Acute effects of ethanol on behavioral responses of male and female zebrafish in the open field test with the influence of a non-familiar object

Towards zebrafish models to unravel translational insights of obsessive-compulsive disorder: A neurobehavioral perspective

Obsessive-compulsive disorder (OCD) is a chronic and debilitating illness that has been considered a polygenic and multifactorial disorder, challenging effective therapeutic interventions. Although invaluable advances have been obtained from human and rodent studies, several molecular and mechanistic aspects of OCD etiology are still obscure. Thus, the use of non-traditional animal models may foster innovative approaches in this field, aiming to elucidate the underlying mechanisms of disease from an evolutionary perspective. The zebrafish (Danio rerio) has been increasingly considered a powerful organism in translational neuroscience research, especially due to the intrinsic features of the species. Here, we outline target mechanisms of OCD for translational research, and discuss how zebrafish-based models can contribute to explore neurobehavioral aspects resembling those found in OCD. We also identify possible advantages and limitations of potential zebrafish-based models, as well as highlight future directions in both etiological and therapeutic research. Lastly, we reinforce the use of zebrafish as a promising tool to unravel the biological basis of OCD, as well as novel pharmacological therapies in the field.

Embryonic ethanol exposure and optogenetic activation of hypocretin neurons stimulate similar behaviors early in life associated with later alcohol consumption

The initiation of alcohol use early in life is one of the strongest predictors of developing a future alcohol use disorder. Clinical studies have identified specific behaviors during early childhood that predict an increased risk for excess alcohol consumption later in life. These behaviors, including increased hyperactivity, anxiety, novelty-seeking, exploratory behavior, impulsivity, and alcohol-seeking, are similarly stimulated in children and adolescent offspring of mothers who drink alcohol during pregnancy. Here we tested larval zebrafish in addition to young pre-weanling rats and found this repertoire of early behaviors along with the overconsumption of alcohol during adolescence to be increased by embryonic ethanol exposure. With hypocretin/orexin (Hcrt) neurons known to be stimulated by ethanol and involved in mediating these alcohol-related behaviors, we tested their function in larval zebrafish and found optogenetic activation of Hcrt neurons to stimulate these same early alcohol-related behaviors and later alcohol intake, suggesting that these neurons have an important role in producing these behaviors. Together, these results show zebrafish to be an especially useful animal model for investigating the diverse neuronal systems mediating behavioral changes at young ages that are produced by embryonic ethanol exposure and predict an increased risk for developing alcohol use disorder.

Assessing the exploratory profile of two zebrafish populations: influence of anxiety-like phenotypes and independent trials on homebase-related parameters and exploration

Anxiety is a protective behavior when animals face aversive conditions. The open field test (OFT) is used to assess the spatio-temporal dynamics of exploration, in which both homebase formation and recognition of environmental cues may reflect habituation to unfamiliar conditions. Because emotional- and affective-like states influence exploration patterns and mnemonic aspects, we aimed to verify whether the exploratory behaviors of two zebrafish populations showing distinct baselines of anxiety differ in two OFT sessions. Firstly, we assessed the baseline anxiety-like responses of short fin (SF) and leopard (LEO) populations using the novel tank test (NTT) and light-dark test (LDT) in 6-min trials. Fish were later tested in two consecutive days in the OFT, in which the spatial occupancy and exploratory profile were analyzed for 30min. In general, LEO showed pronounced diving behavior and scototaxis in the NTT and LDT, respectively, in which an "anxiety index" corroborated their exacerbated anxiety-like behavior. In the OFT, the SF population spent less time to establish the homebase in the 1^st trial, while only LEO showed a markedly reduction in the latency to homebase formation in the 2^nd trial. Both locomotion and homebase-related activities were decreased in the 2^nd trial, in which animals also revealed increased occupancy in the center area of the apparatus. Moreover, we verified a significant percentage of homebase conservation for both populations, while only SF showed reduced the number of trips and increased the average length of trips. Principal component analyses revealed that distinct factors accounted for total variances between trials for each population tested. While homebase exploration was reduced in the 2^nd trial for SF, an increased occupancy in the center area and hypolocomotion were the main factors that contribute to the effects observed in LEO during re-exposure to the OFT. In conclusion, our novel data support the homebase conservation in zebrafish subjected to independent OFT sessions, as well as corroborate a population-dependent effect on specific behavioral parameters related to exploration.

Expanding the use of homebase-related parameters to investigate how distinct stressful conditions affect zebrafish behaviors

Stress is a physiological reaction that allows the organisms to cope with challenging situations daily. Thus, elucidating the behavioral outcomes following different stressors is of great importance in translational research. Here, we aimed to characterize the main factors which explain similarities and differences of two stress protocols on zebrafish exploratory activity. To answer this point, we performed behavioral analyses aiming to simplify the data structure associated with homebase-related measurements in an integrated manner. Adult zebrafish were exposed to conspecific alarm substance for 5 min (acute stress protocol - AS) or submitted to 7 days of unpredictable chronic stress (UCS). Immediately after AS or in the subsequent day following UCS (8^th day), fish were individually tested in the open field and the behaviors were recorded for 30 min to posterior identification of homebase locations. For both protocols, behavioral clustering revealed two major clusters, grouping homebase- and locomotor-related parameters, respectively. While AS increased both positive and negative correlations between exploratory and locomotor endpoints, a significant increase in negative correlations was found in UCS-challenged fish. Comparison of the principal component analyses data set revealed a reduced exploratory activity using the homebase in AS group, while decreased locomotion in the periphery and anxiety-like behaviors were evidenced in UCS fish. In conclusion, our findings revealed a different structure of behavior in zebrafish following AS and UCS protocols, supporting the existence of distinct behavioral strategies to cope with acute and chronic stress. Furthermore, we expand the use of homebase-related measurements as a valuable tool to investigate complex behavioral modulations in future translational neuropsychiatry research.

Piperine loaded metal organic frameworks reverse doxorubicin induced chemobrain in adult zebrafish

The study's primary goal was to enhance medicinal potential of piperine (PIP)-loaded zeolitic imidazolate frameworks-8 (PIP@ZIF-8) against doxorubicin (DOX)-induced cognitive impairments in zebrafish. Herein, PIP@ZIF-8 was synthesized via easy, economical and reproducible ultrasonication method followed by spray drying technology. ZIF-8's structural integrity has been confirmed by PXRD, and even after PIP was encapsulated, the structure of ZIF-8 remained unchanged. Pure ZIF-8 and PIP@ZIF-8 were subjected to TEM analysis, which revealed hexagonal morphology with a nanosize range. FTIR and UV-Visible spectroscopy studies confirmed the drug loading of ZIF-8. Studies on in vitro release revealed 71.48 ± 7.21% and 34.56 ± 5.35% PIP release from PIP@ZIF-8 and unformulated PIP, respectively in pH 7.4. The highest antioxidant scavenging results were obtained with vitamin C (73.77 ± 6.7%) at an intensity of 200 μg/ml, though it was 65.09 ± 2.5% and 57.99 ± 3.1% for PIP@ZIF-8 and PIP, respectively. In vivo studies on zebrafish showed that DOX administration remarkably impaired cognitive activity in T-Maze, and downregulated spatial memory and locomotor activity in the open field test. In addition, DOX administration caused a downregulation in GSH and SOD levels and increase in LPO, AChE and TNF-α levels compared to the vehicle group along with changes in brain histopathology. Further, PIP@ZIF-8 reversed the DOX-induced cognitive impairments by its antioxidant and neuroprotective properties. It can be concluded that PIP@ZIF-8 has a promising therapeutic potential against the chemotherapy-induced cognitive impairments in zebrafish.

Hippocampal ceRNA networks from chronic intermittent ethanol vapor-exposed male mice and functional analysis of top-ranked lncRNA genes for ethanol drinking phenotypes

The molecular mechanisms regulating the development and progression of alcohol use disorder (AUD) are largely unknown. While noncoding RNAs have previously been implicated as playing key roles in AUD, long-noncoding RNA (lncRNA) remains understudied in relation to AUD. In this study, we first identified ethanol-responsive lncRNAs in the mouse hippocampus that are transcriptional network hub genes. Microarray analysis of lncRNA, miRNA, circular RNA, and protein coding gene expression in the hippocampus from chronic intermittent ethanol vapor- or air- (control) exposed mice was used to identify ethanol-responsive competing endogenous RNA (ceRNA) networks. Highly interconnected lncRNAs (genes that had the strongest overall correlation to all other dysregulated genes identified) were ranked. The top four lncRNAs were novel, previously uncharacterized genes named Gm42575, 4930413E15Rik, Gm15767, and Gm33447, hereafter referred to as Pitt1, Pitt2, Pitt3, and Pitt4, respectively. We subsequently tested the hypothesis that CRISPR/Cas9 mutagenesis of the putative promoter and first exon of these lncRNAs in C57BL/6J mice would alter ethanol drinking behavior. The Drinking in the Dark (DID) assay was used to examine binge-like drinking behavior, and the Every-Other-Day Two-Bottle Choice (EOD-2BC) assay was used to examine intermittent ethanol consumption and preference. No significant differences between control and mutant mice were observed in the DID assay. Female-specific reductions in ethanol consumption were observed in the EOD-2BC assay for Pitt1, Pitt3, and Pitt4 mutant mice compared to controls. Male-specific alterations in ethanol preference were observed for Pitt1 and Pitt2. Female-specific increases in ethanol preference were observed for Pitt3 and Pitt4. Total fluid consumption was reduced in Pitt1 and Pitt2 mutants at 15% v/v ethanol and in Pitt3 and Pitt4 at 20% v/v ethanol in females only. We conclude that all lncRNAs targeted altered ethanol drinking behavior, and that lncRNAs Pitt1, Pitt3, and Pitt4 influenced ethanol consumption in a sex-specific manner. Further research is necessary to elucidate the biological mechanisms for these effects. These findings add to the literature implicating noncoding RNAs in AUD and suggest lncRNAs also play an important regulatory role in the disease.

The critical impact of sex on preclinical alcohol research - Insights from zebrafish

Sex is an important biological variable that is widely recognized in studies of alcohol-related effects. Complementing clinical and preclinical rodent research, the zebrafish (Danio rerio) is the second most used laboratory species, and a powerful model organism in biomedicine. Like clinical and rodent models, zebrafish demonstrate overt sex differences in alcohol-related responses. Collectively, this evidence shows that the zebrafish becomes a sensitive model species to further probe in-depth sex differences commonly reported in alcohol research.

Sex-Specific Effects of Acute Ethanol Exposure on Locomotory Activity and Exploratory Behavior in Adult Zebrafish (Danio rerio)

The zebrafish (Danio rerio) is an established model organism in pharmacology and biomedicine, including in research on alcohol use disorders and alcohol-related disease. In the past 2 decades, zebrafish has been used to study the complex effects of ethanol on the vertebrate brain and behavior in both acute, chronic and developmental exposure paradigms. Sex differences in the neurobehavioral response to ethanol are well documented for humans and rodents, yet no consensus has been reached for zebrafish. Here, we show for the first time that male zebrafish of the AB strain display more severe behavioral impairments than females for equal exposure concentrations. Adult zebrafish were immersed in 0, 1 or 2% (v/v) ethanol for 30 min, after which behavior was individually assessed in the zebrafish Multivariate Concentric Square Field™ (zMCSF) arena. Males exposed to 2% ethanol showed clear signs of sedation, including reduced activity, increased shelter seeking and reduced exploration of shallow zones. The 1% male group displayed effects in the same direction but of smaller magnitude; this group also explored the shallow areas less, but did not show a general reduction in activity nor an increase in shelter seeking. By contrast, 1 and 2% exposed females showed no alterations in explorative behavior. Females exposed to 2% ethanol did not display a general reduction in activity, rather activity gradually increased from hypoactivity to hyperactivity over the course of the test. This mixed stimulatory/depressant effect was only quantifiable when locomotory variables were analyzed over time and was not apparent from averages of the whole 30-min test, which may explain why previous studies failed to detect sex-specific effects on locomotion. Our results emphasize the importance of explicitly including sex and time as factors in pharmacological studies of zebrafish behavior. We hypothesize that the lower sensitivity of female zebrafish to ethanol may be explained by their greater body weight and associated larger distribution volume for ethanol, which may render lower brain ethanol concentrations in females.