Barbara D. Fontana

Modulatory action of taurine on ethanol-induced aggressive behavior in zebrafish.

Alcohol is a potent agent for eliciting aggression in vertebrates. Taurine (TAU) is an amino sulfonic acid with pleiotropic actions on brain function. It is one of the most abundant molecules present in energy drinks frequently used as mixers for alcoholic beverages. However, the combined effects of TAU and ethanol (EtOH) on behavioral parameters such as aggression are poorly understood. Considering that zebrafish is a suitable vertebrate to assess agonistic behaviors using noninvasive protocols, we investigate whether TAU modulates EtOH-induced aggression in zebrafish using the mirror-induced aggression (MIA) test. Since body color can be altered by pharmacological agents and may be indicative of emotional state, we also evaluated the actions of EtOH and TAU on pigment response. Fish were acutely exposed to TAU (42, 150, and 400mg/L), EtOH (0.25%), or cotreated with both molecules for 1h and then placed in the test apparatus for 6min. EtOH, TAU 42, TAU 400, TAU 42/EtOH and TAU 400/EtOH showed increased aggression, while 150mg/L TAU only increased the latency to attack the mirror. This same concentration also prevented EtOH-induced aggression, suggesting that it antagonizes the effects of acute alcohol exposure. Representative ethograms revealed the existence of different aggressive patterns and our results were confirmed by an index used to estimate aggression in the MIA test. TAU did not alter pigment intensity, while EtOH and all cotreated groups presented a substantial increase in body color. Overall, these data show a biphasic effect of TAU on EtOH-induced aggression of zebrafish, which is not necessarily associated with changes in body color.

The developing utility of zebrafish models of neurological and neuropsychiatric disorders: A critical review

ABSTRACT Zebrafish (Danio rerio) have become a powerful tool in neuroscience research due to their genetic tractability, molecular/physiological conservation, small body size, ease of experimental manipulations in vivo, and rich behavioral repertoire. Zebrafish models and tests are particularly useful in genetics research, neurophenotyping, CNS drug screening, as well as in modeling complex neurological and psychiatric disorders. Here, we discuss selected examples of successful application of zebrafish models to mimicking various aspects of brain pathology, and emphasize their developing utility for studying the underlying molecular and genetic mechanisms. We also summarize recent advances in zebrafish‐based CNS disease modeling, and outline new research strategies that may significantly improve translational neuroscience and experimental neurology research, and drug discovery. HIGHLIGHTSNon‐mammalian models of human brain disorder are critical for translational neuroscience.The zebrafish is a suitable organism to model neurological and psychiatric disorders.New strategies for improving CNS research using zebrafish are discussed.We also highlight the advantages and difficulties of zebrafish brain disease modeling in vivo.

Conspecific alarm substance differently alters group behavior of zebrafish populations: Putative involvement of cholinergic and purinergic signaling in anxiety- and fear-like responses

Graphical abstract Figure. No Caption available. HighlightsAlarm substance induces fear in zebrafish shoals of two populations.Leo shoals show pronounced basal defensive responses in comparison to WT fish.Only WT shows enhanced shoaling and diving response triggered by alarm substance.The cholinergic and purinergic systems may play a role in defensive behaviors. ABSTRACT The zebrafish (Danio rerio) is an emergent model organism for assessing fear and anxiety‐like phenotypes. The short fin wild type (WT), and leopard (leo) are two zebrafish populations that present several behavioral differences, in which leo displays pronounced defensive responses. Mounting evidence suggests a modulatory role for cholinergic and purinergic signaling in fear and anxiety, but the involvement of these neurotransmitter systems in the behavioral profile of zebrafish is obscure. Here we tested whether the acute exposure to conspecific alarm substance (AS), an experimental protocol that induces fear, alters shoaling behavior, diving response, acetylcholinesterase (AChE) activity, and nucleotide hydrolysis in brain tissue of WT and leo. When four fish were concomitantly exposed to AS extracted from a donor fish of similar phenotype, both populations presented a significant increase of erratic movements without changes in freezing bouts. An increased shoal cohesion and a decreased vertical distribution were observed only in WT exposed to AS. The respective population also revealed a significant increase in AChE and ecto‐5′‐nucleotidase activities after the exposure period. The comparison of basal endpoints between populations showed that leo displays a higher social cohesion, few vertical transitions and enhanced AChE and ecto‐5′‐nucleotidase activities. In conclusion, we suggest that the effects of AS on defensive behaviors depend on the population, indicating the existence of distinct neurochemical mechanisms involved. Furthermore, this report shows the first evidence of a potential role of cholinergic and purinergic systems in fear‐ and anxiety‐like responses of zebrafish populations.

Different effects of caffeine on behavioral neurophenotypes of two zebrafish populations

ABSTRACT Caffeine is a substance present in several foods and drinks of common western diet. Although high caffeine concentrations induce anxiogenic properties in various species, the influence of the different baselines of anxiety levels on caffeine‐mediated responses is poorly understood. The short‐fin wild‐type (WT) and leopard (leo) zebrafish populations present significant behavioral differences, in which leo shows exacerbated anxiety‐like responses. Since behavioral neurophenotyping may be easily assessed in adult zebrafish by associating temporal and spatial three‐dimensional reconstructions of locomotion, we investigated the effects of caffeine on exploration and anxiety‐like behavior of WT and leo zebrafish. Moreover, the whole‐body cortisol content was assessed in the absence and presence of caffeine. For this purpose, animals were acutely exposed to caffeine (25, 50, 100 and 200 mg/L) for 15 min and further tested in the novel tank. Endpoint data and 3D reconstruction plots revealed that caffeine was anxiogenic in both WT and leo populations by altering vertical swimming, freezing, and erratic movements depending on the concentration. Prominent anxiogenic effects during habituation to novelty were observed in WT, suggesting a fundamental role of the phenotype in caffeine‐mediated neurobehavioral responses. Although untreated leo showed higher baseline cortisol levels than control WT, caffeine increased whole‐body cortisol in both populations. Moreover, caffeine induced aberrant swimming profiles in WT and leo following 200 mg/L exposure, which could reflect nonspecific toxicity and/or seizure‐like behaviors. Collectively, our novel findings show that caffeine effects in zebrafish differ in a population‐dependent manner. HIGHLIGHTSBehavioral effects of caffeine were tested in WT and leo zebrafish populations.Behavioral neurophenotyping was analyzed by endpoints and 3D swimming traces.Caffeine increased anxiogenic‐like behaviors and whole‐body cortisol of zebrafish.Caffeine prominently impaired the habituation to novelty in WT.High caffeine concentrations induced abnormal behavior in zebrafish.

Understanding taurine CNS activity using alternative zebrafish models

HighlightsTaurine has pleiotropic effects in brain, but its exact mechanisms are obscure.The use of alternative models to assess the CNS mechanisms of taurine is discussed.Zebrafish models of brain disorders are emergent in translational neuroscience.Zebrafish is an interesting model organism to assess the neurophysiology of taurine. Abstract Taurine is a highly abundant “amino acid” in the brain. Despite the potential neuroactive role of taurine in vertebrates has long been recognized, the underlying molecular mechanisms related to its pleiotropic effects in the brain remain poorly understood. Due to the genetic tractability, rich behavioral repertoire, neurochemical conservation, and small size, the zebrafish (Danio rerio) has emerged as a powerful candidate for neuropsychopharmacology investigation and in vivo drug screening. Here, we summarize the main physiological roles of taurine in mammals, including neuromodulation, osmoregulation, membrane stabilization, and antioxidant action. In this context, we also highlight how zebrafish models of brain disorders may present interesting approaches to assess molecular mechanisms underlying positive effects of taurine in the brain. Finally, we outline recent advances in zebrafish drug screening that significantly improve neuropsychiatric translational researches and small molecule screens.

Extending the analysis of zebrafish behavioral endophenotypes for modeling psychiatric disorders: Fear conditioning to conspecific alarm response

Anxiety, trauma- and stressor-related disorders are severe psychiatric conditions that affect human population worldwide. Given their genetic tractability, evolutionarily conserved neurotransmitter systems, and extensive behavioral repertoire, zebrafish have become an emergent model organism in translational neuroscience. Here, we investigate whether a single exposure to conspecific alarm substance (CAS) produces fear conditioning in zebrafish using a conditioned place aversion (CPA) paradigm, as well as the persistence of aversive responses at different time intervals. While CAS elicited freezing and erratic movements at conditioning phase, zebrafish showed a robust avoidance for the CAS-paired compartment and increased risk assessment up to 7 days postconditioning. Additionally, we observed the existence of two behavioral phenotypes (high- and low-avoider fish) that present different fear-like responses at conditioning phase and evasion of the conditioning side at postconditioning trials. Collectively, we show a prolonged conditioned place aversion in zebrafish after a single CAS conditioning session, reinforcing the use of fear conditioning protocols as valuable strategies for modeling psychiatric disorders-related phenotypes in zebrafish.

Nicotine increases fear responses and brain acetylcholinesterase activity in a context-dependent manner in zebrafish.

ABSTRACT Nicotine is an alkaloid with positive effects on learning and memory processes. Exposure to conspecific alarm substance (CAS) elicits fear responses in zebrafish, but the effects of nicotine on aversive behaviors and associative learning in this species remain unclear. Here, we evaluated whether nicotine enhances contextual fear responses in zebrafish and investigated a putative involvement of brain acetylcholinesterase (AChE) in associative learning. Fish were exposed to 1 mg/L nicotine for 3 min and then kept in non‐chlorinated water for 20 min. Later, animals were transferred to experimental tanks in the absence or presence of 3.5 mL/L CAS for 5 min (training session). After 24 h, fish were tested in tanks with similar or altered context in the absence of CAS (post‐training session) and brain AChE activity was further assessed. At training, CAS increased freezing, erratic movements, and decreased the time spent in top area, while nicotine abolished the effects of CAS on erratic movements. Nicotine/CAS group tested in a similar context showed exacerbated freezing and reduced transitions to top area. Moreover, a decrease in distance traveled was observed in control, nicotine, and nicotine/CAS groups at post‐training. Nicotine also stimulated brain AChE activity in CAS‐exposed animals reintroduced in tanks with similar context. Although freezing bouts and time spent in top could serve as behavioral endpoints that reflect CAS‐induced sensitization, the effects of nicotine occurred in a context‐dependent manner. Collectively, our data suggest an involvement of cholinergic signaling in aversive learning, reinforcing the growing utility of zebrafish models to explore the neurobehavioral effects of nicotine in vertebrates. HighlightsThe effects of nicotine on zebrafish contextual fear responses were tested.Nicotine abolished the effects of alarm substance on erratic movements at training.Nicotine exacerbates freezing when fish were retested in the aversive context.Nicotine‐induced changes in brain AChE activity depends on the context.

Single pentylenetetrazole exposure increases aggression in adult zebrafish at different time intervals

Epilepsy is characterized by abnormal and recurrent hyperexcitability in brain cells. Various comorbidities are associated with epilepsy, including irritability and aggressive behavior. Aggression is a negative effect observed in epileptic patients that may be harmful to other individuals, impairing social relations. Thus, developing novel experimental models to assess behavioral phenotypes that may comorbid with neurological disorders are of great interest. Here, we investigate whether pentylenetetrazole (PTZ) increases aggression in zebrafish following a single exposure. Animals were exposed to 10 mM PTZ for 20 min and aggression-towards mirror was measured at different time intervals after recovering period (1 h, 3 h, 6 h, 24 h, 48 h, and 72 h). We observed that zebrafish showed exacerbated aggression, as well as an increased number of entries in the virtual conspecific area from 1 h to 48 h after PTZ. However, no behavioral differences were observed after 72 h. Overall, our novel findings show that a single PTZ exposure evokes aggression in a time-dependent manner, reinforcing the use of zebrafish models to explore epilepsy-related comorbidities.

Taurine modulates acute ethanol-induced social behavioral deficits and fear responses in adult zebrafish

Ethanol (EtOH) is a central nervous system (CNS) depressant drug that modifies various behavioral domains (i.e., sociability, aggressiveness, and memory) by promoting disinhibition of punished operant behavior and neurochemical changes. Taurine (TAU) is a β-amino sulfonic acid with pleiotropic roles in the brain. Although exogenous TAU is found in energy drinks and often mixed with alcohol in beverages, the putative risks of mixing TAU and EtOH are poorly explored. Here, we investigated whether TAU modulates social and fear responses by assessing shoaling behavior, preference for conspecifics, and antipredatory behavior of adult zebrafish acutely exposed to EtOH. Zebrafish shoals (4 fish per shoal) were exposed to water (control), TAU (42, 150, and 400 mg/L), 0.25% (v/v) EtOH alone or in association with TAU for 1 h, and their behaviors were analyzed at different time intervals (0-5 min, 30-35 min, and 55-60 min). The effects of TAU and EtOH were further tested in a social preference test and during exposure to a predator. Both EtOH and TAU co-treated fish showed a higher shoal dispersion, while TAU 400/EtOH group shoal area had a similar profile when compared to control. However, in the social preference test, TAU 400/EtOH impaired the seeking for conspecifics. Regarding fear-like behaviors, TAU-cotreated fish showed a prominent reduction in risk assessments when compared to EtOH alone. Overall, we demonstrate that TAU modulates EtOH-induced changes in different behavioral domains, suggesting a complex relationship between social and fear-like responses.