Amygdala-ventral pallidum pathway decreases dopamine activity after chronic mild stress in rats

Proteomic Insights Into Susceptibility and Resistance to Chronic-Stress-Induced Depression or Anxiety in the Rat Striatum

Chronic stress is a key factor for the onset of anxiety and depression disorders. However, the stress-induced common and unique molecular basis of the two psychiatric disorders is not fully known and still needs to be explored. Previously, we employed a chronic mild stress (CMS) procedure to induce a rat model including depression-susceptible (Dep-Sus), anxiety-susceptible (Anx-Sus), and insusceptible (Insus) cohorts. In this work, we continuously analyze the striatal proteomes of the three stressed cohorts by the use of comparative proteomics and bioinformatics approaches. Through isobaric tags for relative and absolute quantitation (iTRAQ)-based analysis, 386 abnormally expressed proteins in total were identified. These deregulated proteins are involved in various biological functions and significant pathways that are potentially connected with resistance and susceptibility to CMS-caused anxious- or depressive-like behaviors and, hence, could act as suggestive protein targets. A further parallel reaction monitoring-based independent investigation shows that alterations in Pak5, Dgkg, Scn4b, Rb1cc1, and Acin1; Ggps1, Fntb, Nudt19, Ufd1, and Ndufab1; and Dnajb12, Hbb2, Ap2s1, Ip6k1, and Stk4 were specifically connected with Dep-Sus, Anx-Sus, or Insus groups, respectively, potentially indicating that identical CMS treatment results in the different changes in the striatal protein regulations. Overall, our current proteomics study of the striatum provides an important molecular foundation and comprehensive insights into common and specific deregulations correlated with pathophysiological mechanisms that underlie resistance and susceptibility to chronic stress-induced anxiety or depression.

Proteomic Response of Rat Pituitary Under Chronic Mild Stress Reveals Insights Into Vulnerability and Resistance to Anxiety or Depression

Chronic stress as one of the most significant risk factor can trigger overactivity of hypothalamic-pituitary-adrenal (HPA) axis in depression as well as anxiety. Yet, the shared and unique neurobiological underpinnings underlying the pituitary abnormality in these two disorders have not been made clear. We previously have established depression-susceptible, anxiety-susceptible and insusceptible groups using a valid chronic mild stress (CMS) model. In this work, the possible protein expression changes in the rat pituitary of these three groups were continuously investigated through the use of the comparative quantitative proteomics and bioinformatics approaches. The pituitary-proteome analysis identified totally 197 differential proteins as a CMS response. These deregulated proteins were involved in diverse biological functions and significant pathways potentially connected with the three different behavioral phenotypes, likely serving as new investigative protein targets. Afterwards, parallel reaction monitoring-based independent analysis found out that expression alterations in Oxct1, Sec24c, Ppp1cb, Dock1, and Coq3; Lama1, Glb1, Gapdh, Sccpdh, and Renbp; Sephs1, Nup188, Spp1, Prodh1, and Srm were specifically linked to depression-susceptible, anxiety-susceptible and insusceptible groups, respectively, suggesting that the same CMS had different impacts on the pituitary protein regulatory system. Collectively, the current proteomics research elucidated an important molecular basis and furnished new valuable insights into neurochemical commonalities and specificities of the pituitary dysfunctional mechanisms in HPA axis underlying vulnerability and resistance to stress-induced anxiety or depression.

Comparative Proteomics of Rat Olfactory Bulb Reveal Insights into Susceptibility and Resiliency to Chronic-stress-induced Depression or Anxiety

Chronic stress causes the abnormality of olfactory bulb (OB) in both anxiety and depression, however, the unique and common neurobiological underpinnings are still poorly understood. Previously, we built the three groups by chronic mild stress (CMS), depression-susceptible (Dep-Sus): with depression-like behavior, anxiety-susceptible (Anx-Sus): with anxiety-like behavior and insusceptible (Insus): without depression- and anxiety-like behaviors. To continuously explore the protein expression changes in these three groups, comparative quantitative proteomics analysis was conducted on the rat OB as crucial part of the olfactory system. Next, bioinformatics analyses were implemented whereas protein expressions were independently analyzed by parallel reaction monitoring (PRM) or Western blot (WB). The OB-proteome analysis identified totally 133 differentially expressed proteins as a CMS response. These deregulated proteins were involved in multiple functions and significant pathways potentially correlated with phenotypes of maladaptive behavior of depression or anxiety as well as adaptive behavior, and hence might act as potential candidate protein targets. The subsequent PRM-based or WB-based analyses showed that changes in Nefl, Mtmr7 and Tk2; Prkaca, Coa3, Cox6c2, Lamc1 and Tubal3; and Pabpn1, Nme3, Sos1 and Lum were uniquely associated with Dep-Sus, Anx-Sus, and Insus groups, respectively. These phenotype-specific deregulated proteins were primarily involved in multiple metabolic and signaling pathways, suggesting that the identical CMS differently impacted the olfactory protein regulation system and biological processes. To sum up, our present data as a useful proteomics underpinning provided the common and distinct molecular insights into the biochemical understanding of OB dysfunction underlying susceptibility and resiliency to chronic-stress-induced anxiety or depression.

Endoplasmic Reticulum Stress Is Associated with the Mesencephalic Dopaminergic Neuron Injury in Stressed Rats

An increasing number of people are in a state of stress due to social and psychological pressures, which may result in mental disorders. Previous studies indicated that mesencephalic dopaminergic neurons are associated with not only reward-related behaviors but also with stress-induced mental disorders. To explore the effect of stress on dopaminergic neuron and potential mechanism, we established stressed rat models of different time durations and observed pathological changes in dopaminergic neurons of the ventral tegmental area (VTA) through HE and thionine staining. Immunohistochemistry coupled with microscopy-based multicolor tissue cytometry (MMTC) was employed to investigate the number changes of dopaminergic neurons. Double immunofluorescence labelling was used to investigate expression changes of endoplasmic reticulum stress (ERS) protein GRP78 and CHOP in dopaminergic neurons. Our results showed that prolonged stress led to pathological alteration in dopaminergic neurons of VTA, such as missing of Nissl bodies and pyknosis in dopaminergic neurons. Immunohistochemistry with MMTC indicated that chronic stress exposure resulted in a significant decrease in dopaminergic neurons. Double immunofluorescence labelling showed that the endoplasmic reticulum stress protein took part in the injury of dopaminergic neurons. Taken together, these results indicated the involvement of ERS in mesencephalic dopaminergic neuron injury induced by stress exposure.

Early Pup Removal Leads to Social Dysfunction and Dopamine Deficit in Late Postpartum Rats: Prevention by Social Support

Offspring interaction is among the most highly motivated behaviors in maternal mammals and is mediated by mesolimbic dopamine (DA) system activation. Disruption or loss of significant social relationships is among the strongest individual predictors of affective dysregulation and depression onset in humans. However, little is known regarding the effects of disrupted mother–infant attachment (pup removal) in rat dams. Here, we tested the effects of permanent pup removal in rat dams, which were assigned to one of three groups on postpartum day (PD) 1: pups; pups removed, single-housed; or pups removed, co-housed with another dam who also had pups removed; and underwent a behavioral test battery during PD 21–23. In vivo electrophysiological recordings of ventral tegmental area (VTA) DA neurons were performed on PD 22 and 23 in a subset of animals. Pup removal did not impact sucrose consumption or anxiety-like behavior, but increased passive forced swim test (FST) coping responses. Pup-removal effects on social behavior and VTA activity were sensitive to social buffering: only single-housed dams exhibited reduced social motivation and decreased numbers of active DA neurons. Dams that had pups removed and were co-housed did not exhibit changes in social behavior or VTA function. Moreover, no changes in social behavior, FST coping, or VTA activity were found in socially isolated adult virgin females, indicating that effects observed in dams are specific to pup loss. This study showed that deprivation of species-expected social relationships (pups) during the postpartum precipitates an enduring negative affect state (enhanced passive coping, blunted social motivation) and attenuated VTA DA function in the dam, and that a subset of these effects is partially ameliorated through social buffering.

The role of SIRT1 in the basolateral amygdala in depression-like behaviors in mice

Previous investigations have implicated the basolateral amygdala (BLA) epigenetic mechanisms in the pathophysiology of depression. SIRT1 is a NAD+-dependent class III histone deacetylase, widely expresses in BLA. However, epigenetic mechanisms in the BLA under the regulation of SIRT1 in the depression are largely uncharacterized. Under the chronic unpredictable chronic mild stress (CUMS) mouse model, we used adeno-associated viral vectors (AAV) that encoded SIRT1-shRNA or SIRT1 to specifically knockdown or overexpress SIRT1 in BLA neurons, respectively. CUMS procedure induced significant depression symptoms including the decreased sucrose preference, the less bodyweight gained, the decreased immobile latency and the increased immobile time both in forced swim test (FST) and tail suspension test (TST). Knockdown of SIRT1 in BLA glutamatergic neurons reversed these depression-like behaviors and restored the synaptic abnormalities. Overexpression of SIRT1 in BLA glutamatergic neurons induced depression-like behaviors in non-stressed control mice. The result of protein expressions and ultrastructural changes were consistent with the behavioral results. Our study suggested that downregulation of SIRT1 in BLA has certain beneficial effect on CUMS-induced depression-like behaviors such as anorexia, anhedonia, hopelessness and despair. In addition, the increased expression of SIRT1 may be the immediate cause of depressive-like symptoms. The abnormal expression of SIRT1 may affect the transcriptional regulation mechanism and signaling protein acetylation, affecting neuroplasticity and ultimately contribute to MDD. In the stress-susceptible mice, these two mechanisms may co-exist, but the specific mechanism needs further research.

Adult food choices depend on sex and exposure to early-life stress: Underlying brain circuitry, adipose tissue adaptations and metabolic responses

Exposure to early-life stress (ES) increases the risk to develop obesity later in life, and these effects may be sex-specific, but it is currently unknown what underlies the ES-induced metabolic vulnerability. We have previously shown that ES leads to a leaner phenotype under standard chow diet conditions, but to increased fat accumulation when exposed to an unhealthy obesogenic diet. However these diets were fed without a choice. An important, yet under investigated, element contributing to the development of obesity in humans is the choice of the food. There is initial evidence that ES leads to altered food choices but a thorough testing on how ES affects the choice of both the fat and sugar component, and if this is similar in males and females, is currently missing. We hypothesized that ES increases the choice for unhealthy foods, while it at the same time also affects the response to such a diet. In a mouse model for ES, in which mice are exposed to limited nesting and bedding material from postnatal day (P)2–P9, we investigated if ES exposure affected i) food choice with a free choice high-fat high-sugar diet (fcHFHS), ii) the response to such a diet, iii) the brain circuits that regulate food intake and food reward and iv) if such ES effects are sex-specific. We show that there are sex differences in food choice under basal circumstances, and that ES increases fat intake in females when exposed to a mild acute stressor. Moreover, ES impacts the physiologic response to the fcHFHS and the brain circuits regulating food intake in sex-specific manner. Our data highlight sex-specific effects of ES on metabolic functioning and food choice.

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Strong sex differences exist in food choice and metabolism in mice.

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Early-life stress (ES) increases fat intake in females after mild acute stress exposure.

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The physiological response to the diet is affected by ES in a sex-dependent manner.

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ES modulates the hedonic feeding circuitry.

Intersectional analysis of chronic mild stress-induced lncRNA-mRNA interaction networks in rat hippocampus reveals potential anti-depression/anxiety drug targets

Despite studies providing insight into the neurobiology of chronic stress, depression and anxiety, long noncoding RNA (lncRNA)-mediated mechanisms underlying the common and distinct pathophysiology of these stress-induced disorders remain nonconclusive. In a previous study, we used the chronic mild stress paradigm to separate depression-susceptible, anxiety-susceptible and insusceptible rat subpopulations. In the current study, lncRNA and messenger RNA (mRNA) expression was comparatively profiled in the hippocampus of the three stress groups using microarray technology. Groupwise comparisons identified distinct sets of lncRNAs and mRNAs associated with the three different behavioral phenotypes of the stressed rats. To investigate the regulatory roles of the dysregulated lncRNAs upon mRNA expression, correlations between the differential lncRNAs and mRNAs were first analyzed by combined use of weighted gene coexpression network analysis and ceRNA theory-based methods. Subsequent functional analysis of strongly correlated mRNAs indicated that the dysregulated lncRNAs were involved in various biological pathways and processes to specifically induce rat susceptibility or resiliency to depression or anxiety. Further intersectional analysis of phenotype-associated and drug-associated lncRNA-mRNA networks and subnetworks assisted in identifying 16 hub lncRNAs as potential targets of anti-depression/anxiety drugs. Collectively, our study established the molecular basis for understanding the similarities and differences in pathophysiological mechanisms underlying stress-induced depression or anxiety and stress resiliency, revealing several important lncRNAs that represent potentially new therapeutic drug targets for depression and anxiety disorders.

Estrogen administration attenuates post-stroke depression by enhancing CREB/BDNF/TrkB signaling in the rat hippocampus

A previous study demonstrated that 17β-estradiol (E2), which is an antidepressant, can ameliorate post-stroke depression (PSD); however, the underlying mechanisms governing this remain largely unknown. Therefore, the present study developed a PSD model in rats, which was induced by left middle cerebral artery occlusion followed by exposure to chronic mild stress for 2 weeks. The results revealed that the activity of the cAMP response element-binding protein (CREB), a cellular transcription factor, and the associated brain-derived neurotrophic factor (BDNF)/tyrosine kinase B (TrkB) signaling were all attenuated in the hippocampus in PSD rats. The depression-like behaviors were significantly improved after treatment with E2, along with increased CREB and the BDNF/TrkB signaling activity. These results provide novel insight into the molecular basis of PSD, and suggest the potential involvement of CREB/BDNF/TrkB signaling in E2-mediated improvement of PSD in rats.

Chronic unpredictable stress negatively regulates hippocampal neurogenesis and promote anxious depression-like behavior via upregulating apoptosis and inflammatory signals in adult rats

Psychological and physical stress play a pivotal role in etiology of anxiety and depression. Chronic psychological and physical stress modify various physiological phenomena, as a consequence of which oxidative stress, decreased neurotransmitter level, elevated corticosterone level and altered NSC homeostasis is observed. However, the precise mechanism by which chronic stress induce anxious depression and modify internal milieu is still unknown. Herein, we show that exposure to CUS increase oxidative stress, microgliosis, astrogliosis while it reduces hippocampal NSC proliferation, neuronal differentiation and maturation in adult rats. CUS exposure in rats reduce dopamine and serotonin level in cortex and hippocampus, which result in increased anxiety and depression-like phenotypes. We also found elevated level of NF-κB and TNF-α while decreased anti-inflammatory cytokine IL-10 level, that led to increased expression of Bax and cleaved Caspase-3 whereas down regulation of antiapoptotic protein Bcl2. Additionally, CUS altered adult hippocampal neurogenesis, increased gliosis and neuronal apoptosis in cerebral cortex and hippocampus which might be associated with reduced AKT and increased ERK signaling, as seen in the rat brain tissue. Taken together, these results indicate that CUS induce oxidative stress and neuroinflammation which directly affects NSC dynamics, monoamines levels and behavioral functions in adult rats.

Resilience to anhedonia-passive coping induced by early life experience is linked to a long-lasting reduction of Ih current in VTA dopaminergic neurons

Exposure to aversive events during sensitive developmental periods can affect the preferential coping strategy adopted by individuals later in life, leading to either stress-related psychiatric disorders, including depression, or to well-adaptation to future adversity and sources of stress, a behavior phenotype termed “resilience”.

We have previously shown that interfering with the development of mother-pups bond with the Repeated Cross Fostering (RCF) stress protocol can induce resilience to depression-like phenotype in adult C57BL/6J female mice. Here, we used patch-clamp recording in midbrain slice combined with both in vivo and ex vivo pharmacology to test our hypothesis of a link between electrophysiological modifications of dopaminergic neurons in the intermediate Ventral Tegmental Area (VTA) of RCF animals and behavioral resilience. We found reduced hyperpolarization-activated (I_h) cation current amplitude and evoked firing in VTA dopaminergic neurons from both young and adult RCF female mice. In vivo, VTA-specific pharmacological manipulation of the I_h current reverted the pro-resilient phenotype in adult early-stressed mice or mimicked behavioral resilience in adult control animals.

This is the first evidence showing how pro-resilience behavior induced by early events is linked to a long-lasting reduction of I_h current and excitability in VTA dopaminergic neurons.

Neural circuits and activity dynamics underlying sex-specific effects of chronic social isolation stress

Exposure to prolonged stress in critical developmental periods induces heightened vulnerability to psychiatric disorders, which may have sex-specific consequences. Here we investigate the neuronal circuits mediating behavioral changes in mice after chronic adolescent social isolation stress. Escalated aggression is exhibited in stressed males, while social withdrawal is shown in stressed females. In vivo multichannel recordings of free-moving animals indicate that pyramidal neurons in prefrontal cortex (PFC) from stressed males exhibit the significantly decreased spike activity during aggressive attacks, while PFC pyramidal neurons from stressed females show a blunted increase of discharge rates during sociability tests. Chemogenetic and electrophysiological evidence shows that PFC hypofunctioning and BLA principal neuron hyperactivity contribute to the elevated aggression in stressed males, while PFC hypofunctioning and VTA dopamine neuron hypoactivity contribute to the diminished sociability in stressed females. These results establish a framework for understanding the circuit and physiological mechanisms underlying sex-specific divergent effects of stress.

Analysis of Chronic Mild Stress-Induced Hypothalamic Proteome: Identification of Protein Dysregulations Associated With Vulnerability and Resiliency to Depression or Anxiety

Chronic stress as a known risk factor leads to hyperactivity of the hypothalamus-pituitary-adrenal (HPA) axis in both depression and anxiety. However, the stress-induced dysfunction of the HPA axis in these disorders especially the common and unique molecular dysregulations have not been well-explored. Previously, we utilized a chronic mild stress (CMS) paradigm to segregate and gain depression-susceptible, anxiety-susceptible, and insusceptible groups. In this study, we continue to examine the possible protein expression alterations of the hypothalamus as the center of the HPA axis in these three groups by using a proteomic approach. Though isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative analysis, a total of 593 dysregulated proteins were identified. These were potentially associated with vulnerability and adaptability of CMS-caused depression or anxiety and therefore might become novel investigative protein targets. Further independent analysis using parallel reaction monitoring (PRM) indicated that 5, 7, and 21 dysregulated proteins were specifically associated with depression-susceptible, anxiety-susceptible, and insusceptible groups, respectively, suggesting that the same CMS differently affected the regulation system of the rat hypothalamic proteome. In summary, the current proteomic research on the hypothalamus provided insights into the specific and common molecular basis for the HPA dysfunction mechanisms that underlie resiliency and vulnerability to stress-induced depression or anxiety.

Chronic mild stress-induced protein dysregulations correlated with susceptibility and resiliency to depression or anxiety revealed by quantitative proteomics of the rat prefrontal cortex

Chronic stress is a significant risk factor for depression as well as anxiety disorders. Yet, the stress-induced specific and common molecular dysregulations of these disorders have not been fully understood. Previously, we constructed a chronic mild stress (CMS) rat model to separate and obtain depression-susceptible, anxiety-susceptible, and insusceptible groups. In this study, the prefrontal cortical proteomes of the three stressed groups were comparatively profiled utilizing isobaric tags for relative and absolute quantitation (iTRAQ)-coupled tandem mass spectrometry approach. A total of 212 protein dysregulations were identified, potentially correlating to susceptibility or resilience to CMS-induced depression or anxiety, and thus might serve as potential protein targets for further investigation. In addition, independent analysis by parallel reaction monitoring identified changes in Gfap, Rhog, Gnai2, Ppp1r1b, and Uqcrh; Tubb6, Urod, Cul1, Spred1, and Gpcpd1; Acadl, Ppp1r1a, Grm2, Mtor, Lsm8, Cplx2, and Tsta3 that were distinctly correlated to depression-susceptible, anxiety-susceptible, or insusceptible groups, respectively. This suggested that identical CMS had different effects on the protein regulation system of the rat prefrontal cortex. Collectively, the present proteomics study of the prefrontal cortex established a significant molecular basis and offered new insights into the specificity and commonality of pathophysiologic mechanisms underlying susceptibility and resiliency to stress-induced depression or anxiety.

Discovering the Lost Reward: Critical Locations for Endocannabinoid Modulation of the Cortico-Striatal Loop That Are Implicated in Major Depression

Depression, the most prevalent psychiatric disorder in the Western world, is characterized by increased negative affect (i.e., depressed mood, cost value increase) and reduced positive affect (i.e., anhedonia, reward value decrease), fatigue, loss of appetite, and reduced psychomotor activity except for cases of agitative depression. Some forms, such as post-partum depression, have a high risk for suicidal attempts. Recent studies in humans and in animal models relate major depression occurrence and reoccurrence to alterations in dopaminergic activity, in addition to other neurotransmitter systems. Imaging studies detected decreased activity in the brain reward circuits in major depression. Therefore, the location of dopamine receptors in these circuits is relevant for understanding major depression. Interestingly, in cortico-striatal-dopaminergic pathways within the reward and cost circuits, the expression of dopamine and its contribution to reward are modulated by endocannabinoid receptors. These receptors are enriched in the striosomal compartment of striatum that selectively projects to dopaminergic neurons of substantia nigra compacta and is vulnerable to stress. This review aims to show the crosstalk between endocannabinoid and dopamine receptors and their vulnerability to stress in the reward circuits, especially in corticostriatal regions. The implications for novel treatments of major depression are discussed.

Neuroticism and reward-related ventral striatum activity: Probing vulnerability to stress-related depression

Elevated neuroticism may confer vulnerability to the depressogenic effects of stressful life events (SLEs). However, the mechanisms underlying this susceptibility remain poorly understood. Accumulating evidence suggests that stress-related disruptions in neural reward processing might undergird links between stress and depression. Using data from the Saint Louis Personality and Aging Network (SPAN) study and Duke Neurogenetics Study (DNS), we examined whether neuroticism moderates links between stressful life events (SLE) and depression as well as SLEs and ventral striatum (VS) response to reward. In the longitudinal SPAN sample (n = 971 older adults), SLEs prospectively predicted future depressive symptoms, especially among those reporting elevated neuroticism, even after accounting for prior depressive symptoms and previous SLE exposure (NxSLE interaction: p = .016, ΔR² = 0.003). Cross-sectional analyses of the DNS, a young adult college sample with neuroimaging data, replicated this interaction (n = 1,343: NxSLE interaction: p = .019, ΔR² = 0.003) and provided evidence that neuroticism moderates the association between SLEs and reward-related VS response (n = 1,195, NxSLE: p = .017, ΔR² = 0.0048). Blunted left VS response to reward was associated with a lifetime depression diagnosis, r = -0.07, p = .02, but not current depressive symptoms, r = -0.003, p = .93. These data suggest that neuroticism may promote vulnerability to stress-related depression and that sensitivity to stress-related reductions in VS response may be a potential neural mechanism underlying vulnerability to clinically significant depression. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Understanding stress: Insights from rodent models

Through incorporating both physical and psychological forms of stressors, a variety of rodent models have provided important insights into the understanding of stress physiology. Rodent models also have provided significant information with regards to the mechanistic basis of the pathophysiology of stress-related disorders such as anxiety disorders, depressive illnesses, cognitive impairment and post-traumatic stress disorder. Additionally, rodent models of stress have served as valuable tools in the area of drug screening and drug development for treatment of stress-induced conditions. Although rodent models do not accurately reproduce the biochemical or physiological parameters of stress response and cannot fully mimic the natural progression of human disorders, yet, animal research has provided answers to many important scientific questions. In this review article, important studies utilizing a variety of stress models are described in terms of their design and apparatus, with specific focus on their capabilities to generate reliable behavioral and biochemical read-out. The review focusses on the utility of rodent models by discussing examples in the literature that offer important mechanistic insights into physiologically relevant questions. The review highlights the utility of rodent models of stress as important tools for advancing the mission of scientific research and inquiry.

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Stressful life events may lead to the onset of severe psychopathologies in humans.

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Rodents may model many features of stress exposure in human populations.

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Induction of stress via pharmacological and psychological manipulations alter rodent behavior.

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Mechanistic rodent studies reveal key molecular targets critical for new therapeutic targets.

Reduced Information Transmission of Medial Prefrontal Cortex to Basolateral Amygdala Inhibits Exploratory Behavior in Depressed Rats

Depression is a mental and neurological disease that reduces the desire for exploration. Dysregulation of the information transmission between medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) is associated with depression. However, which direction of information transmission (mPFC-BLA or BLA-mPFC) related to the decline of exploratory interests in depression is unclear. Therefore, it is important to determine what specific changes occur in mPFC and BLA information transmission in depressed rats during exploratory behavior. In the present study, local field potentials (LFPs) were recorded via multi-electrodes implanted in the mPFC and BLA for the control and depression groups of rats when they were exploring in an open field. The theta band was determined to be the characteristic band of exploratory behavior. The direct transfer function (DTF) was used to calculate the mPFC and BLA bidirectional information flow (IF) to measure information transmission. Compared with the control group, the theta IF of mPFC-BLA in the depression group was significantly reduced, and there was no significant difference in theta IF of BLA-mPFC between the two groups. Our results indicated that the reduction of mPFC-BLA information transmission can inhibit the exploratory behavior of depressed rats.

The pathophysiological impact of stress on the dopamine system is dependent on the state of the critical period of vulnerability

Unregulated stress during critical periods of development is proposed to drive deficits consistent with schizophrenia in adults. If accurate, reopening the critical period could make the adult susceptible to pathology. We evaluated the impact of early adolescent and adult stress exposure (combination of daily footshock for 10 days and 3 restraint sessions) on (1) midbrain dopamine (DA) neuron activity, (2) ventral hippocampal (vHipp) pyramidal neuron activity, and (3) the number of parvalbumin (PV) interneurons in the vHipp and their associated perineuronal nets (PNNs). Ventral tegmental area (VTA) DA neuron population activity and vHipp activity was increased 1-2 and 5-6 weeks post-adolescent stress, along with a decrease in the number of PV+, PNN+, PV + /PNN + cells in the vHipp, which are consistent with the MAM model of schizophrenia. In contrast, adult stress decreased VTA DA neuron population activity only at 1-2 weeks post stress, which is consistent with what has been observed in animal models of depression, without impacting vHipp activity and PV/PNN expression. Administration of valproate (VPA), which can re-instate the critical period of plasticity via histone deacetylase (HDAC) inhibition, caused adult stress to produce changes similar to those induced by adolescent stress, presumably by increasing stress vulnerability to early adolescent levels. Our findings indicate that timing of stress is a critical determinant of the pathology produced in the adult: adolescent stress led to circuit deficits that recapitulates schizophrenia, whereas adult stress induced a depression-like hypodopaminergic state. Reopening the critical period in the adult restores vulnerability to stress-induced pathology resembling schizophrenia.

Stress and the dopaminergic reward system

Dopamine regulates reward-related behavior through the mesolimbic dopaminergic pathway. Stress affects dopamine levels and dopaminergic neuronal activity in the mesolimbic dopamine system. Changes in mesolimbic dopaminergic neurotransmission are important for coping with stress, as they allow adaption to behavioral responses to various environmental stimuli. Upon stress exposure, modulation of the dopaminergic reward system is necessary for monitoring and selecting the optimal process for coping with stressful situations. Aversive stressful events may negatively regulate the dopaminergic reward system, perturbing reward sensitivity, which is closely associated with chronic stress-induced depression. The mesolimbic dopamine system is excited not only by reward but also by aversive stressful stimuli, which adds further intriguing complexity to the relationship between stress and the reward system. This review focuses on lines of evidence related to how stress, especially chronic stress, affects the mesolimbic dopamine system, and discusses the role of the dopaminergic reward system in chronic stress-induced depression.

Evaluation of electrochemical methods for tonic dopamine detection in vivo

Dysfunction in dopaminergic neuronal systems underlie a number of neurologic and psychiatric disorders such as Parkinson's disease, drug addiction, and schizophrenia. Dopamine systems communicate via two mechanisms, a fast "phasic" release (sub-second to second) that is related to salient stimuli and a slower "tonic" release (minutes to hours) that regulates receptor tone. Alterations in tonic levels are thought to be more critically important in enabling normal motor, cognitive, and motivational functions, and dysregulation in tonic dopamine levels are associated with neuropsychiatric disorders. Therefore, development of neurochemical recording techniques that enable rapid, selective, and quantitative measurements of changes in tonic extracellular levels are essential in determining the role of dopamine in both normal and disease states. Here, we review state-of-the-art advanced analytical techniques for in vivo detection of tonic levels, with special focus on electrochemical techniques for detection in humans.

Remediation of chronic immobilization stress-induced negative affective behaviors and altered metabolism of monoamines in the prefrontal cortex by inactivation of basolateral amygdala

Exposure to chronic stress precipitates depression and anxiety. Stress-induced responses are differentially regulated by the prefrontal cortex (PFC) and basolateral amygdala (BLA). For instance, repeated stress leads to hypertrophy of BLA, resulting in the emergence of affective symptoms. Chronic stress-induced changes in the metabolism of monoamines are central in the manifestation of affective symptoms. Interestingly, BLA via its reciprocal connections modulates prefrontal cortical monoaminergic responses to acute stress. However, the effects of BLA inactivation on chronic stress-induced affective behaviors and monoaminergic changes in the PFC are relatively unknown. Thus, we hypothesized that inactivation of BLA might prevent chronic immobilization stress (CIS)-induced depressive-, anxiety-like behaviors, and associated monoaminergic alterations in the prelimbic (PrL) and anterior cingulate cortex (ACC) subregions of PFC. We used two different BLA silencing strategies, namely ibotenic acid lesion and reversible temporary inactivation using lidocaine. We found that CIS precipitates depressive- and anxiety-like behaviors. Further, CIS-induced negative affective behaviors were associated with decreased levels of 5-HT, DA, and NE, and increased 5-HIAA/5-HT, DOPAC + HVA/DA, and MHPG/NE ratio in the PrL and ACC, suggesting enhanced metabolism. Interestingly, BLA lesion prior to CIS blocked the emergence of depressive- and anxiety-like behaviors. Moreover, the lesion of BLA prior to CIS was sufficient to prevent alterations in levels of monoamines and their metabolites in the PrL and ACC. Thereafter, we evaluated whether the effects of BLA lesion could be mirrored by temporary inactivation of BLA, specifically during stress. Remarkably, temporary inactivation of BLA during stress recapitulated the effects of lesion. Our results have implications for understanding the role of BLA in chronic stress-induced metabolic alterations in prefrontal cortical monoaminergic systems, and associated mood and anxiety disorders. The current study supports the hypothesis that combating amygdalar hyperactivity might be a viable strategy for the management of stress and associated affective disorders.

Differences in Functional Connectivity Networks Related to the Midbrain Dopaminergic System-Related Area in Various Psychiatric Disorders

OBJECTIVE

Disruptions in the dopamine system have been observed in psychiatric disorders. Since dopamine is mainly produced in the ventral tegmental area (VTA), elucidating the differences in the VTA neural network across psychiatric disorders would facilitate a greater understanding of the pathophysiological mechanisms underlying these disorders. However, no study has compared VTA-seed-based functional connectivity across psychiatric disorders. Therefore, we conducted a resting-state functional magnetic resonance imaging (rs-fMRI) study to perform a seed-based fMRI analysis, using the VTA as a seed.

METHODS

We included participants with major depressive disorder (MDD; n = 45), schizophrenia (n = 32), and bipolar disorder (BPD; n = 30), along with healthy control participants (n = 46) who were matched for age, gender, and handedness.

RESULTS

The results showed that patients with MDD and BPD had altered VTA-related connectivity in the superior frontal gyrus, frontal pole regions, hippocampus, cerebellum, and posterior cingulate cortex. Some of these differences in connectivity were also found between affective disorders and schizophrenia; however, there were no differences between the schizophrenia and control groups. Connectivity between the VTA and the hippocampus was correlated with positive symptoms in the schizophrenia group. The connectivity was not associated with medication dose, and the results remained significant after controlling for dose.

CONCLUSIONS

The results suggest that altered brain functional connectivity related to VTA networks could be associated with the distinctive pathophysiologies of psychiatric disorders, especially affective disorders.

The Effect of Swimming on Anxiety-Like Behaviors and Corticosterone in Stressed and Unstressed Rats

This study assessed the effect of swimming training on anxiety-like behaviors and corticosterone. Thirty adult male Wistar rats were randomly assigned to five study conditions: swimming training (ST); exposure to chronic mild stress (CS); exposure to chronic mild stress followed by swimming training (CS + ST); exposure to chronic mild stress followed by a recovery period (CS + recovery); control. The exercise training consisted of 60 min of swimming exercise per day, for five days a week, and four consecutive weeks. A chronic mild stress program (CMS) was applied for a period of four weeks. Anxiety-like behaviors were measured by open field test (OFT). The number of excrements and blood corticosterone were used as physiological parameters of anxiety. To assess corticosterone, blood samples were taken 48 h after the last session of experiments. Compared to other study conditions, the lowest anxiety-like behaviors and corticosterone concentrations were observed in the ST condition in unstressed rats. In stressed rats, as in the ST + CS group, swimming training probably reduced some anxiety behaviors, but the results showed increased corticosterone compared to control and CS + Recovery. Anxiety parameters and corticosterone concentrations were greatest in the CS condition. In the ST group, anxiety parameters were less than for the ST + CS group. In the CS + Recovery group, anxiety parameters were less than for the CS group. In summary, self-paced swimming training could attenuate some anxiety parameters in both stressed and non-stressed rats. The effect of swimming training in unstressed rats was more prominent than in stressed rats. In stressed rats, a period of recovery was more effective than swimming training in reducing corticosterone. Mechanisms of anxiety reduction other than cortisol should be investigated in future research.

Dysregulation of Midbrain Dopamine System and the Pathophysiology of Schizophrenia

Dysregulation of the dopamine system is central to many models of the pathophysiology of psychosis in schizophrenia. However, emerging evidence suggests that this dysregulation is driven by the disruption of upstream circuits that provide afferent control of midbrain dopamine neurons. Furthermore, stress can profoundly disrupt this regulatory circuit, particularly when it is presented at critical vulnerable prepubertal time points. This review will discuss the dopamine system and the circuits that regulate it, focusing on the hippocampus, medial prefrontal cortex, thalamic nuclei, and medial septum, and the impact of stress. A greater understanding of the regulation of the dopamine system and its disruption in schizophrenia may provide a more complete neurobiological framework to interpret clinical findings and develop novel treatments.

Antidepressant efficacy of a selective organic cation transporter blocker in a mouse model of depression

Current antidepressants act principally by blocking monoamine reuptake by high-affinity transporters in the brain. However, these antidepressants show important shortcomings such as slow action onset and limited efficacy in nearly a third of patients with major depression disorder. Here, we report the development of a prodrug targeting organic cation transporters (OCT), atypical monoamine transporters recently implicated in the regulation of mood. Using molecular modeling, we designed a selective OCT2 blocker, which was modified to increase brain penetration. This compound, H2-cyanome, was tested in a rodent model of chronic depression induced by 7-week corticosterone exposure. In male mice, prolonged administration of H2-cyanome induced positive effects on several behaviors mimicking symptoms of depression, including anhedonia, anxiety, social withdrawal, and memory impairment. Importantly, in this validated model, H2-cyanome compared favorably with the classical antidepressant fluoxetine, with a faster action on anhedonia and better anxiolytic effects. Integrated Z-scoring across these depression-like variables revealed a lower depression score for mice treated with H2-cyanome than for mice treated with fluoxetine for 3 weeks. Repeated H2-cyanome administration increased ventral tegmental area dopaminergic neuron firing, which may underlie its rapid action on anhedonia. H2-cyanome, like fluoxetine, also modulated several intracellular signaling pathways previously involved in antidepressant response. Our findings provide proof-of-concept of antidepressant efficacy of an OCT blocker, and a mechanistic framework for the development of new classes of antidepressants and therapeutic alternatives for resistant depression and other psychiatric disturbances such as anxiety.

Prelimbic medial prefrontal cortex disruption during adolescence increases susceptibility to helpless behavior in adult rats

Major depressive disorder (MDD) is a disabling mental disorder worldwide. Several animal models have been used to study the neurobiology of this disorder, including the learned helplessness (LH) paradigm, in which susceptible animals show helpless behavior indicated by fails to escape a controllable footshock. This behavior has been associated with a downregulation of ventral tegmental area (VTA) dopamine (DA) system activity. The prelimbic portion of the prefrontal cortex (plPFC) plays an important role in the modulation of helpless behavior, but so far there is no evidence indicating that its developmental disruption alters susceptibility to helpless behavior. We investigated the impact of plPFC lesion performed at adolescence (postnatal day 31-33) or adulthood (postnatal day 70-72) on anxiety responses (elevated plus-maze), susceptibility to helpless behavior, and the VTA DA system activity in adult Sprague-Dawley rats. Whereas adult plPFC lesions induced neither anxiety responses nor increased susceptibility to helpless behavior (plPFC lesion: 33.3% of helplessness; controls: 30.8% of helplessness rats), adolescent plPFC lesions induced anxiety responses and increased the proportion of rats showing helpless at adulthood (plPFC lesion: 92.3% helplessness; controls: 42.1% helplessness rats). Moreover, only helpless rats in the groups showed a decreased VTA DA system population activity that was confined to the medial portion of the VTA. These findings suggest that the impairment of plPFC activity during adolescence occurs during a critical window for the development of helpless behavior in adult rats, indicating that predisposition or early life adverse events that impair plPFC activity may enhance susceptibility to depression in adulthood.

Stress induces insertion of calcium-permeable AMPA receptors in the OFC-BLA synapse and modulates emotional behaviours in mice

Stress increases the risk of neuropsychiatric disorders, such as major depression. Exposure to stress has been reported to induce various neuronal changes, such as alterations in synaptic transmission and structure. However, a causal link between stress-induced neural circuit alterations and changes in emotional behaviours is not well understood. In the present study, we focused on a projection pathway from the orbitofrontal cortex (OFC) to the basolateral nucleus of the amygdala (BLA) as a crucial circuit for negative emotions and examined the effect of stress on OFC-BLA excitatory synaptic transmission using optogenetic and whole-cell patch-clamp methods in mice. As a stress-inducing procedure, we used repeated tail-shock, which increased stress-related behaviours. We found greater α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/N-methyl-D-aspartate current ratios and insertion of calcium-permeable AMPA receptors (AMPARs) in the OFC-BLA synapse after stress. These stress-induced synaptic and behavioural changes were reduced by a blockade of protein kinase A, which plays a principal role in stress-induced targeting of AMPARs into the synaptic membrane. To examine a possible causal relationship between alterations in synaptic transmission in the OFC-BLA pathway and stress-related behaviour, we performed optogenetic activation or chemogenetic inactivation of OFC-BLA transmission in mice. We found that optogenetic activation and chemogenetic inactivation of OFC-BLA transmission increased and decreased stress-related behaviour, respectively. In conclusion, we have demonstrated that stress altered the postsynaptic properties of the OFC-BLA pathway. These synaptic changes might be one of the underlying mechanisms of stress-induced behavioural alterations.

Blue Light Deprivation Produces Depression-Like Responses in Mongolian Gerbils

BACKGROUND

Depression is a leading cause of disability worldwide and is a major contributor to the overall global burden of disease, but its etiology is poorly understood. It has been reported that a disrupted biological rhythm, in terms of a shortened light duration and total darkness, can cause depression-like behaviors in animals. Blue light was reported to have an inhibitory effect on melatonin, which is considered an important clock rhythm biomarker. In the present study, we investigated the effects of blue light deprivation on depressive-like behaviors in gerbils and explored the underlying mechanisms.

METHODS

Gerbils were housed under white light with a filter to block the blue light or without a filter. The behaviors of the gerbils were observed. The biological rhythm, 5-HT, hypothalamic-pituitary-adrenal (HPA) axis and melanopsin pathway were analyzed.

RESULTS

We found that blue light deprivation (BLD) induced depression-like behavior in gerbils. Melatonin lost its rhythm, and corticosterone (CORT) levels decreased in the morning in the BLD group. Lower corticotropin-releasing hormone (CRH) in the hypothalamus and lower adrenocorticotropin hormone (ACTH)/CORT in serum were observed after BLD. Furthermore, 5-HT in the serum and brain were decreased after BLD. Additionally, BLD affected the blue light sensitivity protein melanopsin and its pathway, with downregulation of the proteins melanopsin, PKCα, and c-Fos and the mRNA levels of c-fos and trpc3 and upregulation of the protein p-PKCα.

CONCLUSIONS

Our findings indicated that BLD might produce depression-like behaviors in gerbils. Melatonin arrhythmicity, HPA axis abnormalities, 5-HT decreases and melanopsin pathway changes might be associated with the depression behavioral phenotype in gerbils.

Postpartum changes in affect-related behavior and VTA dopamine neuron activity in rats

The onset of motherhood is accompanied by alterations in emotional and affective behaviors. Many new mothers experience transient and mild depressive symptoms that typically resolve spontaneously (i.e. postpartum blues) but increase the risk for postpartum depression (PPD). There is little data regarding the neural adaptations occurring in response to parturition and shortly after birth that may be associated with these affective changes. Although the dopamine (DA) system is involved in affect, maternal motivation and PPD, little is known about postpartum DA function. We compared affective behavior in virgin and postpartum adult female rats at early and late time points. In vivo extracellular recordings of VTA DA neurons were performed to evaluate 3 parameters: number of active DA neurons (i.e. population activity), firing rate, and firing pattern. Compared with virgins, postpartum rats exhibited increased anxiety-like behavior in the elevated plus maze at 1-day postpartum; reduced social motivation at 1- and 3-days postpartum, reduced anxiety-like behavior in the novelty suppressed feeding test throughout the first week postpartum and increased forced swim test immobility at 1-day postpartum. 1- and 3-day postpartum females exhibited attenuated VTA population activity without changes in firing rate or pattern. None of these effects were observed in late postpartum females when compared with virgins. These data suggest that parturition induces time-dependent changes in a subset of affect-related behaviors and DA function during the postpartum period in rodents, with early postpartum females exhibiting depression-related phenotypes (i.e. low social motivation, higher immobility, blunted DA activity).

Transient and sustained effects of dopamine and serotonin signaling in motivation-related behavior

Pharmacological studies of antidepressants and atypical antipsychotics have suggested a role of dopamine and serotonin signaling in depression. However, depressive symptoms and treatment effects are difficult to explain based simply on brain-wide decrease or increase in the concentrations of these molecules. Recent animal studies using advanced neuronal manipulation and observation techniques have revealed detailed dopamine and serotonin dynamics that regulate diverse aspects of motivation-related behavior. Dopamine and serotonin transiently modulate moment-to-moment behavior at timescales ranging from sub-second to minutes and also produce persistent effects, such as reward-related learning and stress responses that last longer than several days. Transient and sustained effects often exhibit specific roles depending on the projection sites, where distinct synaptic and cellular mechanisms are required to process the neurotransmitters for each transient and sustained timescale. Therefore, it appears that specific aspects of motivation-related behavior are regulated by distinct synaptic and cellular mechanisms in specific brain regions that underlie the transient and sustained effects of dopamine and serotonin signaling. Recent clinical studies have implied that subjects with depressive symptoms show impaired transient and sustained signaling functions; moreover, they exhibit heterogeneity in depressive symptoms and neuronal dysfunction. Depressive symptoms may be explained by the dysfunction of each transient and sustained signaling mechanism, and distinct patterns of impairment in the relevant mechanisms may explain the heterogeneity of symptoms. Thus, detailed understanding of dopamine and serotonin signaling may provide new insight into depressive symptoms.

Motivation, risk-taking and sensation seeking behavior in propofol anesthesia exposed peripubertal rats

Adolescent neurodevelopment confer vulnerability to the actions of treatments that produce adaptations in neurocircuitry underlying motivation, impulsivity and reward. Considering wide usage of a sedative-hypnotic agent propofol in clinical practice, we examined whether propofol is a challenging treatment for peripubertal brain. Motivation/hedonic behavior (sucrose preference test), approach/avoidance behavior (elevated plus maze test) and response to dissociative drug phencyclidine (PCP) were studied in peripubertal rats (the rodent model of periadolescence) after propofol anesthesia exposure (PAE). Neurodegeneration (Fluoro-Jade staining) and the expression of proteins (Western blot) involved in excitatory synaptic transmission and activity-dependent synaptic stabilization in the medial prefrontal cortex (mPFC) and striatum (components of motivation/reward circuitry; process both appetitive and aversive events) were examined as well. In peripubertal rats PAE produced 1) transient brain-region specific changes in the expression of N-methyl-d-aspartate (NMDA) receptor subunits NR2A and NR2B, PSD-95 and N-cadherin, without neurotoxicity, 2) hyperlocomotor response to PCP, 3) no changes in preference for palatable 1% sucrose solution and a decrease in food eaten, 4) preference for 20% sucrose solution without changes in food eaten, 5) stretch-attended postures and open arms entries in the elevated plus maze test. Overall, these novel findings show that PAE leaves transient synaptic trace recognized as early form of synaptic plasticity related to passive drug exposure in the brain systems implicated in motivation/reward, increases drug-responsiveness, favors risk-taking and preference of novel/intense stimuli repairing otherwise present motivational deficiency. These findings accentuate multifaceted response to propofol in peripuberty and the importance of environmental stability for the most favorable neurobehavioral recovery.

Amygdala subnucleus volumes in psychosis high-risk state and first-episode psychosis

Structural and functional abnormalities of the amygdala in schizophrenia have been well documented. Post-mortem studies suggest that the lateral nucleus is particularly affected in schizophrenia. It is not known whether the amygdala subnuclei are differently affected at the time of the first-episode psychosis or already at high-risk state. 75 first-episode psychosis patients (FEP), 45 clinical high-risk patients (CHR) and 76 population controls participated in this cross-sectional case-control study. Participants underwent T1-weighted 3T MRI scans, from which the amygdala was segmented using a newly developed automated algorithm. Because early adverse events increase risk for psychosis and affect the amygdala, we also tested whether experiences of childhood maltreatment associate with the putative amygdala subnuclei abnormalities. Compared to the population controls, FEP had smaller volumes of the lateral, and basal nuclei. In CHR, only the lateral nucleus was significantly smaller compared to the control subjects. Experience of childhood maltreatment was inversely associated with lateral nucleus volumes in FEP but not in CHR. These results show that the lateral and basal nuclei of the amygdala are already affected in FEP. These volumetric changes may reflect specific cellular abnormalities that have been observed in post-mortem studies in schizophrenia in the same subnuclei. Decreased volume of the lateral nucleus in CHR suggest that a smaller lateral nucleus could serve as a potential biomarker for psychosis risk. Finally, we found that the lateral nucleus volumes in FEP may be sensitive to the effects of childhood maltreatment.

Reduced Reward Responsiveness in Women With Moderate - to - Severe Premenstrual Syndrome: Evidence From a Probabilistic Reward Task

Nearly 50% of women of reproductive age worldwide experience premenstrual syndrome (PMS). Women with PMS exhibit low positive affect and low frontal electroencephalography asymmetry scores, both of which are associated with reward processing. These findings suggest that women with PMS may exhibit deficiencies in reward processing. A probabilistic reward task based on signal detection approach was used to assess reward responsiveness in 30 women with moderate-to-severe PMS and 31 controls without PMS. The results revealed that in the late luteal phase, the women with moderate-to-severe PMS exhibited lower response bias and lower hit rate toward more frequently rewarded stimuli (rich stimuli) than the controls. By contrast, the response bias and hit rate did not differ between the two groups in the follicular phase. The group differences still remained after controlling for anhedonic symptoms. Furthermore, trial-by-trial probability analyses revealed that women with moderate-to-severe PMS exhibited a trend of having a higher miss rate for rich stimuli than the controls. In particular, when a rich stimulus was preceded by an infrequently rewarded stimulus (a rewarded lean stimulus), participants in the PMS group exhibited a trend for higher miss rate than those in the control group in the late luteal and follicular phases. However, group differences in the probability analyses were nonsignificant after controlling for anhedonic symptoms. These results provide preliminary evidence that women with moderate-to-severe PMS exhibit dysfunctional reward responsiveness and impaired ability to modulate their behavior as a function of prior reinforcement.

The molecular and cellular mechanisms of depression: a focus on reward circuitry

Depression is a complex disorder that takes an enormous toll on individual health. As affected individuals display a wide variation in their clinical symptoms, the precise neural mechanisms underlying the development of depression remain elusive. Although it is impossible to phenocopy every symptom of human depression in rodents, the preclinical field has had great success in modeling some of the core affective and neurovegetative depressive symptoms, including social withdrawal, anhedonia, and weight loss. Adaptations in select cell populations may underlie these individual depressive symptoms and new tools have expanded our ability to monitor and manipulate specific cell types. This review outlines some of the most recent preclinical discoveries on the molecular and neurophysiological mechanisms in reward circuitry that underlie the expression of behavioral constructs relevant to depressive symptoms.

α7 nicotinic receptor full agonist reverse basolateral amygdala hyperactivity and attenuation of dopaminergic neuron activity in rats exposed to chronic mild stress

Neuroimaging and preclinical studies showing that nicotinic receptors (nAChR) may play a role in mood control has increased interest in targeting the cholinergic system for treatment of major depressive disorder. Indeed, modulation of nAChRs in the basolateral amygdala (BLA) are sufficient to produce an anti-immobility effect in the mouse tail suspension test. However, how α7 nAChR modulation impacts BLA neuronal activity in vivo as well as the downstream mechanisms involved in its mood-related effects are not understood. In this work, we used the unpredictable chronic mild stress (CMS) model to investigate the mechanisms underlying the antidepressant-like effect of an α7 nAChR full agonist on BLA-induced changes in dopaminergic neurotransmission. Male adult Sprague-Dawley rats were exposed to four weeks of CMS. Behavioral and electrophysiological experiments were performed within one week following stress. CMS exposure increased rats' immobility time in the forced swimming test, decreased the number of spontaneously active dopamine neurons in the ventral tegmental area and increased the firing rate of putative projection neurons in the BLA. Stress-induced behavioral and electrophysiological changes were reversed by a single systemic administration of PNU282987. In summary, our findings corroborate previous descriptions of a potential rapid antidepressant effect for the α7 nAChR full agonist. This effect appears to involve a mechanism distinct from those of classic antidepressants: normalization of BLA hyperactivity and, consequently, of DA hypofunction. These observations corroborate the role of α7 nAChR as a potential target for novel antidepressant drug development.

Antidepressant effects of ketamine on depression-related phenotypes and dopamine dysfunction in rodent models of stress

Depression, the most prevalent psychiatric disorder, is characterized by increased negative affect (i.e. depressed mood) and reduced positive affect (i.e. anhedonia). Stress is a risk factor for depression in humans, and animal models of chronic stress are typically used to study neurobehavioral alterations relevant to depression. Common behavioral outcomes in rodent models of chronic stress include anhedonia, social dysfunction and behavioral despair. For example, chronically stressed rodents exhibit reduced reward preference, as measured by a loss of preference for sucrose solutions and time spent interacting with a novel conspecific, while also exhibiting less time struggling against inescapable stressors (e.g. forced swim, tail suspension). In both humans and rodents, anhedonia is associated with dysfunction of the dopamine (DA) system. Unlike traditional antidepressants, which are limited by inadequate efficacy and delayed therapeutic response, acute ketamine administration rapidly alleviates depressive symptoms in humans and reverses stress-induced changes in animal models. These effects are partially mediated via actions on the DA system. This review summarizes the clinical effects of ketamine, the neurobiological underpinnings of depression with a focus on DA dysfunction, as well as antidepressant effects of ketamine on depression-related endophenotypes (i.e. anhedonia, despair) and ventral tegmental area (VTA) activity in rodent models of repeated stress. Moreover, we discuss evidence regarding sex differences in ketamine's antidepressant effects, wherein females appear to be more sensitive to lower dose ketamine, as well as novel findings suggesting that ketamine has prophylactic effects with regard to protection against the neurobehavioral impact of future stressors.

Stress during critical periods of development and risk for schizophrenia

Schizophrenia is a neurodevelopmental disorder with genetic predisposition, and stress has long been linked to its etiology. While stress affects all stages of the illness, increasing evidence suggests that stress during critical periods of development may be particularly detrimental, increasing individual's vulnerability to psychosis. To thoroughly understand the potential causative role of stress, our group has been focusing on the prenatal methylazoxymethanol acetate (MAM) rodent model, and discovered that MAM offspring display abnormal stress reactivity and heightened anxiety prepubertally, prior to the manifestation of a hyperdopaminergic state. Furthermore, pharmacologically treating anxiety during prepuberty prevented the emergence of the dopamine dysfunction in adulthood. Interestingly, sufficiently strong stressors applied to normal rats selectively during early development can recapitulate multiple schizophrenia-related phenotypes of MAM rats, whereas the same stress paradigm during adulthood only produced short-term depression-related deficits. Altogether, the evidence is thus converging: developmental disruption (genetic or environmental) might render animals more susceptible to the deleterious effects of stress during critical time windows, during which unregulated stress can lead to the emergence of psychosis later in life. As an important region regulating the midbrain dopamine system, the ventral hippocampus is particularly vulnerable to stress, and the distinct maturational profile of its fast-spiking parvalbumin interneurons may largely underlie such vulnerability. In this review, by discussing emerging evidence spanning clinical and basic science studies, we propose developmental stress vulnerability as a novel link between early predispositions and environmental triggering events in the pathophysiology of schizophrenia. This promising line of research can potentially provide not only insights into the etiology, but also a "roadmap" for disease prevention.

Hippocampal proteomic changes of susceptibility and resilience to depression or anxiety in a rat model of chronic mild stress

Chronic stressful occurrences are documented as a vital cause of both depression and anxiety disorders. However, the stress-induced molecular mechanisms underlying the common and distinct pathophysiology of these disorders remains largely unclear. We utilized a chronic mild stress (CMS) rat model to differentiate and subgroup depression-susceptible, anxiety-susceptible, and insusceptible rats. The hippocampus was analyzed for differential proteomes by combining mass spectrometry and the isobaric tags for relative and absolute quantitation (iTRAQ) labeling technique. Out of 2593 quantified proteins, 367 were aberrantly expressed. These hippocampal protein candidates might be associated with susceptibility to stress-induced depression or anxiety and stress resilience. They provide the potential protein systems involved in various metabolic pathways as novel investigative protein targets. Further, independent immunoblot analysis identified changes in Por, Idh2 and Esd; Glo1, G6pdx, Aldh2, and Dld; Dlat, Ogdhl, Anxal, Tpp2, and Sdha that were specifically associated to depression-susceptible, anxiety-susceptible, or insusceptible groups respectively, suggesting that identical CMS differently impacted the mitochondrial and metabolic processes in the hippocampus. Collectively, the observed alterations to protein abundance profiles of the hippocampus provided significant and novel insights into the stress regulation mechanism in a CMS rat model. This might serve as the molecular basis for further studies that would contributed to a better understanding of the similarities and differences in pathophysiologic mechanisms underlying stress-induced depression or anxiety, and stress resiliency.

Female rats are resistant to the long-lasting neurobehavioral changes induced by adolescent stress exposure

Stress during adolescence is a risk factor for neuropsychiatric diseases, including schizophrenia. We recently observed that peripubertal male rats exposed to a combination of daily footshock plus restraint stress exhibited schizophrenia-like changes. However, numerous studies have shown sex differences in neuropsychiatric diseases as well as on the impact of coping with stress. Thus, we decided to evaluate, in adolescent female rats, the impact of different stressors (restraint stress [RS], footshock [FS], or the combination of FS and RS [FS+RS]) on social interaction (3-chamber social approach test/SAT), anxiety responses (elevated plus-maze/EPM), cognitive function (novel object recognition test/NOR), and dopamine (DA) system responsivity by evaluating locomotor response to amphetamine and in vivo extracellular single unit recordings of DA neurons in the ventral tegmental area (VTA) in adulthood. The impact of FS+RS during early adulthood was also investigated. Adolescent stress had no impact on social behavior, anxiety, cognition and locomotor response to amphetamine. In addition, adolescent stress did not induce long-lasting changes in VTA DA system activity. However, a decrease in the firing rate of VTA DA neurons was found 1-2 weeks post-adolescent stress. Similar to adolescent stress, adult stress did not induce long-lasting behavioral deficits and changes in VTA DA system activity, but FS+RS decreased VTA DA neuron population activity 1-2 weeks post-adult stress. Our results are consistent with previous studies showing that female rodents appear to be more resilient to developmental stress-induced persistent changes than males and may contribute to the delayed onset and lesser severity of schizophrenia in females.

Dopaminergic impact of cART and anti-depressants on HIV neuropathogenesis in older adults

The success of combination antiretroviral therapy (cART) has transformed HIV infection into a chronic condition, resulting in an increase in the number of older, cART-treated adults living with HIV. This has increased the incidence of age-related, non-AIDS comorbidities in this population. One of the most common comorbidities is depression, which is also associated with cognitive impairment and a number of neuropathologies. In older people living with HIV, treating these overlapping disorders is complex, often creating pill burden or adverse drug-drug interactions that can exacerbate these neurologic disorders. Depression, NeuroHIV and many of the neuropsychiatric therapeutics used to treat them impact the dopaminergic system, suggesting that dopaminergic dysfunction may be a common factor in the development of these disorders. Further, changes in dopamine can influence the development of inflammation and the regulation of immune function, which are also implicated in the progression of NeuroHIV and depression. Little is known about the optimal clinical management of drug-drug interactions between cART drugs and antidepressants, particularly in regard to dopamine in older people living with HIV. This review will discuss those interactions, first examining the etiology of NeuroHIV and depression in older adults, then discussing the interrelated effects of dopamine and inflammation on these disorders, and finally reviewing the activity and interactions of cART drugs and antidepressants on each of these factors. Developing better strategies to manage these comorbidities is critical to the health of the aging, HIV-infected population, as the older population may be particularly vulnerable to drug-drug interactions affecting dopamine.

Hierarchical control systems for the regulation of physiological homeostasis and affect: Can their interactions modulate mood and anhedonia?

Predominant concepts assert that conscious willful processes do not assert a significant influence on autonomic functions associated with physiological homeostasis (e.g., thermal regulation). The singular purpose of this review is to promote a reappraisal of concepts regarding the circumscribed role of hierarchical control systems. To effect this reappraisal, we assess the interaction between top-down and bottom-up regulatory mechanisms, specifically by highlighting the intersection between the "physiological" (specifically thermoregulatory pathways) and the "psychological" (specifically mood/anhedonia related processes). This reappraisal suggests that the physiological and psychological processes can interact in unanticipated ways, and is grounded in multiple lines of recent experimental evidence. For example, behavioral techniques that through a combination of hormesis (forced breathing, cold exposure) and meditation appear to exert unusual effects on homeostatic function (cold tolerance) and suppression of aberrant auto-immune responses. The molecular correlates of these effects (the putative release of endogenous cannabinoids and endorphins) may exert salutary effects on mood/anhedonia, even more significant than those exerted by cognitive behavioral techniques or meditation alone. By focusing on this interaction, we present a putative mechanistic model linking physiology with psychology, with particular implications for disturbances of mood/anhedonia. We suggest that volitional changes in breathing patterns can activate primary control centers for descending pain/cold stimuli in periaqueductal gray, initiating a stress-induced analgesic response mediated by endocannabinoid/endorphin release. The analgesic effects, and the feelings of euphoria generated by endocannbinoid release are prolonged via a top-down "outcome expectancy" control mechanism regulated by cortical areas. By focusing on modification strategies that principally target homeostatic function (but may also exert ancillary effects on mood), we articulate a novel framework for how hierarchical control systems for the regulation of physiological homeostasis and affect interact. This interaction may allow practitioners of focused modification strategies to assert increased control over key components of the affective system, allowing for viable treatment approaches for patients with disturbances of mood/anhedonia.

Resilience to adversity is associated with increased activity and connectivity in the VTA and hippocampus

Accumulating evidence suggests altered function of the mesolimbic reward system resulting from exposure to early adversity. The present study investigated the combined long-term impact of adversity until young adulthood on neuronal reward processing and its interaction with individual resilience processes. In this functional magnetic resonance imaging study, 97 healthy young adults performed a reward-based decision-making task. Adversity as well as resilience were assessed retrospectively using the validated childhood trauma questionnaire, trauma history questionnaire and a resilience scale. Subjects with high adversity load showed reduced reward-related bottom-up activation in the ventral striatum (VS), ventral tegmental area (VTA) and hippocampus (HP) as compared to the low adversity group. However, high resilience traits in individuals with high adversity load were associated with an increased activation in the VTA and HP, indicating a possible resilience-related protective mechanism. Moreover, when comparing groups with high to low adversity, psychophysiological interaction analyses highlighted an increased negative functional coupling between VS and VTA as well as between VS and anteroventral prefrontal cortex (avPFC) during reward acceptance, and an impaired top-down control of the VS by the avPFC during reward rejection. In turn, combination of high adversity and high resilience traits was associated with an improved functional coupling between VTA, VS and HP. Thereby, the present findings identify neural mechanisms mediating interacting effects of adversity and resilience, which could be targeted by early intervention and prevention.

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.