Delayed behavioral and genomic responses to acute combined stress in zebrafish, potentially relevant to PTSD and other stress-related disorders: Focus on neuroglia, neuroinflammation, apoptosis and epigenetic modulation

Minocycline reduces neurobehavioral deficits evoked by chronic unpredictable stress in adult zebrafish

Chronic stress-related brain disorders are widespread and debilitating, and often cause lasting neurobehavioral deficits. Minocycline, a common antibiotic and an established inhibitor of microglia, emerges as potential treatment of these disorders. The zebrafish (Danio rerio) is an important emerging model organism in translational neuroscience and stress research. Here, we evaluated the potential of minocycline to correct microglia-mediated behavioral, genomic and neuroimmune responses induced by chronic unpredictable stress (CUS) in adult zebrafish. We demonstrated that CUS evoked overt behavioral deficits in the novel tank, light-dark box and shoaling tests, paralleled by elevated stress hormones (CRH, ACTH and cortisol), and upregulated brain expression of the 'neurotoxic M1' microglia-specific biomarker gene (MHC-2) and pro-inflammatory cytokine genes (IL-1β, IL-6 and IFN-γ). CUS also elevated peripheral (whole-body) pro-inflammatory (IL-1β, IFN-γ) and lowered anti-inflammatory cytokines (IL-4 and IL-10), as well as reduced whole-brain serotonin, dopamine and norepinephrine levels, and increased brain dopamine and serotonin turnover. In contrast, minocycline attenuated most of these effects, also reducing CUS-elevated peripheral levels of IL-6 and IFN-γ. Collectively, this implicates microglia in zebrafish responses to chronic stress, and suggests glial pathways as potential evolutionarily conserved drug targets for treating stress-evoked neuropathogenesis. Our findings also support the growing translational value of zebrafish models for understanding complex molecular mechanisms of brain pathogenesis and its therapy.

Acute Behavioral and Neurochemical Effects of Sulpiride in Adult Zebrafish

Affective and psychotic disorders are highly prevalent and severely debilitating mental illnesses that often remain untreated or treatment-resistant. Sulpiride is a common antipsychotic (neuroleptic) drug whose well-established additional (e.g., antidepressant) therapeutic effects call for further studies of a wider spectrum of its CNS effects. Here, we examined effects of acute 20-min exposure to sulpiride (50-200 mg/L) on anxiety- and depression-like behaviors, as well as on brain monoamines, in adult zebrafish (Danio rerio). Overall, sulpiride exerted overt anxiolytic-like effects in the novel tank test and showed tranquilizing-like effects in the zebrafish tail immobilization test, accompanied by lowered whole-brain dopamine and its elevated turnover, without affecting serotonin or norepinephrine levels and their turnover. Taken together, these findings support complex behavioral pharmacology of sulpiride in vivo and reconfirm high sensitivity of zebrafish-based screens to this and, likely, other related clinically active neuroleptics.

Activation of NOS-cGMP pathways promotes stress-induced sensitization of behavioral responses in zebrafish

Nitric oxide (NO) is a molecule involved in plasticity across levels and systems. The role of NOergic pathways in stress-induced sensitization (SIS) of behavioral responses, in which a particular stressor triggers a state of hyper-responsiveness to other stressors after an incubation period, was assessed in adult zebrafish. In this model, adult zebrafish acutely exposed to a fear-inducing conspecific alarm substance (CAS) and left undisturbed for an incubation period show increased anxiety-like behavior 24 h after exposure. CAS increased forebrain glutamate immediately after stress and 30 min after stress, an effect that was accompanied by increased nitrite levels immediately after stress, 30 min after stress, 90 min after stress, and 24 h after stress. CAS also increased nitrite levels in the head kidney, where cortisol is produced in zebrafish. CAS-elicited nitrite responses in the forebrain 90 min (but not 30 min) after stress were prevented by a NOS-2 blocker. Blocking NOS-1 30 min after stress prevents SIS; blocking NOS-2 90 min after stress also prevents stress-induced sensitization, as does blocking calcium-activated potassium channels in this latter time window. Stress-induced sensitization is also prevented by blocking guanylate cyclase activation in both time windows, and cGMP-dependent channel activation in the second time window. These results suggest that different NO-related pathways converge at different time windows of the incubation period to induce stress-induced sensitization.

Efficacy of ginsenoside Rg1 on rodent models of depression: A systematic review and meta-analysis

RATIONALE

Depression is a prevalent psychiatric disease, and ginsenoside Rg1 is a bioactive compound extracted from the root of Panax ginseng C.A.Mey. To systematically investigate the effectiveness of Rg1 in rodent models of depression and provide evidence-based references for treating depression.

METHODS

Electronic searches for rodent studies were performed from inception to October 2022, e.g., PUBMED and EMBASE. Data extraction and quality evaluation were performed for the references, and meta-analysis was performed on the selected data using Review Manager 5.3.5. The outcomes were analyzed via a random-effect model and presented as mean difference (MD) with 95% confidence intervals (CIs).

RESULTS

A total of 24 studies and 678 animals were included in this meta-analysis. Rg1 remarkably improved depressive-like symptoms of depressed rodents, including the sucrose preference test (25.08, 95% CI: 20.17-30.00, Z = 10.01, P < 0.00001), forced swimming test (MD = -37.69, 95% CI: (-45.18, -30.2); Z = 9.86, P < 0.00001), and the tail suspension test (MD = -22.93, seconds, 95% CI: (-38.49, -7.37); Z = 2.89, P = 0.004).

CONCLUSIONS

The main antidepressant mechanism of Rg1 was concluded to be the neurotransmitter system, oxidant stress system, and inflammation. Conclusively, this study indicated the possible protective and therapeutic effects of Rg1 for treating depression via multiple mechanisms.

Zebrafish Model in Illuminating the Complexities of Post-Traumatic Stress Disorders: A Unique Research Tool

Post-traumatic stress disorder (PTSD) is a debilitating psychological condition that may develop in certain individuals following exposure to life-threatening or traumatic events. Distressing symptoms, including flashbacks, are characterized by disrupted stress responses, fear, anxiety, avoidance tendencies, and disturbances in sleep patterns. The enduring effects of PTSD can profoundly impact personal and familial relationships, as well as social, medical, and financial stability. The prevalence of PTSD varies among different populations and is influenced by the nature of the traumatic event. Recently, zebrafish have emerged as a valuable model organism in studying various conditions and disorders. Zebrafish display robust behavioral patterns that can be effectively quantified using advanced video-tracking tools. Due to their relatively simple nervous system compared to humans, zebrafish are particularly well suited for behavioral investigations. These unique characteristics make zebrafish an appealing model for exploring the underlying molecular and genetic mechanisms that govern behavior, thus offering a powerful comparative platform for gaining deeper insights into PTSD. This review article aims to provide updates on the pathophysiology of PTSD and the genetic responses associated with psychological stress. Additionally, it highlights the significance of zebrafish behavior as a valuable tool for comprehending PTSD better. By leveraging zebrafish as a model organism, researchers can potentially uncover novel therapeutic interventions for the treatment of PTSD and contribute to a more comprehensive understanding of this complex condition.

Inflammation in Development and Aging: Insights from the Zebrafish Model

Zebrafish are an emergent animal model to study human diseases due to their significant genetic similarity to humans, swift development, and genetic manipulability. Their utility extends to the exploration of the involvement of inflammation in host defense, immune responses, and tissue regeneration. Additionally, the zebrafish model system facilitates prompt screening of chemical compounds that affect inflammation. This study explored the diverse roles of inflammatory pathways in zebrafish development and aging. Serving as a crucial model, zebrafish provides insights into the intricate interplay of inflammation in both developmental and aging contexts. The evidence presented suggests that the same inflammatory signaling pathways often play instructive or beneficial roles during embryogenesis and are associated with malignancies in adults.

Neuronal and Astroglial Localization of Glucocorticoid Receptor GRα in Adult Zebrafish Brain (Danio rerio)

Glucocorticoid receptor α (GRα), a ligand-regulated transcription factor, mainly activated by cortisol in humans and fish, mediates neural allostatic and homeostatic functions induced by different types of acute and chronic stress, and systemic inflammation. Zebrafish GRα is suggested to have multiple transcriptional effects essential for normal development and survival, similarly to mammals. While sequence alignments of human, monkey, rat, and mouse GRs have shown many GRα isoforms, we questioned the protein expression profile of GRα in the adult zebrafish (Danio rerio) brain using an alternative model for stress-related neuropsychiatric research, by means of Western blot, immunohistochemistry and double immunofluorescence. Our results identified four main GRα-like immunoreactive bands (95 kDa, 60 kDa, 45 kDa and 35 kDa), with the 95 kDa protein showing highest expression in forebrain compared to midbrain and hindbrain. GRα showed a wide distribution throughout the antero-posterior zebrafish brain axis, with the most prominent labeling within the telencephalon, preoptic, hypothalamus, midbrain, brain stem, central grey, locus coeruleus and cerebellum. Double immunofluorescence revealed that GRα is coexpressed in TH+, β₂-AR+ and vGLUT+ neurons, suggesting the potential of GRα influences on adrenergic and glutamatergic transmission. Moreover, GRα was co-localized in midline astroglial cells (GFAP+) within the telencephalon, hypothalamus and hindbrain. Interestingly, GRα expression was evident in the brain regions involved in adaptive stress responses, social behavior, and sensory and motor integration, supporting the evolutionarily conserved features of glucocorticoid receptors in the zebrafish brain.

Roles of neuropathology-associated reactive astrocytes: a systematic review

In the contexts of aging, injury, or neuroinflammation, activated microglia signaling with TNF-α, IL-1α, and C1q induces a neurotoxic astrocytic phenotype, classified as A1, A1-like, or neuroinflammatory reactive astrocytes. In contrast to typical astrocytes, which promote neuronal survival, support synapses, and maintain blood-brain barrier integrity, these reactive astrocytes downregulate supportive functions and begin to secrete neurotoxic factors, complement components like C3, and chemokines like CXCL10, which may facilitate recruitment of immune cells across the BBB into the CNS. The proportion of pro-inflammatory reactive astrocytes increases with age through associated microglia activation, and these pro-inflammatory reactive astrocytes are particularly abundant in neurodegenerative disorders. As the identification of astrocyte phenotypes progress, their molecular and cellular effects are characterized in a growing array of neuropathologies.

Efficacy of combined subanesthetic ketamine infusion and cervical sympathetic blockade as a symptomatic treatment of PTSD/TBI in a special forces patient with a 1-year follow-up: A case report

Co-occurrence of posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) symptoms are particularly prevalent in the special operations forces' community, along with other related conditions (e.g., endocrine dysregulation, sleep disorders, chronic pain). Ketamine infusion (KI) has been shown to increase neuroplasticity as well as memory improvement and cervical sympathetic block (CSB) has been shown to improve cognitive function, reduce sympathetic overactivity, and improve other symptoms of PTSD. We want to report the efficacious use of a single intervention consisting of bilateral CSB technique with subanesthetic KI X5 in a Special Operations Forces patient, diagnosed with PTSD with comorbid TBI, evaluated during treatment and at 1-year follow-up. We postulated KI and CSB would have a synergistic effect. Our patient received KI starting at 0.5 mg/kg, which was escalated daily. KI was combined with right-sided ultrasound-guided CSB (C6 and C4 levels). This was followed the next day by left-sided CSB and KI. Patient's PTSD symptoms were evaluated using the Posttraumatic Stress Disorder Checklist (PCL-5), Beck Depression Inventory (BDI), Beck Anxiety Inventory (BAI), suicidal ideation and other related factors by Concise Health Risk Tracking Self Report (CHRTSR). All measures were assessed prior to treatment, during treatment, and 394 days after. KI combined with CSB showed immediate and prolonged benefits 394 days later regarding the symptoms of PTSD, anxiety, depression, suicidal ideation, and cognitive deterioration (patient report). KI combined with CSB can markedly reduce symptoms of PTSD, psychiatric comorbidities, and cognitive dysfunction.

Animal Inflammation-Based Models of Neuropsychiatric Disorders

Mounting evidence links psychiatric disorders to central and systemic inflammation. Experimental (animal) models of psychiatric disorders are important tools for translational biopsychiatry research and CNS drug discovery. Current experimental models, most typically involving rodents, continue to reveal shared fundamental pathological pathways and biomarkers underlying the pathogenetic link between brain illnesses and neuroinflammation. Recent data also show that various proinflammatory factors can alter brain neurochemistry, modulating the levels of neurohormones and neurotrophins in neurons and microglia. The role of "active" glia in releasing a wide range of proinflammatory cytokines also implicates glial cells in various psychiatric disorders. Here, we discuss recent animal inflammation-related models of psychiatric disorders, focusing on their translational perspectives and the use of some novel promising model organisms (zebrafish), to better understand the evolutionally conservative role of inflammation in neuropsychiatric conditions.

Neuroprotective Potential of Hydroalcoholic Extract of Centella asiatica Against 3-Nitropropionic Acid-Induced Huntington's Like Symptoms in Adult Zebrafish

Huntington's disease (HD) is an inherited neurodegenerative disease. 3-Nitropropionic acid (3-NP) causes increased reactive oxygen species production and neuroinflammation. Centella asiatica (CA) is a strong antioxidant. The aim of this study is to investigate the effect of hydroalcoholic extract of C. asiatica (HA-CA) on 3-NP-induced HD in adult zebrafish. Adult zebrafish (∼5-6 months old) weighing 470 to 530 mg was used and treated with 3-NP (5 mg/kg intraperitoneal [i.p.]). The animals received HA-CA (80 and 100 mg/L) daily for up to 28 days in water. Tetrabenazine (3 mg/kg i.p.) was used as a standard drug. We have done an open field test (for locomotor activity), a novel tank diving test (for anxiety), and a light and dark tank test (for memory), followed by biochemical analysis (acetyl-cholinesterase [AchEs], nitrite, lipid peroxidation [LPO], and glutathione [GSH]) and histopathology to further confirm memory dysfunctions. 3-NP-treated zebrafish exhibit reductions in body weight, progressive neuronal damage, cognition, and locomotor activity. The HA-CA group significantly reduced the 3-NP-induced increase in LPO, AchEs, and nitrite levels while decreasing GSH levels. Oral administration of HA-CA (80 or 100 mg/L) significantly reduces 3-NP-induced changes in body weight and behaviors, in addition to neuroinflammation in the brain by lowering tumor necrosis factor-α and interleukin-1β levels. Moreover, HA-CA significantly decreases the 3-NP-induced neuronal damage in the brain. HA-CA ameliorates neurotoxicity and neurobehavioral deficits in 3-NP-induced HD-like symptoms in adult zebrafish.

Epigenetic histone acetylation modulating prenatal Poly I:C induced neuroinflammation in the prefrontal cortex of rats: a study in a maternal immune activation model

Introduction: Neuroinflammation in the central nervous system, particularly the prefrontal cortex (PFC), plays a role in the pathogenesis of schizophrenia, which has been found to be associated with maternal immune activation (MIA). Recent evidence suggests that epigenetic regulation involves in the MIA-induced neurodevelopmental disturbance. However, it is not well-understood how epigenetic modulation is involved in the neuroinflammation and pathogenesis of schizophrenia.

Methods: This study explored the modulation of histone acetylation in both neuroinflammation and neurotransmission using an MIA rat model induced by prenatal polyriboinosinic-polyribocytidylic acid (Poly I:C) exposure, specifically examining those genes that were previously observed to be impacted by the exposure, including a subunit of nuclear factor kappa-B (Rela), Nod-Like-Receptor family Pyrin domain containing 3 (Nlrp3), NMDA receptor subunit 2A (Grin2a), 5-HT2A (Htr2a), and GABAA subunit β3 (Gabrb3).

Results: Our results revealed global changes of histone acetylation on H3 (H3ace) and H4 (H4ace) in the PFC of offspring rats with prenatal Poly I:C exposure. In addition, it revealed enhancement of both H3ace and H4ace binding on the promoter region of Rela, as well as positive correlations between Rela and genes encoding histone acetyltransferases (HATs) including CREB-binding protein (CBP) and E1A-associated protein p300 (EP300). Although there was no change in H3ace or H4ace enrichment on the promoter region of Nlrp3, a significant enhancement of histone deacetylase 6 (HDAC6) binding on the promoter region of Nlrp3 and a positive correlation between Nlrp3 and Hdac6 were also observed. However, prenatal Poly I:C treatment did not lead to any specific changes of H3ace and H4ace on the promoter region of the target genes encoding neurotransmitter receptors in this study.

Discussion: These findings demonstrated that epigenetic modulation contributes to NF-κB/NLRP3 mediated neuroinflammation induced by prenatal Poly I:C exposure via enhancement of histone acetylation of H3ace and H4ace on Rela and HDAC6-mediated NLRP3 transcriptional activation. This may further lead to deficits in neurotransmissions and schizophrenia-like behaviors observed in offspring.

Effect of Early-Life Exposure of Polystyrene Microplastics on Behavior and DNA Methylation in Later Life Stage of Zebrafish

Microplastic contamination has received increasing attention in recent years, and concern regarding the toxicity of microplastics to the environment and humans has increased. In this study, we investigated the neurodevelopmental toxicity of polystyrene microplastics (PSMPs) in the zebrafish Danio rerio under different exposure scenarios. Zebrafish were exposed to PSMPs during embryonic stage and then allowed the fish to recover. The neurodevelopmental toxic responses were investigated using fish behavior and behavior-related gene expression. Early-life exposure to PSMPs did not alter fish behavior at the early stage; however, it led to hyperactivity later life stage. Generally, oxidative stress (i.e., sod2 and nrf2a)- and nervous system (i.e., slc6a4b, npy, and nrbf2)-related gene expression increased in all PSMPs-exposed fish. DNA hypomethylation was observed in fish challenged for a second time using the same PSMPs. Taken together, the current results imply that PSMPs have neurodevelopmental toxic potential when introduced early in life.

Biology of cyclooxygenase-2: An application in depression therapeutics

Depressive Disorder is a common mood disorder or affective disorder that is dominated by depressed mood. It is characterized by a high incidence and recurrence. The onset of depression is related to genetic, biological and psychosocial factors. However, the pathogenesis is still unclear. In recent years, there has been an increasing amount of research on the inflammatory hypothesis of depression, in which cyclo-oxygen-ase 2 (COX-2), a pro-inflammatory cytokine, is closely associated with depression. A variety of chemical drugs and natural products have been found to exert therapeutic effects by modulating COX-2 levels. This paper summarizes the relationship between COX-2 and depression in terms of neuroinflammation, intestinal flora, neurotransmitters, HPA axis, mitochondrial dysfunction and hippocampal neuronal damage, which can provide a reference for further preventive control, clinical treatment and scientific research on depression.

Understanding how stress responses and stress-related behaviors have evolved in zebrafish and mammals

Stress response is essential for the organism to quickly restore physiological homeostasis disturbed by various environmental insults. In addition to well-established physiological cascades, stress also evokes various brain and behavioral responses. Aquatic animal models, including the zebrafish (Danio rerio), have been extensively used to probe pathobiological mechanisms of stress and stress-related brain disorders. Here, we critically discuss the use of zebrafish models for studying mechanisms of stress and modeling its disorders experimentally, with a particular cross-taxon focus on the potential evolution of stress responses from zebrafish to rodents and humans, as well as its translational implications.

Classical HDACs in the regulation of neuroinflammation

Neuroinflammation is a key factor of the pathology of various neurological diseases (brain injury, depression, neurodegenerative diseases). It is a complex and orderly process that relies on various types of glial cells and peripheral immune cells. Inhibition of neuroinflammation can reduce the severity of neurological diseases. The initiation, progression, and termination of inflammation require gene activation, epigenetic modification, transcriptional translation, and post-translational regulation, all of which are tightly regulated by different enzymes. Epigenetics refers to the regulation of epigenetic gene expression by epigenetic changes (DNA methylation, histone modification, and non-coding RNAs such as miRNA) that are not dependent on changes in gene sequence and are heritable. Histone deacetylases (HDACs) are a group of important enzymes that regulate epigenetics. They can remove the acetyl group on the lysine ϵ-amino group of the target protein, thereby affecting gene transcription or altering protein activity. HDACs are involved in the regulation of immunity and inflammation. HDAC inhibitor (HDACi) has also become a new hotspot in the research of anti-inflammatory drugs. Therefore, the aim of the current review is to discuss and summarize the role and mechanism of different HDACs in neuroinflammation and the corresponding role of HDACi in neurological diseases, and to providing new ideas for future research on neuroinflammation-related diseases and drug development.

Zebrafish as an Animal Model for Testing Agents with Antidepressant Potential

Depression is a serious mental disease that, according to statistics, affects 320 million people worldwide. Additionally, a current situation related to the COVID-19 pandemic has led to a significant deterioration of mental health in people around the world. So far, rodents have been treated as basic animal models used in studies on this disease, but in recent years, Danio rerio has emerged as a new organism that might serve well in preclinical experiments. Zebrafish have a lot of advantages, such as a quick reproductive cycle, transparent body during the early developmental stages, high genetic and physiological homology to humans, and low costs of maintenance. Here, we discuss the potential of the zebrafish model to be used in behavioral studies focused on testing agents with antidepressant potential.

Using zebrafish (Danio rerio) models to understand the critical role of social interactions in mental health and wellbeing

Social behavior represents a beneficial interaction between conspecifics that is critical for maintaining health and wellbeing. Dysfunctional or poor social interaction are associated with increased risk of physical (e.g., vascular) and psychiatric disorders (e.g., anxiety, depression, and substance abuse). Although the impact of negative and positive social interactions is well-studied, their underlying mechanisms remain poorly understood. Zebrafish have well-characterized social behavior phenotypes, high genetic homology with humans, relative experimental simplicity and the potential for high-throughput screens. Here, we discuss the use of zebrafish as a candidate model organism for studying the fundamental mechanisms underlying social interactions, as well as potential impacts of social isolation on human health and wellbeing. Overall, the growing utility of zebrafish models may improve our understanding of how the presence and absence of social interactions can differentially modulate various molecular and physiological biomarkers, as well as a wide range of other behaviors.

Decoding the role of zebrafish neuroglia in CNS disease modeling

Neuroglia, including microglia and astrocytes, is a critical component of the central nervous system (CNS) that interacts with neurons to modulate brain activity, development, metabolism and signaling pathways. Thus, a better understanding of the role of neuroglia in the brain is critical. Complementing clinical and rodent data, the zebrafish (Danio rerio) is rapidly becoming an important model organism to probe the role of neuroglia in brain disorders. With high genetic and physiological similarity to humans and rodents, zebrafish possess some common (shared), as well as some specific molecular biomarkers and features of neuroglia development and functioning. Studying these common and zebrafish-specific aspects of neuroglia may generate important insights into key brain mechanisms, including neurodevelopmental, neurodegenerative, neuroregenerative and neurological processes. Here, we discuss the biology of neuroglia in humans, rodents and fish, its role in various CNS functions, and further directions of translational research into the role of neuroglia in CNS disorders using zebrafish models.