Effects of Alcohol on Inhibitory Avoidance Learning in Zebrafish (Danio rerio)

Repeated exposure to ethanol alters memory acquisition and neurotransmission parameters in zebrafish brain

Alcohol is widely consumed worldwide and its abuse can cause cognitive dysfunction, affecting memory and learning due to several neurophysiological changes. An imbalance in several neurotransmitters, including the cholinergic and glutamatergic systems, have been implicated in these effects. Zebrafish are sensitive to alcohol, respond to reward stimuli, and tolerate and exhibit withdrawal behaviors. Therefore, we investigated the effects of repetitive exposure to ethanol (REE) and the NMDA receptor antagonist dizocilpine (MK-801) on memory acquisition and glutamatergic and cholinergic neurotransmission. Memory was assessed using the inhibitory avoidance and object recognition tasks. Brain glutamate levels and the activity of Na+-dependent transporters were evaluated as indexes of glutamatergic activity, while acetylcholinesterase (AChE) and choline acetyltransferase (ChAT), enzyme activity were evaluated as indexes of cholinergic activity. Behavioral assessments showed that REE impaired aversive and spatial memory, an effect that MK-801 mimicked. Glutamate levels, but not transporter activity, were significantly lower in the REE group; similarly, REE increased the activity of AChE, but not ChAT, activity. These findings suggest that intermittent exposure to ethanol leads to impairments in zebrafish memory consolidation, and that these effects could be associated with alterations in parameters related to neurotransmission systems mediated by glutamate and acetylcholine. These results provide a better understanding of the neurophysiological and behavioral changes caused by repetitive alcohol use.

Duration of aversive memory in zebrafish after a single shock

Studies on memory consolidation and reconsolidation, memory loss, and the associated biochemical mechanisms have garnered interest in the past decades due to knowledge of memory performance-affecting factors such as stress, emotions, sleep, age, several neurological diseases, drugs, and chemical pollutants. Memory research has been using animal models, with increased interest in the zebrafish model. This freshwater fish species shows a wide range of behaviors relevant to memory research such as social behavior, aggression, and predator avoidance; however, few studies have investigated the duration of long-term memory. Hence, we designed an experiment to test memory duration by exposing zebrafish to avoidance conditioning using electroshock as the aversive stimulus. Zebrafish were trained to avoid the black side of a black-and-white tank and subsequently tested for aversive memory at 24 h, 48 h, 72 h, 96 h, 168 h, and 240 h. At the 72 h-interval, another zebrafish group was trained and exposed to MK-801(NMDAr antagonist) and then tested. The fish retained memories of the task and avoided the black side of the tank for up to 7 days. At 10 days post-training, the animals could no longer retrieve the aversive memory. Zebrafish treated with MK-801 did not retrieve memory. Knowledge of memory and of long-term memory duration is crucial for optimizing the zebrafish model for use in research investigating cognitive impairments such as memory loss and its ramifications. Additionally, identifying a long-term aversive memory lasting up to 7 days in zebrafish enables further research into the neuronal changes underlying this persistence. Such in-depth investigation could bring valuable insights into memory mechanisms and facilitate targeted interventions for memory-related conditions.

Embryonic alcohol exposure alters cholinergic neurotransmission and memory in adult zebrafish

Alcohol is the most consumed addictive substance worldwide that elicits multiple health problems. Consumption of alcoholic beverages by pregnant women is of great concern because pre-natal exposure can trigger fetal alcohol spectrum disorder (FASD). This disorder can significantly change the embryo's normal development, mainly by affecting the central nervous system (CNS), leading to neurobehavioral consequences that persist until adulthood. Among the harmful effects of FASD, the most reported consequences are cognitive and behavioral impairments. Alcohol interferes with multiple pathways in the brain, affecting memory by impairing neurotransmitter systems, increasing the rate of oxidative stress, or even activating neuroinflammation. Here, we aimed to evaluate the deleterious effects of alcohol on the cholinergic signaling and memory in a FASD zebrafish model, using inhibitory avoidance and novel object recognition tests. Four months after the embryonic exposure to ethanol, the behavioral tests indicated that ethanol impairs memory. While both ethanol concentrations tested (0.5 % and 1 %) disrupted memory acquisition in the inhibitory avoidance test, 1 % ethanol impaired memory in the object recognition test. Regarding the cholinergic system, 0.5 % ethanol decreased ChAT and AChE activities, but the relative gene expression did not change. Overall, we demonstrated that FASD model in zebrafish impairs memory in adult individuals, corroborating the memory impairment associated with embryonic exposure to ethanol. In addition, the cholinergic system was also affected, possibly showing a relation with the cognitive impairment observed.

Therapeutic intervention of vitamin B12 in mitigating chronic alcoholism induced alterations in adult zebrafish (Danio rerio): a holistic in vivo approach

BACKGROUND

Chronic alcoholism refers to the unpleasant symptoms directly resulting from excessive drinking. Increased alcohol metabolites and an unbalanced oxidative state are likely to blame for the reported effects under these circumstances. According to preclinical and clinical research, vitamin B12 can act on several organ systems with demonstrated neuroprotective, antioxidant, and glutamate modulating properties.

OBJECTIVE

This research sought to examine the ameliorative effects of vitamin B12 (VtB12) in persistent alcohol (AlOH) exposed adult zebrafish with the help of following parameters like the anxiety related behavior test, Oxidative stress, and antioxidant assays, histological and immunofluorescence analysis.

METHODS

Zebrafish pretreated with 0.40% AlOH (v/v) for 120 min (+AlOH) or not (-AlOH), were exposed for 6 h to home tank water (-VtB12) or to 59 µg-VtB12/kg-fish food (+VtB12) to analyze anxiety behavior in the geotaxis (novel tank) test as well as the oxidative brain damage in the adult zebrafish.

RESULTS

Adult zebrafish exposed to chronic AlOH showed a decrease in the distance travelled, average and mobility speed, and increased the average frozen time, the explored area, and total no. of the site explored in the trapezoid tank. AlOH exposure also resulted in oxidative damage, enhanced lipid peroxidation, advanced oxidative protein products, decreased enzymatic and non-enzymatic antioxidant activities, and enhanced reactive oxygen species generation. Additionally, VtB12 supplementation improved neurogenesis, evident in increased Nissl cell numbers and NeuN expression in the brain.

CONCLUSION

Chronic alcoholism may be effect on the brain cells as well as on the neuro-behavior of zebrafish. This research demonstrated that VtB12 shows promise as a neuroprotective agent against chronic alcoholism induced alterations in zebrafish's brain.

Benzophenone-3 causes oxidative stress in the brain and impairs aversive memory in adult zebrafish

Oxybenzone (BP-3) is an ultraviolet (UV) filter widely used in industries that is directly or indirectly released into the aquatic environment. However, little is known about its effects on brain performance. Here, we investigated whether BP-3 exposure affects the redox imbalance in zebrafish and how they respond to a task that requires memory of an aversive situation. Fish were exposed to BP-3 10 and 50 μg L-1 for 15 days and then tested using an associative learning protocol with electric shock as a stimulus. Brains were extracted for reactive oxygen species (ROS) measurement and qPCR analysis of antioxidant enzyme genes. ROS production increased for exposed animals, and catalase (cat) and superoxide dismutase 2 (sod 2) were upregulated. Furthermore, learning and memory were reduced in zebrafish exposed to BP-3. These results suggested that BP-3 may lead to a redox status imbalance, causing impaired cognition and reinforcing the need to replace the toxic UV filters with filters that minimize environmental effects.

Zebrafish Modeling of Autism Spectrum Disorders, Current Status and Future Prospective

Autism spectrum disorder (ASD) refers to a complicated range of childhood neurodevelopmental disorders which can occur via genetic or non-genetic factors. Clinically, ASD is associated with problems in relationships, social interactions, and behaviors that pose many challenges for children with ASD and their families. Due to the complexity, heterogeneity, and association of symptoms with some neuropsychiatric disorders such as ADHD, anxiety, and sleep disorders, clinical trials have not yielded reliable results and there still remain challenges in drug discovery and development pipeline for ASD patients. One of the main steps in promoting lead compounds to the suitable drug for commercialization is preclinical animal testing, in which the efficacy and toxicity of candidate drugs are examined in vivo. In recent years, zebrafish have been able to attract the attention of many researchers in the field of neurological disorders such as ASD due to their outstanding features. The presence of orthologous genes for ASD modeling, the anatomical similarities of parts of the brain, and similar neurotransmitter systems between zebrafish and humans are some of the main reasons why scientists draw attention to zebrafish as a prominent animal model in preclinical studies to discover highly effective treatment approaches for the ASD through genetic and non-genetic modeling methods.

Embryonic Exposure to Ethanol Increases Anxiety-Like Behavior in Fry Zebrafish

AIMS

Fetal alcohol spectrum disorder (FASD) is an umbrella term to describe the effects of ethanol (Eth) exposure during embryonic development, including several conditions from malformation to cognitive deficits. Zebrafish (Danio rerio) are a translational model popularly applied in brain disorders and drug screening studies due to its genetic and physiology homology to humans added to its transparent eggs and fast development. In this study, we investigated how early ethanol exposure affects zebrafish behavior during the initial growth phase.

METHODS

Fish eggs were exposed to 0.0 (control), 0.25 and 0.5% ethanol at 24 h post-fertilization. Later, fry zebrafish (10 days old) were tested in a novel tank task and an inhibitory avoidance protocol to inquire about morphology and behavioral alterations.

RESULTS

Analysis of variance showed that ethanol doses of 0.25 and 0.5% do not cause morphological malformations and did not impair associative learning but increased anxiety-like behavior responses and lower exploratory behavior when compared to the control.

CONCLUSION

Our results demonstrate that one can detect behavioral abnormalities in the zebrafish induced by embryonic ethanol as early as 10 days post-fertilization and that alcohol increases anxious behavior during young development in zebrafish.

Does early ethanol exposure increase seeking-like behavior in zebrafish?

Fetal alcohol spectrum disorder (FASD) is the most common cause of birth defects. The severe variations are in fetal alcohol syndrome (FAS) but the most frequent cases are alcohol-related neurodevelopmental disorder (ARND), which is of a difficult diagnosis. ARND characteristics include impaired social behavior, anxiety and depression prevalence, cognitive deficits, and an increased chance for drug addiction. Here, we aimed to test whether early alcohol exposure leads to later alcohol preference. We hypothesize that early alcohol exposure increases the reinforcing effects on later experiences, raising the chance of addiction in adult life. Lately, the zebrafish has been a valuable model on alcohol research, allowing embryonic exposure and the study of the ontogenetic effects. For this, embryos were exposed to three different alcohol treatments: 0.0%, 0.25% and 0.5%, for 2 hr, at 24-hr post-fertilization. Then we evaluated the effects of embryonic alcohol exposure on conditioned place preference in two developmental stage: fry (10 days post-fertilization (dpf)) and young (90 dpf) zebrafish. Results show that control fish presented alcohol associative learning, which means, changes in place preference due to alcohol exposure, at both ontogenetic phases. However, zebrafish exposed to 0.25 and 0.5% alcohol during embryogenesis did not show conditioning response at any evaluated stage. These results suggest perception and cognitive deficits due to embryonic alcohol exposure that can alter alcohol responsiveness throughout a lifetime. Although low alcohol doses do not provoke malformation, it has been shown to induce several neurological and behavioral changes that are termed as Alcohol-Related Neurodevelopmental Disorders. These results may contribute to future investigations on how embryonic exposure affects the neurocircuitry related to perception and associative learning processing.

Behavioral Screening of Alcohol Effects and Individual Differences in Zebrafish (Danio rerio)

AIM

To better understand the individual differences that make up a population, this study aimed to evaluate the effects of different alcoholic concentrations on the behavioral profiles of zebrafish (Danio rerio).

METHODS

For this purpose, adult animals were separated into two behavioral profiles: bold and shy, according to the emergence order. Bold and shy fish were individually tested for exploration after exposure to the drug. Acute exposure treatments were alcohol 0.00, 0.10, 0.25 and 0.50%. The behavioral parameters evaluated were speed while moving, maximum speed, total distance traveled and distance from the bottom of the tank.

RESULTS

For the groups that did not receive alcohol, bold animals showed higher speed while moving. Shy 0.00% and shy 0.10% had the highest maximum speed compared with other concentrations and profiles. For the distance from the bottom tank, our results showed that the increase induced by the low acute dose (0.10%) was observed for both profiles.

CONCLUSIONS

Our results corroborate with previous findings that alcohol affects the behavioral profiles of zebrafish differently, with bold animals apparently more resistant to these changes.

Understanding the neurobiological effects of drug abuse: Lessons from zebrafish models

Drug abuse and brain disorders related to drug comsumption are public health problems with harmful individual and social consequences. The identification of therapeutic targets and precise pharmacological treatments to these neuropsychiatric conditions associated with drug abuse are urgently needed. Understanding the link between neurobiological mechanisms and behavior is a key aspect of elucidating drug abuse-related targets. Due to various molecular, biochemical, pharmacological, and physiological features, the zebrafish (Danio rerio) has been considered a suitable vertebrate for modeling complex processes involved in drug abuse responses. In this review, we discuss how the zebrafish has been successfully used for modeling neurobehavioral phenotypes related to drug abuse and review the effects of opioids, cannabinoids, alcohol, nicotine, and psychedelic drugs on the central nervous system (CNS). Moreover, we summarize recent advances in zebrafish-based studies and outline potential advantages and limitations of the existing zebrafish models to explore the neurochemical bases of drug abuse and addiction. Finally, we discuss how the use of zebrafish models may present fruitful approaches to provide valuable clinically translatable data.

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-human animals, and is associated with several neurophenotypes in rodents and fishes. Zebrafish (Danio rerio) is a versatile vertebrate model system widely used in translational neuropsychiatric research owing to their highly conserved genetic homology, well-characterized physiological responses, and extensive behavioral repertoire. Although spontaneous left- and right-biased responses, and associated behavioral domains (e.g., stress reactivity, aggression, and learning), have previously been observed in other teleost species, no information relating to whether spontaneous motor left–right-bias responses of zebrafish predicts other behavioral domains has been described. Thus, we aimed to investigate the existence and incidence of natural left–right bias in adult zebrafish, exploiting an unconditioned continuous free movement pattern (FMP) Y-maze task, and to explore the relationship of biasedness on performance within different behavioral domains. This included learning about threat cues in a Pavlovian fear conditioning test, and locomotion and anxiety-related behavior in the novel tank diving test. Although laterality did not change locomotion or anxiety-related behaviors, we found that biased animals displayed a different search strategy in the Y-maze, making them easily discernable from their unbiased counterparts, and increased learning associated to fear cues. In conclusion, we showed, for the first time, that zebrafish exhibit a natural manifestation of motor behavioral lateralization which can influence aversive learning responses.

Individual Differences in Hatching Time Predict Alcohol Response in Zebrafish

There are significant individual differences in response to alcohol: some people seem to exhibit higher alcohol sensitivity, while others are more resistant. These differences are related to alcohol metabolism, inherited traits, environmental/social pressure, personal habits and other indeterminate causes. In order to test how individual differences in hatching time are related to behavioral response to different alcohol concentrations, we separated zebrafish larvae into two categories according to egg emergence time: eggs hatched between 48 and 72 hours post-fertilization (hpf) were considered early emerging (EE), while those hatched from 72 to 96 hpf were considered late emerging (LE). On the 30th day post fertilization, EE and LE fish were exposed to four alcohol concentrations: 0.00% (control), 0.10%, 0.25% and 0.50%, and behavior was recorded for 60 min. We observed average and maximum swimming speed, distance traveled, and freezing time (immobility that indicates state of anxiety). For EE fish, 0.10% alcohol did not change behavior, while 0.25% and 0.50% increased freezing and decreased locomotion. By contrast, LE fish increased locomotion when exposed to both 0.10 and 0.25% alcohol, and increased freezing time at 0.50% alcohol. These results show that zebrafish behavioral profiles exhibit different sensitivities to alcohol, likely due to traits that can be tracked from early life stages and may indicate individuals’ predisposition to alcohol tolerance and dependence.

Taurine prevents memory consolidation deficits in a novel alcohol-induced blackout model in zebrafish

Ethanol is one of the most consumed substance worldwide that impairs learning and memory processes, resulting in amnesia or blackout. Due to the genetic conservation, rich behavioral repertoire, and high pharmacological tractability, the zebrafish (Danio rerio) has emerged as a powerful model organism for assessing preventive strategies against the noxious effects of ethanol in vertebrates. Here, we used an inhibitory avoidance apparatus to investigate the potential preventive effects of taurine in a novel ethanol-induced amnesia model in zebrafish. The experimental tank consisted of two compartments of the same size, one dark and another white, which were separated by a guillotine-type door. Three parallel metal bars coupled to an electrical stimulator were connected on each lateral wall of the dark compartment as electrical stimulus source. Differences on the latency to enter the dark compartment were used as retention indexes. A mild electric shock (125 mA, 3 ± 0.2 V) at 10 and 1000 Hz did not promote significant learning, while 100 Hz facilitated memory retention. Posttraining administration of MK-801 blocked this response, reinforcing the predictive validity of the test. Treatments were performed immediately after the training session using the 100 Hz frequency. Animals were exposed to water (control), taurine (42, 150, 400 mg/L), ethanol (0.25%, 1.0% v/v) or taurine plus ethanol to assess the effects on memory consolidation. Test session was performed 24 h following training. Ethanol at 0.25% did not affect memory consolidation, but 1.0% impaired memory without changing locomotion. Although taurine alone did not modulate learning, all concentrations tested exerted prevented ethanol-induced memory impairment. Overall, we describe a novel ethanol-induced blackout model, where a high ethanol concentration acutely impairs memory consolidation in zebrafish. Moreover, since taurine showed a protective role, we reinforce the growing utility of zebrafish models for assessing the deleterious effects of ethanol and potential therapeutic strategies.

Individual differences in response to alcohol exposure in zebrafish (Danio rerio)

Personality traits are related to many aspects of one's life, including risk taking, sociability, and behavioral changes caused by psychoactive substances. This study aimed to investigate individual differences and behavioral changes due to alcohol exposure in zebrafish (Danio rerio). To that end, adult animals were separated into two behavioral profiles: bold and shy, according to their risk taking behavior in an emergence test. Bold and shy fish were allowed to explore a 5-chamber tank and were tested for exploration and sociability (shoaling behavior) following alcohol exposure. The acute drug exposure treatments were 0.0%, 0.1% and 0.5% (v/v%) alcohol. The behavioral parameters evaluated were average and maximum swimming speed, total distance traveled, total time spent immobile, and time spent near a shoal or exploring the tank. For the groups that received no alcohol (0.0% alcohol), shy individuals spent more time near the shoal than bold fish. However, 0.5% alcohol increased bold fish responsiveness to the shoal, while both 0.1% and 0.5% alcohol diminished shoaling in shy fish. Our results show that the behavioral profiles of zebrafish are affected differently by alcohol, with shy animals seemingly more sensitive to behavioral change due to drug exposure. Moreover, we confirm zebrafish as a model for alcohol induced functional (exploration and social behavior) changes that could be useful in high throughput drug screens.