Pregnant rats were treated on either gestational day (GD) 7, 12, or 17 with single doses of trime... more Pregnant rats were treated on either gestational day (GD) 7, 12, or 17 with single doses of trimethyltin chloride (TMT) ip at either 0, 5, 7, or 9 mg/kg. A significant effect of dose was manifest as decreased maternal weight at term, which persisted during lactation until postnatal day (PND) 15 in some groups. For all treatments combined, term weights of dams exposed on GDs 7 and 12 were greater than those treated on GD 17. Litter sizes were decreased for groups treated on GD 17 with 9 mg/kg TMT. Pups treated in utero and exhibiting treatment-induced decreases in weight at or near birth remained smaller than untreated animals into adulthood (PND 280). By PND 20, weights of pups treated on GD 7 greater than GD 12 greater than GD 17. Neuropathology of pups sacrificed on PND 1 was minimal in all animals with lesions only identified in animals treated on GDs 12 or 17 which consisted of subtle degenerative changes in the CA3 and CA4 regions of Ammon's horn of the hippocampus. Muscarinic cholinergic receptor binding in whole brains from pups on PND 1 did not show any significant changes compared to controls for any dose or day of exposure. These data indicate that prenatal TMT exposure results in postnatal toxicity in treated pups but only in the presence of maternal toxicity.
Brain dysmorphogenesis and persistent psychomotor disturbances are hallmarks of developmental met... more Brain dysmorphogenesis and persistent psychomotor disturbances are hallmarks of developmental methylmercury (MeHg) exposure, but the molecular mechanisms underlying these effects are poorly understood. Targets of developmental MeHg exposure include neural cell adhesion molecules (NCAMs), sialoglycoconjugate molecules whose proper temporal and spatial expression is important at all stages of neurodevelopment and especially during synaptic structuring. To investigate the effects of MeHg on the temporal expression of NCAM during development, rat pups were dosed with 7.0 mg/kg MeHgCl (s.c.) on alternate days from postnatal days (PNDs) 3-13 and killed on PNDs 15, 30 and 60. Brain MeHg concentrations were determined in a subset of litters injected with CH(3)203Hg. Expression of NCAM180 protein and of NCAM180 polysialylation was examined in whole cerebellum homogenates, cerebellar synaptosomes and isolated cerebellar growth cones by Western blotting and immunocytochemical staining. NCAM sialyltransferase activity was assayed in preparations of purified Golgi apparatus from the cerebelli of rats treated in vivo, or following in vitro incubation with 0, 1, 2.5, or 7.5 microM MeHg for 2 h. At PND15, no change in NCAM180 protein expression was observed in any cerebellar preparations, but decreased polysialylation of NCAM180 was observed in cerebellar whole homogenates, synaptosomes and isolated growth cones. At PND30, both NCAM180 protein expression and NCAM180 polysialylation were elevated in whole homogenate preparations but not in synaptosomes. NCAM180 expression in MeHg-treated rats was similar to controls at PND60, 47 days after the last methylmercury administration. In vivo studies of cerebellar Golgi sialyltransferase activity revealed significant reductions in PND15 MeHg-treated rats as compared to controls, but no changes in sialyltransferase activity in PND30 and PND60 animals. In vitro experiments revealed decreasing sensitivity of cerebellar sialyltransferases to MeHg as the developmental age of the rat increased. Toxic perturbation of the developmentally-regulated expression of polysialylated NCAM during brain formation may disturb the stereotypic formation of neuronal contacts and could contribute to the behavioral and morphological disturbances observed following MeHg poisoning.
Tissue samples from the cerebral and cerebellar cortex of neonatal rats which had been prenatally... more Tissue samples from the cerebral and cerebellar cortex of neonatal rats which had been prenatally exposed to low doses of methylmercury were examined by electro.
Female guinea pigs were dosed po with 1.0 mg CH3 203Hg/kg as methylmercuric chloride, 10 times ov... more Female guinea pigs were dosed po with 1.0 mg CH3 203Hg/kg as methylmercuric chloride, 10 times over a 3-week period. Tissue distribution, excretion, and accumulation of inorganic and organic mercury were studied. The highest concentration of mercury was found in the kidney. The greatest decreases of mercury levels were observed in the small bowel, red blood cells, liver, and cerebrum. The half-life of whole body clearance, based on a single compartment model, was 31.6 days. Mercury in the kidney, liver, and cerebrum was bound mainly by nuclear and soluble fractions. The highest ratio of inorganic to total mercury was seen in the kidney, 60% of this being as inorganic mercury. Excretion of mercury in the feces was measured throughout the experiment. The relationship of organic to inorganic mercury was relatively constant at about 1:3. Data on the effects of methyl mercury on tissue concentrations of zinc and copper show that the only change in the copper content was a marked increase in the kidney.
... References. ENVIRONVU.NrAt. RESEARCH 13, 171185 (1977) Ultrastructural Study of the Latent Ef... more ... References. ENVIRONVU.NrAt. RESEARCH 13, 171185 (1977) Ultrastructural Study of the Latent Effects of Methyl Mercury on the Nervous System After Prenatal Exposure Louis W. C1IANc,KENNETH R. REUHt. ... Nucleus (N), rough endoplasmic reticulum (RER). x 14,500 Fi(;. ...
Abstract Rana pipiens tadpoles were allowed to be raised in water containing various concentratio... more Abstract Rana pipiens tadpoles were allowed to be raised in water containing various concentrations of methylmercuric chloride or were injected with 0.025 ml of 0.1% aqueous solutions of methylmercuric chloride (0.025 mg Hg), every other day for 10 days. All the tadpoles which were raised in water containing more than 0.05 ppm mercury died within 48 hours. The distention of the body cavities and eventual death of these tadpoles was believed to be the result of a disturbance of the osmotic regulatory system by the mercury. Total arrest of further development and differentiation was observed in tadpoles which were raised in water containing 0.001–0.01 ppm mercury. Extensive deposition of blood pigment (hemosiderosis) was observed in the livers of the mercury-injected tadpoles. Such hemosiderotic condition was thought to be predisposed by hemolysis of the red blood cells by mercury followed by severe peripheral edema and hemopoietic reactions in the kidneys of these tadpoles.
Cellular heterogeneity and structural complexity of the nervous system, coupled with regional and... more Cellular heterogeneity and structural complexity of the nervous system, coupled with regional and cellular differences in the metabolic capabilities of neurons, glia and other non-neuronal elements, may underlie the selective cellular involvement following exposure to neurotoxicants. Determination of the role of biotransformation of xenobiotics in neural pathoclisis requires an understanding of the cellular distribution of both phase I and phase II enzyme systems in the brain. While ependyma, choroid plexus and endothelial linings of blood vessels throughout the nervous system appear to contain appreciable amounts of several isoforms of cytochrome P450 (CYP450), glia and neurons tend to be highly specific in which forms of CYP450 they express. Regional and cellular heterogeneity similarly characterize the distribution of glutathione (GSH) and the conjugating enzyme glutathione S-transferase (GST) in the brain. While all cells of the embryonic nervous system express high levels of GSH and pi-GST (with lesser amounts of alpha- and mu-class), by adulthood neurons and non-neuronal cells differ in the distribution of GSH and isoforms of GST. Neurons (except the dorsal root ganglia and the cerebellar granule cells) become GSH-negative but contain alpha-, mu-, and pi-GST. Glia, ependyma, choroid plexus and neurovascular cells are rich in GSH and variously express GSTs. The differences found in the cellular distribution of GSH and GSTs may contribute to changes in the vulnerability of the nervous system to neurotoxicants at different ages. A comprehensive understanding of the neurotoxicological and pharmacological consequences of the cellular heterogeneity in the localization the CYP450s and glutathione S-transferases pre- and postnatally will require systematic study of the distribution, substrate specificity, and inducibility of the various isoforms of these enzyme systems.
8 Autism and Oxidative Stress: Evidence from an Animal Model Michelle A. Cheh, 1 Alycia K. Hallad... more 8 Autism and Oxidative Stress: Evidence from an Animal Model Michelle A. Cheh, 1 Alycia K. Halladay, 2, 3 Carrie L. Yochum, 2 Kenneth R. Reuhl, 3 Marianne Polunas, 3 Xue Ming, 4 and George C. Wagner2,* Departments of 1Neuroscience, 2Psychology, and 3Pharmacology ...
Normal development of the nervous system depends upon complex physical interactions between cells... more Normal development of the nervous system depends upon complex physical interactions between cells and their local environment. These interactions are mediated by several families of cell adhesion molecules (CAMs). Differential expression and function of CAMs are operative in neural tube formation, neuron migration, in post-migratory differentiation, and maintenance of mature neural structure. CAMs also facilitate contact-dependent cell processes, such as formation of cell junctions. Temporal regulation of these molecules during development may provide "windows of vulnerability" to toxicants. In addition to their extracellular binding activities, some CAMs have membrane-spanning domains by which they communicate directly with the cytoskeleton, permitting extracellular signals to be rapidly translated into cell responses via modifications in cytoskeletal organization. These cytologic changes are particularly critical during migration, neurite formation and synaptogenesis. Toxic perturbation of adhesion molecules can have catastrophic effects on morphogenetic processes both directly and via events which depend upon cytoskeletal rearrangement. Toxicants can also act directly upon the cytoskeleton, resulting secondarily in changes of the membrane distribution and function of CAMs. Toxicant-induced changes in CAMs and cytoskeleton may occur contemporaneously. Interference of cell adhesion-cytoskeleton interactions may be a pivotal molecular event dictating developmental consequences of neurotoxicant exposure.
PDF file - 153K, The increase of methylated CpG islands in Cdh1 (E-cadherin) and Gstp1/2 genes in... more PDF file - 153K, The increase of methylated CpG islands in Cdh1 (E-cadherin) and Gstp1/2 genes in prostates bearing the PhIP-induced adenocarinoma
Fundamentals of the structure and function of the nervous system (G.D. Zeevalk). Selective vulner... more Fundamentals of the structure and function of the nervous system (G.D. Zeevalk). Selective vulnerability in the nervous system (T.A. Sarafian, A.M. Verity). Degenerative and regenerative events in the central and peripheral nervous systems (E.D. Hall). Neurotoxicant-induced oxidative events in the nervous system (S. Bondy). Cytoskeletal elements in neurotoxicity (S.J. Pyle). Role of cell signaling in neurotoxicity (L.G. Costa). Cell adhesion molecules as targets of neurotoxicants (K.R. Reuhl, G.B. Grunwald). Neurotransmitter receptors (A.T. Eldefrawi, M. Eldefrawi). Ion channels (T. Narahashi). Phosphoprotein phosphatases as potential mediators of neurotoxicity (E.F. da Cruz e Silva, J.P. O'Callaghan). Myelin and myelinating cells as affected by toxicants (P. Morell, A.D. Toews). Glial cells (M.A. Philbert, M. Aschner). Behavioral screening for neurotoxicity (V.C. Moser). Neural, behavioral, and measurement considerations in the detection of motor impairment (M.C. Newland). Soma...
Pregnant rats were treated on either gestational day (GD) 7, 12, or 17 with single doses of trime... more Pregnant rats were treated on either gestational day (GD) 7, 12, or 17 with single doses of trimethyltin chloride (TMT) ip at either 0, 5, 7, or 9 mg/kg. A significant effect of dose was manifest as decreased maternal weight at term, which persisted during lactation until postnatal day (PND) 15 in some groups. For all treatments combined, term weights of dams exposed on GDs 7 and 12 were greater than those treated on GD 17. Litter sizes were decreased for groups treated on GD 17 with 9 mg/kg TMT. Pups treated in utero and exhibiting treatment-induced decreases in weight at or near birth remained smaller than untreated animals into adulthood (PND 280). By PND 20, weights of pups treated on GD 7 greater than GD 12 greater than GD 17. Neuropathology of pups sacrificed on PND 1 was minimal in all animals with lesions only identified in animals treated on GDs 12 or 17 which consisted of subtle degenerative changes in the CA3 and CA4 regions of Ammon's horn of the hippocampus. Muscarinic cholinergic receptor binding in whole brains from pups on PND 1 did not show any significant changes compared to controls for any dose or day of exposure. These data indicate that prenatal TMT exposure results in postnatal toxicity in treated pups but only in the presence of maternal toxicity.
Brain dysmorphogenesis and persistent psychomotor disturbances are hallmarks of developmental met... more Brain dysmorphogenesis and persistent psychomotor disturbances are hallmarks of developmental methylmercury (MeHg) exposure, but the molecular mechanisms underlying these effects are poorly understood. Targets of developmental MeHg exposure include neural cell adhesion molecules (NCAMs), sialoglycoconjugate molecules whose proper temporal and spatial expression is important at all stages of neurodevelopment and especially during synaptic structuring. To investigate the effects of MeHg on the temporal expression of NCAM during development, rat pups were dosed with 7.0 mg/kg MeHgCl (s.c.) on alternate days from postnatal days (PNDs) 3-13 and killed on PNDs 15, 30 and 60. Brain MeHg concentrations were determined in a subset of litters injected with CH(3)203Hg. Expression of NCAM180 protein and of NCAM180 polysialylation was examined in whole cerebellum homogenates, cerebellar synaptosomes and isolated cerebellar growth cones by Western blotting and immunocytochemical staining. NCAM sialyltransferase activity was assayed in preparations of purified Golgi apparatus from the cerebelli of rats treated in vivo, or following in vitro incubation with 0, 1, 2.5, or 7.5 microM MeHg for 2 h. At PND15, no change in NCAM180 protein expression was observed in any cerebellar preparations, but decreased polysialylation of NCAM180 was observed in cerebellar whole homogenates, synaptosomes and isolated growth cones. At PND30, both NCAM180 protein expression and NCAM180 polysialylation were elevated in whole homogenate preparations but not in synaptosomes. NCAM180 expression in MeHg-treated rats was similar to controls at PND60, 47 days after the last methylmercury administration. In vivo studies of cerebellar Golgi sialyltransferase activity revealed significant reductions in PND15 MeHg-treated rats as compared to controls, but no changes in sialyltransferase activity in PND30 and PND60 animals. In vitro experiments revealed decreasing sensitivity of cerebellar sialyltransferases to MeHg as the developmental age of the rat increased. Toxic perturbation of the developmentally-regulated expression of polysialylated NCAM during brain formation may disturb the stereotypic formation of neuronal contacts and could contribute to the behavioral and morphological disturbances observed following MeHg poisoning.
Tissue samples from the cerebral and cerebellar cortex of neonatal rats which had been prenatally... more Tissue samples from the cerebral and cerebellar cortex of neonatal rats which had been prenatally exposed to low doses of methylmercury were examined by electro.
Female guinea pigs were dosed po with 1.0 mg CH3 203Hg/kg as methylmercuric chloride, 10 times ov... more Female guinea pigs were dosed po with 1.0 mg CH3 203Hg/kg as methylmercuric chloride, 10 times over a 3-week period. Tissue distribution, excretion, and accumulation of inorganic and organic mercury were studied. The highest concentration of mercury was found in the kidney. The greatest decreases of mercury levels were observed in the small bowel, red blood cells, liver, and cerebrum. The half-life of whole body clearance, based on a single compartment model, was 31.6 days. Mercury in the kidney, liver, and cerebrum was bound mainly by nuclear and soluble fractions. The highest ratio of inorganic to total mercury was seen in the kidney, 60% of this being as inorganic mercury. Excretion of mercury in the feces was measured throughout the experiment. The relationship of organic to inorganic mercury was relatively constant at about 1:3. Data on the effects of methyl mercury on tissue concentrations of zinc and copper show that the only change in the copper content was a marked increase in the kidney.
... References. ENVIRONVU.NrAt. RESEARCH 13, 171185 (1977) Ultrastructural Study of the Latent Ef... more ... References. ENVIRONVU.NrAt. RESEARCH 13, 171185 (1977) Ultrastructural Study of the Latent Effects of Methyl Mercury on the Nervous System After Prenatal Exposure Louis W. C1IANc,KENNETH R. REUHt. ... Nucleus (N), rough endoplasmic reticulum (RER). x 14,500 Fi(;. ...
Abstract Rana pipiens tadpoles were allowed to be raised in water containing various concentratio... more Abstract Rana pipiens tadpoles were allowed to be raised in water containing various concentrations of methylmercuric chloride or were injected with 0.025 ml of 0.1% aqueous solutions of methylmercuric chloride (0.025 mg Hg), every other day for 10 days. All the tadpoles which were raised in water containing more than 0.05 ppm mercury died within 48 hours. The distention of the body cavities and eventual death of these tadpoles was believed to be the result of a disturbance of the osmotic regulatory system by the mercury. Total arrest of further development and differentiation was observed in tadpoles which were raised in water containing 0.001–0.01 ppm mercury. Extensive deposition of blood pigment (hemosiderosis) was observed in the livers of the mercury-injected tadpoles. Such hemosiderotic condition was thought to be predisposed by hemolysis of the red blood cells by mercury followed by severe peripheral edema and hemopoietic reactions in the kidneys of these tadpoles.
Cellular heterogeneity and structural complexity of the nervous system, coupled with regional and... more Cellular heterogeneity and structural complexity of the nervous system, coupled with regional and cellular differences in the metabolic capabilities of neurons, glia and other non-neuronal elements, may underlie the selective cellular involvement following exposure to neurotoxicants. Determination of the role of biotransformation of xenobiotics in neural pathoclisis requires an understanding of the cellular distribution of both phase I and phase II enzyme systems in the brain. While ependyma, choroid plexus and endothelial linings of blood vessels throughout the nervous system appear to contain appreciable amounts of several isoforms of cytochrome P450 (CYP450), glia and neurons tend to be highly specific in which forms of CYP450 they express. Regional and cellular heterogeneity similarly characterize the distribution of glutathione (GSH) and the conjugating enzyme glutathione S-transferase (GST) in the brain. While all cells of the embryonic nervous system express high levels of GSH and pi-GST (with lesser amounts of alpha- and mu-class), by adulthood neurons and non-neuronal cells differ in the distribution of GSH and isoforms of GST. Neurons (except the dorsal root ganglia and the cerebellar granule cells) become GSH-negative but contain alpha-, mu-, and pi-GST. Glia, ependyma, choroid plexus and neurovascular cells are rich in GSH and variously express GSTs. The differences found in the cellular distribution of GSH and GSTs may contribute to changes in the vulnerability of the nervous system to neurotoxicants at different ages. A comprehensive understanding of the neurotoxicological and pharmacological consequences of the cellular heterogeneity in the localization the CYP450s and glutathione S-transferases pre- and postnatally will require systematic study of the distribution, substrate specificity, and inducibility of the various isoforms of these enzyme systems.
8 Autism and Oxidative Stress: Evidence from an Animal Model Michelle A. Cheh, 1 Alycia K. Hallad... more 8 Autism and Oxidative Stress: Evidence from an Animal Model Michelle A. Cheh, 1 Alycia K. Halladay, 2, 3 Carrie L. Yochum, 2 Kenneth R. Reuhl, 3 Marianne Polunas, 3 Xue Ming, 4 and George C. Wagner2,* Departments of 1Neuroscience, 2Psychology, and 3Pharmacology ...
Normal development of the nervous system depends upon complex physical interactions between cells... more Normal development of the nervous system depends upon complex physical interactions between cells and their local environment. These interactions are mediated by several families of cell adhesion molecules (CAMs). Differential expression and function of CAMs are operative in neural tube formation, neuron migration, in post-migratory differentiation, and maintenance of mature neural structure. CAMs also facilitate contact-dependent cell processes, such as formation of cell junctions. Temporal regulation of these molecules during development may provide "windows of vulnerability" to toxicants. In addition to their extracellular binding activities, some CAMs have membrane-spanning domains by which they communicate directly with the cytoskeleton, permitting extracellular signals to be rapidly translated into cell responses via modifications in cytoskeletal organization. These cytologic changes are particularly critical during migration, neurite formation and synaptogenesis. Toxic perturbation of adhesion molecules can have catastrophic effects on morphogenetic processes both directly and via events which depend upon cytoskeletal rearrangement. Toxicants can also act directly upon the cytoskeleton, resulting secondarily in changes of the membrane distribution and function of CAMs. Toxicant-induced changes in CAMs and cytoskeleton may occur contemporaneously. Interference of cell adhesion-cytoskeleton interactions may be a pivotal molecular event dictating developmental consequences of neurotoxicant exposure.
PDF file - 153K, The increase of methylated CpG islands in Cdh1 (E-cadherin) and Gstp1/2 genes in... more PDF file - 153K, The increase of methylated CpG islands in Cdh1 (E-cadherin) and Gstp1/2 genes in prostates bearing the PhIP-induced adenocarinoma
Fundamentals of the structure and function of the nervous system (G.D. Zeevalk). Selective vulner... more Fundamentals of the structure and function of the nervous system (G.D. Zeevalk). Selective vulnerability in the nervous system (T.A. Sarafian, A.M. Verity). Degenerative and regenerative events in the central and peripheral nervous systems (E.D. Hall). Neurotoxicant-induced oxidative events in the nervous system (S. Bondy). Cytoskeletal elements in neurotoxicity (S.J. Pyle). Role of cell signaling in neurotoxicity (L.G. Costa). Cell adhesion molecules as targets of neurotoxicants (K.R. Reuhl, G.B. Grunwald). Neurotransmitter receptors (A.T. Eldefrawi, M. Eldefrawi). Ion channels (T. Narahashi). Phosphoprotein phosphatases as potential mediators of neurotoxicity (E.F. da Cruz e Silva, J.P. O'Callaghan). Myelin and myelinating cells as affected by toxicants (P. Morell, A.D. Toews). Glial cells (M.A. Philbert, M. Aschner). Behavioral screening for neurotoxicity (V.C. Moser). Neural, behavioral, and measurement considerations in the detection of motor impairment (M.C. Newland). Soma...
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