Conditioned taste aversion induced by inhalation exposure to methyl bromide in rats

The toxic effect of methyl bromide vapor was assessed by a conditioned taste aversion regime. Rats kept under a water deprivation schedule for 7 days, were permitted access to 0.3% (w/v) sodium saccharin, and were exposed to methyl bromide at 0, 25, 50, and 100 ppm for 4 h. 3 days after the exposure, saccharin preference tests were carried out, revealing dose-dependent saccharin aversion in the exposure group. This result suggests that the conditioned taste aversion method is effective for assessing the toxicity of gaseous substances such as methyl bromide.     

Neurophysiological and psychological disorders and occupational exposure to organic solvents

A number of reports, particularly from Scandinavian countries, claim that painters and workers in other trades in which prolonged occupational exposure to organic solvents may occur develop a type of mental illness characterized principally by impairment of memory and co-ordination and some deterioration of personality. The condition, called 'organic solvent disease', is recognized as a cause of premature retirement and is classed as an occupational disease in certain countries. The conclusions of these reports have been contested and the existence of such a disease entity has been questioned. The publications reporting adverse neurological, neurophysiological and psychological disorders in solvent-exposed workers, and the methods used to determine adverse effects, have therefore been evaluated. In addition, data from animal behavioural studies have been examined but were found to have little or no to have little or no relevance to the reported human disease. The human data indicate that, of the solvents studied, only CS2 provided clear evidence of neurotoxic damage detectable by clinical and pathological examination as well as by neurophysiological measurements (e.g. nerve conduction velocity and nerve action potentials) or neuropsychological techniques (e.g. Rorschach inkblot test and WAIS intelligence tests). In the case of several other solvents and mixtures of solvents commonly used in industry, the evidence of CNS impairment, based principally on the response to questionnaires and the results of neuropsychological and neurophysiological examinations was questionable. A critical evaluation of the reliability of these methods in detecting minor deviations from normal and of their ability to provide acceptable evidence of CNS dysfunction or damage leaves little doubt that these methods are of value in investigating personality, intelligence and memory in the clinical examination of individual patients. However, evidence indicates that they are not suitable for use in epidemiological studies, principally because the variability of response in normal individuals is ill-defined and insufficiently investigated. The same conclusion was arrived at in evaluating the contribution of electroencephalography, computerized axial tomography scanning and other electrophysiological examinations to the diagnosis of brain changes in groups of solvent-exposed and unexposed workers. Furthermore, the personality changes identified (by neuropsychological tests) in painters and other workers exposed to solvents could well be produced by ageing, exposure to lead or mercury, excessive alcohol intake, psychoactive drugs or the ordinary stresses of everyday life.(ABSTRACT TRUNCATED AT 400 WORDS)     

Coumarins and related compounds in members of the connaraceae

Members of the Cnestis, Agelea and Byrsocarpus genera (Connaraceae) examined, viz. C. corniculatus, C. ferruginea, A. nitida, A. obliqua, A. trifolia and B. coccineus, all of which are toxic to rabbits, contained dicoumarol and 4-hydroxycoumarin, the concentration of dicoumarol being relatively low in fresh leaves. Coumarin and a glycoside of coumaric acid were also present in some species. The production of dicoumarol may be due to the presence of a micro-organism, since it was present in higher concentration in mouldy leaves.     

Development of an animal model of solvent abuse for use in evaluation of extreme tricholoroethyylene inhalation

Self-intoxication by inhalation of vapors of trichloroethylene (TCE) and other solvents in widespread. In order to develop exposure protocols which typify episodes of TCE “sniffing”, male Wistar-Munich rats were exposed to TCE vapor levels ranging from 9000 to 16 000 ppm. TCE in concentrations of 14 000 ppm and greater quickly produced loss of righting reflex. Recovery from the narcosis was very rapid. Central nervous system (CNS) depression was found to be cumulative in rats subjected for 5 h to alternating periods of 5 min of 15 000 ppm TCE and 15 min of fresh air. Ethanol markedly potentiated depression in these subjects. No evidence of liver or kidney damage was seen in rats subjected to the repetitive 5-h TCE inhalation regimen, nor in rats fasted for 16 h before the TCE-exposure session. Oral admnistration of 5 ml/kg body wt of ethanol 1 h, 16 h, or once daily for 3 days before the TCE-exposure regimen had little if any potentiating effect on hepatorenal toxicity potential. Animals that received ethanol and were fasted before TCE exposure exhibited slight elevations in SGOT and SGPT levels.     

Effects of acrylamide given during gestation on dopamine receptor binding in rat pups

Acrylamide (20 $\text{mg}\text{kg}$) was administered by gavage to time-pregnant Fischer 344 rats daily from day 7 to day 16 of gestation. Acrylamide did not affect the number, size, or body weights of litters obtained but did decrease the [³H]spiroperidol binding in striatal membranes of 2-week-old pups. This effect could not be seen at 3 weeks of age. Scatchard analysis showed that acrylamide changed the affinity as well as the number of dopamine receptor sites. There were no signs of maternal toxicity in dosed mothers as evaluated by their body weights or general appearance.     

Changes in free amino acid contents of rat brain induced by exposure to methyl bromide

Rats were exposed to methyl bromide (MB) for 24 h at 10–120 ppm or for 3 weeks at 1–10 ppm. Changes in free amino acid contents of rat midbrain were measured by high-performance liquid chromatography (HPLC). MB increased glutamine and aspartic acid contents dose-dependently by short- and long-term exposure. Alanine content was markedly increased by long-term exposure to 10 ppm MB. Glycine was dose-dependently increased, except at 120 ppm. The harmful effect of MB on the central nervous system is discussed in relation to the changes in amino acid metabolism.     

Effects of ddt on muscarine- and nicotine-like binding sites in cns of immature and adult mice

Immature (10 days of age) and adult (60 days of age) mice were given a single peroral administration of 0.5 mg p,p'-DDT/kg body wt. or a fat emulsion vehicle. The mice were killed 24 h or 7 days post-treatment and the muscarine- and nicotine-like binding sites were measured in the cerebral cortex and in the cerebellum using [³H]quinuclidinyl benzilate ([³H]QNB) and [³H]α-bungarotoxin ([³H]α-BTX), respectively, as ligands. A significant decrease in the [³H]QNB binding to the muscarine-like receptors in the cerebral cortex was seen in the 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT)-treated adults after 7 days. The effects on the muscarine-like receptors appeared to be different in the immature mice compared to the adults, showing an increase between 24 h and 7 days post-treatment in the immature and a decrease in the adults. No change was seen on the nicotine-like receptors.     

不同剂量丙泊酚对大鼠脑内血红素氧化酶-2活性的影响

目的 :研究不同剂量丙泊酚对大鼠脑内血红素氧化酶 2 (HO 2 )活性的影响。方法 :正常SD大鼠 2 4只 ,随机分为 4组 :对照组 ,丙泊酚小、中、大剂量组 ,每组各 6只 ,依次腹腔注射生理盐水 10mL·kg- 1、丙泊酚 5 0 ,10 0 ,2 0 0mg·kg- 1。应用免疫组织化学方法 ,光镜观察丙泊酚麻醉大鼠小脑、端脑和脑桥HO 2阳性神经元的分布。并采用计算机彩色图像分析仪测定各组HO 2阳性细胞数或阳性产物面积。结果 :(1)大鼠脑内HO 2阳性神经元分布广泛。 (2 )腹腔注射丙泊酚各剂量组能明显抑制大鼠脑内HO 2活性。结论 :丙泊酚可能抑制大鼠脑内HO 2活性     

Sub-chronic toxicity of low concentrations of industrial volatile organic pollutants in vitro

Organic solvents form an important class of pollutants in the ambient air and have been associated with neurotoxicity and immunotoxicity in humans. Here we investigated the biological effects of sub-chronic exposure to industrially important volatile organic solvents in vitro. Jurkat T cells were exposed to toluene, n-hexane and methyl ethyl ketone (MEK) individually for 5 days and solvent exposure levels were confirmed by headspace gas chromatography. A neuroblastoma cell line (SH-SY5Y) was exposed to toluene for the same period. Following exposure, cells were harvested and toxicity measured in terms of the following endpoints: membrane damage (LDH leakage), perturbations in intracellular free Ca(2+), changes in glutathione redox status and dual-phosphorylation of MAP kinases ERK1/2, JNK and p38. The results show that sub-chronic exposure to the volatile organic solvents causes membrane damage, increased intracellular free calcium and altered glutathione redox status in both cell lines. However, acute and sub-chronic solvent exposure did not result in MAP kinase phosphorylation. Toxicity of the solvents tested increased with hydrophobicity. The lowest-observed-adverse-effect-levels (LOAELs) measured in vitro were close to blood solvent concentrations reported for individuals exposed to the agents at levels at or below their individual threshold limit values (TLVs).     

In vitro effects of acetylcholinesterase reactivators on monoamine oxidase activity

Administration of acetylcholinesterase (AChE) reactivators (oximes) is usually used in order to counteract the poisoning effects of nerve agents. The possibility was suggested that oximes may show some therapeutic and/or adverse effects through their action in central nervous system. There are no sufficient data about interaction of oximes with monoaminergic neurotransmitter's systems in the brain. Oxime-type AChE reactivators pralidoxime, obidoxime, trimedoxime, methoxime and HI-6 were tested for their potential to affect the activity of monoamine oxidase of type A (MAO-A) and type B (MAO-B) in crude mitochondrial fraction of pig brains. The compounds were found to inhibit fully MAO-A with half maximal inhibitory concentration (IC₅₀) of 0.375 mmol/l (pralidoxime), 1.53 mmol/l (HI-6), 2.31 mmol/l (methoxime), 2.42 mmol/l (obidoxime) and 4.98 mmol/l (trimedoxime). Activity of MAO-B was fully inhibited by HI-6 and pralidoxime only with IC₅₀ 4.81 mmol/l and 11.01 mmol/l, respectively. Methoxime, obidoxime and trimedoxime displayed non-monotonic concentration dependent effect on MAO-B activity. Because oximes concentrations effective for MAO inhibition could not be achieved in vivo at the cerebral level, we suppose that oximes investigated do not interfere with brain MAO at therapeutically relevant concentrations.     

Effects of toluene inhalation on brain biogenic amines in the rat

The effects of toluene exposure on the biogenic amine concentrations in the central nervous system were investigated in the rat. Toluene was administered via inhalation to groups of rats at concentrations of 0, l00, 300, or 1000 ppm. After an 8-h continuous exposure, animals were sacrificed and whole brain concentrations of dopamine (DA), norepinephrine (NE), and 5-hydroxytryptamine (5-HT) were determined. The data indicated a significant increase in whole brain concentrations of DA following the 100-ppm exposure. A regional analysis of DA, NE, and 5-HT concentrations in rats exposed to 1000 ppm of toluene for 8-h indicated a significant increase in DA concentration in the striatum. A significant increase in NE concentrations was detected in the medulla and midbrain while 5-HT concentrations were significantly increase in the cerebellum, medulla, and striatum. The results indicate that toluene action results in elevated concentrations of behaviorally significant neuro-transmitters.     

Behavioral modulation of neuronal calcium/calmodulin-dependent protein kinase II activity: differential effects on nicotine-induced spinal and supraspinal antinociception in mice

Recent studies have implicated the involvement of Ca(2+)-dependent mechanisms, in particular calcium/calmodulin-dependent protein kinase II (CaM kinase II) in nicotine-induced antinociception using the tail-flick test. The spinal cord was suggested as a possible site of this involvement. The present study was undertaken to investigate the hypothesis that similar mechanisms exist for nicotine-induced antinociception in the hot-plate test, a response thought to be centrally mediated. In order to assess these mechanisms, i.c.v. administered CaM kinase II inhibitors were evaluated for their effects on antinociception produced by either i.c.v. or s.c. administration of nicotine in both tests. In addition, nicotine's analgesic effects were tested in mice lacking half of their CaM kinase II (CaM kinase II heterozygous) and compare it to their wild-type counterparts. Our results showed that although structurally unrelated CaM kinase II inhibitors blocked nicotine's effects in the tail-flick test in a dose-related manner, they failed to block the hot-plate responses. In addition, the antinociceptive effects of systemic nicotine in the tail-flick but not the hot-plate test were significantly reduced in CaM kinase II heterozygous mice. These observations indicate that in contrast to the tail-flick response, the mechanism of nicotine-induced antinociception in the hot-plate test is not mediated primarily via CaM kinase II-dependent mechanisms at the supraspinal level.     

Effect of alcohol intake on some disturbances induced by chronic exposure to carbon disulphide in rats. I. Behavioural alterations

Female white Wistar rats were exposed to CS2 vapour (0.8 mg CS2/1 air) 11 months and to 10% ethanol as the only drinking liquid for the last 3 months of exposure. Spontaneous exploratory motor activity (SEMA), open-field behaviour, passive avoidance performance and the avoidance acquisition were tested. Ethanol did not change the exploratory motor activity and behaviour of CS2-exposed rats in the open-field and passive avoidance tests but it affected their performance in the conditioned avoidance test. The analysis of data suggests that ethanol may adversely affect memory and learning ability in CS2-exposed rats.     

Metabolomics analysis reveals elevation of 3-indoxyl sulfate in plasma and brain during chemically-induced acute kidney injury in mice: investigation of nicotinic acid receptor agonists

An investigative renal toxicity study using metabolomics was conducted with a potent nicotinic acid receptor (NAR) agonist, SCH 900424. Liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) techniques were used to identify small molecule biomarkers of acute kidney injury (AKI) that could aid in a better mechanistic understanding of SCH 900424-induced AKI in mice. The metabolomics study revealed 3-indoxyl sulfate (3IS) as a more sensitive marker of SCH 900424-induced renal toxicity than creatinine or urea. An LC-MS assay for quantitative determination of 3IS in mouse matrices was also developed. Following treatment with SCH 900424, 3IS levels were markedly increased in murine plasma and brain, thereby potentially contributing to renal- and central nervous system (CNS)-related rapid onset of toxicities. Furthermore, significant decrease in urinary excretion of 3IS in those animals due to compromised renal function may be associated with the elevation of 3IS in plasma and brain. These data suggest that 3IS has a potential to be a marker of renal and CNS toxicities during chemically-induced AKI in mice. In addition, based on the metabolomic analysis other statistically significant plasma markers including p-cresol-sulfate and tryptophan catabolites (kynurenate, kynurenine, 3-indole-lactate) might be of toxicological importance but have not been studied in detail. This comprehensive approach that includes untargeted metabolomic and targeted bioanalytical sample analyses could be used to investigate toxicity of other compounds that pose preclinical or clinical development challenges in a pharmaceutical discovery and development.     

Effects of Resibufogenin and Cinobufagin on voltage-gated potassium channels in primary cultures of rat hippocampal neurons

Outward delayed rectifier potassium channel and outward transient potassium channel have multiple important roles in maintaining the excitability of hippocampal neurons. The present study investigated the effects of two bufadienolides, Resibufogenin (RBG) and Cinobufagin (CBG), on the outward delayed rectifier potassium current (I_K) and outward transient potassium current (I_A) in rat hippocampal neurons. RBG and CBG have similar structures and both were isolated from the venom gland of toad skin. RBG inhibited both I_K and I_A, whereas CBG inhibited I_K without noticeable effect on I_A. Moreover, at 1 μM concentration both RBG and CBG could alter some channel kinetics and gating properties of I_K, such as steady-state activation and inactivation curves, open probability and time constants. These findings suggested that I_K is probably a target of bufadienolides, which may explain the mechanisms of bufadienolides’ pathological effects on central nervous system.     

Evaluation of the cytotoxicity of 10 chemicals in human and rat hepatocytes and in cell lines: Correlation between in vitro data and human lethal concentration

The cytotoxicity of 10 chemicals from the Multicentre Evaluation of In vitro Cytotoxicity (MEIC) list (nos 21–30) was evaluated in human and rat cultured hepatocytes and in two established cell lines (HepG2 and 3T3) according to the MEIC programme organized by the Scandinavian Society of Cell Toxicology. The MTT test was used as the endpoint of cytotoxicity after 24hr of exposure to the chemicals. Theophylline, phenobarbital and paraquat were the least cytotoxic compounds in the cellular systems (IC₅₀ = 450-17,000 μm) except for the 3T3 cells. The seven remaining chemicals (dextropropoxyphene, propranolol, arsenic trioxide, cupric sulfate, mercuric chloride, thioridazine and thallium sulfate) showed a similar relative cytotoxic ranking in the four in vitro systems in the lower range of concentrations (IC₅₀ = 2–350 μm). The data suggest that these 10 chemicals have a basal cytotoxic effect common to the four in vitro systems, and probably none of these compounds could be considered either hepatotoxic or species specific. The correlation between in vitro data and human lethal blood concentrations showed that the predictability of the in vitro systems was similar to that of in vivo rodent tests (LD₅₀) only when low cytotoxic concentrations (IC₁₀) were used for correlation.     

Acute toxicologic and neurotoxic effects of inhaled 1,2-dichloroethane in adult Fischer 344 rats

Acute toxicologic and neurotoxic effects were evaluated in Fischer 344 rats exposed to 0, 50, 200, 600, or 2000 ppm 1,2-dichloroethane (ethylene dichloride; EDC) for 4 h or 0, 50, 100 or 150 ppm for 8 h. Neurobehavioral and neuropathologic effects were assessed using a functional observational battery (FOB; baseline, days 1, 8, and 15), and by light microscopy, respectively. Acute toxicologic effects were assessed by bronchoalveolar lavage (BAL) and histopathology of the respiratory tract and selected target organs. Neurobehavioral effects consistent with central nervous system (CNS) depression were present at concentrations >200 ppm and were restricted to day 1. There were no neuropathologic changes in the CNS, however, olfactory epithelial regeneration 15 days after exposure to ?200 ppm was observed. The no-observed-effect concentration (NOEC) for behavioral neurotoxicity was 200 ppm EDC for 4 h. There were no effects on BAL parameters in any exposure group. Exposure to 2000 ppm EDC altered adrenal gland, kidney, and liver weights, and resulted in morphologic alterations in the kidney and liver. Degeneration/necrosis of the olfactory epithelium was observed at ?200 ppm for 4 h and ?100 ppm for 8 h. Based on olfactory epithelial degeneration/necrosis, the most sensitive indicator of toxicity in this study, the overall NOEC was 50 ppm EDC for up to 8 h in rats.     

Effect of P-glycoprotein-mediated efflux on cerebrospinal fluid concentrations in rhesus monkeys

Brain penetration of drugs which are subject to P-glycoprotein (Pgp)-mediated efflux is attenuated, as manifested by the fact that the cerebrospinal fluid concentration (C_CSF), a good surrogate of the unbound brain concentration (C_ub), is lower than the unbound plasma concentration (C_up) for Pgp substrates. In rodents, the attenuation magnitude of brain penetration by Pgp-mediated efflux has been estimated by correlating the ratio of CSF to plasma exposures (C_CSF/C_p) with the unbound fraction in plasma (f_u) upon the incorporation of the in vivo or in vitro Pgp-mediated efflux ratios (ERs). In the present work, we investigated the impact of Pgp-mediated efflux on C_CSF in monkeys. Following intravenous administration to cisterna magna ported rhesus monkeys, the CSF and plasma concentrations were determined for 25 compounds from three discovery programs. We also evaluated their f_u in rhesus plasma and ER in human and African green monkey MDR-transfected LLC-PK1 cells. These compounds varied significantly in the f_u (0.025-0.73), and 24 out of 25 are considered Pgp substrates based on their appreciable directional transport (ER > 2). The C_CSF/C_p was significantly lower than the corresponding f_u (≥3-fold) for 16 compounds regardless of a significant correlation (R² = 0.59, p = 4 × 10⁻⁵) when the C_CSF/C_p was plotted against the f_u. When the f_u was normalized to the ER (f_u/ER) the correlation was improved (R² = 0.75, p = 8 × 10⁻⁸). More importantly, only one compound showed the C_CSF/C_p that exceeded 3-fold of the normalized f_u. The results suggest that the impact of Pgp-mediated efflux in monkeys, similar to the case in rodents, is reasonably reflected by the gradient between the free concentrations in plasma and in CSF. Therefore, f_u and Pgp ER may serve as useful measurements in estimating in vivo C_CSF/C_p ratios in monkeys, and potentially in humans.     

Effects of enhancing mitochondrial oxidative phosphorylation with reducing equivalents and ubiquinone on 1-methyl-4-phenylpyridinium toxicity and complex I-IV damage in neuroblastoma cells

The effects of increasing mitochondrial oxidative phosphorylation (OXPHOS), by enhancing electron transport chain components, were evaluated on 1-methyl-4-phenylpyridinium (MPP+) toxicity in brain neuroblastoma cells. Although glucose is a direct energy source, ultimately nicotinamide and flavin reducing equivalents fuel ATP produced through OXPHOS. The findings indicate that cell respiration/mitochondrial O(2) consumption (MOC) (in cells not treated with MPP+) is not controlled by the supply of glucose, coenzyme Q(10) (Co-Q(10)), NADH+, NAD or nicotinic acid. In contrast, MOC in whole cells is highly regulated by the supply of flavins: riboflavin, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), where cell respiration reached up to 410% of controls. In isolated mitochondria, FAD and FMN drastically increased complex I rate of reaction (1300%) and (450%), respectively, having no effects on complex II or III. MPP+ reduced MOC in whole cells in a dose-dependent manner. In isolated mitochondria, MPP+ exerted mild inhibition at complex I, negligible effects on complexes II-III, and extensive inhibition of complex IV. Kinetic analysis of complex I revealed that MPP+ was competitive with NADH, and partially reversible by FAD and FMN. Co-Q(10) potentiated complex II ( approximately 200%), but not complex I or III. Despite positive influence of flavins and Co-Q(10) on complexes I-II function, neither protected against MPP+ toxicity, indicating inhibition of complex IV as the predominant target. The nicotinamides and glucose prevented MPP+ toxicity by fueling anaerobic glycolysis, evident by accumulation of lactate in the absence of MOC. The data also define a clear anomaly of neuroblastoma, indicating a preference for anaerobic conditions, and an adverse response to aerobic. An increase in CO(2), CO(2)/O(2) ratio, mitochondrial inhibition or O(2) deprivation was not directly toxic, but activated metabolism through glycolysis prompting depletion of glucose and starvation. In conclusion, the results of this study indicate that the mechanism of action for MPP+, involves the inhibition of complex I and and more specifically complex IV, leading to impaired OXPHOS and MOC. Moreover, flavin dervatives control the rate of complex I/cellular respiration and Co-Q10 augments complex II [corrected].     

Quantitative prediction of histamine H1 receptor occupancy by the sedative and non-sedative antagonists in the human central nervous system based on systemic exposure and preclinical data

Significant histamine H1 receptor occupation in the central nervous system (CNS) is associated with sedation. Here we examined the time profiles of the H1 receptor occupancy (RO) in the CNS using sedative (diphenhydramine and ketotifen) and non-sedative (bepotastine and olopatadine) antagonists at their therapeutic doses by integrating in vitro and animal data. A pharmacokinetic model was constructed to associate plasma concentrations and receptor binding in the brain. Dissociation and association rate constants with the H1 receptor and plasma and brain unbound fractions were determined in vitro. Passive and active clearances across the blood–brain barrier (BBB) were estimated based on physicochemical properties and microdialysis studies in mice and monkeys. The estimated RO values were comparable with the reported values determined at time to maximum concentration (T_max) of plasma by positron-emission tomography in humans. The simulation suggested that the predicted maximum ROs by bepotastine and olopatadine were greater than the reported values. Sensitivity analysis showed that active transport across BBB had a significant impact on the RO duration of the H1 antagonists examined. The present study demonstrated that modeling and simulation permits a reasonable RO estimation in the human CNS. Our findings will facilitate the development of CNS-acting drugs.