Adolescent stress increases depression-like behaviors and alters the excitatory-inhibitory balance in aged mice

Itaconate inhibits corticosterone-induced necroptosis and neuroinflammation via up-regulating menin in HT22 cells

Corticosterone (CORT) damages hippocampal neurons as well as induces neuroinflammation. The tricarboxylic acid cycle metabolite itaconate has an anti-inflammatory role. Necroptosis is a form of programmed cell death, also known as inflammatory cell death. Menin is a multifunctional scaffold protein, which deficiency aggravates neuroinflammation. In this study, we explored whether itaconate inhibits CORT-induced neuroinflammation as well as necroptosis and further investigated the mediatory role of Menin in this protective effect of itaconate by using an exposure of CORT to HT22 cells (a hippocampal neuronal cell line). The viability of HT22 cells was examined by the cell counting kit 8 (CCK-8). The morphology of HT22 cells was observed by transmission electron microscope (TEM). The expressions of necroptosis-related proteins (p-RIP1/RIP1, p-RIP3/RIP3, and p-MLKL/MLKL) were evaluated by western blotting. The contents of inflammatory factors were detected by an enzyme-linked immunosorbent assay (ELISA) kit. Our results showed that CORT increases the contents of pro-inflammatory factors (IL-1β, TNF-α) as well as decreases the contents of anti-inflammatory factors (IL-4, IL-10) in HT22 cells. We also found that CORT increases the expressions of necroptosis-related proteins (p-RIP1/RIP1, p-RIP3/RIP3, and p-MLKL/MLKL) and decreases the cell viability in HT22 cells, indicating that CORT induces necroptosis in HT22 cells. Itaconate improves CORT-induced neuroinflammation and necroptosis. Furthermore, itaconate upregulates the expression of Menin in CORT-exposed HT22 cells. Importantly, silencing Menin abolishes the antagonistic effect of itaconate on CORT-induced necroptosis and neuroinflammation. In brief, these results indicated that itaconate protects HT22 cells against CORT-induced neuroinflammation and necroptosis via upregulating Menin.

Gamma oscillations in the mPFC: A potential predictive biomarker of depression and antidepressant effects

Gamma oscillations have attracted much attention in the field of mood disorders, but their role in depression remains poorly understood. This study aimed to investigate whether gamma oscillations in the medial prefrontal cortex (mPFC) could serve as a predictive biomarker of depression. Chronic restraint stress (CRS) or lipopolysaccharide (LPS) were used to induce depression-like behaviors in mice; local field potentials (LFPs) in the mPFC were recorded by electrophysiological techniques; We found that both CRS and LPS induced significant depression-like behaviors in mice, including increasing immobility durations in the forced swimming test (FST) and tail suspension test (TST) and increasing the latency to feed in the novelty-suppressed feeding test (NSFT). Electrophysiological results suggested that CRS and LPS significantly reduced low and high gamma oscillations in the mPFC. Furthermore, a single injection of ketamine or scopolamine for 24 h significantly increased gamma oscillations and elicited rapid-acting antidepressant-like effects. In addition, fluoxetine treatment for 21 days significantly increased gamma oscillations and elicited antidepressant-like effects. Taken together, our findings suggest that gamma oscillations are strongly associated with depression, yielding new insights into investigating the predictive biomarkers of depression and the time course of antidepressant effects.

Transcutaneous auricular vagus nerve stimulation ameliorates adolescent depressive- and anxiety-like behaviors via hippocampus glycolysis and inflammation response

BACKGROUND

Transcutaneous auricular vagus nerve stimulation (taVNS) is a crucial neuromodulation therapy for depression, yet its molecular mechanism remains unclear. Here, we aim to unveil the underlying mechanisms of antidepression by systematically evaluating the change of gene expression in different brain regions (i.e., hippocampus, anterior cingulate cortex, and medial prefrontal cortex).

METHODS

The adolescent depression rat model was established by chronic unpredictable mild stress (CUMS), followed by the taVNS treatment for 3 weeks. The open field test (OFT), forced swimming test (FST), elevated plus maze test (EPM), and new object recognition (NOR) test were used to evaluate depressive- and anxiety-like behaviors. Gene expression analysis of three brain regions was conducted by RNA sequencing (RNA-seq) and further bioinformatics methods.

RESULTS

The depressive- and anxiety-like behaviors in CUMS-exposed rats were manifested by decreased spontaneous locomotor activity of OFT, increased immobility time of FST, increased entries and time in the closed arms of EPM, and decreased new object index of NOR. Furthermore, CUMS exposure also led to alterations in gene expression within the hippocampus (HIP), anterior cingulate cortex (ACC), and medial prefrontal cortex (mPFC), suggesting a potential link between adolescent stress and pathological changes within these brain regions. TaVNS could significantly ameliorate depressive- and anxiety-like behaviors. Its effects on these three brain regions were found related to regulation of the metabolism, and there were some brain region-specific findings. Compared with ACC and mPFC, taVNS has a more concrete effect on HIP by regulating the inflammation response and glycolysis.

CONCLUSION

taVNS is capable of ameliorating adolescent depressive- and anxiety-like behaviors by regulating plenty of genes in the three brain regions. Suppressed level of inflammatory response and enhanced glycolysis manifests the dominant role of taVNS in HIP, which provides a theoretical foundation and data support for the molecular mechanism of antidepression by taVNS.

Social environment enrichment alleviates anxiety-like behavior in mice: Involvement of the dopamine system

Rearing environment plays a vital role in maintaining physical and mental health of both animals and humans. Plenty of studies have proved that physical environment enrichment in adolescence has protective effects on emotion, social behavior, learning and memory deficits. However, the following effects of social environment enrichment in adolescence remain largely elusive. Using the paradigm of companion rotation (CR), the present study found that social environment enrichment reduced anxiety-like behaviors of early adult male C57BL/6J mice. CR group also showed significantly higher expression of tyrosine hydroxylase in the ventral tegmental area and dopamine 1 receptor mRNA in the nucleus accumbens shell than control group. Taken together, these findings demonstrate that CR from adolescence to early adulthood can suppress the level of anxiety and upregulate dopaminergic neuron activity in early adult male C57BL/6J mice.

[Movement as a Neuromodulator: How Physical Activity Influences the Physiology of Adolescent Depression]

Movement as a Neuromodulator: How Physical Activity Influences the Physiology of Adolescent Depression Abstract: In the context of adolescent depression, physical activity is becoming increasingly recognized for its positive effects on neuropathology. Current scientific findings indicate that physical training affects the biological effects of depression during adolescence. Yet the pathophysiology of adolescent depression is not yet fully understood. Besides psychosocial and genetic influences, various neurobiological factors are being discussed. One explanation model describes a dysfunction of the hypothalamus-pituitary-adrenal axis (HPA axis) with a sustained elevation in cortisol concentration. Recent studies highlight neuroimmunological processes and a reduced concentration of growth factors as causative factors. These changes appear to lead to a dysregulation of the excitation and inhibition balance of the cerebral cortex as well as to cerebral morphological alterations. Regular physical training can potentially counteract the dysregulation of the HPA axis and normalize cortisol levels. The release of proinflammatory cytokines is inhibited, and the expression of growth factors involved in adult neurogenesis is stimulated. One should ensure the synergistic interaction of biological and psychosocial factors when designing the exercise schedule (endurance or strength training, group or individual sports, frequency, duration, and intensity). Addressing these open questions is essential when integrating physical activity into the guidelines for treating depressive disorders in children and adolescents.

LPS-induced acute neuroinflammation, involving interleukin-1 beta signaling, leads to proteomic, cellular, and network-level changes in the prefrontal cortex of mice

Neuroinflammation induced by peripheral infections leads to various neuropsychiatric symptoms both in humans and laboratory animals, e.g., to the manifestation of sickness behavior that resembles some features of clinical depression. However, in addition to depression-like behavior, there are other symptoms of acute systemic inflammation that can be associated with the impairment of prefrontal cortex (PFC)-regulated cognitive functions. Thus, we investigated the electrophysiological and proteomic alterations of the PFC using brain slices and the lipopolysaccharide (LPS) model of acute peripheral infection in male mice. Based on the gene expression differences of the coreceptor (Il1rap) of interleukin-1 beta (IL-1β) between neuron types in our previous single-cell sequencing dataset, we first compared the electrophysiological effects of IL-1β on PFC pyramidal cells and interneurons. We found that pyramidal cells are more responsive to IL-1β, as could be presumed from our transcriptomic data. To examine the possible circuit-level correlates of the cellular changes, frontal electroencephalographic (EEG) activity and fronto-occipital functional connectivity were analyzed in LPS-treated mice and significant changes were found in the fronto-occipital EEG correlation and coherence in the delta and high-gamma frequency bands. The upregulation of the prefrontal IL-1 system (IL-1β and its receptor) after LPS treatment was revealed by immunoassays simultaneously with the observed EEG changes. Furthermore, we investigated the LPS-induced alterations of the synaptic proteome in the PFC using 2-D differential gel electrophoresis and mass spectrometry and found 48 altered proteins mainly related to cellular signaling, cytoskeletal organization, and carbohydrate/energy metabolism. Thus, our results indicate remarkable electrophysiological and molecular changes in the PFC related to acute systemic inflammation that may explain some of the concomitant behavioral and physiological symptoms.

Integrating the Neurodevelopmental and Dopamine Hypotheses of Schizophrenia and the Role of Cortical Excitation-Inhibition Balance

The neurodevelopmental and dopamine hypotheses are leading theories of the pathoetiology of schizophrenia, but they were developed in isolation. However, since they were originally proposed, there have been considerable advances in our understanding of the normal neurodevelopmental refinement of synapses and cortical excitation-inhibition (E/I) balance, as well as preclinical findings on the interrelationship between cortical and subcortical systems and new in vivo imaging and induced pluripotent stem cell evidence for lower synaptic density markers in patients with schizophrenia. Genetic advances show that schizophrenia is associated with variants linked to genes affecting GABA (gamma-aminobutyric acid) and glutamatergic signaling as well as neurodevelopmental processes. Moreover, in vivo studies on the effects of stress, particularly during later development, show that it leads to synaptic elimination. We review these lines of evidence as well as in vivo evidence for altered cortical E/I balance and dopaminergic dysfunction in schizophrenia. We discuss mechanisms through which frontal cortex circuitry may regulate striatal dopamine and consider how frontal E/I imbalance may cause dopaminergic dysregulation to result in psychotic symptoms. This integrated neurodevelopmental and dopamine hypothesis suggests that overpruning of synapses, potentially including glutamatergic inputs onto frontal cortical interneurons, disrupts the E/I balance and thus underlies cognitive and negative symptoms. It could also lead to disinhibition of excitatory projections from the frontal cortex and possibly other regions that regulate mesostriatal dopamine neurons, resulting in dopamine dysregulation and psychotic symptoms. Together, this explains a number of aspects of the epidemiology and clinical presentation of schizophrenia and identifies new targets for treatment and prevention.

Psychopharmacological properties and therapeutic profile of the antidepressant venlafaxine

Major depression (MD) is one of the most common psychiatric disorders worldwide. Currently, the first-line treatment for MD targets the serotonin system but these drugs, notably the selective serotonin reuptake inhibitors, usually need 4 to 6 weeks before the benefit is felt and a significant proportion of patients shows an unsatisfactory response. Numerous treatments have been developed to circumvent these issues as venlafaxine, a mixed serotonin-norepinephrine reuptake inhibitor that binds and blocks both the SERT and NET transporters. Despite this pharmacological profile, it is difficult to have a valuable insight into its ability to produce more robust efficacy than single-acting agents. In this review, we provide an in-depth characterization of the pharmacological properties of venlafaxine from in vitro data to preclinical and clinical efficacy in depressed patients and animal models of depression to propose an indirect comparison with the most common antidepressants. Preclinical studies show that the antidepressant effect of venlafaxine is often associated with an enhancement of serotonergic neurotransmission at low doses. High doses of venlafaxine, which elicit a concomitant increase in 5-HT and NE tone, is associated with changes in different forms of plasticity in discrete brain areas. In particular, the hippocampus appears to play a crucial role in venlafaxine-mediated antidepressant effects notably by regulating processes such as adult hippocampal neurogenesis or the excitatory/inhibitory balance. Overall, depending on the dose used, venlafaxine shows a high efficacy on depressive-like symptoms in relevant animal models but to the same extent as common antidepressants. However, these data are counterbalanced by a lower tolerance. In conclusion, venlafaxine appears to be one of the most effective treatments for treatment of major depression. Still, direct comparative studies are warranted to provide definitive conclusions about its superiority.

Expression of Calbindin, a Marker of Gamma-Aminobutyric Acid Neurons, Is Reduced in the Amygdala of Oestrogen Receptor β-Deficient Female Mice

Oestrogen receptor β (ERβ) knock-out female mice display increased anxiety and decreased threshold for synaptic plasticity induction in the basolateral amygdala. This may suggest that the γ-aminobutyric acid (GABA) inhibitory system is altered. Therefore, the immunoreactivity of main GABAergic markers-i.e., calbindin, parvalbumin, calretinin, somatostatin, α1 subunit-containing GABA_A receptor and vesicular GABA transporter-were compared in the six subregions (LA, BL, BM, ME, CE and CO) of the amygdala of adult female wild-type and ERβ knock-out mice using immunohistochemistry and quantitative methods. The influence of ERβ knock-out on neuronal loss and glia was also elucidated using pan-neuronal and astrocyte markers. The results show severe neuronal deficits in all main amygdala regions in ERβ knock-out mice accompanied by astroglia overexpression only in the medial, basomedial and cortical nuclei and a decrease in calbindin-expressing neurons (CB+) in the amygdala in ERβ knock-out mice compared with controls, while other markers of the GABAergic system remain unchanged. Concluding, the lack of ERβ led to failure in the structural integrity of the CB+ subpopulation, reducing interneuron firing and resulting in a disinhibitory effect over pyramidal function. This fear-promoting excitatory/inhibitory alteration may lead to the increased anxiety observed in these mice. The impact of neuronal deficits and astroglia overexpression on the amygdala functions remains unknown.

The potential roles of excitatory-inhibitory imbalances and the repressor element-1 silencing transcription factor in aging and aging-associated diseases

Disruptions to the central excitatory-inhibitory (E/I) balance are thought to be related to aging and underlie a host of neural pathologies, including Alzheimer's disease. Aging may induce an increase in excitatory signaling, causing an E/I imbalance, which has been linked to shorter lifespans in mice, flies, and worms. In humans, extended longevity correlates to greater repression of genes involved in excitatory neurotransmission. The repressor element-1 silencing transcription factor (REST) is a master regulator in neural cells and is believed to be upregulated with senescent stimuli, whereupon it counters hyperexcitability, insulin/insulin-like signaling pathway activity, oxidative stress, and neurodegeneration. This review examines the putative mechanisms that distort the E/I balance with aging and neurodegeneration, and the putative roles of REST in maintaining neuronal homeostasis.

The social instability stress paradigm in rat and mouse: A systematic review of protocols, limitations, and recommendations

BACKGROUND

Social stress is an important environmental risk factor for the development of psychiatric disorders, including depression and anxiety disorders. Social stress paradigms are commonly used in rats and mice to gain insight into the pathogenesis of these disorders. The social instability stress (SIS) paradigm entails frequent (up to several times a week) introduction of one or multiple unfamiliar same-sex home-cage partners. The subsequent recurring formation of a new social hierarchy results in chronic and unpredictable physical and social stress.

PURPOSE

We compare and discuss the stress-related behavioral and physiological impact of SIS protocols in rat and mouse, and address limitations due to protocol variability. We further provide practical recommendations to optimize reproducibility of SIS protocols.

METHODS

We conducted a systematic review in accordance with the PRISMA statement in the following three databases: PubMed, Web of Science and Scopus. Our search strategy was not restricted to year of publication but was limited to articles in English that were published in peer-reviewed journals. Search terms included "social* instab*" AND ("animal" OR "rodent" OR "rat*" OR "mice" OR "mouse").

RESULTS

Thirty-three studies met our inclusion criteria. Fifteen articles used a SIS protocol in which the composition of two cage mates is altered daily for sixteen days (SIS16D). Eleven articles used a SIS protocol in which the composition of four cage mates is altered twice per week for 49 days (SIS49D). The remaining seven studies used SIS protocols that differed from these two protocols in experiment duration or cage mate quantity. Behavioral impact of SIS was primarily assessed by quantifying depressive-like, anxiety-like, social-, and cognitive behavior. Physiological impact of SIS was primarily assessed using metabolic parameters, hypothalamus-pituitary-adrenal axis activity, and the assessment of neurobiological parameters such as neuroplasticity and neurogenesis.

CONCLUSION

Both shorter and longer SIS protocols induce a wide range of stress-related behavioral and physiological impairments that are relevant for the pathophysiology of depression and anxiety disorders. To date, SIS16D has only been reported in rats, whereas SIS49D has only been reported in mice. Given this species-specific application as well as variability in reported SIS protocols, additional studies should determine whether SIS effects are protocol duration- or species-specific. We address several issues, including a lack of consistency in the used SIS protocols, and suggest practical, concrete improvements in design and reporting of SIS protocols to increase standardization and reproducibility of this etiologically relevant preclinical model of social stress.

Parvalbumin interneuron alterations in stress-related mood disorders: A systematic review

Stress-related psychiatric disorders including depression involve complex cellular and molecular changes in the brain, and GABAergic signaling dysfunction is increasingly implicated in the etiology of mood disorders. Parvalbumin (PV)-expressing neurons are fast-spiking interneurons that, among other roles, coordinate synchronous neuronal firing. Mounting evidence suggests that the PV neuron phenotype is altered by stress and in mood disorders. In this systematic review, we assessed PV interneuron alterations in psychiatric disorders as reported in human postmortem brain studies and animal models of environmental stress. This review aims to 1) comprehensively catalog evidence of PV cell function in mood disorders (humans) and stress models of mood disorders (animals); 2) analyze the strength of evidence of PV interneuron alterations in various brain regions in humans and rodents; 3) determine whether the modulating effect of antidepressant treatment, physical exercise, and environmental enrichment on stress in animals associates with particular effects on PV function; and 4) use this information to guide future research avenues. Its principal findings, derived mainly from rodent studies, are that stress-related changes in PV cells are only reported in a minority of studies, that positive findings are region-, age-, sex-, and stress recency-dependent, and that antidepressants protect from stress-induced apparent PV cell loss. These observations do not currently translate well to humans, although the postmortem literature on the topic remains limited.

An electrophysiological model of major depression: Relevance to clinical subtyping and pharmacological management

We present a neurochemical model of unipolar major depressive disorder that makes predictions for optimizing pharmacological treatment of this debilitating neuropsychiatric disorder. We suggest that there are two principal electrophysiological subtypes of depression, with the more common one involving a high excitatory/inhibitory (E/I) electrophysiological ratio, and a less common low E/I subtype. The high E/I subtype is paradoxically a variant of previous conceptions of atypical depression, whereas the low E/I subtype is a variant of melancholic depression. We focus on the ratio of norepinephrine (NE) to serotonin (5HT) as primary determinants of E/I ratio, which have opposing effects on mood regulation. We suggest that high NE/5HT (or E/I) ratio depressions should be treated with pharmacological agents that boost 5HT (such as SSRIs) and/or drugs that reduce noradrenergic transmission (such as clonidine, guanfacine, propranolol, prazosin). In contrast, low NE/5HT (or E/I) depressions should be treated with agents that boost NE (such as most tricyclics) and/or drugs that reduce serotonergic transmission. Our model predicts that the rapidly acting antidepressant ketamine (and possibly scopolamine), which has an acutely excitatory electrophysiological profile that may be followed by sustained increased inhibition, should improve the high NE/5HT subtype and worsen the low subtype.

Limited contextual memory and transcriptional dysregulation in the medial prefrontal cortex of mice exposed to early protein malnutrition are intergenerationally transmitted

Memory contextualization is vital for the subsequent retrieval of relevant memories in specific situations and is a critical dimension of social cognition. The inability to properly contextualize information has been described as characteristic of psychiatric disorders like autism spectrum disorders, schizophrenia, and post-traumatic stress disorder. The exposure to early-life adversities, such as nutritional deficiency, increases the risk to trigger alterations in different domains of cognition related to those observed in mental diseases. In this work, we explored the consequences of exposure to perinatal protein malnutrition on contextual memory in a mouse model and assessed whether these consequences are transmitted to the next generation. Female mice were fed with a normal or hypoproteic diet during pregnancy and lactation. To evaluate contextual memory, the object-context mismatch test was performed in both sexes of F1 offspring and in the subsequent F2 generation. We observed that contextual memory was altered in mice of both sexes that had been subjected to maternal protein malnutrition and that the deficit in contextual memory was transmitted to the next generation. The basis of this alteration seems to be a transcriptional dysregulation of genes involved in the excitatory and inhibitory balance and immediate-early genes within the medial prefrontal cortex (mPFC) of both generations. The expression of genes encoding enzymes that regulate H3K27me3 levels was altered in the mPFC and partially in sperm of F1 malnourished mice. These results support the hypothesis that early nutritional deficiency represents a risk factor for the emergence of symptoms associated with mental disorders.

Hippocampal GABAergic interneurons and their co-localized neuropeptides in stress vulnerability and resilience

Studies in humans and rodents suggest a critical role for the hippocampal formation in cognition and emotion, but also in the adaptation to stressful events. Successful stress adaptation promotes resilience, while its failure may lead to stress-induced psychopathologies such as depression and anxiety disorders. Hippocampal architecture and physiology is shaped by its strong control of activity via diverse classes of inhibitory interneurons that express typical calcium binding proteins and neuropeptides. Celltype-specific opto- and chemogenetic intervention strategies that take advantage of these biochemical markers have bolstered our understanding of the distinct role of different interneurons in anxiety, fear and stress adaptation. Moreover, some of the signature proteins of GABAergic interneurons have a potent impact on emotion and cognition on their own, making them attractive targets for interventions. In particular, neuropeptide Y is a promising endogenous agent for mediating resilience against severe stress. In this review, we evaluate the role of the major types of interneurons across hippocampal subregions in the adaptation to chronic and acute stress and to emotional memory formation.