We are grateful for the support from the NIH SBIR Phase II #R44OD024874 to H.C. and M.P.H.L. The authors would also like to acknowledge the financial support provided by the Consejo Nacional de Humanidades, Ciencias y Tecnologias (CONAHCYT) in Mexico through the fellowship titled Beca CONAHCYT Para Estudios de Doctorado en el Extranjero.

Adhering strictly to ethical guidelines ensures the well-being and appropriate handling of the zebrafish involved in our experiments. All experimental activities were conducted in accordance with the standards set forth by the Institutional Animal Care and Use Committees (IACUC). The experiments and findings detailed here were executed with the approval of IACUC under the authorized protocol AUP-21-066.
1. Preparation and storage of stock solutions
CAUTION: Prepare the tricaine stock solution in a fume hood, wearing appropriate personal protective equipment (PPE).
<ol>
	<li>Measure 400 mg of tricaine powder and dissolve it in 97.9 mL of deionized (DI) water. Place a magnetic stirrer into the container and gradually mix the solution.</li>
	<li>Adjust the pH by incrementally adding less than 17 mL of NaOH solution. Continue adding NaOH drops until the pH reaches a range of 6.8.-7.2.</li>
	<li>Determine the final concentration of tricaine solution, accounting for the added NaOH necessary to adjust the pH and store. 
	NOTE: Tricaine solution is light sensitive and should be stored in an amber-colored container at 4 &#176;C when not in use.</li>
	<li>Measure 258.13 mg of Amiodarone and dissolve it in 1 L of DI water. Insert a magnetic stirrer into the container and stir for a few minutes until the solution is completely dissolved and clear of any powder. Store the solution inside a refrigerator at 4&#176;C when not in use. 
	NOTE: Amiodarone must be prepared inside a fume hood and stored inside a refrigerator at 4 &#176;C. Always wear the appropriate PPE.</li>
</ol>
2. Fish husbandry
<ol>
	<li>Maintain the fish in individual tanks linked to a circulating water system, keeping the temperature between 28-29&#176;C.</li>
	<li>Ensure continuous monitoring of water quality and adhere to a 14 h/10 h day-night cycle.</li>
	<li>Divide the 40 fish into four groups, each consisting of 10 fish, and house them in separate tanks.</li>
</ol>
3. Setting up the device
NOTE: The procedure outlined in step 3.2 must be performed for each chamber of the device (Figure 1). While each chamber can be set up differently, for consistency in the experiment, it is advisable to maintain uniform settings across all chambers.
<ol>
	<li>Connect the device to a power source and initiate operation by pressing the Red Button located on the front panel.</li>
	<li>Navigate through the device&#39;s touchscreen to choose the chamber to be configured.
	<ol>
		<li>Adjust the low-pass filter setting to 0.1 Hz and the high-pass filter setting to 500 Hz. Adjust the gain setting to 10,000.</li>
	</ol>
	</li>
	<li>Lift the front lid to access the four chambers. Prior to starting the experiment, immerse each chamber&#39;s sponge (standard cellulose sponge) in Tricaine solution, then squeeze out any excess liquid.</li>
	<li>Rotate the four-electrode array to ensure the sponge is accessible before introducing the fish.</li>
</ol>
4. Amiodarone treatment
NOTE: Utilize the water from the fish tanks (fish water) to prepare diluted solutions of Amiodarone and Tricaine. Steps 4.3 and 4.4 must be repeated for each group separated in step 2.3 for each solution prepared in step 4.1.
<ol>
	<li>Follow the steps described below to dilute the Amiodarone stock solution.
	<ol>
		<li>Dilute 8.75 mL of stock solution into 41.25 mL of fish water to achieve a 70 &#181;M concentration.</li>
		<li>Dilute 12.5 mL of stock solution into 37.5 mL of fish water to achieve a 100 &#181;M concentration.</li>
		<li>Dilute 25 mL of stock solution into 25 mL of fish water to achieve a 200 &#181;M concentration.</li>
	</ol>
	</li>
	<li>Prepare the anesthesia solution by diluting 4 mL of Tricaine stock solution into 100 mL of fish water, resulting in a Tricaine concentration of 0.16 mg/mL</li>
	<li>Submerge each fish individually in the prepared Amiodarone solution for 5 min. Use timers to accurately monitor the immersion duration.</li>
	<li>Transfer the fish into Tricaine solution for 2-3 min for anesthesia. Ensure the treatment does not cause the death of the fish. If a fish exhibits abnormal behavior, such as losing color or a significant reduction in gill movement, remove it from the solution immediately and place it back into clean fish water.</li>
</ol>
5. ECG data collection
NOTE: Immediately follow these instructions after completing step 4.4. Repeat the process for each chamber before sealing the device. The chambers are designed to accommodate fish ranging from 4-10 mm in width and 25-50 mm in length.
<ol>
	<li>Lift the fish out of the Tricaine solution and place it onto the sponge, ensuring its ventral side faces up.</li>
	<li>Position the electrode array in a rhombus shape over the fish&#39;s chest area to capture ECG signals from four different points simultaneously (Figure 2A,B). Make sure to adjust each electrode carefully so every pin makes contact with the fish&#39;s skin.
	<ol>
		<li>Rotate each electrode, lowering the pin until it makes contact with the fish&#39;s underside. If the pin is too high, turn the corresponding thumbscrew clockwise to lower it until it touches the fish.</li>
		<li>Perform the adjustment described above for the electrodes in all chambers.</li>
	</ol>
	</li>
	<li>Close the chambers&#39; lid once all electrode arrays are correctly positioned over the fish in the operational chambers.</li>
	<li>Mark each chamber for recording by selecting it on the touchscreen, then initiate the recording by clicking the Record button on-screen.</li>
	<li>Click the Stop button after 2 min and then click on Save button from the prompt windows that pop ups on-screen after stopping. Save the information either on a disk or to the cloud, depending on specific research needs.</li>
</ol>
6. Troubleshooting the four-electrode array positioning system
NOTE: Occasionally, one or several electrodes might fail to capture a clear ECG signal, necessitating repositioning. Use the following steps to troubleshoot the electrode array when needed.
<ol>
	<li>Press the Stop button on the device interface to halt the recording process and identify the channel or channels with inconsistent signals.</li>
	<li>Lift the front lid for access to the electrode chambers. Identify which chamber(s) and specific electrodes are causing issues.</li>
	<li>Turn the top thumbscrew clockwise to adjust the electrode&#39;s proximity to the fish. This action will lower the electrode closer to the fish.</li>
	<li>Repeat step 6.3 as needed. If merely moving closer does not solve the issue, rotate the electrode to a different spot on the fish until a satisfactory signal is achieved.</li>
</ol>
7. Extracting and analyzing data
NOTE: All the basic data analysis presented in this paper uses the Wavelet technique21 to reduce various types of noise and standard deviation of normal sinus beats (SDNN) to calculate the beat-to-beat variance of HR in one-minute segments.
<ol>
	<li>Once data has been saved to either the disk or the cloud, retrieve it for analysis or send it directly to a cloud server for further processing.</li>
	<li>Navigate to the saved data by clicking the Browse button on the screen and select the data sets to use.</li>
	<li>Select the Extract button on the options on-screen and attach a USB drive to the back part of the device to extract the data.</li>
	<li>Follow the device prompts to save the selected data sets onto the external drive for subsequent retrieval and analysis.</li>
</ol>

Zebra II: Advanced ECG System for Multichannel Zebrafish Cardiovascular Studies

<ol>
	<li>Tsao, C. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heart+disease+and+stroke+statistics-2022+update:+A+report+from+the+American+heart+association.">Heart disease and stroke statistics-2022 update: A report from the American heart association.</a> Circulation. 145 (8), e153-e639 (2022).</li><li>Zulkifly, H., Lip, G. Y. H., Lane, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epidemiology+of+atrial+fibrillation.">Epidemiology of atrial fibrillation.</a> Int J Clin Pract. 72 (3), e13070 (2018).</li><li>Ferreira, C., Provid&#234;ncia, R., Ferreira, M. J., Gon&#231;alves, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atrial+fibrillation+and+non-cardiovascular+diseases:+A+systematic+review.">Atrial fibrillation and non-cardiovascular diseases: A systematic review.</a> Arq Bras Cardiol. 105 (5), 519-526 (2015).</li><li>Hu, Z., Ding, L., Yao, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atrial+fibrillation:+mechanism+and+clinical+management.">Atrial fibrillation: mechanism and clinical management.</a> Chin Med J. 136 (22), 2668-2676 (2023).</li><li>Babapoor-Farrokhran, S., Rasekhi, R. T., Gill, D., Babapoor, S., Amanullah, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Arrhythmia+in+COVID-19.">Arrhythmia in COVID-19.</a> SN Comp Clin Med. 2 (9), 1430-1435 (2020).</li><li>Arnaout, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zebrafish+model+for+human+long+QT+syndrome.">Zebrafish model for human long QT syndrome.</a> Proc Natl Acad Sci. 104 (27), 11316-11321 (2007).</li><li>Koopman, C. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+zebrafish+grime+mutant+uncovers+an+evolutionarily+conserved+role+for+Tmem161b+in+the+control+of+cardiac+rhythm.">The zebrafish grime mutant uncovers an evolutionarily conserved role for Tmem161b in the control of cardiac rhythm.</a> Proc Natl Acad Sci. 118 (9), e2018220118 (2021).</li><li>Genge, C. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Reviews of Physiology, Biochemistry and Pharmacology. , (2016).</li><li>Nemtsas, P., Wettwer, E., Christ, T., Weidinger, G., Ravens, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adult+zebrafish+heart+as+a+model+for+human+heart?+An+electrophysiological+study.">Adult zebrafish heart as a model for human heart? An electrophysiological study.</a> J Mol Cell Cardiol. 48 (1), 161-171 (2010).</li><li>Sun, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micro-electrocardiograms+to+study+post-ventricular+amputation+of+Zebrafish+heart.">Micro-electrocardiograms to study post-ventricular amputation of Zebrafish heart.</a> Ann Biomed Engg. 37 (5), 890-901 (2009).</li><li>Lin, M. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+a+rapid+and+economic+in+vivo+electrocardiogram+platform+for+cardiovascular+drug+assay+and+electrophysiology+research+in+adult+zebrafish.">Development of a rapid and economic in vivo electrocardiogram platform for cardiovascular drug assay and electrophysiology research in adult zebrafish.</a> Sci Rep. 8 (1), 15986 (2018).</li><li>Chaudhari, G. H., Chennubhotla, K. S., Chatti, K., Kulkarni, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimization+of+the+adult+zebrafish+ECG+method+for+assessment+of+drug-induced+QTc+prolongation.">Optimization of the adult zebrafish ECG method for assessment of drug-induced QTc prolongation.</a> J Pharmacol Toxicol Methods. 67 (2), 115-120 (2013).</li><li>Liu, C. C., Li, L., Lam, Y. W., Siu, C. W., Cheng, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improvement+of+surface+ECG+recording+in+adult+zebrafish+reveals+that+the+value+of+this+model+exceeds+our+expectation.">Improvement of surface ECG recording in adult zebrafish reveals that the value of this model exceeds our expectation.</a> Sci Rep. 6, 25073 (2016).</li><li>Stoyek, M. R., Rog-Zielinska, E. A., Quinn, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Age-associated+changes+in+electrical+function+of+the+zebrafish+heart.">Age-associated changes in electrical function of the zebrafish heart.</a> Prog Biophys Mol Biol. 138, 91-104 (2018).</li><li>Cao, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wearable+multi-channel+microelectrode+membranes+for+elucidating+electrophysiological+phenotypes+of+injured+myocardium.">Wearable multi-channel microelectrode membranes for elucidating electrophysiological phenotypes of injured myocardium.</a> Integ Biol. 6 (8), 789-795 (2014).</li><li>Lenning, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-time+monitoring+and+analysis+of+zebrafish+electrocardiogram+with+anomaly+detection.">Real-time monitoring and analysis of zebrafish electrocardiogram with anomaly detection.</a> Sensors. 18 (1), 61 (2018).</li><li>Yu, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flexible+microelectrode+arrays+to+interface+epicardial+electrical+signals+with+intracardial+calcium+transients+in+zebrafish+hearts.">Flexible microelectrode arrays to interface epicardial electrical signals with intracardial calcium transients in zebrafish hearts.</a> Biomed Microdev. 14 (2), 357-366 (2012).</li><li>Cho, S. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zebrafish+as+an+animal+model+in+epilepsy+studies+with+multichannel+EEG+recordings.">Zebrafish as an animal model in epilepsy studies with multichannel EEG recordings.</a> Sci Rep. 7 (1), 3099 (2017).</li><li>Le, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+electrocardiogram+monitoring+in+Zebrafish+with+prolonged+mild+anesthesia.">Continuous electrocardiogram monitoring in Zebrafish with prolonged mild anesthesia.</a> , 2610-2613 (2020).</li><li>Le, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+wireless+ECG+system+for+prolonged+monitoring+of+multiple+zebrafish+for+heart+disease+and+drug+screening+studies.">A novel wireless ECG system for prolonged monitoring of multiple zebrafish for heart disease and drug screening studies.</a> Biosensors Bioelectron. 197, 113808 (2022).</li><li>Kouzehgar, K., Eslamian, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chapter+2+-+Application+of+experimental+data+and+soft+computing+techniques+in+determining+the+outflow+and+breach+characteristics+in+embankments+and+landslide+dams.">Chapter 2 - Application of experimental data and soft computing techniques in determining the outflow and breach characteristics in embankments and landslide dams.</a> Handbook Hydroinfo. 3, 11-31 (2023).</li><li>Milan, D. J., Jones, I. L., Ellinor, P. T., MacRae, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+recording+of+adult+zebrafish+electrocardiogram+and+assessment+of+drug-induced+QT+prolongation.">In vivo recording of adult zebrafish electrocardiogram and assessment of drug-induced QT prolongation.</a> Am J Physiol Heart Circ Physiol. 291 (1), H269-H273 (2006).</li></ol>

Hung Cao and Michael Lau are the founders of Sensoriis, Inc. Sensoriis's system Zebra II was developed under NIH support, SBIR Phase II grant #R44OD024874. The University of California, Irvine, has reviewed and approved Hung Cao's relationship with Sensoriis, Inc. in accordance with its conflict-of-interest policies. The other authors declare no conflict of interest.

The current steps were modified and improved according to this new device version from a previous study made by our team20. Here, a labeled computer-aided design (CAD) of the device is also included.
As highlighted in the protocol's troubleshooting guide, the device necessitates the user to execute certain critical steps with diligence and precision, as these steps crucially affect the ECG signal's quality. Consistent with findings from our prior study...

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. According to the 2024 AHA Update Report, around 2552 people die every day of CVDs in the U.S., and the average direct and indirect cost of CVD was estimated at $378.0 billion in 2017-20181. Atrial fibrillation (AF) is one of the most common cardiac arrhythmias in the U.S.2 and is associated with an unfavorable prognosis, increasing the risk of stroke and death in both CVDs and non-cardiovascular disease scenarios, leading to an increased risk of adverse outcomes3. This type of arrhythmia is distinguished by its rapid and irregular electrical activity in the atria, which usually results in a fast and irregular ventricular rhythm4. Further, given the recent events of COVID-19, there has been an increased number of studies and evidence that show an increased appearance of arrhythmia in relation to COVID-19, mostly to sinus bradycardia5. On the opposite side of AF, sinus bradycardia presents a decreased and slower heart rhythm, with a heart rate lower than 60 beats per minute (bpm). This diagnosis requires an electrocardiogram (ECG) showing a normal sinus rhythm at a rate lower than 60 bpm.
The zebrafish, Danio rerio, has proven to be an ideal model for cardiovascular and drug development studies because of its homology to humans in both morphology, physiology, and genetics6,7. Despite only having two discernible chambers compared to the four-chambered heart in humans, the zebrafish possesses a similar contractile structure with an analogous conduction system8,9. Hence, the zebrafish model is suitable for researching cardiac arrhythmias and exploring the association between related genetic pathways and electrophysiological characteristics through ECG analysis. Regarding the sensor design for ECG recording in zebrafish, conventional needle electrodes are commonly used10. Other studies presented alternatives for conventional needles by designing a different type of needle made of different materials11, these incorporated materials such as tungsten filament, stainless steel, and silver wire to assess the quality of the recorded data. Together with the portable ECG kit, they sought to establish a universal platform for both research and educational labs.
The needle system was also deployed in other studies11,12,13,14 for carrying out research on biological and/or drug-induced effects, in which it showed encouraging outcomes. However, to obtain optimal signals, it was necessary to carefully insert the needles through the zebrafish&#39;s dermis. This invasive procedure can cause injury to the fish&#39;s heart due to the sharpness of the needles, thus possibly changing signal morphology13. Furthermore, accurately placing the electrode on the small heart without causing harm to ensure clear ECG capture presents a significant learning curve. Consequently, various substitute probe systems have been introduced, such as microelectrode arrays (MEA) and 3D-printed sensors. Both our team and other researchers have successfully utilized MEA for data acquisition, achieving data that offer a good signal-to-noise ratio (SNR) along with high spatial and temporal resolution15,16,17. For example, we introduced an MEA that envelops the heart of the fish, allowing the capture of site-specific ECG signals15,16. In contrast, another team developed a different kind of MEA based on a flexible printed circuit board (FPCB) crafted from polyimide film aimed at recording multiple electroencephalograms (EEGs) for epilepsy research18. While MEAs enable the recording of numerous signals, they are limited by the capacity to assess only one fish at a time due to the restricted number of electrode channels. In response to this limitation, we have recently showcased an advanced system capable of simultaneous ECG recordings from multiple fish19. This system employs two electrodes, each 125 &#181;m in thickness and made of polyimide, with gold-sputtered electrodes positioned at the bottom of their housing to facilitate data acquisition. However, the inclusion of a water circulation pump introduced noise, affecting the signal-to-noise ratio (SNR) quality of the ECG signals. Additionally, the use of bulky and costly data collection tools, which required a wired connection to a computer, was necessitated. On the market, systems like iWORX offer improved portability through a compact amplifier, yet they face unresolved issues: (i) their recording time is too short (3-5 min) for experiments needing longer durations, such as those involving acute drug effects; (ii) the requirement for anesthetizing the animals, which can stress them and skew innate cardiac electrophysiological data; (iii) manual, sequential measurements hinder research with large numbers of fish; and (iv) the need for offline, labor-intensive ECG data processing. Importantly, no high-throughput systems incorporating microelectronics for analyzing mutant phenotypes have yet emerged. Therefore, the creation of high-throughput systems that enable extended ECG recording is crucial for uncovering links between arrhythmic phenotypes and mutant genotypes, identifying multiple arrhythmic phenotypes associated with single mutant genotypes, and testing the effectiveness of cardiac drugs using the zebrafish model. Consequently, we introduced, in 2022, the groundbreaking prototype of the Zebra II system. This novel system is equipped to perform extended ECG recordings from several fish at once. To achieve this, an in-house electronic system was crafted, utilizing the Internet of Things (IoT) technology for wireless data transmission and enabling data analysis through a mobile application. The inclusion of IoT technology not only bolstered the system&#39;s flexibility and portability but also facilitated remote collaborations for research on zebrafish models. In a prior study, we validated the system&#39;s efficacy through extensive testing, showcasing its ability to 1) acquire ECG data simultaneously from four fish; 2) perform continuous ECG recordings for up to 1 h, which significantly exceeds the capacity of existing systems that only capture a few minutes; 3) minimize the confounding effects of anesthesia by employing a 50% reduced concentration of Tricaine. Furthermore, the system demonstrated a strong capability for lengthy ECG recordings across various experiments, such as those involving sodium-induced sinoatrial (SA) block, temperature-induced heart rate changes, and drug-induced arrhythmias in both Tg(SCN5A-D1275N) mutant and wildtype fish under controlled experimental conditions. The system&#39;s adoption of multiple electrode channels for extended ECG recording further enables the execution of randomized controlled trials, allowing for two fish per experimental group to be studied under identical conditions20. In this paper, we introduce the upgraded version of the system, featuring a 4-point electrode. This enhancement enables users to capture ECG readings from various locations on the fish, significantly reducing the chance of obtaining low-quality ECG signals. Moreover, this iteration builds upon and refines the majority of the functionalities outlined in previous research19. This evolved ECG system shows great promise in addressing existing limitations, thereby substantially facilitating the analysis of arrhythmic phenotypes and the screening of drugs in zebrafish. The innovative addition of the 4-point electrode was rigorously tested through a brief study on drug-induced arrhythmia in wild-type zebrafish, further validating its effectiveness.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Amiodarone Hydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>PHR1164-1G</td>
			<td>Amiodarone powder</td>
		</tr>
		<tr>
			<td>Benchtop pH/mV Meter</td>
			<td>Sper Scientific</td>
			<td>10500308</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyle3-Aminobenzoate, Methanesulfonic Acid Salt, 98%, ACROS Organics</td>
			<td>Fisher Scientific</td>
			<td>AC118002500</td>
			<td>Tricaine powder</td>
		</tr>
		<tr>
			<td>Isotemp Hot Plate Stirrer</td>
			<td>Fisher Scientific</td>
			<td>SP88854200</td>
			<td></td>
		</tr>
		<tr>
			<td>Zebra II System</td>
			<td>Sensoriis</td>
			<td>N/A</td>
			<td>Commercial Zebrafish ECG Recording System</td>
		</tr>
		<tr>
			<td>Zebrafish ECG System</td>
			<td>iWorx</td>
			<td>ZS-200</td>
			<td>Commercial Zebrafish ECG Recording System</td>
		</tr>
	</tbody>
</table>

zebra ii as a novel system to record electrophysiological signals in zebrafish

Zebrafish and their mutant lines have been extensively used in biomedical investigations, cardiovascular studies, and drug screening. In the current study, the commercial version of the novel system, Zebra II, is presented. The protocol demonstrates electrocardiogram (ECG) acquisition and analysis from multiple zebrafish within controllable working environments. The device is composed of an external and independent perfusion system, a 4-point electrode, temperature sensors, and an embedded electronic system. In previous studies, the device prototype underwent validation against the established iWORX system through several tests, demonstrating similar data quality and ECG response to drug interventions. Following this, the study delved into examining the impact of anesthetic drugs and temperature fluctuations on zebrafish ECG, necessitating instant data evaluation. Thanks to the apparatus&#39;s capacity for consistent delivery of anesthetics and drugs, it was possible to extend ECG data collection up to 1 h, markedly longer than the 5 min duration supported by current systems. This paper introduces a pioneering, cloud-based, automated analysis utilizing data from four zebrafish, offering an efficient method for conducting combination experiments and significantly reducing time and effort. The system proved effective in capturing and analyzing ECG, especially in detecting drug-induced arrhythmias in wild-type zebrafish. Additionally, the capability to gather data across multiple channels facilitated the execution of randomized controlled trials with zebrafish models. The developed ECG system overcomes existing limitations, showing the potential to greatly expedite drug discovery and cardiovascular research involving zebrafish.

The ability to simultaneously record ECG signals from multiple fish significantly distinguishes this device, offering a considerable advantage in reducing the time required for drug or cardiac research on zebrafish or other similar species (Figure 1). Recording accurate ECG signals can be challenging due to the anatomical variations among fish, especially when it comes to electrode placement. Traditionally, obtaining a clear ECG signal involves positioning the active electrode over the heart...

Zebra II as A Novel System to Record Electrophysiological Signals in Zebrafish

The study introduces Zebra II, an advanced system for prolonged ECG acquisition and analysis in zebrafish. This system features an independent perfusion system and multiple-point electrodes for handling multiple fish in controlled environments. Acute effects of Amiodarone were assessed and analyzed with wild-type zebrafish.

Zebrafish and their mutant lines have been extensively used in biomedical investigations, cardiovascular studies, and drug screening. In the current ...

zebra-ii-as-novel-system-to-record-electrophysiological-signals

Research

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Bioengineering

324 Views.  UC Irvine. The study introduces Zebra II, an advanced system for prolonged ECG acquisition and analysis in zebrafish. This system features an independent perfusion system and multiple-point electrodes for handling multiple fish in controlled environments. Acute effects of Amiodarone were assessed and analyzed with wild-type zebrafish. 

Video: Zebra II as A Novel System to Record Electrophysiological Signals in Zebrafish

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic valve leaflets are composed of interstitial cells suspended within an extracellular matrix (ECM) and are lined with an endothelial cell monolayer. The valve withstands a harsh, dynamic environment and is constantly exposed to shear, flexion, tension, and compression. Research has shown calcific lesions in diseased valves occur in areas of high mechanical stress as a result of endothelial disruption or interstitial matrix damage1-3. Hence, it is not surprising that epidemiological studies have shown high blood pressure to be a leading risk factor in the onset of aortic valve disease4. 
The only treatment option currently available for valve disease is surgical replacement of the diseased valve with a bioprosthetic or mechanical valve5. Improved understanding of valve biology in response to physical stresses would help elucidate the mechanisms of valve pathogenesis. In turn, this could help in the development of non-invasive therapies such as pharmaceutical intervention or prevention. Several bioreactors have been previously developed to study the mechanobiology of native or engineered heart valves6-9. Pulsatile bioreactors have also been developed to study a range of tissues including cartilage10, bone11 and bladder12. The aim of this work was to develop a cyclic pressure system that could be used to elucidate the biological response of aortic valve leaflets to increased pressure loads. 
The system consisted of an acrylic chamber in which to place samples and produce cyclic pressure, viton diaphragm solenoid valves to control the timing of the pressure cycle, and a computer to control electrical devices. The pressure was monitored using a pressure transducer, and the signal was conditioned using a load cell conditioner. A LabVIEW program regulated the pressure using an analog device to pump compressed air into the system at the appropriate rate. The system mimicked the dynamic transvalvular pressure levels associated with the aortic valve; a saw tooth wave produced a gradual increase in pressure, typical of the transvalvular pressure gradient that is present across the valve during diastole, followed by a sharp pressure drop depicting valve opening in systole. The LabVIEW program allowed users to control the magnitude and frequency of cyclic pressure. The system was able to subject tissue samples to physiological and pathological pressure conditions. This device can be used to increase our understanding of how heart valves respond to changes in the local mechanical environment.

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

A cyclic pressure bioreactor capable of subjecting heart valve tissue to physiological and pathological pressure conditions has been designed. A LabVIEW program allows users to control pressure magnitude, amplitude and frequency. This device can be used to study the mechanobiology of heart valve tissue or isolated cells.

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic ...

Skin Tattooing As A Novel Approach For DNA Vaccine Delivery

Nucleic acid-based vaccination is a topic of growing interest, especially plasmid DNA (pDNA) encoding immunologically important antigens. After the engineered pDNA is administered to the vaccines, it is transcribed and translated into immunogen proteins that can elicit responses from the immune system. Many ways of delivering DNA vaccines have been investigated; however each delivery route has its own advantages and pitfalls. Skin tattooing is a novel technique that is safe, cost-effective, and convenient. In addition, the punctures inflicted by the needle could also serve as a potent adjuvant. Here, we a) demonstrate the intradermal delivery of plasmid DNA encoding enhanced green fluorescent protein (pCX-EGFP) in a mouse model using a tattooing device and b) confirm the effective expression of EGFP in the skin cells using confocal microscopy.

Skin tattooing is a potent and safe way to delivery DNA vaccine intradermally. Here, a DNA plasmid encoding EGFP is delivered by tattooing to the skin of a laboratory mouse, and the expression of EGFP in the skin cells is then inspected by confocal microscopy.

Nucleic acid-based vaccination is a topic of growing interest, especially plasmid DNA (pDNA) encoding immunologically important antigens. After the ...

In vivo and In vitro Rearing of Entomopathogenic Nematodes (Steinernematidae and Heterorhabditidae)

Entomopathogenic nematodes (EPN) (Steinernematidae and Heterorhabditidae) have a mutualistic partnership with Gram-negative Gamma-Proteobacteria in the family Enterobacteriaceae. Xenorhabdus bacteria are associated with steinernematids nematodes while Photorhabdus are symbionts of heterorhabditids. Together nematodes and bacteria form a potent insecticidal complex that kills a wide range of insect species in an intimate and specific partnership. Herein, we demonstrate in vivo and in vitro techniques commonly used in the rearing of these nematodes under laboratory conditions. Furthermore, these techniques represent key steps for the successful establishment of EPN cultures and also form the basis for other bioassays that utilize these organisms for research. The production of aposymbiotic (symbiont&#8211;free) nematodes is often critical for an in-depth and multifaceted approach to the study of symbiosis. This protocol does not require the addition of antibiotics and can be accomplished in a short amount of time with standard laboratory equipment. Nematodes produced in this manner are relatively robust, although their survivorship in storage may vary depending on the species used. The techniques detailed in this presentation correspond to those described by various authors and refined by P. Stock&#8217;s Laboratory, University of Arizona (Tucson, AZ, USA). These techniques are distinct from the body of techniques that are used in the mass production of these organisms for pest management purposes.

In vivo and In vitro Rearing of Entomopathogenic Nematodes Steinernematidae and Heterorhabditidae

The goal of this presentation is to demonstrate in vivo and in vitro techniques for the rearing of entomopathogenic nematodes. In vivo methods consider the rearing of these nematodes with an insect host, whereas the in vitro methods utilize rich agar media.

Entomopathogenic nematodes (EPN) (Steinernematidae and Heterorhabditidae) have a mutualistic partnership with Gram-negative Gamma-Proteobacteria in the ...

Planar Gradient Diffusion System to Investigate Chemotaxis in a 3D Collagen Matrix

The importance of cell migration can be seen through the development of human life. When cells migrate, they generate forces and transfer these forces to their surrounding area, leading to cell movement and migration. In order to understand the mechanisms that can alter and/or affect cell migration, one can study these forces. In theory, understanding the fundamental mechanisms and forces underlying cell migration holds the promise of effective approaches for treating diseases and promoting cellular transplantation. Unfortunately, modern chemotaxis chambers that have been developed are usually restricted to two dimensions (2D) and have complex diffusion gradients that make the experiment difficult to interpret. To this end, we have developed, and describe in this paper, a direct-viewing chamber for chemotaxis studies, which allows one to overcome modern chemotaxis chamber obstacles able to measure cell forces and specific concentration within the chamber in a 3D environment to study cell 3D migration. More compelling, this approach allows one to successfully model diffusion through 3D collagen matrices and calculate the coefficient of diffusion of a chemoattractant through multiple different concentrations of collagen, while keeping the system simple and user friendly for traction force microscopy (TFM) and digital volume correlation (DVC) analysis.

Cell migration is an important part of human development and life. In order to understand the mechanisms that can alter cell migration, we present a planar gradient diffusion system to investigate chemotaxis in a 3D collagen matrix, which allows one to overcome modern diffusion chamber limitations of existing assays.

The importance of cell migration can be seen through the development of human life. When cells migrate, they generate forces and transfer these forces to ...

A Novel Technique for Generating and Observing Chemiluminescence in a Biological Setting

Intraoperative imaging techniques have the potential to make surgical interventions safer and more effective; for these reasons, such techniques are quickly moving into the operating room. Here, we present a new approach that utilizes a technique not yet explored for intraoperative imaging: chemiluminescent imaging. This method employs a ruthenium-based chemiluminescent reporter along with a custom-built nebulizing system to produce ex vivo or in vivo images with high signal-to-noise ratios. The ruthenium-based reporter produces light following exposure to an aqueous oxidizing solution and re-reduction within the surrounding tissue. This method has allowed us to detect reporter concentrations as low as 6.9 pmol/cm2. In this work, we present a visual guide to our proof-of-concept in vivo studies involving subdermal and intravenous injections in mice. The results suggest that this technology is a promising candidate for further preclinical research and might ultimately become a useful tool in the operating room.

This protocol describes a new intraoperative imaging technique that uses a ruthenium complex as a source of chemiluminescent light emission, thereby producing high signal-to-noise ratios during in vivo imaging. Intraoperative imaging is an expanding field that could revolutionize the way that surgical procedures are performed.

Intraoperative imaging techniques have the potential to make surgical interventions safer and more effective; for these reasons, such techniques are ...

DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers

Mechanical properties of complex, polymer-based soft matter, such as cells or biopolymer networks, can be understood in neither the classical frame of flexible polymers nor of rigid rods. Underlying filaments remain outstretched due to their non-vanishing backbone stiffness, which is quantified via the persistence length (lp), but they are also subject to strong thermal fluctuations. Their finite bending stiffness leads to unique, non-trivial collective mechanics of bulk networks, enabling the formation of stable scaffolds at low volume fractions while providing large mesh sizes. This underlying principle is prevalent in nature (e.g., in cells or tissues), minimizing the high molecular content and thereby facilitating diffusive or active transport. Due to their biological implications and potential technological applications in biocompatible hydrogels, semiflexible polymers have been subject to considerable study. However, comprehensible investigations remained challenging since they relied on natural polymers, such as actin filaments, which are not freely tunable. Despite these limitations and due to the lack of synthetic, mechanically tunable, and semiflexible polymers, actin filaments were established as the common model system. A major limitation is that the central quantity lp cannot be freely tuned to study its impact on macroscopic bulk structures. This limitation was resolved by employing structurally programmable DNA nanotubes, enabling controlled alteration of the filament stiffness. They are formed through tile-based designs, where a discrete set of partially complementary strands hybridize in a ring structure with a discrete circumference. These rings feature sticky ends, enabling the effective polymerization into filaments several microns in length, and display similar polymerization kinetics as natural biopolymers. Due to their programmable mechanics, these tubes are versatile, novel tools to study the impact of lp on the single-molecule as well as the bulk scale. In contrast to actin filaments, they remain stable over weeks, without notable degeneration, and their handling is comparably straightforward.

Semiflexible polymers display unique mechanical properties that are extensively applied by living systems. However, systematic studies on biopolymers are limited since properties such as polymer rigidity are inaccessible. This manuscript describes how this limitation is circumvented by programmable DNA nanotubes, enabling experimental studies on the impact of filament rigidity.

Mechanical properties of complex, polymer-based soft matter, such as cells or biopolymer networks, can be understood in neither the classical frame of ...

A Novel Surgical Technique As a Foundation for In Vivo Partial Liver Engineering in Rat

Organ engineering is a novel strategy to generate liver organ substitutes that can potentially be used in transplantation. Recently, in vivo liver engineering, including in vivo organ decellularization followed by repopulation, has emerged as a promising approach over ex vivo liver engineering. However, postoperative survival was not achieved. The aim of this study is to develop a novel surgical technique of in vivo selective liver lobe perfusion in rats as a prerequisite for in vivo liver engineering. We generate a circuit bypass only through the left lateral lobe. Then, the left lateral lobe is perfused with heparinized saline. The experiment is performed with 4 groups (n = 3 rats per group) based on different perfusion times of 20 min, 2 h, 3 h, and 4 h. Survival, as well as the macroscopically visible change of color and the histologically determined absence of blood cells in the portal triad and the sinusoids, is taken as an indicator for a successful model establishment. After selective perfusion of the left lateral lobe, we observe that the left lateral lobe, indeed, turned from red to faint yellow. In a histological assessment, no blood cells are visible in the branch of the portal vein, the central vein, and the sinusoids. The left lateral lobe turns red after reopening the blocked vessels. 12/12 rats survived the procedure for more than one week. We are the first to report a surgical model for in vivo single liver lobe perfusion with a long survival period of more than one week. In contrast to the previously published report, the most important advantage of the technique presented here is that perfusion of 70% of the liver is maintained throughout the whole procedure. The establishment of this technique provides a foundation for in vivo partial liver engineering in rats, including decellularization and recellularization.

A Novel Surgical Technique As a Foundation for In Vivo Partial Liver Engineering in Rat

We establish a novel surgical technique for an in vivo single liver lobe perfusion model in rat as a prerequisite for further studying in vivo partial liver engineering in the future.

Organ engineering is a novel strategy to generate liver organ substitutes that can potentially be used in transplantation. Recently, in vivo liver ...

Use of High-Throughput Automated Microbioreactor System for Production of Model IgG1 in CHO Cells

Automated microscale bioreactors (15 mL) can be a useful tool for cell culture engineers. They facilitate the simultaneous execution of a wide variety of experimental conditions while minimizing potential process variability. Applications of this approach include: clone screening, temperature and pH shifts,&#160;media and supplement optimization. Furthermore, the small reactor volumes are conducive to large Design of Experiments that investigate a wide range of conditions. This allows upstream processes to be significantly optimized before scale-up where experimentation is more limited in scope due to time and economic constraints. Automated microscale bioreactor systems offer various advantages over traditional small scale cell culture units, such as shake flasks or spinner flasks. However, during pilot scale process development&#160;significant care must be taken to ensure that these advantages are realized. When run with care, the system can enable high level automation, can be programmed to run DOE&#39;s with a higher number of variables&#160;and can reduce sampling time when integrated with a nutrient analyzer or cell counter. Integration of the expert-derived heuristics presented here, with current automated microscale bioreactor experiments can minimize common pitfalls that hinder meaningful results. In the extreme, failure to adhere to the principles laid out here can lead to equipment damage that requires expensive repairs. Furthermore, the microbioreactor systems have small culture volumes&#160;making characterization of cell culture conditions difficult. The number and amount of samples taken in-process in batch mode culture is limited as operating volumes cannot fall below 10 mL. This method will discuss the benefits and drawbacks of microscale bioreactor systems.

A detailed protocol for the concurrent operation of 48 parallel cell cultures under varied conditions in a microbioreactor system is presented. Cell culture process, harvest and subsequent antibody titer analysis are described.

Automated microscale bioreactors (15 mL) can be a useful tool for cell culture engineers. They facilitate the simultaneous execution of a wide variety of ...

Purification and Analytics of a Monoclonal Antibody from Chinese Hamster Ovary Cells Using an Automated Microbioreactor System

Monoclonal antibodies (mAbs) are one of the most popular and well-characterized biological products manufactured today. Most commonly produced using Chinese hamster ovary (CHO) cells, culture and process conditions must be optimized to maximize antibody titers and achieve target quality profiles. Typically, this optimization uses automated microscale bioreactors (15 mL) to screen multiple process conditions in parallel. Optimization criteria include culture performance and the critical quality attributes (CQAs) of the monoclonal antibody (mAb) product, which may impact its efficacy and safety. Culture performance metrics include cell growth and nutrient consumption, while the CQAs include the mAb's N-glycosylation and aggregation profiles, charge variants, and molecular weight. This detailed protocol describes how to purify and subsequently analyze HCCF samples produced by an automated microbioreactor system to gain valuable performance metrics and outputs. First, an automated protein A fast protein liquid chromatography (FPLC) method is used to purify the mAb from harvested cell culture samples. Once concentrated, the glycan profiles are analyzed by mass spectrometry using a specific platform (refer to the Table of Materials). Antibody molecular weights and aggregation profiles are determined using size exclusion chromatography-multiple angle light scattering (SEC-MALS), while charge variants are analyzed using microchip capillary zone electrophoresis (mCZE). In addition to the culture performance metrics captured during the bioreactor process (i.e., culture viability, cell counts, and common metabolites including glutamine, glucose, lactate, and ammonia), spent media is analyzed to identify limiting nutrients to improve the feeding strategies and overall process design. Therefore, a detailed protocol for the absolute quantification of amino acids by liquid chromatography-mass spectrometry (LC-MS) of spent media is also described. The methods used in this protocol take advantage of high-throughput platforms that are compatible for large numbers of small-volume samples.

A detailed protocol for the purification and subsequent analysis of a monoclonal antibody from harvested cell culture fluid (HCCF) of automated microbioreactors has been described. Use of analytics to determine critical quality attributes (CQAs) and maximizing limited sample volume to extract vital information is also presented.

Monoclonal antibodies (mAbs) are one of the most popular and well-characterized biological products manufactured today. Most commonly produced using ...

A Human 3D Extracellular Matrix-Adipocyte Culture Model for Studying Matrix-Cell Metabolic Crosstalk

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of cellular function. The ECM plays a particularly important role in adipose tissue function in obesity, and alterations in adipose tissue ECM deposition and composition are associated with metabolic disease in mice and humans. Tractable in vitro models that permit dissection of the roles of the ECM and cells in contributing to global tissue phenotype are sparse. We describe a novel 3D in vitro model of human ECM-adipocyte culture that permits study of the specific roles of the ECM and adipocytes in regulating adipose tissue metabolic phenotype. Human adipose tissue is decellularized to isolate ECM, which is subsequently repopulated with preadipocytes that are then differentiated within the ECM into mature adipocytes. This method creates ECM-adipocyte constructs that are metabolically active and retain characteristics of the tissues and patients from which they are derived. We have used this system to demonstrate disease-specific ECM-adipocyte crosstalk in human adipose tissue. This culture model provides a tool for dissecting the roles of the ECM and adipocytes in contributing to global adipose tissue metabolic phenotype and permits study of the role of the ECM in regulating adipose tissue homeostasis.

We describe a 3D human extracellular matrix-adipocyte in vitro culture system that permits dissection of the roles of the matrix and adipocytes in contributing to adipose tissue metabolic phenotype.

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of ...