Behavioural responses of zebrafish larvae to acute ethosuximide exposure

Tools for photomotor response assay standardization in ecotoxicological studies: Example of exposure to gentamicin in the freshwater planaria Schmidtea mediterranea

Photomotor response assay (PMR) is very useful in an ecotoxicological context because it allows evaluation of behavioral response to potential toxic compounds. However, a lack of procedure standardization makes results comparison difficult between labs and organisms. Here, we aimed to propose five different tools to standardize the PMR procedure so that it may be applied to all model species, regarding: (1) the minimum total sample size, (2) the acclimation period, (3) the number and duration of light and dark phases alternation, (4) the measured behavior, and (5) the statistical analysis. As an example of procedure application, we analyzed the effect of an exposure to the antibiotic gentamicin on the locomotion behavior during PMR in an invertebrate species: the asexual freshwater planaria Schmidtea mediterranea. We encourage future studies using PMR to follow these five tools to improve data analysis and results comparability.

Deficiency of nde1 in zebrafish induces brain inflammatory responses and autism-like behavior

The cytoskeletal protein NDE1 plays an important role in chromosome segregation, neural precursor differentiation, and neuronal migration. Clinical studies have shown that NDE1 deficiency is associated with several neuropsychiatric disorders including autism. Here, we generated nde1 homologous deficiency zebrafish (nde1^−/−) to elucidate the cellular molecular mechanisms behind it. nde1^−/− exhibit increased neurological apoptotic responses at early infancy, enlarged ventricles, and shrank valvula cerebelli in adult brain tissue. Behavioral analysis revealed that nde1^−/− displayed autism-like behavior traits such as increased locomotor activity and repetitive stereotype behaviors and impaired social and kin recognition behaviors. Furthermore, nde1 mRNA injection rescued apoptosis in early development, and minocycline treatment rescued impaired social behavior and overactive motor activity by inhibiting inflammatory cytokines. In this study, we revealed that nde1 homozygous deletion leads to abnormal neurological development with autism-related behavioral phenotypes and that inflammatory responses in the brain are an important molecular basis behind it.

•

nde1^−/− zebrafish display autism-like behavior features

•

nde1 deficiency results in immune responses in the brain

•

Minocycline treatment inhibits immune responses in the adult nde1^−/− brain

•

Minocycline rescued the impaired social behavior and locomotor activity

Lasting effects of mild embryonic ethanol exposure on voltage-gated ion channels in adult zebrafish brain

The zebrafish is increasingly well utilized in alcohol research, particularly in modeling human fetal alcohol spectrum disorders (FASD). FASD results from alcohol reaching the developing fetus intra utero, a completely preventable yet prevalent and devastating life-long disorder. The hope with animal models, including the zebrafish, is to discover the mechanisms underlying this disease, which may aid treatment and diagnosis. In the past, we developed an embryonic alcohol exposure regimen that is aimed at mimicking the milder, and most prevalent, forms of FASD in zebrafish. We have found numerous lasting alterations in behavior, neurochemistry, neuronal markers and glial cell phenotypes in this zebrafish FASD model. Using the same model (2 h long bath immersion of 24 h post-fertilization old zebrafish eggs into 1% vol/vol ethanol), here we conduct a proof of concept analysis of voltage-gated cation channels, investigating potential embryonic alcohol induced changes in L-, T- and N- type Ca⁺⁺ and the SCN1A Na⁺ channels using Western blot followed by immunohistochemical analysis of the same channels in the pallium and cerebellum of the zebrafish brain. We report significant reduction of expression in all four channel proteins using both methods. We conclude that reduced voltage-gated cation channel expression induced by short and low dose exposure to alcohol during embryonic development of zebrafish may contribute to the previously demonstrated lasting behavioral and neurobiological changes.

Screening selected medicinal plants for potential anxiolytic activity using an in vivo zebrafish model

RATIONALE

Medicinal plants are used extensively in many countries to treat conditions related to the central nervous system (CNS), and there is renewed interest to explore natural products, which may exhibit CNS activity.

OBJECTIVE

In this study, seven plants were selected based on literature reports of their ethnopharmacological use in treating anxiety-related conditions and assayed in a zebrafish model.

METHODS

Crude extracts were prepared with solvents of different polarities, and the maximum tolerated concentration (MTC) of these crude extracts was established. The anxiolytic activity of the crude extracts was determined using 5-day post-fertilization (dpf) zebrafish larvae. General locomotor activity and reverse-thigmotaxis behavior (indicative of anxiolytic activity) were analyzed under continuous illumination and alternating light-dark challenges, which induced anxiety in the zebrafish larvae.

RESULTS

Of the 28 extracts tested, 13 were toxic according to the MTC values obtained. Larvae were subsequently treated with the 15 non-toxic extracts, at a dose determined in the MTC assay or with 1% DMSO as control. The anxiolytic activity (reverse-thigmotaxis) was demonstrated by an increase in the percentage time spent by the larvae in the central arena of the well. Of the 15 non-toxic extracts tested, the Sceletium tortuosum water extract exhibited the most promising anxiolytic activity.

CONCLUSIONS

The zebrafish model was effective in studying anxiety-related behavior. Thus, the study confirmed that S. tortuosum mitigates anxiety in zebrafish larvae, a step towards the full in vivo validation of the traditional use of the plant.

Dual role of T-type calcium channels in anxiety-related behavior

T-type calcium channels are low voltage activated calcium channels that are widely expressed in various brain regions including stress-responsive regions. These channels regulate the diverse functions of the central nervous system, and modulation of these channels is shown to modulate the anxiety. Studies have described that modulation of T-type calcium channels may either aggravate or ameliorate anxiety-related behavior, suggesting the dual role of these channels. The studies employing animals with overexpression of T-type calcium channels reported their anxiety-inducing role. Therefore, the blockade of these channels using various pharmacological agents such as ethosuximide, plant extracts of linalool or rosemary, and corticotropin-releasing factor (CRF) is reported to ameliorate anxiety. On the contrary, knockout of the gene encoding these channels predisposes the rodents to anxiety-related disorders, suggesting the anxiety-attenuating role of these channels. It may be possible that these channels in normal or basal state attenuate anxiety, whereas activation of these channels in stressful condition may produce anxiety. The present review describes the dual role of T-type calcium channels in anxiety-related behavior in both preclinical and clinical studies.

Efficacy and safety of a novel topical agent for gallstone dissolution: 2-methoxy-6-methylpyridine

BACKGROUND

Although methyl-tertiary butyl ether (MTBE) is the only clinical topical agent for gallstone dissolution, its use is limited by its side effects mostly arising from a relatively low boiling point (55 °C). In this study, we developed the gallstone-dissolving compound containing an aromatic moiety, named 2-methoxy-6-methylpyridine (MMP) with higher boiling point (156 °C), and compared its effectiveness and toxicities with MTBE.

METHODS

The dissolubility of MTBE and MMP in vitro was determined by placing human gallstones in glass containers with either solvent and, then, measuring their dry weights. Their dissolubility in vivo was determined by comparing the weights of solvent-treated gallstones and control (dimethyl sulfoxide)-treated gallstones, after directly injecting each solvent into the gallbladder in hamster models with cholesterol and pigmented gallstones.

RESULTS

In the in vitro dissolution test, MMP demonstrated statistically higher dissolubility than did MTBE for cholesterol and pigmented gallstones (88.2% vs. 65.7%, 50.8% vs. 29.0%, respectively; P < 0.05). In the in vivo experiments, MMP exhibited 59.0% and 54.3% dissolubility for cholesterol and pigmented gallstones, respectively, which were significantly higher than those of MTBE (50.0% and 32.0%, respectively; P < 0.05). The immunohistochemical stains of gallbladder specimens obtained from the MMP-treated hamsters demonstrated that MMP did not significantly increase the expression of cleaved caspase 9 or significantly decrease the expression of proliferation cell nuclear antigen.

CONCLUSIONS

This study demonstrated that MMP has better potential than does MTBE in dissolving gallstones, especially pigmented gallstones, while resulting in lesser toxicities.

Cannabidiol modulates phosphorylated rpS6 signalling in a zebrafish model of Tuberous Sclerosis Complex

Tuberous sclerosis complex (TSC) is a rare disease caused by mutations in the TSC1 or TSC2 genes and is characterized by widespread tumour growth, intractable epilepsy, cognitive deficits and autistic behaviour. CBD has been reported to decrease seizures and inhibit tumour cell progression, therefore we sought to determine the influence of CBD on TSC pathology in zebrafish carrying a nonsense mutation in the tsc2 gene. CBD treatment from 6 to 7 days post-fertilization (dpf) induced significant anxiolytic actions without causing sedation. Furthermore, CBD treatment from 3 dpf had no impact on tsc2^-/- larvae motility nor their survival. CBD treatment did, however, reduce the number of phosphorylated rpS6 positive cells, and their cross-sectional cell size. This suggests a CBD mediated suppression of mechanistic target of rapamycin (mTOR) activity in the tsc2^-/- larval brain. Taken together, these data suggest that CBD selectively modulates levels of phosphorylated rpS6 in the brain and additionally provides an anxiolytic effect. This is pertinent given the alterations in mTOR signalling in experimental models of TSC. Additional work is necessary to identify upstream signal modulation and to further justify the use of CBD as a possible therapeutic strategy to manage TSC.