Cardiovascular Performance Measurement in Water Fleas by Utilizing High-Speed Videography and ImageJ Software and Its Application for Pesticide Toxicity Assessment

Non-invasive recording of heartbeats in Danio rerio and Daphnia magna to assess the toxicity of imidacloprid and glyphosate

Non-invasive optical registration and subsequent analysis of heart rate (HR) and heart rate variability (HRV) in transparent aquatic animals have recently been proposed as convenient toxicological endpoints, well-suited for automation data acquisition and processing. This approach was evaluated in experiments involving juvenile Daphnia magna and zebrafish (Danio rerio) embryos exposed to glyphosate solutions (20 mg/L, 2 mg/L, 0.2 mg/L, and 0.02 mg/L) and imidacloprid solutions (30 mg/L, 3 mg/L, 0.3 mg/L, and 0.03 mg/L). The findings indicate that cardiac performance assessment is a promising approach for short-term toxicity evaluation. However, the sensitivity of this physiological endpoint to various external factors may limit its broader application. Results from the two model species highlight their differing sensitivities to the tested substances, emphasizing the need for thorough preliminary studies before establishing this method as a standardized toxicological tool. The potential development and improvement of techniques for assessing heart rate in zebrafish and daphnids are discussed.

Water acidification aggravates lithium-induced toxicity represented by energy supply, oxidative stress, and cell fate in Daphnia magna neonates

Lithium is extensively utilized in industrial energy production, particularly in lithium-ion batteries, and in pharmaceuticals for the treating clinical mood disorders. Consequently, lithium is frequently detected in various environmental matrices. It has been reported to cause a range of toxic effects on aquatic organisms including oxidative stress, neurological disorders, and reproductive suppression. Water acidification is a global issue with numerous negative impacts on aquatic organisms. It can alter the physio-chemical properties and bioavailability of metal ions. The acidic leaching process during lithium battery treatment and global water acidification both suggest that lithium contamination often occurs in acidic environments. In the present study, Daphnia magna neonates were exposed to four treatments (control, lithium alone, low pH, and combined) to investigate whether an acidic environment exacerbates the toxic effects of lithium on aquatic organisms and to explore potential toxic action mechanisms. The results indicated that low pH posed a significant threat to the growth and reproduction of D. magna. When exposed to both lithium and low pH, there was increased lithium accumulation and an energy trade-off response, leading to increased energy allocation to reproduction and reduced energy for growth. Lithium exposure stimulated D. magna activity, while low pH inhibited it, suggesting that an imbalance in energy consumption and supply. Combined exposure to lithium and low pH resulted in severe oxidative stress due to mitochondrial dysfunction, under-utilization of energy substances, and increased ionic homeostasis disturbances. Consequently, the exposed organism altered apoptosis and autophagy processes to maintain homeostasis. The present study demonstrated that lithium and water acidification posed a population-level threat to D. magna, and their combined exposure significantly largely exacerbated the toxic effects.

Acute and chronic effects of the antifouling booster biocide Irgarol 1051 on the water flea Moina macrocopa revealed by multi-biomarker determination

Irgarol 1051 is an herbicide extensively utilized in antifouling paint due to its ability to inhibit photosynthesis. Irgarol and its photodegradation products are highly persistent in waters and sediments, although they are present in low concentrations. However, our understanding of the harmful effects of Irgarol on non-target organisms remains limited. In this study, we assessed the effects of acute (24 h) and chronic (14 days across three generations) exposure to different concentrations (including the 1/10 NOEC, NOEC, and 1/10 LC50 calculated from the 24-h acute toxicity test) of Irgarol using the water flea Moina macrocopa. Acute exposure to 1/10 LC50 significantly decreased survival, feeding rate, thoracic limb activity, heart rate, and acetylcholinesterase activity. Elevated levels of intracellular reactive oxygen species and malondialdehyde, along with a significant increase in catalase and superoxide dismutase activity, suggested the induction of oxidative stress in response to 1/10 LC50. An initial boost in glutathione level and the enzymatic activities of glutathione peroxidase and glutathione reductase, followed by a plunge, implies some compromise in the antioxidant defense system. Upon chronic exposure to the NOEC value, both generations F1 and F2 displayed a significant decrease in survival rate, body length, number of neonates per brood, and delayed sexual maturation, suggesting maternal transfer of potential damage through generations. Taken together, Irgarol induced acute toxicity through physiological and cholinergic damage, accompanied by the induction of oxidative stress, in the water flea. Even its sub-lethal concentrations can induce detrimental effects across generations when consistently exposed.

Evaluation of arsenic induced genotoxicity and its impact on life processes of Daphnia magna

Heavy metals like arsenic is ubiquitously present in the environment. Geologic and anthropogenic activities are the root cause behind high concentration of arsenic in natural water bodies demanding strict monitoring of water quality prior to human consumption and utilization. In the present study, we have employed Daphnia magna for studying the biological effects of environmentally relevant high concentration of arsenic in water. In acute toxicity study, the LC50 value for 24hr exposure was found to be 2.504 mg/L, which gradually decreased with increase in time period (24hr- 96hr) to 2.011 mg/ L at 96hr. Sub-chronic toxicity was evaluated over 12 days using sub-lethal concentrations (5 %, 10 %, 15 %, and 20 % of the 24-hr LC50). Survivability in Daphnia showed a decreasing trend from 96 % to 91 % with increase in arsenic concentrations from 5 % of LC50 24 hr value to 20 % of LC 50 24hr value respectively. Alongside decreased survivability, there was a significant reduction in body size, with organisms exposed to the highest concentration of arsenic measuring 0.87±0.01 mm compared to 1.51±0.10 mm in the control group. Reproductive potential declined concentration dependently with exposure, with the highest reduction observed at 20 % of LC50 24hr value, where offspring numbers decreased to 7±1 from 23±5 in the control. Heart rate decreased in concentration and time-dependent manners, with the lowest rates observed at the highest arsenic concentration (279±16 bpm after 24hr and 277±27 bpm after 48hr). Comet assay and micronucleus assay conducted after 48 hrs of exposure revealed concentration-dependent genotoxic effects in Daphnia magna. Our results indicate negative impact on physiology and reproduction of Daphnia magna at environmentally existent concentration of arsenic. Also Daphnia magna could serve as a sensitive test system for investigating arsenic contamination in water bodies.

Evaluation of Cardiotoxicity of Cancer Chemotherapeutics Using Daphnia magna as a Preclinical Model

One of the major concerns following cancer treatment is cardiotoxicity. Therefore, it is important to predict potential cardiotoxicity of cancer chemotherapeutics at the preclinical phase. Current models of cardiotoxicity testing involve either cell culture models or rodent models. We developed a simple invertebrate animal model for rapid screening of cardiotoxicity of cancer chemotherapeutics. Daphnia magna (water flea, a crustacean) has a transparent body and a large myogenic heart that can be easily monitored under a microscope. Using this model, we have previously described comparative cardiotoxicity of several kinase inhibitors that were approved for the treatment of multiple cancers. In this article, we describe the step-wise protocols for evaluating the heart rate and survival of D. magna with relevant information on troubleshooting. © 2024 Wiley Periodicals LLC. Basic Protocol 1: Culturing and maintenance of D. magna Basic Protocol 2: Experimental design for evaluating heart rate of Daphnia Basic Protocol 3: Long-term effect on Daphnia survival upon drug exposure.

Ciliated Epibionts Modify the Cardiac Stress Reaction to Perceived Predation in Daphnia

When animals perceive an acute stressor like a predator, they typically undergo a suite of physiological changes that function to improve survival during the encounter, such as elevation in cardiac output, to supply more energy to muscles. If bodily energy is limited, such as by parasites or infections, these functions could become less efficient and lessen host survival. In the aquatic world of microorganisms, individuals can become colonized by other organisms on their surface (epibionts), which could sap energy from their host from their weight, or even compete with the host for food. Here, we tested if one epibiont (a ciliated protozoan, Vorticella spp.) affects its hosts' ability to mount a physiological stress reaction. We collected wild daphnia (Daphnia ambigua) that had varying burdens of these on their bodies and exposed them to a simulated stressor (crushed daphnia, to simulate nearby predation) under a microscope while monitoring for changes in their heart rates in real time. Out of 121 daphnia, those with no Vorticella epibionts showed no meaningful changes in their heart rate after exposure, but those with light or heavy burdens showed immediate elevations (within 5 min). Moreover, the heart rates of heavily burdened daphnia continued to rise for 1.5 h thereafter, to as much as 17% higher than at baseline. These patterns were unexpected, as they suggest that the ciliated epibionts act to elevate their hosts' physiological reaction, rather than dampen it, perhaps by churning the water column around the host, thereby enhancing the chemical alarm cue. The procedures used in this study may be useful for future investigations into the acute stress reactions of daphnia or other microorganisms.

A simple and rapid pre-clinical in vivo model reveals comparative cardiotoxicity profiles of kinase inhibitors

Despite significant success, targeted therapeutics such as kinase inhibitors (KIs) still pose adverse events such as the cardiotoxicity. There is a lot of variation in the type and intensity of cardiotoxicity caused by different KIs and current pre-clinical models are inadequate to predict it. Thus, there is a need to develop more simple and rapid models for screening of novel KIs at the pre-clinical step itself. We thus aimed to establish a rapid and robust pre-clinical animal model for predicting cardiotoxicity of KIs and identify comparative cardiotoxicity profiles of a panel of FDA-approved KIs. Heart rate measurement and survival analysis of Daphnia was performed at regular intervals following treatment with ten KIs that were approved for the treatment of various cancers. The heart rates of Daphnia as well as the survival varied between KIs in a dose and time dependent manner suggesting differential cardiotoxicity profiles of various KIs. Further, the correlation between the cardiotoxicity and survival also varied among the ten KIs. Importantly, sorafenib and vemurafenib displayed maximum and least cardiotoxicity, respectively. The comparative cardiotoxicity profiles also are in conformity with the previous studies indicating the utility of Daphnia as a valuable and relevant animal model to rapidly predict the cardiotoxicity of novel KIs at a pre-clinical stage.

Geographic origin shapes the adaptive divergences of Rotaria rotatoria (Rotifera, Bdelloidea) to thermal stress: Insights from ecology and transcriptomics

Global warming has raised concerns regarding the potential impact on aquatic biosafety and health. To illuminate the adaptive mechanisms of bdelloid rotifers in response to global warming, the ecological and transcriptomic characteristics of two strains (HX and ZJ) of Rotaria rotatoria were investigated at 25°C and 35°C. Our results showed an obvious genetic divergence between the two geographic populations. Thermal stress significantly reduced the average lifespan of R. rotatoria in both strains, but increased the offspring production in the ZJ strain. Furthermore, the expression levels of genes Hsp70 were significantly upregulated in the HX strain, while GSTo1 and Cu/Zn-SOD were on the contrary. In the ZJ strain, the expression levels of genes Hsp70, CAT2, and GSTo1 were upregulated under thermal stress. Conversely, a significant decrease in the expression level of the Mn-SOD gene was observed in the ZJ strain under thermal stress. Transcriptomic profiling analysis revealed a total of 105 and 5288 differentially expressed genes (DEGs) in the HX and ZJ strains under thermal stress, respectively. The PCA results showed clear differences in gene expression pattern between HX and ZJ strains under thermal stress. Interestingly, compared to the HX strain, numerous downregulated DEGs in the ZJ strain were enriched into pathways related to metabolism under thermal stress, suggesting that rotifers from the ZJ strain prioritize resource allocation to reproduction by suppressing costly metabolic processes. This finding is consistent with the life table results. This study provides new insights into the adaptive evolution of aquatic animals in the context of global climate change.

Cardiotoxic and neurobehavioral effects of sucralose and acesulfame in Daphnia: Toward understanding ecological impacts of artificial sweeteners

Artificial sweeteners are widely used in food and pharmaceuticals, but their stability and persistence raise concerns about their impact on aquatic life. Although standard toxicity tests do not reveal lethal effects, recent studies suggest a potential neurotoxic mode of action. Using environmentally relevant concentrations, we assessed the effects of sucralose and acesulfame, common sugar substitutes, on Daphnia magna focusing on biochemical (acetylcholinesterase activity; AChE), physiological (heart rate), and behavioural (swimming) endpoints. We found dose-dependent increases in AChE and inhibitory effects on heart rate and behaviour for both substances. Moreover, acesulfame induced a biphasic response in AChE activity, inhibiting it at lower concentrations and stimulating at higher ones. For all endpoints, the EC50 values were lower for acesulfame than for sucralose. Additionally, the relationship between acetylcholinesterase and heart rate differed depending on the substance, suggesting possible differences in the mode of action between sucralose and acesulfame. All observed EC50 values were at μg/l levels, i.e., within the levels reported for wastewater, with adverse effects observed at as low as 0.1 μg acesulfame /l. Our findings emphasise the need to re-evaluate risk assessment thresholds for artificial sweeteners and provide evidence for the neurotoxic effects of artificial sweeteners in the environment, informing international regulatory standards.

Toxic effects of four emerging pollutants on cardiac performance and associated physiological parameters of the thick-shell mussel (Mytilus coruscus)

Robust cardiac performance is critical for the health and even survival of an animal; however, it is sensitive to environmental stressors. At present, little is known about the cardiotoxicity of emerging pollutants to bivalve mollusks. Thus, in this study, the cardiotoxic effects of four emergent pollutants, carbamazepine (CBZ), bisphenol A (BPA), tetrabromobisphenol A (TBBPA), and tris(2-chloroethyl) phosphate (TCEP), on the thick-shell mussel, Mytilus coruscus, were evaluated by heartbeat monitoring and histological examinations. In addition, the impacts of these pollutants on parameters that closely related to cardiac function including neurotransmitters, calcium homeostasis, energy supply, and oxidative status were assessed. Our results demonstrated that 28-day exposure of the thick-shell mussel to these pollutants resulted in evident heart tissue lesions (indicated by hemocyte infiltration and myocardial fibrosis) and disruptions of cardiac performance (characterized by bradyrhythmia and arrhythmia). In addition to obstructing neurotransmitters and calcium homeostasis, exposure to pollutants also led to constrained energy supply and induced oxidative stress in mussel hearts. These findings indicate that although do differ somehow in their effects, these four pollutants may exert cardiotoxic impacts on mussels, which could pose severe threats to this important species and therefore deserves more attention.

Using DeepLabCut for markerless cardiac physiology and toxicity estimation in water fleas (Daphnia magna)

Daphnia magna is one species of water flea that has been used for a long time for ecotoxicity studies. In addition, Daphnia has a myogenic heart that is very useful for cardiotoxicity studies. Previous attempts to calculate the cardiac parameter endpoints in Daphnia suffer from the drawback of tedious operation and high variation due to manual counting errors. Even the previous method that utilized deep learning to help the process suffer from either overestimation of parameters or the need for specialized equipment to perform the analysis. In this study, we utilized DeepLabCut software previously used for animal pose tracking and demonstrated that ResNet_152 was the best fit for training the network. The trained network also showed comparable results with ImageJ and Kymograph, which was mostly done manually. In addition to that, several macro scripts in either Excel or Python format were developed to help summarize the data for faster analysis. The trained network was then challenged to analyze the potential cardiotoxicity of imidacloprid and pendimethalin in D. magna, and it showed that both pesticides cause alteration in their cardiac performance. Overall, this method provides a simple and automatic method to analyze the cardiac performance of Daphnia by utilizing DeepLabCut. The method proposed in this paper can contribute greatly to scientists conducting fast and accurate cardiotoxicity measurements when using Daphnia as a model.

The Effect of the Pyrethroid Pesticide Fenpropathrin on the Cardiac Performance of Zebrafish and the Potential Mechanism of Toxicity

Fenpropathrin, a pyrethroid insecticide, has been widely used for many years in agricultural fields. It works by disturbing the voltage-gated sodium channel, leading to paralysis and the death of the target animal. While past studies have focused on neurodegeneration following fenpropathrin poisoning in humans, relatively few pieces of research have examined its effect on other peripheral organs. This study successfully investigated the potential toxicity of fenpropathrin on the cardiovascular system using zebrafish as an animal model. Zebrafish larvae exposed to varying doses of fenpropathrin underwent an evaluation of cardiac physiology by measuring the heart rate, stroke volume, cardiac output, and shortening fraction. The blood flow velocity and the dorsal aorta diameter were also measured to assess the impact of fenpropathrin exposure on the vascular system. Furthermore, molecular docking was performed to evaluate the pesticide binding affinity to various proteins associated with the cardiovascular system, revealing the potential mechanism of the fenpropathrin cardiotoxic effect. The findings demonstrated a significant dose-dependent increase in the heart rate stroke volume, cardiac output, shortening fraction, and ejection fraction of zebrafish larvae after 24 h of acute treatment with fenpropathrin. Additionally, zebrafish treated at a concentration of 1 ppm exhibited significantly larger blood vessels in diameter and an increased blood flow velocity compared to the control group. According to molecular docking, fenpropathrin showed a high affinity for various voltage-gated sodium channels like scn1lab, cacna1sb, and clcn3. Finally, from the results, we found that fenpropathrin caused cardiomegaly, which may have been induced by the voltage-gated sodium channel disruption. This study highlights the significant disruption of fenpropathrin in the cardiovascular system and emphasizes the need for further research on the health implications of this pesticide.

HeartCV: a tool for transferrable, automated measurement of heart rate and heart rate variability in transparent animals

Heart function is a key component of whole-organismal physiology. Bioimaging is commonly, but not exclusively, used for quantifying heart function in transparent individuals, including early developmental stages of aquatic animals, many of which are transparent. However, a central limitation of many imaging-related methods is the lack of transferability between species, life-history stages and experimental approaches. Furthermore, locating the heart in mobile individuals remains challenging. Here, we present HeartCV: an open-source Python package for automated measurement of heart rate and heart rate variability that integrates automated localization and is transferrable across a wide range of species. We demonstrate the efficacy of HeartCV by comparing its outputs with measurements made manually for a number of very different species with contrasting heart morphologies. Lastly, we demonstrate the applicability of the software to different experimental approaches and to different dataset types, such as those corresponding to longitudinal studies.

Finding the Missing Property Concepts in Pesticide-Likeness

Poor bioavailability of pesticides is one of the major bottlenecks in the development of pesticides. Applications of the concept of pesticide-likeness have been widely accepted as one of the ways to break the bottleneck. At present, the evaluation of pesticide-likeness is mainly based on absorption, distribution, metabolism, excretion, and toxicity (ADME-T) property concepts of pesticides. However, a few significant property concepts of pesticides are ignored in the research of pesticide-likeness. Herein, we summarize the current study of ADME-T and other property concepts and analyze physicochemical properties for pesticides in the last 30 years, such as Fsp³, log P, and chiral centers. On the basis of these analyses, we propose that molecular complexity and residual property concepts of pesticides should be considered in the pesticide-likeness study. We hope that this work can help pesticide researchers and students, who are less knowledgeable in the field, to assess pesticide-likeness.

Using DeepLabCut as a Real-Time and Markerless Tool for Cardiac Physiology Assessment in Zebrafish

DeepLabCut (DLC) is a deep learning-based tool initially invented for markerless pose estimation in mammals. In this study, we explored the possibility of adopting this tool for conducting markerless cardiac physiology assessment in an important aquatic toxicology model of zebrafish (Danio rerio). Initially, high-definition videography was applied to capture heartbeat information at a frame rate of 30 frames per second (fps). Next, 20 videos from different individuals were used to perform convolutional neural network training by labeling the heart chamber (ventricle) with eight landmarks. Using Residual Network (ResNet) 152, a neural network with 152 convolutional neural network layers with 500,000 iterations, we successfully obtained a trained model that can track the heart chamber in a real-time manner. Later, we validated DLC performance with the previously published ImageJ Time Series Analysis (TSA) and Kymograph (KYM) methods. We also evaluated DLC performance by challenging experimental animals with ethanol and ponatinib to induce cardiac abnormality and heartbeat irregularity. The results showed that DLC is more accurate than the TSA method in several parameters tested. The DLC-trained model also detected the ventricle of zebrafish embryos even in the occurrence of heart abnormalities, such as pericardial edema. We believe that this tool is beneficial for research studies, especially for cardiac physiology assessment in zebrafish embryos.

Physiological response of Simocephalus vetulus to five antibiotics and their mixture under 48-h acute exposure

Antibiotics, widely known as major environmental xenobiotics, are increasingly being released into ecosystems due to their essential functions in human health and production. During the COVID-19 pandemic waves, antibiotic use increases remarkably in treating bacterial coinfections. Antibiotics were initially expected only to affect prokaryotes, but recent research has shown that they can disturb the biological systems of eukaryotes, especially vulnerable aquatic creatures, through both direct and indirect processes. However, their toxicity to the freshwater cladoceran Simocephalus vetulus, an essential link in the aquatic food web, has never been evaluated. The effects of four fluoroquinolones (ciprofloxacin: CFX, ofloxacin: OFX, gatifloxacin: GFX, delafloxacin: DFX), tetracycline (TET), and a mixture of these medicines (MIX) on S. vetulus thoracic limb rate (TLR) were examined in this study. After S. vetulus was exposed to 20 and 40 mg GFX L^-1, 90% and 100% mortality rates were recorded. At 2.5-10 mg L^-1, GFX dramatically lowered the TLR of S. vetulus, resulting in a median effective concentration of 9.69 mg L^-1. TLRs increased when the organisms were exposed to 10-40 mg L^-1 of CFX and 1.25-40 mg L^-1 of OFX. However, DFX and TET exposures did not affect TLRs. Exposure to MIX reduced TLR only at 40 mg L^-1, suggesting an antagonistic interaction among the five pharmaceuticals. This study demonstrated that S. vetulus physiological responses to antibiotics, even in the same class, are complex and elusive. Beyond a common additive concentration principle, the antagonistic interaction of antibiotic mixture indicates a high level of uncertainty in terms of ecological dangers. We initially introduce S. vetulus to ecotoxicological studies of antibiotics, presenting the species as a low-cost model for physiological investigations of environmental xenobiotics.

Automated Cardiac Chamber Size and Cardiac Physiology Measurement in Water Fleas by U-Net and Mask RCNN Convolutional Networks

Simple Summary

With the rapid development of technology, artificial intelligent become a major breakthrough that can help human with laborious job. Previously cardiac imaging in Daphnia was also suffer from laborious and tedious process to extract some information from it. Thus the aim of this study was to develop a simple artificial intelligent based method to help anyone in this field to perform analysis in fast, reliable, and less tedious manner. In this study, we compare U-Net and Mask RCNN and found out that Mask RCNN was perform better than U-Net in cardiac chamber area estimation. From this data, several parameter like heart rhythm, stroke volume, ejection fraction, fractional shortening, and cardiac output can be extracted. The validation was done by comparing the normal and Roundup exposed group and it show that Roundup can increase the stroke volume, cardiac output, and the shortening fraction of Daphnia magna.

Abstract

Water fleas are an important lower invertebrate model that are usually used for ecotoxicity studies. Contrary to mammals, the heart of a water flea has a single chamber, which is relatively big in size and with fast-beating properties. Previous cardiac chamber volume measurement methods are primarily based on ImageJ manual counting at systolic and diastolic phases which suffer from low efficiency, high variation, and tedious operation. This study provides an automated and robust pipeline for cardiac chamber size estimation by a deep learning approach. Image segmentation analysis was performed using U-Net and Mask RCNN convolutional networks on several different species of water fleas such as Moina sp., Daphnia magna, and Daphnia pulex. The results show that Mask RCNN performs better than U-Net at the segmentation of water fleas’ heart chamber in every parameter tested. The predictive model generated by Mask RCNN was further analyzed with the Cv2.fitEllipse function in OpenCV to perform a cardiac physiology assessment of Daphnia magna after challenging with the herbicide of Roundup. Significant increase in normalized stroke volume, cardiac output, and the shortening fraction was observed after Roundup exposure which suggests the possibility of heart chamber alteration after roundup exposure. Overall, the predictive Mask RCNN model established in this study provides a convenient and robust approach for cardiac chamber size and cardiac physiology measurement in water fleas for the first time. This innovative tool can offer many benefits to other research using water fleas for ecotoxicity studies.

Vital signal sensing and manipulation of a microscale organ with a multifunctional soft gripper

[Figure: see text].

An OpenCV-Based Approach for Automated Cardiac Rhythm Measurement in Zebrafish from Video Datasets

Cardiac arrhythmia has been defined as one of the abnormal heart rhythm symptoms, which is a common problem dealt with by cardiologists. Zebrafish were established as a powerful animal model with a transparent body that enables optical observation to analyze cardiac morphology and cardiac rhythm regularity. Currently, research has observed heart-related parameters in zebrafish, which used different approaches, such as starting from the use of fluorescent transgenic zebrafish, different software, and different observation methods. In this study, we developed an innovative approach by using the OpenCV library to measure zebrafish larvae heart rate and rhythm. The program is designed in Python, with the feature of multiprocessing for simultaneous region-of-interest (ROI) detection, covering both the atrium and ventricle regions in the video, and was designed to be simple and user-friendly, having utility even for users who are unfamiliar with Python. Results were validated with our previously published method using ImageJ, which observes pixel changes. In summary, the results showed good consistency in heart rate-related parameters. In addition, the established method in this study also can be widely applied to other invertebrates (like Daphnia) for cardiac rhythm measurement.

Exploiting the Freshwater Shrimp Neocaridina denticulata as Aquatic Invertebrate Model to Evaluate Nontargeted Pesticide Induced Toxicity by Investigating Physiologic and Biochemical Parameters

As a nicotinoid neurotoxic insecticide, imidacloprid (IMI) works by disrupting nerve transmission via nicotinic acetylcholine receptor (nAChR). Although IMI is specifically targeting insects, nontarget animals such as the freshwater shrimp, Neocaridina denticulata, could also be affected, thus causing adverse effects on the aquatic environment. To investigate IMI toxicity on nontarget organisms like N. denticulata, their physiology (locomotor activity, heartbeat, and gill ventilation) and biochemical factors (oxidative stress, energy metabolism) after IMI exposure were examined. IMI exposure at various concentrations (0.03125, 0.0625, 0.125, 0.25, 0.5, and 1 ppm) to shrimp after 24, 48, 72 h led to dramatic reduction of locomotor activity even at low concentrations. Meanwhile, IMI exposure after 92 h caused reduced heartbeat and gill ventilation at high concentrations. Biochemical assays were performed to investigate oxidative stress and energy metabolism. Interestingly, locomotion immobilization and cardiac activity were rescued after acetylcholine administration. Through molecular docking, IMI demonstrated high binding affinity to nAChR. Thus, locomotor activity and heartbeat in shrimp after IMI exposure may be caused by nAChR blockade and not alterations caused by oxidative stress and energy metabolism. To summarize, N. denticulata serves as an excellent and sensitive aquatic invertebrate model to conduct pesticide toxicity assays that encompass physiologic and biochemical examinations.