Involvement of GABAergic system in the antidepressant-like effects of chrysin (5,7-dihydroxyflavone) in ovariectomized rats in the forced swim test: comparison with neurosteroids
Graphical abstract
Introduction
The neurobiology of depression involves neurotransmitters and hormonal functions. The prevalence of depression is higher in women than in men, indicating sexual dimorphism [1], which is partially attributable to cultural factors but also biological effects of sexual hormones (i.e., estradiol, progesterone, and their reduced metabolites, such as allopregnanolone). Sexual hormones can interact with neurotransmitters systems, the stress response axis, and neuronal plasticity [2]. The steroid hormones progesterone and allopregnanolone produce time-dependent effects on neurotransmitter pathways via both direct and indirect actions. Such indirect actions can modulate the γ-aminobutyric acid (GABA)ergic system. Low brain concentrations of steroid hormones can decrease GABAergic neurotransmission and produce anxiety- and depression-like behavior [3]. The premenstrual period, postpartum period, and natural or surgical menopause are characterized by low concentrations of ovarian hormones that can trigger symptoms of depression and anxiety, which evolve into depression and anxiety disorders in many cases [4,5]. Steroid hormones have been proposed as potential therapeutic agents to treat symptoms of anxiety and depression.
Chemical compounds that are derived from plants represent also a potential therapeutic alternative to ameliorate the emotional and affective symptoms of menopause. Such plants as M. tomentosa, M. grandiflora, and Hypericum perforatum, among others, have been used as traditional medicines for the treatment of anxiety and depression symptoms. Metabolites that are contained in plant extracts have been proposed to interact with the GABAergic system [6]. For example, some flavonoids have been shown in preclinical studies to exert potential anxiolytic-like effects through actions on GABAA receptors [7].
The flavonoid chrysin (5,7-dihydroxyflavone) has multiple biological effects. Chronic treatment with chrysin (5 or 20 mg/kg for 28 days) exerted antidepressant-like effects in cycling female mice that were exposed to chronic unpredictable stress and then evaluated in the tail suspension test [8]. Chrysin treatment at the same doses for 14 days in an olfactory bulbectomy model exerted antidepressant-like effects in the forced swim test (FST) [9]. These effects were similar to fluoxetine and associated with neuroplasticity that involved an increase in brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the hippocampus and prefrontal cortex in mice [10]. These mechanisms imply changes in neurotrophin levels and plastic changes that are related to chronic treatment with chrysin for 14-28 days. Chrysin has also been shown to exert anxiolytic-like effects in male mice and ovariectomized female rats at lower doses [[11], [12], [13], [14], [15]]. These effects were related to activation of the GABAA receptor system [7]. Such actions on GABAA receptors were observed at the first administration of chrysin, which produced immediate effects, in contrast to the chronic effects of chrysin that were previously reported. However, unknown are the antidepressant-like effects of chrysin in female rats with the absence of ovarian hormones that is caused by ovariectomy.
Ovariectomy is used in rats as a surgical menopause model [16]. From 1-week post-surgery, ovariectomized (OVX) rats exhibited anxiety-like behavior in the elevated plus maze compared with rats in the proestrus-estrus phase, and this effect was even greater at 12 and 15 weeks post-ovariectomy [16,17]. The administration of 17β-estradiol [18,19] and the phytoestrogen genistein [20] significantly reduced anxiety-like behavior in OVX rats through actions on the estrogen β receptor, and these effects were similar to diazepam [17]. Interestingly, some neurosteroids (e.g., progesterone and allopregnanolone) that act on GABAA receptors also exerted anxiolytic- and antidepressant-like effects when they were intraperitoneally injected or microinjected in the lateral septal nucleus, hippocampus, and nucleus accumbens in rats [[21], [22], [23], [24], [25], [26]]. Moreover, N,N-dihexyl-2-(4-fluorophenyl)indole-3-acetamide (FGIN-1-27), a 18-kDa translocator protein agonist that induces neurosteroidogenesis, was shown to produce anxiolytic-like effects in non-mammalian models [27]. Therefore, these neurosteroids act acutely as natural anxiolytic and antidepressant agents.
GABAergic compounds, including neurosteroids and plant-derived flavonoids, exert anxiolytic- and antidepressant-like effects through actions on GABAA receptors, and chrysin has been reported to be a GABAergic compound with anxiolytic properties, but the antidepressant-like effects of chrysin in female rats with the absence ovarian hormones are unknown. The present study investigated the mechanism of action of chrysin to either support or refute its potential use to ameliorate clinical symptoms of depression that are associated with low ovarian hormones, such as during natural or surgical menopause in women. Menopause is a physiological state that is characterized by changes in the sensitivity of serotonergic, dopaminergic, and GABAergic receptors [28,29]. The present study compared the effects of acute chrysin administration with the effects of progesterone and allopregnanolone on depression-like behavior in ovariectomized rats. We evaluated the participation of the GABA binding site on GABAA receptors in the acute antidepressant-like effects of chrysin using the competitive antagonist bicuculline.
Section snippets
Ethics
All of the experimental procedures were strictly performed in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals - National Research Council [30] and Norma Oficial Mexicana para el Cuidado y Uso de Animales de Laboratorio - NOM-062-ZOO [31]. All efforts were made to minimize animal discomfort during the study.
Animals
Sixty-three adult female Wistar rats, weighing 200-250 g at the beginning of the experiments, were used. The rats were housed four per cage
Results
Five rats were removed from the study because they had irregular ovarian cycles. Another two rats were removed from the study because they had evident signs of deteriorating health after ovariectomy. Therefore, the present results correspond to a total of 56 rats that were distributed into eight groups (n = 7/group).
Discussion
The present study explored the mechanism of action of the antidepressant-like effects of the flavonoid Chry compared with P4 and Allo as reference GABAergic compounds with proven antidepressant-like effects in the FST. In OVX rats, Chry exerted behavioral effects that were similar to P4 and Allo. Furthermore, Bic blocked the antidepressant-like effects of Chry, P4, and Allo, thus supporting participation of the GABAergic system in the pharmacological actions of Chry. These findings are relevant
Conclusion
The present findings contribute to our understanding of the mechanisms of action of the flavonoid chrysin by demonstrating that the acute antidepressant-like actions of chrysin in the FST are regulated by the GABA binding site of the GABAA receptor in OVX rats, similar to the actions of some neurosteroids. These findings encourage additional research to explore the utility of chrysin to ameliorate symptoms of depression in humans, particularly in menopause women.
Author Contributions
JFRL and JCE conceived the project, developed the experimental design, and wrote the protocol. JFRL, JCE, FHL, and JAS performed the experiments and measured the behavioral variables. JCE, MGLM, and CM performed the statistical analysis and interpreted the results. JFR, JCE, and CM wrote the manuscript. All of the authors reviewed, discussed, and approved the final version of the manuscript.
Declaration of Competing Interest
There are no conflicts of interest to declare.
Acknowledgements
This study is part of SIREI project no. DGI: 26650201961 registered by J.F. Rodríguez-Landa, which was partially supported by Sistema Nacional de Investigadores CONACyT-México (Exp. 32753), and Programa “Habilitación del Perfil Internacional para Académicos de la Universidad Veracruzana – HAPI-UV, Convocatoria 2019-2” during a research visit the Laboratório de Neurociências e Comportamento, Faculdade de Psicologia, Instituto de Estudos em Saúde e Biológicas, Universidade Federal do Sul e
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