Selective degeneration of CA1 pyramidal cells by chronic application of bismuth

The olfactory bulb: A link between environmental agents and narcolepsy

Narcolepsy with cataplexy is a lifelong sleep disorder associated with orexin/hypocretin deficiency in the central nervous system. In addition to a genetic predisposition, a variety of environmental factors, such as influenza viruses, have been implicated in the pathogenesis of the disease. In this article, a hypothesis is proposed that environmental agents access the olfactory bulb and trigger neuroinflammation, which in turn induces neurodegeneration of orexinergic neurons in the lateral hypothalamus and other neuronal subpopulations regulating the sleep-wake cycle, which triggers the development of narcolepsy.

Influence of bismuth on the number of neurons in cerebellum and hippocampus of normal and hypoxia-exposed mouse brain: a stereological study

The industrial use of bismuth is increasing. In medicine, bismuth compounds have long been used in the treatment of gastrointestinal disorders, recently in combination with antibiotics for the treatment of Helicobacter pylori-associated peptic ulcers. Bismuth-induced encephalopathy is a known side-effect. One of the symptoms of bismuth encephalopathy is ataxia, suggesting possible cerebellar involvement. The introduction of autometallography (AMG) for tracing BiS/BiSe nanocrystals has provided histochemical evidence supporting the cerebellum being involved in bismuth encephalopathy, but the effect of bismuth on the neuron number in the cerebellum has never been evaluated. In vitro studies have indicated that CA1 neurons may be targets for bismuth intoxication, but results have been conflicting. Recently, the loss of dorsal root ganglion cells was reported after moderate bismuth exposure. This raises the question whether the use of another neurotoxic stimulus, such as hypoxia, amplifies the toxic effects of bismuth. Despite AMG-detectable bismuth accumulations, stereological examinations revealed no statistically significant decrease in the number of Purkinje, CA1 or CA3 neurons or in the volume of the cerebellar granule layer. Surprisingly, intermittent hypoxia led to a statistically significant loss of Purkinje cells without affecting the hippocampus. Bismuth neither ameliorated nor exacerbated the hypoxic effects on the cerebellum.

Bismuth tracing in organotypic cultures of rat hippocampus

Bismuth is known to have neurotoxic side effects in humans and animals. In the 1970s France experienced about a thousand cases of patients suffering from bismuth-induced encephalopathy. Studies suggest that bismuth may provoke a selective degeneration of CA1 pyramidal cells in the organotypic cultures of rat hippocampus. A currently established technique for the histochemical visualization of bismuth was applied on hippocampal tissue cultures allowing the tracing of bismuth in concentrations hitherto not possible. The accumulation and subcellular localization of bismuth is demonstrated in the tissue cultures of rat hippocampus. CA1 pyramidal cells in the rat hippocampus exhibit the highest uptake of bismuth. High bismuth citrate concentrations (10 microM) are able to totally destroy the cytoarchitecture of the hippocampus. At ultrastructural levels bismuth was found to be located exclusively in lysosome-like organelles.

Autometallographic tracing of bismuth in human brain autopsies

For decades, drugs containing bismuth have been used to treat gastrointestinal disorders. Although a variety of adverse effects, including neurological syndromes, have been recorded, the biological/toxicological effects of bismuth ions are far from disclosed. Until recently, only quantitative assessments were possible, but resent research has made histochemical tracing of bismuth possible. The technique involves silver enhancement of bismuth crystallites by autometallography (AMG). In the present study, the localization of bismuth was traced by AMG in sections of paraffin-embedded brain tissue obtained by autopsy from 6 patients suffering from bismuth intoxication in a period ranging from 1975 through 1977. Tissue was analyzed at light and electron microscopical levels, and the presence of bismuth further confirmed by proton-induced x-ray emission (PIXE). Clinical data and bismuth concentrations in blood, cerebellum, and thalamus were measured by atomic absorption spectrophotometry (AAS) and are reported here. Histochemical analyses demonstrate that bismuth accumulated in neurons and glia cells in the brain regions examined (neocortex, cerebellum, thalamus, hippocampus). Cerebellar blood vessels stained most intensely. The PIXE and AAS data correlated with the histochemical staining patterns and intensities. At the ultrastructural level, bismuth was found to accumulate intracellularly in lysosomes and extracellularly in the basement membranes of some vessels.

Histochemical tracing of bismuth in testis from rats exposed intraperitoneally to bismuth subnitrate

The histochemical silver amplification technique autometallography (AMG), was used to trace bismuth in the testis of Wistar rats injected intraperitoneally with bismuth subnitrate. In the seminiferous tubules, bismuth was located in lysosomes of Sertoli cells closely associated with heads of spermatids in the late stages of the spermatogenesis, i.e. shortly before the release of Step 19 spermatids in Stage XIII. No bismuth-specific AMG silver grains were detected in the spermatogenic cell line. However, tails of free sperm cells located in the tubular lumen showed autometallographic grains in close contact to the nine outer microtubule doublets in the axonema. Leydig cells concentrated huge amounts of AMG-bismuth in their lysosomes. Furthermore, parallel exposure to selenium significantly increased the amount of histochemically traceable bismuth in the rat testis.

A simple in vitro model of ischemia based on hippocampal slice cultures and propidium iodide fluorescence

This protocol describes a model of cerebral ischemia based on organotypic hippocampal slice cultures and quantitative assessment of cell death by use of propidium iodide and image analysis. The cultures were made from rat hippocampal slices that were obtained at postnatal day 4-7 and allowed to develop for >14 days in vitro. For induction of 'in vitro ischemia', the cultures were washed in glucose free buffer and the culture chamber flooded with a nitrogen/carbon dioxide mixture until the oxygen concentration was <1.0%. The cultures were exposed to this atmosphere for 30-35 min, washed in serum-free medium, and returned to ordinary growth medium. After 24 h, dead cells were quantified by use of propidium iodide. The cell death resulting from the oxygen/glucose deprivation was largely confined to the CA1 region and was blocked by NMDA-receptor antagonists but not by antagonists to AMPA-receptors or metabotropic glutamate receptors. The type of cell death was judged to be necrotic, based on ultrastructural observations. The oxygen/glucose deprived cultures exhibited increased phosphorylation of the MAP kinase cascade. This activation of the MAP kinase cascade was blocked by NMDA-receptor antagonists. The in vitro model described in the present report is simple to use and reproduces many features of in vivo ischemia, including the preferential vulnerability of CA1 cells. The model should be suited to analyses of the mechanisms underlying the regionally selective cell death in the hippocampus and ischemic cell death in general.

Tracing of the entorhinal-hippocampal pathway in vitro

In vitro tract tracing allowing for continuous observation of the perforant path is a crucial prerequisite for experimental studies on the entorhinal-hippocampal interaction in an organotypic slice culture containing the entorhinal cortex, the perforant path, and the dentate gyrus (OEHSC). We prepared horizontal slices of the temporal entorhinal-hippocampal region of the rat on a vibratome, and the perforant path axons were traced by application of the fluorescent tracer Mini Ruby on the entorhinal cortex. After 2 days in vitro (div), the perforant path became visible in most cultures. Entorhinal neurons and single perforant fibers could be followed to the outer molecular layers of the dentate gyrus by in vitro fluorescence microscopy and it was possible to monitor the perforant path directly over a period of 25 div. Moreover, ultrastructural analysis proved the existence of traced perforant path boutons forming synapses with spines and dendritic shafts in the outer molecular layers of the dentate gyrus. Transsection of the prelabelled perforant path in vitro resulted in anterograde degeneration and subsequent phagocytosis of axonal material by activated microglial cells in the zone of denervation. In conclusion, in vitro tracing demonstrates the maintenance of the entorhinal-hippocampal pathway in OEHSCs and permits monitoring of dynamic changes in the prelabeled perforant path after various lesion paradigms, e.g., transsection or neurotoxin treatment. This approach permits further studies on the efficacy of neuroprotectants, cytokines, and growth factors in the treatment of lesion-induced neuronal degeneration.

Trimethyltin (TMT) neurotoxicity in organotypic rat hippocampal slice cultures

The neurotoxic effects of trimethyltin (TMT) on the hippocampus have been extensively studied in vivo. In this study, we examined whether the toxicity of TMT to hippocampal neurons could be reproduced in organotypic brain slice cultures in order to test the potential of this model for neurotoxicological studies, including further studies of neurotoxic mechanisms of TMT. Four-week-old cultures, derived from 7-day-old donor rats and grown in serum-free medium, were exposed to TMT (0.5-100 microM) for 24 h followed by 24 h in normal medium. TMT-induced neurodegeneration was then monitored by (a) propidium iodide (PI) uptake, (b) lactate dehydrogenase (LDH) efflux into the culture medium, (c) cellular cobalt uptake as an index of calcium influx, (d) ordinary Nissl cell staining, and (e) immunohistochemical staining for microtubule-associated protein 2 (MAP-2). Cellular degeneration as assessed by densitometric measurements of PI uptake displayed a dose and time-dependent increase, with the following ranking of vulnerability of the hippocampal subfields: FD>CA4>/=CA3c>CA1>CA3ab. This differential neuronal vulnerability observed by PI uptake was confirmed by MAP-2 immunostaining and corresponded to in vivo cell stain observations of rats acutely exposed to TMT. The mean PI uptake of the cultures and the LDH efflux into the medium were highly correlated. The combined results obtained by the different markers indicate that the hippocampal slice culture method is a feasible model for further studies of TMT neurotoxicity.

Long-term hippocampal slices: a model system for investigating synaptic mechanisms and pathologic processes

Organotypic cultures provide a unique strategy with which to examine many aspects of brain physiology and pathology. Long-term slice cultures from the hippocampus, a region involved in memory encoding and one that exhibits early degeneration in Alzheimer's disease and ischemia, are particularly valuable in this regard due to their expression of synaptic plasticity mechanisms (e.g., long-term potentiation) and responsiveness to pathological insults (e.g., excitotoxicity). Long-term slices can be prepared from hippocampi at the second or third postnatal week of development and thus incorporate a number of relatively mature features; further signs of maturation and the preservation of adult-like characteristics occur over succeeding weeks. The stability of the cultured slice renders it an appropriate model for studying 1) prolonged regulation/stabilization events linked to synaptogenesis and certain forms of plasticity, 2) temporal patterns of cellular atrophy associated with pathogenic conditions such as ischemia and epilepsia, and 3) slow processes associated with aging and age-related pathologies.