Biology subjects

Varga, Z. K.

Publications and source records attributed to Varga, Z. K..

10 recordsLinked to original sources

bioRxiv2026

SEROTONERGIC ANXIETY IS A STRESS INTENSITY-DEPENDENT STATE MEDIATED BY DOPAMINERGIC SIGNALING

Despite the central role attributed to serotonin in anxiety, its involvement and therapeutic efficacy are inconsistent, raising the possibility that serotonergic recruitment depends on the stress history from which anxiety emerges. Using larval zebrafish, we combined graded glucocorticoid exposure with chemogenetic DRN manipulation, whole-brain activity mapping, and pharmacology to test whether stress intensity determines serotonergic involvement in anxiety.Increasing stress intensity did not simply increase anxiety severity but generated distinct anxiety phenotypes. Lower glucocorticoid exposure produced context-general anxiety that required the serotonergic DRN, whereas higher exposure produced context-dependent, DRN-independent anxiety. Whole-brain mapping identified a posterior tubercular/hypothalamic dopaminergic region associated with DRN-dependent anxiolysis, while D1, but not D2 receptor antagonism abolished the anxiolytic effect of DRN ablation. Finally, environmentally relevant nanomolar concentrations of methylphenidate reduced anxiety-like behavior, further supporting dopaminergic modulation of anxiety. Together, our findings identify stress intensity as a determinant of serotonergic recruitment during anxiety, reveal a downstream contribution of D1-dependent dopaminergic signaling, and provide a framework for understanding the mechanistic heterogeneity of anxiety and its variable response to serotonergic treatments.

neuroscience↗

bioRxiv2026

Organization, development, and plasticity of the serotonergic dorsal raphe nucleus projectome

The dorsal raphe nucleus (DRN) is the main source of serotonin (5-HT) in the central nervous system. 5-HT DRN neurons modulate a wide range of physiological functions and brain states via their widespread and heterogeneous projections. Yet the organizational logic, developmental dynamics, and experience-dependent plasticity of these projections remain poorly understood. By reconstructing the whole brain projections of 81 individual 5-HT DRN neurons across developmental stages in the larval zebrafish, we find that these neurons exhibit diverse projection patterns, ranging from broadly distributed to spatially confined. We identify two previously uncharacterized, projection-defined subpopulations within the larval dorsal raphe nucleus, which selectively target either the telencephalon or the spinal cord. This organization is consistent with the existence of anatomically distinct serotonergic pathways that may differentially influence forebrain and sensorimotor circuits. Longitudinal analysis revealed that the gross architecture of 5-HT neurons remained stable during larval development, although region-specific remodeling occurred in all neurons. Importantly, stress exposure during the first week of development, but not thereafter, altered the density of 5-HT DRN projections to telencephalic regions, suggesting a critical window of increased plasticity during early life. Collectively, our findings clarify the developmental trajectory, maturation, and stress-induced plasticity of the serotonergic circuitry, providing important insights for deciphering the pathophysiology of stress-related mental disorders.

neuroscience↗

bioRxiv2025

Early life chronic stress-disrupted activity of the dorsal raphe nucleus selectively drives behavioral impairments

Stress elicits variable systemic and neural changes in vertebrates, with outcomes ranging from adaptive to pathological. Several studies have implicated the dorsal raphe nucleus (DRN), a brainstem nucleus containing a heterogeneous population of serotonergic (5-HT) neurons, in the adaptive stress response and the pathological changes resulting from chronic stress. However, it is not known whether early life chronic stress affects the developing DRN activity, or whether the stress-induced changes affect 5-HT DRN neurons in a subregion- or phenotype-specific manner. To answer these questions, we used in vivo 2-photon calcium imaging of 5-HT DRN neurons in larval zebrafish exposed to chronic unpredictable stress during early life. We found that early life chronic stress prevented the normal habituation of the serotonergic system to a repeated acute stressor by altering the balance of excitatory/inhibitory responses within the DRN. Interestingly, these changes were most pronounced in a subset of stress-vulnerable serotonergic cells co-expressing GABAergic markers. Further, using chemogenetic ablation of 5-HT DRN neurons, we showed that stress-induced plasticity of the DRN contributed to changes in startle response habituation and in locomotive activity, but not in anxiety-like behaviors. Collectively, our results emphasize the role of stress-induced plasticity of DRN neurons in the selective regulation of maladaptive behavioral outcomes.

neuroscience↗

bioRxiv2025

Genome-wide association study reveals KCNQ3 gene as a risk factor for fear-related behavior in dogs and zebrafish

Freezing behavior, characterised by attentive immobility as a reaction to a perceived threat, is widely studied in the context of fear, anxiety and stress. To uncover the genetic factors underlying this behavior, we conducted a genome-wide association study (GWAS) in kennel-housed beagle dogs. Our analysis identified a single-nucleotide polymorphism (SNP) in intron 5 of the KCNQ3 gene on chromosome 13 associated with freezing behavior in response to unfamiliar environments and people. To validate this finding, we used a zebrafish model, where CRISPR/Cas9-induced kcnq3 deficiencies led to heightened fear and arousal in two behavioral tests. KCNQ3 is implicated in several neurodevelopmental and psychiatric disorders, and our results highlight its evolutionarily conserved role in modulating fear responses. In dogs, an enriched environment can mitigate the adverse effects of KCNQ3 deficiency by reducing threat perception, highlighting the role of gene-environment interactions in shaping behavioral responses. TeaserKCNQ3 influences fear responses across species, with gene-environment interactions shaping freezing behavior in dogs.

animal behavior and cognition↗

bioRxiv2024

Paradise fish (Macropodus opercularis) as novel translational model for emotional and cognitive function

Zebrafish have revolutionised physiological screening in vertebrates, but the interpretation of individual-based behavioural assays is burdened by the strong sociality of this species. We propose the use of a solitaire fish species, the paradise fish to keep the advantages and compensate for the limitations of the zebrafish model. We compared juvenile paradise fish and zebrafish in social and non-social exploratory tasks, anxiety tests and in a working memory assay to assess their performance in these individual-based models. We found that in contrast to zebrafish, paradise fish did not show social approach in the U-shape sociability test, their novelty exploration was not biased by the presence of a conspecific in the slalom test, and was not impaired by social isolation in the showjump or in the swimming plus-maze (SPM) anxiety tests. While social circumstances did not affect the anxiety of paradise fish, it was sensitive to the anxiolytic drug buspirone. Intra- and interest repeatability measures of the anxiety tests revealed that paradise fish express more consistent exploratory and defensive behaviours regarding time and context compared to zebrafish. Behavioural consistency in paradise fish was also supported by arm alternation as a predominant choice of exploration in the y-maze task. In summary, our results indicate that the behaviour of paradise fish is less biased by social cues and is more effective and repeatable in individual-based assays than zebrafish behaviour. We hypothesise that the two phenomena are connected and novelty exploration, anxiety and working memory can be more reliably measured and are translatable in a solitaire species.

animal behavior and cognition↗

bioRxiv2024

Pretrauma cognitive traits predict trauma-induced fear generalization and associated prefrontal functioning in a longitudinal model of posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is a chronic psychiatric condition that develops in susceptible individuals exposed to traumatic stress, challenging clinicians to identify risk factors and mechanisms for mitigating vulnerability. Here we investigated behavioral predictors of high fear generalization, a core PTSD symptom, and its neural correlates longitudinally in rats. In a comprehensive behavioral test battery of emotional and cognitive function, pretrauma lower operant learning performance emerged as high predictor of fear generalization following trauma. Posttrauma operant training facilitated fear extinction, suggesting an overlap in neural circuits governing operant learning and fear expression. Neuronal activity mapping revealed significant changes in the medial prefrontal cortex (mPFC) in high fear generalizers, with alterations in CRH/VIP+ interneuron functioning. Silencing prefrontal Crh expression after fear memory consolidation enhanced mPFC activation and reduced fear expression, favoring resilience. These findings highlight operant learning and mPFC alterations as vulnerability markers and mediators of excessive fear generalization, with implications for prevention and targeted therapy in PTSD.

neuroscience↗

bioRxiv2024

Endocannabinoid biomarkers of vulnerability to the development of trauma-induced generalized fear responses

Traumatic experiences result in the development of posttraumatic stress disorder (PTSD) in 10-25% of exposed individuals. While human clinical studies suggest that susceptibility is potentially linked to endocannabinoid (eCB) signaling, neurobiological PTSD susceptibility factors are poorly understood. Employing a rat model of PTSD, we characterized distinct resilient and susceptible subpopulations based on generalized fear, a core symptom of PTSD. In these groups, we assessed i.) eCB levels by mass spectrometry and expression variations of eCB system- and iii.) neuroplasticity-related genes by real-time quantitative PCR in the circuitry relevant in trauma-induced changes. Furthermore, employing supervised and semi-supervised machine learning based statistical analytical models, we assessed iv.) gene expression patterns with the most robust predictive power regarding PTSD susceptibility. According to our findings, in our model, generalized fear responses occurred with sufficient variability to characterize distinct resilient and susceptible subpopulations. Susceptible subjects showed lower prelimbic and higher ventral hippocampal levels of eCB 2-arachidonoyl-glycerol (2-AG) compared to resilient subjects. Ventral hippocampal 2-AG content positively correlated with the strength of fear generalization. Furthermore, susceptibility was associated with i.) neuronal prefrontal, hippocampal and amygdalar hypoactivity, ii.) marked decrease in the expression of genes of transcription factors modulating neuroplasticity and iii.) an altered expression pattern of eCB-related genes, including enzymes involved in eCB metabolism. Unsupervised and semi-supervised statistical approaches highlighted that hippocampal gene expression patterns possess strong predictive power regarding susceptibility. Taken together, the marked eCB and neuroplasticity changes in susceptible individuals associated with abnormal activity patterns in the fear circuitry possibly contribute to context coding deficits, resulting in generalized fear. HighlightsO_LIWe assessed endocannabinoid and neuroplasticity correlates of PTSD susceptibility C_LIO_LIPosttrauma generalized fear strength separates susceptible and resilient individuals C_LIO_LISusceptible individuals show altered endocannabinoid levels in the fear circuitry C_LIO_LINeuroplasticity and endocannabinoid gene expression patterns predict susceptibility C_LI

neuroscience↗

bioRxiv2023

Improving anxiety research: novel approach to reveal trait anxiety through summary measures of multiple states

The reliability and validity of preclinical anxiety testing is essential for translating animal research into clinical use. However, the commonly used anxiety tests lack inter-test correlations and face challenges with repeatability. While translational animal research should be able to capture stable individual anxiety traits, the current approach employs a single type of test at a single time that only measures transient states of animals, heavily influenced by experimental conditions. Here, we propose a validated, optimized test battery capable of reliably capturing trait anxiety in rats and mice of both sexes. Instead of developing novel tests, we combined widely used tests (elevated plus-maze, open field and light-dark test) to provide instantly applicable adjustments for better predictive validity. We repeated these tests three times to capture behaviour across multiple challenges, which we combined to generate summary measures (SuMs). Our approach resolved between-test correlation issues and provided better predictions for subsequent outcomes under anxiogenic conditions or fear conditioning. SuMs were also able to reveal differences in anxiety in an etiological stress model. Finally, we tested our methods efficacy in discovering anxiety-related molecular pathways through RNA sequencing of the medial prefrontal cortex. Using SuMs, we identified four-times more molecular correlates of trait anxiety as compared to transient anxiety states, pointing out novel functional gene clusters. Furthermore, 16% of these molecular correlates of anxiety were replicated in amygdalar samples, as well. In summary, we provide a novel approach to capture trait anxiety in rodents, offering improved predictions for potential therapeutic targets for personalized medicine.

neuroscience↗

bioRxiv2019

Conserved serotonergic background of experience-dependent challenge-responding in zebrafish (Danio rerio)

Forming effective responses to threatening stimuli requires the adequate and coordinated emergence of stress-related internal states. Such ability depends on early-life experiences and, in connection, the adequate formation of neuromodulatory systems, particularly serotonergic signaling. Here, we assess the serotonergic background of experience-dependent behavioral responsiveness employing a zebrafish (Danio rerio) model. For the first time, we have characterized a period during the behavioral metamorphosis in which zebrafish are highly reactive to their environment. Absence of social stimuli during this phase established by isolated rearing fundamentally altered the behavioral phenotype of post-metamorphic zebrafish in a challenge-specific manner, partially due to a decline in responsiveness and an inability to develop stress-associated arousal state. In line with this, isolation differently affected whole-brain 5-HT signaling in resting and stress-induced conditions, an effect that was present at the level of the dorsal pallium and was negatively associated with responsiveness. Administration of the 5HT1AR partial agonist buspirone prevented the isolation-induced serotonin response to novelty in the forebrain and rescued stress-induced arousal along with challenge-induced behaviors, which altogether indicates a functional connection between these changes. In summary, there is a consistent negative association between behavioral responsiveness and serotonergic signaling in zebrafish, which is well recognizable through the modifying effects of developmental perturbation and pharmacological manipulations as well. Our results imply a conserved serotonergic mechanism that context-dependently modulates environmental reactivity and is highly sensitive to experiences acquired during a specific early-life time-window, a phenomenon that was previously only suggested in mammals.\n\nSignificance statementThe ability to respond to challenges is a fundamental factor in survival. We show that zebrafish that lack appropriate social stimuli in a sensitive developmental period show exacerbated alertness in non-stressful conditions while failing to react adequately to stressors. This shift is reflected inversely by central serotonergic signaling, a system that is implicated in numerous mental disorders in humans. Serotonergic changes in brain regions modulating responsivity and behavioral impairment were both prevented by the pharmacological blockade of serotonergic function. These results imply a serotonergic mechanism in zebrafish that transmits early-life experiences to the later phenotype by shaping stress-dependent behavioral reactivity, a phenomenon that was previously only suggested in mammals. Zebrafish provide new insights into early-life-dependent neuromodulation of behavioral stress-responses.

neuroscience↗

bioRxiv2018

The swimming plus-maze test: a novel high-throughput model for assessment of anxiety-related behaviour in larval zebrafish. (Danio rerio)

Larval zebrafish (Danio rerio) has the potential to supplement rodent models due to the availability of resource efficient methods implying high-throughput screening and high-resolution imaging techniques. Although behavioural models are available in larvae, only a few, insensitive approaches can be employed to assess anxiety. Here we present the swimming plus-maze (SPM) test paradigm to assess anxiety-related states in young zebrafish. The \"+\" shaped apparatus consists of arms of different depth representing differentially aversive context. The paradigm was validated i.) in larval and juvenile zebrafish, ii.) after administration of compounds affecting human anxiety and iii.) in differentially aversive experimental conditions. Furthermore, we compared the SPM with conventional \"anxiety tests\" of larvae such as the open tank and light/dark tank tests to identify their shared characteristics. We clarified that the preference towards deeper water is conserved trough the ontogenesis and can be abolished by anxiolytic or enhanced by anxiogenic agents, respectively. The behavioural read-out is insensitive to the aversiveness of the platform and unrelated to behaviours assessed by conventional tests utilizing larval fish. Taken together, we developed a sensitive high-throughput test measuring anxiety-related responses of larval zebrafish, which likely reflect bottom-dwelling behaviour of adults, potentially supporting larva-based integrative approaches.

animal behavior and cognition↗