Metabolic deposition of selenium and cadmium into the hair and other tissues of the guinea pig

To better understand the significance of hair trace-element measurements and their relationships with the trace-element levels in body organs and fluids, a series of controlled animal experiments were conducted in which several trace elements were periodically measured during a 90-day chronic exposure to selenium and cadmium. Chronic selenium exposure appeared to be reflected by elevated selenium levels in the hair, kidneys, and liver. Chronic cadmium exposure, although reflected by kidney and liver elevation, appeared not to be reflected by corresponding increases in its concentration in the hair.     

Effects of feeding and starvation on growth and swimming activity in an obligatory air-breathing fish

Reared in (tubular) aquaria containing different depths of water, Ophiocephalus striatus (0.7 g, 4.5 cm body length), an obligatory air-breathing tropical fish, swam long or short distances to enable themselves to exchange atmospheric air. In each tested depth (2.5, 5.0, 15.5, 31.0 and 40.0 cm) series, one group was starved, while the other was fed ad libitum twice a day on fish muscle. In the shallowest water (2.5 cm depth), the feeding group surfaced 1,294 times, travelling 64.7 m at an energy cost of 20.4 mg dry fish substance/g live fish/day, against those exposed to the deepest water (40 cm depth), which expended 35.8 mg/g/day, swimming 1,503.4 m on 1,879 visits to the surface. The starving group surfaced only 482 times, travelling 24.1 m at an expense of 5.8 mg/g/day in the shallowest water, while those at 40 cm depth surfaced 504 times, swimming 403.2 m at an energy cost of 7.4 mg/g/day. Owing to the sustained swimming activity and the consequent fatigue, the test individuals belonging to both groups in all the tested series hang to the surface for a definite interval, repaying the O₂ debt. Observations were also made to assess the duration of hanging to precisely estimate the distance travelled. Irrespective of changes in depths of water, the duration of hanging to surface was only 3.0 hr/day for the feeding groups, while it was as much as 15.5 hr/day for the starving groups. The maximum sustained metabolic level of O.striatus reared in 40 cm depth was equivalent to 1.23 ml O₂/g/hr, which is about 2 times higher than the value reported for the active metabolism of swimming Oncorhynchus nerka at 15°C in Brett's (1964) respirometer. O.striatus reared in 2.5 cm depth fed 32.0 mg and converted 6.7 mg dry food/g live fish/day, while those exposed to the deepest water fed 49.1 mg, but converted only 5.5 mg/g/day. Culturing obligatory air-breathing fishes in shallow waters will be advantageous.     

Five tropical air-breathing fishes, six different strategies to defend against ammonia toxicity on land

Most tropical fishes are ammonotelic, producing ammonia and excreting it as NH3 by diffusion across the branchial epithelia. Hence, those air-breathing tropical fishes that survive on land briefly or for an extended period would have difficulties in excreting ammonia when out of water. Ammonia is toxic, but some of these air-breathing fishes adopt special biochemical adaptations to ameliorate the toxicity of endogenous ammonia accumulating in the body. The amphibious mudskipper Periophthalmodon schlosseri, which is very active on land, reduces ammonia production by suppressing amino acid catabolism (strategy 1) during aerial exposure. It can also undergo partial amino acid catabolism, leading to the accumulation of alanine (strategy 2) to support locomotory activities on land. In this case, alanine formation is not an ammonia detoxification process but reduces the production of endogenous ammonia. The snakehead Channa asiatica, which exhibits moderate activities on land although not truly amphibious, accumulates both alanine and glutamine in the muscle, with alanine accounting for 80% of the deficit in reduction in ammonia excretion during air exposure. Unlike P. schlosseri, C. asiatica apparently cannot reduce the rates of protein and amino acid catabolism and is incapable of utilizing partial amino acid catabolism to support locomotory activities on land. Unlike alanine formation, glutamine synthesis (strategy 3) represents an ammonia detoxification mechanism that, in effect, removes the accumulating ammonia. The four-eyed sleeper Bostrichyths sinensis, which remains motionless during aerial exposure, detoxifies endogenous ammonia to glutamine for storage. The slender African lungfish Protopterus dolloi, which can aestivate on land on a mucus cocoon, has an active ornithine-urea cycle and converts endogenous ammonia to urea (strategy 4) for both storage and subsequent excretion. Production of urea and glutamine are energetically expensive and appear to be adopted by fishes that remain relatively inactive on land. The Oriental weatherloach Misgurnus anguillicaudatus, which actively burrows into soft mud during drought, manipulates the pH of the body surface to facilitate NH3 volatilization (strategy 5) and develops high ammonia tolerance at the cellular and subcellular levels (strategy 6) during aerial exposure. Hence, with regard to excretory nitrogen metabolism, modern tropical air-breathing fishes exhibit a variety of strategies to survive on land, and they represent a spectrum of specimens through which we may examine various biochemical adaptations that would have facilitated the invasion of the terrestrial habitat by fishes during evolution.     

Involvement of Erks activation in cadmium‐induced AP‐1 transactivation in vitro and in vivo

Cadmium is a potent and effective carcinogen in rodents and has recently been accepted by IARC (International Agency for Research on Cancer) as a category 1 carcinogen. Cadmium-induced upregulation of intracellular signaling pathways leading to increased mitogenesis is thought to be a major mechanism for the carcinogenic activity following chronic cadmium exposure. In the present study, we found that exposure of cells to cadmium induced significant activation of AP1 and all three members of the MAP kinase family in mouse epidermal JB6 cells. The induction of AP1 activity by cadmium appears to involve activation of Erks, since the induction of AP1 activity by cadmium was blocked by pretreatment of cells with PD98058. Interestingly, the induction of AP1 by cadmium was greatly enhanced by the chemical tumor promoter, TPA and the growth factor EGF, but not by ultraviolet C radiation. In vivo studies demonstrated that cadmium could also induce transactivation of AP1 in AP1luciferase report transgenic mice. Considering the role of AP1 activation in tumor promotion, the results presented in this study provide a possible molecular mechanism for cadmiuminduced carcinogenesis.     

Cadmium biomonitoring and renal dysfunction among a population environmentally exposed to cadmium from smelting in China (ChinaCad)

Cadmium, an environmental pollutant, can have adverse effects on the human body. The kidney is the critical organ. In order to improve the understanding of the dose-response relationship between cadmium exposure and health effects, and especially renal dysfunction, a study on a general population group in China was performed. This study was therefore concerned with cadmium exposure biomarkers, such as the concentrations in blood (BCd) and urine (UCd), and effect biomarkers of renal dysfunction, such as ₂-microglobulin (₂m), retinol binding protein (RBP) and albumin (ALB). To improve the evaluation of exposure levels in relation to the adverse health effects of cadmium exposure in the general population, a quality control program was conducted to determine analytical quality in the determination of cadmium in blood and urine and for ₂m, creatinine, ALB and RBP. The measurements showed that analytical quality was adequate. The exposure and effect biomarkers were studied in the population groups living in three areas, namely a control area and two Cd polluted areas. In the highly exposed area, most of the BCd values were higher than 5 g/l and most of the UCd values were higher than 5 g/g creatinine. ₂-microglobulin, retinol binding protein, and albumin in urine were all significantly higher in the population living in the heavily polluted area than in that in the control area. Based on data from all three areas, a marked dose-response relationship between UCd or BCd and the prevalence of renal dysfunction was demonstrated. The number of abnormalities in kidney was related to the level of cadmium exposure. Only one index of renal tubular dysfunction was affected in subjects exposed to low levels of cadmium, but more than two indices of renal function were affected in those exposed to high levels.     

Defences against ammonia toxicity in tropical air-breathing fishes exposed to high concentrations of environmental ammonia: a review

In the tropics, air-breathing fishes can be exposed to environmental ammonia when stranded in puddles of water during the dry season, during a stay inside a burrow, or after agricultural fertilization. At low concentrations of environmental ammonia, NH₃ excretion is impeded, as in aerial exposure, leading to the accumulation of endogenous ammonia. At high concentrations of environmental ammonia, which results in a reversed NH₃ partial pressure gradient (P_NH3), there is retention of endogenous ammonia and uptake of exogenous ammonia. In this review, several tropical air-breathing fishes (giant mudskipper, African catfish, oriental weatherloach, swamp eel, four-eyed sleeper, abehaze and slender African lungfish), which can tolerate high environmental ammonia exposure, are used as examples to demonstrate how eight different adaptations can be involved in defence against ammonia toxicity. Four of these adaptations deal with ammonia toxicity at branchial and/or epithelial surfaces: (1) active excretion of NH₄⁺; (2) lowering of environmental pH; (3) low NH₃ permeability of epithelial surfaces; and (4) volatilization of NH₃, while another four adaptations ameliorate ammonia toxicity at the cellular and subcellular levels: (5) high tolerance of ammonia at the cellular and subcellular levels; (6) reduction in ammonia production; (7) glutamine synthesis; and (8) urea synthesis. The responses of tropical air-breathing fishes to high environmental ammonia are determined apparently by behavioural adaptations and the nature of their natural environments.Communicated by I.D. Hume     

Environmental and injected cadmium are sequestered by two major isoforms of basal copper, zinc-metallothionein in gibel (Carassius auratus langsdorfi) liver

Gibels were exposed to cadmium in their aquarium at a concentration of 10 micrograms Cd/l for up to 39 weeks. Distributions of cadmium, copper and zinc in the liver soluble fraction were determined along with sulfur by high performance liquid chromatography-inductively coupled argon plasma-atomic emission spectrometry. Cadmium was sequestered by the two major isoforms of gibel metallothionein as in the case of cadmium injected intraperitoneally into gibel. Several peaks with cadmium, copper, zinc and sulfur were observed other than the two major isoforms and their relative ratios were different between the control and cadmium-exposed fishes.     

Latitudinal variation in the shape of the species body size distribution: an analysis using freshwater fishes

Many taxonomic and ecological assemblages of species exhibit a right-skewed body size-frequency distribution when characterized at a regional scale. Although this distribution has been frequently described, factors influencing geographic variation in the distribution are not well understood, nor are mechanisms responsible for distribution shape. In this study, variation in the species body size-frequency distributions of 344 regional communities of North American freshwater fishes is examined in relation to latitude, species richness, and taxonomic composition. Although the distribution of all species of North American fishes is right-skewed, a negative correlation exists between latitude and regional community size distribution skewness, with size distributions becoming left-skewed at high latitudes. This relationship is not an artifact of the confounding relationship between latitude and species richness in North American fishes. The negative correlation between latitude and regional community size distribution skewness is partially due to the geographic distribution of families of fishes and apparently enhanced by a nonrandom geographic distribution of species within families. These results are discussed in the context of previous explanations of factors responsible for the generation of species size-frequency distributions related to the fractal nature of the environment, energetics, and evolutionary patterns of body size in North American fishes.     

Correlation of the number of pineal “synaptic” ribbons and spherules with the level of serum melatonin over a 24-hour period in male rabbits

Summary Previous studies have shown that pineal synaptic ribbons and spherules may respond differently under normal and experimental conditions. It has been suggested that the increase in the number of ribbons may be a prerequisite for enhanced melatonin formation. In the present study, the number of ribbons and spherules as well as the level of serum melatonin were monitored over a 24-h period in the male rabbit, the pineal gland of which is known to contain many spherules. It was found that both the number of ribbons and the levels of serum melatonin show the typical nocturnal increase, exhibiting peaks at 02:00 and 06:00 h, respectively. There is a good correlation (R = 0.8) of the two parameters. The spherules, in contrast, show no statistically significant circadian changes in number and cannot be correlated with the levels of serum melatonin. It is concluded that ribbons and spherules may differ in function and that the ribbons may be somehow involved in the regulation of melatonin formation.Supported by the Deutsche Forschungsgemeinschaft (Grant Vo 135/7) within the project SPP Neuroendokrinologie     

Antioxidant enzyme activity and lipid peroxidation in liver of female rats co-exposed to lead and cadmium: Effects of vitamin E and Mn2+

The oxidative status of liver of female rats exposed to lead acetate and cadmium acetate either alone or in combination at a dose of 0.05?mg/kg body wt intraperitoneally for 15 days was studied. After the administration of lead alone, the activity of superoxide dismutase (SOD) decreased in liver, whereas no changes were observed in catalase (CAT) activity, and glutathione (GSH) and thiobarbituric acid (TBARS) levels. Cadmium exposure and combined exposure to lead and cadmium led to decrease in GSH content and increased TBARS levels. Moreover, animals exposed to either cadmium alone or in combination with lead showed a decrease in SOD activity and an increase in CAT activity. The in vitro experiments showed that vitamin E failed to restore the antioxidant enzyme activities in metal treated postmitochondrial supernatant fraction of liver. But Mn²⁺ ions protected the mitochondria from lipid peroxidation and could completely restore Mn-superoxide dismutase (Mn-SOD) activity following metal intoxication. The results of this study indicate that despite the ability of lead and cadmium to induce oxidative stress the effect in liver is not intensified by combined exposure to both lead and cadmium. The observed changes in various oxidative stress parameters in the liver of rats co-exposed to lead and cadmium may result from an independent effect of lead and /cadmium and also from their interaction such as changes in metal accumulation and content of essential elements like Cu, Zn and Fe. These results suggest that when lead and cadmium are present together in similar concentrations, cadmium mediates major effects due to its more reactive nature.     

Antioxidant enzyme activity and lipid peroxidation in liver of female rats co-exposed to lead and cadmium: effects of vitamin E and Mn2+

The oxidative status of liver of female rats exposed to lead acetate and cadmium acetate either alone or in combination at a dose of 0.05 mg/kg body wt intraperitoneally for 15 days was studied. After the administration of lead alone, the activity of superoxide dismutase (SOD) decreased in liver, whereas no changes were observed in catalase (CAT) activity, and glutathione (GSH) and thiobarbituric acid (TBARS) levels. Cadmium exposure and combined exposure to lead and cadmium led to decrease in GSH content and increased TBARS levels. Moreover, animals exposed to either cadmium alone or in combination with lead showed a decrease in SOD activity and an increase in CAT activity. The in vitro experiments showed that vitamin E failed to restore the antioxidant enzyme activities in metal treated postmitochondrial supernatant fraction of liver. But Mn²⁺ ions protected the mitochondria from lipid peroxidation and could completely restore Mn-superoxide dismutase (Mn-SOD) activity following metal intoxication. The results of this study indicate that despite the ability of lead and cadmium to induce oxidative stress the effect in liver is not intensified by combined exposure to both lead and cadmium. The observed changes in various oxidative stress parameters in the liver of rats co-exposed to lead and cadmium may result from an independent effect of lead and /cadmium and also from their interaction such as changes in metal accumulation and content of essential elements like Cu, Zn and Fe. These results suggest that when lead and cadmium are present together in similar concentrations, cadmium mediates major effects due to its more reactive nature.     

氨氮和镉胁迫对芙蓉鲤鲫抗氧化系统和免疫机能的影响

为探究氨氮、镉单一及联合胁迫对鱼类氧化防御系统及非特异性免疫系统的影响, 以芙蓉鲤鲫(Cyprinus capio furong.♀×Carassius auratus red var.♂)为研究对象, 通过静态毒理学实验方法模拟亚急性胁迫, 在胁迫后不同时间点对芙蓉鲤鲫的肝脏进行取样, 并测定其抗氧化指标和非特异性免疫指标。结果显示, 氨氮和镉单一及联合胁迫后肝脏丙二醛(MDA)含量、酸性磷酸酶(ACP)活性和髓过氧化物酶(MPO)活性均出现不同程度的升高, 过氧化氢酶(CAT)活性均呈先下降后升高的趋势。氨氮胁迫后肝脏超氧化物歧化酶(SOD)活性、谷胱甘肽过氧化物酶(GSH-PX)活性、碱性磷酸酶(AKP)活性及谷胱甘肽(GSH)含量均呈先升高后下降的变化趋势。镉胁迫后肝脏SOD和GSH-PX活性在6d时均显著高于对照组, GSH含量在4d时显著低于对照组, AKP活性呈先降低后升高的趋势。氨氮和镉联合胁迫后肝脏SOD和GSH-PX活性在6d和8d时显著增加, AKP活性在8d时显著升高, GSH含量呈先降低后升高的变化趋势。结果表明, 氨氮和镉单一及联合胁迫均可诱导芙蓉鲤鲫产生氧化应激, 激活了鱼体的氧化防御系统和非特异性免疫系统。研究可为深入探讨芙蓉鲤鲫的健康养殖和逆境生理响应机制提供基础资料。     

The source of lamellar mitochondria-rich cells in the air-breathing fish, Trichogaster leeri

Pavement cells and the mitochondria-rich cells (MRCs) are two of the main types of cells in fish gill epithelia. The pavement cells are generally responsible for gas exchange and MRCs for ion regulation. MRCs are found especially in the trailing edge and the interlamellar region of gill filament. In some species, MRCs are also observed in the gill lamellae. A previous study reported the likelihood of having lamellar MRCs in air-breathing fishes. Nevertheless, the source of lamellar MRCs is unclear. We used the air-breathing fish, Trichogaster leeri, to investigate the source of proliferated cells on the lamellae when 5-bromo-2-deoxyuridine (BrdU) was injected at different times before fish were sampled from deionized water. There were two major findings in this study. First, undifferentiated cells were found in the lamellae, as well as in the filaments. And, within 12-24 hr, a proliferated cell, identified as BrdU cell, could differentiate to an MRC in the gill lamellae. Second, the filaments and the lamellae in T. leeri responded to ionic stress differently but the proportion of the proliferated MRCs to the BrdU cells remained constant. Our results suggested that the lamellar MRCs were mainly differentiated from the cells that proliferated earlier from the lamellae.     

Activities of superoxide dismutase and catalase in erythrocytes and plasma transaminases of goldfish (Carassius auratus gibelio Bloch.) exposed to cadmium

Four groups of goldfish were exposed to cadmium in a concentration of 20 mg Cd/l water under aquarium conditions. The duration of exposure was 1, 4, 7 and 15 days. It was shown that the activity of superoxide dismutase (SOD) in the red blood cells (RBC) significantly decreased after the first day of cadmium exposure. However, the SOD activity increased after 7 and 15 days of cadmium treatment. Elevated activity of catalase (CAT) was found in erythrocytes of cadmium-treated fishes after 15 days, whereas plasma GOT levels was increased after 7 and 15 days and GPT levels after 1, 4, 7 and 15 days of cadmium treatment. This was accompanied by a significant decrease of blood hemoglobin concentrations (after 15 days) and hematocrit values (after 7 and 15 days). However, the concentration of blood glucose significantly increased after 1, 4, 7 and 15 days of cadmium exposure. These results indicate that cadmium causes oxidative stress and tissue damage in the exposed fishes.     

A gene (Bmn) controllingβ-mannosidase activity in the mouse is located in the distal part of chromosome 3

A gene (Bmn) with a major effect on -mannosidase activity in kidney and liver of the house mouse was revealed by assay with the synthetic substratep-nitrophenyl--d-mannoside. Activity is low in DBA/2J and CSB mice and high in C57BL/6J mice. By the use of the BXD series of recombinant inbred strains and by crosses between C57BL and CSB, it was possible to map the gene to the distal part of chromosome 3 by demonstration of linkage to a gene for cadmium resistance,cdm, as well as to theAdh-3 locus.This work was supported by Swedish Natural Science Research Council Project B-BU 2992-108.     

Application of Silicon and Selenium in Rice for Reducing Cadmium Stress

Rice is an essential part of the human diet in most parts of the world; On the other hand, the industrialization of societies has led to pollution of the environment, including heavy metal contamination of soil and water, which negatively affects rice production and quality. Therefore, finding ways to increase the yield and quality of this strategic crop seems essential. Several studies have been conducted in recent decades to find effective and inexpensive solutions to reduce the adverse effects of heavy metals in rice fields. Due to the negative effect of cadmium pollution on rice quality and yield, the current study aimed to investigate cadmium absorption and transfer mechanisms in rice (from absorption by roots to loading in grains), and its effects on rice morphology, physiology, and biochemistry (such as biomass, nutrient absorption, antioxidant defenses). Also, rice’s natural mechanisms for detoxifying cadmium were discussed. This study also intended to identify the absorption and transfer pathways of silicon and selenium in rice, their roles in improving rice structures, and their antagonistic effects on reducing cadmium stress (absorption, transport, and toxicity of cadmium).     

The origin and evolution of the surfactant system in fish: insights into the evolution of lungs and swim bladders

Several times throughout their radiation fish have evolved either lungs or swim bladders as gas-holding structures. Lungs and swim bladders have different ontogenetic origins and can be used either for buoyancy or as an accessory respiratory organ. Therefore, the presence of air-filled bladders or lungs in different groups of fishes is an example of convergent evolution. We propose that air breathing could not occur without the presence of a surfactant system and suggest that this system may have originated in epithelial cells lining the pharynx. Here we present new data on the surfactant system in swim bladders of three teleost fish (the air-breathing pirarucu Arapaima gigas and tarpon Megalops cyprinoides and the non-air-breathing New Zealand snapper Pagrus auratus). We determined the presence of surfactant using biochemical, biophysical, and morphological analyses and determined homology using immunohistochemical analysis of the surfactant proteins (SPs). We relate the presence and structure of the surfactant system to those previously described in the swim bladders of another teleost, the goldfish, and those of the air-breathing organs of the other members of the Osteichthyes, the more primitive air-breathing Actinopterygii and the Sarcopterygii. Snapper and tarpon swim bladders are lined with squamous and cuboidal epithelial cells, respectively, containing membrane-bound lamellar bodies. Phosphatidylcholine dominates the phospholipid (PL) profile of lavage material from all fish analyzed to date. The presence of the characteristic surfactant lipids in pirarucu and tarpon, lamellar bodies in tarpon and snapper, SP-B in tarpon and pirarucu lavage, and SPs (A, B, and D) in swim bladder tissue of the tarpon provide strong evidence that the surfactant system of teleosts is homologous with that of other fish and of tetrapods. This study is the first demonstration of the presence of SP-D in the air-breathing organs of nonmammalian species and SP-B in actinopterygian fishes. The extremely high cholesterol/disaturated PL and cholesterol/PL ratios of surfactant extracted from tarpon and pirarucu bladders and the poor surface activity of tarpon surfactant are characteristics of the surfactant system in other fishes. Despite the paraphyletic phylogeny of the Osteichthyes, their surfactant is uniform in composition and may represent the vertebrate protosurfactant.     

Protective effects of melatonin against oxidation of guanine bases in DNA and decreased microsomal membrane fluidity in rat liver induced by whole body ionizing radiation

The aim of the study was to examine the potential protective effect of melatonin against whole body ionizing radiation (800 cGy). Changes in 8-hydroxy-2-deoxyguanosine (8-OH-dG) levels, an index of DNA damage, and alterations in membrane fluidity (the inverse of membrane rigidity) and lipid peroxidation in microsomal membranes, as indices of damage to lipid and protein molecules in membranes, were estimated. Measurements were made in rat liver, 12 h after their exposure to radiation. To test the potential protective effects of melatonin, the indole was injected (i.p. 50 mg/kg b.w.) at 120, 90, 60 and 30 min prior to radiation exposure. Both 8-OH-dG levels and microsomal membrane rigidity increased significantly 12 h after radiation exposure. Melatonin completely counteracted the effects of ionizing radiation. Changes in 8-OH-dG levels and membrane fluidity are early sensitive parameters of DNA and microsomal membrane damage, respectively, induced by ionizing radiation and our findings document the protective effects of melatonin against ionizing radiation.     

Cytotoxic potency of trialkyltins to C6 glioma cells <Emphasis Type="Italic">in vitro</Emphasis>: impact of exposure conditions

Because of a possible role of astrocytes in trialkyltin-induced neurotoxicity in vivo various studies have been performed using cultures of astrocytes or glioma cells in vitro. With respect to cytotoxic potencies of trialkyltins these studies gave rather divergent results. Therefore the aim of the present study was to clarify whether variations of experimental conditions could be responsible for the differences of the cytotoxic activities of trimethyltin (TMT), triethyltin (TET) and tributyltin (TBT). Experiments were performed with rat C6 glioma cells. Toxicity was determined by measuring the reduction of the cell protein content. Cultures of proliferating and growth-arrested cells did not differ in their sensitivity. Exposure duration (1–72 h) had a strong but differing influence on the cytotoxic potency of the trialkyltins. After short exposure times the potencies differed largely (TMT < TET < TBT), whereas they became more and more similar with increasing exposure duration. The potency–time relationships for TMT and TET could be described by the equation: EC₅₀ = k x t ^–n, while for TBT an incipient value (EC_50,) had to be included: EC₅₀ = EC ₅₀ + k x t ^–n. Addition of serum albumin to the culture medium decreased the cytotoxic potency of the trialkyltins. However, the impact of protein binding on their bioavailability was relatively low. The cytotoxic potency of the alkyltins was not dependent on the concentration of C6 cells. Taken together, neither differences in exposure conditions nor in the proliferative status of the cells are sufficient to account for the discrepancies in published results for trialkyltin cytotoxicity to astrocytes. Instead they may – at least partially – be explained by differing sensitivities of the endpoints used. Furthermore, C6 glioma cells respond considerably more sensitively to trialkytins than primary astrocytes, which questions their applicability as models for astrocyte toxicity.     

Hypoxia tolerance and air-breathing ability correlate with habitat preference in coral-dwelling fishes

Hypoxia tolerance and air-breathing occur in a range of freshwater, estuarine and intertidal fishes. Here it is shown for the first time that coral reef fishes from the genera Gobiodon, Paragobiodon and Caracanthus, which all have an obligate association with living coral, also exhibit hypoxia tolerance and a well-developed air-breathing capacity. All nine species maintained adequate respiration in water at oxygen concentrations down to 15–25% air saturation. This hypoxia tolerance is probably needed when the oxygen levels in the coral habitat drops sharply at night. Air-breathing abilities of the species correlated with habitat association, being greatest (equaling oxygen uptake in water) in species that occupy corals extending into shallow water, where they may become air exposed during extreme low tides. Air-breathing was less well-developed or absent in species inhabiting corals from deeper waters. Loss of scales and a network of subcutaneous capillaries appear to be key adaptations allowing cutaneous respiration in air. While hypoxia tolerance may be an ancestral trait in these fishes, air-breathing is likely to be a more recent adaptation exemplifying convergent evolution in the unrelated genera Gobiodon and Caracanthus in response to coral-dwelling lifestyles.