Detecting necrotic neurons with fluoro-jade stain.

Fluoro-jade, a novel stain for detection of neuropathic lesions by fluorescence microscopy, was validated on the models of toxic neuropathy induced with 3-acetylpyridine (3-AP) or with acrylamide (ACR). Groups of male and female albino rats of Wistar strain were either exposed to a single administration of 80 mg/kg i.p. 3-AP followed 5 hours later by 300 mg/kg of nicotinamide i.p. and examined at days 3 and 15, or to 15 daily doses of 30 mg/kg p.o. ACR and examined at day 15. Following in-life behavioral observations and measurements, the rats were fixed by perfusion with formalin. Additional animals treated with same dose of 3-AP and nicotinamide were submitted to purposeful autolysis for 4 or 16 hours before immersion fixation with formalin on test day 3. In-life observations showed in 3-AP-treated animals signs of severe general toxicity, sensorimotor dysfunction and decreased motor activity starting shortly after the treatment and persisting throughout the observation period. ACR-treated rats started to develop abnormal gait on test day 8 and by day 15 developed reduced grip strength, increased landing footsplay and decreased motor activity. Fluoro-jade, applied to paraffin sections of the nervous system, detected selectively and sensitively the necrotic neurons in the brain, especially those in the inferior olivary nucleus of animals treated with 3-AP, at test day 3, as well as the necrotic Purkinje cells in the cerebellum of ACR-treated animals at test day 15. Chromatolytic neurons in the dorsal root ganglia of ACR-treated animals did not stain positively, indicating that this kind of reversible neuronal remodeling is not detectable using fluoro-jade. Necrotic neurons were still stained by fluoro-jade after 4 hour autolysis, but following 16 hour autolysis the results became false negative. There was no false positive fluorescence in fresh or autolytic tissues, except that emitted by red blood cells in unperfused specimens. The study confirmed the validity of fluoro-jade as a stain suitable for detecting necrotic neurons in toxicological safety studies.

Teased-fiber technique for peripheral myelinated nerves: methodology and interpretation.

Teased-fiber technique is the best approach for studying peripheral myelinated nerve fibers in their continuity. It enables the assessment of size of myelin segments formed by Schwann cells and characterization of pathologic changes affecting the internodia, the paranodal regions, and the invested axons. Fiber teasing is performed on prestained proximodistally oriented portions of peripheral nerves. Specimens about 10 mm long are stained for 24-48 hours in Sudan black and then transferred to glycerin, where, using a pair of fine forceps and a stereomicroscope, they are separated into smaller fiber bundles from which single fibers are isolated. The work is performed on a glass slide with an adhesive surface (albuminized or "superfrost"), on which the fibers are placed in strict proximodistal orientation. Following drying in an oven, the slides are mounted with glycerin-gelatine (same as used for frozen sections). The changes, when present, can usually be recognized during the preparation, but fibers are reexamined and changes confirmed in mounted slides. Photographic reconstruction of the fibers facilitates their assessment and enables the documentation of findings. The teased-fiber technique is auxiliary to histopathology, and to limit the workload and save costs, it can be performed on only a few specimens selected for better characterization of changes recognized or suspected in tissue sections. In particular, segmental demyelination and early stages of Wallerian or secondary axonal degeneration can be recognized in teased fibers. Segmental demyelination is characterized by loss of fully myelinated segments and their replacement by newly formed short and thin segments, remyelinating the preserved axon. The early stage of secondary axonal degeneration is recognized by formation of ovoidal fiber fragments in the midinternodal region.

Morphologic characterization of spontaneous nervous system tumors in mice and rats.

Spontaneous rodent nervous system tumors, in comparison to those of man, are less well differentiated. Among the central nervous system (CNS) tumors, the "embryonic" forms (medulloblastoma, pineoblastoma) occur both in rodents and humans, whereas the human "adult" forms (gliomas, ependymomas, meningiomas) have fewer counterparts in rodents. In general, the incidence of spontaneous CNS tumors is higher in rats (>1%) than in mice (>0.001%). A characteristic rat CNS tumor is the granular cell tumor. Usually it is associated with the meninges, and most meningeal tumors in rats seem to be totally or at least partly composed of granular cells, which have eosinophilic granular cytoplasm, are periodic acid-Schiff reaction (PAS)-positive, and contain lysosomes. Such tumors are frequently found on the cerebellar surface or at the brain basis. Rat astrocytomas are diffuse, frequently multifocal, and they invade perivascular spaces and meninges. The neoplastic cells with round to oval nuclei and indistinct cytoplasm grow around preexisting neurons, producing satellitosis. In large tumors, there are necrotic areas surrounded by palisading cells. Extensive damage of brain tissue is associated with the presence of scavenger cells that react positively with histiocytic/macrophage markers. The neoplastic astrocytes do not stain positively for glial fibrillary acidic protein; they probably represent an immature phenotype. In contrast to neoplastic oligodendroglia, they bind the lectin RCA-1. Astrocytomas are frequently located in the brain stem, especially the basal ganglia. Rat oligodendroglial tumors are well circumscribed and frequently grow in the walls of brain ventricles. Their cells have water-clear cytoplasm and round, dark-staining nuclei. Atypical vascular endothelial proliferation occurs, especially at the tumor periphery. Occasionally in the oligodendrogliomas, primitive glial elements with large nuclei occur in the form of cell groups that form rows and circles. Primitive neuroectodermal tumors of rats, such as pineal tumors or medulloblastomas, appear to have features similar to those found in man. In mice, the meningeal tumors are mostly devoid of granular cells and the astrocytomas are similar to those occurring in rats, whereas spontaneous oligodendrogliomas are observed extremely rarely. Tumorlike lesions, such as lipomatous hamartomas or epidermoid cysts, are occasionally encountered in the mouse CNS. It is suggested that we classify rodent CNS lesions as "low grade" and "high grade" rather than as "benign" and "malignant." The size of CNS tumors is generally related to their malignancy. Tumors of the peripheral nervous system are schwannomas and neurofibromas or neurofibrosarcomas consisting of Schwann cells, fibroblasts, and perineural cells. Well-differentiated schwannomas are characterized by S-100 positivity and the presence of basement membrane. They show either Antoni A pattern with fusiform palisading cells or Antoni B pattern, which is sparsely cellular and has a clear matrix. The rat develops specific forms of schwannomas in the areas of the submandibular salivary gland, the external ear, the orbit, and the endocardium. Spontaneous ganglioneuromas occur in the rat adrenal medulla or thyroid gland. Compared to experimentally induced neoplasms, the spontaneous tumors of the rodent nervous system are poor and impractical models of human disease, although they may serve as general indicators of the carcinogenic potential of tested chemicals.

Spongiform neuropathy induced in dogs by prolonged, low-level administration of 6-aminonicotinamide (6-ANA).

The objective of this study was to demonstrate the effects of prolonged exposure to 6-ANA at low dose-levels in dogs. A male and a female Beagle dog received daily oral repetitive doses of 1 mg/kg or less for 20 weeks. Both dogs showed lacrimation, conjunctivitis, reduced motility and anemia since the second week of treatment. The female dog was more affected than the male and at the end of treatment period it had tremor, hanging lower jaw, stepping gait of the hind limbs, hunched posture, and general debilitation. Post-mortem examination of the female dog revealed prominent brain edema with pressure atrophy of the dorsal cranial bones. Microscopic examination of the nervous system revealed spongiform neuropathy in both animals mainly affecting the telencephalic cortex and hippocampal fascia dentata, the substantia gelatinosa in the spinal cord and the dorsal root and autonomic ganglia. The changes were produced by vacuolation of astrocytes in the central nervous system and perineuronal satellite cells in the ganglia. Examination of the other organs revealed thymic atrophy and high hematopoietic activity of the bone marrow in both dogs. The male had severe interstitial edema and vacuolar degeneration of the testicular seminiferous tubules and the female had marked chronic pyelonephritis. This chemically induced spongiform neuropathy in dogs obviously represents a subchronic form of the "energy deprivation syndrome" induced by impaired glucose utilization. Vacuolar degeneration of the testicular seminiferous epithelium may have the same pathogenesis.

Trimethylphosphate: a 30-month chronic toxicity/carcinogenicity study in Wistar rats with administration in drinking water.

Trimethylphosphate (TMPO) was administered to 50 male and 50 female Wistar rats through their drinking water at doses of 0, 1, 10, or 100 mg/kg body weight up to 30 months. The dosage of 100 mg/kg was reduced to 50 mg/kg in week 54 for reasons of tolerance, and the animals were euthanized in week 100. Additional 10 animals per dose and sex were treated for 12 months and then euthanized for interim analysis. Weakness of the hind limbs, increased incidences of sunken flanks, distended abdomen, and poor general condition were observed in both sexes of the 100/50 mg/kg group beginning with week 46. Food intake was reduced in high dose males. At 10 mg/kg body weights were up to 10% (males) and at 100/50 mg/kg up to 20% (males) or 15% (females) lower than in controls. Mortality was not affected in animals receiving up to 10 mg/kg. At 100/50 mg/kg it was markedly increased, reaching about 70% at week 100. Relatively slight hematologic changes (reduced hemoglobin, hematocrit, erythrocyte counts, increased reticulocyte numbers, and thrombocyte counts as well as a shift in the differential blood count) at 100/50 mg/kg are interpreted as changes most probably secondary to the other toxic effects. Increased cholesterol concentrations in plasma, shifts in the serum protein electrophoresis (males), increased organ weights (females), and an increased incidence of necroses and lymphocytic infiltrations point to a treatment-related effect on the liver at 100/50 mg/kg. Slightly increased protein excretion, increased relative kidney weights, and an increased incidence of chronic progressive nephropathy are considered treatment-related but rather secondary effects at 100/50 mg/kg. At 100/50 mg/kg an increased incidence and severity of bilateral tubular atrophy in the testes was diagnosed. The most important toxic effect was neurotoxicity, consisting of degeneration and loss of nerve fibers in the peripheral nerves and the spinal cord, associated with myopathic changes, and occurring at 100/50 mg/kg. The no-observed-adverse-effect-level, based on the suppression of body weight gain, is 1 mg/kg in males and 10 mg/kg in females. The incidence, time of occurrence, spectrum of types, and localizations of tumors provided no indication of a tumorigenic/carcinogenic effect of the test substance. TMPO is therefore considered not to be carcinogenic in Wistar rats.

Optimal conduct of the neuropathology evaluation of organophosphorus induced delayed neuropathy in hens.

Susceptibility of various areas of the nervous system to TOCP (triorthocresyl phosphate) induced delayed neuropathy was assessed in groups of seven hens respectively, intoxicated with a single oral does of 500 or 1000 mg/kg body weight. 18 hens were used as negative controls. About 3 weeks after the treatment the hens were submitted to fixation by whole body perfusion and their nervous system processed either to paraffin sections stained with Bodian's silver stain and luxol counterstain, or to semi-thin plastic sections stained with toluidine blue. The examined areas were the cerebellum, the spinal cord at upper cervical, thoracic and lumbar level, the sciatic nerve, and the posterior tibial nerve. The extent of nerve fiber degeneration was assessed independently by two pathologists using a semiquantitative scoring system. The most susceptible areas were the cerebellum and the tibial nerve, followed by the upper cervical spinal cord. Within the cerebellum the nerve fibers in the rostral lobules, especially IV and Va, were affected. Whereas the resolution of plastic section was superior to that of paraffin sections in the cerebellum (mid-longitudinal level) and the spinal cord (transverse level), in the peripheral nerves the lesions were best recognized in the longitudinal, paraffin sections. There was very good agreement between both pathologists with respect to detection and grading of lesions in the most susceptible areas, but poor agreement in the areas of low susceptibility, indicating the danger of false results when lesions are not very distinct. In the susceptible areas the lesions induced with 500 mg/kg were sufficiently prominent, indicating that this dose-level is acceptable as positive control. In the hen nervous system, examination of the most susceptible areas, especially the rostral cerebellar lobules, appears to be suitable for detection of any kind of organophosphorus induced, delayed neuropathy.

Spontaneous demyelinating myelopathy in aging laboratory mice.

Spontaneous demyelination has been observed to occur sporadically in the thoracic spinal cord of aging laboratory mice used in routine long-term chemical safety studies. Positive immunohistochemical reaction for VP-1 (virus protein) indicated that the demyelination was associated with Theiler's murine encephalomyelitis virus infection. Although this rare spontaneous lesion has no bearing on the quality of chemical safety studies, its knowledge is essential for the appropriate interpretation of study results.

Susceptibility of various areas of the nervous system of hens to TOCP-induced delayed neuropathy.

Sensitivity of in-life parameters, biochemical endpoints, and susceptibility of various areas of the chicken nervous system to delayed neuropathy induced by tri-orthocresyl phosphate (TOCP) was assessed. Groups of hens were exposed to a single oral dose of TOCP of 0, 50, 200 or 500 mg/kg and the animals observed for 21 days. Perfusion fixed, paraffin embedded tissue sections were stained with Bodian's silver and Luxol blue and semi-thin epoxy sections with toluidine blue. Sciatic and tibial nerves, lumbosacral, midthoracic, and upper cervical spinal cord, medulla oblongata and cerebellum were examined using a semiquantitative scoring system. In pair-dosed hens inhibition of brain and spinal cord neurotoxic esterase (NTE) and cholinesterase and of plasma and erythrocyte cholinesterases was determined 24 hr and 48 hr after administration. At all dose levels NTE in brain and spinal cord and plasma cholinesterase was inhibited markedly. Quantitative inhibition of NTE was seen also in absence of neuropathy. Ataxia and body weight loss occurred in high-dose animals only, while dose-related neuropathy was seen in the distal tibial nerve, medulla oblongata and cerebellum. Ataxia was correlated best with neuropathy in peripheral nerves while degeneration of nerve fibers in the cerebellum, seen best in mid-longitudinal sections, was the most sensitive histological indicator of TOCP-induced delayed neuropathy. The particular susceptibility of spinocerebellar neurons was recognized long ago, but often has been neglected in delayed neurotoxicity studies and respective guidelines. Optimal sensitivity of toxicity tests is a prerequisite for risk assessment, can be cost efficient, and nowadays should be a main interest of animal welfare in order to reduce animals' suffering. Based on these data, determination of NTE inhibition together with histopathological examination of longitudinal sections of distal tibial nerves, mid-longitudinal sections of rostral cerebellum and cross sections of upper cervical spinal cord represents an optimally sensitive and cost efficient test requirement.

The dorsal fascia dentata as a probe of fixation quality in the rodent brain.

In microscopic sections of the rodent brain the dorsal fascia dentata frequently shows perineuronal swelling and neuronal swelling and shrinkage. Factors influencing the occurrence of such changes, which may mimic excitotoxic effects, have been examined using various schedules of anaesthesia and perfusion fixation. Laboratory mice anaesthetized with a low dose of sodium pentobarbital manifested prolonged excitation in comparison to those anaesthetized with a high dose: the occurrence of tremor and convulsions, however, was not related to the morphological changes in the fascia dentata. The changes were diminished by increasing the perfusion pressure (from 80 to 120 mmHg), by reducing the duration of the wash-out period with buffer (from 45 to 15 seconds) and by prolonging the perfusion time (from 7 to 15 minutes). They were abolished when 5% solution of glutaraldehyde was used instead of a 2.5%. The results show that the quality of brain fixation may be best assessed according to the morphology of the dorsal fascia dentata, and that the occurrence of acute swelling and shrinkage in this area should not be mistaken for pathological changes.

Functional and morphological characterization of neuropathy induced with 5-lipoxygenase inhibitor CGS 21595.

Peripheral toxic neuropathy induced in rats with a 5-lipoxygenase inhibitor CGS 21,595 was characterized using special functional tests and pathological procedures. Functional tests included measurement of grip strength, landing foot splay, assessment of sensorimotor and autonomic functions and monitoring of motor activity. Pathological procedures consisted of perfusion fixation, embedding in plastic, teasing of isolated nerve fibers, and light and electron microscopy. Male and female albino rats received the test article orally by gavage on 5 days per week. To characterize the development of the lesion animals treated with 1000 mg/kg were examined and sacrificed at 2-week intervals until termination at 10 weeks. In a separate study, the dose-effect relationship was examined in groups of animals treated with 50,200 or 1000 mg/kg for 10 weeks. Neurotoxicity occurred only in animals treated with 1000 mg/kg and was first detected following 4 weeks of treatment. Although there were no overt clinical signs of neurotoxicity, functional examination detected a reduction of grip strength, increased landing foot splay and reduced motor activity. Neuropathological examination revealed peripheral segmental demyelination affecting predominantly the Schwann cells in the ventral spinal nerve roots. Owing to its unusual localization in the nervous system and to subtlety of functional signs, peripheral segmental demyelination represents a special diagnostic challenge in toxicological safety studies.

The use of an unbaited tunnel maze in neurotoxicology: I. Trimethyltin-induced brain lesions.

In our laboratory we use an unbaited 6-arm radial tunnel maze (6-arm RTM) to assess working and reference memory in the course of neurotoxicity studies. The 6-arm RTM is believed to measure parameters comparable to those assessed in radial-arm mazes, but without the need of food deprivation and rewarding of animals. This is especially useful in the course of neurotoxicity studies as interferences of e.g. food deprivation with drug pharmacokinetics can be avoided. Since the 6-arm RTM is less evaluated than conventional mazes the aim of this study was to further confirm mean error score as measure of 'working memory', left-right discrimination within each radial arm (expressed as percent "blind-alley" visits) as measure of 'reference memory', and number of arm entries/min as a measure of motor activity. Therefore, hippocampal lesions were induced by injecting animals with the neurotoxicant trimethyltin (TMT). TMT at a dose of 5 mg/kg slightly lesioned hippocampal CA3 pyramidal cells in 3 of 8 animals, but did not affect behavioral measures in the 6-arm RTM. In all surviving animals treated with 7 or 9 mg/kg TMT moderate to marked loss of CA3 pyramidal cells was observed, while in 4 of these 7 rats CA4 pyramidal cells were also affected. Other brain lesions were not observed. TMT-induced brain lesions led to increased mean error score and number of arm visits during the retention phase and after changing maze configuration, whereas percent "blind-alley" visits were not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Transneuronal spread of intraperitoneally administered herpes simplex virus type 1 from the abdomen via the vagus nerve to the brains of mice.

The MacIntyre strain of Herpes simplex virus type 1 was inoculated intraperitoneally into young male mice. Immunohistochemical detection of the virus antigen demonstrated the passage of virus from the gastro-intestinal myenteric plexus towards the brain and its distribution within the areas of brain related to the principal nuclei of the vagus nerve. Selective trapping of the virus in the autonomic nerves and subsequent localization of antigen behind the blood-brain barrier may prevent therapeutic effects of agents tested in this model.

Contribution of immunohistochemistry toward the diagnosis of tumors of laboratory rats.

A polyclonal antibody detecting S-100 protein (S-100) and a monoclonal antibody demonstrating epithelial cell (Lu-5) were used in addition to routine, hematoxylin-eosin stain to improve the identification of tumors of neural or epithelial origin diagnosed in conventionally treated tissue from rat bioassays. Among 108 lesions tested for S-100, 51 reacted positively; they included benign and malignant schwannoma, endomyocardial disease, some cases of benign and malignant thymoma, and renal tubular adenoma. S-100 protein is considered particularly useful for discriminating of neoplasms of Schwann cell origin from mesenchymal tumors. 31 of 51 lesions tested for Lu-5 reacted positively: they comprised adenoma, carcinoma, benign and malignant thymoma and atriocaval node tumor of the heart. Lu-5 was especially useful to distinguish epithelial from mesenchymal neoplasms and was capable of identifying epithelial elements in lymphocyte-rich thymomas as well as in dedifferentiated or autolytic tumors. The binding of both antibodies in neoplastic tissue was compared with a complete set of anatomically normal rat tissues.

Primary tumours of the thymus in the rat.

The features of 192 primary thymic tumours occurring in the rat are described. Of these neoplasms, 170 were classified as benign thymomas, one as a benign fibrous histiocytoma, 20 as various types of malignant thymoma, 3 lympho-epithelioma-like carcinomas, one mixed small cell undifferentiated-squamous cell carcinoma, one sarcoma-like carcinoma, 4 undifferentiated carcinomas, 11 squamous cell carcinomas and the one remaining tumour as a carcinoid. A mouse, anti-epithelial, monoclonal antibody, lu-5, was used to confirm the epithelial nature of the malignant thymomas, and neuron-specific enolase to confirm the diagnosis of carcinoid. The tumours showed many features in common with those reported in man.