Circuit-specific hippocampal ΔFosB underlies resilience to stress-induced social avoidance

Neurobiology and systems biology of stress resilience

Stress resilience is the phenomenon that some people maintain their mental health despite exposure to adversity or show only temporary impairments followed by quick recovery. Resilience research attempts to unravel the factors and mechanisms that make resilience possible and to harness its insights for the development of preventative interventions in individuals at risk for acquiring stress-related dysfunctions. Biological resilience research has been lagging behind the psychological and social sciences but has seen a massive surge in recent years. At the same time, progress in this field has been hampered by methodological challenges related to finding suitable operationalizations and study designs, replicating findings, and modeling resilience in animals. We embed a review of behavioral, neuroimaging, neurobiological, and systems biological findings in adults in a critical methods discussion. We find preliminary evidence that hippocampus-based pattern separation and prefrontal-based cognitive control functions protect against the development of pathological fears in the aftermath of singular, event-type stressors [as found in fear-related disorders, including simpler forms of posttraumatic stress disorder (PTSD)] by facilitating the perception of safety. Reward system-based pursuit and savoring of positive reinforcers appear to protect against the development of more generalized dysfunctions of the anxious-depressive spectrum resulting from more severe or longer-lasting stressors (as in depression, generalized or comorbid anxiety, or severe PTSD). Links between preserved functioning of these neural systems under stress and neuroplasticity, immunoregulation, gut microbiome composition, and integrity of the gut barrier and the blood-brain barrier are beginning to emerge. On this basis, avenues for biological interventions are pointed out.

Neurobiological basis of stress resilience

A majority of humans faced with severe stress maintain normal physiological and behavioral function, a process referred to as resilience. Such stress resilience has been modeled in laboratory animals and, over the past 15 years, has transformed our understanding of stress responses and how to approach the treatment of human stress disorders such as depression, post-traumatic stress disorder (PTSD), and anxiety disorders. Work in rodents has demonstrated that resilience to chronic stress is an active process that involves much more than simply avoiding the deleterious effects of the stress. Rather, resilience is mediated largely by the induction of adaptations that are associated uniquely with resilience. Such mechanisms of natural resilience in rodents are being characterized at the molecular, cellular, and circuit levels, with an increasing number being validated in human investigations. Such discoveries raise the novel possibility that treatments for human stress disorders, in addition to being geared toward reversing the damaging effects of stress, can also be based on inducing mechanisms of natural resilience in individuals who are inherently more susceptible. This review provides a progress report on this evolving field.

Electroacupuncture intervention alleviates depressive-like behaviors and regulates gut microbiome in a mouse model of depression

Electroacupuncture (EA) is a neuroregulatory therapy for depression. Nonetheless, the effects of EA on the gut microbiome in mice models of depression are not well established. Here, using a chronic unpredictable mild stress (CUMS) model in mice, we evaluated the antidepressant effects of EA and changes in gut microbiota with behavioral tests and 16S rRNA gene sequencing. The results found that EA increased the time spent in the center area of the open-field test and the percentage of sucrose preference and reduced the immobility time in the tail suspension test in CUMS-treated mice. Furthermore, the genus Lachnoclostridium, Ruminococcaceae_UCG-002 and Rikenellaceae_RC9_gut_group were enriched in the CUMS group, which was positively correlated with depressive-like behaviors. Whereas phylum Actinobacteria and genus Allobaculum, Bifidobacterium, Dubosiella, Rikenella and Ileibacterium were enriched in the EA and CUMS + EA groups, all of which were negatively correlated with depressive-like behaviors. This study characterizes gut microbiota under EA treatment and provides new insights into the association of anti-depressive-like effects of EA and gut microbiota.

Activity-dependent FosB gene expression negatively regulates mast cell functions

Mast cells are innate immune cells that play a crucial role in numerous physiological processes across tissues by releasing pre-stored and newly synthesized mediators in response to stimuli, an activity largely driven by changes in gene expression. Given their widespread influence, dysfunction in mast cells can contribute to a variety of pathologies including allergies, long COVID, and autoimmune and neuroinflammatory disorders. Despite this, the specific transcriptional mechanisms that control mast cell mediator release remain poorly understood, significantly hindering the development of effective therapeutic strategies. We found that the two proteins encoded by the transcription factor FosB, FOSB and the highly stable variant ΔFOSB, are robustly expressed upon stimulation in both murine and human mast cell progenitors. Motivated by these findings, we generated a novel mouse model with targeted ablation of FosB gene expression specifically in mast cells (MC FosB- ) by crossing a mast cell-specific Cre reporter line (Mcpt5-Cre) with a Cre-dependent floxed FosB mouse lines. We found that mast cell progenitors derived from MC FosB- mice, compared to wild types (WT), exhibit baseline increased histamine content and vesicle numbers. Additionally, they show enhanced calcium mobilization, degranulation, and histamine release following allergy-related IgE-mediated stimulation, along with heightened IL-6 release in response to infection-like LPS stimulation. In vivo experiments with IgE- mediated and LPS challenges revealed that MC FosB- mice experience greater drops in body temperature, heightened activation of tissue-resident mast cells, and increased release of pro-inflammatory mediators compared to their WT counterparts. These findings suggest that FosB products play a crucial regulatory role in moderating stimulus-induced mast cell activation in response to both IgE and LPS stimuli. Lastly, by integrating CUT&RUN and RNAseq data, we identified several genes targeted by ΔFOSB that could mediate these observed effects, including Mir155hg, CLCF1, DUSP4, and Trib1. Together, this study provides the first evidence that FOSB/ΔFOSB modulate mast cell functions and provides a new possible target for therapeutic interventions aimed at ameliorating mast cell-related diseases.

Discrete prefrontal neuronal circuits determine repeated stress-induced behavioral phenotypes in male mice

Chronic stress is a major risk factor for psychiatric disorders, including depression. Although depression is a highly heterogeneous syndrome, it remains unclear how chronic stress drives individual differences in behavioral responses. In this study, we developed a subtyping-based approach wherein stressed male mice were divided into four subtypes based on their behavioral patterns of social interaction deficits and anhedonia, the core symptoms of psychiatric disorders. We identified three prefrontal cortical neuronal projections that regulate repeated stress-induced behavioral phenotypes. Among them, the medial prefrontal cortex (mPFC)→anterior paraventricular thalamus (aPVT) pathway determines the specific behavioral subtype that exhibits both social deficits and anhedonia. Additionally, we identified the circuit-level molecular mechanism underlying this subtype: KDM5C-mediated epigenetic repression of Shisa2 transcription in aPVT projectors in the mPFC led to social deficits and anhedonia. Thus, we provide a set of biological aspects at the cellular, molecular, and epigenetic levels that determine distinctive stress-induced behavioral phenotypes.

Pathological features and molecular signatures of early olfactory dysfunction in 3xTg-AD model mice

BACKGROUND

Olfactory dysfunction is known to be an early manifestation of Alzheimer's disease (AD). However, the underlying mechanism, particularly the specific molecular events that occur during the early stages of olfactory disorders, remains unclear.

METHODS

In this study, we utilized transcriptomic sequencing, bioinformatics analysis, and biochemical detection to investigate the specific pathological and molecular characteristics of the olfactory bulb (OB) in 4-month-old male triple transgenic 3xTg-AD mice (PS1M146V/APPSwe/TauP301L).

RESULTS

Initially, during the early stages of olfactory impairment, no significant learning and memory deficits were observed. Correspondingly, we observed significant accumulation of amyloid-beta (Aβ) and Tau pathology specifically in the OB, but not in the hippocampus. In addition, significant axonal morphological defects were detected in the olfactory bulb, cortex, and hippocampal brain regions of 3xTg-AD mice. Transcriptomic analysis revealed a significant increase in the expression of neuroinflammation-related genes, accompanied by a significant decrease in neuronal activity-related genes in the OB. Moreover, immunofluorescence and immunoblotting demonstrated an activation of glial cell biomarkers Iba1 and GFAP, along with a reduction in the expression levels of neuronal activity-related molecules Nr4a2 and FosB, as well as olfaction-related marker OMP.

CONCLUSION

In sum, the early accumulation of Aβ and Tau pathology induces neuroinflammation, which subsequently leads to a decrease in neuronal activity within the OB, causing axonal transport deficits that contribute to olfactory disorders. Nr4a2 and FosB appear to be promising targets for intervention aimed at improving early olfactory impairment in AD.

Chronic Desipramine Reverses Deficits in Cell Activity, Norepinephrine Innervation, and Anxiety-Depression Phenotypes in Fluoxetine-Resistant cF1ko Mice

Selective serotonin (5-HT) reuptake inhibitors are only 30% effective for remission in subjects with major depression, and the best treatments for SSRI-resistant patients remain unclear. To model SSRI resistance, we used cF1ko mice with conditional deletion of the repressor Freud-1/CC2D1A in adult 5-HT neurons. Within weeks, this deletion leads to overexpression of 5-HT1A autoreceptors, reduced serotonergic activity, and fluoxetine-resistant anxiety-depression phenotype. We hypothesized that desipramine (DES), which targets norepinephrine (NE), may be effective in cF1ko mice. The actions of chronic DES treatment on behavior, chronic cellular activation, and NE projections were examined in both sexes of cF1ko and WT mice. In contrast to fluoxetine, chronic DES reversed the behavioral phenotypes in cF1ko mice, while in WT littermates DES slightly increased anxiety and depression-like behaviors. Deficits in FosB+ cell counts were seen in the entorhinal cortex, hippocampal CA2/3 layer, and BLA of cF1ko mice and were reversed by chronic DES treatment, especially in GABAergic neurons. In cF1ko mice, widespread reductions were seen in NE axons, varicosities, and especially 30-60% reductions in NE synaptic and triadic contacts, particularly to inhibitory gephyrin-positive sites. DES treatment also reversed these reductions in NE innervation. These results indicate the dynamic plasticity of the adult noradrenergic system within weeks of altering serotonergic function that can be normalized by DES treatment. Accompanying these changes, DES but not fluoxetine reversed the behavioral alterations in cF1ko mice, suggesting a key role for noradrenergic plasticity in antidepressant response in this model of reduced serotonin activity.

The defects of the hippocampal ripples and theta rhythm in depression, and the effects of physical exercise on their amelioration

Adverse environmental stress causes depressive symptoms with the impairments of memory formation, cognition, and motivation, however, their underlying neural bases have not been well understood, especially based on the observation of living animals. In the present study, therefore, the mice model of restraint-induced stress was examined electrophysiologically to investigate the alterations of hippocampal sharp wave ripples (SWRs) and theta rhythms. In addition, the therapeutic effects of physical exercise on the amelioration of those hippocampal impairments were examined in combination with a series of behavioral tests. The data demonstrated that chronic restraint stress caused the reductions of occurrence and amplitude of hippocampal SWRs and the decreases of occurrence, duration, and power of theta rhythms, while physical exercise significantly reverted them to the levels of healthy control. Furthermore, hippocampal adult neurogenesis and microglial activation, previously reported to be involved in the etiology of depression, were histologically examined in the mice. The results showed that the impairment of neurogenesis and alleviation of microglial activation were induced in the depressed mice. On the other hand, physical exercise considerably ameliorated those pathological conditions in the affected brain. Consistently, the data of behavioral tests in mice suggested that physical exercise ameliorated the symptomatic defects of motivation, memory formation, and cognition in the depressed mice. The impairments of hippocampal SWRs and theta rhythms in the affected hippocampus are linked with the symptomatic impairments of cognition and motivation, and the defect of memory formation, respectively, in depression. Taken together, this study demonstrated the implications of impairment of the hippocampal SWRs and theta rhythms in the etiology of depression and their usefulness as diagnostic markers of depression.

Antinociceptive effect of intermittent fasting via the orexin pathway on formalin-induced acute pain in mice

It has been suggested that stress responses induced by fasting have analgesic effects on nociception by elevating the levels of stress-related hormones, while there is limited understanding of pain control mechanisms. Here, we investigated whether acute or intermittent fasting alleviates formalin-induced pain in mice and whether spinal orexin A (OXA) plays a role in this process. 6, 12, or 24 h acute fasting (AF) and 12 or 24 h intermittent fasting (IF) decreased the second phase of pain after intraplantar formalin administration. There was no difference in walking time in the rota-rod test and distance traveld in the open field test in all groups. Plasma corticosterone level and immobility time in the forced swim test were increased after 12 h AF, but not after 12 h IF. 12 h AF and IF increased not only the activation of OXA neurons in the lateral hypothalamus but also the expression of OXA in the lateral hypothalamus and spinal cord. Blockade of spinal orexin 1 receptor with SB334867 restored formalin-induced pain and spinal c-Fos immunoreactivity that were decreased after 12 h IF. These results suggest that 12 h IF produces antinociceptive effects on formalin-induced pain not by corticosterone elevation but by OXA-mediated pathway.

rTMS ameliorates depressive-like behaviors and regulates the gut microbiome and medium- and long-chain fatty acids in mice exposed to chronic unpredictable mild stress

INTRODUCTION

Repetitive transcranial magnetic stimulation (rTMS) is a clinically useful therapy for depression. However, the effects of rTMS on the metabolism of fatty acids (FAs) and the composition of gut microbiota in depression are not well established.

METHODS

Mice received rTMS (15 Hz, 1.26 T) for seven consecutive days after exposure to chronic unpredictable mild stress (CUMS). The subsequent depressive-like behaviors, the composition of gut microbiota of stool samples, as well as medium- and long-chain fatty acids (MLCFAs) in the plasma, prefrontal cortex (PFC), and hippocampus (HPC) were evaluated.

RESULTS

CUMS induced remarkable changes in gut microbiotas and fatty acids, specifically in community diversity of gut microbiotas and PUFAs in the brain. 15 Hz rTMS treatment alleviates depressive-like behaviors and partially normalized CUMS induced alterations of microbiotas and MLCFAs, especially the abundance of Cyanobacteria, Actinobacteriota, and levels of polyunsaturated fatty acids (PUFAs) in the hippocampus and PFC.

CONCLUSION

These findings revealed that the modulation of gut microbiotas and PUFAs metabolism might partly contribute to the antidepressant effect of rTMS.

Cell Type-Specific Whole-Genome Landscape of ΔFOSB Binding in the Nucleus Accumbens After Chronic Cocaine Exposure

BACKGROUND

The ability of neurons to respond to external stimuli involves adaptations of gene expression. Induction of the transcription factor ΔFOSB in the nucleus accumbens, a key brain reward region, is important for the development of drug addiction. However, a comprehensive map of ΔFOSB's gene targets has not yet been generated.

METHODS

We used CUT&RUN (cleavage under targets and release using nuclease) to map the genome-wide changes in ΔFOSB binding in the 2 main types of nucleus accumbens neurons-D1 or D2 medium spiny neurons-after chronic cocaine exposure. To annotate genomic regions of ΔFOSB binding sites, we also examined the distributions of several histone modifications. Resulting datasets were leveraged for multiple bioinformatic analyses.

RESULTS

The majority of ΔFOSB peaks occur outside promoter regions, including intergenic regions, and are surrounded by epigenetic marks indicative of active enhancers. BRG1, the core subunit of the SWI/SNF chromatin remodeling complex, overlaps with ΔFOSB peaks, a finding consistent with earlier studies of ΔFOSB's interacting proteins. Chronic cocaine use induces broad changes in ΔFOSB binding in both D1 and D2 nucleus accumbens medium spiny neurons of male and female mice. In addition, in silico analyses predict that ΔFOSB cooperatively regulates gene expression with homeobox and T-box transcription factors.

CONCLUSIONS

These novel findings uncover key elements of ΔFOSB's molecular mechanisms in transcriptional regulation at baseline and in response to chronic cocaine exposure. Further characterization of ΔFOSB's collaborative transcriptional and chromatin partners specifically in D1 and D2 medium spiny neurons will reveal a broader picture of the function of ΔFOSB and the molecular basis of drug addiction.

Neurosteroid influence on affective tone

Affective disorders such as depression and anxiety are among the most prevalent psychiatric illnesses and causes of disability worldwide. The recent FDA-approval of a novel antidepressant treatment, ZULRESSO® (Brexanolone), a synthetic neurosteroid has fueled interest into the role of neurosteroids in the pathophysiology of depression as well as the mechanisms mediating the antidepressant effects of these compounds. The majority of studies examining the impact of neurosteroids on affective states have relied on the administration of exogenous neurosteroids; however, neurosteroids can also be synthesized endogenously from cholesterol or steroid hormone precursors. Despite the well-established influence of exogenous neurosteroids on affective states, we still lack an understanding of the role of endogenous neurosteroids in modulating affective tone. This review aims to summarize the current literature supporting the influence of neurosteroids on affective states in clinical and preclinical studies, as well as recent evidence suggesting that endogenous neurosteroids may set a baseline affective tone.

Circuit- and laminar-specific regulation of medial prefrontal neurons by chronic stress

BACKGROUND

Chronic stress exposure increases the risk of mental health problems such as anxiety and depression. The medial prefrontal cortex (mPFC) is a hub for controlling stress responses through communicating with multiple limbic structures, including the basolateral amygdala (BLA) and nucleus accumbens (NAc). However, considering the complex topographical organization of the mPFC neurons in different subregions (dmPFC vs. vmPFC) and across multiple layers (Layer II/III vs. Layer V), the exact effects of chronic stress on these distinct mPFC output neurons remain largely unknown.

RESULTS

We first characterized the topographical organization of mPFC neurons projecting to BLA and NAc. Then, by using a typical mouse model of chronic restraint stress (CRS), we investigated the effects of chronic stress on the synaptic activity and intrinsic properties of the two mPFC neuronal populations. Our results showed that there was limited collateralization of the BLA- and NAc-projecting pyramidal neurons, regardless of the subregion or layer they were situated in. CRS significantly reduced the inhibitory synaptic transmission onto the BLA-projecting neurons in dmPFC layer V without any effect on the excitatory synaptic transmission, thus leading to a shift of the excitation-inhibition (E-I) balance toward excitation. However, CRS did not affect the E-I balance in NAc-projecting neurons in any subregions or layers of mPFC. Moreover, CRS also preferentially increased the intrinsic excitability of the BLA-projecting neurons in dmPFC layer V. By contrast, it even caused a decreasing tendency in the excitability of NAc-projecting neurons in vmPFC layer II/III.

CONCLUSION

Our findings indicate that chronic stress exposure preferentially modulates the activity of the mPFC-BLA circuit in a subregion (dmPFC) and laminar (layer V) -dependent manner.

Identification of a GABAergic neural circuit governing leptin signaling deficiency-induced obesity

The hormone leptin is known to robustly suppress food intake by acting upon the leptin receptor (LepR) signaling system residing within the agouti-related protein (AgRP) neurons of the hypothalamus. However, clinical studies indicate that leptin is undesirable as a therapeutic regiment for obesity, which is at least partly attributed to the poorly understood complex secondary structure and key signaling mechanism of the leptin-responsive neural circuit. Here, we show that the LepR-expressing portal neurons send GABAergic projections to a cohort of α3-GABAA receptor expressing neurons within the dorsomedial hypothalamic nucleus (DMH) for the control of leptin-mediated obesity phenotype. We identified the DMH as a key brain region that contributes to the regulation of leptin-mediated feeding. Acute activation of the GABAergic AgRP-DMH circuit promoted food intake and glucose intolerance, while activation of post-synaptic MC4R neurons in the DMH elicited exactly opposite phenotypes. Rapid deletion of LepR from AgRP neurons caused an obesity phenotype which can be rescued by blockage of GABAA receptor in the DMH. Consistent with behavioral results, these DMH neurons displayed suppressed neural activities in response to hunger or hyperglycemia. Furthermore, we identified that α3-GABAA receptor signaling within the DMH exerts potent bi-directional regulation of the central effects of leptin on feeding and body weight. Together, our results demonstrate a novel GABAergic neural circuit governing leptin-mediated feeding and energy balance via a unique α3-GABAA signaling within the secondary leptin-responsive neural circuit, constituting a new avenue for therapeutic interventions in the treatment of obesity and associated comorbidities.

Inducible CRISPR Epigenome Systems Mimic Cocaine Induced Bidirectional Regulation of Nab2 and Egr3

Substance use disorder is a chronic disease and a leading cause of disability around the world. The NAc is a major brain hub mediating reward behavior. Studies demonstrate exposure to cocaine is associated with molecular and functional imbalance in NAc medium spiny neuron subtypes (MSNs), dopamine receptor 1 and 2 enriched D1-MSNs and D2-MSNs. We previously reported repeated cocaine exposure induced transcription factor early growth response 3 (Egr3) mRNA in NAc D1-MSNs, and reduced it in D2-MSNs. Here, we report our findings of repeated cocaine exposure in male mice inducing MSN subtype-specific bidirectional expression of the Egr3 corepressor NGFI-A-binding protein 2 (Nab2). Using CRISPR activation and interference (CRISPRa and CRISPRi) tools combined with Nab2 or Egr3-targeted sgRNAs, we mimicked these bidirectional changes in Neuro2a cells. Furthermore, we investigated D1-MSN- and D2-MSN-specific expressional changes of histone lysine demethylases Kdm1a, Kdm6a, and Kdm5c in NAc after repeated cocaine exposure in male mice. Since Kdm1a showed bidirectional expression patterns in D1-MSNs and D2-MSNs, like Egr3, we developed a light-inducible Opto-CRISPR-KDM1a system. We were able to downregulate Egr3 and Nab2 transcripts in Neuro2A cells and cause similar bidirectional expression changes we observed in D1-MSNs and D2-MSNs of mouse repeated cocaine exposure model. Contrastingly, our Opto-CRISPR-p300 activation system induced the Egr3 and Nab2 transcripts and caused opposite bidirectional transcription regulations. Our study sheds light on the expression patterns of Nab2 and Egr3 in specific NAc MSNs in cocaine action and uses CRISPR tools to further mimic these expression patterns.SIGNIFICANCE STATEMENT Substance use disorder is a major societal issue. The lack of medication to treat cocaine addiction desperately calls for a treatment development based on precise understanding of molecular mechanisms underlying cocaine addiction. In this study, we show that Egr3 and Nab2 are bidirectionally regulated in mouse NAc D1-MSNs and D2-MSNs after repeated exposure to cocaine. Furthermore, histone lysine demethylations enzymes with putative EGR3 binding sites showed bidirectional regulation in D1- and D2-MSNs after repeated exposure to cocaine. Using Cre- and light-inducible CRISPR tools, we show that we can mimic this bidirectional regulation of Egr3 and Nab2 in Neuro2a cells.

High-frequency repetitive transcranial magnetic stimulation regulates neural oscillations of the hippocampus and prefrontal cortex in mice by modulating endocannabinoid signalling

BACKGROUND

Neural oscillations play a role in the antidepressant effects of repetitive transcranial magnetic stimulation (rTMS). However, the effects of high-frequency rTMS on the neural oscillations of the medial prefrontal cortex (mPFC) and hippocampus (HPC) and its molecular mechanism have not been fully clarified.

METHODS

The depressive-like behaviours, local field potentials (LFPs) of the ventral HPC (vHPC)-mPFC, and alternations of endocannabinoid system (ECS) in the HPC and mPFC were observed after rTMS treatment. Meanwhile, depressive-like behaviours and LFPs were also observed after cannabinoid type-1 receptor (CB1R) antagonist AM281 or monoacylglycerol lipase inhibitor JZL184 injection. Moreover, the antidepressant effect of rTMS was further assessed in glutamatergic-CB1R and gamma-amino butyric acid (GABA)-ergic -CB1R knockout mice.

RESULTS

Alternations of endocannabinoids and energy value and synchronisation of mPFC-vHPC, especially the decrease of theta oscillation induced by CUMS, were alleviated by rTMS. JZL184 has similar effects to rTMS and AM281 blocked the effects of rTMS. GABAergic-CB1R deletion inhibited CUMS-induced depressive-like behaviours whereas Glutaminergic-CB1R deletion dampened the antidepressant effects of rTMS.

LIMITATIONS

The immediate effect of rTMS on field-potential regulation was not observed. Moreover, the role of region-specific regulation of the ECS in the antidepressant effect of rTMS was unclear and the effects of cell-specific CB1R knockout on neuronal oscillations of the mPFC and vHPC should be further investigated.

CONCLUSION

Endocannabinoid system mediated the antidepressant effects and was involved in the regulation of LFP in the vHPC-mPFC of high-frequency rTMS.

Protective effect of Nr4a2 (Nurr1) against LPS-induced depressive-like behaviors via regulating activity of microglia and CamkII neurons in anterior cingulate cortex

Neuroinflammation is tightly associated with onset of depression. The nuclear receptor related 1 protein (Nurr1, also called Nr4a2), its roles in dopaminergic neurons is well understood, which can alleviate inflammation. Nevertheless, potential effects of Nr4a2 on neuroinflammation associated with depression still remains unclear. Chronic lipopolysaccharides (LPS) stress induced depressive-behaviors were confirmed via behavioral tests. Differentially expressed genes were detected by using RNA-sequencing. The anterior cingulate cortex (ACC) tissues were collected for biochemical experiments. The Golgi-Cox staining and virus labeling were used to evaluate the dendritic spines. We applied fluoxetine (FLX) and amodiaquine dihydrochloride (AQ, a highly selective agonist of Nr4a2) in mice. Overexpression experiments were performed by injecting with AAV-Nr4a2-EGFP into ACC. Chemogenetic activation of CamkII neurons via injecting the hM3Dq virus. Mice treated with LPS displayed depressive- and anxiety-like behaviors. The reduction of Nr4a2 and FosB induced by LPS were rescued by pretreatment with FLX or AQ. More importantly, LPS-induced behavior deficits in mice were also alleviated via fluoxetine treatment and pharmacological activation the expression of Nr4a2. Meanwhile, enhancing the level of Nr4a2 could improve dendritic spines loss of neuron and morphological changes in microglia. Overexpression of Nr4a2 in ACC reversed the depressive- and anxiety-like behaviors caused by LPS administration. Activation of CamkII neurons in ACC could robustly increase the expression of Nr4a2 and improve LPS-induced behavior deficits. Our findings demonstrate that the Nr4a2 may regulate depressive-like behaviors via alleviating the impairment of morphology and function on microglia and CamkII neurons induced by chronic neuroinflammation.

Poststress social isolation exerts anxiolytic effects by activating the ventral dentate gyrus

After aversive stress, people either choose to return to their previously familiar social environment or tend to adopt temporary social withdrawal to buffer negative emotions. However, which behavior intervention is more appropriate and when remain elusive. Here, we unexpectedly found that stressed mice experiencing social isolation exhibited less anxiety than those experiencing social contact. Within the first 24 h after returning to their previous social environment, mice experienced acute restraint stress (ARS) displayed low social interest but simultaneously received excessive social disturbance from their cage mates, indicating a critical time window for social isolation to balance the conflict. To screen brain regions that were differentially activated between the poststress social isolation and poststress social contact groups, we performed ΔFosB immunostaining and found that ΔFosB + signals were remarkably increased in the vDG of poststress social isolation group compared with poststress social contact group. There were no significant differences between the two groups in the other anxiety- and social-related brain regions, such as prelimbic cortex, infralimbic cortex, nucleus accumbens, etc. These data indicate that vDG is closely related to the differential phenotypes between the poststress social isolation and poststress social contact groups. Electrophysiological recording, further, revealed a higher activity of vDG in the poststress social isolation group than the poststress social contact group. Chemogenetically inhibiting vDG excitatory neurons within the first 24 h after ARS completely abolished the anxiolytic effects of poststress social isolation, while stimulating vDG excitatory neurons remarkably reduced anxiety-like behaviors in the poststress social contact group. Together, these data suggest that the activity of vDG excitatory neurons is essential and sufficient to govern the anxiolytic effect of poststress social isolation. To the best of our knowledge, this is the first report to uncover a beneficial role of temporal social isolation in acute stress-induced anxiety. In addition to the critical 24-h time window, activation of vDG is crucial for ameliorating anxiety through poststress social isolation.

Effects of (S)-ketamine on depression-like behaviors in a chronic variable stress model: a role of brain lipidome

Introduction: Compelling evidence indicates that a single sub-anesthetic dose of (S)-ketamine elicits rapid and robust antidepressant effects. However, the underlying mechanisms behind the antidepressant effects of (S)-ketamine remain unclear. Methods: Here, using a chronic variable stress (CVS) model in mice, we analyzed changes inthe lipid compositions of the hippocampus and prefrontal cortex (PFC) with a mass spectrometry-based lipidomic approach. Results: Similar to previous research outcomes, the current study also showed that (S)-ketamine reversed depressive-like behaviors in mice produced by CVS procedures. Moreover, CVS induced changes inthe lipid compositions of the hippocampus and PFC, notably in the contents of sphingolipids, glycerolipids, and fatty acyls. With the administration of (S)-ketamine, CVS-induced lipid disturbances were partially normalized, particularly in the hippocampus. Conclusion: Altogether, our results indicated that (S)-ketamine could rescue CVS-induced depressive-like behaviors in mice through region-specific modulation of the brain lipidome, contributing to the understanding of (S)-ketamine's antidepressant effects.

ΔFosB accumulation in hippocampal granule cells drives cFos pattern separation during spatial learning

Mice display signs of fear when neurons that express cFos during fear conditioning are artificially reactivated. This finding gave rise to the notion that cFos marks neurons that encode specific memories. Here we show that cFos expression patterns in the mouse dentate gyrus (DG) change dramatically from day to day in a water maze spatial learning paradigm, regardless of training level. Optogenetic inhibition of neurons that expressed cFos on the first training day affected performance days later, suggesting that these neurons continue to be important for spatial memory recall. The mechanism preventing repeated cFos expression in DG granule cells involves accumulation of ΔFosB, a long-lived splice variant of FosB. CA1 neurons, in contrast, repeatedly expressed cFos. Thus, cFos-expressing granule cells may encode new features being added to the internal representation during the last training session. This form of timestamping is thought to be required for the formation of episodic memories.

Transcriptome profiling of the ventral pallidum reveals a role for pallido-thalamic neurons in cocaine reward

Psychostimulant exposure alters the activity of ventral pallidum (VP) projection neurons. However, the molecular underpinnings of these circuit dysfunctions are unclear. We used RNA-sequencing to reveal alterations in the transcriptional landscape of the VP that are induced by cocaine self-administration in mice. We then probed gene expression in select VP neuronal subpopulations to isolate a circuit associated with cocaine intake. Finally, we used both overexpression and CRISPR-mediated knockdown to test the role of a gene target on cocaine-mediated behaviors as well as dendritic spine density. Our results showed that a large proportion (55%) of genes associated with structural plasticity were changed 24 h following cocaine intake. Among them, the transcription factor Nr4a1 (Nuclear receptor subfamily 4, group A, member 1, or Nur77) showed high expression levels. We found that the VP to mediodorsal thalamus (VP → MDT) projection neurons specifically were recapitulating this increase in Nr4a1 expression. Overexpressing Nr4a1 in VP → MDT neurons enhanced drug-seeking and drug-induced reinstatement, while Nr4a1 knockdown prevented self-administration acquisition and subsequent cocaine-mediated behaviors. Moreover, we showed that Nr4a1 negatively regulated spine dynamics in this specific cell subpopulation. Together, our study identifies for the first time the transcriptional mechanisms occurring in VP in drug exposure. Our study provides further understanding on the role of Nr4a1 in cocaine-related behaviors and identifies the crucial role of the VP → MDT circuit in drug intake and relapse-like behaviors.

Encore: Behavioural animal models of stress, depression and mood disorders

Animal studies over the past two decades have led to extensive advances in our understanding of pathogenesis of depressive and mood disorders. Among these, rodent behavioural models proved to be of highest informative value. Here, we present a comprehensive overview of the most popular behavioural models with respect to physiological, circuit, and molecular biological correlates. Behavioural stress paradigms and behavioural tests are assessed in terms of outcomes, strengths, weaknesses, and translational value, especially in the domain of pharmacological studies.

Aging Promotes Chronic Stress-Induced Depressive-Like Behavior by Activating NLRP1 Inflammasome-Driven Inflammatory Signaling in Mice

NLRP1 inflammasome has been reported to participate in many neurological disorders. Our previous study has demonstrated that NLRP1 inflammasome is implicated in chronic stress-induced depressive-like behaviors in mice. Age has been reported to be related to depression. Here we examine whether NLRP1 inflammasome is involved in the effect of age on depressive disorder. Two chronic stress stimuli, chronic social defeat stress (CSDS) and repeat social defeat stress (RSDS), were used to establish a depression model in mice of different ages. We found that aged mice exhibited worse depressive-like behaviors and locomotor activity compared to young mice. Interestingly, the expression of hippocampal NLRP1 inflammasome complexes and the levels of the inflammatory cytokines were increased in an age-dependent manner. Also, chronic stress-induced increase in the expression of the hippocampal chemokine C-X-C motif ligand 1 (CXCL1), and its cognate receptor, CXC-motif receptor 2 (CXCR2), was more remarkable in aged mice than that in young mice. Moreover, aged mice exhibited lower hippocampal BDNF levels compared to young mice. Hippocampal Nlrp1a knockdown reduced the levels of pro-inflammatory cytokines and the expression of CXCL1/CXCR2, restored BDNF levels, and alleviated chronic stress-induced depressive-like behaviors in aged mice. Our results suggest that NLRP1 inflammasome-CXCL1/CXCR2-BDNF signaling contributes to the effect of age on chronic stress-induced depressive-like behavior in mice.

Neuroplastic changes in c-Fos, ΔFosB, BDNF, trkB, and Arc expression in the hippocampus of male Roman rats: differential effects of sexual activity

Sexual activity causes differential changes in the expression of markers of neural activation (c‐Fos and ΔFosB) and neural plasticity (Arc and BDNF/trkB), as determined either by Western Blot (BDNF, trkB, Arc, and ΔFosB) or immunohistochemistry (BDNF, trkB, Arc, and c‐Fos), in the hippocampus of male Roman high (RHA) and low avoidance (RLA) rats, two psychogenetically selected rat lines that display marked differences in sexual behavior (RHA rats exhibit higher sexual motivation and better copulatory performance than RLA rats). Both methods showed (with some differences) that sexual activity modifies the expression levels of these markers in the hippocampus of Roman rats depending on: (i) the level of sexual experience, that is, changes were usually more evident in sexually naïve than in experienced rats; (ii) the hippocampal partition, that is, BDNF and Arc increased in the dorsal but tended to decrease in the ventral hippocampus; (iii) the marker considered, that is, in sexually experienced animals BDNF, c‐Fos, and Arc levels were similar to those of controls, while ΔFosB levels increased; and (iv) the rat line, that is, changes were usually larger in RHA than RLA rats. These findings resemble those of early studies in RHA and RLA rats showing that sexual activity influences the expression of these markers in the nucleus accumbens, medial prefrontal cortex, and ventral tegmental area, and show for the first time that also in the hippocampus sexual activity induces neural activation and plasticity, events that occur mainly during the first phase of the acquisition of sexual experience and depend on the genotypic/phenotypic characteristics of the animals.

Stressor-Induced Reduction in Cognitive Behavior is Associated with Impaired Colonic Mucus Layer Integrity and is Dependent Upon the LPS-Binding Protein Receptor CD14

Purpose

Commensal microbes are impacted by stressor exposure and are known contributors to cognitive and social behaviors, but the pathways through which gut microbes influence stressor-induced behavioral changes are mostly unknown. A murine social stressor was used to determine whether host-microbe interactions are necessary for stressor-induced inflammation, including neuroinflammation, that leads to reduced cognitive and social behavior.

Methods

C57BL/6 male mice were exposed to a paired fighting social stressor over a 1 hr period for 6 consecutive days. Y-maze and social interaction behaviors were tested following the last day of the stressor. Serum cytokines and lipopolysaccharide binding protein (LBP) were measured and the number and morphology of hippocampal microglia determined via immunohistochemistry. Intestinal mucous thickness and antimicrobial peptide expression were determined via fluorescent staining and real-time PCR (respectively) and microbial community composition was assessed using 16S rRNA gene amplicon sequencing. To determine whether the microbiota or the LBP receptor (CD14) are necessary for stressor-induced behavioral changes, experiments were performed in mice treated with a broad-spectrum antibiotic cocktail or in CD14-/- mice.

Results

The stressor reduced Y-maze spontaneous alternations, which was accompanied by increased microglia in the hippocampus, increased circulating cytokines (eg, IL-6, TNF-α) and LBP, and reduced intestinal mucus thickness while increasing antimicrobial peptides and cytokines. These stressor-induced changes were largely prevented in mice given broad-spectrum antibiotics and in CD14-/- mice. In contrast, social stressor-induced alterations of social behavior were not microbe-dependent.

Conclusion

Stressor-induced cognitive deficits involve enhanced bacterial interaction with the intestine, leading to low-grade, CD14-dependent, inflammation.

ΔFOSB: A Potentially Druggable Master Orchestrator of Activity-Dependent Gene Expression

ΔFOSB is a uniquely stable member of the FOS family of immediate early gene AP1 transcription factors. Its accumulation in specific cell types and tissues in response to a range of chronic stimuli is associated with biological phenomena as diverse as memory formation, drug addiction, stress resilience, and immune cell activity. Causal connections between ΔFOSB expression and the physiological and behavioral sequelae of chronic stimuli have been established in rodent and, in some cases, primate models for numerous healthy and pathological states with such preclinical observations often supported by human data demonstrating tissue-specific ΔFOSB expression associated with several specific syndromes. However, the viability of ΔFOSB as a target for therapeutic intervention might be questioned over presumptive concerns of side effects given its expression in such a wide range of cell types and circumstances. Here, we summarize numerous insights from the past three decades of research into ΔFOSB structure, function, mechanisms of induction, and regulation of target genes that support its potential as a druggable target. We pay particular attention to the potential for targeting distinct ΔFOSB isoforms or distinct ΔFOSB-containing multiprotein complexes to achieve cell type or tissue specificity to overcome off-target concerns. We also cover critical gaps in knowledge that currently limit the exploitation of ΔFOSB's therapeutic possibilities and how they may be addressed. Finally, we summarize both current and potential future strategies for generating small molecules or genetic tools for the manipulation of ΔFOSB in the clinic.

Gene-Targeted, CREB-Mediated Induction of ΔFosB Controls Distinct Downstream Transcriptional Patterns Within D1 and D2 Medium Spiny Neurons

BACKGROUND

The onset and persistence of addiction phenotypes are, in part, mediated by transcriptional mechanisms in the brain that affect gene expression and, subsequently, neural circuitry. ΔFosB is a transcription factor that accumulates in the nucleus accumbens (NAc)-a brain region responsible for coordinating reward and motivation-after exposure to virtually every known rewarding substance, including cocaine and opioids. ΔFosB has also been shown to directly control gene transcription and behavior downstream of both cocaine and opioid exposure, but with potentially different roles in D1 and D2 medium spiny neurons (MSNs) in NAc.

METHODS

To clarify MSN subtype-specific roles for ΔFosB and investigate how these coordinate the actions of distinct classes of addictive drugs in NAc, we developed a CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9-based epigenome editing tool to induce endogenous ΔFosB expression in vivo in the absence of drug exposure. After inducing ΔFosB in D1- or D2-MSNs or both, we performed RNA sequencing on bulk male and female NAc tissue (n = 6-8/group).

RESULTS

We found that ΔFosB induction elicits distinct transcriptional profiles in NAc by MSN subtype and by sex, establishing for the first time that ΔFosB mediates different transcriptional effects in males versus females. We also demonstrated that changes in D1-MSNs, but not those in D2-MSNs or both, significantly recapitulate changes in gene expression induced by cocaine self-administration.

CONCLUSIONS

Together, these findings demonstrate the efficacy of a novel molecular tool for studying cell type-specific transcriptional mechanisms and shed new light on the activity of ΔFosB, a critical transcriptional regulator of drug addiction.

Calmodulin acetylation: A modification to remember

The formation of new memories appears to require alterations in the shape and strength of synapses within the hippocampus, yet our knowledge of the molecular mechanisms underlying these changes remains incomplete. Zhang and colleagues provide new understanding of memory formation by uncovering the lysine acetyltransferase SRC3 as the key driver of the novel posttranslational modification of calmodulin (CaM) acetylation, which regulates CaM's activity and subsequent activation of CaMKII. This new pathway is demonstrated to be both necessary and sufficient for CA3→CA1 synapse long-term potentiation (LTP) and fear memory formation, and this approach may act as a blueprint for future investigation of the role of acetylation of other proteins in neuronal functions.

Upregulation of FosB/ΔFosB in limbic circuits after tooth exodontia-induced occlusal instability in an experimental model of unpredictable chronic stress

Psychological stress and occlusal alterations are contributing etiologic factors for temporomandibular and muscular disorders in the orofacial area. The neural modulation recruited for this relationship, however, is not elucidated. The aim of this study was to investigate potential central mechanisms involved in the exodontia-induced occlusal instability associated with unpredictable chronic stress (UCS). Male adult Wistar rats were submitted to occlusal instability (unilateral molar teeth extraction) and/or to a UCS protocol and treated with diazepam or vehicle. The anxiety-like behavior was evaluated by elevated plus maze (EPM) and open field (OF) tests. Limbic structures such as the central nucleus of the amygdala (CeA), paraventricular nucleus of the hypothalamus (PVN), dorsal periaqueductal gray matter (dPAG) and nucleus accumbens core (NAc) were analyzed for expression of FosB/ΔFosB (immediate early genes) by immunohistochemistry. Exodontia and/or UCS decreased the time spent in the open arms at the EPM and the distance travelled at the OF, and increased the immobility time at the OF, suggesting anxiety-like behavior. In addition, exodontia induction resulted in an upregulation of FosB/ΔFosB in the CeA, PVN and dPAG, while UCS and exodontia + UCS upregulate FosB/ΔFosB immunoreactivity in the CeA, PVN, dPAG and NAc. Treatment with diazepam decreased the expression of FosB/ΔFosB in all analyzed structures of animals subject to UCS and exodontia + UCS, while promoted a reduction in the FosB/ΔFosB expression in the CeA, PVN and dPAG in animals subject to exodontia. Our findings showed an anxiogenic effect of exodontia and UCS, which is correlated with intranuclear neuron activation of limbic structures in a spatially dependent manner and that is prevented by the administration of diazepam.

Quantitative standardization of resident mouse behavior for studies of aggression and social defeat

Territorial reactive aggression in mice is used to study the biology of aggression-related behavior and is also a critical component of procedures used to study mood disorders, such as chronic social defeat stress. However, quantifying mouse aggression in a systematic, representative, and easily adoptable way that allows direct comparison between cohorts within or between studies remains a challenge. Here, we propose a structural equation modeling approach to quantify aggression observed during the resident-intruder procedure. Using data for 658 sexually experienced CD-1 male mice generated by three research groups across three institutions over a 10-year period, we developed a higher-order confirmatory factor model wherein the combined contributions of latency to the first attack, number of attack bouts, and average attack duration on each trial day (easily observable metrics that require no specialized equipment) are used to quantify individual differences in aggression. We call our final model the Mouse Aggression Detector (MAD) model. Correlation analyses between MAD model factors estimated from multiple large datasets demonstrate generalizability of this measurement approach, and we further establish the stability of aggression scores across time within cohorts and demonstrate the utility of MAD for selecting aggressors which will generate a susceptible phenotype in social defeat experiments. Thus, this novel aggression scoring technique offers a systematic, high-throughput approach for aggressor selection in chronic social defeat stress studies and a more consistent and accurate study of mouse aggression itself.

A Cre-Dependent CRISPR/dCas9 System for Gene Expression Regulation in Neurons

Site-specific genetic and epigenetic targeting of distinct cell populations is a central goal in molecular neuroscience and is crucial to understand the gene regulatory mechanisms that underlie complex phenotypes and behaviors. While recent technological advances have enabled unprecedented control over gene expression, many of these approaches are focused on selected model organisms and/or require labor-intensive customization for different applications. The simplicity and modularity of clustered regularly interspaced short palindromic repeats (CRISPR)-based systems have transformed genome editing and expanded the gene regulatory toolbox. However, there are few available tools for cell-selective CRISPR regulation in neurons. We designed, validated, and optimized CRISPR activation (CRISPRa) and CRISPR interference (CRISPRi) systems for Cre recombinase-dependent gene regulation. Unexpectedly, CRISPRa systems based on a traditional double-floxed inverted open reading frame (DIO) strategy exhibited leaky target gene induction even without Cre. Therefore, we developed an intron-containing Cre-dependent CRISPRa system (SVI-DIO-dCas9-VPR) that alleviated leaky gene induction and outperformed the traditional DIO system at endogenous genes in HEK293T cells and rat primary neuron cultures. Using gene-specific CRISPR sgRNAs, we demonstrate that SVI-DIO-dCas9-VPR can activate numerous rat or human genes (GRM2, Tent5b, Fos, Sstr2, and Gadd45b) in a Cre-specific manner. To illustrate the versatility of this tool, we created a parallel CRISPRi construct that successfully inhibited expression from a luciferase reporter in HEK293T cells only in the presence of Cre. These results provide a robust framework for Cre-dependent CRISPR-dCas9 approaches across different model systems, and enable cell-specific targeting when combined with common Cre driver lines or Cre delivery via viral vectors.

The central nervous system can directly regulate breast cancer progression and blockage by quercetin

Background

Neuroinflammation involving the central nervous system (CNS), such as depression, is associated with a significantly increased risk of cancer and cancer-specific mortality due to breast cancer. It is of great significance to learn about the regulatory process of CNS in breast cancer progression.

Methods

We established a depressive MMTV-PyVT mouse model. The expression levels of neurotransmitters in the serum of depression animal models were assessed by enzyme-linked immunosorbent assay (ELISA). Changes of the microglia cells in the mice's brains were evaluated by immunofluorescence and reverse transcription-polymerase chain reaction (RT-PCR). Breast cancer progression was assessed by immunohistochemistry (IHC) analysis. To further investigate the mechanism by which ant-depressant drugs disrupt breast cancer progression, protein sequencing and network pharmacology were applied to identify related targets. Furthermore, we used conditioned medium from BV-2 microglia to culture breast cancer cells and treated the cells with quercetin at different concentrations; cell viability was assessed by the MTT assay.

Results

Our results show a possible regulatory target between neuroinflammation in the CNS and development of breast cancer, along with the reversal effect of quercetin on breast cancer progression.

Conclusions

Chronic stress may be an indicator of breast cancer and that quercetin could be an effective treatment for breast cancer patients with chronic stress.

Gene-environment interactions mediate stress susceptibility and resilience through the CaMKIIβ/TARPγ-8/AMPAR pathway

Although stressful events predispose individuals to psychiatric disorders, such as depression, not all people who undergo a stressful life experience become depressed, suggesting that gene-environment interactions (GxE) determine depression risk. The ventral hippocampus (vHPC) plays key roles in motivation, sociability, anhedonia, despair-like behaviors, anxiety, sleep, and feeding, pointing to the involvement of this brain region in depression. However, the molecular mechanisms underlying the cross talk between the vHPC and GxE in shaping behavioral susceptibility and resilience to chronic stress remain elusive. Here, we show that Ca2+/calmodulin-dependent protein kinase IIβ (CaMKIIβ) activity in the vHPC is differentially modulated in GxE mouse models of depression susceptibility and resilience, and that CaMKIIβ-mediated TARPγ-8 phosphorylation enhances the expression of AMPA receptor subunit GluA1 in the postsynaptic sites to enable stress resilience. We present previously missing molecular mechanisms underlying chronic stress-elicited behavioral changes, providing strategies for preventing and treating stress-related psychiatric disorders.

Repeated Neonatal Isoflurane Exposure is Associated with Higher Susceptibility to Chronic Variable Stress-induced Behavioural and Neuro-inflammatory Alterations

Numerous studies have reported that prolonged or multiple exposures to anaesthetics in early life lead to detrimental effects on brain function, most having focused on neurocognitive function, and relatively few on long term neuropsychiatric performance. The present study investigated the impact of repeated neonatal isoflurane exposure on chronic variable stress (CVS)-induced psychiatric and behavioural outcomes together with CVS-related neuronal activity and neuro-inflammatory reactivity in relevant brain circuits. In the present study, C57BL/6J mice received either three exposures to isoflurane at postnatal days 7, 8, and 9 or a control exposure. From postnatal day 45, mice were exposed to a mild, 3-week, CVS paradigm or none and the CVS-related neuropsychiatric performance was evaluated using a series of behavioural tests. The neuronal activity in relevant brain regions was measured by ΔFosB immunopositivity and CVS-related neuroinflammation was assessed by analysing levels of pro-inflammatory cytokines IL-1α, IL-1β, IL-6, and TNF-α. In mice experiencing serial neonatal isoflurane exposure, we detected a significant enhancement in anxiety levels following CVS procedures, together with enhanced neuronal activity, and exacerbated neuroinflammation in the basolateral amygdaloid nuclei (BLA) and hippocampal dentate gyrus (DG) regions. No such change was found in control mice. These results indicate an association between early multiple isoflurane exposures in infant mice and susceptibility to a CVS-evoked anxious phenotype accompanied by enhanced neuronal activity in BLA and DG regions and high inflammatory reactivity in response to CVS.

Evolution of stress responses refine mechanisms of social rank

Social rank functions to facilitate coping responses to socially stressful situations and conditions. The evolution of social status appears to be inseparably connected to the evolution of stress. Stress, aggression, reward, and decision-making neurocircuitries overlap and interact to produce status-linked relationships, which are common among both male and female populations. Behavioral consequences stemming from social status and rank relationships are molded by aggressive interactions, which are inherently stressful. It seems likely that the balance of regulatory elements in pro- and anti-stress neurocircuitries results in rapid but brief stress responses that are advantageous to social dominance. These systems further produce, in coordination with reward and aggression circuitries, rapid adaptive responding during opportunities that arise to acquire food, mates, perch sites, territorial space, shelter and other resources. Rapid acquisition of resources and aggressive postures produces dominant individuals, who temporarily have distinct fitness advantages. For these reasons also, change in social status can occur rapidly. Social subordination results in slower and more chronic neural and endocrine reactions, a suite of unique defensive behaviors, and an increased propensity for anxious and depressive behavior and affect. These two behavioral phenotypes are but distinct ends of a spectrum, however, they may give us insights into the troubling mechanisms underlying the myriad of stress-related disorders to which they appear to be evolutionarily linked.

Intergenerational changes in hippocampal transcription in an animal model of maternal depression

Chronic stress during early life, such as exposure to social conflict or deficits in parental care, can have persistent adverse behavioural effects. Offspring in a rodent model of maternal depression and early life stress have increased susceptibility to maternal depression themselves, suggesting a pathway by which maternal stress could be intergenerationally inherited. The overall aim of this study was to explore the genetic regulatory pathways underlying how maternal social stress and reduced care mediates stress-related behavioural changes in offspring across generations. This study investigated a social stress-based rat model of postpartum depression and the intergenerational inheritance of depressed maternal care where F0 (dams exposed to male intruder stress during lactation) and F1 offspring are directly exposed to social stress. RNASeq was used to investigate genome-wide transcriptome changes in the hippocampus of F1 and F2 generations. Transcriptome analyses revealed differential expression of 69 genes in the F1 generation and 14 in the F2 between controls versus social stress differences. Many of these genes were receptors and calcium-binding proteins in the F1 and involved in cellular oxidant detoxification in F2. The present data identify and characterize changes in the neural expression of key genes involved in the regulation of depression maintained between the generations, suggesting a potential neural pathway for the intergenerational transmission of depressed maternal care and maternal anxiety in the CSS model. Further work is needed to understand to what extent these results are due to molecular germline inheritance and/or the social propagation of deficits in maternal care.