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Morphologic lesions have received only limited attention as in vitro endpoints of toxicity. In the present work, "tissue" and cell morphology of control and toxicant-treated primary dissociated cerebrocortical cell cultures from fetal mice were examined using phase-contrast and bright-field microscopy. In untreated control cultures, a reproducible sequence of developmental events included cellular reaggregation, intercolony bridging with cell migration, and neuronal apoptosis, with maturation yielding confluent monolayers containing both neurons and glia. Because even mature cultures had regions of varying differentiation, an understanding of the normal developmental sequence was essential when assessing toxicant-treated cultures for damage. Chemicals induced neuronotoxic, gliotoxic, and cytotoxic (i.e., nonspecific) patterns of morphologic damage in growing (< 6 day old) or mature (6-15 day old) cultures in both a concentration-dependent and cell type-specific manner. In addition, exposure to some toxicants consistently reduced the staining intensity for glial fibrillary acidic protein in the astrocyte carpet prior to the appearance of structural damage. These data indicate that histopathologic endpoints, including methods for neural-specific markers, represent potentially valuable criteria for in vitro assessments of neurotoxicity.

Edwardsiella tarda, an opportunistic bacterial pathogen, was isolated from dying largemouth bass (Micropterus salmoides) during an epizootic in a eutrophic lake system, Lochloosa Lake, Florida, USA. Approximately 1,500 adult fish died over a 6-wk period during the late summer and early fall of 1991. A mixed population of aerobic bacteria (E. tarda, Aeromonas hydrophila, and Pseudomonas sp.) was isolated from deep cutaneous ulcers and intestines of moribund bass. However, E. tarda in pure culture was the only bacterium isolated from several viscera of several fish; E. tarda may be the etiologic agent responsible for some episodes of seasonal mortality in largemouth bass.

Fibromas were observed on the lips of adult female and juvenile angel fish (Pterophyllum scalare) from 3 Florida farm populations. Tumor prevalence in each population was < 1%. Affected fish were clinically normal except for those with large tumors, which had weight loss caused by physical obstruction of food intake. Fibromas originated as elevated masses from the mucocutaneous junction near the midline of the upper and/or lower lips. Characteristic features included dense fibrous stroma covered by thickened, stratified squamous epithelium, numerous intraneoplastic teeth, and scattered foci of stromal inflammation. Electron microscopy revealed intracytoplasmic type-A retrovirus-like particles in stromal cells from all tumors. Attempts to transmit fibromas, using a cell-free tumor ultrafiltrate, were unsuccessful. The relationship of the intraneoplastic viral particles to the development of lip fibromas in angel fish is uncertain.

Anesthesia and surgery in a Quarter Horse affected with hyperkalemic periodic paralysis resulted in euthanasia after 7 days of postoperative recumbency. Initial recovery was uneventful after extensive sinus surgery, but within 2 hours, the horse had severe muscle weakness. Plasma electrolyte concentrations were within the normal range during the period of recumbency. There was no clinical or laboratory evidence of severe muscle damage. Despite treatment with acetazolamide, isoproterenol, and intensive nursing, the horse was unable to stand for more than a few seconds and developed severe decubital ulcers. Ultrastructural examination revealed nemaline rods and swollen mitochondria in disrupted myofibers.

Five cats were treated with an azathioprine suspension (2.2 mg/kg of body weight on alternate days) and 2 cats were given vehicle (controls) for 9 weeks. Complete blood and platelet counts and serum biochemistry variables were monitored weekly. Bone marrow aspirates were evaluated every 3 weeks, and core bone marrow biopsy was performed at the end of the study. Profound neutropenia (less than 600 cells/microliters) was observed in all treated cats, and 1 cat developed pancytopenia. Treatment was discontinued if the WBC count was less than 3,000 cells/microliters. Four weeks after discontinuation of azathioprine, 1 treated cat again was given azathioprine at a lower dosage (1.1 mg of azathioprine/kg on alternate days) and neutropenia recurred within 2 weeks. During treatment, 3 cats developed thrombocytosis, and 2 developed thrombocytopenia. In 4 of 5 cats, neutropenia and thrombocytopenia resolved when azathioprine was discontinued. Bone marrow cytologic examination during treatment revealed reduction of the neutrophil line, with relative increase in monocytes. Core bone marrow biopsy at the completion of the study revealed hypocellular marrow with marked decrease in the myeloid series in cats given azathioprine. One of the cats that was treated with azathioprine had a hypercellular marrow with increased numbers of mature granulocytes and precursors; however, azathioprine had been discontinued 3 weeks prior to biopsy. Alterations in serum biochemical variables were not associated with azathioprine. Two cats that were treated with azathioprine developed respiratory tract infections, and 1 of them was euthanatized during the study.

Humoral signals (neurotransmitters and hormones) control cell division, migration, and differentiation processes which define the organization of brain pathways. Alterations in maternal, fetal, and neonatal biochemistry during critical periods of neurogenesis may irreparably alter the circuitry and, thus, postnatal behavior of young animals. Secalonic acid D (SAD), an ergochrome mycotoxin, causes behavioral and neurochemical deficits in developing mice following prenatal (transplacental) or early postnatal (transmammary) exposure. SAD-induced functional abnormalities include delays in reflex behaviors, integrated neuromuscular activity and strength, stress adaptation responses, and sensory discrimination. These behavioral changes are associated with reductions of brain monoamine neurotransmitter levels in both fetuses and neonates. SAD also alters concentrations of maternal plasma corticosteroids and fetal cyclic nucleotides during midgestation. SAD thus modulates several chemicals in pregnant mice and their fetuses which contribute to brain development, suggesting that this mycotoxin may pose a neuroteratogenic hazard to other immature mammals, including human infants.

Interactions between test chemicals and pollutants can confound toxicology studies. To test the sensitivity of the regenerating olfactory epithelium to additional challenge with the olfactory epithelial toxicant methyl bromide (MeBr), Fischer 344 (F344) rats received 2 6-hr inhalation exposures (separated by a 28-day recovery period) to either 0 or 175 ppm MeBr. The regenerating epithelium was resistant to the second MeBr exposure. In addition, histopathologic examination revealed squamous epithelial hyperplasia in the vestibule; inflammation, epithelial necrosis, mucosal erosions, and squamous metaplasia of the respiratory epithelium in the anterior nose; and olfactory sensory cell loss in the dorsal medial meatus. These changes could not be attributed to MeBr, but they were correlated with housing in filter-capped cages between MeBr exposures and were presumably caused by volatile pollutants from soiled bedding. Moreover, olfactory sensory cell loss in the dorsal medial meatus was associated with local resistance to MeBr-induced damage in rats with pollutant-induced changes. Analysis of cage air revealed a progressive increase in ammonia levels between bedding changes (up to 50 ppm), but exposure to 300 ppm ammonia in an additional experiment reproduced only the anterior nasal lesions and not olfactory sensory cell loss. This study demonstrates that 1) regenerating olfactory epithelium is refractory to further MeBr toxicity; 2) pollutants from soiled bedding (in addition to ammonia) produce nasal lesions; and 3) pollutant-induced changes modify the nasal response to inhaled MeBr.

Suckling mice exposed to secalonic acid D (SAD) mycotoxin postnatally (by gavaging dams with 0, 15 or 25 mg/kg on postgestational days 1 to 10) or prenatally (by gavaging with 25 mg/kg on gestational day 13 to produce a positive behavioral teratogenic control group) manifested subtle preweaning neurobehavioral, neurochemical and growth deficits. Gestational length, maternal weight gain, neonatal sex ratio and physical appearance of pups at birth were unaffected by treatment. Prenatal SAD (25 mg/kg) delayed (p less than 0.05) ontogeny of swimming on postnatal days (PND) 11 and 13 and reduced norepinephrine (NE) and dopamine (DA) levels in prosencephalon on PND 7 and in cerebellum-pons on PND 7-16. In the postnatal treatment groups, pup body weight gains were decreased from PND 9-22. Swimming was delayed in the 15 mg/kg postnatal exposure group on PND 11 and 13, while 25 mg/kg delayed swimming on PND 11-15. Postnatal exposure to 25 mg/kg also reduced NE and DA levels in prosencephalon and cerebellum-pons on PND 7-16. SAD thus caused concomitant ontogenetic delays in growth, swimming behavior and brain catecholamine levels following either prenatal (transplacental) or early postnatal (transmammary) exposure. These data indicate that both in utero and lactational exposures must be considered when assessing potential risks posed to developing mammals by environmental neurotoxicants.

A mare with chronic cachexia had multiple skin nodules, abdominal masses (attached and free floating), and large lymph nodes. Fine-needle aspiration cytologic evaluation of a skin mass revealed multinucleated giant cells surrounding eosinophilic material. Histologic evaluation revealed extensive amyloid deposits within the masses, lymph nodes, and the interstitium of many organs. The presence of systemic (visceral) and organ-limited (cutaneous) forms of amyloid is rare in horses. Amyloid congophilia was retained after potassium permanganate oxidation. The fibrils were thus distinct from the AA (secondary) fibrils that are found in most cases of equine amyloidosis, suggesting that this mare may have had primary amyloidosis. Regardless of fibril type, the presence of multinucleated giant cells in association with eosinophilic material in cytologic preparations of skin nodules may suggest a differential diagnosis of amyloidosis in horses.

Pregnant mice (dams) were gavaged once on gestational day 13 with 4 ml/kg of dimethylsulfoxide vehicle containing 0 (groups 15, 25 and negative control) or 25 (positive behavioral teratogenic control group) mg/kg of secalonic acid D (SAD). While nursing their offspring, dams were gavaged on postgestational days 1 to 10 with vehicle containing 0 (negative and positive control groups), 15 (group 15) or 25 (group 25) mg/kg/day of SAD. Gestational lengths, maternal pregnancy weights, litter sizes, neonatal sex ratios, neonatal physical appearance and female birth weights were unaffected by prenatal treatment, but male pups born to positive control dams weighed less (p less than 0.05) than negative control group. Compared to negative control, the positive control dams gained significantly more weight while nursing their offspring. Prenatal (positive control) and postnatal (15, 25) SAD exposure delayed ontogeny of surface righting, olfactory discrimination and hindlimb grip behaviors in males and females, and testes descent in males. Negative geotaxis in male and female offspring of group 25 and male offspring of positive control group, as well as times of incisor eruptions of both sexes in groups 15 and 25 were delayed. A significant dose-response effect in olfactory discrimination existed between the groups exposed to postnatal SAD. SAD was behaviorally teratogenic following both prenatal and early postnatal exposure.

Mice were gavage-fed on day 13 of pregnancy with 0 (groups N, 15, 25) or 25 (group P) mg/kg of secalonic acid D (SAD) and again while nursing their offspring on postgestational days 1-10 with 0 (N,P), 15(15) or 25(25) mg/kg/day. SAD residues were present in the stomach of pups nursed by SAD-treated dams. Postnatal exposure to SAD decreased (P less than 0.05) body weight gains of offspring. Treatment decreased the developmental levels of norepinephrine and dopamine in the prosencephalon (forebrain) and cerebellum-pons of the offspring on postnatal days (PND) 7 and 7-16, respectively. On PND 7-16 serotonin and 5-hydroxyindoleacetic acid levels decreased in the prosencephalon and cerebellum-pons of offspring exposed prenatally (P) or postnatally (15,25) to SAD.