The Tapping Assay: A Simple Method to Induce Fear Responses in Zebrafish

Cocktail effects of tire wear particles leachates on diverse biological models: A multilevel analysis

Tire wear particles (TWP) stand out as a major contributor to microplastic pollution, yet their environmental impact remains inadequately understood. This study delves into the cocktail effects of TWP leachates, employing molecular, cellular, and organismal assessments on diverse biological models. Extracted in artificial seawater and analyzed for metals and organic compounds, TWP leachates revealed the presence of polyaromatic hydrocarbons and 4-tert-octylphenol. Exposure to TWP leachates (1.5 to 1000 mg peq L-1) inhibited algae growth and induced zebrafish embryotoxicity, pigment alterations, and behavioral changes. Cell painting uncovered pro-apoptotic changes, while mechanism-specific gene-reporter assays highlighted endocrine-disrupting potential, particularly antiandrogenic effects. Although heavy metals like zinc have been suggested as major players in TWP leachate toxicity, this study emphasizes water-leachable organic compounds as the primary causative agents of observed acute toxicity. The findings underscore the need to reduce TWP pollution in aquatic systems and enhance regulations governing highly toxic tire additives.

Impairments of cerebellar structure and function in a zebrafish KO of neuropsychiatric risk gene znf536

Genetic variants in ZNF536 contribute to the risk for neuropsychiatric disorders such as schizophrenia, autism, and others. The role of this putative transcriptional repressor in brain development and function is, however, largely unknown. We generated znf536 knockout (KO) zebrafish and studied their behavior, brain anatomy, and brain function. Larval KO zebrafish showed a reduced ability to compete for food, resulting in decreased total body length and size. This phenotype can be rescued by segregating the homozygous KO larvae from their wild-type and heterozygous siblings, enabling studies of adult homozygous KO animals. In adult KO zebrafish, we observed significant reductions in anxiety-like behavior and social interaction. These znf536 KO zebrafish have decreased cerebellar volume, corresponding to decreased populations of specific neuronal cells, especially in the valvular cerebelli (Va). Finally, using a Tg[mbp:mgfp] line, we identified a previously undetected myelin structure located bilaterally within the Va, which also displayed a reduction in volume and disorganization in KO zebrafish. These findings indicate an important role for ZNF536 in brain development and implicate the cerebellum in the pathophysiology of neuropsychiatric disorders.

An Open-Source Programmable Interface for Sensory-Motor Biotests with Zebrafish (Danio rerio)

Assessment of animals' sensory-motor functions requires precise and electronically controlled stimuli to induce and quantify specific behavioral phenotypes. However, accessible and inexpensive tools for conducting diverse sensory-motor biotests with fish are lacking. In this work, we present an open-source software and hardware interface that enables automated delivery of three independent and fully programmable stimuli for behavioral bioassays. We demonstrate the proof-of-concept application of this low-cost technology in establishing reproducible fear responses using a mechanical tap-startle stimulus in larval zebrafish. This response is characterized by a sudden burst of motion in response to a nondirectional mechanical stimulus delivered to the fish chamber. We propose that the simplicity and flexibility of this interface offer innovative opportunities for studying sensory-motor functions in various fields, including neurobiology, neuropharmacology, neurotoxicology, and aquatic ecotoxicology.

β-Carboline (FG-7142) modulates fear but not anxiety-like behaviour in zebrafish

The β-Carboline FG-7142 is a partial inverse agonist at the benzodiazepine allosteric site on the GABA-A receptor that induces anxiogenic, proconvulsant, and appetite-reducing effects in many species, including humans. Seizure-kindling effects have been well studied, however anxiogenic properties are relatively unexplored. This study aimed to investigate concentration-dependent effects of FG-7142 on anxiety-like behaviour and fear responses in zebrafish (Danio rerio) using the open-field test (OF) and novel object approach test (NOA). A U-shaped distribution was found with maximal responses in increased immobility and reduced distance moved at 10 µM in the NOA but not the OF. Follow up experiments demonstrated a lack of effect in repeated OF testing and no changes in opercular movements. Furthermore, the effect of FG-7142 was reversed with ethanol treatment. These results suggest that FG-7142 elicits a 'freezing' response in zebrafish via the introduction of novelty, suggesting fear-induction. These findings indicate that FG-7142 may act as an agent to promote acute fear responses in zebrafish.

The ram cichlid (Mikrogeophagus ramirezi) learns an associative task: a new fish species for memory research

Fish are the most species rich and evolutionarily oldest vertebrate taxon. This represents opportunities for biologists who intend to employ laboratory animals in their comparative or translational research. Yet, the overwhelming majority of such studies use a single fish species, the zebrafish, a suboptimal strategy from the comparative standpoint. Neuronal plasticity (learning and memory) is perhaps one of the most complex biological phenomena from a mechanistic standpoint, and thus its analysis could benefit from the use of evolutionarily ancient and simple vertebrate model organisms, i.e., fish species. However, learning & memory research with the zebrafish has been replete with problems. Here, we employ a novel fish species, the ram cichlid, we argue will be particularly appropriate for this purpose for practical as well as ethological/ecological reasons. First, we investigate whether the ram cichlid exhibits innate preference for certain colours (red, blue, yellow or green) in a four-choice task, the plus maze. Subsequently, we pair the apparently least preferred colour (green, the conditioned stimulus or CS) with food reward (the unconditioned stimulus, US) in the plus maze, a CS-US associative learning task. After eight pairing trials, we run a probe trial during which only the CS is presented. At this trial, we find significant preference to the CS, i.e., acquisition of memory of CS-US association. We argue that our proof-of-concept study demonstrating fast acquisition of CS-US association in the ram cichlid, coupled with the universal utility of some genome editing methods, will facilitate the mechanistic analysis of learning and memory.

Zebrafish (Danio rerio): A newcomer with great promise in behavioral neuroscience

Behavioral neuroscience is an interdisciplinary field aimed at understanding the neurobiology of behavior. Numerous investigators turn to animals to model and understand the mechanisms underlying vertebrate brain function including human brain disorders, species that share evolutionary history with us. The zebrafish is a relatively new study species for such purposes. However, as this review attempts to demonstrate, it will likely have a good future in behavioral neuroscience. It is a simple vertebrate that is small and cheap to keep and study in the laboratory. Yet, it is similar enough to our own species, thus, we are able to use it for both translational as well as basic research. In this invited review, I will discuss its advantages and some of its disadvantages, the reasons and counterarguments why it should or should not be employed in research. I will focus on its utility in behavioral neuroscience, and will also provide a brief historical account of the evolution between zebrafish research and the science represented by the International Behavioral Neuroscience Society.

The effect of fish density and tank size on the behavior of adult zebrafish: A systematic analysis

The zebrafish has been employed in several fields of biology due to its translational relevance and its simplicity and ease of maintenance. As a result, zebrafish are kept in thousands of laboratories around the world. Current industry standards favor keeping the largest possible number of fish in the smallest possible volume of water to increase efficiency and reduce costs. However, physiological and psychological stress resulting from such crowding may impact a variety of phenotypes, from brain function and behavior to cardiovascular function and cancer. Nevertheless, surprisingly little is known about what constitutes an optimal housing environment for the zebrafish, e.g., no systematic analyses have been performed to test the role of housing density and tank volume despite recent sporadic reports implying negative effects of the standard practice of crowding. Here, we conduct the first proof of concept analysis examining the potential impact of housing density and tank volume on the behavior of zebrafish. We randomly assigned adult zebrafish to one of three tank sizes (1.5, 10, or 50 L) with one of three housing densities (1, 2, or 4 fish/L), a 3 × 3 between subject experimental design, and maintained the fish in their corresponding condition for 2 weeks. Subsequently, we tested the behavior of the fish singly in a novel open tank for 12 min and quantified several of their swim path parameters using a video-tracking system. We found significant additive and interacting effects of tank size and/or housing density on swim path parameters including immobility, swim speed, turn angle, and distance to bottom and to stimulus. Although we had only three fish densities and three tank sizes and we did not explore the effects of more extreme conditions and although the interpretation of the above behavioral effects is speculative at this point, the results already demonstrate that both tank size and housing density exerts significant effects on the zebrafish and thus should be considered in zebrafish husbandry.