Biomedical subjects

K R Reuhl

Publications and source records attributed to K R Reuhl.

At least 55 records · Page 3Linked to original sources

PubMed1992

Ectopic impulse generation in dorsal root ganglion neurons during methylmercury intoxication: an electrophysiological and morphological study.

Electrophysiological function and morphology of dorsal root ganglion (DRG) neurons were investigated in female Wistar rats following administration of methylmercury (5 mg/kg/day for 10 days). Neurons were classified according to the conduction velocities of their peripheral axons and perikaryal action potential characteristics as types A alpha, A beta A delta and C. In methylmercury-treated rats, the majority of DRG neuron action potential characteristics were not significantly altered. However, axonal conduction velocities were slowed in all type A ganglion cells, leading to significant delays in action potential onset in types A beta and A delta neurons. An initial complex-soma inflection was observed on the rising phase of the action potential of some cells. These inflection potentials had longer conduction times and lower amplitudes in treated animals. Repetitive discharge, characterized by 3-5 action potentials upon single peripheral nerve stimulation, was observed in 8 of 38 cells recorded in treated animals, predominantly in type A beta (4/8) and A beta (3/12) neurons; direct current injection into repetitively discharging cells via the recording electrode elicited only single action potentials. Extracellular recordings from dorsal root filaments confirmed that the repetitive action potentials arising in the DRG were conducted to the spinal cord. Morphological examination of DRG revealed damage in up to 10% of neurons, consisting of loss of Nissl staining, cytoplasmic vacuolization, and proliferation of satellite cells. Large, pale neurons appeared preferentially involved. Rarely, neuronophagia was observed. Further microscopic examination of proximal and distal sections of sciatic and tibial nerves revealed only occasional degeneration of myelinated axons. While morphological alterations did not appear to offer a structural basis for the multiple firing, it is speculated that repetitive action potential discharge may contribute to the paresthesias associated with MeHg intoxication.

Action Potentials↗

PubMed1991

Taxol protects the microtubules of concanavalin A-activated lymphocytes from disassembly by methylmercury, but DNA synthesis is still inhibited.

We have shown previously that there is a good correlation between the degree of microtubule disassembly by methylmercury (MeHg) and the extent of inhibition of DNA replication in Concanavalin A (Con A)-stimulated mouse splenic lymphocytes. The purpose of this study was to determine if these two events are causally related and to examine the effects of MeHg-induced microtubule disassembly on earlier events of the stimulation process. We show that early steps constituting the activation pathway, such as the Con A-induced increase in Ca2+ influx and the expression of interleukin 2 receptor, are not inhibited by concentrations of MeHg that disassemble microtubules. RNA synthesis is not affected by short-term (3 h) treatment with MeHg, but longer treatment (24 h) inhibits RNA synthesis. In contrast, DNA synthesis is effectively inhibited by a 3-h treatment with MeHg. In lymphocytes treated with taxol, microtubules are not disassembled by MeHg; however, the inhibition of RNA and DNA synthesis persists. We conclude that the inhibition of nucleic acid synthesis by MeHg is not causally related to MeHg-induced microtubule disassembly.

Alkaloids↗

PubMed1991

Cellular and regional distribution of reduced glutathione in the nervous system of the rat: histochemical localization by mercury orange and o-phthaldialdehyde-induced histofluorescence.

Differences in the cellular distribution of antioxidant defense mechanisms in heterogeneous tissue such as the nervous system are likely critical determinants of differential sensitivity to toxicants. Regional and cellular localization of reduced glutathione (GSH) in central and peripheral nervous tissue was determined from the pattern of fluorescence observed in tissue sections stained with mercury orange; localization was confirmed using a novel histofluorochromatic staining method, o-phthaldialdehyde (OPT). Excellent concordance between the distribution of fluorescence obtained with mercury orange and OPT staining was observed. Depletion of GSH by treatment with diethyl maleate resulted in a diminution in both mercury orange and OPT histofluorescence. Generally, strong staining of the CNS neuropil was seen with little or no observable fluorescence in neuronal somata. The cerebellar granular cells were an exception, exhibiting fluorescence with both mercury orange and OPT. Cerebellar Purkinje cells exhibited nonuniform fluorescence with mercury orange but generally uniform staining with OPT. In contrast to the patterns observed in the CNS, the sciatic nerve and the sensory cell bodies of the lumbar dorsal root ganglia exhibited prominent fluorescence with both mercury orange and OPT. Reduced glutathione in the central nervous system appears primarily localized in the neuropil and white matter tracts; with a few exceptions, the neuronal somata do not appear to contain appreciable amounts of GSH. The heterogeneous distribution of GSH and enzymes involved in the detoxification and/or excretion of xenobiotics in the nervous system may form a basis for selective cellular and/or regional expression of neurotoxicity.

Animals↗

PubMed1991

Delayed expression of neurotoxicity: the problem of silent damage.

A prolonged period of latency between toxic exposure and disease is a recognized phenomenon in oncology, but is a relatively new concept in neurotoxicology. Suggestions that exposure to neurotoxic compounds may be followed years or decades later by clinically evident neurological disease have received considerable anecdotal support but little empirical evidence. In recent years, evidence has emerged linking environmental factors to several neurodegenerative diseases, including amyotrophic lateral sclerosis and the Parkinsonism-dementia complex. While these diseases have not been definitively demonstrated to arise from exposure to toxins or toxicants, nevertheless the possibility exists that xenobiotic exposure could lead to neurological conditions possessing a period of clinical "silence" prior to expression. Detection of such damage using standard toxicology testing protocols poses a major challenge. Lessons learned from neurodegenerative diseases can be profitably applied to the study of the long-term effects of xenobiotics on the brain and elucidation of the role of aging on the expression of neurotoxicity.

Aging↗

PubMed1990

Synaptic terminal degeneration and remodeling at the rat neuromuscular junction resulting from a single exposure to acrylamide.

Repetitive exposure to low doses of acrylamide results in extensive pathological changes at the neuromuscular junction (NMJ), but it remains undetermined if a single exposure to a larger dose will produce a similar neuropathological outcome. In the present study, morphometric and ultrastructural analyses of rat soleus NMJ were performed to determine early pathological effects of an intraperitoneal injection of 100 mg/kg acrylamide. Widespread nerve terminal degeneration, terminal sprouting, and endplate lengthening were evident as early as 4 days after injection. Degenerating terminal branches were swollen and exhibited enhanced argyrophilia. Ultrastructurally, the majority of terminals exhibited axolemmal abnormalities, neurofilament accumulations, and a paucity of synaptic vesicles; occasional swollen terminals lacked neurofilaments but contained increased numbers of tubulovesicular profiles. This early morphological pattern of nerve terminal changes suggests that acrylamide may disrupt both synaptic vesicle recycling and neurofilament degradation. These findings indicate that a single high dose of acrylamide triggers pathological lesions and remodeling in motor nerve terminals virtually identical to those resulting from multiple low doses.

Acrylamide↗

PubMed1990

Smooth muscle actin expression during P19 embryonal carcinoma differentiation in cell culture.

P19 embryonal carcinoma (EC) cells can be induced in vitro to differentiate into cells resembling those normally formed in the embryo. Among these cell types is one whose morphology is fibroblast-like. Using indirect immunofluorescence and Western blot analysis with antibodies directed against various isoforms of actin, many of these fibroblast-like cells were found to express smooth muscle actin isoforms. Northern blot analysis of RNA indicated the presence of a smooth muscle-specific isoform of myosin heavy-chain mRNA in immortal lines of these fibroblast-like cells. These results suggest that these fibroblast-like cells resemble fetal myofibroblastic or myoepithelial cells, which have a wide distribution during embryonic development.

Actins↗

PubMed1989

Effects of chronic developmental lead exposure on monkey neuroanatomy: visual system.

The effects of lead on specific areas of the visual system were examined in two groups of monkeys (Macaca fascicularis). The first group (N = 3) received 2000 micrograms Pb/kg/day from infancy onward, while the second group (N = 4) received 25 micrograms Pb/kg/day from birth onward. Monkeys were killed at approximately 6 years of age. Areas of the visual system, including optic nerve, lateral geniculate nucleus, and primary area V1 and one visual projection area V2, were examined by a combination of light and electron microscopy and Golgi impregnation. No effect of lead on optic nerve was identified, nor were there consistent differences in the lateral geniculate nucleus. Within areas V1 and V2, the neuronal volume density was significantly reduced in the high dose compared to the low dose group. Moreover, analysis of the dendritic arborization by Golgi analysis revealed a relative decrease in the number of arborizations among pyramidal neurons in both areas V1 and V2. These data suggest that lead exposure beginning during the early postnatal period may result in changes in cytoarchitecture in visual areas V1 and V2.

Animals↗

PubMed1989

A transfected H-ras oncogene does not inhibit differentiation of cardiac and skeletal muscle from embryonal carcinoma cells.

P19 embryonal carcinoma (EC) cells can be induced to differentiate in vitro into a variety of cell types, including cardiac and skeletal myocytes. We have isolated P19 cells stably transformed with either the activated human H-ras oncogene or with a chimeric gene in which the H-ras oncogene was controlled by a muscle-specific promoter. These P19 lines exhibited ubiquitous and muscle-specific expression of the activated H-ras protein, respectively. In both lines of P19 cells, normal cardiac and skeletal muscle differentiation was observed. Since the activated H-ras prevents differentiation of myoblast cell lines, our results suggest that the EC-derived muscle progenitor cell differs from continuous myoblast cell lines, perhaps by lacking a complementing oncogene responsible for myoblast immortalization.

Actins↗

PubMed1989

Cell lines with developmental potential restricted to mesodermal lineages isolated from differentiating cultures of pluripotential P19 embryonal carcinoma cells.

Embryonal carcinoma (EC) cells are developmentally pluripotential cells which can be induced to differentiate in cell culture to form a wide variety of cell types. To investigate the lineage relationships between cells of different types, we set out to isolate cell lines with multiple but restricted developmental potentials from differentiating cultures of P19 cells, a line of EC. By selecting for differentiated cells capable of anchorage-independent growth, we isolated cell lines which differentiated in high density cultures to form at least two cell types; myocytes that resembled fetal skeletal muscle cells and loose connective tissue cells that secreted large amounts of type I collagen. These results suggest that skeletal myocytes and connective tissue share a common precursor and that stem cells with limited but multiple developmental potentials can be isolated from differentiating cultures of P19 cells.

Animals↗

PubMed1988

Effects of methyl mercury on the microtubule system of mouse lymphocytes.

The effects of in vivo and in vitro methyl mercury (MeHg) treatments on the microtubule system of murine splenic lymphocytes were examined by immunofluorescence microscopy. In vitro exposures to 1 to 10 microM MeHg resulted in time- and concentration-dependent microtubule disassembly. Lymphocytes isolated from mice receiving a single 10 mg/kg injection displayed microtubule damage when examined 2 and 5 days post-treatment. The capacity of in vivo and in vitro treated lymphocytes to respond to the mitogen concanavalin A (Con A) was generally inhibited by MeHg. There was a good correlation between the degree of microtubule disassembly and the inhibition of mitogen responsiveness. In vivo and in vitro treatments that resulted in extensive microtubule damage suppressed the ConA response and blocked lymphocytes early in the stimulation sequence. In vitro MeHg treatment late in mitogenesis caused a rapid, concentration-dependent inhibition of [3H]thymidine incorporation. These results suggest that damage to the microtubule system can serve as an indicator of MeHg toxicity and may underlie the toxicant's effects on lymphocyte functions.

Animals↗

PubMed1988

The effects of methylmercury on the cytoskeleton of murine embryonal carcinoma cells.

Immunofluorescence staining with antibodies to tubulin and vimentin and staining with phalloidin have been used to examine the effects of methylmercury on the cytoskeleton of embryonal carcinoma cells in culture. Exposure of embryonal carcinoma cells to methylmercury (0.01 to 10 microns) resulted in concentration- and time-dependent disassembly of microtubules in interphase and mitotic cells. These effects were reversible when cultures were washed free of methylmercury. Spindle microtubules were more sensitive than those of interphase cells. Spindle damage resulted in an accumulation of cells in prometaphase/metaphase, which correlated with a temporary delay in the resumption of normal proliferation rate upon removal of methylmercury. Of the interphase cytoskeletal components, microtubules were the first affected by methylmercury. Vimentin intermediate filaments appeared relatively insensitive to methylmercury, but showed a reorganization secondary to the microtubule disassembly. Actin microfilaments appeared unchanged in cells showing complete absence of microtubules. Our results 1) support previous reports suggesting that microtubules are a primary target of methylmercury, 2) document a differential sensitivity of mitotic and interphase microtubule systems and 3) demonstrate the relative insensitivities of other cytoskeletal components.

Animals↗

PubMed1988

Effects of methylmercury on retinoic acid-induced neuroectodermal derivatives of embryonal carcinoma cells.

Immunofluorescence staining with antibodies to tubulin, neurofilaments and glial filaments was used to study the effects of methylmercury on the differentiation of retinoic acid-induced embryonal carcinoma cells into neurons and astroglia and on the cytoskeleton of these neuroectodermal derivatives. Methylmercury did not prevent undifferentiated embryonal carcinoma cells from developing into neurons and glia. Treatment of committed embryonal carcinoma cells with methylmercury doses exceeding 1 microM resulted in the formation of neurons with abnormal morphologies. In differentiated cultures, microtubules were the first cytoskeletal element to be affected. Their disassembly was time- and concentration-dependent. Microtubules in glial cells and in neuronal perikarya were more sensitive than those in neuronal processes. Neurofilaments and glial filaments appeared relatively insensitive to methylmercury treatment but showed reorganization after complete disassembly of the microtubules. The data demonstrate 1) the sensitivity of microtubules of both neurons and glia to methylmercury-induced depolymerization, and 2) the heterogeneous response of neuronal microtubules to methylmercury, presumably reflecting posttranslational modifications of different subpopulations of microtubules in the perikarya and neurite.

Animals↗

PubMed1988

Differentiation and maturation of embryonal carcinoma-derived neurons in cell culture.

We have previously shown that retinoic acid-treated cultures of the P19 line of embryonal carcinoma cells differentiate into neurons, glia, and fibroblast-like cells (Jones-Villeneuve et al., 1982). We report here that the monoclonal antibody HNK-1 reacts with the neurons at a very early stage of their differentiation and is, therefore, an early marker of the neuronal lineage. Cells in differentiated P 19 cultures synthesized acetylcholine but not catecholamines, suggesting that at least some of the neurons are cholinergic. The neurons also carry high-affinity uptake sites for GABA but not for serotonin. In long-term cultures, neuronal processes differentiated into axons and dendrites, which formed synapses. This biological system should prove valuable for examining the development and maturation of cholinergic neurons, since their differentiation occurs in cell culture.

Acetylcholine↗

PubMed1988

Adverse pregnancy outcome in the monkey (Macaca fascicularis) after chronic caffeine exposure.

Caffeine and the related methylxanthine theophylline are consumed regularly by pregnant women. In a study originally designed to assess the neurotoxic potential of caffeine in the infant, 40 female monkeys (Macaca fascicularis) were divided into three groups and administered caffeine in their drinking water at concentrations equivalent to 0, 10 to 15 or 25 to 35 mg/kg/day of caffeine 7 days a week. After a period of adaptation to caffeine these monkeys were mated with untreated males. Reproductive failure in the form of stillbirths and miscarriages was observed in the treated groups. Subsequently, 12 control monkeys and 1 low-dose monkey were added to the study and most of the original monkeys rebred. The second round of pregnancies confirmed that the treated monkeys had an increased rate of stillbirths and miscarriages. The precise cause of death of the stillborn infants could not be determined. Maternal weight gain and infant birth weights decreased in a dose-related manner. These results indicate that in utero exposure to methylxanthines (caffeine and/or its major metabolite theophylline) adversely affects pregnancy outcome in the monkey.

Abortion, Veterinary↗

PubMed1987

The role of aggregation in embryonal carcinoma cell differentiation.

Cultures of the P19 line of embryonal carcinoma cells differentiate into various cell types including cardiac muscle when aggregated and exposed to medium containing 1% dimethylsulfoxide (DMSO). DMSO-treated aggregates became completely covered with an epithelial cell type 3 to 4 days following drug exposure. This epithelial cell was tentatively identified as primitive extraembryonic endoderm by its ultrastructural appearance and its possession of cytokeratin intermediate filaments. Muscle cells developed within the interior of DMSO-treated aggregates. They first became apparent 5 to 6 days after DMSO exposure and were characterized by the presence of striated muscle-specific myosin, immature myofibrils, and intercalated discs. We determined the proportion of cells developing into epithelium and muscle in aggregates of various sizes and showed that the proportion of epithelium was highest in small aggregates whereas muscle cells developed only in aggregates of relatively large size. The muscle was usually associated with necrotic areas which developed within the interior of large aggregates. Our results suggest that cardiac muscle differentiation in the aggregates requires both the DMSO-induced formation of an epithelial cell coat and one other condition which may be the proximity to necrotic areas.

Cell Aggregation↗

PubMed1987

Restricted replication of herpes simplex virus type 1 in murine embryonal carcinoma cells.

Herpes simplex virus type 1 (HSV-1) has a broad host range but the KOS strain of HSV-1 did not replicate efficiently in murine embryonal carcinoma (EC) cells. The yield of infectious HSV-1 from EC cells was 100- to 1000-fold lower than that from fibroblast cell lines of mouse, monkey or human origin. The thymidine kinase (TK) gene of HSV-1 is expressed early during the infectious cycle. The levels of TK mRNA and of TK activity in infected EC cells were only two- to threefold lower than levels from infected fibroblast cells. Infected EC cells supported replication of about half as much HSV-1 DNA as did fibroblast cells. The reduced yield of infectious virus was consistent with a paucity of virions in infected EC cells examined by electron microscopy, suggesting a major block late during the HSV-1 infectious cycle. We isolated a variant strain of HSV-1, called KOSEC, which replicated as efficiently in EC cells as in mouse fibroblasts. KOSEC infected EC and fibroblast cells, synthesized more TK mRNA, more TK enzyme, and more HSV-1 DNA than did the same cells infected with the KOS stain. Both HSV-1 strains induced similar levels of synthesis of gD, an early viral glycoprotein. By co-infection of EC cells with the KOS and KOSEC virus, both the elevated virus yield and the elevated TK synthesis seen in KOSEC-infected cells appeared to be recessive. Apparently a viral mutation that affects expression of some early viral functions can also overcome the EC cell restriction to HSV-1 replication.

Animals↗

PubMed1987

Fatal pneumococcal meningitis in a colony-born monkey (Macaca fascicularis).

This report describes the clinical course and pathological findings in a four-year-old male cynomolgus monkey (Macaca fascicularis) which succumbed to fulminant pneumococcal meningitis. The extremely rapid course of this infection emphasizes the importance of early recognition of the clinical manifestations of meningitis in the correct diagnosis and rapid treatment of the condition.

Animals↗

PubMed1986

Trimethyltin as a selective adrenal chemosympatholytic agent in vivo: effect precedes both clinical and histopathological evidence of toxicity.

Trimethyltin (TMT) is a potent neuronotoxiciant but there is little data regarding its systemic effects. In this study, female BALB/c mice were administered either 0.9% saline or 2.75 mg TMT/kg intraperitoneally (i.p.). The animals were then housed in room air or in glass chambers flushed with either 10%, 40%, or 100% oxygen. Mice were sacrificed at 4, 8, 24, and 48 h after treatment and adrenals analyzed for various neurotransmitters by ion-pairing HPLC with electrochemical detection. In addition, adrenal S-adenosylmethionine (SAM) and blood ketone bodies were determined Sections of adrenals were evaluated by electron microscopy for histopathological changes. In vivo treatment with the toxicant resulted in a significant decrease in adrenal epinephrine and norepinephrine levels as early as 8 h following treatment. This effect preceded the appearance of both clinical signs and histopathological changes in the hippocampus by 12-24 h. With exposure to TMT in room air, mouse adrenal content of epinephrine fell from 1861.3 +/- 97.3 ng/4 mg to 1493.3 +/- 137.0 ng/4 mg while norepinephrine levels fell from 779.6 +/- 32.3 ng/4 mg to 503.4 +/- 44.3 ng/4 after 8 h. Supplementation with 40% oxygen did not attenuate this effect but in the case of mice treated with TMT and housed in 100% oxygen for 48 h, actually exacerbated the adrenal epinephrine depletion. Housing in approximately half normal atmospheric oxygen (10%) neither prevented nor enhanced the effects of TMT. The epinephrine/norepinephrine ratios were: control, 2.44; TMT (room air), 1.56; TMT (10% O2), 1.72; TMT (40% O2), 1.44; TMT (100% O2), 1.07. None of the conditions used in this study caused a decrease in adrenal dopamine, 5-hydroxyindole acetic acid (5-HIAA), 5-hydroxytryptamine (5-HT) or in the level of SAM. TMT treatment significantly increased blood ketone bodies indicating additional metabolic dysfunction. The significance of these findings in relation to TMT neuronotoxicity and fatty liver syndrome are discussed.

3-Hydroxybutyric Acid↗