Paired helical filaments in spinal ganglion neurons of elderly rats

Ultrastructure of dorsal root ganglia

Dorsal root ganglia (DRG) contains thousands of sensory neurons that transmit information about our external and internal environment to the central nervous system. This includes signals related to proprioception, temperature, and nociception. Our understanding of DRG has increased tremendously over the last 50 years and has established the DRG as an active participant in peripheral processes. This includes interactions between neurons and non-neuronal cells such as satellite glia cells and macrophages that contribute to an increasingly complex cellular environment that modulates neuronal function. Early ultrastructural investigations of the DRG have described subtypes of sensory neurons based on differences in the arrangement of organelles such as the Golgi apparatus and the endoplasmic reticulum. The neuron-satellite cell complex and the composition of the axon hillock in DRG have also been investigated, but, apart from basic descriptions of Schwann cells, ultrastructural investigations of other cell types in DRG are limited. Furthermore, detailed descriptions of key components of DRG, such as blood vessels and the capsule that sits at the intersection of the meninges and the connective tissue covering the peripheral nervous system, are lacking to date. With rising interest in DRG as potential therapeutic targets for aberrant signalling associated with chronic pain conditions, gaining further insights into DRG ultrastructure will be fundamental to understanding cell-cell interactions that modulate DRG function. In this review, we aim to provide a synopsis of the current state of knowledge on the ultrastructure of the DRG and its components, as well as to identify areas of interest for future studies.

Geniposide ameliorates learning memory deficits, reduces tau phosphorylation and decreases apoptosis via GSK3β pathway in streptozotocin-induced alzheimer rat model

Intracerebral-ventricular (ICV) injection of streptozotocin (STZ) induces an insulin-resistant brain state that may underlie the neural pathogenesis of sporadic Alzheimer disease (AD). Our previous work showed that prior ICV treatment of glucagon-like peptide-1 (GLP-1) could prevent STZ-induced learning memory impairment and tau hyperphosphorylation in the rat brain. The Chinese herbal medicine geniposide is known to relieve symptoms of type 2 diabetes. Because geniposide is thought to act as a GLP-1 receptor agonist, we investigated the potential therapeutic effect of geniposide on STZ-induced AD model in rats. Our result showed that a single injection of geniposide (50 μM, 10 μL) to the lateral ventricle prevented STZ-induced spatial learning deficit by about 40% and reduced tau phosphorylation by about 30% with Morris water maze test and quantitative immunohistochemical analysis, respectively. It has been known that tau protein can be phosphorylated by glycogen synthase kinase-3 (GSK3) and STZ can increase the activity of GSK3β. Our result with Western blot analysis showed that central administration of geniposide resulted in an elevated expression of GSK3β(pS-9) but suppressed GSK3β(pY-216) indicating that geniposide reduced STZ-induced GSK3β hyperactivity. In addition, ultrastructure analysis showed that geniposide averted STZ-induced neural pathology, including paired helical filament (PHF)-like structures, accumulation of vesicles in synaptic terminal, abnormalities of endoplasmic reticulum (ER) and early stage of apoptosis. In summary, our study suggests that the water soluble and orally active monomer of Chinese herbal medicine geniposide may serve as a novel therapeutic agent for the treatment of sporadic AD.

Ultrastructural study of Betz cells in the primary motor cortex of the human brain

The ultrastructure of Betz cells in the 5th layer of the primary motor cortex of 17 neurologically and psychiatrically normal control individuals was studied. Normal-appearing Betz cells showed a wide range of features including novel electron-dense inclusion bodies (Bunina-like bodies) resembling Bunina bodies characteristic of amyotrophic lateral sclerosis (ALS), accumulations of neurofilaments (10 nm in diameter), bundles of filaments (20-25 nm in diameter) thicker than neurofilaments, lamellar structures, lamellar bodies and structures similar to Hirano bodies. Among these 'abnormal' features, the presence of Bunina-like bodies may be an age-related nonspecific degenerative change, since they appeared more frequently in elderly individuals. The presence of these abnormal features--particularly the Bunina-like bodies--in the Betz cells of normal human brains must be considered in the assessment of the pathognomonic significance of such structures in ALS and other neurological diseases that affect the motor cortex.

Ultrastructural study of rat hippocampus after chronic administration of aluminum L-glutamate: an acceleration of the aging process

An ultrastructural study of rat hippocampus was performed on young (group 1) and old (group 4) rats receiving daily subcutaneous injections of aluminum L-glutamate and on old untreated rats (group 5). Young controls were treated with sodium L-glutamate (group 2) and physiological saline (group 3). Group 1 showed vacuolated astrocytes with numerous lipofuscin deposits, mitochondrial swelling, a thinning of the myelin sheath, and many multivesicular bodies invading the cytoplasm. Cellular structure did not appear to be affected in groups 2 and 3. Group 4 showed swollen mitochondria, a demyelination process in axonal regions, sizable perivascular oedema with vessel retraction and gliofilament bundles. In this group, lipofuscin deposits in astrocytes were associated with multivesicular bodies that thinned the myelin sheath to the breaking point; however, no excitotoxic glutamate-induced effects were observed. In group 5, extreme cytoplasmic vacuolation was observed, with massive mitochondrial swelling, considerable thinning of the myelin sheath (at times to the breaking point), sizable vacuolar degeneration and gliofilament bundles. These results indicate that ultrastructural alterations in the hippocampus, such as cell vacuolization, massive mitochondrial swelling and the demyelination process, occur with aging and independently of aluminum intoxication. Similar alterations were observed in aluminum L-glutamate-intoxicated young rats, but not in controls. These results are consistent with aluminum-induced acceleration of the aging process.

Neurons and microvessels of the nodose (vagal sensory) ganglion in young adult and aged rats: morphometric and enzyme histochemical studies

The neuron cell bodies and microvessels in sections of the nodose (vagal sensory) ganglion (NG) of Wistar rats of 4- and 24-months of age have been examined morphometrically and by quantitative enzyme histochemistry. The range of neuronal somata areas was similar at the two ages and distributed unimodally, ranging approximately from 200-1500 microns 2 with the largest somata occurring in the older age group. The range of microvessel diameters was also comparable but the largest microvessels were seen in the older animals. The histological arrangement of the ganglion permitted analyses to be made of 'neuronal' and 'axonal' areas independently. The number of microvessels per unit area was less in regions of the ganglion occupied by axons at both ages. Random transects indicated that the percentage area occupied by neuron somata decreases and that of axons increases with age. Overall, however, the results suggest that the histological organization, the size of vagal sensory neurons, the ganglionic microvessels, and the relationship between them, does not change greatly in Wistar rats of up to 2 years of age. Ultrastructural features of the aged sensory neurons included the presence of secondary lysosomes, disrupted rough endoplasmic reticulum, swollen Golgi cisternae, and the presence of much filamentous material in the perikaryon similar to that seen in chromatolytic neurons. However, analysis of electron micrographs did not reveal significant changes in the numbers of mitochondria or Golgi bodies. There was an overall increased thickness in the microvascular wall in the older animals with the endothelium and pericyte covering being significantly increased, but the thickness of the basal lamina was unchanged. The activities of neuronal NADH tetrazolium reductase, succinate dehydrogenase and cytochrome oxidase were all increased with age. The results suggest that vagal sensory neurons are not greatly affected by age in the rat.

Age-related reduction of the satellite cell sheath around spinal ganglion neurons in the rabbit

The volumes of the nerve cell bodies and those of the enveloping satellite cell sheaths from spinal ganglia of young adult and aged rabbits were determined by morphometric methods using the electron microscope. The mean volume of the nerve cell bodies was greater in the old rabbits than in young adults; this is probably related to the larger body size of the old animals. The mean volume of the satellite cell sheaths was, however, smaller in the aged rabbits than in the young adults. Consequently the volume ratio between the satellite cell sheaths and the related nerve cell bodies was significantly smaller in the aged animals. Since satellite cells play an important role in the support of the neuron, the reduction in volume of the perineuronal sheath could be associated with a decrease in the trophic activity of satellite cells towards the enveloped neuron with consequences for neuronal activity. Furthermore, in the satellite cell sheaths of old rabbits, the number and extension of gaps that leave the neuronal surface directly exposed to the basal lamina were significantly increased. Since spinal ganglia lack a blood-nervous tissue barrier, only the satellite cell sheath controls the traffic of material to the nerve cell body. Because the neuronal surface unprotected by the satellite cell envelopment is significantly more extensive in the spinal ganglia of old rabbits than in those of young adults, the nerve cells of the former are more exposed to potential damage by harmful substances. A dense undercoating was seen very frequently beneath the portions of the neuronal plasma membrane not covered by satellite cells.

Cytoskeletal changes in rat cortical neurons induced by long-term intraventricular infusion of leupeptin

Neurofibrillary tangles (NFTs), which are composed of paired helical filament (PHF)-like filaments, were induced by the long-term intraventricular infusion of leupeptin, a potent protease inhibitor. The fibrils composing the NFTs were 20 nm in maximal width and had periodic constrictions at 40-nm intervals. They were identical to the PHF that had been found in aged rat neurons. Dystrophic axons filled with mainly tubular structures were also abundantly found in the parietal and temporal isocortices, which were not affected in the acute or subacute phases of leupeptin treatment. An immunohistochemical study using antibodies related to the neuronal cytoskeleton showed that neuronal cytoskeletal changes accompanying ubiquitination occurred in dystrophic axons distributed widely in the isocortex as well as the hippocampal formation. The present findings suggest that long-term administration of leupeptin accelerates the neuronal ageing process in rats and causes other neuronal changes: NFT formation, such as seen in the aged brain or in neurodegenerative diseases including Alzheimer's disease, in addition to accumulation of lipofuscin granules and degeneration of neuronal processes. In other words, some disturbance of the balance between proteases and their inhibitors may play an important role in the neuronal ageing process, and some regulatory intervention in the intraneuronal protease activity may provide a new therapeutic strategy for the neurodegenerative diseases.

Immunocytochemical and ultrastructural studies of the motor cortex in amyotrophic lateral sclerosis

This report concerns an immunocytochemical and ultrastructural study of the motor cortices of 11 patients with amyotrophic lateral sclerosis (ALS). Specimens from 12 normal individuals served as controls. Antibodies against phosphorylated neurofilament (PNF; 200 kDa), ubiquitin, glial fibrillary acidic protein (GFAP) and phosphorylated tau protein were used. The pyramidal cells of layer III of all ALS patients were stained, with varying intensities, by the antibody to PNF. By contrast, Betz cells reacted less frequently with this antibody. Staining for GFAP was noted in numerous astrocytes in layer III and at the transition between white matter and motor cortex of most patients. Ubiquitin-positive inclusions were only occasionally seen in Betz cell and pyramidal cell of layer V. These observations indicate that alterations of the motor cortex occur first in the pyramidal cells of layer III rather than in Betz cells. Pyramidal cells and Betz cells were not stained by the antibody to phosphorylated tau protein. In controls, pyramidal cells and Betz cells were less frequently stained with the anti-neurofilament antibody than those from ALS patients. Immunoreactivity of GFAP in layer III and at the junction of white matter and motor cortex was observed in only one patient. Ultrastructural examination revealed that the Betz cells of some ALS patients had Bunina bodies (BB), Lewy body-like inclusions (LBI) and skein-like inclusions (SI), as well as bundles of filaments that were thicker than neurofilaments; some of these filaments appeared to be constricted. The incidence of these inclusions was lower than that seen in anterior horn neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphorylated neurofilament epitopes in neuronal perikarya in the septum, mesencephalon and dorsal root ganglia of mammals and birds

We and other researchers have previously described the presence of axon-specific phosphorylated neurofilament epitopes in the cell bodies of three neuronal types in the rat: bipolar septofimbrial neurons and the large light A-type cells in the dorsal root ganglia and the mesencephalic nucleus of the Vth nerve. This spontaneous presence of phosphorylated neurofilaments at the level of the perikaryon contrasts with the induced appearance of these epitopes in axotomized neurons. We have undertaken a study of this phenomenon in rat, mouse, gerbil, rabbit, pig and chicken to analyse its species distribution. Phosphorylated neurofilament positive perikarya could be detected in the dorsal root ganglia and mesencephalic nucleus of the Vth nerve in all analysed species. Although this labelling has been shown to be specific for A-type cells in rat, in pig small cells were preferentially labelled, whereas the largest cells were mostly completely devoid of label. In the septofimbrial nucleus, phosphorylated neurofilament positive perikarya were seen in rat, mouse, gerbil and rabbit. In the pig, only a phosphatase-insensitive neurofilament antibody labelled these neurons. In the chicken, the labelling was completely absent. These observations establish the widespread species distribution of perikaryal phosphorylated neurofilament epitopes in the dorsal root ganglia and mesencephalic nucleus of the Vth nerve. In the septofimbrial nucleus however, this phenomenon seems to be restricted to rodents and lagomorphs. We discuss possible explanations for these cytoskeletal singularities in dorsal root ganglia, the mesencephalic nucleus of the Vth nerve and septofimbrial neurons.

Paired helical filament-like inclusions and Hirano bodies in the mesencephalic nucleus of the trigeminal nerve in the aged rat

The alterations appearing in trigeminal mesencephalic primary sensory neurons during ageing have been analyzed by electron microscopy in the Wistar-Louvain rat. Two phases have been distinguished, similar to those observed in dorsal root ganglion neurons. Up to 24 months, the mesencephalic trigeminal neurons progressively accumulate lipofuscins, while filamentous inclusions start to appear around 24 months of age. Hirano bodies and paired helical filament-like structures have been identified in animals aged 24 months or more. This time-course parallels the one observed previously in dorsal root ganglion neurons, indicating that the blood-brain barrier does not seem to influence the ageing of mesencephalic trigeminal neurons. The relationship between the paired helical filament-like inclusions and Hirano bodies, as well as similar structures already described by other authors, is discussed.

Ultrastructural study of Bunina bodies in the anterior horn neurons of patients with amyotrophic lateral sclerosis

We ultrastructurally investigated Bunina bodies (BB) in the anterior horn neurons of 20 amyotrophic lateral sclerosis patients with BB. As for novel findings, filaments thicker than neurofilaments were not uncommonly observed inside the BB. They were occasionally observed around the periphery of the BB. Some of them were composed of bundles of filaments which appeared constricted at 40-50 nm intervals and were 20-25 nm in maximum width. Others consisted of bundles of unconstricted filaments measuring about 20-25 nm in diameter. The BB occasionally contained bundles of filaments of about 20 nm in diameter that closely resembled those found in ubiquitin-positive skein-like inclusions. It seems that some molecular disturbances such as ubiquitin play a role in the formation of the constricted and unconstricted filaments. Probably cytoskeletal or non-cytoskeletal proteins in anterior horn cells are damaged and accumulate to form aggregation of the filaments associated with BB.

Neurofibrillary tangles in the neurons of spinal dorsal root ganglia of patients with progressive supranuclear palsy

Neurofibrillary tangles (NFTs) occur in neurons of human central nervous system (CNS) both in aged subjects and patients with several degenerative diseases, with a certain topographical predilection. In surveying the NFT distribution in nervous tissue of patients with progressive supranuclear palsy (PSP), we found silver-positive fibrillary tangles in the neurons of dorsal root ganglia (DRG) in two of five patients. By immunohistochemistry, these tangles were stained with antibodies to human tau protein, paired helical filaments (PHFs) and ubiquitin. Electron microscopy revealed that they were mainly composed of PHFs that were morphologically indistinguishable from PHFs in the NFTs of CNS typically seen in Alzheimer's disease brains. Our data demonstrate for the first time that the neurons of DRG produce NFTs in PSP and suggest that the pathological process(es) leading to tangle formation can occur in the neurons of the peripheral nervous system in this disease condition.

Age-dependent changes in the ultrastructure and in the molecular composition of rat brain microtubules

An age-dependent increase of a cathepsin D-like protease activity that preferentially degrades high molecular weight microtubule-associated proteins (MAPs) has been previously described. Microtubules (MT) purified from rat brain of different ages in the presence of several protease inhibitors retained undegraded MAPs through cycles of polymerization, and revealed several age-dependent changes in the relative amounts of MAPs and MT-associated kinases. MAP2 immunoreactivity was found significantly lower in MT preparations from aged animals in contrast with a relative increase of tau molecules. In addition, the phosphorylation of MAP2 by its associated cyclic AMP-dependent protein kinase was also altered, consecutively to the partial loss of the enzyme during polymerization cycles and an age-dependent decrease in the ability of the cyclic nucleotide to stimulate MAP2-bound kinase activity. The evidence of an unusually high packing density of sedimented MT from old rat brains further suggested the modification with aging of the physical structure of the arm-like projections of MAPs, in addition to a lower amount in high molecular weight MAPs. These results support the hypothesis of a selective alteration with aging of the mechanical and regulatory properties of brain MT, consecutive to a change in the composition and/or the structure of MAPs.

What's new in the pathology of neuronal cytoskeleton: the significance of neurofibrillary tangles

Neurofibrillary tangles are a neuronal change observed in various conditions, linked with dementia when affecting the cerebral cortex as in Alzheimer's disease. They may be found locally close to fibrous or vascular tumors, or affect extensive regions of the neocortex while the cerebellum and the medulla are not affected. Recent immunological and biochemical studies demonstrate that the MT-associated protein tau is the main component of the tangles, in an abnormally phosphorylated state. A consequence of the formation of tangles is a decreased assembly of MT in axons and dendrites, with disturbances of neuroplasmic flow. The relations between tangles and amyloid, as seen in Alzheimer's and Down's diseases are topographical, tangles accumulating in particular in neurites close to the amyloid in the senile plaques (but also at distance in cell bodies and neurites). Genetically and biochemically A4 or beta-amyloid and tau differ. The exact relation between the beta-pleated proteins of tangles and amyloid remain poorly understood.

Paired twisted filaments in human pinealocytes

Paired twisted filaments (PTF) have been confirmed and described ultrastructurally in the normal human pineal gland for the first time. The PTF showed a peculiar double helical structure, measuring 12 to 25 nm in maximal helix width with a half-periodicity of 30 to 35 nm (periodicity of the constrictions). Each filament was about 10 nm wide. The PTF formed parallel aggregates in the perikaryotic cytoplasm of the pinealocytes. In 8 of 12 autopsied middle-aged to elderly individuals, the PTF were present in a small proportion of pinealocytes. The identity of the PTF remains unclear in terms of their apparent similarity to the paired helical filaments observed previously in aged rats. However, the age distribution of individuals with PTF suggests that the intermediate filaments of human pinealocytes are more susceptible to early deterioration during aging than those of other cerebral neurons.

Reduced axonal transport of the G4 molecular form of acetylcholinesterase in the rat sciatic nerve during aging

Aging in the sciatic nerve of the rat is characterized by various alterations, mainly cytoskeletal impairment, the presence of residual bodies and glycogen deposits, and axonal dystrophies. These alterations could form a mechanical blockade in the axoplasm and disturb the axoplasmic transports. However, morphometric studies on the fiber distribution indicate that the increase of the axoplasmic compartment during aging could obviate this mechanical blockade. Analysis of the axoplasmic transport, using acetylcholinesterase (AChE) molecular forms as markers, demonstrates a reduction in the total AChE flow rate, which is entirely accounted for by a significant bidirectional 40-60% decrease in the rapid axonal transport of the G4 molecular form. However, the slow axoplasmic flow of G1 + G2 forms, as well as the rapid transport of the A12 form of AChE, remain unchanged. Our results support the hypothesis that the alterations observed in aged nerves might be related either to the impairment in the rapid transport of specific factor(s) or to modified exchanges between rapidly transported and stationary material along the nerves, rather than to a general defect in the axonal transport mechanisms themselves.

Ultrastructural changes in the frontal cortex and hippocampus in the ageing marmoset

The ultrastructure of the cells and capillaries of the frontal cortex and hippocampus was studied in marmosets to assess age-related changes. The appearances in the brains of four marmosets, more than 12 years of age, were compared with those of two young marmosets aged 26 and 21 months. There was widespread accumulation of lipofuscin in neurons, glial cells, perivascular macrophages and pericytes, but not in endothelial cells. Many of the nerve cell nuclei showed marked membrane infolding, alteration of nuclear morphology and occasional inclusions. A few degenerated and dystrophic axons containing abnormal organelles were seen. The capillaries displayed irregularly thickened and split basal laminae. No neurofibrillary tangles, neuritic plaques, amyloid deposits or granulovacuoles were present. These changes are compared to those occurring in other animal species and in man during ageing.

Neurofibrillary tangles in human upper cervical ganglia. Morphological study with immunohistochemistry and electron microscopy

Neurofibrillary tangles (NFTs) are one of the main pathological hallmarks of Alzheimer's disease or senile dementia, and are seen in the cerebral cortex and some other nuclei in the central nervous system (CNS). No NFTs have been reported in the human peripheral nervous system, although NFTs were recognized in the dorsal root ganglion of the aged rodents. We report here the presence of NFTs in the upper cervical ganglia (UCGs), but not in the stellate nor in the celiac ganglia, of an elderly patient, who was not demented and had only minimal senile changes in the CNS. Immunohistochemically the antibodies to microtubule-associated protein 2, paired helical filaments and ubiquitin stained positively the NFTs in the UCGs. On electron microscopic examination a periodical twisted pattern of the filaments was identified; these findings suggest that the NFTs of the UCGs have just the same properties as those of the cerebral cortex. This is the first report of the demonstration of NFTs in the peripheral ganglia and might contribute to the study of mechanism of NFT production.

Cytoskeletal protein abnormalities in neurodegenerative diseases

The nervous system is a rich source of filamentous proteins that assume critical roles in determining and maintaining neuronal form and function. Neurons contain three major classes of these cytoskeletal organelles: microtubules, intermediate filaments, and microfilaments. They also contain a variety of proteins that organize them and serve to connect them with each other. Such major neurodegenerative diseases as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, as well as a variety of toxic neuropathies, are characterized pathologically by intraneuronal filamentous inclusions. Recent studies using biochemical and immunocytochemical techniques have established that these abnormalities represent disorganized states of the neuronal cytoskeleton and have determined some of the specific molecular constituents of these inclusions. This knowledge has led to new ways of thinking about their origins.

Dementia of Alzheimer type (DAT)--a review of its morbid anatomy

The most important morphological findings in dementia of Alzheimer type (DAT) are Alzheimer neurofibrillary tangles, senile plaques, amyloid angiopathy, granulovacuolar degeneration and Hirano bodies. The morphological and immunocytochemical findings in these changes are described, in particular those related to the pathological cytoskeleton. Their possible relationship to the disturbed synthesis of neurotransmitters recently demonstrated is considered, and their relevance for the clinical syndrome of dementia is discussed. Hypothetical etiologies (ageing per se, genetics, infection and chronic intoxication) are briefly mentioned.