Selective vulnerability in acute energy deprivation syndromes

The topography and cellular events in the experimental lesions caused by chlorosugars, 6-aminonicotinamide, dinitrobenzene and tribromoimidazole in animals are considered in relation to those features in human acute thiamine deficiency (Wernicke's) encephalopathy and for comparison in Leigh's disease. The topography and cellular changes when closely examined are different and particular to each condition, although there is a basic cellular process common to all. The pathogenesis of each condition must be considered as multifactorial and a search for the factors responsible for the neuronal and cellular selective vulnerability of different regions of the neuraxis will lead us to understanding the pathogenesis of the disease process in each instance. The experimental models offer much for the understanding of the human conditions, particularly in the search for satisfactory therapeutic strategies.

Routes of excretion of neuronal lysosomal dense bodies after ventricular infusion of leupeptin in the rat: a study using ubiquitin and PGP 9.5 immunocytochemistry

To determine the rate and routes of removal of lysosomal, lipofuscin-like dense bodies from neurons, the protease inhibitor, leupeptin, was infused into the lateral ventricle of rats for up to nine days. After seven days a number of animals were then allowed to recover. The formation and later disappearance of dense bodies was followed by morphology and immunocytochemistry. After 48 h of infusion lysosomal dense bodies in large numbers appeared in cortical, hippocampal and cerebellar neurons, which also showed increased ubiquitin immunoreactivity, as well as in other cell types. By 3-4 days ubiqutin-immunoreactive dense bodies were equally distributed between neurons and astroglia. After seven to nine days of infusion ubiquitin immunoreactive dense bodies filled neuronal perikarya, dendrites and expanded initial segments of many axons and were abundant in glial processes. All dense bodies studied by electron microscopy were ubiquitin immunoreactive. After four days of recovery dense bodies were markedly fewer in neuronal perikarya, and virtually all were now within glial processes. From 7 to 28 days of recovery, when most neurons appeared normal, lipofuscin bodies remained in axon initial segments and in reduced numbers in glial processes, particularly around blood vessels and beneath the pia of hippocampus and of cerebellar cortex. Thus, neurons probably have a steady passage of short lived proteins through the lysosomal excretory pathway. The observed temporal sequence of events on recovery suggests that secondary lysosomes probably pass rapidly from neuronal perikarya and dendrites to astrocytes and thus to the vascular bed or pia-arachnoid. The mechanism of cell-to-cell transfer is not clear from this study.

The neurotoxicity of alpha-chlorohydrin in rats and mice: I. Evolution of the cellular changes

Mice and rats are found to be equally susceptible to developing symmetrical brain stem lesions on exposure to alpha-chlorohydrin and in both species the earliest neurotoxic changes are strictly confined to glial cells, particularly astrocytes; haemorrhages are not found in either species. Minimal evidence of increased vascular leakage of horse-radish peroxidase (HRP) in rats is shown by increased HRP content of perivascular cells within the lesions. Later macrophage invasion and capillary proliferation is accompanied by rare focal leakiness of HRP. Gross astrocytic damage, therefore, does not necessarily impair integrity of the blood-brain barrier. While early in intoxication, astrocytes are severely distended with fluid and their organelles seriously disorganized, they do not die but rapidly regenerate their processes. They thus appear to undergo a process of 'clasmatodendrosis' from which they recover. Comparisons are made with the genesis of symmetrical brain stem lesions in other acute energy deprivation syndromes, including Wernicke's encephalopathy.

Methyl bromide intoxication and acute energy deprivation syndromes

The case reported in this issue of symmetrical brain stem damage associated with exposure to methylbromide has affinities with a number of analogous syndromes associated with tissue energy deprivation. Attention is drawn to topographical and metabolic similarities and differences in these conditions, and suggestions are made for possible ways of mitigating the damage in future cases that may also be of value in Wernicke and Leigh's diseases.

Ubiquitin, PGP 9.5 and dense body formation in trimethyltin intoxication: differential neuronal responses to chemically induced cell damage

Ubiquitin in normal cells may be important in degrading or transferring short-lived or aberrant proteins to lysosomal dense bodies. To examine its role in degrading proteins produced by a chemical insult, changes in the distribution of ubiquitin and the carboxy-terminal hydrolase, PGP 9.5, have been studied in rat hippocampal neurons and cerebellar Purkinje cells in trimethyltin intoxication. Here tubulovesicular dense bodies (TVBs) form from 12h onwards associated with vacuolation of the Golgi apparatus. Striking accumulations of lysosomal dense bodies follow in hippocampal pyramidal cells but not in cerebellar Purkinje cells; many of the hippocampal neurons later die, while the Purkinje cells generally survive. Ubiquitin immunoreactivity was diffusely increased in hippocampal pyramidal and Purkinje cells 6 h after dosing. By 12 h both diffuse and granular ubiquitin immunoreactivity was present that intensified over 24 and 48 h. Both by light and electron microscopy TVBs showed ubiquitin immunoreactivity, but dense bodies in hippocampal perikarya did not stain with an anti-ubiquitin antibody. PGP 9.5 immunoreactivity was not altered in hippocampal cells at any time, while Purkinje and Golgi cell dendrites and perikarya showed intensified labelling at 3 h that reached a peak of 12 h. At 48 h Western blot analysis of hippocampal homogenates showed significant increases in high molecular weight (HMW) ubiquitin conjugates, while cerebellar homogenates showed an increase in ubiquitin-histone conjugates. Northern blot analyses showed no change in ubiquitin or PGP9.5 gene expression in hippocampus or cerebellum. These findings suggest that the material in the TVBs in hippocampal cells is not being degraded by the ubiquitin system but passes ubiquitinated into the lysosomal system, while material in Purkinje cell TVBs is degraded by the ubiquitin system, suggesting it may have a different composition in each type of neuron.

Vascular factors in the neurotoxic damage caused by 1,3-dinitrobenzene in the rat

Using a 3 x 10 mg/kg dose schedule of 1,3-dinitrobenzene (DNB) over two days in Fischer rats, we have found the following changes in vascular function and structure during the early phase of the symmetrical brain stem lesions. 1. Marked increase in cerebral blood flow generally but especially in the inferior colliculi, from 6 h after the final dose of DNB. 2. Increasing incidence of petechial haemorrhages in inferior colliculi, cerebellar roof, vestibular and superior olivary nuclei from 12 h. 3. Focal leakage of horseradish peroxidase and many sleeve-like arteriolar haemorrhages seen in vibratome sections and by scanning electron microscopy (SEM) in these regions from 12 h. 4. Periarteriolar oedema and protein leakage present in step-serial sections in these regions from 12 h, with astrocyte swelling and occasional small infarcts. These changes suggest that the vascular bed may play an important role in the pathogenesis of these lesions, perhaps in parallel with early astroglial damage. They are discussed in relation to (i) the known presence of xanthine oxidase in the vascular bed of the brain and the likelihood of "useless redox cycling' with free radical generation from this enzyme's interaction with nitroheterocyclic compounds, and (ii) the possible role of free radical damage to endothelial cells in this intoxication and in the analogous lesions of natural and experimental Wernicke's encephalopathy.

What have we learnt from Graham Frederick Young? Reflections on the mechanism of thallium neurotoxicity

The recent death of the psychopathic poisoner, Graham Frederick Young, prompts the question: has our knowledge of the toxic effects of thallium been increased as a result of his activities? The answer is 'yes' but very little. However, the poisonings led to a re-examination of the topography and pathogenesis of thallium intoxication and the suggestion that there are close similarities with chronic thiamine deficiency neuropathy and arsenical neuropathy. They might be termed chronic energy deprivation neuropathies and are associated with damage to other organs with high energy requirements, namely skin and its appendages, testis and heart. While the exact metabolic 'lesion' in thallium intoxication is not yet known, circumstantial evidence continues to suggest that it may be related to the known interaction of this ion with riboflavin, with consequent effects upon energy generation mechanisms associated with tissue flavoproteins.

Regional variations in nerve cell responses to trimethyltin intoxication in Mongolian gerbils and rats; further evidence for involvement of the Golgi apparatus

The different responses of neurons with distinctive variations in morphology and function, confirm earlier observations of the lack of uniformity in the reaction of nerve cells to trimethyltin. Thus, hippocampal pyramidal and cortical neurons in both rat and Mongolian gerbil (M. unguiculatus) show abundant lysosomal dense bodies and disorganisation of the protein-synthesising apparatus. Cerebellar Purkinje cells in gerbil, but not in rat, show striking increases in smooth membrane systems, while dense bodies are insignificant in both species; large motor-type neurons in brain stem and spinal cord in both species do not accumulate dense bodies, but their rough endoplasmic reticulum (RER) may undergo intense vacuolation with or without subsequent cell death; and by contrast, spinal ganglion cells of both species may form an excess of dense bodies and, in the gerbil, vacuolation of RER. In contrast with these varied responses to trimethyltin most neurons, large and small, in both species regularly undergo striking vacuolation of the Golgi apparatus in the earliest phase of the intoxication, a constant feature that probably reflects the site of the primary cytotoxic lesion; all other changes we consider are secondary to such damage to the Golgi apparatus, however this may come about. These observations are discussed in relation to earlier reports of the variable effects of trimethyltin and with the metabolic changes reported in trimethyltin intoxication that in general accord with these morphological conclusions.

Selective degeneration of cerebellar cortical neurons caused by cycad neurotoxin, L-beta-methylaminoalanine (L-BMAA), in rats

Both the racemate and the L-form of BMAA (beta-methylaminoalanine), when injected intraperitoneally into young rats, produced acute signs of cerebellar dysfunction and degeneration of cerebellar stellate, basket, Purkinje and Golgi cells, but not granule cells. Degenerative changes were also occasionally seen in cerebellar roof nuclei which may be secondary in nature. No other changes were found in the remainder of the central nervous system. The doses of the L-form of BMAA producing these changes were from 6 to 14 mumols/g body weight, i.e. the lower and upper levels of the dose range used by Vega and Bell (1967) and equivalent to 75 and 183 mg/rat. Doses of 1 to 4 mg/g body weight of the racemate were given to young rats less than 100 g in weight, but no changes were apparent after daily doses of the racemate of 0.5 mg/g body weight. Damage to cerebellar neurons is considered to be the result of excitotoxic activity. All cells showing degeneration are GABAergic, although not all are known to possess N-methyl-D-aspartate (NMDA) receptors. The present finding of selective cerebellar neuron damage may not conflict with the earlier findings of others, but our results suggest that L-BMAA has unusual glutamate receptor binding properties.

Trichloroethylene cranial neuropathy: is it really a toxic neuropathy or does it activate latent herpes virus?

The mechanism of the cranial neuropathy associated with heavy exposure to trichloroethylene (or dichloroethylene) is unknown. In severe cases there is destructive spread of the neuropathic process from the Vth cranial nerve nuclei up and down the brain stem in a manner that is difficult to explain on accepted neurotoxicological principles. However, there is a close association reported of this form of trigeminal neuropathy with reactivation of orofacial herpes simplex that suggests the possibility that the chemical, which readily gains entrance into the nervous system, may be responsible for reactivating the latent virus. This novel hypothesis is discussed in the light of current understanding of latency in herpes simplex infection in nervous tissue.

Motoneuron disease: a disorder secondary to solvent exposure?

There seems to be a statistically significant association between work in the leather industry and subsequent development of motoneuron disease. The reason for this association may be occupational exposure to solvents, which may damage motoneurons either directly or through activation of latent virus.

Persistent mercury in nerve cells 16 years after metallic mercury poisoning

A male subject, after exposure to mercury metal at work in 1968, developed classical signs of mercurialism from which he made a slow clinical recovery. He subsequently developed psychoneurotic symptoms and became an alcoholic; he never returned to work and died in 1984. No histological changes relevant to mercury intoxication were found in the brain, but staining by Danscher & Schroeder's method for mercury showed many positively staining lysosomal dense bodies in a large proportion of nerve cells, and the presence of mercury was confirmed by elemental X-ray analysis. The mercury content of the brain was increased, much of it being present in colloidal form.

Lesion localisation: implications for the study of functional effects and mechanisms of action

In some toxic neuropathies we see only distal "dying back" of longer and larger diameter axons, the perikaryon appearing to be intact. Some of these are the result of chronic energy deprivation, others are not. In other neuropathies sensory and autonomic neuron cell bodies are damaged without apparent selectivity. Toxic neuropathies often mimic the neurological effects of vitamin deficiencies by causing juxtaposed lesions in the same metabolic pathways. In acute energy deprivation toxic syndromes in the CNS, the pattern of damage is restricted to specific grey centres: there are variations in this pattern according to the site of the metabolic lesion, the species studied, the development of seizures, and other factors. Such toxic responses mimic human and animal disease states, such as Wernicke's encephalopathy and Leigh's disease, both of which are essentially acute energy deprivation syndromes.

Nuclear and nucleolar damage in adriamycin-induced toxicity to rat sensory ganglion cells

A single dose (10 mg/kg) of Adriamycin was given to 23 adult Wistar rats and the spinal ganglia were studied from 6 h to 15 days after. As previously described, this drug results in the appearance of 'clear' areas in the nuclei of rat spinal ganglion cells as seen by light and by electron microscopy. The 'clear' areas become less conspicuous during the week before the onset of cytoplasmic degeneration. In addition, nucleolar changes become increasingly evident with time after injection. Fibrillar centres enlarge and nucleolar segregation is present from 24 h onwards, although the latter is invariably partial and more readily seen with the electron microscope. Nucleolar fragmentation is seen more frequently from 3 days onwards and nucleolar enlargement is common from 6 days. Early cytoplasmic abnormalities are associated with pronounced loss of Nissl substance. Adriamycin must bind extensively to nuclear DNA in spinal ganglion cells, causing the 'cleared' nuclear areas and the changes in dense chromatin. In addition, the binding of Adriamycin to nucleolar DNA with disturbance to nucleolar functions must be important in producing later cytoplasmic changes that precede cell death. There are thus similarities between the action of Adriamycin on these cells and those of Cisplatin, although in the latter intoxication the nuclear effects are significantly less prominent.

The effects of cisplatin on rat spinal ganglia: a study by light and electron microscopy and by morphometry

Cisplatin given in doses of 0.5-2 mg to Wistar and to Sprague-Dawley rats produced nucleolar segregation of the dense fibrillar from the granular component in spinal root ganglion cells. The nucleolar segregation, found to the same extent in large and small neurons, was confirmed by specific silver staining and by electron microscopy. After repeated doses of 1 mg or 0.5 mg, up to 40% of affected nucleoli were observed by light microscopy. Focal clearing of the nucleoplasm of nuclei also occurred. Disorganisation of ribosomes was found in more severely intoxicated animals, especially in large light cells with shrinkage of the Nissl substance and apparent increase in neurofilaments, the latter occasionally distending the initial segment of the axon, but never extending further. Hypertrophy of the satellite cells with increase in the perineuronal intercellular spaces, often associated with irregular, scalloped nuclear and cell outlines, suggested that neuron shrinkage had occurred. This was confirmed by morphometry and marked alterations were found in nucleolar-to-nuclear and nucleolar-to-cell diameter ratios, nuclear and cell diameters were also somewhat reduced without change in the nucleus-to-cell ratios. Peripheral sensory nerve degeneration was not seen, and the animals died from non-neural causes. The probable role of these events in the production of sensory neuropathy is discussed.

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.

Morphometric effects of vincristine on nerve regeneration in the rat

Administration of vincristine (200, 100 or 50 micrograms/kg/week) for 6 months during regeneration of the sciatic nerve after crush injury caused a dose-dependent reduction in nerve fibre size and failure of removal of myelin debris. Successfully regenerating neurites showed an unusual amount of shape distortion. The ratio of myelin sheath thickness to axon circumference was reduced, but the ratio of myelin sheath thickness to axon area was normal. Microtubule concentration was diminished in axons, but neurofilament density was unaffected. Unmyelinated axons were reduced in number but their axon diameter distribution was not affected. Fibres on the non-crushed side appeared normal. The toxicity of vincristine to regenerating nerves is probably related to increased blood-nerve permeability occurring both at the site of crush and along the degenerating nerve.

Evolution of the intracellular changes in neurons caused by trimethyltin

Rats have been given a single dose of trimethyltin (10 mg/kg) and the intracellular events have been followed particularly in hippocampus, cerebral cortex, cerebellum and spinal ganglion cells. The earliest change visible occurs 12 h after this dose and is found to be dense membrane-bound bodies, probably derived from branching tubulo-vesicular smooth endoplasmic reticulum formations. These occur in close connection with rought endoplasmic reticulum and polyribosomes and appear also to have some association with the Golgi complex. At 24 h there is a general vacuolation of Golgi cisterns and SER membranes, and the membrane-bound dense body formation is greatly increased. SER abnormalities are particularly conspicuous in Purkinje cells. In spinal ganglion cells, while vacuolation of Golgi cisterns is intense, dense bodies are inconspicuous and are replaced by increased autophagosomes, often of great complexity. By 48 h vacuolation of Golgi cisterns has waned, but accumulation of dense bodies and secondary lysosomes has steadily increased. In spinal ganglion cells autophagosomes only are increased as the Golgi vacuolation declines. At later times steady increases of lysosomal dense bodies is seen generally accompanied in hippocampal pyramidal cells and dentate fascia cells by abundant cell death. The suggestion is put forward that the Golgi complex may be the seat of the critical metabolic lesion and disturbances to protein transfer and protein synthesis follow. No explanation for the selective loss of hippocampal h1-5 (CA1-CA4 except Sommer's sector) pyramidal cells and of small dentate fascia neurons can be derived from these conclusions.

The problems of neurons with long axons

Neurons with long axons are unique among cells in having to maintain a very large area of membrane. In this respect they have problems in common with red cells: the latter are separated from the source of their metabolites in time, the former by distance. In equilibrium, maintenance mechanisms are adequate; but in conditions of energy deprivation or deprivation of antioxidant substances such as glutathione and alpha-tocopherol, or when the transport of materials within the neuron is physically obstructed, the system may break down and the longest fibres will always suffer first. The problems are logistical, just as are those of red cells. The association between red-cell disease and neuropathy is not entirely fortuitous.