Combined Danio rerio embryo morbidity, mortality and photomotor response assay: A tool for developmental risk assessment from chronic cyanoHAB exposure

Freshwater harmful algal blooms produce a broad array of bioactive compounds, with variable polarity. Acute exposure to cyanotoxins can impact the liver, nervous system, gastrointestinal tract, skin, and immune function. Increasing evidence suggests chronic effects from low-level exposures of cyanotoxins and other associated bioactive metabolites of cyanobacterial origin. These sundry compounds persist in drinking and recreational waters and challenge resource managers in detection and removal. A systematic approach to assess the developmental toxicity of cyanobacterial metabolite standards was employed utilizing a robust and high throughput developmental Danio rerio embryo platform that incorporated a neurobehavioral endpoint, photomotor response. Subsequently, we applied the platform to cyanobacterial bloom surface water samples taken from temperate recreational beaches and tropical lake subsistence drinking water sources as a model approach. Dechorionated Danio rerio embryos were statically immersed beginning at four to six hours post fertilization at environmentally relevant concentrations, and then assessed at 24 h and 5 days for morbidity, morphological changes, and photomotor response. At least one assessed endpoint deviated significantly for exposed embryos for 22 out of 25 metabolites examined. Notably, the alkaloid lyngbyatoxin-a resulted in profound, dose-dependent morbidity and mortality beginning at 5 μg/L. In addition, hydrophobic components of extracts from beach monitoring resulted in potent morbidity and mortality despite only trace cyanotoxins detected. The hydrophilic extracts with several order of magnitude higher concentrations of microcystins resulted in no morbidity or mortality. Developmental photomotor response was consistently altered in environmental bloom samples, independent of the presence or concentration of toxins detected in extracts. While limited with respect to more polar compounds, this novel screening approach complements specific fingerprinting of acutely toxic metabolites with robust assessment of developmental toxicity, critical for chronic exposure scenarios.

Developmental Exposure to Low Concentrations of Organophosphate Flame Retardants Causes Life-Long Behavioral Alterations in Zebrafish

As the older class of brominated flame retardants (BFRs) are phased out of commercial use because of findings of neurotoxicity with developmental exposure, a newer class of flame retardants have been introduced, the organophosphate flame retardants (OPFRs). Presently, little is known about the potential for developmental neurotoxicity or the behavioral consequences of OPFR exposure. Our aim was to characterize the life-long neurobehavioral effects of 4 widely used OPFRs using the zebrafish model. Zebrafish embryos were exposed to 0.1% DMSO (vehicle control); or one of the following treatments; isopropylated phenyl phosphate (IPP) (0.01, 0.03, 0.1, 0.3 µM); butylphenyl diphenyl phosphate (BPDP) (0.003, 0.03, 0.3, 3 µM); 2-ethylhexyl diphenyl phosphate (EHDP) (0.03, 0.3, 1 µM); isodecyl diphenyl phosphate (IDDP) (0.1, 0.3, 1, 10 µM) from 0- to 5-days postfertilization. On Day 6, the larvae were tested for motility under alternating dark and light conditions. Finally, at 5-7 months of age the exposed fish and controls were tested on a battery of behavioral tests to assess emotional function, sensorimotor response, social interaction and predator evasion. These tests showed chemical-specific short-term effects of altered motility in larvae in all of the tested compounds, and long-term impairment of anxiety-related behavior in adults following IPP, BPDP, or EHDP exposures. Our results show that OPFRs may not be a safe alternative to the phased-out BFRs and may cause behavioral impacts throughout the lifespan. Further research should evaluate the risk to mammalian experimental models and humans.

Developmental ethanol exposure impairs locomotor movement in Japanese medaka (Oryzias latipes) larvae targeting epigenome

Evidence indicated ethanol exposure during development disrupts brain functions that induces fetal alcohol spectrum disorder (FASD) phenotypes with behavioral abnormalities. We aimed to investigate whether prenatal ethanol exposure has any potential impact on behavior of a FASD fish model. Fertilized Japanese medaka (Oryzias latipes) eggs were exposed to 100-300 mM ethanol or 2 mM 5-azacytidine (5-azaC), 0-2 day post fertilization (dpf), in embryo-rearing medium (ERM). Survived embryos were maintained in clean ERM and used either for gene expression analysis on 2- and 6-dpf or allowed to hatch for behavioral study. Photomotor response of 3-4 day post hatch larvae were tracked for 3 h with light-dark transitions. It was observed that larval swimming was phototactic; enhanced in presence of light, declined in dark. Phototactic response was also observed in larvae prenatally exposed to ethanol or 5-azaC; however, the total distance swum by these larvae compared to controls declined. Further analysis indicated that, in light phases, total swimming activity and average swimming speed were reduced in larvae prenatally exposed to ethanol (300 mM) or 5-azaC. Expression analysis of baz1a and baz2a in embryos indicated developmental regulation. Ethanol (100-300 mM) or 5-azaC (2 mM) were able to modulate downregulation of both baz1a and baz2a mRNAs only in 6 dpf embryos of 300 mM ethanol and 5-azaC (2 mM) groups. These studies indicated that prenatal exposure to ethanol or 5-azaC was able to disrupt movements and thus swimming behavior in FASD phenotypes probably due to delayed remodeling of genome and epigenome.

[Myeloid and erythroid hematopoietic transcription factor expression decline after knockdown of lmna genes in zebrafish embryos]

Objective: To investigate the effect of lmna gene down-regulation on early hematopoietic development of zebrafish. Methods: Phosphorodiamidate morpholino oligomer (PMO) technology was used to downregulate lmna gene expression in Zebrafish. Zebrafish embryos injected phosphorodiamidate morpholino antisense oligonucleotide of lmna gene mRNA by microinjection at unicellular stage were taken as the experimental group, and those injected meaningless phosphorodiamidate morpholino antisense oligonucleotide were taken as the control. The embryos were collected at 18, 24, 30 and 36 hpf after the fertilization. The real-time fluorescent quantitative PCR (RT-PCR) and whole embryo in situ hybridization methods were used to detect the expression of myeloid hematopoietic transcription factor pu. 1 and erythroid hematopoietic transcription factor gata1 in zebrafish. Results: RT-PCR showed that the expressions of pu. 1 and gata1 decreased in the experimental group compared with the control group (all P<0.05). Whole embryo in situ hybridization showed that the blue-black positive hybridization signals of pu. 1 and gata1 in experimental group were shallow than those in the control group. Conclusion: Myeloid hematopoietic and erythroid hematopoietic of zebrafish are blocked with the downregulation of lmna gene.

csrnp1a is necessary for the development of primitive hematopoiesis progenitors in zebrafish

The CSRNP (cystein-serine-rich nuclear protein) transcription factors are conserved from Drosophila to human. Functional studies in mice, through knockout for each of their paralogs, have resulted insufficient to elucidate the function of this family of proteins in vertebrate development. Previously, we described the function of the zebrafish ortholog, Csnrp1/Axud1, showing its essential role in the survival and proliferation of cephalic progenitors. To extend our understanding of this family, we have studied the function of its paralog csrnp1a. Our results show that csrnp1a is expressed from 0 hpf, until larval stages, particularly in cephalic territories and in the intermediate cell mass (ICM). Using morpholinos in wild type and transgenic lines we observed that Csrnp1a knockdown generates a mild reduction in head size and a depletion of blood cells in circulation. This was combined with in situ hybridizations to analyze the expression of different mesodermal and primitive hematopoiesis markers. Morphant embryos have impaired blood formation without disruption of mesoderm specification, angiogenesis or heart development. The reduction of circulating blood cells occurs at the hematopoietic progenitor level, affecting both the erythroid and myeloid lineages. In addition, cell proliferation was also altered in hematopoietic anterior sites, specifically in spi1 expression domain. These and previous observations suggest an important role of Csnrps transcription factors in progenitor biology, both in the neural and hematopoietic linages.

Embryo exposure to elevated cortisol level leads to cardiac performance dysfunction in zebrafish

In zebrafish (Danio rerio), de novo cortisol synthesis commences only after hatching, providing an interesting model to study the effects of maternal stress and abnormal cortisol deposition on embryo development and performance. We hypothesized that elevated cortisol levels during pre-hatch embryogenesis compromise cardiac performance in developing zebrafish. Cortisol was microinjected into one-cell embryos to elevate basal cortisol levels during embryogenesis. Elevated embryo cortisol content increased heart deformities, including pericardial edema and malformed chambers, and lowered resting heartbeat post-hatch. This phenotype coincided with suppression of key cardiac genes, including nkx2.5, cardiac myosin light chain 1, cardiac troponin type T2A, and calcium transporting ATPase, underpinning a mechanistic link to heart malformation. The attenuation of the heartbeat response to a secondary stressor post-hatch also confirms a functional reduction in cardiac performance. Altogether, high cortisol content during embryogenesis, mimicking increased deposition due to maternal stress, decreases cardiac performance and may reduce zebrafish offspring survival.

Cadmium, lead and their mixtures with copper: Paracentrotus lividus embryotoxicity assessment, prediction, and offspring quality evaluation

The aim of this research was to assess the combined effects of three heavy metals (copper, lead, cadmium) on the fertilization and offspring quality of the sea urchin Paracentrotus lividus at EC50, NOEL, and EC1 concentrations. The observed data were compared with the predictions derived from approaches of Concentration Addition (CA) and Independent Action (IA) in order to evaluate the proper prediction of the observed mixture toxic effect. The P. lividus embryotoxicity of trace metals decreases as follows: Cu > Pb > Cd at all toxicity concentration tested. EC50 mixture revealed less toxic only than Cu; EC50 was 0.80 (± 0.07) mg/l, the offspring malformations were mainly P1 type (skeletal alterations) up to 20% mixture concentration, and P2 type from 70% concentration. The NOEL and EC1 mixtures evidenced that all compounds contribute to the overall toxicity, even if present at low concentrations: the former EC50 was 0.532 (± 0.058) mg/l and the latter was 1.081 (± 0.240) mg/l. The developmental defects observed were mainly P1 type in both mixtures. Both CA and IA models did not accurately predict mixture toxicity for EC50 and NOEL mixtures. Instead, EC1 mixture effects seemed well represented by the IA model. The protective action of the CA model, although quite accurate when applied to simple biological systems like algae and bacteria, but failed to represent the worst-case in this study with more complex organisms. It would be useful to introduce in the models one or more factors that take into account the complexity of these biological systems.

Protective effects of vitamin E against 3,3',4,4',5-pentachlorobiphenyl (PCB126) induced toxicity in zebrafish embryos

3,3',4,4',5-Pentachlorinated biphenyls 126 (PCB126) is a global environmental contaminant that can induce cellular oxidative stress. We investigated whether vitamin E can protect against toxicity from PCB126 during zebrafish (Danio rerio) development. Zebrafish embryos were exposed to 100nM PCB126 and compared with a second group that was co-exposed with 100muM vitamin E until 5 days post fertilization. PCB126 induced pericardial sac edema, yolk sac edema, and growth retardation in zebrafish embyos. In contrast, vitamin E co-exposure group did not show any gross changes. Real-time PCR results showed that vitamin E co-exposure group were restored to control group for the expression levels of heat shock protein 70 Cognate, aryl hydrocarbon receptor type-2, cytochrome P450 1A, and superoxide dismutase-1. These data give insights into the use of vitamin E to reduce PCB126-mediated toxicity and into the use of zebrafish embryos for exploring mechanisms underlying the oxidative potential of AHR agonists.

CYP1A/regucalcin gene expression and edema formation in zebrafish embryos exposed to 2,3,7,8-Tetrachlorodibenzo-p-dioxin

In this study, zebrafish eggs were exposed to a relatively low concentration (50 pg/mL) of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) for 72 h and then transferred to vehicle/TCDD-free water for the remainder of the experiments. Mortality, heart rates, edema severity, CYP1A, and regucalcin gene expressions were investigated to study TCDD-induced toxicity in zebrafish during the early life stage. Results indicated that the 50 pg/mL TCDD caused severe and visible developmental toxicity. Further research of the long term and low concentration of TCDD exposure is required.

Aristolochic Acid induces heart failure in zebrafish embryos that is mediated by inflammation

Aristolochic Acid (AA) is a component of Chinese herbs that has been found to be toxic to multiple organs in adults. Its toxicity to developing embryos has not been reported. Here, we describe that AA specifically causes heart defects in developing zebrafish embryos in a dosage-dependent manner. The treated embryos are able to develop their hearts normally up to 24 h postfertilization, when cardiac contraction initiates, but begin to show deformation and reduction of the hearts followed by gradual contractility loss and eventually lethality, suggesting that AA is primarily affecting cardiac physiology rather than cardiogenesis. Histological analyses reveal that the AA-treated hearts develop hypertrophy and disorganization of cardiomyocytes and loss of endocardium. By transmission electron microscopy, we observed broken and disorganized cardiac fibers in the AA-treated hearts. AA induces the expression of proinflammation genes, including cox-2, IL-1beta, and others. The AA-induced cardiac defects can be attenuated by the cox-2 antagonist NS398 via reducing the expression of the inflammatory genes. This attenuation could be further enhanced by known heart failure drugs, such as angiotensin-converting enzyme inhibitor and beta-adrenergic receptor antagonist. In contrast, the heart defects are enhanced by a beta-adrenergic receptor agonist. In summary, AA causes profound toxicity to zebrafish embryos that exhibit pathophysiological and pharmacological features resembling those of heart failure in humans and other model organisms, and thus, zebrafish could be a new model for studies on heart failure.

The first appearance of Rodlet cells in carp (Cyprinus carpio L.) ontogeny and their possible roles during stress and parasite infection

The origin and function of rodlet cells (RCs) are still a matter of discussion. Whereas the exogenous hypothesis considers them parasites, the endogenous hypothesis regards them as a genuine fish cell population with a secretory and/or leukocyte function. In order to shed more light on these questions we focused on the location and appearance of RCs during carp (Cyprinus carpio) ontogeny. Typical RCs were seen at 5days post fertilisation (dpf) between kidney and intestine, at 6dpf in the intestine and at 8dpf in both anterior and posterior kidney and in the abdominal cavity among the mesothelial cells. The RC number increased with age and after 14dpf they were also present in gills. The early appearance of the RCs during carp ontogeny support the endogenous hypothesis stating that RCs are genuine constituents of fish tissue and suggest that they are 'immune cells'. The fact that the RCs of the gills secrete their content into the surrounding water, combined with the strategic location around blood vessels in kidney and within intestinal epithelium, would also support an important role in host defense. To investigate whether RC numbers in gills and kidney are related to typical fluctuations in the physiology during stress and infection we counted their number in gills and kidney after parasite infection and stress. In the gills the number of RCs increased after infection but did not change after stress while in the kidney their number increased after stress and no significant changes were observed after infection.

Metabolic effects of dinoseb, diazinon and esfenvalerate in eyed eggs and alevins of Chinook salmon (Oncorhynchus tshawytscha) determined by 1H NMR metabolomics

Pesticide pulses in the Sacramento River, California, originate from storm-water discharges and non-point source aquatic pollution that can last from a few days to weeks. The Sacramento River and its tributaries have historically supported the majority of California's Chinook salmon (Oncorhynchus tshawytscha) spawning grounds. Three pesticides currently used in the Sacramento Valley-- dinoseb, diazinon, and esfenvalerate-- were chosen to model the exposure of salmon embryos to storm-water discharges. Static-renewal (96 h) exposures to eyed eggs and alevins resulted in both toxicity and significant changes in metabolism assessed in whole-embryo extracts by (1)H nuclear magnetic resonance (NMR) spectroscopy based metabolomics and HPLC with UV detection (HPLC-UV). The 96-h LC(50) values of eyed eggs and alevins exposed to dinoseb were 335 and 70.6 ppb, respectively, and the corresponding values for diazinon were 545 and 29.5 ppm for eyed eggs and alevins, respectively. The 96-h LC(50) of eyed eggs exposed to esfenvalerate could not be determined due to lack of mortality at the highest exposure concentration, but in alevins was 16.7 ppb. All esfenvalerate exposed alevins developed some degree of lordosis or myoskeletal abnormality and did not respond to stimulus or exhibit normal swimming behavior. ATP concentrations measured by HPLC-UV decreased significantly in eyed eggs due to 250 ppb dinoseb and 10 and 100 ppb esfenvalerate (p < 0.05). Phosphocreatine, as measured by HPLC-UV, decreased significantly in eyed eggs due to 250 ppb dinoseb, 10 and 100 ppb esfenvalerate, and 100 ppm diazinon (p < 0.05). Principal components analyses of (1)H NMR metabolite fingerprints of eyed egg and alevin extracts revealed both dose-dependent and mechanism of action-specific metabolic effects induced by the pesticides. Furthermore, NMR based metabolomics proved to be more sensitive than HPLC-UV in identifying significant changes in sublethal metabolism of pesticide exposed alevins. In conclusion, we have demonstrated several benefits of a metabolomics approach for chemical risk assessment, when used in conjunction with a fish embryo assay, and have identified significant metabolic perturbations to the early life stages of Chinook salmon by currently used pesticides.

The zebrafish shocked gene encodes a glycine transporter and is essential for the function of early neural circuits in the CNS

shocked (sho) is a zebrafish mutation that causes motor deficits attributable to CNS defects during the first2dof development. Mutant embryos display reduced spontaneous coiling of the trunk, diminished escape responses when touched, and an absence of swimming. A missense mutation in the slc6a9 gene that encodes a glycine transporter (GlyT1) was identified as the cause of the sho phenotype. Antisense knock-down of GlyT1 in wild-type embryos phenocopies sho, and injection of wild-type GlyT1 mRNA into mutants rescues them. A comparison of glycine-evoked inward currents in Xenopus oocytes expressing either the wild-type or mutant protein found that the missense mutation results in a nonfunctional transporter. glyt1 and the related glyt2 mRNAs are expressed in the hindbrain and spinal cord in nonoverlapping patterns. The fact that these regions are known to be required for generation of early locomotory behaviors suggests that the regulation of extracellular glycine levels in the CNS is important for proper function of neural networks. Furthermore, physiological analysis after manipulation of glycinergic activity in wild-type and sho embryos suggests that the mutant phenotype is attributable to elevated extracellular glycine within the CNS.

Impact of hypoxia on early chick embryo growth and cardiovascular function

Oxygen tension is a critical factor for appropriate embryonic and fetal development. Chronic hypoxia exposure alters cardiovascular (CV) function and structure in the late fetus and newborn, yet the immature myocardium is considered to be less sensitive to hypoxia than the mature heart. We tested the hypothesis that hypoxia during the period of primary CV morphogenesis impairs immature embryonic CV function and embryo growth. We incubated fertile white Leghorn chick embryos in 15% oxygen (hypoxia) or 21% oxygen (control) until Hamburger-Hamilton stage 21 (3.5 d). We assessed in ovo viability and dysmorphic features and then measured ventricular pressure and dimensions and dorsal aortic arterial impedance at stage 21. Chronic hypoxia decreased viability and embryonic wet weight. Chronic hypoxia did not alter heart rate or the ventricular diastolic indices of end-diastolic pressure, maximum ventricular -dP/dt, or tau. Chronic hypoxia decreased maximum ventricular +dP/dt and peak pressure, increased ventricular end-systolic volume, and decreased ventricular ejection fraction, consistent with depressed systolic function. Arterial afterload (peripheral resistance) increased and both dorsal aortic SV and steady-state hydraulic power decreased in response to hypoxia. Thus, reduced oxygen tension during early cardiac development depresses ventricular function, increases ventricular impedance (afterload), delays growth, and decreases embryo survival, suggesting that a critical threshold of oxygen tension is required to support morphogenesis and cardiovascular function in the early embryo.

H2O2 induces abnormal tail flexure inXenopus embryos: similarities with Paraquat teratogenic effects

BACKGROUND

As previously shown, Paraquat (PQ) treatments of Xenopus developing embryos mainly induce a characteristic developmental alteration we named "abnormal tail flexure." PQ oxidative activity has been indicated as the cause of this malformation. Since PQ evokes reactive oxygen species (ROS), among which hydroxyl radicals (OH(*)), and H(2)O(2) can be converted to (OH(*)) via Fenton reaction, we compared here the lethal and teratogenic potentials of both oxidants by using the Frog Embryo Teratogenesis Assay-Xenopus (FETAX), in order to grasp eventual similarities in their teratogenic activity.

METHODS

Xenopus embryos were exposed, from stage 8 to stage 47, at 368, 491, 612, and 735 microM H(2)O(2) and 0.388 microM PQ. The probit analysis of H(2)O(2) mortality and malformed larva percents gave a 598.82 microM Lethal Concentration 50% (LC(50)) and 536.04 microM Teratogenic Concentration 50% (TC(50)) from which a 1.11 Teratogenic Index (T.I.) has been calculated. This T.I. value should allow the classification of H(2)O(2) as a non-teratogenic compound.

RESULTS

A comparison of H(2)O(2) mortality and malformed larva percents with those obtained from PQ exposure showed the higher embryotoxicity of PQ, but, markedly, both compounds mainly induced the "abnormal tail flexure." Histological analysis of both H(2)O(2) and PQ malformed embryo tails showed a similar distorted morphology of both somites and myocytes. Some of muscle cells were necrotic and affected by an apical enlargement as well as a detachment from the connective tissue of intersomitic boundaries.

CONCLUSIONS

In our opinion, both of the tested chemicals likely weaken the mechanical bridge connecting the myocyte contractile apparatus to the extracellular matrix, therefore causing the detachment of some of tail myocytes from their connectival septum as well as their apical enlargement. This could lead to the unbalance of tail tensional forces and, in turn, to the appearance of the "abnormal tail flexure."

Sensitivity of zebrafish to environmental toxins implicated in Parkinson's disease

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra and movement defects, including bradykinesia, tremor, and postural imbalance. Whereas the etiology and pathogenesis of PD is still poorly understood, studies in animal models are providing important insights. One valuable type of animal model for PD is established by treating animals with PD-inducing neurotoxins, including 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, and paraquat. These neurotoxins are thought to inhibit mitochondrial complex I activity leading to oxidative stress, impaired energy metabolism, proteasomal dysfunction, and, eventually, dopamine neuronal loss. However, the genes and pathways that underlie the neurotoxicity of these agents are not known. In this study, we explored the effect of MPTP, rotenone, and paraquat in both adult and larval zebrafish, which are highly amenable to genetic analysis that can lead to the identification of the underlying genes and pathways. Here, we report that adult zebrafish display behavioral alterations, including decreased locomotor activity in response to MPTP, whereas larval zebrafish exhibited developmental, behavioral, and DA sensitivity to these agents. Taken together, these findings suggest that zebrafish could be a valuable model for genetically dissecting the molecular mechanisms underlying the neurotoxicity of PD-inducing agents.

Toxicological effects of mainstream whole smoke solutions on embryonic movements of the developing embryo

Cigarette smoking is unrivaled among developmental toxicants in terms of total adverse impact on the human population. Maternal tobacco use during pregnancy adversely affects prenatal and postnatal growth and increases the risk of behavioral and developmental defects in children and adolescents. In the current study, the effects of different preparations of nicotine and mainstream whole smoke solutions (MSWSS) on embryonic movements during neonatal development were examined in vivo, using the chicken embryo model, recorded in real-time by a video camera. It was observed that low doses of nicotine induced hyperactivity and higher doses induced hypoactivity. Accordingly, a significant (p < 0.01) decrease in movements was observed by application of 10 microg of nicotine and different preparations of MSWSS. A dose-dependent decrease in embryonic movements was observed, which did not recover by the end of experiment. It was concluded that nicotine could alter embryonic movements, which are important during embryogenesis for differentiation and maturation of the body systems.

Early developmental 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure decreases chick embryo heart chronotropic response to isoproterenol but not to agents affecting signals downstream of the beta-adrenergic receptor

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) causes cardiovascular toxicity in laboratory animals, including alteration in several processes in which beta-adrenergic receptor (beta-AR) signaling plays important roles. Thus, our laboratory investigated the effects of TCDD on beta-AR expression and signal transduction. Fertile chicken eggs were injected with vehicle (corn oil), 0.24 or 0.3 pmol TCDD/g egg on incubation day 0 (D0) or D5. On D10, heart function was assessed by ECG in ovo. Exposure to TCDD increased the incidence of arrhythmias and decreased the positive chronotropic responsiveness of the heart to isoproterenol. The reduced beta-AR responsiveness was, in part, independent of any overt morphological changes in the heart as chick embryos exposed to TCDD on D5 displayed an intermediate responsiveness to beta-AR agonist in the absence of the dilated cardiomyopathy observed in chick embryos exposed to TCDD on D0. TCDD did not decrease the chronotropic response of the heart to agents that stimulate signals downstream of the beta-AR. In fact, TCDD-exposed embryos were more sensitive than controls to forskolin, increasing heart rates (HR) 21.8 +/- 3.5 beats per min (bpm) above baseline versus control values at 6.3 +/- 2.7 bpm above baseline. TCDD exposure also augmented the negative chronotropic response of the heart to verapamil, decreasing HR -23.2 +/- 7.4 bpm relative to baseline versus control embryos at -12.7 +/- 5.9 bpm below baseline. Finally, the mean cardiac beta1-AR mRNA expression in D10 embryos was not significantly altered by exposure to TCDD on D0. These findings establish that a functional end point of the developing chick heart is sensitive to TCDD exposure and that the TCDD-induced reduction in beta-AR responsiveness may result from alterations in signal transduction upstream of adenylyl cyclase.

Reproductive impairment in Japanese quail (Coturnix japonica) after in ovo exposure to o,p'-DDT

We have previously described various effects in adult Japanese quail consequent on treatment with oestrogenic compounds in ovo. In the present study, the environmental contaminant o,p'-DDT [1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2,2-trichloroethane] was administered to quail eggs to further evaluate test endpoints for oestrogenic effects related to reproduction in the Japanese quail. Exposure to 2 mg o,p'-DDT/egg (150 micro g/g egg) resulted in impaired sexual behaviour, reduced cloacal gland area and lowered plasma testosterone concentration in males. Females displayed oviductal abnormalities, including retained right oviduct, decreased length of left oviduct, alterations in shell gland morphology and disrupted distribution of carbonic anhydrase in the shell gland. Egg laying was severely impaired. Consequently, a number of endpoints in adult quail may be useful for demonstrating an oestrogen-like mode of action by environmental contaminants during embryonic development.

Zebrafish M2 muscarinic acetylcholine receptor: cloning, pharmacological characterization, expression patterns and roles in embryonic bradycardia

1. A zebrafish M2 muscarinic acetylcholine receptor (mAChR) gene was cloned. It encodes 495 amino acids in a single exon. The derived amino acid sequence is 73.5% identical to its human homologue. 2. Competitive binding studies of the zebrafish M2 receptor and [(3)H]-NMS gave negative log dissociation constants (pK(i)) for each antagonist as follows: atropine (9.16)>himbacine (8.05)>/=4-DAMP (7.83)>AF-DX 116 (7.26)>/=pirenzepine (7.18)>/=tropicamide (6.97)>/=methoctramine (6.82)>/=p-F-HHSiD (6.67)>carbachol (5.20). The antagonist affinity profile correlated with the profile of the human M2 receptor, except for pirenzepine. 3. Reverse transcription polymerase chain reaction and Southern blotting analysis demonstrated that the M2 mAChR mRNA levels increased during the segmentation period (12 h post-fertilization; h.p.f.) in zebrafish. By whole-mount in situ hybridization, the M2 mAChR was first detectable in the heart, vagus motor ganglion, and vagus sensory ganglion at 30, 48 and 60 h.p.f., respectively. 4. The muscarinic receptor that mediates carbachol (CCh)-induced bradycardia was functionally mature at 72 h.p.f. The effect of CCh-induced bradycardia was antagonized by several muscarinic receptor antagonists with the order of potency (pIC(50) values): atropine (6.76)>methoctramine (6.47)>himbacine (6.10)>4-DAMP (5.72)>AF-DX 116 (4.77), however, not by pirenzepine, p-F-HHSiD, or tropicamide (<10 micro M). 5. The effect of CCh-induced bradycardia was abolished completely before 56 h.p.f. by M2 RNA interference, and the bradycardia effect gradually recovered after 72 h.p.f. The basal heart rate was increased in embryos injected with M2 mAChR morpholino antisense oligonucleotide (M2 MO) and the effect of CCh-induced bradycardia was abolished by M2 MO in a dose-dependent manner. In conclusion, the results suggest that the M2 mAChR inhibit basal heart rate in zebrafish embryo and the M2 mAChR mediates the CCh-induced bradycardia.

Embryonic hypertension following exposure to teratogenic doses of 5-fluoro-2'-deoxyuridine

The teratogenicity of 5-fluoro-2'-deoxyuridine (FdU) is well established. Previously, we have demonstrated that teratogenic doses of FdU produce hematomas and suggested that those hematomas produced skeletal malformations in chicken embryos. In this study, the cardiovascular effects of teratogenic doses of FdU in chicken embryos were studied. A dose of either 0.026 micrograms FdU or 0.030 micrograms FdU was injected into the yolk sacs of fertile chicken eggs containing embryos at Hamburger and Hamilton stages 17-19 of development. The embryos were then returned to the incubator. Aortic systolic and diastolic blood pressure, blood velocity and heart rate were measured at stages 21, 24 or 27 using a servonull system and Doppler ultrasound. In addition, mean arterial blood pressure, blood flow, and stroke volume were calculated from these data. Similar data were also recorded from uninjected and saline injected control embryos. Systolic and mean arterial blood pressures were significantly increased in FdU-treated embryos at stage 27. The other parameters measured or calculated were not significantly different from control embryos. Our study suggests that elevated systolic blood pressure in chicken embryos treated with FdU may lead to hematoma formation and subsequent birth defects.

A diabetic-like condition of turkey embryos maintained in shell-less culture

Serum insulin concentration and pancreatic insulin content were determined for turkey embryos incubated in ovo and in long-term shell-less culture (ex ovo). Insulin was undetectable (less than 10 pg) in serum from 87% of the ex ovo embryos compared with their in ovo counterparts. This was evident at all incubation ages, although insulin was detectable in more of the ex ovo embryos on Day 24. Insulin increased in the embryos incubated in ovo from 122 (Day 15) to levels exceeding 2000 pg/ml at hatching. Total pancreatic insulin content was greater in the cultured embryos on Days 15, 17, and 22 compared with their in ovo counterparts. Serum glucose was significantly greater (P less than 0.05) in the ex ovo embryos at all ages. In response to an infusion of L-arginine, serum insulin increased from 566 to 1256 pg/ml in the in ovo embryos, whereas no change was evident in the ex ovo embryos (233 vs 257 pg/ml). When embryos incubated in ovo were injected with insulin, a significant (P less than 0.05) reduction of serum glucose was observed at 60 min after injection. Serum glucose concentrations remained elevated in the embryos incubated ex ovo despite the insulin injection. Liver glucose 6-phosphatase activity, assessed on Days 15 and 22 of incubation, was found to be significantly (P less than 0.05) lower in the ex ovo embryos. Turkey embryos incubated in shell-less culture exhibited chronic hyperglycemia in concert with extremely low circulating levels of insulin. The pancreatic beta cells of these embryos were not responsive to arginine or elevated glucose. Taken together these findings suggest the occurrence of a diabetic-like condition in the ex ovo embryos. This defect in insulin secretion may, in part, be responsible for some of the developmental abnormalities characteristic of the turkey embryo cultured ex ovo.