Molecular profiling of the lateral habenula in a rat model of depression

Brain region-specific roles of brain-derived neurotrophic factor in social stress-induced depressive-like behavior

Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response. Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice is brain region-specific, particularly involving the corticolimbic system, including the ventral tegmental area, nucleus accumbens, prefrontal cortex, amygdala, and hippocampus. Determining how brain-derived neurotrophic factor participates in stress processing in different brain regions will deepen our understanding of social stress psychopathology. In this review, we discuss the expression and regulation of brain-derived neurotrophic factor in stress-sensitive brain regions closely related to the pathophysiology of depression. We focused on associated molecular pathways and neural circuits, with special attention to the brain-derived neurotrophic factor-tropomyosin receptor kinase B signaling pathway and the ventral tegmental area-nucleus accumbens dopamine circuit. We determined that stress-induced alterations in brain-derived neurotrophic factor levels are likely related to the nature, severity, and duration of stress, especially in the above-mentioned brain regions of the corticolimbic system. Therefore, BDNF might be a biological indicator regulating stress-related processes in various brain regions.

Kv3.1 Interaction with UBR5 Is Required for Chronic Inflammatory Pain

Chronic inflammatory pain caused by neuronal hyperactivity is a common and refractory disease. Kv3.1, a member of the Kv3 family of voltage-dependent K+ channels, is a major determinant of the ability of neurons to generate high-frequency action potentials. However, little is known about its role in chronic inflammatory pain. Here, we show that although Kv3.1 mRNA expression was unchanged, Kv3.1 protein expression was decreased in the dorsal spinal horn of mice after plantar injection of complete Freund's adjuvant (CFA), a mouse model of inflammatory pain. Upregulating Kv3.1 expression alleviated CFA-induced mechanical allodynia and heat hyperalgesia, whereas downregulating Kv3.1 induced nociception-like behaviors. Additionally, we found that ubiquitin protein ligase E3 component n-recognin 5 (UBR5), a key factor in the initiation of chronic pain, binds directly to Kv3.1 to drive its ubiquitin degradation. Intrathecal injection of the peptide TP-CH-401, a Kv3.1 ubiquitination motif sequence, rescued the decrease in Kv3.1 expression and Kv currents through competitive binding to UBR5, and consequently attenuated mechanical and thermal hypersensitivity. These findings demonstrate a previously unrecognized pathway of Kv3.1 abrogation by UBR5 and indicate that Kv3.1 is critically involved in the regulation of nociceptive behavior. Kv3.1 is thus a promising new target for treating inflammatory pain.

DHX9/DNA-tandem repeat-dependent downregulation of ciRNA-Fmn1 in the dorsal horn is required for neuropathic pain

Circular RNAs (ciRNAs) are emerging as new players in the regulation of gene expression. However, how ciRNAs are involved in neuropathic pain is poorly understood. Here, we identify the nervous-tissue-specific ciRNA-Fmn1 and report that changes in ciRNA-Fmn1 expression in spinal cord dorsal horn neurons play a key role in neuropathic pain after nerve injury. ciRNA-Fmn1 was significantly downregulated in ipsilateral dorsal horn neurons after peripheral nerve injury, at least in part because of a decrease in DNA helicase 9 (DHX9), which regulates production of ciRNA-Fmn1 by binding to DNA-tandem repeats. Blocking ciRNA-Fmn1 downregulation reversed nerve-injury-induced reductions in both the binding of ciRNA-Fmn1 to the ubiquitin ligase UBR5 and the level of ubiquitination of albumin (ALB), thereby abrogating the nerve-injury-induced increase of ALB expression in the dorsal horn and attenuating the associated pain hypersensitivities. Conversely, mimicking downregulation of ciRNA-Fmn1 in naïve mice reduced the UBR5-controlled ubiquitination of ALB, leading to increased expression of ALB in the dorsal horn and induction of neuropathic-pain-like behaviors in naïve mice. Thus, ciRNA-Fmn1 downregulation caused by changes in binding of DHX9 to DNA-tandem repeats contributes to the genesis of neuropathic pain by negatively modulating UBR5-controlled ALB expression in the dorsal horn.

ANKRD49 promotes the invasion and metastasis of lung adenocarcinoma via a P38/ATF-2 signalling pathway

Lung adenocarcinoma (LUAD) is the most challenging neoplasm to treat in clinical practice. Ankyrin repeat domain 49 protein (ANKRD49) is highly expressed in several carcinomas; however, its pattern of expression and role in LUAD are not known. Tissue microarrays, immunohistochemistry, χ² test, Spearman correlation analysis, Kaplan–Meier, log‐rank test, and Cox's proportional hazard model were used to analyse the clinical cases. The effect of ANKRD49 on the LUAD was investigated using CCK‐8, clonal formation, would healing, transwell assays, and nude mice experiment. Expressions of ANKRD49 and its associated downstream protein molecules were verified by real‐time PCR, Western blot, immunohistochemistry, and/or immunofluorescence analyses. ANKRD49 expression was highly elevated in LUAD. The survival rate and Cox's modelling analysis indicated that there may be an independent prognostic indicator for LUAD patients. We also found that ANKRD49 promoted the invasion and migration in both in in vitro and in vivo assays, through upregulating matrix metalloproteinase (MMP)‐2 and MMP‐9 activities via the P38/ATF‐2 signalling pathway Our findings suggest that ANKRD49 is a latent biomarker for evaluating LUAD prognosis and promotes the metastasis of A549 cells via upregulation of MMP‐2 and MMP‐9 in a P38/ATF‐2 pathway‐dependent manner.

Gene Expression Profiling of the Habenula in Rats Exposed to Chronic Restraint Stress

Chronic stress contributes to the risk of developing depression; the habenula, a nucleus in epithalamus, is associated with many neuropsychiatric disorders. Using genome-wide gene expression analysis, we analyzed the transcriptome of the habenula in rats exposed to chronic restraint stress for 14 days. We identified 379 differentially expressed genes (DEGs) that were affected by chronic stress. These genes were enriched in neuroactive ligand-receptor interaction, the cAMP (cyclic adenosine monophosphate) signaling pathway, circadian entrainment, and synaptic signaling from the Kyoto Encyclopedia of Genes and Genomes pathway analysis and responded to corticosteroids, positive regulation of lipid transport, anterograde trans-synaptic signaling, and chemical synapse transmission from the Gene Ontology analysis. Based on protein-protein interaction network analysis of the DEGs, we identified neuroactive ligand-receptor interactions, circadian entrainment, and cholinergic synapse-related subclusters. Additionally, cell type and habenular regional expression of DEGs, evaluated using a recently published single-cell RNA sequencing study (GSE137478), strongly suggest that DEGs related to neuroactive ligand-receptor interaction and trans-synaptic signaling are highly enriched in medial habenular neurons. Taken together, our findings provide a valuable set of molecular targets that may play important roles in mediating the habenular response to stress and the onset of chronic stress-induced depressive behaviors.

PACAP-expressing neurons in the lateral habenula diminish negative emotional valence

The lateral habenula (LHb) is a small, bilateral, epithalamic nucleus which processes aversive information. While primarily glutamatergic, LHb neurons express genes coding for many neuropeptides, such as Adcyap1 the gene encoding pituitary adenylate cyclase-activating polypeptide (PACAP), which itself has been associated with anxiety and stress disorders. Using Cre-dependent viral vectors, we targeted and characterized these neurons based on their anatomical projections and found that they projected to both the raphe and rostromedial tegmentum but only weakly to ventral tegmental area. Using RiboTag to capture ribosomal-associated mRNA from these neurons and reanalysis of existing single cell RNA sequencing data, we did not identify a unique molecular phenotype that characterized these PACAP-expressing neurons in LHb. In order to understand the function of these neurons, we conditionally expressed hM₃ Dq DREADD selectively in LHb PACAP-expressing neurons and chemogenetically excited these neurons during behavioral testing in the open field test, contextual fear conditioning, sucrose preference, novelty suppressed feeding, and conditioned place preference. We found that Gq activation of these neurons produce behaviors opposite to what is expected from the LHb as a whole-they decreased anxiety-like and fear behavior and produced a conditioned place preference. In conclusion, PACAP-expressing neurons in LHb represents a molecularly diverse population of cells that oppose the actions of the remainder of LHb neurons by being rewarding or diminishing the negative consequences of aversive events.

Stress-Induced Morphological, Cellular and Molecular Changes in the Brain-Lessons Learned from the Chronic Mild Stress Model of Depression

Major depressive disorder (MDD) is a severe illness imposing an increasing social and economic burden worldwide. Numerous rodent models have been developed to investigate the pathophysiology of MDD. One of the best characterized and most widely used models is the chronic mild stress (CMS) model which was developed more than 30 years ago by Paul Willner. More than 2000 published studies used this model, mainly to assess novel compounds with potential antidepressant efficacy. Most of these studies examined the behavioral consequences of stress and concomitant drug intervention. Much fewer studies focused on the CMS-induced neurobiological changes. However, the stress-induced cellular and molecular changes are important as they may serve as potential translational biomarkers and increase our understanding of the pathophysiology of MDD. Here, we summarize current knowledge on the structural and molecular alterations in the brain that have been described using the CMS model. We discuss the latest neuroimaging and postmortem histopathological data as well as molecular changes including recent findings on microRNA levels. Different chronic stress paradigms occasionally deliver dissimilar findings, but the available experimental data provide convincing evidence that the CMS model has a high translational value. Future studies examining the neurobiological changes in the CMS model in combination with clinically effective antidepressant drug intervention will likely deliver further valuable information on the pathophysiology of MDD.

Rostrocaudal subregions of the ventral tegmental area are differentially impacted by chronic stress

RATIONALE

The ventral tegmental area (VTA) is implicated in the pathophysiology of depression and addictive disorders and is subject to the detrimental effects of stress. Chronic stress may differentially alter the activity pattern of its different subregions along the rostrocaudal and dorsoventral axes, which may relate to the variable behavioral sensitivity to stress mediated by these subregions.

OBJECTIVES

Here, chronic stress-exposed rats were tested for depressive-like reactivity. In situ hybridization for zif268 as a marker of neuronal activation was combined with in vivo single-unit recording of dopaminergic neurons to assess modifications in the activity of the rostral VTA (rVTA) and caudal VTA (cVTA). Changes in the expression of stress-responsive glucocorticoid receptors (GR) and brain-derived neurotrophic factor (BDNF) were also assessed.

RESULTS

Stress-induced anhedonia-like, hyper-anxious, and passive-like responding were associated with reductions in dopaminergic burst activity in the cVTA and an increase in local GABAergic activity, particularly in GABA_A receptor sensitivity. On the other hand, stress increased single-spiking activity, burst activity, and zif268 mRNA levels in the rVTA, which were associated with increased glutamatergic tonus and enhanced GR and AMPA receptor (AMPAR) expression. rVTA and cVTA activity differentially correlated with sucrose preference and passivity measures.

CONCLUSIONS

These data demonstrate that the rVTA and cVTA respond differently to stress and suggest that while cVTA activity may be related to passivity-like states, the activity of both subregions appears to be related to anhedonia and the processing of incentive value. These region-dependent abnormalities indicate the multi-modular composition of the VTA, which could provide multiple substrates for different symptom features.

MicroRNA-1224 Splicing CircularRNA-Filip1l in an Ago2-Dependent Manner Regulates Chronic Inflammatory Pain via Targeting Ubr5

Dysfunctions of gene transcription and translation in the nociceptive pathways play the critical role in development and maintenance of chronic pain. Circular RNAs (circRNAs) are emerging as new players in regulation of gene expression, but whether and how circRNAs are involved in chronic pain remain elusive. We showed here that complete Freund's adjuvant-induced chronic inflammation pain significantly increased circRNA-Filip1l (filamin A interacting protein 1-like) expression in spinal neurons of mice. Blockage of this increase attenuated complete Freund's adjuvant-induced nociceptive behaviors, and overexpression of spinal circRNA-Filip1l in naive mice mimicked the nociceptive behaviors as evidenced by decreased thermal and mechanical nociceptive threshold. Furthermore, we found that mature circRNA-Filip1l expression was negatively regulated by miRNA-1224 via binding and splicing of precursor of circRNA-Filip1l (pre-circRNA-Filip1l) in the Argonaute-2 (Ago2)-dependent manner. Increase of spinal circRNA-Filip1l expression resulted from the decrease of miRNA-1224 expression under chronic inflammation pain state. miRNA-1224 knockdown or Ago2 overexpression induced nociceptive behaviors in naive mice, which was prevented by the knockdown of spinal circRNA-Filip1l. Finally, we demonstrated that a ubiquitin protein ligase E3 component n-recognin 5 (Ubr5), validated as a target of circRNA-Filip1l, plays a pivotal role in regulation of nociception by spinal circRNA-Filip1l. These data suggest that miRNA-1224-mediated and Ago2-dependent modulation of spinal circRNA-Filip1l expression regulates nociception via targeting Ubr5, revealing a novel epigenetic mechanism of interaction between miRNA and circRNA in chronic inflammation pain.SIGNIFICANCE STATEMENT circRNAs are emerging as new players in regulation of gene expression. Here, we found that the increase of circRNA-Filip1l mediated by miRNA-1224 in an Ago2-dependent way in the spinal cord is involved in regulation of nociception via targeting Ubr5 Our study reveals a novel epigenetic mechanism of interaction between miRNA and circRNA in chronic inflammation pain.

Dysregulation of the Lateral Habenula in Major Depressive Disorder

Clinical and preclinical evidence implicates hyperexcitability of the lateral habenula (LHb) in the development of psychiatric disorders including major depressive disorder (MDD). This discrete epithalamic nucleus acts as a relay hub linking forebrain limbic structures with midbrain aminergic centers. Central to reward processing, learning and goal directed behavior, the LHb has emerged as a critical regulator of the behaviors that are impaired in depression. Stress-induced activation of the LHb produces depressive- and anxiety-like behaviors, anhedonia and aversion in preclinical studies. Moreover, deep brain stimulation of the LHb in humans has been shown to alleviate chronic unremitting depression in treatment resistant depression. The diverse neurochemical processes arising in the LHb that underscore the emergence and treatment of MDD are considered in this review, including recent optogenetic studies that probe the anatomical connections of the LHb.

Contingency Training Alters Neurobiological Components of Emotional Resilience in Male and Female Rats

Prior research with a rat model of behavioral therapy [i.e., effort-based reward (EBR) contingency training] suggests that strengthened associations between physical effort and desired outcomes enhance neurobiological indices of resilience. In the current study, male and female Long-Evans rats were exposed to either six weeks of EBR training or noncontingent training prior to 10 days of exposure to chronic unpredictable stress (CUS). Subsequently, all animals were exposed to a problem-solving task and then trained in a spatial learning/foraging task, the Dry Land Maze (DLM). Following habituation training and test trials, rats were assessed in a probe trial that generated a prediction error (cognitive uncertainty). Results indicated that, during CUS exposure, contingency-training enhanced dehydroepiandrosterone/corticosterone ratios (consistent with healthier stress responses), especially in male rats. Additionally, contingency training increased exploratory behaviors in the probe trial as well as differentially influenced on-task problem-solving performance in males and females. Following the probe trial, brains were exposed to histological analyses to determine the effects of sex and contingency training on various neurobiological markers. Contingency training decreased BDNF-immunoreactivity (ir) in the hippocampus CA1 and lateral habenula, implicating differential neuroplasticity responses in the training groups. Further, coordinated fos-ir activation in areas associated with emotional resilience (i.e., motivation-regulation) was observed in contingent-trained animals. In sum, the current findings confirm that behavioral training is associated with neurobiological markers of emotional resilience; however, further assessments are necessary to more accurately determine the therapeutic potential for the EBR contingency training model.

Disturbances of diurnal phase markers, behavior, and clock genes in a rat model of depression; modulatory effects of agomelatine treatment

Major depressive disorder (MDD) is a growing problem worldwide. Though, the etiology remains unresolved, circadian rhythm disturbances are frequently observed in MDD and thus is speculated to play a key role herein. The present study focuses on circadian rhythm disturbances in the chronic mild stress (CMS) animal model of depression and examined whether the atypical antidepressant, agomelatine, which is mediating its action via melatonergic and serotonergic receptors, is capable of resynchronizing the perturbed rhythm. Melatonin is often used as a marker of the circadian phase, but the functional and behavioral output is dictated on a cellular level by the molecular clock, driven by the clock genes. We applied in situ hybridization histochemistry to measure the expression levels of the core clock genes, period (Per) 1 and 2 and bone and muscle ARNT-like protein 1 (Bmal1), in multiple brain regions believed to be implicated in depression. Agomelatine showed an antidepressant-like effect in the sucrose consumption test and an anxiolytic-like profile in the elevated zero maze. We found that CMS increased nighttime melatonin release in rats and that agomelatine attenuated this effect. Stress was shown to have a time and region-specific effect on clock gene expression in the brain. Treatment with agomelatine failed to normalize clock gene expression, and the observed modifying effect on gene expression did not associate with the antidepressant-like effect. This suggests that the antidepressant actions of agomelatine are mainly independent of circadian rhythm synchronization and, in this regard, not superior to traditional antidepressants tested in our model.

A little rein on addiction

Rewarding and aversive experiences influence emotions, motivate specific behaviors, and modify future action in animals. Multiple conserved vertebrate neural circuits have been discovered that act in a species-specific manner to reinforce behaviors that are rewarding, while attenuating those with an adverse outcome. A growing body of research now suggests that malfunction of the same circuits is an underlying cause for many human disorders and mental ailments. The habenula (Latin for "little rein") complex, an epithalamic structure that regulates midbrain monoaminergic activity has emerged in recent years as one such region in the vertebrate brain that modulates behavior. Its dysfunction, on the other hand, is implicated in a spectrum of psychiatric disorders in humans such as schizophrenia, depression and addiction. Here, I review the progress in identification of potential mechanisms involving the habenula in addiction.

Up-regulation of ANKDR49, a poor prognostic factor, regulates cell proliferation of gliomas

The Ankyrin repeat domain 49 (ANKRD49) is an evolutionarily conserved protein, which is related to mediate protein–protein interaction. However, the function of ANKRD49 in human glioma remains elusive. Mining through The Cancer Genome Atlas (TCGA) database, we found that the expression of ANKRD49 was increased in glioma tissues and that high expression of ANKRD49 was strongly associated with high disease grade and poor overall survival. To investigate the role of ANKRD49 in malignant glioma, lentivirus expressing shRNA targetting ANKRD49 was constructed in U251 and U87 malignant glioma cells. We demonstrated that ANKRD49 knockdown reduced the proliferation rate of U251 and U87 cells. Further mechanism analysis indicated that depletion of ANKRD49 led to the cell-cycle arrest and induced apoptosis in U251 and U87 cells. ANKRD49 knockdown also changed the expression of key effectors that are involved in stress response, cell cycle, and apoptosis, including p-HSP27 (heat shock protein 27), p-Smad2 (SMAD family member 2), p-p53, p-p38, p-MAPK (mitogen-activated protein kinase), p-SAPK/JNK (stress-activated protein kinase/c-jun n-terminal kinase), cleveagated Caspase-7, p-Chk1 (checkpoint kinase 1), and p-eIF2a (eukaryotic translation initiation factor 2a). Taken together, our findings implicate that ANKRD49 promotes the proliferation of human malignant glioma cells. ANKRD49 maybe an attractive target for malignant glioma therapy.

Differential Peripheral Proteomic Biosignature of Fluoxetine Response in a Mouse Model of Anxiety/Depression

The incorporation of peripheral biomarkers in the treatment of major depressive disorders (MDD) could improve the efficiency of treatments and increase remission rate. Peripheral blood mononuclear cells (PBMCs) represent an attractive biological substrate allowing the identification of a drug response signature. Using a proteomic approach with high-resolution mass spectrometry, the present study aimed to identify a biosignature of antidepressant response (fluoxetine, a Selective Serotonin Reuptake Inhibitor) in PBMCs in a mouse model of anxiety/depression. Following determination of an emotionality score, using complementary behavioral analysis of anxiety/depression across three different tests (Elevated Plus Maze, Novelty Suppressed Feeding, Splash Test), we showed that a 4-week corticosterone treatment (35 μg/ml, CORT model) in C57BL/6NTac male mice induced an anxiety/depressive-like behavior. Then, chronic fluoxetine treatment (18 mg/kg/day for 28 days in the drinking water) reduced corticosterone-induced increase in emotional behavior. However, among 46 fluoxetine-treated mice, only 30 of them presented a 50% decrease in emotionality score, defining fluoxetine responders (CORT/Flx-R). To determine a peripheral biological signature of fluoxetine response, proteomic analysis was performed from PBMCs isolated from the “most” affected corticosterone/vehicle (CORT/V), corticosterone/fluoxetine responders and non-responders (CORT/Flx-NR) animals. In comparison to CORT/V, a total of 263 proteins were differently expressed after fluoxetine exposure. Expression profile of these proteins showed a strong similarity between CORT/Flx-R and CORT/Flx-NR (R = 0.827, p < 1e^-7). Direct comparison of CORT/Flx-R and CORT/Flx-NR groups revealed 100 differently expressed proteins, representing a combination of markers associated either with the maintenance of animals in a refractory state, or associated with behavioral improvement. Finally, 19 proteins showed a differential direction of expression between CORT/Flx-R and CORT/Flx-NR that drove them away from the CORT-treated profile. Among them, eight upregulated proteins (RPN2, HSPA9, NPTN, AP2B1, UQCRC2, RACK-1, TOLLIP) and one downregulated protein, TLN2, were previously associated with MDD or antidepressant drug response in the literature. Future preclinical studies will be required to validate whether proteomic changes observed in PBMCs from CORT/Flx-R mice mirror biological changes in brain tissues.

The mechanism of acute fasting-induced antidepressant-like effects in mice

Acute fasting induced antidepressant‐like effects. However, the exact brain region and mechanism of these actions are still largely unknown. Therefore, in this study the antidepressant‐like effects of acute fasting on c‐Fos expression and BDNF levels were investigated. Consistent with our previous findings, immobility time was remarkably shortened by 9 hrs fasting in the forced swimming test. Furthermore, these antidepressant‐like effects of 9 fasting were inhibited by a 5‐HT_2A/2C receptor agonist (±)‐1‐(2, 5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane hydrochloride (DOI), and the effect of DOI was blocked by pretreatment with a selective 5‐HT_2A receptor antagonist ketanserin. Immunohistochemical study has shown that c‐Fos level was significantly increased by 9 hrs fasting in prefrontal cortex but not hippocampus and habenular. Fasting‐induced c‐Fos expression was further enhanced by DOI in prefrontal cortex, and these enhancements were inhibited by ketanserin. The increased BDNF levels by fasting were markedly inhibited by DOI in frontal cortex and hippocampus, and these effects of DOI on BDNF levels were also blocked by ketanserin. These findings suggest that the antidepressant‐like effects of acute fasting may be exerted via 5‐HT_2A receptor and particularly sensitive to neural activity in the prefrontal cortex. Furthermore, these antidepressant‐like effects are also mediated by CREB and BDNF pathway in hippocampus and frontal cortex. Therefore, fasting may be potentially helpful against depression.

Neuronal substrates underlying stress resilience and susceptibility in rats

Background

Stress and stressful life events have repeatedly been shown as causally related to depression. The Chronic Mild Stress rat model is a valid model of stress-induced depression. Like humans, rats display great heterogeneity in their response to stress and adversity. Hence some individuals are stress-sensitive and prone to develop depression-like behaviour in response to modest stressors, while others are stress-resilient and remain essentially symptom free.

Objectives

Compared to the large body of research, which describes stress-induced maladaptive neurobiological changes, relatively little attention has been devoted to understand resiliency to stress. The aim of the present study was to identify changes in neuronal activity, associated with stress-resilient and stress-susceptible chronic mild stress endophenotypes, by examining c-Fos expression in 13 different brain areas. Changes in c-Fos expression have been reported as associated to stressful conditions.

Methods

Stress-induced modulation of neuronal activation patterns in response to the chronic mild stress paradigm was mapped using the immediate early gene expression c-Fos as a marker. Quantification of the c-Fos-like immunoreactivity responses was done by semi-automated profile counting procedures and design-based stereology.

Results

Exposure to chronic mild stress significantly altered c-Fos expression in a total of 6 out of 13 investigated areas. Chronic mild stress was found to suppress the c-Fos response within the magnocellular ventral lateral geniculate nucleus of both stress subgroups. In the the lateral and ventral orbital cortices of stress-resilient rats, the c-Fos like immunoreactivity response was also repressed by stress exposure. On the contrary the c-Fos response within the amygdala, medial habenula, and infralimbic cortex was increased selectively for the stress-susceptible rats.

Conclusions

The study was initiated to characterize neuronal substrates associated with stress-coping mechanisms. Six areas, all of which represents limbic structures, were found to be sensitive to stress exposure. The effects within these areas associate to the hedonic status of the rats. Hence, these areas might be associated to stress-coping mechanisms underlying the chronic mild stress induced segregation into stress-susceptible and stress-resilient endophenotypes.

The habenula as a critical node in chronic stress-related anxiety

The habenula is activated in response to stressful and aversive events, resulting in exploratory inhibition. Although possible mechanisms for habenula activation have been proposed, the effects of chronic stress on the habenular structure have never been studied. Herein, we assessed changes in volume, cell density and dendritic structure of habenular cells after chronic stress exposure using stereological and 3D morphological analysis. This study shows for the first time that there is a hemispherical asymmetry in the medial habenula (MHb) of the adult rat, with the right MHb containing more neurons than its left counterpart. Additionally, it shows that chronic stress induces a bilateral atrophy of both the MHb and the lateral habenula (LHb). This atrophy was accompanied by a reduction of the number of neurons in the right MHb and the number of glial cells in the bilateral LHb, but not by changes in the dendritic arbors of multipolar neurons. Importantly, these structural changes were correlated with elevated levels of serum corticosterone and increased anxious-like behavior in stressed animals. To further assess the role of the habenula in stress-related anxiety, bilateral lesions of the LHb were performed; interestingly, in lesioned animals the chronic stress protocol did not trigger increases in circulating corticosterone or anxious-like behavior. This study highlights the role of the habenula in the stress responses and how its sub-regions are structurally impacted by chronic stress with physiological and behavioral consequences.

Engaging Research Domain Criteria (RDoC): Neurocircuitry in Search of Meaning

The Research Domain Criteria (RDoC) initiative was implemented to reorient the approach to mental health research from one focused on Diagnostic and Statistical Manual of Mental Disorders (DSM) nosology to one oriented to psychological constructs constrained by neurocircuitry and molecular entities. The initiative has generated significant discussion and valuable reflection on the moorings of psychiatric research. The purpose of this article is to illustrate how a basic or clinical investigator can engage RDoC to explore the neurobiological underpinnings of psychopathology and how a research question can be formulated in RDoC's framework. We utilize a brain region with significant growing interest, the habenula, as an example for probing RDoC's utility. Opportunities to enhance neurocircuitry-psychological construct associations and problems associated with neuronal populations that enable bidirectional circuitry influence are discussed. The exercise reveals areas for further development that could move RDoC from a promising research idea to a successfully engaged foundation for catalyzing clinically relevant discoveries.

Activation of a Habenulo-Raphe Circuit Is Critical for the Behavioral and Neurochemical Consequences of Uncontrollable Stress in the Male Rat

Exposure to uncontrollable stress [inescapable tailshock (IS)] produces behavioral changes that do not occur if the stressor is controllable [escapable tailshock (ES)] an outcome that is mediated by greater IS-induced dorsal raphe nucleus (DRN) serotonin [5-hydroxytryptamine (5-HT)] activation. It has been proposed that this differential activation occurs because the presence of control leads to top-down inhibition of the DRN from medial prefrontal cortex (mPFC), not because uncontrollability produces greater excitatory input. Although mPFC inhibitory regulation over DRN 5-HT activation has received considerable attention, the relevant excitatory inputs that drive DRN 5-HT during stress have not. The lateral habenula (LHb) provides a major excitatory input to the DRN, but very little is known about the role of the LHb in regulating DRN-dependent behaviors. Here, optogenetic silencing of the LHb during IS blocked the typical anxiety-like behaviors produced by IS in male rats. Moreover, LHb silencing blocked the increase in extracellular basolateral amygdala 5-HT during IS and, surprisingly, during behavioral testing the following day. We also provide evidence that LHb-DRN pathway activation is not sensitive to the dimension of behavioral control. Overall, these experiments highlight a critical role for LHb in driving DRN activation and 5-HT release into downstream circuits that mediate anxiety-like behavioral outcomes of IS and further support the idea that behavioral control does not modulate excitatory inputs to the DRN.

MicroRNA Profiling in the Medial and Lateral Habenula of Rats Exposed to the Learned Helplessness Paradigm: Candidate Biomarkers for Susceptibility and Resilience to Inescapable Shock

Depression is a highly heterogeneous disorder presumably caused by a combination of several factors ultimately causing the pathological condition. The genetic liability model of depression is likely to be of polygenic heterogeneity. miRNAs can regulate multiple genes simultaneously and therefore are candidates that align with this model. The habenula has been linked to depression in both clinical and animal studies, shifting interest towards this region as a neural substrate in depression. The goal of the present study was to search for alterations in miRNA expression levels in the medial and lateral habenula of rats exposed to the learned helplessness (LH) rat model of depression. Ten miRNAs showed significant alterations associating with their response to the LH paradigm. Of these, six and four miRNAs were significantly regulated in the MHb and LHb, respectively. In the MHb we identified miR-490, miR-291a-3p, MiR-467a, miR-216a, miR-18b, and miR-302a. In the LHb miR-543, miR-367, miR-467c, and miR-760-5p were significantly regulated. A target gene analysis showed that several of the target genes are involved in MAPK signaling, neutrophin signaling, and ErbB signaling, indicating that neurotransmission is affected in the habenula as a consequence of exposure to the LH paradigm.

Disturbed diurnal rhythm of three classical phase markers in the chronic mild stress rat model of depression

Disturbances of circadian rhythms have been suggested to be a causal factor in the development of major depressive disorder. However, the mechanisms underlying the association between circadian rhythm abnormalities and mood disorders are still unknown. In the current study the association between diurnal pattern of key phase markers (melatonin, corticosterone, and core body temperature) and anhedonic-like behavior was investigated using the highly validated rat chronic mild stress (CMS) model of depression. Phase marker measurements were done after 3.5 weeks of CMS in 48 control rats and 48 anhedonic-like rats at 6 time points within 24h. The results showed that anhedonic-like behavior associates with changes in all three phase markers: an increased dark phase melatonin secretion, an additional peak in corticosterone level in the beginning of the light phase, and hypothermia in the dark phase. The result adds to the validity of the CMS model in general and in particular to be adequate as a model for studying the chronobiology of depressive disorder.

Antidepressant actions of lateral habenula deep brain stimulation differentially correlate with CaMKII/GSK3/AMPK signaling locally and in the infralimbic cortex

High frequency deep brain stimulation (DBS) of the lateral habenula (LHb) reduces symptoms of depression in severely treatment-resistant individuals. Despite the observed therapeutic effects, the molecular underpinnings of DBS are poorly understood. This study investigated the efficacy of high frequency LHb DBS (130Hz; 200μA; 90μs) in an animal model of tricyclic antidepressant resistance. Further, we reported DBS mediated changes in Ca(2+)/calmodulin-dependent protein kinase (CaMKIIα/β), glycogen synthase kinase 3 (GSK3α/β) and AMP-activated protein kinase (AMPK) both locally and in the infralimbic cortex (IL). Protein expressions were then correlated to immobility time during the forced swim test (FST). Antidepressant actions were quantified via FST. Treatment groups comprised of animals treated with adrenocorticotropic hormone alone (ACTH; 100μg/day, 14days, n=7), ACTH with active DBS (n=7), sham DBS (n=8), surgery only (n=8) or control (n=8). Active DBS significantly reduced immobility in ACTH-treated animals (p<0.05). For this group, western blot results demonstrated phosphorylation status of LHb CaMKIIα/β and GSK3α/β significantly correlated to immobility time in the FST. Concurrently, we observed phosphorylation status of CaMKIIα/β, GSK3α/β, and AMPK in the IL to be negatively correlated with antidepressant actions of DBS. These findings suggest that activity dependent phosphorylation of CaMKIIα/β, and GSK3α/β in the LHb together with the downregulation of CaMKIIα/β, GSK3α/β, and AMPK in the IL, contribute to the antidepressant actions of DBS.

Chronic mild stress alters the somatostatin receptors in the rat brain

RATIONALE

The involvement of somatostatin (SST) and its receptors in the pathophysiology of depression and stress has been evidenced by numerous studies.

OBJECTIVES

The purpose of the present study was to find whether chronic mild stress (CMS), an animal model of depression, affects the SST receptors in the rat brain and pituitary, as well as the level of SST in plasma.

METHODS

In CMS model, rats were subjected to 2 weeks of stress and behaviorally characterized using the sucrose consumption test into differently reacting groups based on their response to stress, i.e., stress-reactive (anhedonic), stress-non-reactive (resilient), and invert-reactive rats (characterized by excessive sucrose intake). We measured specific binding of [125I]Tyr3-Octreotide, expression of mRNA encoding sst2R receptors in the rat brains, expression of SST and its receptors in rat pituitary, and the level of SST in the plasma.

RESULTS

The obtained results show decreases in binding of [125I]Tyr3-Octreotide in most of rat brain regions upon CMS and no significant differences between three stressed groups of animals, except for significant up-regulation of sst2 receptor in medial habenula (MHb) in the stress-reactive group. In the same group of animals, significant increase in plasma SST level was observed.

CONCLUSIONS

There are two particularly sensitive sites distinguishing the response to stress in CMS model. In the brain, it is MHb, while on the periphery this predictor is SST level in plasma. These changes may broaden an understanding of the mechanisms involved in the stress response and point to the intriguing role of MHb.

Chronic selective serotonin reuptake inhibition modulates endothelial dysfunction and oxidative state in rat chronic mild stress model of depression

Major depression is known to be associated with cardiovascular abnormalities, and oxidative stress has been suggested to play a role. We tested the hypothesis that antidepressant treatment reduces oxidative stress and endothelial dysfunctions in the chronic mild stress (CMS) model of depression in rats. Rats with >30% reduction in sucrose intake after 4 wk of CMS were defined in the study as CMS-susceptible and compared with unstressed controls. Sixteen CMS-susceptible and eight unstressed rats were treated during weeks 5 to 8 of the CMS protocol with escitalopram. Escitalopram-treated rats with >20% recovery in the sucrose consumption during the last 2 wk of treatment were defined as escitalopram responders. Rats that did not reach these criteria were defined as escitalopram nonresponders. In the open field test, escitalopram responders demonstrated anxiolytic effect of treatment. In mesenteric small arteries, escitalopram affected neither NO nor cyclooxygenase-1 (COX-1)-mediated vasodilation. Escitalopram potentiated endothelium-dependent hyperpolarization-like response, which was suppressed in the vehicle-treated CMS-susceptible rats and reduced COX-2-dependent relaxation, which was elevated in the vehicle-treated CMS-susceptible rats. Escitalopram did not affect blood pressure and heart rate, which were elevated in the vehicle-treated CMS-susceptible rats. Oxidative stress markers were changed in association with CMS in liver, heart, and brain. Escitalopram normalized oxidative stress markers in the majority of tissues. This study demonstrates that the antidepressant effect of escitalopram is associated with partial improvement of endothelial function in small arteries affecting COX-2 and endothelium-dependent hyperpolarization-like pathways.

The Ankyrin Repeat Domain 49 (ANKRD49) Augments Autophagy of Serum-Starved GC-1 Cells through the NF-κB Pathway

The ankyrin repeat domain 49 (ANKRD49) is an evolutionarily conserved protein highly expressed in testes. However, the function of ANKRD49 in spermatogenesis is unknown. In this study, we found that ANKRD49 resides primarily in nucleus of spermatogonia, spermatocytes and round spermatids. ANKRD49 overexpression augments starvation-induced autophagy in male germ GC-1 cells whereas shRNA knockdown of ANKRD49 attenuates the autophagy. Inhibition of NF-κB pathway by its inhibitors or p65 siRNA prevents the ANKRD49-dependent autophagy augmentation, demonstrating that ANKRD49 enhances autophagy via NF-κB pathway. Our findings suggest that ANKRD49 plays an important role in spermatogenesis via promotion of autophagy-dependent survival.