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

Encephalomyelitis, brain tumors, neuromuscular diseases and miscellaneous disorders

Japanese neuropathologists have accomplished and contributed to a considerable number of achievements, and some of these are cited in other articles in this issue. Several of these achievements as well as other miscellaneous discoveries are briefly summarized in the present paper. Specifically these relate to rabies postvaccinal encephalomyelitis, experimental allergic encephalomyelitis, brain tumor research, neuromuscular disorders, schizophrenia, viral infections, glial inclusion body in multiple system atrophy, and the neurobiology of glia.

Calcitonin gene-related peptide- and substance P-immunoreactive axons in the nucleus gracilis of the rat with special reference to axonal dystrophy: light and electron microscopic observations

Calcitonin gene-related peptide (CGRP) and substance P (SP)-immunoreactive (IR) axons in the nucleus gracilis of normal rats (1-15 months of age) were studied by light and electron microscopy. Besides many CGRP-IR and SP-IR varicosities with normal appearance, we found a few swollen (nearly round or oval) varicosities with either CGRP or SP immunoreactivity. Swollen CGRP-IR varicosities were more frequently seen than SP-IR ones, appearing from 3 months of age and increasing in number and size (up to approximately 25 microns in diameter) with advancing age. At the electron microscopic (EM) level, CGRP-IR and SP-IR swollen varicosities showed dystrophic changes, i.e., many membranous dense bodies, and proliferation of microtubules and neurofilaments. CGRP-IR or SP-IR dystrophic axons also contained many mitochondria and sometimes made synaptic contacts with nonreactive dendrites (occasionally with non-IR axons). These findings suggest that the dystrophic CGRP and SP axonal profiles represent a functionally distinct subpopulation of axonal dystrophy in the nucleus gracilis and use CGRP or SP as a neuroactive substance. Using a double-immunostaining method, many of normal CGRP-IR axons were identified to be SP-IR. However, no single dystrophic varicosity was found to contain both CGRP and SP immunoreactivities. These findings suggest that CGRP and SP afferents are independently affected and progress to dystrophic changes.

Ultrastructural changes in the gracile nucleus of the rat after sciatic nerve transection

Ultrastructural changes in the gracile nucleus of the rat have been examined after peripheral nerve injury. The sciatic nerve of adult rats was transected at mid-thigh level, and after survival times ranging from 1 day to 32 weeks sections from the gracile nucleus were prepared for electron microscopic examination. Unoperated animals served as controls. Atypical profiles were regularly observed in the experimental cases at post-operative survival times from 3 days up to 32 weeks. It was sometimes not possible to classify these as preterminal axons or terminals, because synaptic contacts could not be identified. The two most common changes throughout the entire post-operative period were greatly expanded myelinated axons, or unmyelinated profiles containing numerous mitochondria, osmiophilic dense bodies and vacuoles. Atypical profiles were occasionally observed in unoperated control animals. The results clearly show that various types of degenerative changes occur in the gracile nucleus after peripheral nerve injury. These changes differ markedly from previously described transganglionic changes in other systems. It cannot be excluded that some of the changes reflect growth-related reactions, although the typical features of axon regeneration could not be found.

Axonal degeneration of ascending sensory neurons in gracile axonal dystrophy mutant mouse

The distribution of axonal spheroids was examined in the central nervous system of gracile axonal dystrophy (GAD) mutant mice. Only few spheroids are observed in the gracile nucleus of the medulla in normal mice throughout the period examined, while they are first noted in GAD mice as early as 40 days after birth. The incidence of spheroids shifts from the gracile nucleus to the gracile fasciculus of the spinal cord with the progress of disease, suggesting that the degenerating axonal terminals of the dorsal ganglion cells back from the distal presynaptic parts in the gracile nucleus, along the tract of the gracile fasciculus, toward the cell bodies in the dorsal root ganglion. This phenomenon indicates that the distribution of spheroids is age dependent and reflects a dying-back process in degenerating axons. In addition to the gracile nucleus and the gracile fasciculus, which is one of the main ascending tracts of primary sensory neurons, it was noted that the other primary sensory neurons joined with some of the second-order neurons at the dorsal horn and neurons at all levels of the dorsal nucleus (Clarke's column) are also severely affected in this mutant. The incidence of the dystrophic axons are further extended to the spinocerebellar tract and to particular parts of the white matter of the cerebellum, such as the inferior cerebellar peduncle and the lobules of I-III and VIII in the vermis. These results indicate that this mutant mouse is a potential animal model for human degenerative disease of the nervous system, such as neuroaxonal dystrophy and the spinocerebellar ataxia.

Study of axonal dystrophy. III. Posterior funiculus and posterior column of ageing and old rats

Axonal dystrophy in normal ageing can be studied in experimental animals. Primary sensory neurones show two different kinds of change with ageing, i.e. axonal dystrophy and axonal atrophy (degeneration). This paper reports the chronology and topography of these two processes in relation to growth and involution of these neurones throughout the lifespan of the rats used in this study. Axonal spheroids preferentially form at presynaptic terminal regions in many of the collaterals of central branches of the axons, i.e. in the posterior funiculus nuclei, posterior column and posterior funiculus. Axonal dystrophy in normal ageing is essentially a morbid process restricted to the terminal parts of the axon. It shows little tendency to expand retrogradely along the axon. Evidence is presented that spheroids in posterior funiculus also derive from terminal axons. Preference is also noted in the lumbosacral rather than cervical neurons, and in longer (posterior funiculus nuclei) rather than shorter (posterior column) collaterals. Quantitative study of myelinated fibres in posterior funiculus shows that they increase in number until middle age (400 days) of the animals, before beginning to decline. On the other hand, axonal atrophy begins to appear early in small numbers, and increases in numbers with age. Atrophy involves the whole length of the axon within the posterior funiculus from the start, suggesting, therefore, that it does not belong to a dying-back process. It is noteworthy that the main development of axonal dystrophy lies in the earlier half of the animals' life, while that of axonal atrophy lies in the latter half. This fact adds to the evidence that axonal dystrophy, as far as in normal ageing is concerned, is more related to the positive side of neuronal activity, e.g. one form of growth abnormality of axon.

Cell loss in lumbar dorsal root ganglia and transganglionic degeneration after sciatic nerve resection in the rat

The effects of sciatic nerve resection on lumbar dorsal root ganglion cells and their central branches have been studied in the adult rat. A quantitative analysis of the lumbar dorsal root ganglia indicated a 15-30% cell loss on the operated side. Argyrophilia indicating transganglionic degeneration was observed in Fink-Heimer stained sections from the lumbar spinal cord and the brainstem. The areas of degeneration argyrophilia were mainly located in the medial part of the ipsilateral L2-L6 dorsal horn laminae I-IV, the tract of Lissauer, the dorsal funiculus and the gracile nucleus. A few degenerating fibers could also be observed in the ipsilateral dorsal horn laminae V and VI, and in the ipsilateral ventral horn as well as in the contralateral dorsal horn and the gracile nucleus. The results confirm and extend previous findings at other levels and in other species. This suggests that cell loss and transganglionic degeneration may be general phenomena affecting a substantial proportion of primary sensory neurons following peripheral nerve injury.

Experimental striatal degeneration induced by kainic acid administration: relevance to morphological changes in Huntington's disease

In an attempt to reproduce the characteristic neuronal degeneration pattern in the striatum of human patients with Huntington's disease, the histological and ultrastructural features of the degeneration of medium-sized nerve cells in the striatum and its processes are described in young rats induced by a direct injection of a small amount of kainic acid into the striatum. A light microscopic examination revealed initial edema and necrotic changes at the site of injection. The area surrounding the needle track showed neuronal and dendritic swelling and eosinophilic neurons without the apparent involvement of the passing axons. Later changes consisted of a marked neuronal loss particularly of the small cells with consequent severe astrocytosis. Electron microscopy showed specific neuronal alterations in the form of ballooned Golgi apparatuses, swelling of the endoplasmic reticulum, dendritic swelling, proliferated neurofilaments and aggregation of polysomes together with a marked disruption of neuropil. Neuronal debris and small dense bodies appeared. The majority of neuronal loss consisted of medium-sized nerve cells: Type I. Some spheroid bodies and lipid droplets were also observed.

Dystrophic axons in the nucleus gracilis of the normal rat containing cholecystokinin-like immunoreactivity. Light- and electron-microscopic observations

Cholecystokinin immunoreactive (CCKI) axons in the nucleus gracilis of the normal rat were studied by light and electron microscopy using the peroxidase-antiperoxidase (PAP) immunocytochemical method. Immunoreactivity was found in both normal and dystrophic axons at various ages. Slightly enlarged CCKI varicosities were first observed in 2-month-old rats, gradually increased in number (max. at 21 months) and in diameter (up to 20 micron at 21 months), and then decreased (at 27 and 36 months). Dilatated CCKI fibers continuous with dystrophic varicosities also tended to increase proportionally in diameter. The dystrophic CCKI axonal profiles, first identified at the light-microscopic level and then observed under electron microscopy, had consistently characteristic features. In addition, numerous dystrophic nonreactive axonal profiles had morphological features differing from those of dystrophic reactive ones at advanced ages. These findings suggest that CCK may be partly involved in the formation of dystrophic axons in the nucleus gracilis.

Diminished retrograde transport causes axonal dystrophy in the nucleus gracilis. Electron- and light-microscopic study

To examine a possible cause of axonal dystrophy in the nucleus gracilis, dorsal root ganglion (DRG) neurons of rats were investigated by means of electron-microscopic autoradiography and horseradish peroxidase (HRP) tracing method. Following injections of tritiated amino acids into the L6 and S1 DRG, labeling was observed on the initial and halfway developed dystrophic terminals in the ipsilateral gracile nucleus. However, no grains or few, if any, were found on the well developed huge dystrophic endings. Compared with the thoracic and upper lumbar DRG, a decrease in velocity and amount of retrograde HRP transport was demonstrated in the lower lumbar and sacrococcygeal DRG neurons, especially of large cell diameter, irrespective of age of rats. These findings led us to conclude that the axonal dystrophy reflects a state of an anterograde overtransport of the axoplasm caused by a diminished retrograde transport which is specific to lower lumbar and sacrococcygeal DRG large neurons.

Spinal radiculoneuropathy in aging rats: demyelination secondary to neuronal dwindling?

Temporal development of radicular demyelination was studied in male albino rats examined sequentially throughout the lifespan of the animals. The rats were perfusion-fixed with paraformaldehyde and glutaraldehyde and areas of their nervous system including the lumbar spinal roots, the spinal cord, and the peripheral sciatic nerve, were embedded in epoxy resin and submitted to microscopic examination in semithin and ultrathin sections. In addition, a vital fat stain, teasing of single nerve fibers, and estimates of axon diameter and fiber number were obtained. Degenerative changes occurred earlier in the distal portions of nerve fibers than in the spinal roots. The radicular lesion consisted of swelling of myelin and demyelination possibly secondary to shrinkage of axons, resulting in focal accumulation of lipid debris within the spinal roots of old rats. Although the causation of senile neuronal atrophy affecting rat peripheral neurons is not fully obvious, this condition may be exacerbated by such factors as pressure on the nerves and hypoactivity.

Onset and regression of neuroaxonal lesions in sheep with mannosidosis induced experimentally with swainsonine

A group of young sheep were fed a diet containing the alpha-mannosidase inhibitor swainsonine, which resulted in the induction of a neuronal lysosomal mannoside storage disease. Sheep were killed at various intervals during and following the treatment period and the nature and distribution of neuronal and axonal lesions in the brain were assessed by routine light and electron microscopy and by the rapid Golgi impregnation technique. Neuronal mannoside storage, axonal dystrophy and meganeurite formation were induced by 80 days of treatment and the lesions had regressed by 40 days after the end of treatment. The results are discussed in relation to their relevance to the current widespread interest in the pathobiology of neuronal lysosomal storage.

Nasu-Hakola's disease (membranous lipodystrophy). A case report

An autopsy case of Nasu-Hakola's disease (membranous lipodystrophy) was reported. A 29-year-old Japanese woman whose younger sister had been affected with typical Nasu-Hakola's disease with skeletal and neuropsychiatric syndromes and membrano-cystic lesions in the bones developed forgetfulness and lack of initiative. The clinical features were characterized by diminished drive, apathy, euphoria, disturbance of attention, amnestic syndrome, and gait disturbance. The clinical course of her illness was 8 years. The neuropathologic examination revealed marked symmetrical gliosis of the cerebral white matter (sclerosing leukodystrophy) predominantly in the frontal and temporal lobes with slight or moderate demyelination (dissociation glio-myelinique) and widespread axonal changes such as fragmentation and spheroid in the white matter of the cerebral hemisphere, cerebellum, basal ganglia, and brain stem. The ultrastructure of spheroids showed neurofilamentous accumulation. We discussed the importance of axonal changes with regard to the pathogenesis and etiogenesis of the disease.