Zebrafish (Danio rerio) embryo-larvae locomotor activity data analysis: Evaluating anxiolytic effects of the antidepressant compound citalopram

Sceletium tortuosum-derived mesembrine significantly contributes to the anxiolytic effect of Zembrin®, but its anti-depressant effect may require synergy of multiple plant constituents

ETHNOPHARMACOLOGY RELEVANCE

Sceletium tortuosum (L.) N.E.Br. (ST) is an alkaloid-rich succulent plant with various mechanisms of action that infer psychotropic effects. These actions correlate with clinical evidence suggesting efficacy in the treatment of depression and anxiety, in line with its use by indigenous populations. Its low side effect profile suggests potential of ST to improve the overall wellbeing and compliance of millions of patients that experience severe side effects and/or do not respond to current prescription medication. However, to elucidate specific physiological effects of ST extracts, it is necessary to first understand which of its constituents are the major contributors to beneficial effects demonstrated for ST in this context.

AIM OF THE STUDY

To determine an anxiolytic- and antidepressant-like effective concentration of a ST extract by means of a dose response in zebrafish (ZF) larvae, and to assess relative contributions of equivalent concentrations of isolated alkaloids contained in the effective concentration(s).

MATERIALS AND METHODS

A dose response study employing a light-dark transition test (LDTT) was done in ZF larvae (<5 days post fertilization) to track locomotor activity in terms of anxiety-like (hyperlocomotion) and depression-like (hypolocomotion) behaviour. Larvae were treated for 1 h directly before the LDTT with escalating concentrations of a ST extract commercially known as Zembrin® (Zem) ranging from 0.25 to 500 μg/mL and compared to an untreated control group (n = 12 per treatment concentration). LDTT was repeated after 24 h to evaluate long-term exposure toxicity. The concentration that best attenuated hyperlocomotion during the dark phase following light-dark transition was identified as the anxiolytic-like concentration. This concentration, plus one higher and one lower concentration, were used for subsequent tests. The percentage content of each alkaloid (mesembrine, mesembrenone, mesembrenol, and mesembranol) in these concentrations were calculated and applied to additional larvae to identify the most effective anxiolytic-like alkaloid in the LDTT. To identify antidepressant-like therapeutic concentration and equivalent alkaloid concentration, the same treatment concentrations were tested in larvae (n = 12 per treatment concentration) pre-exposed to reserpine for 24 h. Depending on normality of data distribution, Brown-Forsythe and Welch, or Kruskal-Wallis ANOVA were used, with Dunnett or Dunn's multiple comparisons tests.

RESULTS

Only the extreme concentration of Zem (500 μg/mL) elicited toxicity after treatment for 24 h. Zem 12.5 μg/mL was the most effective anxiolytic-like concentration as it significantly decreased locomotor activity (P = 0.05) in the LDTT. Low (5 μg/mL), optimal (12.5 μg/mL) and high (25 μg/mL) Zem concentrations, as well as treatment solutions of single alkaloids (mesembrine, mesembrenone, mesembranol and mesembrenol), prepared to contain equivalent concentrations of each major alkaloid contained within these three concentrations of Zem, were tested further. Only mesembrine concentrations equal to that contained within the optimal and high dose of Zem (12.5 and 25 μg/mL) showed significant anxiolytic-like effects (P < 0.05). Only the highest Zem concentration (25 μg/mL) reversed the effects of reserpine - indicating antidepressant-like properties (P < 0.05) - while isolated alkaloids failed to induce such effects when administered in isolation.

CONCLUSIONS

Current data provide evidence of both anxiolytic- and antidepressant-like effect of whole extract of Zem, with relatively higher concentrations required to achieve antidepressant-like effect. Of all alkaloids assessed, only mesembrine contributed significantly to the anxiolytic-like effects of Zem. No alkaloid alone could be pinpointed as a contributor to the antidepressant-like activity observed for higher concentration Zem. This may be due to synergistic effects of the alkaloids or may be due to other components not tested here. Current data warrants further investigation into mechanisms of action, as well as potential synergy, of ST alkaloids in suitable mammalian in vivo models.

A Mini-Review Regarding the Modalities to Study Neurodevelopmental Disorders-Like Impairments in Zebrafish—Focussing on Neurobehavioural and Psychological Responses

Neurodevelopmental disorders (NDDs) are complex disorders which can be associated with many comorbidities and exhibit multifactorial-dependent phenotypes. An important characteristic is represented by the early onset of the symptoms, during childhood or young adulthood, with a great impact on the socio-cognitive functioning of the affected individuals. Thus, the aim of our review is to describe and to argue the necessity of early developmental stages zebrafish models, focusing on NDDs, especially autism spectrum disorders (ASD) and also on schizophrenia. The utility of the animal models in NDDs or schizophrenia research remains quite controversial. Relevant discussions can be opened regarding the specific characteristics of the animal models and the relationship with the etiologies, physiopathology, and development of these disorders. The zebrafish models behaviors displayed as early as during the pre-hatching embryo stage (locomotor activity prone to repetitive behavior), and post-hatching embryo stage, such as memory, perception, affective-like, and social behaviors can be relevant in ASD and schizophrenia research. The neurophysiological processes impaired in both ASD and schizophrenia are generally highly conserved across all vertebrates. However, the relatively late individual development and conscious social behavior exhibited later in the larval stage are some of the most important limitations of these model animal species.

Consumption and ocurrence of antidepressants (SSRIs) in pre- and post-COVID-19 pandemic, their environmental impact and innovative removal methods: A review

Selective serotonin reuptake inhibitors (SSRIs) are pharmaceuticals whose consumption has increased significantly. They are prescribed as first-line treatment in mental disorders such as depression, obsessive-compulsive disorder, phobias, and anxiety; also, they are indicated as adjuvants in diseases such as fibromyalgia and bulimia nervosa. In addition to being linked to the illegal market to be consumed as recreational drugs. The relevance of this review lies in the fact that worldwide consumption has increased significantly during the COVID-19 pandemic, due to the depression and anxiety that originated in the population. As a consequence of this increase in consumption, concentrations of SSRIs in the environment have increased, and these have become a relevant issue for toxicologists due to the effects that they could generate in different organisms, both aquatic and terrestrial. For this reason, the objective of this article was to do a critical evaluation of the existing data on the characteristics and physicochemical properties of SSRIs, consumption data during the COVID-19 pandemic, its occurrence in the environment and the reports of toxic effects that have been generated in different organisms; we also conclude with an updated review of different methods that have been used for their removal. With this analysis, it can be concluded that, despite SSRIs are pharmaceutical products widely studied since their launching to the market, still currently under investigation to clarify their mechanisms of action to understand the different effects on the organisms, adverse reactions, as well as possible toxicological effects on non-target organisms. On the other hand, it has been proven that although it is already possible to eliminate a significant percentage of SSRIs in the laboratory, due to their physicochemical characteristics and their behavior in complex mixtures in the environment, they have not yet been eradicated, showing a persistence in the soil, subsoil and surface waters of the entire planet that may represent a future risk.

Effects of common environmental endocrine-disrupting chemicals on zebrafish behavior

Environmental endocrine-disrupting chemicals (EDCs), a type of exogenous organic pollutants, are ubiquitous in natural aquatic environments. Therefor, this review focused on the use of the zebrafish as a model to explore the effect of different EDCs on behavior, as well as the molecular mechanisms that drive these effects. Furthermore, our study summarizes the current knowledge on the neuromodulatory effects of different EDCs in zebrafish. This study also reviews the current state of zebrafish behavior research, in addition to the potential mechanisms of single and mixed pollutant-driven behavioral dysregulation at the molecular level, as well as the applications of zebrafish behavior experiments for neuroscience research. This review broadens our understanding of the influence of EDCs on zebrafish behavior and provides guidance for future research.

Does aquatic sediment pollution result in contaminated food sources?

The sediment pollution of the aquatic environment by waste due to anthropogenic activity is of an increasing concern. The contaminants coming from the aquatic environment can enter the aquatic food chain and accumulate in the tissues of fish and shellfish used for human consumption. The aim of this study was to sum up the current level of knowledge concerning the pollution of aquatic sediments and its transfer to aquatic foods as well as to indicate whether such contamination has the potential to affect the health and welfare of aquatic organisms as well as the quality and safety of the species intended for human consumption. Based on the results of scientific studies, the European Food Safety Authority, and the Rapid Alert System for Food and Feed, contamination of fish and seafood occurs predominantly through their diet and the levels of bioaccumulative contaminants are higher in fish which rank higher in the food chain. Contamination of aquatic habitats can not only significantly affect behavior, development, and welfare of aquatic organisms, but it can also affect the safety of fish and seafood for human consumption.