The organophosphate insecticide diazinon and aging: Neurobehavioral and mitochondrial effects in zebrafish exposed as embryos or during aging

Embryonic exposures to cadmium and PAHs cause long-term and interacting neurobehavioral effects in zebrafish

Developmental exposure to either polycyclic aromatic hydrocarbons (PAHs) or heavy metals has been shown to cause persisting and overlapping neurobehavioral effects in animal models. However, interactions between these compounds have not been well characterized, despite their co-occurrence in a variety of environmental media. In two companion studies, we examined the effects of developmental exposure to cadmium (Cd) with or without co-exposure to prototypic PAHs benzo[a]pyrene (BaP, Exp. 1) or fluoranthene (FA, Exp. 2) using a developing zebrafish model. Zebrafish embryos were exposed to Cd (0-0.3 μM), BaP (0-3 μM), FA (0-1.0 μM), or binary Cd-PAH mixtures from 5 to 122 h post fertilization (hpf). In Exp. 1, Cd and BaP produced independent effects on an array of outcomes and interacting effects on specific outcomes. Notably, Cd-induced deficits in dark-induced locomotor stimulation were attenuated by BaP co-exposure in the larval motility test and BaP-induced hyperactivity was attenuated by Cd co-exposure in the adolescent novel tank test. Likewise, in Exp. 2, Cd and FA produced both independent and interacting effects. FA-induced increases on adult post-tap activity in the tap startle test were attenuated by co-exposure with Cd. On the predator avoidance test, FA- and 0.3 μM Cd-induced hyperactivity effects were attenuated by their co-exposure. Taken together, these data indicate that while the effects of Cd and these representative PAHs on zebrafish behavior were largely independent of one another, binary mixtures can produce sub-additive effects for some neurobehavioral outcomes and at certain ages. This research emphasizes the need for detailed risk assessments of mixtures containing contaminants of differing classes, and for clarity on the mechanisms which allow cross-class toxicant interactions to occur.

Protective effects of Biebersteinia multifida on sub-chronic toxicity of DZN in male Wistar rats: biochemical, hematological, and oxidative stress indices

The protective effect of Biebersteinia Multifida on diazinon-induced toxicity in male Wistar rats was investigated over 8 weeks. Impacts of diazinon (10 mg/kg daily), Biebersteinia Multifida (500 mg/kg daily), and coadministration of them on oxidative stress parameters besides hematological and biochemical indices were assessed in various groups. The gas chromatography-mass spectrometry analysis was performed to identify the antioxidant components of plant extract by comparing the mass spectra and retention indices with those given in the literature. Pseudocholinesterase level demonstrated a significant attenuation in the Biebersteinia Multifida+diazinon-treated group in comparison to the diazinon group at the end of the 8th week. Statistical significant differences in hematological and biochemical indices were detectable when the diazinon group was compared to Biebersteinia Multifida+diazinon-treated rats. While diazinon destroyed hepatic and renal functions, Biebersteinia Multifida protected the liver and kidney from diazinon toxic effects by normalizing related function indices at the end of the 8th week. By diminishing malondialdehyde and enhancing the ferric-reducing power, Biebersteinia Multifida minimized the hazardous effect of diazinon-induced oxidative stress. Following these results, the beneficial effects of Biebersteinia Multifida in reducing the toxicity of diazinon should be taken into consideration.

Developmental exposure of zebrafish to neonicotinoid pesticides: Long-term effects on neurobehavioral function

Neonicotinoid compounds are commonly used insecticides which have become increasingly used as replacements of older generations of insecticides, such as organophosphates. Given the established neurotoxicity of cholinergic toxicants, developmental neurotoxicity studies are needed to identify in vertebrate species the potential toxicity of these insecticides which act on nicotinic cholinergic receptors. Previously, developmental exposure to a neonicotinoid insecticide imidacloprid was shown to cause persisting neurobehavioral toxicity in zebrafish. The current study evaluated neurobehavioral effects of embryonic exposure to two other neonicotinoid insecticides, clothianidin (1-100 µM) and dinotefuran (1-100 µM) in zebrafish (5-120 h post-fertilization), concentrations below the threshold for increased lethality and overt dysmorphogenesis. Neurobehavioral tests were conducted at larval (6 days), adolescent (10 weeks) and adult (8 months) ages. Both compounds caused short-term behavioral effects on larval motility, although these effects were distinct from one another. At a lower concentration (1 µM) clothianidin increased dark-induced locomotor stimulation the second time the lights turned off, while a higher concentration (100 µM) reduced activity in the dark at its second presentation. By contrast, dinotefuran (10-100 µM) caused a general decrease in locomotion. Specific longer-term neurobehavioral toxicity after early developmental exposure was also seen. clothianidin (100 µM) reduced locomotor activity in the novel tank in adolescence and adulthood, as well as reduced baseline activity in the tap startle test (1-100 µM) and reduced activity early (1-10 µM) or throughout the predator avoidance test session (100 µM). In addition to locomotor effects, clothianidin altered the diving response in a dose-, age- and time-block-dependent manner (1 µM, 100 µM), causing fish to remain further away from a fast predator cue (100 µM) relative to controls. Dinotefuran produced comparatively fewer effects, increasing the diving response in adulthood (10 µM), but not adolescence, and suppressing initial locomotor activity in the predator avoidance test (1-10 µM). These data indicate that neonicotinoid insecticides may carry some of the same risks for vertebrates posed by other classes of insecticides, and that these adverse behavioral consequences of early developmental exposure are evident well into adulthood.

Organophosphate Insecticide Toxicity in Neural Development, Cognition, Behaviour and Degeneration: Insights from Zebrafish

Organophosphate (OP) insecticides are used to eliminate agricultural threats posed by insects, through inhibition of the neurotransmitter acetylcholinesterase (AChE). These potent neurotoxins are extremely efficacious in insect elimination, and as such, are the preferred agricultural insecticides worldwide. Despite their efficacy, however, estimates indicate that only 0.1% of organophosphates reach their desired target. Moreover, multiple studies have shown that OP exposure in both humans and animals can lead to aberrations in embryonic development, defects in childhood neurocognition, and substantial contribution to neurodegenerative diseases such as Alzheimer's and Motor Neurone Disease. Here, we review the current state of knowledge pertaining to organophosphate exposure on both embryonic development and/or subsequent neurological consequences on behaviour, paying particular attention to data gleaned using an excellent animal model, the zebrafish (Danio rerio).

Cyclophosphamide alters the behaviors of adult Zebrafish via neurotransmitters and gut microbiota

Cyclophosphamide, one of the earliest prescribed alkylating anticancer drugs, has been frequently detected in aquatic environments. However, its effects on fish behavior and associated mechanisms remain largely unknown. In this study, the behaviors, neurochemicals, and gut microbiota of adult zebrafish were investigated after 2 months of exposure to CP at 0.05, 0.5, 5, and 50 µg/L. Behavioral assays revealed that CP increased locomotion and anxiety, and decreased the cognition of zebrafish. The alteration of neurotransmitters and related gene expressions in the dopamine and gamma-aminobutyric acid pathways induced by CP may be responsible for the observed changes in locomotion and cognition of adult zebrafish. Meanwhile, CP increased the anxiety of adult zebrafish through the serotonin, acetylcholine, and histamine pathways in the brain. In addition, increased abundances of Fusobacteriales, Reyanellales, Staphylococcales, Rhodobacterals, and Patescibateria in the intestine at the CP-50 treatment were observed. The study has demonstrated that CP affects the locomotion, anxiety, and cognition in zebrafish, which might be linked with the dysfunction of neurochemicals in the brain. This study further suggests that the gut-brain axis might interact to modulate fish behaviors upon exposure to CP (maybe other organic pollutants). Further research is warranted to test this hypothesis.

Zebrafish Larvae Rapidly Recover from Locomotor Effects and Neuromuscular Alterations Induced by Cholinergic Insecticides

Owing to the importance of acetylcholine as a neurotransmitter, many insecticides target the cholinergic system. Across phyla, cholinergic signaling is essential for many neuro-developmental processes including axonal pathfinding and synaptogenesis. Consequently, early-life exposure to such insecticides can disturb these processes, resulting in an impaired nervous system. One test frequently used to assess developmental neurotoxicity is the zebrafish light-dark transition test, which measures larval locomotion as a response to light changes. However, it is only poorly understood which structural alterations cause insecticide-induced locomotion defects and how persistent these alterations are. Therefore, this study aimed to link locomotion defects with effects on neuromuscular structures, including motorneurons, synapses, and muscles, and to investigate the longevity of the effects. The cholinergic insecticides diazinon and dimethoate (organophosphates), methomyl and pirimicarb (carbamates), and imidacloprid and thiacloprid (neonicotinoids) were used to induce hypoactivity. Our analyses revealed that some insecticides did not alter any of the structures assessed, while others affected axon branching (methomyl, imidacloprid) or muscle integrity (methomyl, thiacloprid). The majority of effects, even structural, were reversible within 24 to 72 h. Overall, we find that both neurodevelopmental and non-neurodevelopmental effects of different longevity can account for the reduced locomotion. These findings provide unprecedented insights into the underpinnings of insecticide-induced hypoactivity.

Melatonin improves meiosis maturation against diazinon exposure in mouse oocytes

AIMS

Organophosphorus pesticide diazinon (DZN) has adverse effects on animals and humans by direct contact or the spread of food chain. The antioxidant melatonin has protective effects on female reproduction. This study aimed to explore the effects of DZN on meiosis maturation in mouse cumulus oocyte complexes (COCs) and the effects of melatonin.

MAIN METHODS

Different concentrations of DZN and melatonin were added during the in vitro maturation of COCs. Then we detected the extrusion rate of the first polar body, the number of sperms binding to oocyte, mitochondrial membrane potential, reactive oxygen species (ROS), early apoptosis. Subsequently, the expression of Juno, CX37, CX43 and ERK1/2 were detected by immunofluorescence staining and Western blotting.

KEY FINDINGS

DZN exposure results in the failure of nuclear and cytoplasmic maturation of oocyte meiosis. Destruction of repositioning and function of mitochondria increases the levels of ROS and early apoptosis. The DZN-exposed oocytes express less Juno resulting to bind less sperms than normal. The loss of gap junctions and failure to activate ERK1/2 also contribute to the failure of cytoplasmic maturation. All these ultimately lead to the poor oocyte quality and low fertility. Appropriate melatonin can effectively restore all these defects.

SIGNIFICANCE

Under DZN exposure, melatonin can significantly improve the quality of oocytes, and melatonin promotes oocyte maturation by protecting gap junction and restoring ERK1/2 pathway, which is a new breakthrough for improving female fertility.