjacent immunolabeled tissue section in Epon and then serially sectioned it to a thickness of 0.75-1.0 micron. By using this method, we were able to measure the area, length, and width of the cell, the area of the nucleus and nucleolus, and the position of the nucleus (i.e., eccentricity). Measurements were performed on ChAT-labeled and nonlabeled cells. The results of our studies demonstrate that cholinergic and noncholinergic cells responded to axotomy in a characteristic yet different fashion from each other and that this response could be quantitatively assayed. In general, labeled and nonlabeled cells on the lesioned side of the septum shrink in response to denervation. This shrunken state was reflected in measurements of cellular area, length, width, and nuclear area. Moreover, other measurements of cellular morphology (i.e., area of the nucleolus, position of the nucleus) indicate that none of the neuronal populations examined in the present study displayed morphologic evidence of regeneration. Our results indicate a dramatic loss of cholinergic perikarya ipsilateral to the lesion. Moreover, although a few neurons do persist they do so in a shrunken state. These data provide an essential baseline for the second study in this series, which will evaluate the effect of nerve growth factor on the survival of denervated septal neurons.

Nodes of Ranvier in acrylamide neuropathy: voltage clamp and electron microscopic analysis of rat sciatic nerve fibres at proximal levels

Adult male rats were injected with acrylamide monomer (50 mg/kg i.p., 3 times/week). The animals developed hind limb paresis and distal motor nerve conduction velocity decreased. Three of 14 examined isolated myelinated sciatic nerve fibres showed a reduced excitability. In the remaining fibres the action potentials were normal. Potential clamp analysis of nodes of Ranvier in the single fibres revealed large delayed nodal K currents in 6 cases. Four of these 6 fibres exhibited a markedly increased membrane capacitance and in 2 fibres an increased Na permeability was found. Electron microscopic examination of sciatic nerves revealed comparatively subtle internodal and nodal-paranodal alterations in large myelinated fibres. Internodally, focal aggregates of tubulovesicular profiles could be found and some Schwann cells were hypertrophic. Paranodally, axonal evaginations penetrated in between the terminating myelin lamellae. Some paranodes had a very thin myelin covering and/or exhibited varying degrees of myelin sheath retraction. In the nodal axon domains lacking an axolemmal undercoating and partly non-undercoated axolemmal protrusions could be found. Similar physiological and morphological alterations occur in the rat sciatic nerve above a neuroma. Therefore, the presently observed proximal changes may, to some extent, represent non-specific alterations, secondary to a target deprivation caused by the distal axon degeneration typical for acrylamide neuropathy.

Morphologic changes in nerve cell bodies induced by experimental graded nerve compression

The effects of experimental nerve fiber compression on the morphology of nerve cell bodies were studied. Rabbit cervical vagus nerves were crushed or subjected to compression at 0 (sham compression), 30, 200, or 400 mm Hg for 2 h. Morphometric measurements and light microscopical evaluation of the nerve cell bodies in the nodose ganglion were carried out 7 days after the injury on the injured and control sides. Crush and compression at 30, 200, or 400 mm Hg induced a slight decrease in total cell profile area compared with the control side, but it was not related to degree of injury. There was a marked decrease in the ratio between nuclear and total cell profile area (nuclear volume density) after compression at 200 and 400 mm Hg, as well as after crush, and to a lesser extent after compression at 30 mm Hg. Compression at 30, 200, or 400 mm Hg as well as crush of the vagus nerve induced migration of the nucleus to the periphery and dispersion of Nissl substance in the cytoplasm of the nerve cell bodies. Sham compression induced no obvious changes in total cell profile area, nuclear volume density, or migration of nucleus. There was a somewhat increased percentage of cells showing dispersion of Nissl substance in sham-compressed animals than in controls. The results show that nerve fiber compression induced pronounced reactive changes in nerve cell bodies, even at low pressures, corresponding to those found in human carpal tunnel syndrome. Such pressures are known to induce reversible inhibition of fast axonal transport as well as inhibition of retrograde axonal transport. The nerve cell body changes in the nodose ganglion may thus be a reaction to disturbances in axonal transport.

Feline dysautonomia: an ultrastructural study of neurones in the XII nucleus

A feline dysautonomia of unknown aetiology has been reported in numerous cats in the United Kingdom since 1981. The consistent histological lesion is a chromatolytic-type change within the neurones of the autonomic nervous system, which is also found less frequently in non-autonomic regions, such as the XII nucleus. This study describes the ultrastructural changes in the XII nucleus within the first 2 weeks of clinical disease. In the abnormal neurones there is a dispersion of the Nissl substance, progressing to dilation of individual cisternae by an electron-dense floccular material. Such cisternae have lost the majority of their ribosomes. Normal Golgi complexes can be seen in neurones where there is only slight dispersion of the Nissl substance, but no Golgi complexes, either normal or abnormal, can be identified in any cell in which the Nissl substance is markedly disrupted. There is proliferation of smooth endoplasmic reticulum in several neurones, and there may also be an increased number of morphologically normal mitochondria. The nuclei of affected neurones are eccentric with crenations of the nuclear envelope, and in some cases nucleolar changes are also observed. Autophagic vacuoles are present in small numbers. Other organelles appear normal. These findings compare closely to those for the autonomic neurones, suggesting that the primary effect of the causal agent(s) is on the protein synthetic pathway of specific neurones.

The axon reaction in spinal ganglion neurons of acrylamide-treated rats

Rats were given acrylamide in doses of either 30 or 50 mg/kg (5 days each week) for up to 3 weeks and killed at weekly intervals. The right sciatic nerve was tied tightly at the level of the major trochanter 4 days before killing the animals by perfusion fixation when ipsilateral and contralateral sensory ganglia (L5 and L6) were removed. The effects on neuronal perikarya of axotomy alone, of acrylamide alone and of these combined were studied by light and electron microscopy. The responses to axotomy and to acrylamide intoxication shared certain features, namely peripheral Nissl substance and to a lesser degree nuclear eccentricity, nucleolemmal crenation and mitochondrial enlargement. Neurofilament loss was present only with acrylamide. In combined axotomy and acrylamide all these five features were prominent. These findings indicate firstly that the individual responses to axotomy and to acrylamide, while sharing several features, are subtly different and secondly that acrylamide appears to impede the vital neuronal responses directed towards repair of the axon.

Delayed swayback in goat kids, a study of 23 cases

The results of a retrospective study of 23 goat kids with delayed swayback are reported. Principal clinical signs were ataxia, loss of postural control, spasticity of the hindlimbs, and muscular weakness, often progressing to permanent recumbency. Denervation of skeletal muscles was demonstrated by electromyography in 2 kids. Three kids slowly recovered during hospitalisation. Histopathological changes were characterized by degeneration of selected neuronal populations with their processes within the central and the peripheral nervous system. Affected systems included upper motor neuron, vestibular, general proprioceptive, and lower motor neuron pathways, with additional involvement of the cerebellar cortex in some animals. Our findings, including limited ultrastructural observations, support the notion that the neuraxon rather than the myelin sheath is the prime target of disease in delayed swayback. The available copper values of affected kids and their unaffected herd mates were significantly lower than those of random control goats, which provides further support for a role of copper deficiency in the aetiology of this disease in the goat.

Peripheral axotomy induces neurofilament decrease, atrophy, demyelination and degeneration of root and fasciculus gracilis fibers

We have recently shown that peripheral axotomy by hindlimb amputation in adult cats sequentially results in neurofilament and microtubule decrease and axonal atrophy, myelin wrinkling, myelin remodeling (de- and remyelination), more atrophy and axonal degeneration in proximal sciatic and L7 segmental nerve fibers. The neuropathologic, morphometric and teased fiber alterations in the myelinated fibers (MF) of roots and sampled levels of fasciculus gracilis in groups of adult cats 24 months after hindlimb amputation have now been studied. We found: a severe decrease of neurofilaments, axonal atrophy, myelin wrinkling, de- and remyelination and axonal loss in posterior root axons; that these morphologic abnormalities extended up the fasciculus gracilis in the appropriate territories established from degenerative studies; that the retrograde effect was less severe in ventral root fibers, although atrophy and sprouting were demonstrated here, and that the cellular sequence of retrograde atrophic degeneration of ascending axons was similar to that observed in proximal stump axons. These findings confirm that primary afferent neurons are more vulnerable to axotomy than lower motor neurons and may provide an additional explanation for the poorer functional restoration of sensory than of motor deficit after root compression and in delayed nerve reconnection. Our observations also have important implications for interpretation of neuropathologic alterations in roots and fasciculus gracilis, since the observed features may be secondary to axotomy of peripheral nerve fibers induced by disease and not evidence of a primary derangement.

Sequential changes of sensory neuron (fluoride-resistant) acid phosphatase in dorsal root ganglion neurons following neurectomy and rhizotomy

Five to seven days after sciatic nerve section in rats, fluoride-resistant acid phosphatase (FRAP) expression in dorsal root ganglion (drg) neurons was markedly decreased. The decrease was in contrast to increased acid phosphatase which has been reported to occur in other neurons after nerve section. FRAP expression in ganglion neurons subsequently increased 14-21 days after nerve section; this preceded the restitution of enzyme expression in the spinal cord substantia gelatinosa. FRAP expression in drg neurons was not decreased after dorsal root section.