氯化甲基汞对秀丽隐杆线虫运动和感觉功能的影响

目的分析神经毒物氯化甲基汞对模式生物秀丽隐杆线虫运动和感觉行为的影响,初步探讨利用秀丽隐杆线虫研究氯化甲基汞神经毒性的可能性。方法采用氯化甲基汞对L1期、L4期幼虫分别急性(30 min)染毒[终浓度分别为0(溶剂对照)~202.5μmol/L和0~1 200μmol/L]和慢性(24 h)染毒[终浓度分别为0(溶剂对照)~80μmol/L和0~150μmol/L]。测定半数致死浓度(LC50)及行为学指标。结果氯化甲基汞致L1期、L4期秀丽隐杆线虫的LC50(30 min)分别为(65.93±8.89)μmol/L和(206.71±35.43)μmol/L,LC50(24 h)分别为(11.59±0.79)μmol/L和(24.89±4.88)μmol/L,L1期秀丽隐杆线虫对氯化甲基汞的毒性较L4期敏感。随着氯化甲基汞暴露剂量的升高,急性和慢性染毒L1期、L4期秀丽隐杆线虫的弯曲频率和头部摆动频率均呈下降的趋势,基本运动能力呈减弱趋势,触碰反应呈迟钝的趋势。结论氯化甲基汞可抑制运动和感觉功能,秀丽隐杆线虫可用于氯化甲基汞神经毒性的研究。     

Mouse extensor digitorum longus muscle preparation as a tool in nutrition research: a quantitative comparison to in vivo and cell culture experiments

Incubated restrained and unrestrained extensor digitorum longus (EDL) muscles from adult non-growing mice were evaluated as a tool in non-steady state nutrition experiments. Energy state was determined by nucleotide determinations in muscles. Protein synthesis was estimated by the amount of L-[U-14C]phenylalanine incorporated into proteins, and protein balance was measured by tyrosine release from muscle proteins. Confluent cultured L6 rat muscle cells served as a reference system in steady state without hypoxia being sensitive to growth factors and regulatory peptides at physiologic concentrations. Irrespective of medium composition, incubated EDL muscles remained in negative protein balance, being unrelated to the resting tension of the incubated muscles. Energy-rich phosphates were not restored to normal levels during incubation, but protein synthesis was not attenuated by the decline in energy state. Fractional protein synthesis (0.05-0.15%/h) remained constant for up to 6 h of EDL incubation, and was comparable to protein synthesis in cultured confluent non-proliferating myocytes (0.20-0.30%/h) and to mixed leg muscles measured in vivo (0.10-0.20%/h). Protein synthesis in incubated EDL muscles reflected alterations in muscle peptide formation in vivo following either oral provision of food or parenteral injection of insulin. EDL muscles were sensitive to in vitro exposure to both insulin (60-125 microU/mL) and insulin-like growth factor 1 (IGF-1) (1000 ng/mL). The sensitivity to insulin seemed to be modified by the nutritional state (starved/fed) of the animals before sacrifice. Protein synthesis in EDL muscles was less responsive to serum-containing growth factors (IGF-1, epidermal growth factor [EGF], platelet-derived growth factor [PDGF]) compared to confluent L6 muscle cells, which probably reflected different receptor expression. Our results demonstrate that protein metabolism in incubated unrestrained mouse EDL muscles reflects in vivo protein metabolism.     

Effects of methylmercury chloride on creatine kinase activity in the rat brain]

The effects of methylmercury chloride (MMC) on creatine kinase (CK) activity in the rat brain were studied. Male Wistar rats were injected subcutaneously with 10 mg MMC/kg body weight/day for 7 consecutive days, and sacrificed on the 15th day when all rats showed a crossing phenomenon of the hind limbs. CK activity was mildly inhibited in the anterior, mid and posterior cerebral cortex. Aspartate aminotransferase and lactate dehydrogenase activities were also inhibited in some parts of the cerebral cortex, almost to the same extent as the CK activity. No definite inhibition of the enzyme activity was found in the striatum and the cerebellum. From this study we concluded that the mild inhibition of CK activity does not seem to play an important role in the genesis of neurotoxicity of MMC.     

2,5-己二酮对大鼠运动及感觉神经元神经生长因子表达的影响

目的　研究正己烷的代谢产物2 ,5 己二酮对大鼠神经系统运动、感觉神经元内源性神经生长因子(NGF)表达的影响。方法　采用原代培养的大鼠背根神经节(DRG)感觉神经元和培养的大鼠脊髓前角运动神经元瘤细胞系VSC4 - 1细胞,用相差显微镜观察细胞形态,同时用免疫组化方法分析不同浓度2 ,5 HD(2 . 5、5 . 0、10 . 0、2 0 . 0mol L)染毒2 4小时后DRG、VSC4 1细胞内NGF含量的变化。结果　与对照组相比,2 ,5 己二酮染毒剂量为5 . 0、10 . 0、2 0 . 0mmol L时,皆可使DRG细胞及VSC4 1细胞NGF表达量显著下降(P <0 . 0 5 ) ;各剂量组间两两比较发现随着染毒剂量增高,两类细胞NGF表达水平的下降有愈为明显的趋势。结论　2 ,5 己二酮可降低大鼠DRG感觉神经元和脊髓前角运动神经元(VSC4 . 1细胞)、内源性NGF的表达水平,并进一步抑制了两类细胞的生长与存活。     

Effects of dietary-fish-oil feeding on muscle growth and damage in the rat

1. Giving diets containing 100 g fully-refined, non-hydrogenated fish oil/kg to rats caused substantial modification of skeletal-muscle-membrane fatty acid composition compared with control animals fed on an equivalent diet containing 100 g maize oil/kg. 2. Total muscle arachidonic acid (20:4 omega 6) was reduced from 138 (SD 25) mg/g total fatty acids to 15 (SD 2) mg/g and phospholipid arachidonic acid content showed equivalent changes. 3. Reduction in muscle arachidonic acid content had no influence on the growth of individual muscles. 4. Variation in muscle fatty acid composition exacerbated the response of muscle to calcium-induced damage assessed by efflux of intracellular creatine kinase (EC 2.7.3.2). 5. It is concluded that metabolites of arachidonic acid are unlikely to be primary controlling factors of muscle growth or specific mediators of muscle sarcolemmal damage leading to enzyme efflux.     

Effects of calcium ionophore on vitamin E-deficient rat muscle

Damage to skeletal muscles may be mediated via free radicals or intracellular calcium overload. To look for inter-relationships between these pathways we have examined the effect of intracellular Ca overload on muscles from rats fed on either a vitamin E-deficient or vitamin E-sufficient diet and assessed the non-enzymic lipid peroxidation in these muscles by examining the production of thiobarbituric acid reactive substances by homogenates. Vitamin E-deficient muscles were more susceptible to Ca-induced intracellular enzyme efflux and this was acutely corrected by supplementation of the external medium with 230 mumol alpha-tocopherol/l. Vitamin E-deficient muscles showed increased levels of basal lipid peroxides and were more susceptible to iron-catalysed lipid peroxidation. Addition of the Ca ionophore A23187 increased lipid peroxidation in vitamin E-deficient muscle homogenates, but had the opposite effect in vitamin E-sufficient muscles. These results demonstrate that vitamin E-deficient muscle has an increased susceptibility to intracellular Ca overload, but that this effect cannot be explained by a direct stimulatory effect of the ionophore on non-enzymic lipid peroxidation.     

Effects of methylmercury chloride on Rana pipiens tadpoles

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.     

Effects of methylmercury on reproduction in American kestrels

Sixty breeding pairs of captive American kestrels (Falco sparverius) were exposed to a range of sublethal dietary concentrations of mercury (Hg), in the form of methylmercuric chloride, and their subsequent reproduction was measured. Egg production, incubation performance, and the number and percent of eggs hatched decreased markedly between 3.3 and 4.6 mg/kg dry weight of Hg (1.2 and 1.7 mg/kg wet wt), in the diet. The number of fledglings and the percent of nestlings fledged were reduced markedly at 0.7 mg/kg dry weight (0.3 mg/kg wet wt) and declined further between 2 and 3.3 mg/kg dry weight (0.7 and 1.2 mg/kg wet wt). Dietary concentrations of >or=4.6 mg/kg dry weight (1.7 mg/kg wet wt) were associated with total fledging failure. The estimated decline in fledged young per pair (24%, Bayesian regression) for kestrels consuming 0.7 mg/kg dry weight (0.3 mg/ kg wet wt) raises concerns about population maintenance in areas subject to high inputs of anthropogenic Hg. Mercury concentrations in 20 second-laid eggs collected from all groups were related to dietary concentrations of Hg, and the Hg concentrations in 19 of these eggs were related to eggs laid and young fledged. Concentrations of Hg in eggs from the highest diet group (5.9 mg/kg dry wt; 2.2 mg/kg wet wt) were higher than egg concentrations reported for either wild birds or for captive birds (nonraptors) fed dry commercial food containing 5 mg/kg methylmercury. Accumulation ratios of Hg from diets to eggs were higher than those reported for feeding studies with other species.     

Effect of methylmercury on the activity of glutathione peroxidase in rat liver

The effect of methylmercury on the activity of glutathione peroxidase in rat liver was studied in vivo. A daily dose of 10mg methylmercuric chloride/kg body weight was administered subcutaneously to 15 male Wistar rats for 10 days, and the glutathione peroxidase activity in the liver was measured to compare with the control activity. A marked decrease was observed in the glutathione peroxidase activity in the experimental animals, which measured as low as 40% in comparison to that in the control animals. It can be speculated that the inhibition of glutathione peroxidase activity plays a significant role in the development of mercury toxicity and that the protective effect of selenium and vitamin E on the mercury intoxication might be partly due to preserving the glutathione peroxidase activity in the antioxidative defense mechanisms.     

Effects of methylmercury on ethanol-induced sleeping time of mice

This study was carried out to clarify the effects of methylmercury intoxication on the ethanol-induced sleeping time of mice. The mice were injected with methylmercury chloride (MMC) (10 mgMMC/kg body weight) subcutaneously for 1, 5 and 10 successive days (1, 5 and 10 inj.), and control mice received only saline. Twenty-four hours, after the last injection, these mice were treated with ethanol (4.5 mgEtOH/kg body weight) intraperitoneally and subsequent sleeping time was observed. After 24 hours, mice were sacrificed to measure the concentration of MMC in various brain regions and liver. A similar experiment with ethanol treatment was also performed to assay the biogenic monoamines in various brain regions and alcohol dehydrogenase (ADH) activity in liver. The results can be summarized as follows: 1) Ethanol-induced sleeping time was 170 min. in the 10 inj. and it was significantly longer than saline, 1 and 5 inj. However, other experimental groups showed no change when compared with saline. 2) Norepinephrine levels increased in white matter and pons + medulla after 1 inj. 3) Dopamine levels increased only in white matter of the 10 inj. when compared with saline. No changes were shown in the other groups. 4) Serotonin levels increased in all the regions after 1 inj. 5) ADH activity in liver did not show any alteration during the experimental period when compared with saline.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of methyl isocyanate on rat muscle cells in culture

Since the Bhopal disaster, in which the causal agent was methyl isocyanate (MIC), exposed people have complained of various disorders including neuromuscular dysfunction. In an attempt to gain some information about the response of muscle tissue to MIC its effects were investigated in cells in culture isolated from muscle of 2 day old rats. After treatment with a range of MIC concentrations (0.025-0.5 microliter/5 ml culture) the total number of nuclei of the two main cell types (fibroblasts and myoblasts) and the number of nuclei in muscle fibres (myotubes) were recorded. At lower doses which had little effect on the total number of nuclei, the formation of muscle fibres--that is, fusion of muscle cells--was prevented as the proportion of nuclei in myotubes was decreased. At higher doses both cell types were killed. This would suggest either an effect on muscle differentiation or a selective toxicity towards myoblasts. The observations were supported by light and electron microscopy.