Proximate causes and ultimate effects of common antidepressants, fluoxetine and venlafaxine, on fish behavior

Impact of chronic fluoxetine exposure on zebrafish: From fatty acid profile to behavior

The consumption of antidepressants, such as fluoxetine, has increased over the years and, as a result, they are increasingly found in aquatic systems. Given the increasing use of zebrafish as an animal model in toxicological studies, this work proposed to evaluate the effects of chronic exposure, for 21 days, to fluoxetine at environmentally relevant concentrations (1, 10, 100, and 1000 ng/L). The behavioral tests performed did not reveal significant effects of fluoxetine. However, oxidative stress and changes in energy metabolism were detected after exposure to the highest concentrations of fluoxetine tested, namely a decrease in glutathione S-transferase (GST) activity (decrease of ca. 31%), increase in catalase (CAT) activity (increase of ca. 71%), and decrease in lactate dehydrogenase (LDH) activity (decrease of ca. 53%). Analysis of the fatty acid profile (FA) revealed a decrease in the omega-3 FA, docosahexaenoic acid (DHA), C22:6 (decrease in relative abundance between 6% and 8% for both the head and body), an increase in omega-6 FA, linoleic acid (LA), C18:2, (increased relative abundance between 8% and 11% in the head and between 5% and 9% in the body), which may suggest changes in the inflammatory state of these organisms. The integrated analysis adopted proved to be useful in detecting subindividual effects of fluoxetine and modes of action in fish.

Mechanistic Insights into 1,2-bis(2,4,6-tribromophenoxy)ethane-Induced Male Reproductive Toxicity in Zebrafish

The novel brominated flame retardant, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), has increasingly been detected in environmental and biota samples. However, limited information is available regarding its toxicity, especially at environmentally relevant concentrations. In the present study, adult male zebrafish were exposed to varying concentrations of BTBPE (0, 0.01, 0.1, 1, and 10 μg/L) for 28 days. The results demonstrated underperformance in mating behavior and reproductive success of male zebrafish when paired with unexposed females. Additionally, a decline in sperm quality was confirmed in BTBPE-exposed male zebrafish, characterized by decreased total motility, decreased progressive motility, and increased morphological malformations. To elucidate the underlying mechanism, an integrated proteomic and phosphoproteomic analysis was performed, revealing a predominant impact on mitochondrial functions at the protein level and a universal response across different cellular compartments at the phosphorylation level. Ultrastructural damage, increased expression of apoptosis-inducing factor, and disordered respiratory chain confirmed the involvement of mitochondrial impairment in zebrafish testes. These findings not only provide valuable insights for future evaluations of the potential risks posed by BTBPE and similar chemicals but also underscore the need for further research into the impact of mitochondrial dysfunction on reproductive health.

Toward a unified framework for studying behavioural tolerance

Behavioural responses are widely held to allow animals to cope with human-induced environmental changes. Less often appreciated is that the absence of behavioural response can also be advantageous. This is particularly true when animals become tolerant to situations that may be perceived as risky, although the actual risk is nonexistent. We provide a framework to understand the causes and consequences of behavioural tolerance. Tolerance can emerge from genetic, epigenetic, or learning mechanisms, each exerting different degrees of influence on its speed of acquisition, reversibility, specificity, and duration. The ultimate impact on fitness hinges on the interplay between these mechanisms and the nature of the stressor. Mechanistic clarity is therefore essential to better understand and manage human-wildlife interactions in the Anthropocene.

Sub-chronic exposure to paroxetine disrupts ecologically relevant behaviours in fish

The functional conservation of important selective serotonin reuptake inhibitor (SSRI) targets in non-target organisms raises concerns about their potential adverse effects on the ecosystems. Although the environmental levels of SSRIs like paroxetine (PAR) have risen, the knowledge regarding the effects of long-term exposure to PAR is limited. This study investigated the impact of sub-chronic exposure (21 days) to two sub-lethal concentrations of PAR (40 and 400 μg/L) on the behaviour of adult zebrafish in different scenarios: basal activity (under dark and light conditions), stress response (evoked by sudden light transitions) and stress response recovery. A new framework was employed for the integrative study of fish's swimming performance based on their innate ability to respond to light shifts. Several swimming-associated parameters (e.g., total swimming distance, time of inactivity, swimming angles) and thigmotaxis were monitored for an integrated analysis in each scenario. Data revealed reduced swimming activity, impaired behavioural response to stress and alterations in stress recovery of PAR-exposed fish. An anxiolytic effect was particularly noticeable in fish basal swimming activity in the dark at 400 μg/L and in the behavioural response to stress (from dark to light) and stress recovery (from light to dark) for organisms exposed to 40 μg/L. The detected PAR-induced behavioural modifications suggest a disruption of brain glucocorticoid signalling that may have implications at the individual level (e.g., changing behavioural responses to predators), with potential repercussions on the population and community levels. Therefore, the applied protocol proved sensitive in detecting behavioural changes induced by PAR.

Addressing the challenges of combined sewer overflows

Europe's ageing wastewater system often combines domestic sewage with surface runoff and industrial wastewaters. To reduce the associated risk of overloading wastewater treatment works during storms, and to prevent wastewater backing-up into properties, Combined Sewer Overflows (CSOs) are designed into wastewater networks to release excess discharge into rivers or coastal waters without treatment. In view of growing regulatory scrutiny and increasing public concern about their excessive discharge frequencies and potential impacts on environments and people, there is a need to better understand these impacts to allow prioritisation of cost-effective solutions.We review: i) the chemical, physical and biological composition of CSOs discharges; ii) spatio-temporal variations in the quantity, quality and load of overflows spilling into receiving waters; iii) the potential impacts on people, ecosystems and economies. Despite investigations illustrating the discharge frequency of CSOs, data on spill composition and loading of pollutants are too few to reach representative conclusions, particularly for emerging contaminants. Studies appraising impacts are also scarce, especially in contexts where there are multiple stressors affecting receiving waters. Given the costs of addressing CSOs problems, but also the likely long-term gains (e.g. economic stimulation as well as improvements to biodiversity, ecosystem services, public health and wellbeing), we highlight here the need to bolster these evidence gaps. We also advocate no-regrets options to alleviate CSO problems taking into consideration economic costs, carbon neutrality, ecosystem benefit and community well-being. Besides pragmatic, risk-based investment by utilities and local authorities to modernise wastewater systems, these include i) more systemic thinking, linking policy makers, consumers, utilities and regulators, to shift from local CSO issues to integrated catchment solutions with the aim of reducing contributions to wastewater from surface drainage and water consumption; ii) broader societal responsibilities for CSOs, for example through improved regulation, behavioural changes in water consumption and disposal of waste into wastewater networks, and iii) greater cost-sharing of wastewater use.

Maternal exposure to bisphenol S reduces anxiety and impairs collective antipredator behavior of male zebrafish (Danio rerio) offspring through dysregulation of their serotonergic system

Bisphenol S (BPS) is a common endocrine-disrupting chemical globally used in several consumer and industrial products. Although previous studies suggested that BPS induces multiple effects in exposed organisms, very little is known about its intergenerational effect on offspring behavior and/or the potential underlying mechanisms. To this end, adult female zebrafish Danio rerio were exposed to BPS (0, 10, 30 µg/L) and 1 µg/L of 17-β-estradiol (E2) as a positive control for 60 days. Afterwards, female fish were bred with untreated males, and their offspring were raised to 6 months old in control water. Maternal exposure to BPS decreased male offspring anxiety and antipredator behaviors while boldness remained unaffected. Specifically, maternal exposure to 10 and 30 µg/L BPS and 1 µg/L E2 were found to impact male offspring anxiety levels as they decreased the total time that individuals spent in the dark zone in the light/dark box test and increased the total track length in the center of the open field test. In addition, maternal exposure to all concentrations of BPS and E2 disrupted antipredator responses of male offspring by decreasing shoal cohesion in the presence of chemical alarm cues derived from conspecifics, which communicated high risk. To elucidate the possible molecular mechanism underlying these neuro-behavioral effects of BPS, we assessed the serotonergic system via changes in mRNA expression of serotonin receptors, including the 5-HT1A, 5-HT1B, and 5-HT1D subtypes, the serotonin transporter and monoamine oxidase (MAO). The impaired anxiety and antipredator responses were associated with reduced levels of 5-HT1A subtype and MAO mRNA expression within the brain of adult male offspring. Collectively, the results of this study demonstrate that maternal exposure to environmental concentrations of BPS can interfere with the serotonergic signaling pathway in the developing brain, subsequently leading to the onset of a suite of behavioral deficits in adult offspring.

Effects of antidepressant exposure on aquatic communities assessed by a combination of morphological identification, functional measurements, environmental DNA metabarcoding and bioassays

The antidepressant fluoxetine is frequently detected in aquatic ecosystems, yet the effects on aquatic communities and ecosystems are still largely unknown. Therefore the aim of this study is to assess the effects of the long-term application of fluoxetine on key components of aquatic ecosystems including macroinvertebrate-, zooplankton-, phytoplankton- and microbial communities and organic matter decomposition by using traditional and non-traditional assessment methods. For this, we exposed 18 outdoor mesocosms (water volume of 1530 L and 10 cm of sediment) to five different concentrations of fluoxetine (0.2, 2, 20 and 200 μg/L) for eight weeks, followed by an eight-week recovery period. We quantified population and community effects by morphological identification, environmental DNA metabarcoding, in vitro and in vivo bioassays and measured organic matter decomposition as a measure of ecosystem functioning. We found effects of fluoxetine on bacterial, algal, zooplankton and macroinvertebrate communities and decomposition rates, mainly for the highest (200 μg/L) treatment. Treatment-related decreases in abundances were found for damselfly larvae (NOEC of 0.2 μg/L) and Sphaeriidae bivalves (NOEC of 20 μg/L), whereas Asellus aquaticus increased in abundance (NOEC <0.2 μg/L). Fluoxetine decreased photosynthetic activity and primary production of the suspended algae community. eDNA assessment provided additional insights by revealing that the algae belonging to the class Cryptophyceae and certain cyanobacteria taxa were the most negatively responding taxa to fluoxetine. Our results, together with results of others, suggest that fluoxetine can alter community structure and ecosystem functioning and that some impacts of fluoxetine on certain taxa can already be observed at environmentally realistic concentrations.

Understanding the differential impacts of two antidepressants on locomotion of freshwater snails (Lymnaea stagnalis)

There is growing evidence of negative impacts of antidepressants on behavior of aquatic non-target organisms. Accurate environmental risk assessment requires an understanding of whether antidepressants with similar modes of action have consistent negative impacts. Here, we tested the effect of acute exposure to two antidepressants, fluoxetine and venlafaxine (0-50 µg/L), on the behavior of non-target organism, i.e., freshwater pond snail, Lymnaea stagnalis. As compounds interact with chemical cues in the aquatic ecosystems, we also tested whether the effects altered in the presence of bile extract containing 5α-cyprinol sulfate (5α-CPS), a characterized kairomone of a natural predator, common carp (Cyprinus carpio). Behavior was studied using automated tracking and analysis of various locomotion parameters of L. stagnalis. Our results suggest that there are differences in the effects on locomotion upon exposure to venlafaxine and fluoxetine. We found strong evidence for a non-monotonic dose response on venlafaxine exposure, whereas fluoxetine only showed weak evidence of altered locomotion for a specific concentration. Combined exposure to compounds and 5α-CPS reduced the intensity of effects observed in the absence of 5α-CPS, possibly due to reduced bioavailability of the compounds. The results highlight the need for acknowledging different mechanisms of action among antidepressants while investigating their environmental risks. In addition, our results underline the importance of reporting non-significant effects and acknowledging individual variation in behavior for environmental risk assessment.

Integrated Studies on Male Reproductive Toxicity of Bis(2-ethylhexyl)-tetrabromophthalate: in Silico, in Vitro, ex Vivo, and in Vivo

Bis(2-ethylhexyl)tetrabromophthalate (TBPH) has been widely detected in the environment and organisms; thus, its toxic effects on male reproduction were systematically studied. First, we found that TBPH can stably bind to the androgen receptor (AR) based on in silico molecular docking results and observed an antagonistic activity, but not agonistic activity, on the AR signaling pathway using a constructed AR-GRIP1 yeast assay. Subsequently, we validated the adverse effects on male germ cells by observing inhibited androgen production and proliferation in Leydig cells upon in vitro exposure and affected general motility and motive tracks of zebrafish sperm upon ex vivo exposure. Finally, the in vivo reproductive toxicity was demonstrated in male zebrafish by reduced mating behavior in F0 generation when paired with unexposed females and abnormal development of their offspring. In addition, reduced sperm motility and impaired germ cells in male zebrafish were also observed, which may be related to the disturbed homeostasis of sex hormones. Notably, the specifically suppressed AR in the brain provides further evidence for the antagonistic effects as above-mentioned. These results confirmed that TBPH affected male reproduction through a classical nuclear receptor-mediated pathway, which would be helpful for assessing the ecological and health risks of TBPH.

Investigating wastewater treatment plant effluent and pharmaceutical exposure on innate cytokine expression of darters (Etheostoma spp.) in the Grand River watershed

Fish live in continuous contact with various stressors and antigenic material present within their environments. The impact of stressors associated with wastewater-exposed environments on fish has become of particular interest in toxicology studies. The objectives of this study were to examine potential effects of wastewater treatment plant (WWTP) effluent-associated stressors on innate cytokine expression within the gills of darter species (Etheostoma spp.), using both field and laboratory approaches. Male and female darters (rainbow, greenside, fantail, and johnny darters) were collected upstream and downstream of the Waterloo WWTP in the Grand River, Ontario. Gill samples were collected from fish in the field and from a second subset of fish brought back to the laboratory. Laboratory fish were acutely exposed (96-h) to an environmentally relevant concentration of venlafaxine (1.0 μg/L), a commonly prescribed antidepressant. To assess the impacts of these stressors on the innate immunity of darters, the expression of key innate cytokines was examined. Minor significant effects on innate cytokine expression were observed between upstream and downstream fish. Moderate effects on cytokine expression were observed in venlafaxine-exposed fish compared to their control counterparts however, changes were not indicative of a biologically significant immune response occurring due to the exposure. Although the results of this study did not display extensive impacts of effluent and pharmaceutical exposure on innate cytokine expression within the gills, they provide a novel avenue of study, illustrating the importance of examining potential impacts that effluent-associated stressors can have on fundamental immune responses of native fish species.

Are early and young life stages of fish affected by paroxetine? A case study with Danio rerio

Paroxetine (PAR) is a selective serotonin reuptake inhibitor (SSRI) antidepressant increasingly detected in surface waters worldwide. Its environmental presence raises concerns about the potential detrimental effects on non-target organisms. Thus, this study aimed to increase knowledge on PAR's potential environmental impacts, assessing the effects of commercial formulation (PAR-c) and active ingredient (PAR-a) on fish. Therefore, the short-term exposure effects of PAR-c and PAR-a were assessed on zebrafish (Danio rerio) embryos/larvae to determine the most toxic formulation [through median lethal (LC50) and effective concentrations (EC50)]. PAR-c and PAR-a induced morphological abnormalities (scoliosis) in a dose-dependent manner from 96 hours post-fertilization onwards, suggesting the involvement of a fully functional biotransformation system. As PAR-c exhibited higher toxicity, it was selected to be tested in the subsequent stage (juvenile stage), which was more sensitive (lower LC50). PAR-c significantly decreased fish swimming activity and disrupted fish stress response. Overall, the results highlight the ability of PAR-c to adversely affect fish swimming performance, an effect that persisted even after exposure ceases (21-day depuration), suggesting that PAR-c may impair individual fitness.

The occurrence of typical psychotropic drugs in the aquatic environments and their potential toxicity to aquatic organisms - A review

Psychotropic drugs (PDs) and their bioactive metabolites often persist in aquatic environments due to their typical physical properties, which made them resistant to removal by traditional wastewater treatment plants (WWTPs). Consequently, such drugs and/or their metabolites are frequently detected in both aquatic environments and organisms. Even at low concentrations, these drugs can exhibit toxic effects on non-target organisms including bony fish (zebrafish (Danio rerio) and fathead minnows) and bivalves (freshwater mussels and clams). This narrative review focuses on the quintessential representatives of three different categories of PDs-antiepileptics, antidepressants, and antipsychotics. The data regarding their concentrations occurring in the environment, patterns of distribution, the degree of enrichment in various tissues of aquatic organisms, and the toxicological effects on them are summarized. The toxicological assessments of these drugs included the evaluation of their effects on the reproductive, embryonic development, oxidative stress-related, neurobehavioral, and genetic functions in various experimental models. However, the mechanisms underlying the toxicity of PDs to aquatic organisms and their potential health risks to humans remain unclear. Most studies have focused on the effects caused by acute short-term exposure due to limitations in the experimental conditions, thus making it necessary to investigate the chronic toxic effects at concentrations that are in coherence with those occurring in the environment. Additionally, this review aims to raise awareness and stimulate further research efforts by highlighting the gaps in the understanding of the mechanisms behind PD-induced toxicity and potential health risks. Ultimately, the study underscores the importance of developing advanced remediation methods for the removal of PDs in WWTPs and encourages a broader discussion on mitigating their environmental impacts.

Aggression repeatability in stressed fish in response to an environmental concentration of sertraline and lunar cycle as evidenced by brain metabolomics

Sertraline is an environmental pollutant which received magnified scientific attention due to its global presence in waters. Adverse effects on feeding, reproduction and other traits were observed mostly in unstressed aquatic organisms. Chronic stress, however, induces significant physiological changes, and the effects of sertraline in stressed fish may differ from those observed in non-stressed individuals. The current laboratory study addresses this gap by repeatedly monitoring the individual aggression of chronically stressed juvenile chub (Squalius cephalus L.) using the non-reversing mirror test at an environmental sertraline concentration of 0.022 g/L every three to four days for a period of 39 days. Specifically, it was hypothesized that the level and repeatability of aggressiveness would be (i) correlated with the concentration of sertraline/norsertraline in the fish brain; (ii) linked to the individual brain metabolomic profile described by LC-HRMS analyses; (iii) related to the lunar cycle. Sertraline led to an increase in fish aggression and more repeatable/consistent behaviour compared to control fish. While the level of sertraline in the brain did not correlate with aggressiveness, aggressive responses increased with higher norsertraline concentration. The observed aggressive behaviour also varied depending on the individual metabolomic profile of the brain. The behavioural outcome and metabolic change in fish brain may indicate that sertraline has demonstrated neuroprotective effects by reducing cortisol release. It is possible that fish exposed to sertraline could suffer a blunted stress response under the chronic stressors in the wild. Aggressiveness of both treatments evolved in time, revealing a sinusoid-like pattern corresponding to a lunar cycle with a peak of the aggressiveness during the new moon. There is a need for future studies to focus on this relationship to reveal its details and general validity. Our results emphasize that long-term behavioural variability should generally be taken into account in laboratory behavioural studies.

35 years of light treatment for mental disorders in the Netherlands

BACKGROUND

Light therapy (LT) for Seasonal Affective Disorders (SAD) has been a well-known and effective treatment for 40 years. The psychiatric university clinic of Groningen, the Netherlands was an early adopter and started research and treatment of SAD in 1987. Research projects on mechanisms, the role of the circadian system, treatment optimization, and investigating new areas for the effects of light treatment have been carried out ever since, leading to a widespread interest across the country.

OBJECTIVE

To provide an overview and description of the historical development of LT for mental disorders in the Netherlands.

METHODS

A non-systematic, review of research on light treatment for mental problems in the Netherlands, published since 1987 was conducted.

RESULTS

The fields of LT and chronotherapy are strongly based in the scientific interests of both chrono-biologists and therapists in the Netherlands. LT has shown effectiveness in treating mood disorders. Likewise, results for other mental disorders have shown some promise, but so far, the outcomes are not always unequivocal and have not always been based on robust data. Ongoing research is discussed.

CONCLUSIONS

LT, and in addition exposure to the right light at the right time is an important issue in mental health. Over the past 3 decades research on light and LT in the Netherlands has become well established and is still growing.

Behavioural responses of fishes to anthropogenic disturbances: Adaptive value and ecological consequences

Aquatic ecosystems are changing at an accelerating rate because of human activities. The changes alter the abundance and distribution of fishes, with potential consequences for ecosystem structure and function. Behavioural responses often underlie these changes in population dynamics, such as altered habitat choice or foraging activity. Here, we present a framework for understanding how and why behaviour is affected by human activities and how the behavioural responses in turn influence higher ecological levels. We further review the literature to assess the present state of the field and identify gaps in our knowledge. We begin with discussing the factors that determine how an individual responds to a change in the environment and whether the response is adaptive or not. In particular, we explain the importance of the evolutionary history of the species. We then search the literature to assess our current knowledge of the impact of human disturbances on the behaviour of fishes and the consequences for ecosystems. The search reveals that much attention has been directed to the impact of human activities on the behaviour of fishes, but that worryingly little is known about the consequences of these responses for populations, communities and ecosystems. Yet, behavioural responses can have profound ecological consequences given that behaviour underly many, if not most, species interactions. Thus, more attention should be paid to the mechanisms and pathways through which behavioural responses influence higher ecological levels. Such information is needed if we are to determine the ultimate effects of human activities on biodiversity and the function and stability of aquatic ecosystems.

Identifying knowledge gaps in understanding the effects of selective serotonin reuptake inhibitors (SSRIs) on fish behaviour

Selective serotonin reuptake inhibitors (SSRIs) are a class of antidepressants increasingly prescribed to treat patients with clinical depression. As a result of the significant negative impact of the COVID-19 pandemic on the population's mental health, its consumption is expected to increase even more. The high consumption of these substances leads to their environmental dissemination, with evidence of their ability to compromise molecular, biochemical, physiological, and behavioural endpoints in non-target organisms. This study aimed to provide a critical review of the current knowledge regarding the effects of SSRI antidepressants on fish ecologically relevant behaviours and personality-dependent traits. A literature review shows limited data concerning the impact of fish personality on their responses to contaminants and how such responses could be influenced by SSRIs. This lack of information may be attributable to a lack of widely adopted standardized protocols for evaluating behavioural responses in fish. The existing studies examining the effects of SSRIs across various biological levels overlook the intra-specific variations in behaviour and physiology associated with different personality patterns or coping styles. Consequently, some effects may remain undetected, such as variations in coping styles and the capacity to handle environmental stressors. This oversight could potentially result in long-term effects with ecological implications. Data support the need for more studies to understand the impact of SSRIs on personality-dependent traits and how they may impair fitness-related behaviours. Given the considerable cross-species similarity in the personality dimensions, the collected data may allow new insights into the correlation between personality and animal fitness.

Cost-Effective Pharmaceutical Implants in Fish: Validating the Performance of Slow-Release Implants for the Antidepressant Fluoxetine

Internal, slow-release implants can be an effective way to manipulate animal physiology or deliver a chemical exposure over long periods of time without the need for an exogenous exposure route. Slow-release implants involve dissolving a compound in a lipid-based carrier, which is inserted into the body of an organism. However, the release kinetics of the compound from the implant to body tissues also requires careful validation. We tested and validated a slow-release implant methodology for exposing fish to a pharmaceutical pollutant, fluoxetine. We tested two lipid-based carriers (coconut oil or vegetable shortening) in the common roach (Rutilus rutilus). The implants contained either a high (50 μg/g), low (25 μg/g), or control (0 μg/g) concentration of fluoxetine, and we measured tissue uptake in the brain, muscle, and plasma of implanted fish over 25 days. The two carriers released fluoxetine differently over time: coconut oil released fluoxetine in an accelerating manner (tissue uptake displayed a positive quadratic curvature), whereas vegetable shortening released fluoxetine in a decelerating manner (a negative quadratic curvature). For both carrier types, fluoxetine was measured at the highest concentration in the brain, followed by muscle and plasma. By comparing the implant exposures with waterborne exposures in the published literature, we showed that the implants delivered an internal exposure that would be similar if fish were exposed in surface waters containing effluents. Overall, we showed that slow-release internal implants are an effective method for delivering chronic exposures of fluoxetine over at least 1-month time scales. Internal exposures can be an especially powerful experimental tool when coupled with field-based study designs to assess the impacts of pharmaceutical pollutants in complex natural environments. Environ Toxicol Chem 2023;42:1326-1336. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Sub-chronic administration of fluoxetine does not alter prey-capture or predator avoidance behaviors in adult South African clawed frogs (Xenopus laevis)

Animals will halt foraging efforts and engage defensive behaviors in response to predator cues. Some researchers have proposed that the switch from appetitive to avoidance behavior resembles anxiety, but most work on this has been performed in a limited number of animal models, primarily zebrafish and rodents. We used adult South African clawed frogs (Xenopus laevis) to determine if the canonical anxiolytic fluoxetine alters predator-induced changes in appetitive and avoidance behavior in a laboratory-based trade-off task that mimics foraging/predator avoidance tradeoffs in the wild. We hypothesized that sub-chronic fluoxetine treatment (20 d) would not affect baseline behavior but would reverse predator-induced changes in food intake, appetitive and avoidance behavior, and the abundance of anxiety related gene transcripts in the optic tectum, a brain area central to ecological decision making in frogs. We found that fluoxetine significantly reduced baseline locomotion compared to vehicle-treated animals. Fluoxetine had no effect on appetitive and avoidance behaviors that were sensitive to predator cues in this assay and did not alter any of the anxiety-related transcripts in the tectum. We conclude that while peripheral sub-chronic administration of fluoxetine significantly reduces locomotion, it does not modify predator-induced changes in approach and avoidance behaviors in this assay. Our findings are not consistent with visual predator cues causing state anxiety in adult frogs.

Effects of common antiepileptic drugs on teleost fishes

Antiepileptic drugs (AEDs) are globally prescribed to treat epilepsy and many other psychiatric disorders in humans. Their high consumption, low metabolic rate in the human body and low efficiency of wastewater treatment plants (WWTPs) in eliminating these chemicals results in the frequent occurrence of these pharmaceutical drugs in aquatic systems. Therefore, aquatic organisms, including ecologically and economically important teleost fishes, may be inadvertently exposed to these chemicals. Due to their physiological similarity with humans, fishes may be particularly vulnerable to AEDs. Almost all AED drugs are detectable in natural aquatic ecosystems, but diazepam (DZP) and carbamazepine (CBZ) are among the most widely detected AEDs to date. Recent studies suggest that these drugs have a substantial capacity to induce neurotoxicity and behavioral abnormality in fishes. Here we review the current state of knowledge regarding the potential mode of action of DZP and CBZ as well as that of some other AEDs on teleosts and put observable behavioral effects into a mechanistic context. We find that following their intended mode of action in humans, AEDs also disrupt the GABAergic, glutamatergic and serotonergic systems as well as parasympathetic neurotransmitters in fishes. Moreover, AEDs have non-specific modes of action in teleosts ranging from estrogenic activity to oxidative stress. These physiological changes are often accompanied by dose-dependent disruptions of anxiety, locomotor activity, social behaviors, food uptake, and learning and memory, but DZP and CBZ consistently induced anxiolytic effects. Thereby, AED exposure severely compromises individual fitness across teleost fish species, which may lead to population and ecosystem impairment. We also showcase promising avenues for future research by highlighting where we lack data when it comes to effects of certain AEDs, AED concentrations and behavioral endpoints.

On the use of antibiotics in plasticity research: Gastropod shells unveil a tale of caution

Through phenotypic plasticity, individual genotypes can produce multiple phenotypes dependent on the environment. In the modern world, anthropogenic influences such as man-made pharmaceuticals are increasingly prevalent. They might alter observable patterns of plasticity and distort our conclusions regarding the adaptive potential of natural populations. Antibiotics are nowadays nearly ubiquitous in aquatic environments and prophylactic antibiotic use is also becoming more common to optimize animal survival and reproductive output in artificial settings. In the well-studied plasticity model system Physella acuta, prophylactic erythromycin treatment acts against gram-positive bacteria and thereby reduces mortality. Here, we study its consequences for inducible defence formation in the same species. In a 2 × 2 split-clutch design, we reared 635 P. acuta in either the presence or absence of this antibiotic, followed by 28-day exposure to either high or low predation risk as perceived through conspecific alarm cues. Under antibiotic treatment, risk-induced increases in shell thickness, a well-known plastic response in this model system, were larger and consistently detectable. Antibiotic treatment reduced shell thickness in low-risk individuals, suggesting that in controls, undiscovered pathogen infection increased shell thickness under low risk. Family variation in risk-induced plasticity was low, but the large variation in responses to antibiotics among families suggests different pathogen susceptibility between genotypes. Lastly, individuals that developed thicker shells had reduced total mass, which highlights resource trade-offs. Antibiotics thus have the potential to uncover a larger extent of plasticity, but might counterintuitively distort plasticity estimates for natural populations where pathogens are a part of natural ecology.

Linking chemical exposure and fish metabolome: Discovering new biomarkers of environmental exposure of Argyrosomus regius to the antidepressant venlafaxine

In this study, a non-target metabolomic approach was used to investigate changes in the metabolome of juvenile meagre (Argyrosomus regius) exposed to venlafaxine (20 µg/L). A total of 24, 22 and 8 endogenous metabolites tentatively identified in liver, brain and plasma, respectively, were significantly changed in venlafaxine exposed meagre, showing tissue-dependent variations in the metabolic profile. The amino acids tryptophan, tyrosine and phenylalanine, which are related to the synthesis, availability, and expression of neurotransmitters (e.g., serotonin, dopamine, epinephrine), showed to be dysregulated by venlafaxine exposure. A high impact was observed in fish brain metabolome that showed a trend of up-regulation for most of the tentatively identified metabolites. In conclusion, the identification of possible biomarkers of exposure in fish metabolome to environmental stressors such as venlafaxine is crucial to assess early signal changes at molecular level, enabling the prevention of deleterious effects at the organism and population levels.

Anti-Depressant Fluoxetine Hampers Olfaction of Goldfish by Interfering with the Initiation, Transmission, and Processing of Olfactory Signals

The ubiquitous presence of fluoxetine (FLX) in aquatic environments poses great threat to fish species. However, little is known about its deleterious impacts on fish olfaction. In this study, the olfactory toxicity of FLX at environmentally realistic levels was assessed by monitoring the behavioral and electroolfactogram (EOG) responses to olfactory stimuli with goldfish (Carassius auratus), and the toxification mechanisms underlying the observed olfaction dysfunction were also investigated. Our results showed that the behavioral and EOG responses of goldfish to olfactory stimuli were significantly weakened by FLX, indicating an evident toxicity of FLX to olfaction. Moreover, FLX exposure led to significant alterations in olfactory initiation-related genes, suppression of ion pumps (Ca²⁺-ATPase and Na⁺/K⁺-ATPase), tissue lesions, and fewer olfactory sensory neurons in olfactory epithelium. In addition to altering the expression of olfactory transmission-related genes, comparative metabolomic analysis found that olfaction-related neurotransmitters (i.e., l-glutamate and acetylcholine) and the olfactory transduction pathway were significantly affected by FLX. Furthermore, evident tissue lesions, aggravated lipid peroxidation and apoptosis, and less neuropeptide Y were observed in the olfactory bulbs of FLX-exposed goldfish. Our findings indicate that FLX may hamper goldfish olfaction by interfering with the initiation, transmission, and processing of olfactory signals.

RNA-seq reveals potential gene biomarkers in fathead minnows (Pimephales promelas) for exposure to treated wastewater effluent

Discharged wastewater treatment plant (WWTP) effluent greatly contributes to the generation of complex mixtures of contaminants of emerging concern (CECs) in aquatic environments which often contain neuropharmaceuticals and other emerging contaminants that may impact neurological function. However, there is a paucity of knowledge on the neurological impacts of these exposures to aquatic organisms. In this study, caged fathead minnows (Pimephales promelas) were exposed in situ in a temperate-region effluent-dominated stream (i.e., Muddy Creek) in Coralville, Iowa, USA upstream and downstream of a WWTP effluent outfall. The pharmaceutical composition of Muddy Creek was recently characterized by our team and revealed many compounds there were at a low microgram to high nanogram per liter concentration. Total RNA sequencing analysis on brain tissues revealed 280 gene isoforms that were significantly differentially expressed in male fish and 293 gene isoforms in female fish between the upstream and downstream site. Only 66 (13%) of such gene isoforms overlapped amongst male and female fish, demonstrating sex-dependent impacts on neuronal gene expression. By using a systems biology approach paired with functional enrichment analyses, we identified several potential novel gene biomarkers for treated effluent exposure that could be used to expand monitoring of environmental effects with respect to complex CEC mixtures. Lastly, when comparing the results of this study to those that relied on a single-compound approach, there was relatively little overlap in terms of gene-specific effects. This discovery brings into question the application of single-compound exposures in accurately characterizing environmental risks of complex mixtures and for gene biomarker identification.

Low doses and lifecycle exposure of waterborne antidepressants in zebrafish model: A survey on sperm traits, reproductive behaviours, and transcriptome responses

Venlafaxine and citalopram have been commonly found in surface water and may disrupt fish reproduction, yet the long-term impact and the underlying mechanism are largely unknown. Here, zebrafish were exposed to 0.1-100 μg/L venlafaxine and citalopram for their entire life cycle from embryo to adult, respectively. After exposure for 180 days, the lowest observable effective concentration (LOEC) of venlafaxine and citalopram to significantly reduce the mean number of egg production in adults were 10 and 1 μg/L, respectively, whereas the fertilization rate displayed no significant changes. Further, we investigated the impacts of venlafaxine and citalopram in a reproductive context, including sperm quality and reproductive behaviour. In contrast, venlafaxine and citalopram exposure did not affect sperm quality but caused a reduction of reproductive behaviour (e.g., mating duration and mating interval) of adults exposed to 1-10 μg/L of the antidepressant. Transcriptomic profiling of the whole ovary revealed that lifecycle venlafaxine and citalopram exposure significantly affected the Na⁺/Cl^- dependent neurotransmitter transporters signaling. Moreover, immune system-mediated ovarian regeneration and creatine metabolism regulated energy metabolism were proposed as the novel mechanism in the observed effects. Taken together, our results highlight the risk of lifecycle venlafaxine and citalopram exposure to fish reproduction and provide novel perspectives for unveiling the mechanism of female reproductive dysfunction.

Differential Molecular Responses of Zebrafish Larvae to Fluoxetine and Norfluoxetine

The occurrence of psychopharmaceuticals in aquatic ecosystems is a growing problem. Fluoxetine (FL) and its metabolite norfluoxetine (NF) are selective serotonin reuptake inhibitors. Although they may be potentially harmful to non-target species, available knowledge on the effects of NF is sparse, relative to FL. This study aimed at contributing to the body of knowledge about the modes-of-action (MoA) of these compounds and their underlying mechanisms eliciting hazardous effects during the early development of the teleost model zebrafish (Danio rerio). One hour post-fertilisation (hpf), embryos were exposed up to 80 hpf to these compounds at levels found in surface waters and higher (FL, 0.0015 and 0.05 µM; NF, 0.00006 and 0.0014 µM). Developmental anomalies were observed at 8, 32 and 80 hpf. Larvae were collected at 80 hpf to assess the expression of 34 genes related to FL and NF MoA and metabolism, using qPCR (quantitative reverse transcription PCR). Results showed that both compounds elicited an increased frequency of embryos exhibiting abnormal pigmentation, relative to controls. Gene expression alterations were more pronounced in FL- than in NF-exposed larvae. Cluster Analysis revealed two groups of genes discriminating between the drugs. for their marked opposing responses. Globally, downregulation of gene expression was typical of FL, whilst upregulation or no alteration was found for NF. These clusters identified were linked to the adrenergic pathway and to the retinoid and peroxisome proliferator-activated nuclear receptors. Overall, our data contradict the prevailing notion that NF is more toxic than FL and unveiled the expression levels of genes drd2b, 5-ht2c and abcc2 as possible markers of exposure to FL.