Anxiolytic and anti-stress effects of acute administration of acetyl-L-carnitine in zebrafish

Studies have suggested that oxidative stress may contribute to the pathogenesis of mental disorders. In this context, molecules with antioxidant activity may be promising agents in the treatment of these deleterious conditions. Acetyl-L-carnitine (ALC) is a multi-target molecule that modulates the uptake of acetyl-CoA into the mitochondria during fatty acid oxidation, acetylcholine production, protein, and membrane phospholipid synthesis, capable of promoting neurogenesis in case of neuronal death. Moreover, neurochemical effects of ALC include modulation of brain energy and synaptic transmission of multiple neurotransmitters, including expression of type 2 metabotropic glutamate (mGlu2) receptors. The aim of this study was to investigate the effects of ALC in zebrafish by examining behavioral and biochemical parameters relevant to anxiety and mood disorders in zebrafish. ALC presented anxiolytic effects in both novel tank and light/dark tests and prevented the anxietylike behavior induced by an acute stressor (net chasing). Furthermore, ALC was able to prevent the lipid peroxidation induced by acute stress in the zebrafish brain. The data presented here warrant further investigation of ALC as a potential agent in the treatment of neuropsychiatric disorders. Its good tolerability also subsidizes the additional studies necessary to assess its therapeutic potential in clinical settings

Enriched environment prevents oxidative stress in zebrafish submitted to unpredictable chronic stress

Background. The enriched environment (EE) is a laboratory housing model that emerged from efforts to minimize the impact of environmental conditions on laboratory animals. Recently, we showed that EE promoted positive effects on behavior and cortisol levels in zebrafish submitted to the unpredictable chronic stress (UCS) protocol. Here, we expanded the characterization of the effects of UCS protocol by assessing parameters of oxidative status in the zebrafish brain and reveal that EE protects against the oxidative stress induced by chronic stress. Methods. Zebrafish were exposed to EE (21 or 28 days) or standard housing conditions and subjected to the UCS protocol for seven days. Oxidative stress parameters (lipid peroxidation (TBARS), reactive oxygen species (ROS) levels, non-protein thiol (NPSH) and total thiol (SH) levels, superoxide dismutase (SOD) and catalase (CAT) activities were measured in brain homogenate. Results. Our results revealed that UCS increased lipid peroxidation and ROS levels, while decreased NPSH levels and SOD activity, suggesting oxidative damage. EE for 28 days prevented all changes induced by the UCS protocol, and EE for 21 days prevented the alterations on NPSH levels, lipid peroxidation and ROS levels. Both EE for 21 or 28 days increased CAT activity. Discussion. Our findings reinforce the idea that EE exerts neuromodulatory effects in the zebrafish brain. EE promoted positive effects as it helped maintain the redox homeostasis, which may reduce the susceptibility to stress and its oxidative impact

Environmental enrichment modulates the response to chronic stress in zebrafish

Several studies have shown that manipulations to the housing environment modulate susceptibility to stress in laboratory animals, mainly in rodents. Environmental enrichment (EE) is one such manipulation that promotes neuroprotection and neurogenesis, besides affecting behaviors such as drug self-administration. Zebrafish are a popular and useful animal model for behavioral neuroscience studies; however, studies evaluating the impact of housing conditions in this species are scarce. In this study, we verified the effects of EE on behavioral (novel tank test) and biochemical [cortisol and reactive oxygen species (ROS)] parameters in zebrafish submitted to unpredictable chronic stress (UCS). Consistent with our previous findings, UCS increased anxiety-like behavior, cortisol and ROS levels in zebrafish. EE for 21 or 28 days attenuated the effects induced by UCS on behavior and cortisol, and prevented the effects on ROS levels. Our findings reinforce the idea that EE exerts neuromodulatory effects across species, reducing vulnerability to stress and its biochemical impact. Also, these results indicate that zebrafish is a suitable model animal to study the behavioral effects and neurobiological mechanisms related to EE

Efeitos da n-acetilcisteína em modelos de estresse crônico imprevisível e exposição ao etanol em peixes-zebra

O estresse crônico e o abuso de álcool são fatores que predispõem os indivíduos a desenvolver transtornos mentais, condições que impactam na qualidade de vida do indivíduo e contribuem para a morbidade e a mortalidade global. A farmacoterapêutica disponível para tratar esses pacientes apresenta eficácia limitada e alta incidência de efeitos adversos. O estresse oxidativo, a hiperativação glutamatérgica, a depleção de glutationa e a neuroinflamação fazem parte dos achados observados em estudos pré-clínicos e clínicos nessas condições. A Nacetilcisteína (NAC) é uma molécula promissora para o tratamento de uma variedade de condições psiquiátricas. Esse fármaco atua em diversos alvos relevantes para o tratamento de transtornos mentais, incluindo ansiedade, depressão e abuso de álcool. Na presente tese, investigamos os efeitos da NAC nesses contextos utilizando como organismo modelo o peixezebra. No modelo de estresse crônico imprevisível, os animais apresentaram aumento na ansiedade (aumento no tempo na área inferior e diminuição nas entradas e tempo de permanência na área superior do aquário) no teste de tanque novo, lipoperoxidação, aumento nas espécies reativas de oxigênio e redução nos níveis de glutationa e na atividade das enzimas superóxido dismutase e catalase. A NAC reverteu o comportamento ansiogênico e o dano oxidativo. No modelo de exposição aguda ao etanol os animais apresentaram dano motor (diminuição da distância e número total de cruzamentos entre as diferentes áreas do aquário), comportamento ansiogênico (diminuição nas entradas e tempo de permanência na área superior do aquário), dano lipídico, aumento nas espécies reativas de oxigênio e depleção de glutationa. A NAC preveniu os efeitos comportamentais e bioquímicos induzidos pela exposição aguda ao etanol. Finalmente, avaliamos os efeitos da NAC em animais abstinentes após exposição crônica ao etanol por oito dias. 24 horas após oito dias de exposição intermitente, o comportamento dos peixes foi testado no teste de tanque novo. A abstinência induziu comportamento ansiogênico (aumento no tempo na área inferior e diminuição nas entradas e tempo de permanência na área superior do aquário) e desequilíbrio do status oxidativo, com peroxidação lipídica, diminuição da glutationa e das atividades da superóxido dismutase e catalase. NAC preveniu os danos. Nosso estudo agrega importantes achados que contribuem para o corpo de evidências existentes que apoiam a avaliação e utilização clínica da NAC em transtornos mentais e condições associadas ao abuso de substâncias.Chronic stress and alcohol abuse are factors that predispose individuals to develop mental disorders, conditions that impact on the individual quality of life and contribute to overall morbidity and mortality. Pharmacotherapeutics available to treat these patients have limited efficacy and a high incidence of adverse effects. Oxidative stress, glutamatergic hyperactivation, glutathione depletion, and neuroinflammation are part of the findings observed in preclinical and clinical studies in these conditions. N-acetylcysteine (NAC) is a promising molecule for the treatment of a variety of psychiatric conditions. This drug acts on several relevant targets for the treatment of mental disorders, including anxiety, depression and alcohol abuse. In the present thesis, we investigated the effects of NAC in these contexts using zebrafish as an organism model. In the unpredictable chronic stress, the animals showed an increase in anxiety (increase in the time in the bottom area and decrease in the entries and time in the top area of the tank) in the novel tank test, lipoperoxidation, reactive oxygen species increase and reduction in glutathione levels and activity of the superoxide dismutase and catalase enzymes. NAC reversed anxiogenic behavior and oxidative damage. In the acute exposure to ethanol, the animals presented motor damage (decrease of distance and a total number of crossings between different areas of the tank), anxiogenic behavior (decrease in entries and time in the top area of the tank), lipid damage, reactive oxygen species increase and glutathione depletion. NAC prevented the behavioral and biochemical effects induced by acute exposure to ethanol. Finally, we evaluated the effects of NAC on abstinent animals after chronic exposure to ethanol for eight days. 24 hours after eight days of intermittent exposure, fish behavior was tested in the novel tank test. Abstinence induced anxiogenic behavior (increase in the time in the bottom and decrease in the entries and time in the top area of the tank) and oxidative status imbalance, lipid peroxidation, reduction of glutathione and superoxide dismutase and catalase activities. NAC prevented the damage. Our study aggregates important findings that contribute to the body of evidence supporting the assessment and clinical use of NAC in mental disorders and conditions associated with substance abuse