Biology subjects

Parker, M. O.

Publications and source records attributed to Parker, M. O..

18 recordsLinked to original sources

bioRxiv2026

Virtual reality exposes fine-scale alterations in behaviour following loss of the ADHD-linked gene adgrl3.1 in zebrafish

Zebrafish have been used a prominent model for high-throughput phenotypic screens of candidate risk gene mutations for several disorders. This also includes models for attention deficit/hyperactivity disorder (ADHD). Traditional behavioural tests, such as the forced light/dark assay, concentrate on basic locomotion measures. However, recently developed visually-driven locomotion assays, for example closed-loop systems using virtual reality, have allowed extraction of richer data on animal locomotion and decision-making under different sensory stimuli. Here, we have used such a system to assess the behaviour in adgrl3.1 mutant fish, an established model for ADHD. Our results show that mutants exhibit a higher baseline excitability and a lower threshold for initiating motor events, demonstrating that collecting behavioural responses in an interactive environment enables a more precise characterisation of ADHD-relevant phenotypes associated with adgrl3.1 disruption. More generally, we establish a scalable translational platform to screen gene-function relationships and possible therapeutic interventions, not only for ADHD but multiple neurodevelopmental disorders.

neuroscience↗

bioRxiv2025

Fentanyl and Alcohol Co-Exposure Induce Robust, Sustained Hyperlocomotion and Neural Circuit Disruption in Larval Zebrafish

The constantly evolving trends in substance abuse are a major concern for health authorities worldwide, and these trends include an increasing prevalence of poly-substance misuse. For instance, opioid overdoses are frequently accompanied by alcohol co-use, yet the combined effects of these substances remain poorly understood. Using zebrafish as a highly relevant vertebrate model of neuropharmacology, we investigated the interactions between fentanyl and alcohol, uncovering a unique and robust hyperlocomotor response characterized by initial locomotor suppression followed by persistent, erratic hyperlocomotion. Alcohol was found to be critical to this phenomenon, as substitution with other GABAA modulators failed to replicate the effect. However, the response was replicable with heroin and remifentanil, suggesting an opioid-class wide effect. In vivo whole brain imaging further demonstrated dysregulated neuronal activity, with co-administration with alcohol causing potentiated neuronal activity compared to individual drug exposures and controls. Collectively, these findings suggested an integral role of ethanol and fentanyl co-administration in dysregulated neuronal responses and reveals a complex neurobehavioral mechanism. These observations suggest further investigation is warranted into the use of the larval zebrafish model for studying the neuropharmacological interactions of multiple substances of abuse.

animal behavior and cognition↗

bioRxiv2025

Genetic disruption of leucine rich repeat transmembrane protein 4 like 1 induces a pro-social behavioural phenotype in zebrafish

BackgroundSocial behaviour encompasses the wide range of interactions that occur between members of the same species. In humans, disruptions in social behaviour are characteristic of many neuropsychiatric disorders, where both genetic risk factors and synaptic dysfunctions can contribute to the phenotype. Among the genes implicated in synaptic regulation, the synaptic adhesion protein leucine-rich repeat transmembrane protein 4 (LRRTM4) has been identified as a key player in maintaining synaptic function and neuronal circuit integrity. Despite its established role in the nervous system, the potential involvement of LRRTM4 in modulating social behaviour and its contribution to social deficits has yet to be explored. MethodsIn the current study, we used zebrafish to study how genetic deletion of lrrtm4l1, a zebrafish orthologue of LRRTM4, affects sociality. For this, the social behaviour of homozygous lrrtm4l1 knockout (KO) zebrafish was analysed in multiple behavioural assays and the brain transcriptome of mutant animals was investigated by RNAseq. ResultsKO zebrafish displayed a pro-social phenotype in multiple behavioural assays. Groups of lrrtm4l1 KO zebrafish formed more cohesive shoals and KO individuals spent more time in the vicinity of conspecifics during a social interaction test. They were also less aggressive and in contrast to wild-type zebrafish did not differentiate in their interactions with known and unknown groups of fish. Neurotranscriptomic analysis revealed 560 differentially expressed genes including changes in glutamatergic neurotransmitter signalling, tryptophan- kynurenine metabolism and synaptic plasticity. ConclusionThese findings suggest that lrrtm4l1 is an important regulator of social behaviour in zebrafish. In a translational perspective, LRRTM4 is a promising potential therapeutic target that warrants further investigation in the framework of neuropsychiatric conditions characterized by major social impairments.

neuroscience↗

bioRxiv2025

Neural and Behavioral Dynamics of Acute Fentanyl Administration and Implications for Hazard Assessment of Novel Synthetic Opioids in Larval Zebrafish

Rationale Synthetic opioids pose a significant public health risk due to their rapid synthesis and potentially lethal potency. New compounds are emerging continuously, meaning current testing platforms struggle to keep pace. Objectives Consequently, there is a critical need for simple, rapid, translatable models to provide a scalable screening platform to identify and hazard-assess emerging synthetic opioids, and test potential intervention strategies. Methods Here, we exposed 4 days post-fertilization (dpf) larval zebrafish to a range of concentrations of the prototypical class representative, fentanyl, to investigate behavioral and neural responses. Results Fentanyl caused low concentration hyperactivity, and high concentration hypolocomotion (sedation) which was reversed by the opioid antagonist naloxone. We confirmed predictive validity by replicating the behavioral responses with other class representatives (diacetylmorphine [heroin] and remifentanil). We also confirmed, pharmacologically, that low concentration hyperlocomotion was mediated by dopamine D2 receptors, replicating effects observed in mammals. Further mechanistic investigation using whole-brain in vivo imaging revealed disrupted connectivity in opioid-related circuits, such as the habenulae and dorsal thalamus, alongside novel pathways, including circuits associated with the pineal gland, torus semicircularis and eminentia granularis, potentially highlighting previously uncharacterized sensory and cerebellar neuronal networks. Conclusions These findings support the use of the larval zebrafish as a scalable model for assessment of synthetic opioids to provide novel insights into opioid-induced behaviors and mechanisms of action that may aid strategies in the growing challenge of interventive treatments for synthetic opioid intoxication. Impact StatementLarval zebrafish reveal neurobehavioral pathways affected by synthetic opioids, offering a valuable tool for rapid hazard assessment.

animal behavior and cognition↗

bioRxiv2024

Environmental Enrichment Reduces adgrl3.1-Related Anxiety and Attention Deficits but Not Impulsivity

Environmental factors play a role in the development and severity of neuropsychiatric disorders. Externalizing disorders (EDs) are linked to genetic and environmental factors and frequently co-occur with internalizing disorders (ID), such as anxiety. Individuals experiencing both ED/ID are often among the most likely to seek healthcare services, as this co-occurrence is associated with more severe symptomatology and greater functional impairment. Here, we investigate the role of environmental enrichment (EE) on a gene associated with impulsivity and attention deficits in zebrafish, adgrl3.1. Zebrafish were reared in either standard or enriched environments (from 15 days-post fertilization), and attention, impulsivity, and anxiety-related phenotypes were assessed at adult stages (4 months-post fertilization) using the open field test and 5-choice serial reaction time task. EE mitigated anxiety-related behaviors in adgrl3.1 knockouts, normalizing locomotor patterns and decreasing thigmotaxis. Although attention deficits were reduced in adgrl3.1-/- fish reared in EE, impulsive behaviors were not. Together, these findings suggest that while EE can alleviate some externalizing and internalizing phenotypes in zebrafish, impulsivity remains resistant to environmental modification. This study suggests that impulsivity is a stable trait in adgrl3.1-/- fish, but highlights the importance of EE in mitigating some externalizing and internalizing symptoms. Summary statementEnvironmental enrichment reduces attention deficits and anxiety-like behavior, but not impulsivity in adgr3.1 knockout zebrafish, highlighting the interaction between genetic and environmental factors in shaping externalizing and internalizing phenotypes.

animal behavior and cognition↗

bioRxiv2024

Social Isolation Intensifies adgrl3.1-Related Externalizing and Internalizing Behaviors in Zebrafish

Externalizing disorders (EDs) are characterized by outward-directed behaviors such as aggression and hyperactivity. They are influenced by gene-environment interactions, yet our understanding of the genetic predispositions and environmental contexts that give rise to them is incomplete. Additionally, people with EDs often exhibit comorbid internalizing symptoms, which can complicate the clinical presentation and treatment strategies. Following on from our previous studies, we examined genes x environment interaction as a risk factor for EDs by looking at internalizing and externalizing behaviors after social isolation. Specifically, we subjected adgrl3.1 knockout zebrafish -- characterized by hyperactivity and impulsivity -- to a 2-week social isolation protocol. We subsequently assessed the impact on anxiety-like behavior, abnormal repetitive behaviors, working memory, and social interactions. Genotype-specific additive effects emerged, with socially isolated adgrl3.1 knockout fish exhibiting intensified comorbid phenotypes, including increased anxiety, abnormal repetitive behaviors, reduced working memory, and altered shoaling, when compared to WT fish. The findings demonstrate that genetic predispositions interact with environmental stressors, such as social isolation, to exacerbate both externalizing and internalizing symptoms. This underlines the necessity for comprehensive diagnostic and intervention strategies.

animal behavior and cognition↗

bioRxiv2024

Spatiotemporal dynamics of locomotor decisions in Drosophila melanogaster

Decision-making in animals often involves choosing actions while navigating the environment, a process markedly different from static decision paradigms commonly studied in laboratory settings. Even in decision-making assays in which animals can freely locomote, decision outcomes are often interpreted as happening at single points in space and single moments in time, a simplification that potentially glosses over important spatiotemporal dynamics. We investigated locomotor decision-making in Drosophila melanogaster in Y-shaped mazes, measuring the extent to which their future choices could be predicted through space and time. We demonstrate that turn-decisions can be reliably predicted from flies locomotor dynamics, with distinct predictability phases emerging as flies progress through maze regions. We show that these predictability dynamics are not merely the result of maze geometry or wall-following tendencies, but instead reflect the capacity of flies to move in ways that depend on sustained locomotor signatures, suggesting an active, working memory-like process. Additionally, we demonstrate that fly mutants known to have sensory and information-processing deficits exhibit altered spatial predictability patterns, highlighting the role of visual, mechanosensory, and dopaminergic signaling in locomotor decision-making. Finally, highlighting the broad applicability of our analyses, we generalize our findings to other species and tasks. We show that human participants in a virtual Y-maze exhibited similar decision predictability dynamics as flies. This study advances our understanding of decision-making processes, emphasizing the importance of spatial and temporal dynamics of locomotor behavior in the lead-up to discrete choice outcomes.

animal behavior and cognition↗

bioRxiv2024

The effect of laboratory diet and feeding on growth parameters in zebrafish

Despite being one of the most used laboratory species in biomedical, behavioural and physiological research, the nutritional requirements of zebrafish (Danio rerio) are poorly understood, and no standardised laboratory diet exists. Diet and feeding regimen can significantly impact the welfare of the fish and in turn experimental reproducibility. Consequently, the establishment of a standardised diet and feeding protocol for laboratory zebrafish is imperative to enhance animal welfare, guarantee research reproducibility and advance the economic and environmental sustainability of laboratory dietary practices. The aim of this systematic review was to determine the optimal feed for juvenile zebrafish growth and development. A comprehensive search was conducted in PubMed, Scopus and Google Scholar to identify relevant studies published up to August 2023 and the studies were selected based on the predefined inclusion/exclusion criteria. A total of 1065 articles were identified in the databases, of which 14 were included in this review. We conducted data extraction and risk-of-bias analysis in the included studies. Statistical comparisons for specific growth rate, weight gain (%) and length gain (%) parameters were performed to determine the optimal feed for enhanced juvenile growth. We identify an insect-based diet as optimal for juvenile growth for all three growth parameters. We also identify areas of potential heterogeneity and conclude by encouraging a standardised laboratory diet to ensure reproducible data and encourage zebrafish welfare.

developmental biology↗

bioRxiv2023

A Unified Approach to Investigating 4 dpf Zebrafish Larval Behaviour through a Standardised Light/Dark Assay

Zebrafish have emerged as a dynamic research model in the domains of neuropsychopharmacology, biological psychiatry and behaviour. Working with larvae [≤] 4 days post-fertilisation (dpf) offers an avenue for high-throughput investigation whilst aligning with the 3Rs principles of animal research. The light/dark assay, which is the most used behavioural assay for larval neuropharmacology research, lacks experimental reliability and standardisation. This study aimed to formulate a robust, reproducible and standardised light/dark behavioural assay using 4 dpf zebrafish larvae. Considerable between-batch and inter-individual variability was found, which we rectified with a normalisation approach to ensure a reliable foundation for analysis. We then identified that 5-minute light/dark transition periods are optimal for locomotor activity. We also found that a 30-minute acclimation in the light was found to produce significantly increased dark phase larval locomotion. Next, we confirmed the pharmacological predictivity of the standardised assay using ethanol which, as predicted, caused hyperlocomotion at low concentrations and hypolocomotion at high concentrations. Finally, the assay was validated by assessing the behavioural phenotype of hyperactive transgenic (adgrl3.1-/-) larvae, which was rescued with psychostimulant medications. Our standardised assay not only provides a clear experimental and analytical framework to work with 4 dpf larvae, but also facilitates between-laboratory collaboration using our normalisation approach.

animal behavior and cognition↗

bioRxiv2023

adgrl3.1-deficient zebrafish show noradrenaline-mediated externalizing behaviors, and altered expression of externalizing disorder-candidate genes, suggesting functional targets for treatment

Externalising disorders (ED) are a cause of concern for public health, and their high heritability make genetic risk factors a priority for research. Adhesion G Protein-Coupled Receptor L3 (ADGRL3) is strongly linked to several EDs, and loss-of-function models have shown impacts of this gene on several core ED-related behaviors. For example, adgrl3.1-/- zebrafish show high levels of hyperactivity. However, our understanding of the mechanisms by which this gene influences behavior is incomplete. Here we characterized, for the first time, externalizing behavioral phenotypes of adgrl3.1-/- zebrafish and found them to be highly impulsive, show boldness in a novel environment, have attentional deficits, and show high levels of hyperactivity. All of these phenotypes were rescued by atomoxetine, demonstrating noradrenergic mediation of the externalizing effects of adgrl3.1. Transcriptomic analyses of the brains of adgrl3.1-/- vs wild type fish revealed several differentially expressed genes and enriched gene clusters that were independent of noradrenergic manipulation. This suggests new putative functional pathways underlying ED-related behaviors, and potential targets for the treatment of ED.

neuroscience↗

bioRxiv2022

A high-throughput test of anxiety for zebrafish (Danio rerio) larvae: the larval diving response (LDR)

BackgroundZebrafish are used in anxiety research as the species naturalistic diving response to a new environment is a reliable and validated marker for anxiety-like behavior. One of the benefits of using zebrafish is the potential for high throughput drug screens in fish at the larval stage. However, at present, tests of anxiety in larvae and adults often measure different endpoints. New MethodHere, for the first time, we have adapted the novel tank diving response test for examining diving behavior in zebrafish larvae to assess anxiety-like behaviors at very early-stages (7 days-post-fertilization [dpf]). Comparison with Existing MethodsCurrent methods to examine anxiety in larvae can show low reliability, and measure different endpoints as in adults, thus calling into question their translational relevance. ResultsWe found that 7dpf zebrafish spent more time at the bottom of a small novel tank. We validated this as anxiety-like behaviors with diazepam reducing, and caffeine increasing the time spent in the bottom of the novel environment. ConclusionsThis new automated and high-throughput screening tool has the potential use for screening of anxiogenic and anxiolytic compounds, and for studies aiming to understand the mechanisms underlying affective disorders.

animal behavior and cognition↗

bioRxiv2020

Effects of D1 agonist on working memory and cognitive flexibility in a zebrafish model of aging

Healthy aging is associated with a decline in memory and executive function, which have both been linked with aberrant dopaminergic signalling. We examined the relationship between cognitive performance and dopamine function of young and aging zebrafish (Danio rerio). We revealed age-related decreases in working memory and cognitive flexibility in the Free-Movement Pattern (FMP) Y-maze. An increase in drd5 gene expression in aging adults coincided with a decrease in cognitive performance. Treatment with a D1/D5 receptor agonist (SKF-38393, 35 M) 30 minutes prior to behavioural assessment resulted in improved working memory in aging zebrafish, but no effect in younger adults. However, an overdosing effect caused by agonist treatment resulted in downregulation of dat expression in 6-month old, treated zebrafish. The translational relevance of these findings was tested in humans by analysing exploratory behaviour in young-adult, 18-35-year olds, and aged adults, 70+ year olds, in a virtual FMP Y-maze. Our findings revealed similar age-related decline in working memory. Thus, strongly supporting zebrafish as a translational model of aging and cognitive decline.

animal behavior and cognition↗

bioRxiv2020

Moderate early-life stress improves adult zebrafish (Danio rerio) spatial short-term memory but does not affect social and anxiety-like responses

Early-life stress (ELS) is defined as a short or chronic period of trauma, environmental or social deprivation, which can affect different neurochemical and behavioral patterns during adulthood. Zebrafish (Danio rerio) have been widely used as a model system to understand human neurodevelopmental disorders and display translationally relevant behavioral and stress-regulating systems. In this study, we aimed to investigate the effects of moderate ELS by exposing young animals (six weeks post-fertilization), for three consecutive days, to three stressors, and analyzing the impact of this on adult zebrafish behavior (sixteen weeks post-fertilization). The ELS impact in adults was assessed though analysis of performance on tests of unconditioned memory (free movement pattern Y-maze test), exploratory and anxiety-related task (novel tank diving test) and social cohesion (shoaling test). Here, we show for the first time that moderate ELS increases the number of pure alternations compared to pure repetitions in the unconditioned Y-maze task, suggesting increased spatial short-term memory, but has no effect on shoal cohesion, locomotor profile or anxiety-like behavior. Overall, our data suggest that moderate ELS may be linked to adaptive flexibility which contributes to build resilience in adult zebrafish by improving short-term spatial memory performance.

animal behavior and cognition↗

bioRxiv2020

A Test of Memory: The Fish, The Mouse, The Fly And The Human

Simple mazes have provided numerous tasks for assessing working memory. The discrete nature of choices in the T-maze has provided a robust protocol with sensitivity to cognitive deficits, whilst the continuous Y-maze reduces manual handling and pre-trial training. We have combined these attributes to develop a new behavioural task for assessing working memory, the Free-movement pattern (FMP) Y-maze. Using sequentially recorded left and right turns we demonstrate that zebrafish and mice use a single dominant strategy predominantly consisting of alternations between left and right choices trial-to-trial. We further tested this protocol with Drosophila and discovered an alternative invertebrate search strategy. Finally, a virtual human FMP Y-maze confirmed a common strategy among all tested vertebrate species, validating the translational power of the task for human research. The FMP Y-maze combines robust investigation of working memory and high translational power, generating a simple task with far-reaching impact.

animal behavior and cognition↗

bioRxiv2019

Zebrafish (Danio rerio) behavioral laterality predicts increased short-term avoidance memory but not stress-reactivity responses

Once considered a uniquely human attribute, behavioral laterality has proven to be ubiquitous among non{square}human animals, being frequently associated with different neurophenotypes in rodents and fish species. Zebrafish (Danio rerio) are a versatile and complementary vertebrate model system that has been widely used in translational neuropsychiatric research due their highly conserved genetic homology, well characterized physiological and extensive behavioral repertoire. Although the spontaneous left- and right-bias responses and associated behavioral domains (e.g. stress reactivity, aggression and learning) have previously been observed in other teleost species, no information regarding the natural left-right bias responses of zebrafish has been described. Thus, we aimed to investigate the existence and incidence of natural left-right bias of adult zebrafish in the Y-maze test and explore any relationship of biasedness on the performance of different behavioral domains. This included learning about threat-cues in the fear conditioning test and locomotion and anxiety-related behavior in the novel tank diving test. In conclusion, we showed for the first time that zebrafish exhibit a natural manifestation of behavioral lateralization which can influence aversive learning responses. Although laterality did not change locomotion or anxiety-related behaviors, we found that biased animals showed a reduction of short-term memory performance in the Y-maze and increase learning associated to fear cues.

animal behavior and cognition↗

bioRxiv2018

Population based forward genetic screen of mutagenized zebrafish identifies loci associated with nicotine preference and human smoking behavior

To facilitate smoking genetics research we determined whether a screen of mutagenized zebrafish for nicotine preference could predict loci affecting smoking behaviour. Of 30 ENU mutagenized families screened, two showed increased or decreased nicotine preference. Out of 25 inactivating mutations in the families, one in the slit3 gene segregated with increased nicotine preference in heterozygous individuals. Focussed SNP analysis of the human SLIT3 locus in cohorts from UK (n=863) and Finland (n=1715) identified two variants that predict cigarette consumption and likelihood of cessation. Characterisation of slit3 mutant larvae and adult fish revealed decreased sensitivity to the dopaminergic and serotonergic antagonist amisulpride, known to affect startle reflex that is correlated with addiction in humans, and increased htr1aa mRNA expression in mutant larvae. No effect on neuronal pathfinding was detected. These findings reveal a role for SLIT3 in development of pathways affecting responses to nicotine in zebrafish and smoking in humans.

genetics↗

bioRxiv2018

Moderate developmental alcohol exposure reduces repetitive alternation in a zebrafish model of fetal alcohol spectrum disorders.

The damaging effects of alcohol on a developing fetus are well known and cause a range of conditions known as fetal alcohol spectrum disorder (FASD). High levels of alcohol exposure lead to physical deformity and severe cognitive deficits, but more moderate exposure leads to a range of subtle cognitive effects such as reduced social behavior, higher propensity to develop addictions, and reduced spatial working memory. Previous studies have demonstrated that following exposure to relatively low levels of ethanol during early brain development (equivalent in humans to moderate exposure) zebrafish display a range of social and behavioral differences. Here, our aim was to test the hypothesis that moderate developmental ethanol exposure would affect aspects of learning and memory in zebrafish. In order to do this, we exposed zebrafish embryos to 20mM [0.12% v/v] ethanol from 2 to 9 dpf to model the effects of moderate prenatal ethanol (MPE) exposure. At 3 months old, adult fish were tested for appetitive and aversive learning, and for spatial alternation in a novel unconditioned y-maze protocol. We found that MPE did not affect appetitive or aversive learning, but exposed-fish showed a robust reduction in repetitive alternations in the y-maze when compared to age matched controls. This study confirms that moderate levels of ethanol exposure to developing embryos have subtle effects on spatial working memory in adulthood. Our data thus suggest that zebrafish may be a promising model system for studying the effects of alcohol on learning and decision-making, but also for developing treatments and interventions to reduce the negative effects of prenatal alcohol.

pharmacology and toxicology↗

bioRxiv2017

A fully automated computer based Skinner box for testing learning and memory in zebrafish

Zebrafish are an important model species with unparalleled potential to advance understanding of the genetics and neurobiology of behaviour through genetic and pharmacological screening and mutant analysis. However, advances using this species have been limited by the lack of robust, standardised methodology and equipment suitable for assessing adult behaviour. Here we describe a simple, fully automated, computer based, operant system for measuring behaviour in juvenile and adult zebrafish and provide detailed protocols for appetitive and aversive assays to assess cognitive function in adult zebrafish. Applications include the study of cognition in zebrafish (and other similar sized fish species) and in zebrafish models of psychiatric and neurodegenerative diseases (e.g., Alzheimers disease, schizophrenia, Huntingtons disease, frontotemporal dementia), and characterisation of the role of select brain regions, neurotransmitter systems and genes in zebrafish. Further, the scalable nature of the system makes the protocols suitable for use in pharmacological and genetic screening programmes.

animal behavior and cognition↗