Biomedical subjects

S C Bondy

Publications and source records attributed to S C Bondy.

At least 73 records · Page 4Linked to original sources

PubMed1991

c-fos and ornithine decarboxylase gene expression in brain as early markers of neurotoxicity.

An increase of proto-oncogene c-fos expression in cerebral cortex of rats treated with subconvulsant doses of the pesticide organochlorine lindane (gamma-hexachlorocyclohexane) has been detected using Northern blots. Immunohistochemical studies show that Fos protein was already increased in neuronal nuclei 3 h after treatment. The administration of the benzodiazepine diazepam prior to lindane totally blocked the activation of this proto-oncogene expression. Parallel to this increased expression of c-fos an activation of the ornithine decarboxylase (ODC) gene and enzyme was also observed. High levels of ODC mRNA and increased enzyme activity in cortex were found in rats following lindane treatment. These changes were attenuated by prior treatment of animals with diazepam. The co-induction of c-fos and ODC suggests a potential link between the ODC/polyamine system and the short-acting proto-oncogenes in stimulus-transcription coupling events.

Animals↗

PubMed1991

Differential effects of difluoromethylornithine on basal and induced activity of cerebral ornithine decarboxylase and mRNA.

The induction of the activity of cerebral ornithine decarboxylase (EC 4.1.1.17) and mRNA by electrical stimulation exhibits regional differences. The effects of the enzyme inhibitor difluoromethylornithine on these regional variations was examined. Administration of this inhibitor resulted in pronounced depression of both basal and induced activity of ornithine decarboxylase in the hippocampus. Basal activity of the enzyme in the neocortex and the cerebellum appeared to be resistant to difluoromethylornithine but the induced enzyme activity was sensitive to the effects of this inhibitor. Susceptibility to difluoromethylornithine may be directly correlated with a slower turnover rate for ornithine decarboxylase. These results suggest that ornithine decarboxylase in the hippocampus may possess a longer half-life than its counterparts in other regions of the brain. Pretreatment with difluoromethylornithine had no effect on the induced ornithine decarboxylase mRNA in the neocortex. Thus, elevated activity of ornithine decarboxylase enzyme, due to electrical stimulation, appears to not have any effect on either the transcription or the decay rate of the induced ornithine decarboxylase mRNA. These findings support the concept of region-specific regulation of cerebral ornithine decarboxylase.

Animals↗

PubMed1991

Subacute exposure to low concentrations of toluene affects dopamine-mediated locomotor activity in the rat.

The effects of low concentrations of toluene (40-80 ppm, 3 days, 6 h/day) were investigated on spontaneous and on apomorphine-induced locomotor activity in the rat, and were correlated to effects on S(-)[N-propyl-3H(N)]-propylnorapomorphine ([3H]NPA) binding in rat neostriatal membranes, on membrane fluidity, membrane leakage, and calcium levels in synaptosomes from the frontoparietal cortex, the neostriatum and the subcortical limbic area, and on serum hormone levels. Toluene exposure (80 ppm, post-exposure delay 18 h) alone did not affect locomotor activity, but attenuated apomorphine-induced (0.05 mg/kg, s.c.) suppression of rearing, and potentiated apomorphine-induced (1 mg/kg, s.c.) increases in locomotion and rearing. Toluene exposure increased the KD value of [3H]NPA binding without affecting the Bmax. All these effects were absent at 40 ppm of toluene or at a post-exposure delay of 42 h. Toluene exposure (80 ppm, post-exposure delay of 18 h) did not affect the serum levels of prolactin, TSH, corticosterone, or aldosterone, or synaptosomal membrane fluidity and calcium levels, whereas membrane leakage was increased in the neostriatum. The present study indicates that the reduction of D-2 receptor affinity by short-term, low-dose toluene exposure is accompanied by a reduced D-2 autoreceptor function and an enhanced postsynaptic D-2 receptor function.

Administration, Inhalation↗

PubMed1991

Disruption of the potential across the synaptosomal plasma membrane and mitochondria by neurotoxic agents.

The effect of a neurotoxic organo-metal, methyl mercuric iodide, and an aromatic solvent, toluene, upon the transmembrane potential (psi), across both the limiting membrane of isolated nerve terminals and their mitochondria, has been studied. Exposure of nerve endings to either of these toxicants in vitro resulted in a dose-dependent diminution of psi that was especially pronounced in the case of mitochondria. This was not prevented by a concurrent exposure to an antioxidant (alpha-tocopherol), or an iron chelator (deferoxamine), or ganglioside GM1. No significant changes were detected in synaptosomal potentials derived from cortices of rats exposed to methyl mercury or toluene at levels known to increase the rate of formation of reactive oxygen species within this region. The special vulnerability of mitochondrial psi to these agents may be due to the disruption of oxidative phosphorylation and may be related to the increase in intrasynaptosomal free ionic calcium that both of these chemicals can induce.

Animals↗

PubMed1991

Persistent protein damage despite reduced oxygen radical formation in the aging rat brain.

The relation between cerebral oxygen radicals and the aging process was investigated in crude synaptosomal (P2) fractions from rats. The rate of formation of oxygen radicals was measured using the probe 2',7'-dichlorofluorescein diacetate (DCFH-DA), which is de-esterified and subsequently oxidized by oxygen radicals to a fluorescent product 2',7'-dichlorofluorescein (DCF). There was a significant age-dependent decrease in the formation rate of oxygen radicals, observed by decreased formation of DCF. No difference in oxygen radical formation was apparent between age groups following an in vitro challenge with an ascorbate/FeSO4 mixture. This age-dependent decrease in cerebral oxygen radical generation coincided with age-dependent increases in superoxide dismutase. No age-related alterations in lipid order in either the hydrophilic or lipophilic membrane regions were observed using fluorescence polarization analysis. Age-dependent losses in cerebral P2 tryptophan fluorescence (a measure of protein degradation), and increased liberation of [14C]protein fragments into the acid-soluble fraction (a measure of overall proteolytic activity) were observed. Results suggest that aging does not proceed as a result of elevated rates of generation of oxygen radicals, a finding that does not support the proposed free radical theory of aging. The observed age-dependent decrease in the formation of oxygen radicals does not effect membrane lipid order. These findings implicate modifications in proteins and activated protein catabolic pathways as major contributing factors in the normal physiological process of senescence.

Aging↗

PubMed1991

Oxygen radical generation as an index of neurotoxic damage.

Biochemical, anatomical, and physiological characteristics of the brain make it especially vulnerable to insult. Specifically, some of these characteristics such as myelin and a high energy requirement provide for the introduction of free radical-induced insult. Recently, the biochemistry of free radicals has received considerable attention. It also has become increasingly suggestive that many drug and chemical-induced toxicities may be evoked via free radicals and oxidative stress. Major points addressed in this work are the regulation of neural-free radical generation by antioxidants and protective enzymes, xenobiotic-induced disruption of cerebral redox status, and specific examples of neurotoxic agent-induced alterations in free radicals as measured by the fluorescent probe dichlorofluorescein. This article considers that free radical mechanisms may contribute significantly to the properties of several diverse neurotoxic agents and proposes that free radicals may be common phenomena of neurotoxicity.

Animals↗

PubMed1990

Prevention of chemically induced changes in synaptosomal membrane order by ganglioside GM1 and alpha-tocopherol.

Synaptosomal membrane order has been studied by analysis of light depolarization by fluorescent dyes intercalated within membranes following exposure to various environmental toxicants. Two probes were explored: 1,6-diphenyl-1,3,5-hexatriene (DPH), signaling predominantly from the lipid-rich membrane core, and 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH), reporting from the more hydrophilic membrane surface. Chlordecone, a neurotoxic insecticide, decreased the anisotropy of either dye and this change could be prevented by prior treatment of synaptosomes with ganglioside GM1 but not alpha-tocopherol. Exposure to an iron-ascorbic acid oxidizing mixture enhanced synaptosomal membrane order and this effect was blocked by preincubation with alpha-tocopherol but not ganglioside GM1. While these interactions may have partially reflected additive anisotropy changes, the protective agents were also effective at concentrations where they did not in themselves modulate membrane order. Methyl mercuric chloride at concentrations up to 100 microM had no discernable effect upon membrane order. It is suggested that these changes in membrane order may underlie some of the previously reported variations in the content of ionic calcium and in the leakiness of synaptosomes.

Animals↗

PubMed1990

Organometal-induced increases in oxygen reactive species: the potential of 2',7'-dichlorofluorescin diacetate as an index of neurotoxic damage.

The effects of the neurotoxic metals methylmercury (MeHg) and trimethyltin (TMT) on oxygen reactive species formation within a crude synaptosomal fraction (P2), using the probe 2',7'-dichlorofluorescin diacetate (DCFH-DA), and intracellular calcium ([Ca2+]i), with the fluorescent indicator fluo-3, have been investigated. Two and seven days after a single injection of MeHg (1 mg/kg) the formation rate of cerebellar oxygen reactive species was significantly increased. Hippocampal and frontocortical oxygen reactive species were elevated 2 days after TMT injection (3 mg/kg). In vitro exposure to MeHg (10-20 microM) increased the formation rate of oxygen reactive species, while TMT (5-40 microM) was without effect. Levels of [Ca2+]i were unaltered in P2 fractions from cerebellum and hippocampus of animals treated with either organometal. The data demonstrate that oxygen reactive species are elevated in brain regions, cerebellum (MeHg) and hippocampus (TMT), believed to be selectively vulnerable to these toxic agents. Findings suggest that oxidative damage may be a mechanism underlying the toxicity of both organometals. The use of DCFH-DA may have potential in the nervous system as an indicator of neurotoxic damage.

Animals↗

PubMed1990

Ganglioside GM1 prevents and reverses toluene-induced increases in membrane fluidity and calcium levels in rat brain synaptosomes.

The effects of exposure to ganglioside GM1 and to toluene in vitro upon synaptosomal integrity have been examined using fluorescence polarization of two probes: 1-[4(trimethylamino)phenyl]-1,3,5-hexatriene (TMA-DPH) and 1,6-diphenyl-1,3,5-hexatriene (DPH) to measure membrane anisotropy, and the fluorescent indicator fura-2 to assay levels of cytosolic calcium [( Ca2+]i). The anisotropy of both TMA-DPH and DPH was decreased by toluene, implying increased membrane fluidity. The decrease in TMA-DPH but not in DPH anisotropy was prevented by pretreatment with GM1 in concentrations as low as 10 microM. This is not an additive interaction since 10 microM of GM1 alone did not significantly modulate TMA-DPH anisotropy. When the GM1 treatment succeeded the addition of toluene the decrease in anisotropy of both probes was reversed. Toluene treatment increased [Ca2+]i in a dose- and time-dependent manner. This increase could partially be both prevented and reversed by treatment with 50 microM of GM1. These effects may reflect an additive interaction, since this concentration of GM1 alone reduced [Ca2+]i. The present results show that toluene increases membrane fluidity and intracellular calcium levels. These effects may be counteracted by the endogenous compound GM1.

Animals↗

PubMed1990

Prevention of chemically induced synaptosomal changes.

The ability of altered environmental conditions to modulate some properties of synaptosomes has been studied. Incubation conditions used included the presence of methyl mercury or an organochlorine insecticide: chlordecone. Other adverse chemical conditions during incubation were the absence of calcium salts from the incubation medium or the addition of agents bringing about enhanced oxidative conditions. Synaptosomal parameters studied were the cytosolic level of free, ionic calcium, [Ca2+]i, the extent of depolarization-induced uptake of radioactive calcium, and the permeability of the limiting membrane. In addition, peroxidative activity was estimated by quantitation of thiobarbituric acid-reactive material. All these facets of synaptosomal function were responsive to the presence of these potentially deleterious changes in the incubation medium. While the response of [Ca2+]i was potentially in either direction, all adverse conditions increased synaptosomal permeability as evaluated by leakage of fura-2 into the extracellular compartment. Pretreatment with ganglioside GM1 in some situations or alpha-tocopherol in others could either wholly or partially prevent the onset of such altered synaptosomal characteristics.

Animals↗

PubMed1990

Electrically stimulated rapid gene expression in the brain: ornithine decarboxylase and c-fos.

A single electroconvulsive shock (ECS) resulted in a major induction of cerebral ornithine decarboxylase (ODC) mRNA and a rapid and transient elevation of ODC enzyme activity. The proto-oncogene c-fos was also transiently induced under the same conditions. Following a rapid rise in mRNA levels, the messages for these proteins take different courses. The c-fos mRNA fell to below control levels by 1 h, while the ODC mRNA remained elevated beyond 24 h. The ECS-induced elevation of ODC enzyme activity was not abolished by adrenalectomy but was attenuated significantly by the anti-convulsant MK-801. These results imply that the induction of cerebral ODC may be neuronal activity dependent, and suggest that the ODC/polyamine system may be linked to the proposed third messenger cascade, involving c-fos, which couples cell stimulation to gene expression, resulting in long-term adaptive responses.

Animals↗

PubMed1990

Cerebral ornithine decarboxylase levels following gestational exposure to cocaine.

The pre- and postnatal developmental course of cerebral ornithine decarboxylase (ODC) has been studied in infant rats after treatment of pregnant dams with cocaine. Levels of cocaine attained in brains and serum of embryos were not initially increased over corresponding maternal values, but were more persistent. However, cocaine was not longer detectable in these tissues 4 days after administration. The cerebral ODC level of treated pups was initially depressed and subsequently elevated relative to control values. These changes were apparent at times when cocaine was not detected in the developing brain. Results indicate that a transient exposure to cocaine in utero may lead to prolonged developmental abnormality.

Aging↗

PubMed1989

Perturbations in cerebral oxygen radical formation and membrane order following vitamin E deficiency.

The effects of dietary vitamin E deficiency on mouse cerebral membrane order and oxygen reactive species were studied. Quantitation of vitamin E levels in several brain regions showed greatest deficiencies in striatum and cerebellum, followed by substantia nigra, and cortex. Vitamin E deficiency increased central-core membrane order in cerebral P2 fraction, but was without effect in the superficial hydrophilic membrane domain. Oxygen radical formation was studied using the probe 2',7'-dichlorofluorescein diacetate. Basal generation rates of oxygen reactive species were 2.5-fold higher when compared to control animals. While hepatic levels of vitamin E are much more reduced than brain levels, in deficient mice, the rate of oxygen radical formation in the liver was unaltered. This implies an special susceptibility of the brain to deficiency of this lipophilic antioxidant vitamin. Data demonstrate that endogenous levels of free radical scavengers, such as vitamin E, may play an important role in maintaining basal oxygen radical levels and membrane integrity. The dietary vitamin E depletion paradigm suggests that a relation exists between elevated levels of oxygen radicals and more rigid hydrophobic central-cores in cerebral membranes, effects that may play a role in mechanisms underlying the neuropathologic lesions observed following vitamin E deficiency.

Animals↗

PubMed1989

Destruction of specific hippocampal cell fields increases ornithine decarboxylase activity: modulation of the biochemical but not the histological changes by ganglioside GM1.

Unilateral injection of colchicine into the dentate gyrus, kainic acid into the CA3 pyramidal cell field, or cerebrospinal fluid into either site produced significant increases in ornithine decarboxylase (ODC) activity in both the injected and noninjected hippocampi. The magnitude as well as the time course of these changes varied with the cytotoxin, the site of injection, and whether or not animals had been pretreated with ganglioside GM1. The ganglioside regimen reduced the ODC response in the injected hippocampus but increased it on the side contralateral to the colchicine injection. In contrast, GM1 enhanced the ODC response produced by kainic acid in the injected but not the uninjected hippocampus. In a subsequent study morphometric analysis of the hippocampus revealed that pretreatment with GM1 did not alter the extent of hippocampal injury induced by either cytotoxin. These data indicate that the changes in ODC activity observed following hippocampal damage represent a complex set of biochemical changes that might serve to protect primary or secondary sites of insult and/or to promote either adaptive or maladaptive neural reorganization. Ganglioside GM1 altered the ODC response without minimizing the histopathological changes induced by the cytotoxins. The role of polyamines in neural, behavioral, and synaptic plasticity is currently under study.

Animals↗

PubMed1989

Increased fragility of neuronal membranes with aging.

Changes in membrane integrity have been implicated as a contributing factor in the aging process. We have examined the relative stability of synaptosomal membranes from young and aged mice, in response to chemically induced damage. The basal characteristics of the resting synaptosomes prepared from mice of either age were indistinguishable, as judged by intracellular levels of ionic calcium and by efflux of the fluorescent probe employed, fura-2. However, the response of isolated nerve endings to the presence of a neurotoxic agent, the insecticide chlordecone, was markedly different. Exposure to this chemical invariably elevated free calcium and increased the rate of leakage of fura-2 into the extracellular space. These effects were much more pronounced in preparations derived from aged animals. The implication of these findings is that neural membranes of aged animals are more susceptible to malfunction induced by xenobiotic agents and are less able to maintain homeostasis under such circumstances.

Aging↗

PubMed1989

Effects of MPTP, MPP+ and paraquat on mitochondrial potential and oxidative stress.

The effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-phenylpyridinium (MPP+) and 1,1-dimethyl-4,4-bipyridinium (paraquat) upon the electrical potential across the plasma and mitochondrial membranes within synaptosomes has been investigated. MPTP selectively depressed plasma membrane potential while MPP+ specifically reduced mitochondrial potential. The structurally similar compound paraquat had no effect on either membrane potential. Enhancement of the lipid peroxidative activity with an Fe-ADP complex depressed both potentials. Paraquat effected increased peroxidative activity in brain homogenates that was less pronounced than that due to Fe-ADP. MPTP reduced basal but stimulated Fe-ADP enhanced peroxidation. The mechanisms underlying the toxicity of MPP+ are likely to differ from those of paraquat, primarily involving impaired mitochondrial function rather than increased oxidative stress.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1989

Triethyllead-induced peroxidative damage in various regions of the rat brain.

Adult male Fisher 344 rats (8-10 wk old) were dosed ip with 1.75 mg/kg body weight of triethyllead chloride (TEL) for 5 consecutive days. Rats were sacrificed 1, 7, or 21 d after the last injection. The rate of lipid peroxidation was significantly elevated in frontal cortex at all three time points assayed (1, 7, or 21 d). However, hippocampal and cerebellar membranes showed no changes in peroxidative capacity at these time points. In order to determine whether cortical membrane damage was reflected in alteration of a restricted protein population, a series of high-affinity receptor binding sites was determined in cortical membranes derived from treated rats 7 d after the last injection of triethyllead. The rate of lipid peroxidation was significantly increased in the frontal cortex of triethyllead treated rats; however, no changes in the binding of [3H]spiroperidol, [3H]quinuclidinyl benzilate, and [3H]benzodiazepine were seen in animals exposed to triethyllead. The cortical wet weight, protein content, and cell number were also unchanged by TEL treatment, reflecting an absence of gross damage.

Animals↗

PubMed1989

Effects of gestational exposure to phencyclidine: distribution and neurochemical alterations in maternal and fetal brain.

Phencyclidine is a widely used drug of abuse and is known to produce a wide variety of psychoactive effects. PCP abuse by pregnant women has been reported to result in the birth of infants exhibiting irritability, jitteriness and hyperactivity with high pitched cries. The present study was designed to evaluate the distribution of PCP in the maternal and fetal brain and the neurochemical effects produced by gestational exposure. Pregnant Sprague-Dawley rats were treated sc with 5 mg/kg PCP on 3 consecutive days (GD 9-11, 12-14, 15-16, or 18-20). On gestational day (GD) 21 all rats were killed by decapitation and maternal and fetal blood was collected for PCP analysis. Brains were dissected from dams and fetuses for PCP and neurochemical analyses. On GD 21 after exposure on GD 18-20, the fetal: maternal ratio of brain PCP concentrations was 11:1. PCP exposure on GD 12-14, 15-17, and 18-20 significantly decreased fetal brain PCP binding sites on GD 21, whereas maternal values were unchanged. Fetal dopaminergic and muscarinic cholinergic receptor binding and neurotransmitter concentrations were unaffected by prenatal PCP exposure. These data demonstrated that maternal PCP exposure resulted in prolonged exposure of the developing CNS and also indicated that gestational exposure to PCP decreased high affinity binding sites of PCP in term fetal brain.

Animals↗