A microfluidic device to study electrotaxis and dopaminergic system of zebrafish larvae

Swim in Plastics: Clean Nanoplastics Cause Minimal Mortality but Alter Neurobehavioral and Molecular Rhythms in Fish

Nanoplastics (NPs) pose potential ecological and health impacts. While previous studies have highlighted inconsistent toxicity levels of NPs, knowledge remains limited about the specific effects of different NPs on embryonic development, early life-stage behaviors, and bodily uptake. This study examines the effects of polystyrene NPs (PS-NPs) with different surface charges, plain polystyrene (PS), amino-modified (PS-NH2), and carboxyl-modified (PS-COOH) on zebrafish early life stages. High-resolution 3D bioimaging confirmed differential internalization: PS-COOH accumulated in the yolk and intestine, while PS-NH2 localized mainly in the intestine. PS-NPs up to 10 ppm did not significantly affect mortality or hatching rates, likely due to effective dialysis, minimizing toxic chemical leaching. PS-NP exposure led to noninflated swim bladders and affected swimming. RNA sequencing identified impacted neurological molecular pathways like circadian rhythm and visual function; weighted gene coexpression network analysis indicated strong correlations between key gene modules and phenotypic traits like eye development and dopamine level. We highlight the low acute toxicity of clean dialyzed NPs despite bodily uptake and surface-charge-dependent sublethal neurotoxicity. Overall, plain PS-NPs induced significant individual-level effects, while charged PS-NPs caused stronger molecular-level alterations; toxicity profiles varied across biological levels, complicating hazard assessment and underscoring the need for population-level studies on ecological impacts.

Protective Effects of Fasudil Against Cisplatin-Induced Ototoxicity in Zebrafish: An In Vivo Study

While cisplatin is an effective anti-tumor treatment, it induces ototoxicity through mechanisms involving DNA damage, oxidative stress, and programmed cell death. Rho-associated coiled-coil-containing protein kinase (ROCK) is essential for numerous cellular processes, including apoptosis regulation. Studies have suggested that ROCK inhibitors could prevent apoptosis and promote regeneration. We aimed to investigate the protective effects of the ROCK inhibitor fasudil against cisplatin-induced ototoxicity in a zebrafish model. The zebrafish larvae were exposed to 1 mM cisplatin alone or 1 mM cisplatin co-administered with varying concentrations of fasudil for 4 h. The surviving hair cell counts, apoptosis, reactive oxygen species (ROS) levels, mitochondrial membrane potential (ΔΨm), caspase 3 activity, and autophagy activation were assessed. Rheotaxis behavior was also examined. Cisplatin reduced hair cell counts; increased apoptosis, ROS production, and ΔΨm loss; and activated caspase 3 and autophagy. Fasudil (100 and 500 µM) mitigated cisplatin-induced hair cell loss, reduced apoptosis, and inhibited caspase 3 and autophagy activation. Rheotaxis in zebrafish was preserved by the co-administration of fasudil with cisplatin. Cisplatin induces hair cell apoptosis in zebrafish, whereas fasudil is a promising protective agent against cisplatin-induced ototoxicity.

Fly Me to the Micron: Microtechnologies for Drosophila Research

Multicellular model organisms, such as Drosophila melanogaster (fruit fly), are frequently used in a myriad of biological research studies due to their biological significance and global standardization. However, traditional tools used in these studies generally require manual handling, subjective phenotyping, and bulk treatment of the organisms, resulting in laborious experimental protocols with limited accuracy. Advancements in microtechnology over the course of the last two decades have allowed researchers to develop automated, high-throughput, and multifunctional experimental tools that enable novel experimental paradigms that would not be possible otherwise. We discuss recent advances in microtechnological systems developed for small model organisms using D. melanogaster as an example. We critically analyze the state of the field by comparing the systems produced for different applications. Additionally, we suggest design guidelines, operational tips, and new research directions based on the technical and knowledge gaps in the literature. This review aims to foster interdisciplinary work by helping engineers to familiarize themselves with model organisms while presenting the most recent advances in microengineering strategies to biologists.

Loss of Panx1 function in zebrafish alters motor behavior in a lab-on-chip model of Parkinson's disease

Pannexin 1 (Panx1) forms ATP-permeable membrane channels that play roles in purinergic signaling in the nervous system. A link between Panx1 activity and neurodegenerative disorders including Parkinson's disease (PD) has been suggested, but experimental evidence is limited. Here, a zebrafish model of PD was produced by exposing panx1a+/+ and panx1a-/- zebrafish larvae to 6-hydroxydopamine (6-OHDA). Electrical stimulation in a microfluidic chip and quantitative real-time-qPCR of zebrafish larvae tested the role of Panx1 in both pathological and normal conditions. After 72-h treatment with 6-OHDA, the electric-induced locomotor activity of 5 days post fertilization (5dpf) panx1a+/+ larvae were reduced, while the stimulus did not affect locomotor activity of age-matched panx1a-/- larvae. A RT-qPCR analysis showed an increase in the expression of genes that are functionally related to dopaminergic signaling, like the tyrosine hydroxylase (th2) and the leucine-rich repeat kinase 2 (lrrk2). Extending the 6-OHDA treatment duration to 120 h caused a significant reduction in the locomotor response of 7dpf panx1a-/- larvae compared to the untreated panx1a-/- group. The RT-qPCR data showed a reduced expression of dopaminergic signaling genes in both genotypes. It was concluded that the absence of Panx1a channels compromised dopaminergic signaling in 6-OHDA-treated zebrafish larvae and that the increase in the expression of dopaminergic genes was transient, most likely due to a compensatory upregulation. We propose that zebrafish Panx1a models offer opportunities to shed light on PD's physiological and molecular basis. Panx1a might play a role on the progression of PD, and therefore deserves further investigation.

Behavioural responses of zebrafish with sound stimuli in microfluidics

Neuronal activities of the human brain responsible for cognitive features have been theorized through several animal models that exhibited various complementary spatial learning modes by generating a flexible repertoire of behavioral strategies. However, for such studies associated with a neurodegenerative disease, which can be further manipulated to provide therapeutic strategies, the animal models employed in their developmental stages have been preferred over the adult ones. This pilot work was incepted to underscore the spatial memory capabilities that strengthened the intricate mechanism of memory acquisition potential in one of the low-order evolutionarily conserved species, such as zebrafish larvae. Initially, a reliable and more easily reproducible microfluidic platform integrating simple and intricate paths was designed to learn and test the spatial information in zebrafish larvae of 4-6 d.p.f. under non-invasive acoustic stimuli. Further, to acquire spatial information as the representation of spatial memory formation in zebrafish larvae, the acoustic startle responses were evaluated by quantifying various dynamic behaviors under distinct operating parameters. After significant conditioning sessions, the spatial memory was tested by employing variable 'freezing'. By the end of the 30 min-long test session, 6 d.p.f. larvae were found to exhibit the highest value of freezing of approximately 43% and 20% in the short and long paths, respectively. Even though a substantial rate of memory loss was observed, it can be envisaged to serve several behavioral strategies that process the dynamic cognitive memory among distinct spatiotemporal environments. Further, the proposed behavioral paradigm had the advantage of being more adaptable and reliably replicable by other researchers. As a consequence, different hypotheses can be readily tested to generate more reproducible findings towards distinct neurobehavioral characteristics. Therefore, the proposed paradigm for the consolidation of spatial memory based on the non-invasive spatial avoidance strategies could provide an enduring framework of reference for behavioral studies using zebrafish larvae.

Simultaneous screening of zebrafish larvae cardiac and respiratory functions: a microfluidic multi-phenotypic approach

Multi-phenotypic screening of multiple zebrafish larvae plays an important role in enhancing the quality and speed of biological assays. Many microfluidic platforms have been presented for zebrafish phenotypic assays, but multi-organ screening of multiple larvae, from different needed orientations, in a single device that can enable rapid and large-sample testing is yet to be achieved. Here, we propose a multi-phenotypic quadruple-fish microfluidic chip for simultaneous monitoring of heart activity and fin movement of 5-7-day postfertilization zebrafish larvae trapped in the chip. In each experiment, fin movements of four larvae were quantified in the dorsal view in terms of fin beat frequency (FBF). Positioning of four optical prisms next to the traps provided the lateral views of the four larvae and enabled heart rate (HR) monitoring. The device's functionality in chemical testing was validated by assessing the impacts of ethanol on heart and fin activities. Larvae treated with 3% ethanol displayed a significant drop of 13.2 and 35.8% in HR and FBF, respectively. Subsequent tests with cadmium chloride highlighted the novel application of our device for screening the effect of heavy metals on cardiac and respiratory function at the same time. Exposure to 5 $\mu$g/l cadmium chloride revealed a significant increase of 8.2% and 39.2% in HR and FBF, respectively. The device can be employed to monitor multi-phenotypic behavioral responses of zebrafish larvae induced by chemical stimuli in various chemical screening assays, in applications such as ecotoxicology and drug discovery.

Dopaminergic signaling regulates zebrafish larvae's response to electricity

Electrical stimulation of brain or muscle activities has gained attention for studying the molecular and cellular mechanisms involved in electric-induced responses. We recently showed zebrafish's response to electricity. Here, we hypothesized that this response is affected by the dopaminergic signaling pathways. The effects of multiple dopamine agonists and antagonists on the electric response of 6 days-postfertilization zebrafish larvae were investigated using a microfluidic device with enhanced control of experimentation and throughput. All dopamine antagonists decreased locomotor activities, while dopamine agonists did not induce similar behaviors. The D2-selective dopamine agonist quinpirole enhanced the movement. Exposure to nonselective and D1-selective dopamine agonists apomorphine and SKF-81297 caused no significant change in the electric response. Exposing larvae that were pretreated with nonselective and D2-selective dopamine antagonists butaclamol and haloperidol to apomorphine and quinpirole, respectively, restored the electric locomotion. These results reveal a correlation between electric response and dopamine signaling pathway. Furthermore, they demonstrate that electric-induced zebrafish larvae locomotion can be conditioned by modulating dopamine receptor functions. Our electrofluidic assay has profound application potential for fundamental electric-induced response research and brain disorder studies especially those related to the dopamine imbalance and as a chemical screening method when investigating biological pathways and behaviors. This article is protected by copyright. All rights reserved.

Microfluidic devices for behavioral screening of multiple Zebrafish Larvae: Design investigation process

Microfluidic devices have been introduced for phenotypic screening of zebrafish larvae in both fundamental and pre-clinical research. One of the remaining challenges for the broad use of microfluidic devices is their limited throughput, especially in behavioural assays. Previously, we introduced the tail locomotion of a semi-mobile zebrafish larva evoked on-demand with electric signal in a microfluidic device. Here, we report the lessons learned for increasing the number of specimens from one to four larvae in this device. Multiple parameters including loading and testing time per fish and loading and orientation efficiencies were refined to optimize the performance of modified designs. Simulations of the flow and electric field within the final device provided insight into the flow behavior and functionality of traps when compared to previous single-larva devices. Outcomes led to a new design which decreased the testing time per larva by approximately 60%. Further, loading and orientation efficiencies increased by more than 80%. Critical behavioural parameters such as response duration and tail beat frequency were similar in both single and quadruple-fish devices. The developed microfluidic device has significant advantages for greater throughput and efficiency when behavioral phenotyping is required in various applications, including chemical testing in toxicology and gene screening. This article is protected by copyright. All rights reserved.

Phenotypic chemical and mutant screening of zebrafish larvae using an on-demand response to electric stimulation

Behavioral responses of zebrafish larvae to environmental cues are important functional readouts that should be evoked on-demand and studied phenotypically in behavioral, genetical and developmental investigations. Very recently, it was shown that zebrafish larvae execute a voluntary and oriented movement toward the positive electrode of an electric field along a microchannel. Phenotypic characterization of this response was not feasible due to larva's rapid movement along the channel. To overcome this challenge, a microfluidic device was introduced to partially immobilize the larva's head while leaving its mid-body and tail unrestrained in a chamber to image motor behaviors in response to electric stimulation, hence achieving quantitative phenotyping of the electrically evoked movement in zebrafish larvae. The effect of electric current on the tail-beat frequency and response duration of 5-7 days postfertilization zebrafish larvae was studied. Investigations were also performed on zebrafish exposed to neurotoxin 6-hydroxydopamine and larvae carrying a pannexin1a (panx1a) gene knockout, as a proof of principle applications to demonstrate on-demand movement behavior screening in chemical and mutant assays. We demonstrated for the first time that 6-hydroxydopamine leads to electric response impairment, levodopa treatment rescues the response and panx1a is involved in the electrically evoked movement of zebrafish larvae. We envision that our technique is broadly applicable as a screening tool to quantitatively examine zebrafish larvae's movements in response to physical and chemical stimulations in investigations of Parkinson's and other neurodegenerative diseases, and as a tool to combine recent advances in genome engineering of model organisms to uncover the biology of electric response.

Multiscale brain research on a microfluidic chip

One major challenge in current brain research is generating an integrative understanding of the brain's functions and disorders from its multiscale neuronal architectures and connectivity. Thus, innovative neurotechnology tools are urgently required for deciphering the multiscale functional and structural organizations of the brain at hierarchical scales from the molecular to the organismal level by multiple brain research initiatives launched by the European Union, United States, Australia, Canada, China, Korea, and Japan. To meet this demand, microfluidic chips (μFCs) have rapidly evolved as a trans-scale neurotechnological toolset to enable multiscale studies of the brain due to their unique advantages in flexible microstructure design, multifunctional integration, accurate microenvironment control, and capacity for automatic sample processing. Here, we review the recent progress in applying innovative μFC-based neuro-technologies to promote multiscale brain research and uniquely focus on representative applications of μFCs to address challenges in brain research at each hierarchical level. We discuss the current trend of combinational applications of μFCs with other neuro- and biotechnologies, including optogenetics, brain organoids, and 3D bioprinting, for better multiscale brain research. In addition, we offer our insights into the existing outstanding questions at each hierarchical level of brain research that could potentially be addressed by advancing microfluidic techniques. This review will serve as a timely guide for bioengineers and neuroscientists to develop and apply μFC-based neuro-technologies for promoting basic and translational brain research.

Single-cell Analysis with Microfluidic Devices

A microfluidic device as a pivotal research tool in chemistry and life science is now widely recognized. Indeed, microfluidic techniques have made significant advancements in fundamental research, such as the inherent heterogeneity of single-cells studies in cell populations, which would be helpful in understanding cellular molecular mechanisms and clinical diagnosis of major diseases. Single-cell analyses on microdevices have shown great potential for precise fluid control, cell manipulation, and signal output with rapid and high throughput. Moreover, miniaturized devices also have open functions such as integrating with traditional detection methods, for example, optical, electrochemical or mass spectrometry for single-cell analysis. In this review, we summarized recent advances of single-cell analysis based on various microfluidic approaches from different dimensions, such as in vitro, ex vivo, and in vivo analysis of single cells.

Microfluidic devices for embryonic and larval zebrafish studies

Zebrafish or Danio rerio is an established model organism for studying the genetic, neuronal and behavioral bases of diseases and for toxicology and drug screening. The embryonic and larval stages of zebrafish have been used extensively in fundamental and applied research due to advantages offered such as body transparency, small size, low cost of cultivation and high genetic homology with humans. However, the manual experimental methods used for handling and investigating this organism are limited due to their low throughput, labor intensiveness and inaccuracy in delivering external stimuli to the zebrafish while quantifying various neuronal and behavioral responses. Microfluidic and lab-on-a-chip devices have emerged as ideal technologies to overcome these challenges. In this review paper, the current microfluidic approaches for investigation of behavior and neurobiology of zebrafish at embryonic and larval stages will be reviewed. Our focus will be to provide an overview of the microfluidic methods used to manipulate (deliver and orient), immobilize and expose or inject zebrafish embryos or larvae, followed by quantification of their responses in terms of neuron activities and movement. We will also provide our opinion in terms of the direction that the field of zebrafish microfluidics is heading toward in the area of biomedical engineering.