Infantile neuroaxonal dystrophy. A disease characterized by altered terminal axons and synaptic endings

Exploring therapeutic strategies for infantile neuronal axonal dystrophy (INAD/PARK14)

Infantile neuroaxonal dystrophy (INAD) is caused by recessive variants in PLA2G6 and is a lethal pediatric neurodegenerative disorder. Loss of the Drosophila homolog of PLA2G6, leads to ceramide accumulation, lysosome expansion, and mitochondrial defects. Here, we report that retromer function, ceramide metabolism, the endolysosomal pathway, and mitochondrial morphology are affected in INAD patient-derived neurons. We show that in INAD mouse models, the same features are affected in Purkinje cells, arguing that the neuropathological mechanisms are evolutionary conserved and that these features can be used as biomarkers. We tested 20 drugs that target these pathways and found that Ambroxol, Desipramine, Azoramide, and Genistein alleviate neurodegenerative phenotypes in INAD flies and INAD patient-derived neural progenitor cells. We also develop an AAV-based gene therapy approach that delays neurodegeneration and prolongs lifespan in an INAD mouse model.

Phospholipase PLA2G6, a Parkinsonism-Associated Gene, Affects Vps26 and Vps35, Retromer Function, and Ceramide Levels, Similar to α-Synuclein Gain

Mutations in PLA2G6 (PARK14) cause neurodegenerative disorders in humans, including autosomal recessive neuroaxonal dystrophy and early-onset parkinsonism. We show that loss of iPLA2-VIA, the fly homolog of PLA2G6, reduces lifespan, impairs synaptic transmission, and causes neurodegeneration. Phospholipases typically hydrolyze glycerol phospholipids, but loss of iPLA2-VIA does not affect the phospholipid composition of brain tissue but rather causes an elevation in ceramides. Reducing ceramides with drugs, including myriocin or desipramine, alleviates lysosomal stress and suppresses neurodegeneration. iPLA2-VIA binds the retromer subunits Vps35 and Vps26 and enhances retromer function to promote protein and lipid recycling. Loss of iPLA2-VIA impairs retromer function, leading to a progressive increase in ceramide. This induces a positive feedback loop that affects membrane fluidity and impairs retromer function and neuronal function. Similar defects are observed upon loss of vps26 or vps35 or overexpression of α-synuclein, indicating that these defects may be common in Parkinson disease.

High expression of α-synuclein in damaged mitochondria with PLA2G6 dysfunction

To clarify the role of α-synuclein (αSyn) in neuronal membrane remodeling, we analyzed the expression of αSyn in neurons with a dysfunction of PLA2G6, which is indispensable for membrane remodeling. αSyn/phosphorylated-αSyn (PαSyn) distribution and neurodegeneration were quantitatively estimated in PLA2G6-knockout (KO) mice, which demonstrate marked mitochondrial membrane degeneration. We also assessed the relationship between αSyn deposits and mitochondria in brain tissue from patients with PLA2G6-associated neurodegeneration (PLAN) and Parkinson’s disease (PD), and quantitatively examined Lewy bodies (LBs) and neurons. The expression level of αSyn was elevated in PLA2G6-knockdown cells and KO mouse neurons. Strong PαSyn expression was observed in neuronal granules in KO mice before onset of motor symptoms. The granules were mitochondrial outer membrane protein (TOM20)-positive. Ultramicroscopy revealed that PαSyn-positive granules were localized to mitochondria with degenerated inner membranes. After symptom onset, TOM20-positive granules were frequently found in ubiquitinated spheroids, where PαSyn expression was low. Axons were atrophic, but the neuronal loss was not evident in KO mice. In PLAN neurons, small PαSyn-positive inclusions with a TOM20-positive edge were frequently observed and clustered into LBs. The surfaces of most LBs were TOM20-positive in PLAN and TOM20-negative in PD brains. The high proportion of LB-bearing neurons and the preserved neuronal number in PLAN suggested long-term survival of LB-bearing neurons. Elevated expression of αSyn/PαSyn in mitochondria appears to be the early response to PLA2G6-deficiency in neurons. The strong affinity of αSyn for damaged mitochondrial membranes may promote membrane stabilization of mitochondria and neuronal survival in neurons.

Etiology and pathophysiology of autistic behavior: clues from two cases with an unusual variant of neuroaxonal dystrophy

Two unrelated individuals with autistic behavior had numerous swollen axon terminals (spheroids) located in specific brain regions relevant to their behavioral symptoms. Spheroids are characteristic of neuroaxonal dystrophy, but the clinical profile and anatomic distribution of the lesions in these two patients differed from those of previously described patients with neuroaxonal dystrophy. Spheroids were numerous in the sensory nuclei of the spinal cord and medulla, specific nuclei and the reticular formation of the brainstem tegmentum, hypothalamus, anterior and dorsomedial thalamus, hippocampus, and cingulate and orbitofrontal cortices. Spheroids were sparse in the primary and association cortices and basal ganglia and absent in the hemispheric white matter. Cerebellar atrophy was present in both cases but associated with spheroids in only one case. These cases represent a new variant of neuroaxonal dystrophy in which behavioral symptoms characteristic of autism dominated the clinical picture. Neuroaxonal dystrophy should be included in the list of diseases that may be found in persons with autism.

Infantile neuroaxonal dystrophy: clinical spectrum and diagnostic criteria

OBJECTIVE

To present clinical, neurophysiologic, and neuroradiologic findings in 13 patients with infantile neuroaxonal dystrophy (INAD), focusing on aspects that assist early diagnosis.

BACKGROUND

Clinicopathologic diagnostic criteria for INAD were delineated by Aicardi and Castelein in 1979, but atypical cases are reported frequently and little is known of the diagnostic utility of MRI.

METHODS

The authors reviewed the clinical, neurophysiologic, and MRI findings of 13 patients who met the diagnostic criteria for INAD.

RESULTS

Symptoms onset was between 6 months and 2 years of age. In nine patients the clinical course was typical, with rapid motor and mental deterioration; in four patients progression was slower and the clinical picture was different. Electromyographic (EMG) signs of chronic denervation, fast rhythms on EEG and abnormal visual evoked potentials were observed in all patients during the disease course. Cerebellar atrophy with signal hyperintensity in the cerebellar cortex on T2-weighted images were the most characteristic MRI findings; hypointensity in the pallida and substantia nigra was also observed in two patients. alpha-N-acetyl-galactosaminidase activity on leukocytes was normal in the 10 patients tested.

CONCLUSIONS

EMG and MRI abnormalities are the earliest and most suggestive signs of INAD, which has a clinical and radiologic spectrum that is broader than reported previously.

Neuroaxonal dystrophy in infantile alpha-N-acetylgalactosaminidase deficiency

Morphologic alterations in biopsies of central and peripheral nervous tissue were investigated at the light-and electron-microscopic level in the first cases of lysosomal alpha-N-acetylgalactosaminidase deficiency. Widespread spheroid formation was observed in terminal and preterminal axons. Neocortical and peripheral autonomic axons contained tubulovesicular and lamelliform membranous arrays, prominent acicular clefts, and electron-dense axoplasmic matrix, the typical ultrastructural abnormalities corresponding to axonal spheroids in many inherited and acquired axonopathies. Central and peripheral membranous distal axonal spheroids were the only neuropathologic abnormality identified; other alterations resembling those in various neuronopathic lysosomal storage diseases were not observed. The morphologic findings and the distribution of the lesion in the present disorder are remarkably similar to those reported in the inherited infantile form of neuroaxonal dystrophy with normal alpha-N-acetylgalactosaminidase activity (Seitelberger disease).

Neurotoxicity of glycidamide, an acrylamide metabolite, following intraperitoneal injections in rats

Acrylamide (2-propenamide) monomer produces central-peripheral distal axonopathy in humans and some animal species. Its neurotoxicity is characterized by abnormal sensation, decreased motor strength, and ataxia. Acrylamide forms adducts with glutathione, proteins, and DNA. Recent studies demonstrated that acrylamide is metabolized to its epoxide, glycidamide (2,3-epoxy-1-propanamide). We studied the neurotoxicity potential of glycidamide in male Sprague-Dawley rats. Animals (groups of 6) were injected ip daily with either aqueous acrylamide or glycidamide at an acrylamide-equivalent dose of 50 mg/kg (0.70 mmol/kg). Both treatments resulted initially in the rats circling, which was followed by the onset of ataxia at 7-9 d and hindlimb paralysis at 12-14 d. Treated animals showed muscle wasting. At termination, acrylamide- and glycidamide-treated rats weighed 105% and 86% of initial weight, respectively, compared to 145% for controls. Animals were anesthetized and perfused with 10% neutral phosphate-buffered formalin 12 or 14 d after beginning of treatment. Both treatment groups exhibited similar neuropathologic changes in the central and peripheral nervous systems. More severe lesions were produced by glycidamide. A marked increase in the number of affected Purkinje cells in the cerebellum, which exhibited changes ranging from pyknosis to cell death, were present. The brainstem exhibited axonal degeneration with chromatolytic necrosis in midbrain medial and lateral reticular nuclei. The spinal cord was characterized by spongy form changes with vacuoles of different sizes in various levels. These results suggest that glycidamide is an active neurotoxic metabolite of acrylamide.

Impaired visual evoked potential and primary axonopathy of the optic nerve in the diabetic BB/W-rat

The spontaneously diabetic BB/W-rat has emerged as an important model system for somatic and autonomic diabetic polyneuropathy. In this study we examined visual evoked potentials and the presence of morphometric and structural changes in the optic nerve and the retinal ganglion cells and their afferent axons contained in the retinal nerve fibre layer. A six-month duration of diabetes mellitus was associated with significant increases in the latencies of the visual evoked potentials. The latency of the first positive potential showed a 44% increase, and that of the first negative potential was prolonged by 41%. No significant changes were demonstrated at any of the amplitudes. In the optic nerve mean myelinated fibre size was significantly reduced to 82% of control values, which was accounted for by a significant reduction in axonal size. Axo-glial dysjunction, a prominent structural defect of diabetic somato-sensory neuropathy in both man and diabetic rodents, was non-significantly increased in the optic nerve. In diabetic animals retinal ganglion cells displayed dystrophic changes. No such changes were observed in age- and sex-matched control animals. Proximal axons of the retinal nerve fibre layer showed an increase in dystrophic axons in diabetic BB/W-rats. Morphometric analysis of optic nerve capillaries revealed no abnormalities except for basement membrane thickening. The present data suggest that the diabetic BB/W-rat develops a central sensory neuropathy, characterized functionally by prolonged latencies of the visual evoked potentials and structurally by an axonopathy of optic nerve fibres.

Caudate nucleus pathology in Parkinson's disease: ultrastructural and biochemical findings in biopsy material

Ultrastructural and biochemical properties of caudate nucleus (CN) biopsies in two patients with advanced Parkinson's disease (PD) were compared with three CN specimens removed during surgery for intracranial tumors. An additional two specimens from neurologically intact patients (59 and 86 years old) were removed during autopsy (performed 3 and 4 h post mortem, respectively) for electron microscopic studies. Dopamine levels in PD were reduced to less than 15% of control values. Both PD patients showed frequent dystrophic neurites and transsynaptic degeneration of neurons and neuritic processes. These changes were not found in CN from the four control individuals. Only a few dystrophic neurites were noticed in one 67-year-old control patient. The development of neuroaxonal dystrophy in CN is consistent with a dying-back process, probably accompanying abnormalities of axonal transport in PD. Transsynaptic degeneration of neurons in CN very likely represents a morphological marker of disease severity. The occurrence of this change may account for the poor clinical response of patients with advanced PD to intracerebral implantation of dopaminergic tissues.

Neuroaxonal dystrophy in neuronal storage disorders: evidence for major GABAergic neuron involvement

The formation of focal granular enlargements within axons (axonal spheroids or "torpedoes"; neuroaxonal dystrophy) is a well known phenomenon occurring in a variety of neurological diseases. The relative susceptibility of different types of neurons to this kind of axonal pathology, however, is largely unknown. An immunocytochemical study directed at localizing glutamic acid decarboxylase (GAD), the synthetic enzyme for the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA), in various CNS regions in feline models of lysosomal storage disorders has revealed vast numbers of axonal spheroids containing this enzyme. In some storage diseases (GM1 and GM2 gangliosidosis), GAD-immunoreactive spheroids were a common occurrence in many brain regions, whereas in other disorders these structures were more limited in distribution (alpha-mannosidosis), or were absent (mucopolysaccharidosis type I). Axonal spheroids unreactive for GAD were encountered in large numbers in subcortical white matter in GM2 gangliosidosis, but were infrequently observed in the other diseases. The incidence and distribution of GAD-immunoreactive spheroids in the various diseases under study were found to correlate closely with the type and degree of neurological deficits exhibited by affected animals. This study indicates that the neuroaxonal dystrophy occurring in some types of storage disorders commonly involves axons of GABAergic neurons and suggests that a resulting defect in neurotransmission in inhibitory circuits may be an important factor underlying brain dysfunction in this family of diseases.

Terminal axon pathology in infantile neuroaxonal dystrophy

In order to clarify the pathogenesis of infantile neuroaxonal dystrophy, ultrastructural studies of the terminal and nonterminal axons of motor and autonomic nerves in muscle and skin, of which structures are much simpler than those of the central nervous system, were performed in 5 patients affected by infantile neuroaxonal dystrophy. The primary lesion was located in the axon terminal; the majority of terminal axons were dystrophic with tubulo-membranous profiles, while there were only a few dystrophic axons in the nonterminal axons. According to these findings, it is logical to consider that interruption of axonal transport at the site of the "turnaround" process is a cause of dystrophic change of the terminal axon in infantile neuroaxonal dystrophy.

Distal terminal axonopathy produced by 2,4-dithiobiuret: effects of long-term intoxication in rats

It has been well established that 2,4-dithiobiuret (DTB) intoxication in rats produces a rapidly progressive hindlimb paralysis within days. The cause of this has, until recently, been explained on the basis of a physiological abnormality that involves a prejunctional impairment in the neuromuscular transmission alone. The morphological correlate of the electrophysiological abnormalities has now been provided. This study describes the sequential morphological alterations resulting from a chronic long-term DTB intoxication (1 mg/kg per day, IP) in the rat nervous system up to 48 days. The findings indicate that DTB neurotoxicity evolves as a central peripheral distal axonopathy initially affecting the motor nerve terminals which show accumulation of interconnecting branched tubulovesicular profiles. With continued exposure, nerve terminal swelling and degeneration took place. Similar pathological changes in distal axons were observed progressively involving the small intramuscular nerve bundles close to the nerve terminals. Central nervous system axons in the long descending tracts of spinal cord and the cerebellar vermis showed similar changes but to a lesser extent in later stage of intoxication.

Somatosensory evoked potentials in Hallervorden-Spatz-neuroaxonal-dystrophy complex with dorsal column involvement

Two patients with a marked hypointensity of the globus pallidus on magnetic resonance imaging (MRI), which is known to be diagnostic for Hallervorden-Spatz disease (HSD), are presented. Patient 1 fell ill at about 10 years of age with visual disturbance, spastic paraplegia and mild ataxia, while patient 2 was affected during the second year of life with clinical features compatible with infantile neuroaxonal dystrophy (INAD). The two patients had certain clinical features in common; upper and lower motor neuron involvement, visual disturbance secondary to optic nerve atrophy, and dorsal column dysfunction, the evidence of which was seen from abnormal somatosensory evoked potentials (SEPs) obtained after posterior tibial nerve stimulation. In both patients, electron microscopic examination of the biopsied skin or sural nerve showed dystrophic axons, spheroids, and involvement of the peripheral nerve was indicated. Sharing of these clinical, pathological and MRI characteristics by the two patients supports the view of Seitelberger, who regarded HSD and INAD as constituents of a single disease entity, therefore the two patients were described as belonging to a disease spectrum of "Hallervorden-Spatz-neuroaxonal-dystrophy complex (HS-ND)." Sensory impairment has been a rare clinical feature in "HS-ND" complex, although its existence is not inconceivable considering the usual affection of the dorsal column/lemniscal pathway with spheroids. SEP was considered very useful in disclosing this often unmanifested sensory disturbance in "HS-ND" complex.

Axonal dystrophy in the posterior column nuclei of young adult epileptics with chronic phenytoin intoxication

Axonal spheroids in the posterior column nuclei of phenytoin-intoxicated epileptics were classified according to their predominant subcellular components into six types, and their incidences were compared with those in controls. Spheroids from phenytoin-intoxicated epileptics showed significantly higher proportions of the tubulomembranous (TM) and layered membrane loop (LML) types in the gracile nucleus, appearance of the same types in the cuneate nucleus, and a significant decrease of the neurofilamentous (NF) type in both nuclei. The incidences of the complex body (CB) and granular material types and of the homogeneous dense-body (HDB) type, which appeared only in the gracile nucleus, showed no difference between the intoxicated patients and the controls. The NF, CB and HDB types were therefore considered to be nonspecific. It was thought that chronic phenytoin intoxication might induce dystrophic changes, such as those characterized by the presence of the TM and LML types, in the axon terminals of the gracile and cuneate nuclei, possibly due to some abnormalities of the axoplasmic transport system.

Inhibition of proteolysis blocks anterograde-retrograde conversion of axonally transported vesicles

To test the hypothesis that proteolysis is required for anterograde-retrograde (A-R) conversion of membranous organelles at axon tips, a new experimental paradigm was developed. By cutting the sciatic nerves of rats, a concentrated population of axon tips was produced, and proteases in the axon tips were locally inhibited by immersing the cut end of the nerve into a solution containing protease inhibitors (E-64 or leupeptin). Membranous organelles were pulse-labeled with [3H]leucine at the nerve cell body, and the amount of retrogradely transported radiolabeled vesicles from the axon tips was quantified with a proximal collection ligature. The results show that protease inhibition decreased the amount of radioactivity that was transported retrogradely from the axon tips and correspondingly increased the amount that remained in the tips. Ultrastructural analyses showed that the protease-inhibited axon tips were greatly distended by 40-80 nm membranous tubules. By contrast, the control axon tips had relatively few of these membranous tubules. These results show that protease inhibition at the axon tip blocks the removal of membranous elements from the axon tips by retrograde transport. We propose that proteolysis is an A-R converting mechanism which is critically required at the axon tip for the conversion of 40-80 nm membranous tubules into retrograde organelles. Apparently, the 40-80 nm membranous tubules are normally transient intermediates in the A-R conversion pathway, and they rapidly accumulate in the axon tip if the mechanisms that convert them into retrograde organelles are blocked. These 40-80 nm tubules also accumulate in certain pathologies and in the aging process.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnosis of juvenile-adult form of neuroaxonal dystrophy by electron microscopy of rectum and skin biopsy

Images

Axonal pathology of the skin in infantile neuroaxonal dystrophy

Ultrastructural studies on the skin of two patients affected by infantile neuroaxonal dystrophy (INAD) were performed to evaluate its diagnostic value and to discuss the etiology of INAD. While the majority of terminal axons around intradermal glands were dystophic consisting of tubulomembranous and tubulovesicular profiles sometimes accompanied by synaptic vesicles, there were only few dystophic axons inside intradermal nerve bundles. These observations suggest that the primary lesion of INAD is located in terminal and presynaptic axons. Therefore, terminal axons have to be investigated when a diagnostic skin biopsy is performed in INAD.

Pathology of skeletal muscle and intramuscular nerves in infantile neuroaxonal dystrophy

Biopsies of the biceps muscle and sural nerve were taken from a girl aged 2 years with infantile neuroaxonal dystrophy (INAD). In addition to the typical axonal spheroid bodies in a number of the i.m. nerve fibers, the neuromuscular junctions (NMJs) and motor nerve endings also contained axonal swellings. The sural nerve, except for three dystrophic fibers, was almost completely normal. A teased nerve preparation showed four additional abnormal fibers with focal axonal enlargement similar to those in giant axonal neuropathy (GAN). These results suggest that a biceps muscle biopsy may be more useful than a sural nerve biopsy for the diagnosis of INAD, because the muscle contains abnormal peripheral nerves and NMJs in high frequency.

Histological and ultrastructural features of dystrophic isocortical axons in infantile neuroaxonal dystrophy (Seitelberger's disease)

The histological and ultrastructural features of axonal swellings are described in a cerebral biopsy specimen from a 6-year-old girl with infantile neuroaxonal dystrophy. In agreement with previous reports, several swellings were identified as axonal terminals, and it is postulated that the prevailing axonal swellings in cerebral cortex represent dystrophic boutons. Microscopically, dystrophic cortical boutons are morphologically different from typical subcortical spheroids and can be easily identified in routine histological preparations. Five ultrastructural elements were present in most axonal swellings: clusters of characteristic membranous bodies, stacks of elongated membranes, mitochondria, groups of vesicles, and an amorphous matrix. In spite of widespread axonal enlargement, the cerebral cortex was not thickened, and, in fact, the gyri looked atrophic in computerized axial tomograms. These findings suggest that some normal cortical element must be deficient, but such a structure remains to be identified.

Neurobiological studies of experimental diphenylhydantoin intoxication--III. Electron microscopic studies on development and disintegration mechanism of altered axon terminals and synaptic endings in rat cerebellum with chronic diphenylhydantoin intoxication

The processes of development and disintegration of axonal spheroids were electron microscopically studied in the rat cerebellum with chronic diphenylhydantoin intoxication. According to the severity and character of membrane accumulation, the whole course ranging from development to disintegration of altered axon terminals and synaptic endings in the DPH-intoxicated rat cerebellum was classified into the following four stages--initial, moderate, advanced and terminal. The initial stage was characterized by the appearance of a small number of interconnected tubules 150 to 350 A in diameter in non-enlarged axon terminals and synaptic endings. Usually these tubular structures tended to congregate in a certain part of axoplasm so that there were no intimate relationships between them and ordinary cell organelles. The moderate stage was characterized by an increased number of interconnected tubules in slightly or moderately swollen axon terminals and synaptic endings. The advanced stage was characterized by an extraordinary number of interconnected tubules in extremely highly swollen axon terminals and synaptic endings. Membranous scrolls and/or membranous strands separated by a cleft-like space were also found in an association with interconnected tubules so that the morphological organization of spheroids in the rat cerebellum with chronic DPH intoxication was very analogous to those of infantile neuroaxonal dystrophy. The terminal stage was characterized by the following three axonal events, i.e., rarefaction and coagulation necroses, and phagocytosis of spheroids by glial elements, presumably astrocytic in origin. The formation and fate of such axonal spheroids have not as yet been shown and discussed by electron microscopists. Thus the present paper was the first to reveal the electron microscopic observations suggestive of the details of development and disintegration mechanisms of spheroids by means of animal experimentations.

Morphological alterations of Purkinje cell axons and presynaptic terminals in organotypic cerebellar cultures exposed to ionizing irradiation

Ionizing irradiation induced marked morphological alterations in the Purkinje cell axons and axonic terminals in vitro. The myelinated segments demonstrated a very poor development of the myelin sheath. The axoplasm demonstrated various alterations of the mitochondria, and the smooth endoplasmic reticulum and the numerous elongated presynaptic terminals contained large aggregates of tubulovesicular structures and neurofilaments arranged in parallel and reticular array.

Study of axonal dystrophy. II Dystrophy and atrophy of the presynaptic boutons: a dual pathology

In succession to the previous quantitative work, a qualitative study has been carried out on the nature of a dual pathology affecting presynaptic boutons in the posterior tract nuclei of ageing rats. Based on the morphology of dystrophic boutons in early stage, it is concluded that the initial and therefore essential characteristic of dystrophic process is an abnormal increase of normal axonal components within the presynaptic boutons, and that various abnormal substructures of spheroids hitherto reported in the literature are probably the results of their secondary metamorphosis. The dystrophic process within the posterior tract nuclei is a selective one, involving presynaptic boutons and preterminal axons only of the posterior tract fibres. Comparison of the frequency of early dystrophic boutons and of fully grown-up spheroids indicates that a small percentage of boutons deriving from posterior tract fibres become dystrophic and of these dystrophic boutons only a small percentage again continue to develop unto large spheroids, throughout lifespan of the animals. On the other hand, in search of a morphological counterpart for the age-related decrease of volume ratio of presynaptic boutons to the neuropil, some dubious atrophic changes were also found in presynaptic boutons, which could have been easily missed from observation if studied qualitatively alone. Accordingly, no less numerous boutons other than dystrophic ones are supposed to atrophy 'independently' and to disappear 'silently' during the same period. The dystrophic and the atrophic changes involve different boutons (of different or the same terminal axons) within the same gray matter. This dual pathology of boutons needs further elucidation of its neurocytopathological as well as neurobiological background in the future.

Morphometric evaluation of primary sensory neurons in experimental p-bromophenylacetylurea intoxication

To evaluate the three-dimensional pathology of lumbar primary sensory neurons in p-bromophenylacetylurea intoxication, the number and size distribution of neurons and of myelinated fibers were evaluated at the L-6 spinal ganglion level and at proximal and distal levels of sural nerve and thoracic (proximal) and cervical (distal) levels of Goll's tract, respectively, 2 and 6 weeks after the intoxication in rats. The number and size distribution of ganglion neuron cell bodies were not significantly different between intoxicated and control rats. The distal level of sural nerve had significantly fewer large myelinated fibers than did control, and a significantly higher frequency of fibers undergoing degeneration. Proximal levels of sural nerve showed similar, but less severe changes. Similarly, the myelinated fibers of Goll's tract were significantly more affected at cervical than at thoracic level. Therefore, by morphometric criteria both centrally and peripherally directed myelinated fibers are most affected distally and less affected proximally while neuron cell bodies are not affected at all. These three-dimensional morphological changes must be taken into consideration in formulating possible mechanisms for the development of this neuropathy.

Fundamental aspects of the developing brain: synapse formation

The phenomena presiding over synaptogenesis in the developing brain, notably death of neurons and the nerve growth factor are described as well as the neurobiological and ultrastructural features of synapse maturation. Synapse and connection specificity in the brain versus plasticity are given consideration. Infantile neuroaxonal dystrophy is suggested as a possible example of defective synaptogenesis.

Infantile neuroaxonal dystrophy and giant axonal neuropathy: are they related?

Light and electron microscopic findings from two sural nerve biopsies obtained at a one-year interval from a patient with the clinical features of Seitelberger's disease are described. Ballooned axons with accumulations of membranous profiles, vesicles, mitochondria, and a homogeneous center were present, and there were masses of 90 A filaments in endothelial, endoneurial, perineurial, and Schwann cells. These pathological alterations were less prominent in the second nerve biopsy, which showed a more pronounced decrease in myelinated fibers. The case shows that a generalized increase of 90 A filaments in structures of the peripheral nervous system is not a phenomenon exclusively occurring in patients with giant axonal neuropathy and, furthermore, that it may be a transitory feature.

Morphological investigations on axonal swellings and spheroids in various human diseases

Axonal swellings and spheroids in various human diseases were studied by light and electron microscopy. 4 cases of infantile neuroaxonal dystrophy, 2 of degenerative diseases, 2 brain tumors and 3 of cerebrovascular disease were examined. Ultrastructurally most spheroids in infantile neuroaxonal dystrophy consisted of interconnected tubules, stacked membranotubular profiles, alternating layered membranes and accumulations of neurofilaments. Combinations of these four constituents were seen only in infantile neuroaxonal dystrophy. "Torpedos" (fusiform swelling of the axon of a Purkinje cell) consisted exclusively of neurofilaments. Spheroids in case 6 (mental retardation) and 7 (atypical teratoma) consisted of interwoven skeins of neurofilaments and grouped mitochondria. Spheroids in case 8 (demyelination) and 9 (cerebrovascular disease) consisted of packed complex bodies and mitochondria. Spheroids in cases 10 and 11 (cerebrovascular disease) consisted of degenerating organelles only. The morphological differences between cases 9, 10 and 11 probably depends on the severity and timing of the cerebral injury. Most spheroids show similar histological and histochemical properties, but ultrastructural study may give some clue to the origin of the bodies.

Juvenile neuroaxonal dystrophy: clinical, electrophysiological, and neuropathological features

We describe 2 brothers with progressive myoclonus epilepsy that began in the second decade and was associated with cerebellar ataxia and intellectual deterioration. Electroencephalographic and cerebral evoked potential studies showed findings associated with myoclonus epilepsy. Neuropathological examination of 1 of the brothers, who died at age 23 years, revealed widespread changes of neuroaxonal dystrophy without pigment deposition in the basal ganglia. We propose the term juvenile neuroaxonal dystrophy (JNAD) to distinguish this condition on clinical grounds from infantile neuroaxonal dystrophy on the one hand, and on clinical and pathological grounds from Hallervorden-Spatz disease on the other hand. JNAD, while exceedinly rare, must be considered in the differential diagnosis of the progressive myoclonus epilepsies.

Generalized giant axonal neuropathy: a filament-forming disease of neuronal, endothelial, glial, and schwann cells in a patient without kinky hair

The process of Giant Axonal Neuropathy (GAN) is not restricted to the peripheral nerves, but also involves the central nervous system. In a 25 year old man with normal hair, abundant axon swellings and spheroids were observed in the spinal cord, brain system, and cerebral cortex. The findings in the sural nerve have already been published by Boltshauser et al. (1977). Accumulations of filaments in the axons and in the perineural cells were accompanied by Rosenthal fibres. The ultrastructural pattern of GAN differs clearly from that of Neuroaxonal Dystrophies.

Spastic paraplegia with neurogenic amyotrophy manifesting ballooned axons in sural nerve

A 21-year-old man had progressive symmetric, distal muscle atrophy and weakness, as well as spasticity of the limbs. Histologic examination of the sural nerve disclosed swollen axons containing membranous tubular profiles, ring tubules, large mitochondria with abnormal cristae, and glycogen like granules. Peripheral sensory nerve fibers also were affected. The pathologic features of the peripheral nerves were similar to those of infantile neuroaxonal dystrophy. Sural nerve biopsy may be useful in the study of pathologic processes in spastic paraplegia.

Infantile neuroaxonal dystrophy. Ultrastructural study of peripheral nerve

Ultrastructural study of the biopsied sural nerve in a case of infantile neuroaxonal dystrophy was made. The characteristic change in the ballooned axons is an accumulation of membranous profiles associated with mitochondria, glycogen like granules, dense bodies, vesicles and electron lucent material. The membranous profile is classified into three morphological types and discussed on each of them. Probably tubulomembranous profile of the first type is most common and may be cardinal deposit in this condition. These membranous structures of various types might be, however, only different manifestations occurring on the same morbid process. Enormous amount of glycogen like granules and mitochondria might be related to the metabolic derangement of carbohydrate in the ballooned axons. Electron lucent material we observed was not described in the previous papers on this condition. We added one more example showing that nerve biopsy is helpful to confirm the diagnosis in infantile neuroaxonal dystrophy.

A quantitative electron microscopic study of atypical structures in normal human cerebral cortex

Biopsy samples of the cerebral cortex from four normal human brains were examined in the electron microscope for the presence of abnormalities related to neurones and neuroglia. Atypical forms of axons, axon terminals and dendrites, many of them similar to those described in a variety of pathological and experimental material, were found to occur in small but appreciable numbers. Neuroglia exhibiting atypical inclusions occurred but were much less common. Physiologically altered neuronal perikarya were not encountered apart from one neuronal death. An area of 3.6 x 10(5) mu2 was scanned from each brain and atypical structures were categorised and counted. The possible implications of the presence of these structures in normal brain in discussed and the need for neuropathologists and neuroanatomists to be aware of the existence of atypical forms of neuronal processes in normal human and animal brains is emphasised.

Pathologic axons and synapses in human neuropsychiatric disorders

Ultrastructural studies of cerebral biopsy specimens from patients with various forms of psychomotor retardation and dementia have disclosed pathologic changes in axons and presynaptic or postsynaptic processes. The clinical disorders with lesions in axons and presynaptic terminals are reviewed. Three basic abnormalities have been detected: proliferation of tubulovesicular structures which probably originate from the smooth endoplasmic reticulum, "abnormal" mitochondria, and proliferation of 80 to 100 A filaments. Understanding of the pathogenesis of human disorders associated with axonic or "synaptic" lesions will probably depend on progress in areas of basic biomedical research concerned with the synthesis and turnover of biological membranes and the packaging and secretion of neurotransmitters, elucidation of mechanisms of cytoplasmic streaming and axoplasmic flow, and biophysical and biochemical characteristics and functions of "fibrous" proteins (neurotubules, neurofilaments, pathologic fibrous proteins). In several cases of mental retardation of unknown etiology, abnormal dendritic spines of cortical neurons have been observed with the use of the Golgi method. These dendritic (postsynaptic) disorders have been attributed to defective development ("dysgenesis"). The knowledge provided by ultrastructural analysis of brain tissue from the human disorders of mental retardation or dementia is "still formless, incomplete, lacking the essential threads of connection," and only future developments in lacking neurobiology will make possible the dissection of the primary phenomena from the secretory and probably irrelevant findings.

Infantile neuroaxonal dystrophy. An electron microscopic study of a case clinically resembling neuronal ceroid-lipofuscinosis

An unusual case of infantile neuroaxonal dystrophy (INAD) in which seizures were the presenting and predominant clinical feature is described. Although the clinical manifestations were indistinguishable from neuronal ceroid-lipofuscinosis, the diagnosis was readily established by electron microscopic examination of the brain biopsy specimen. Even after the ultrastructural features were known, the dystrophic axons were not evident by light microscopy. This case broadens the clinical picture of INAD to include seizures as the presenting complaint and suggests that some patients with childhood epilepsy who "deteriorate" may have this genetically determined disease.

Infantile neuroaxonal dystrophy (Seitelberger's disease). A light and ultrastructural study

The findings in a case of infantile neuroaxonal dystrophy are presented. Light microscopy shows wide distribution of spheroids, cerebullar atrophy and striatal degeneration. Electron microscopy shows numerous spheroids consisting of tubulo-vesiculo-membranous profiles. The dystrophic changes appear first in the axon seem to be modified by axostasis and/or transneuronal degeneration in addition to the dystrophic changes. The participation of the endoplasmic reticulum and microtubules in spheroid formation and their relation to the malformation of the synaptic vesicles have been discussed. Diverse mitochondrial abnormalities and Hiranolike body are also described.