Effect of U and 137Cs chronic contamination on dopamine and serotonin metabolism in the central nervous system of the rat

A comparative study of the typical toxic metals in serum by patients of schizophrenia and healthy controls in China

Toxic metals are ubiquitous environmental pollutants, and their potential risks associated with the development of schizophrenia remain a subject of debate. In this study, we investigated the associations between six typical toxic metals (mercury, lead, chromium, silver, antimony, and uranium) in serum with the risk of schizophrenia using a case-control study design. In total, 109 patients with schizophrenia (cases) and 106 normal subjects (controls) from Shandong Province, China were recruited. Fasting blood samples were collected from all participants, as well as serum samples from the cases before and after medical treatment. The six metals were analyzed by inductively coupled plasma mass spectrometry. Only three metals (antimony, silver and uranium) had acceptable detection rates of >80%. The concentrations of antimony and uranium were significantly higher in the cases than in the controls, while no significant difference for silver. Moreover, the serum concentrations of antimony and uranium were significantly lower after medical treatment. Clear dose-response relationships between serum metal concentrations and the risk of schizophrenia were observed, even after adjusting for potential covariates. This suggests that higher levels of antimony and uranium may be one of the factors associated with an elevated risk of schizophrenia.

The neurotoxicology of uranium

The brain is a target of environmental toxic pollutants that impair cerebral functions. Uranium is present in the environment as a result of natural deposits and release by human applications. The first part of this review describes the passage of uranium into the brain, and its effects on neurological functions and cognitive abilities. Very few human studies have looked at its cognitive effects. Experimental studies show that after exposure, uranium can reach the brain and lead to neurobehavioral impairments, including increased locomotor activity, perturbation of the sleep-wake cycle, decreased memory, and increased anxiety. The mechanisms underlying these neurobehavioral disturbances are not clearly understood. It is evident that there must be more than one toxic mechanism and that it might include different targets in the brain. In the second part, we therefore review the principal mechanisms that have been investigated in experimental models: imbalance of the anti/pro-oxidant system and neurochemical and neurophysiological pathways. Uranium effects are clearly specific according to brain area, dose, and time. Nonetheless, this review demonstrates the paucity of data about its effects on developmental processes and the need for more attention to the consequences of exposure during development.

Toxicity studies on depleted uranium in primary rat cortical neurons and in Caenorhabditis elegans: what have we learned?

Depleted uranium (DU) is the major by-product of the uranium enrichment process for its more radioactive isotopes, retaining approximately 60% of its natural radioactivity. Given its properties as a pyrophoric and dense metal, it has been extensively used in armor and ammunitions. Questions have been raised regarding the possible neurotoxic effects of DU in humans based on follow-up studies in Gulf War veterans, where a decrease in neurocognitive behavior in a small population was noted. Additional studies in rodents indicated that DU readily traverses the blood-brain barrier, accumulates in specific brain regions, and results in increased oxidative stress, altered electrophysiological profiles, and sensorimotor deficits. This review summarizes the toxic potential of DU with emphasis on studies on thiol metabolite levels, high-energy phosphate levels, and isoprostane levels in primary rat cortical neurons. Studies in Caenorhabditis elegans detail the role of metallothioneins, small thiol-rich proteins, in protecting against DU exposure. In addition, recent studies also demonstrate that only one of the two forms, metallothionein-1, is important in the accumulation of uranium in worms.

Comparison of the effects of enriched uranium and 137-cesium on the behaviour of rats after chronic exposure

PURPOSE

A radionuclide that accumulates in the central nervous system is likely to exert both a chemical and a radiological effect. The present study aimed at assessing the behavioral effect of two radionuclides previously shown to accumulate in the central nervous system after chronic exposure--uranium and cesium.

MATERIALS AND METHODS

Rats were exposed for 9 months to drinking water contaminated with either enriched uranium at a dosage of 40 mg U x l(-1) or 137-cesium at a dosage of 6500 Bq x l(-1), which correspond to the highest concentrations measured in some wells in the south of Finland (uranium) or in the milk in Belarus in the year following the Chernobyl accident (137-cesium).

RESULTS

At this level of exposure, 137-cesium had no effect on the locomotor activity measured in an open-field, on immobility time in a forced swimming test, on spontaneous alternation in a Y-maze and on novel object exploration in an object recognition test. Enriched uranium exposure specifically reduced the spontaneous alternation measured in the Y-maze after 3 and 9 months exposure although it did not affect the other parameters.

CONCLUSION

Enriched uranium exposure altered the spatial working memory capacities and this effect was correlated with previously described accumulation of uranium in the hippocampus which is one of the cerebral areas involved in this memory system.

Chronic contamination of rats with 137 cesium radionuclide: impact on the cardiovascular system

Cardiovascular system impairment has been observed in children and in liquidators exposed to the Chernobyl nuclear power plant accident. No experimental studies of animals have analyzed whether these disorders might be attributed to chronic ingestion of low levels of cesium 137 ((137)Cs). Biochemical, physiological, and molecular markers of the cardiovascular system were analyzed in rats exposed through drinking water to (137)Cs at a dose of 500 Bq kg(-1) (6500 Bq l(-1)). Plasma concentrations of CK and CK-MB were higher (+52%, P < 0.05) in contaminated rats. No histological alteration of the heart was observed, but gene expression was modified in the atria. Specifically, levels of ACE (angiotensin converting enzyme) and BNP (brain natriuretic peptide) gene expression increased significantly (P < 0.05). ECG analysis did not disclose any arrhythmia except ST- and RT-segment shortening (-9% and -11%, respectively, P < 0.05) in rats exposed to (137)Cs. Mean blood pressure decreased (-10%, P < 0.05), and its circadian rhythm disappeared. Overall, chronic contamination by an extreme environmental dose of (137)Cs for 3 months did not result in cardiac morphological changes, but the cardiovascular system impairments we observed could develop into more significant changes in sensitive animals or after longer contamination.

Neurotoxic Potential of Depleted Uranium—Effects in Primary Cortical Neuron Cultures and in Caenorhabditis elegans

Depleted uranium (DU) is an extremely dense metal that is used in radiation shielding, counterbalances, armor, and ammunition. In light of the public concerns about exposure to DU and its potential role in Gulf War Syndrome (GWS), this study evaluated the neurotoxic potential of DU using focused studies on primary rat cortical neurons and the nematode Caenorhabditis elegans. We examined cell viability, cellular energy metabolism, thiol metabolite oxidation, and lipid peroxidation following exposure of cultured neurons to DU, in the form of uranyl acetate. We concurrently evaluated the neurotoxicity of uranyl acetate in C. elegans using various neuronal-green fluourescent protein reporter strains to visualize neurodegeneration. Our studies indicate that uranyl acetate has low cytotoxic potential, and uranium exposure does not result in significant changes in cellular energy metabolism, thiol metabolite oxidation, or lipid peroxidation. Furthermore, our C. elegans studies do not show any significant neurodegeneration following uranyl acetate exposure. Together, these studies suggest that DU, in the form of uranyl acetate, has low neurotoxic potential. These findings should alleviate the some of public concerns regarding DU as an etiologic agent of neurodegenerative conditions associated with GWS.

Evaluation of the effect of chronic exposure to 137Cesium on sleep–wake cycle in rats

Since the Chernobyl accident, the most significant problem for the population living in the contaminated areas is chronic exposure by ingestion of radionuclides, notably (137)Cs, a radioactive isotope of cesium. It can be found in the whole body, including the central nervous system. The present study aimed to assess the effect of (137)Cs on the central nervous system and notably on open-field activity and the electroencephalographic pattern. Rats were exposed up to 90 days to drinking water contaminated with (137)Cs at a dosage of 400 Bq kg(-1), which is similar to that ingested by the population living in contaminated territories. At this level of exposure, no significant effect was observed on open-field activity. On the other hand, at 30 days exposure, (137)Cs decreased the number of episodes of wakefulness and slow wave sleep and increased the mean duration of these stages. At 90 days exposure, the power of 0.5-4 Hz band of (137)Cs-exposed rats was increased in comparison with controls. These electrophysiological changes may be due to a regional (137)Cs accumulation in the brain stem. In conclusion, the neurocognitive effects of (137)Cs need further evaluation and central disorders of population living in contaminated territories must be considered.

Chronic ingestion of uranyl nitrate perturbs acetylcholinesterase activity and monoamine metabolism in male rat brain

Recent animal studies have shown that uranium can reach the brain after chronic exposure. However, little information is available on the neurological effects of chronic long-term exposure to uranium. In the present study, the effects during 1.5, 6 and 9-month periods of chronic ingestion of uranyl nitrate (UN) in drinking water (40 mg of uranium per litre) on cholinergic acetylcholinesterase (AChE) activity and on dopaminergic and serotoninergic metabolisms were investigated in several areas of male Srague Dawley rat brains. Uranium brain accumulation and distribution was also investigated after 1.5 and 9 months. Both after 1.5, 6 and 9 months of exposure, AChE activity was unaffected in the striatum, hippocampus and frontal cortex. Nevertheless, AChE activity was transitionally perturbed in the cerebellum after 6 months of exposure. After 1.5 months of exposure, DA level increased in hypothalamus. After 6 months of exposure, a tiny but significant modification of the DAergic turnover ratio was detected in the frontal cortex. And after 9 months, UN produced a significant decrease in the 5HIAA level and the 5HTergic turn-over ratio in the frontal cortex and also a decrease in the DOPAC level and DAergic turn-over ratio in the striatum. Uranium brain accumulation was statistically significant in striatum after 1.5 months and in striatum, hippocampus and frontal cortex after 9 months of exposure. Although neurochemical changes did not always correlated with increased accumulation of uranium in specific areas, these results suggest that chronic ingestion of UN can cause chronic and progressive perturbations of physiological level of neurotransmitter systems. Considering previous reports on behavioural uranium-induced effects and the involvement of neurotransmitters in various behavioural processes, it would be crucial to determine whether these neurochemical disorders were accompanied by neurobehavioral deficits even at 40 mg of uranium per litre exposure.