Repeated stress causes cognitive impairment by suppressing glutamate receptor expression and function in prefrontal cortex

The Acute Stress Response in the Multiomic Era

Studying the stress response is a major pillar of neuroscience research not only because stress is a daily reality but also because the exquisitely fine-tuned bodily changes triggered by stress are a neuroendocrinological marvel. While the genome-wide changes induced by chronic stress have been extensively studied, we know surprisingly little about the complex molecular cascades triggered by acute stressors, the building blocks of chronic stress. The acute stress (or fight-or-flight) response mobilizes organismal energy resources to meet situational demands. However, successful stress coping also requires the efficient termination of the stress response. Maladaptive coping-particularly in response to severe or repeated stressors-can lead to allostatic (over)load, causing wear and tear on tissues, exhaustion, and disease. We propose that deep molecular profiling of the changes triggered by acute stressors could provide molecular correlates for allostatic load and predict healthy or maladaptive stress responses. We present a theoretical framework to interpret multiomic data in light of energy homeostasis and activity-dependent gene regulation, and we review the signaling cascades and molecular changes rapidly induced by acute stress in different cell types in the brain. In addition, we review and reanalyze recent data from multiomic screens conducted mainly in the rodent hippocampus and amygdala after acute psychophysical stressors. We identify challenges surrounding experimental design and data analysis, and we highlight promising new research directions to better understand the stress response on a multiomic level.

Low corticosterone levels attenuate late life depression and enhance glutamatergic neurotransmission in female rats

Sustained elevation of corticosterone (CORT) is one of the common causes of aging and major depression disorder. However, the role of elevated CORT in late life depression (LLD) has not been elucidated. In this study, 18-month-old female rats were subjected to bilateral adrenalectomy or sham surgery. Their CORT levels in plasma were adjusted by CORT replacement and the rats were divided into high-level CORT (H-CORT), low-level CORT (L-CORT), and Sham group. We showed that L-CORT rats displayed attenuated depressive symptoms and memory defects in behavioral tests as compared with Sham or H-CORT rats. Furthermore, we showed that glutamatergic transmission was enhanced in L-CORT rats, evidenced by enhanced population spike amplitude (PSA) recorded from the dentate gyrus of hippocampus in vivo and increased glutamate release from hippocampal synaptosomes caused by high frequency stimulation or CORT exposure. Intracerebroventricular injection of an enzymatic glutamate scavenger system, glutamic-pyruvic transmine (GPT, 1 μM), significantly increased the PSA in Sham rats, suggesting that extracelluar accumulation of glutamate might be the culprit of impaired glutamatergic transmission, which was dependent on the uptake by Glt-1 in astrocytes. We revealed that hippocampal Glt-1 expression level in the L-CORT rats was much higher than in Sham and H-CORT rats. In a gradient neuron-astrocyte coculture, we found that the expression of Glt-1 was decreased with the increase of neural percentage, suggesting that impairment of Glt-1 might result from the high level of CORT contributed neural damage. In sham rats, administration of DHK that inhibited Glt-1 activity induced significant LLD symptoms, whereas administration of RIL that promoted glutamate uptake significantly attenuated LLD. All of these results suggest that glutamatergic transmission impairment is one of important pathogenesis in LLD induced by high level of CORT, which provide promising clues for the treatment of LLD.

Reduced adaptation of glutamatergic stress response is associated with pessimistic expectations in depression

Stress is a significant risk factor for the development of major depressive disorder (MDD), yet the underlying mechanisms remain unclear. Preclinically, adaptive and maladaptive stress-induced changes in glutamatergic function have been observed in the medial prefrontal cortex (mPFC). Here, we examine stress-induced changes in human mPFC glutamate using magnetic resonance spectroscopy (MRS) in two healthy control samples and a third sample of unmedicated participants with MDD who completed the Maastricht acute stress task, and one sample of healthy control participants who completed a no-stress control manipulation. In healthy controls, we find that the magnitude of mPFC glutamate response to the acute stressor decreases as individual levels of perceived stress increase. This adaptative glutamate response is absent in individuals with MDD and is associated with pessimistic expectations during a 1-month follow-up period. Together, this work shows evidence for glutamatergic adaptation to stress that is significantly disrupted in MDD.

Cellular senescence as a driver of cognitive decline triggered by chronic unpredictable stress

When an individual is under stress, the undesired effect on the brain often exceeds expectations. Additionally, when stress persists for a long time, it can trigger serious health problems, particularly depression. Recent studies have revealed that depressed patients have a higher rate of brain aging than healthy subjects and that depression increases dementia risk later in life. However, it remains unknown which factors are involved in brain aging triggered by chronic stress. The most critical change during brain aging is the decline in cognitive function. In addition, cellular senescence is a stable state of cell cycle arrest that occurs because of damage and/or stress and is considered a sign of aging. We used the chronic unpredictable stress (CUS) model to mimic stressful life situations and found that, compared with nonstressed control mice, CUS-treated C57BL/6 mice exhibited depression-like behaviors and cognitive decline. Additionally, the protein expression of the senescence marker p16^INK4a was increased in the hippocampus, and senescence-associated β-galactosidase (SA-β-gal)-positive cells were found in the hippocampal dentate gyrus (DG) in CUS-treated mice. Furthermore, the levels of SA-β-gal or p16^INK4a were strongly correlated with the severity of memory impairment in CUS-treated mice, whereas clearing senescent cells using the pharmacological senolytic cocktail dasatinib plus quercetin (D + Q) alleviated CUS-induced cognitive deficits, suggesting that targeting senescent cells may be a promising candidate approach to study chronic stress-induced cognitive decline. Our findings open new avenues for stress-related research and provide new insight into the association of chronic stress-induced cellular senescence with cognitive deficits.

An emerging role for microglia in stress‐effects on memory

Stressful experiences evoke, among others, a rapid increase in brain (nor)epinephrine (NE) levels and a slower increase in glucocorticoid hormones (GCs) in the brain. Microglia are key regulators of neuronal function and contain receptors for NE and GCs. These brain cells may therefore potentially be involved in modulating stress effects on neuronal function and learning and memory. In this review, we discuss that stress induces (1) an increase in microglial numbers as well as (2) a shift toward a pro‐inflammatory profile. These microglia have (3) impaired crosstalk with neurons and (4) disrupted glutamate signaling. Moreover, microglial immune responses after stress (5) alter the kynurenine pathway through metabolites that impair glutamatergic transmission. All these effects could be involved in the impairments in memory and in synaptic plasticity caused by (prolonged) stress, implicating microglia as a potential novel target in stress‐related memory impairments.

Sex-dependent long-term effects of prepubescent stress on the posterior parietal cortex

Adolescence is a time of intense cortical development and a period of heightened sensitivity to insult. To determine how sex affects the short- and long-term outcomes of early-adolescent stress exposure, we subjected prepubescent (postnatal day 30) male and female mice to repeated multiple concurrent stressors (RMS). In the posterior parietal cortex (PPC), RMS caused the elimination of excitatory synapses in deeper layers while inhibitory synapse density was predominantly diminished in superficial layers. These short-term effects coincided with reduced visuo-spatial working memory and were similar in both sexes. The loss of excitatory synapses and impaired working memory persisted in males past a 30-day recovery period. In contrast, we observed a remarkable recovery of excitatory transmission and behavioral performance in females. Inhibitory synapse density recovered in both sexes. We have also observed a late onset anxiety phenotype in RMS exposed females that was absent in males. Overall, our results indicate that there are marked sex differences in the long-term effects of prepubescent stress on cortical synapses and behavior.

Down-regulation of MST1 in hippocampus protects against stress-induced depression-like behaviours and synaptic plasticity impairments

Depression is a common mental disorder, and its main environmental risk factor is chronic stress. The activation of mammalian STE20-like kinase 1 (MST1), a key factor involved in the underlying pathophysiology of stress, can trigger synaptic plasticity impairment, neuronal dysfunction and neuroinflammation. However, it is unclear whether down-regulation of MST1 in the hippocampus protects against stress-induced behavioural dysfunctions. In this study, three mouse models were used to assess the role of MST1 in stress. Various behavioural tests, in vivo electrophysiological recordings, Western blotting, Golgi staining and immunofluorescence assay were used. The data showed that the level of phospho-MST1 (T183) was significantly increased in the hippocampus of mice subjected to chronic unpredictable mild stress (CUMS) and that mice with MST1 overexpression showed depression-like behaviours. Importantly, the impairment of cognitive functions and the hippocampal synaptic plasticity induced by CUMS were significantly improved by MST1 knockdown, suggesting that MST1 down-regulation effectively protected against stress-induced behavioural dysfunctions. Moreover, MST1 knockdown suppressed CUMS-induced microglial activation, reduced the abnormal expression of inflammatory cytokines and impeded the activation of p38, implying that the antidepressant-like effects of MST1 knockdown were associated with inhibiting the p38 pathway. These findings suggest that hippocampal MST1 is an essential regulator of stress, which can be an ideal target for the development of antidepressants in the future.

Child maltreatment, cognitive functions and the mediating role of mental health problems among maltreated children and adolescents in Uganda

BACKGROUND

Child maltreatment poses high risks to the mental health and cognitive functioning of children not only in childhood but also in later life. However, it remains unclear whether child maltreatment is directly associated with impaired cognitive functioning or whether this link is mediated by mental health problems. Our study aimed at examining this research question among children and adolescents in Uganda.

METHODS

A sample of 232 school-going children and adolescents with a mean age of 14.03 (SD = 3.25) was assessed on multiple forms of maltreatment using the Maltreatment and Abuse Chronology Exposure-Pediatric Version (pediMACE). Executive functions were assessed by the Tower of London task and working memory by the Corsi Block Tapping task, while mental health problems were assessed using the Child PTSD Symptom Scale for PTSD and the Center for Epidemiological Studies Depression Scale for Children (CES-DC).

RESULTS

In total, 232 (100%) of the participant reported to have experienced at least one type of maltreatment in their lifetime including emotional, physical, and sexual violence as well as neglect. We found a negative association between child maltreatment and executive functions (β = - 0.487, p < 0.001) and working memory (β = - 0.242, p = 0.001). Mental health problems did not mediate this relationship.

CONCLUSIONS

Child maltreatment seems to be related to lower working memory and executive functioning of affected children and adolescents even after controlling for potential cofounders. Our study indicates that child maltreatment the affects children's cognitive functionality beyond health and well-being.

Hair Cortisol Concentration and Perceived Chronic Stress in Low-Income Urban Pregnant and Postpartum Black Women

Black women are more likely to experience short- or long-term health consequences from their labor and delivery and die from pregnancy-related causes than White women. Similarly, infants born to Black women also have heightened health risks. Developing research suggests that a contributing factor to Black health disparities may be maternal chronic stress. A widely used biomarker for chronic stress is hair cortisol concentration (HCC). Few prior studies have explored the HCC of pregnant Black women or comprehensively examined perceived chronic stress in this population. Using a mixed-methods focus group framework, we assessed HCC and perceived chronic stress among low-income pregnant and postpartum Black women. Four focus groups were conducted (N = 24). The mean HCC for our pregnant Black participants was greater than pregnant White women in reviewed published studies. The high levels of stress evidenced at all pregnancy stages indicate that many of these women are experiencing chronic stress, which can contribute to higher Black maternal morbidity and mortality rates, and possibly infant mortality rates. From the open coding of the focus group transcripts, 4 themes emerged: chronic stress, experiences of racism, experiences of trauma, and negative thinking. Selective coding based on these themes revealed cumulative experiences of chronic stress, various traumatic experiences, and frequent encounters with racism. Negative thinking styles were observed across the 4 focus groups. More studies of HCC and perceived stress among pregnant Black women are encouraged. Findings suggest the need for tailored multi-level interventions given the layers of stressors present in this population.

Photobiomodulation Therapy Ameliorates Glutamatergic Dysfunction in Mice with Chronic Unpredictable Mild Stress-Induced Depression

Accumulating evidence indicates that dysfunction of the glutamatergic neurotransmission has been widely involved in the pathophysiology and treatment of depression. Photobiomodulation therapy (PBMT) has been demonstrated to regulate neuronal function both in vitro and in vivo. Herein, we aim to investigate whether the antidepressant phenotype of PBMT is associated with the improvement of glutamatergic dysfunction and to explore the mechanisms involved. Results showed that PBMT decreased extracellular glutamate levels via upregulation of glutamate transporter-1 (GLT-1) and rescued astrocyte loss in the cerebral cortex and hippocampus, which also alleviated dendritic atrophy and upregulated the expression of AMPA receptors on the postsynaptic membrane, ultimately exhibiting behaviorally significant antidepressant effects in mice exposed to chronic unpredictable mild stress (CUMS). Notably, PBMT also obtained similar antidepressant effects in a depressive mouse model subcutaneously injected with corticosterone (CORT). Evidence from in vitro mechanistic experiments demonstrated that PBMT treatment significantly increased both the GLT-1 mRNA and protein levels via the Akt/NF-κB signaling pathway. NF-κB-regulated transcription was in an Akt-dependent manner, while inhibition of Akt attenuated the DNA-binding efficiency of NF-κB to the GLT-1 promoter. Importantly, in vitro, we further found that PKA activation was responsible for phosphorylation and surface levels of AMPA receptors induced by PBMT, which is likely to rescue excitatory synaptic transmission. Taken together, our research suggests that PBMT as a feasible therapeutic approach has great potential value to control the progression of depression.

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.

Role of trace amine‑associated receptor 1 in the medial prefrontal cortex in chronic social stress-induced cognitive deficits in mice

Emerging evidence supports an essential role of trace amine-associated receptor 1 (TAAR1) in neuropsychiatric disorders such as depression and schizophrenia. Stressful events are critical contributors to various neuropsychiatric disorders. This study examined the role of TAAR1 in mediating the negative outcomes of stressful events. In mice that experienced chronic social defeat stress but not acute stress, a significant reduction in the TAAR1 mRNA level was found in the medial prefrontal cortex (mPFC), a brain region that is known to be vulnerable to stress experience. Conditional TAAR1 knockout in the mPFC mimicked the cognitive deficits induced by chronic stress. In addition, chronic treatment with the selective TAAR1 partial agonist RO5263397 ameliorated chronic stress-induced changes in cognitive function, dendritic arborization, and the synapse number of pyramidal neurons in the mPFC but did not affect chronic stress-induced anxiety-like behaviors. Biochemically, chronic stress reduced the ratio of vesicular transporters of glutamate-1 (VGluT1) / vesicular GABA transporter (VGAT) in the mPFC，most prominently in the prelimbic cortex, and RO5263397 restored the excitatory-inhibitory (E/I) imbalance. Together, the results of this study reveal an essential role of TAAR1 in mediating chronic stress-induced cognitive impairments and suggest that TAAR1 agonists may be uniquely useful to treat MDD-related cognitive impairments.

Medial prefrontal cortex encoding of stress and anxiety

The prefrontal cortex (PFC) is involved in adaptive control of behavior and optimizing action selection. When an organism is experiencing an aversive event, such as a sustained state of anxiety or an overt experience of fear or stress, the mechanisms that govern PFC regulation of action selection may be critical for survival. A large body of literature has shown that acute aversive states influence the activity of PFC neurons and the release of neurotransmitters in this region. These states also result in long-term neurobiological changes in the PFC and expression of PFC-dependent motivated behaviors. The mechanism for how these changes lead to modifying action selection is only recently beginning to emerge. Here, we review animal and human studies into the neural mechanisms which may mediate the adaptive changes in the PFC that emerge during negative affective states. We then highlight recent advances in approaches for understanding how anxiety influences action selection and related cortical processes. We conclude by proposing that PFC neurons selectively influence action encoding during conditions where actions toward obtaining a reward or avoiding harm are executed under a fog of fear and anxiety.

Synaptic and behavioral effects of chronic stress are linked to dynamic and sex-specific changes in microglia function and astrocyte dystrophy

Emerging evidence indicates that males and females display different neurobiological responses to chronic stress which contribute to varied behavioral adaptations. In particular, pyramidal neurons undergo dendritic atrophy and synapse loss in the prefrontal cortex (PFC) of male, but not female, mice. Our recent work shows that chronic stress also provokes microglia-mediated neuronal remodeling, which contributes to synaptic deficits in the PFC and associated behavioral consequences in males. Separate studies indicate that chronic stress promotes astrocyte dystrophy in the PFC which is associated with behavioral despair. Notably, these prior reports focused primarily on stress effects in males. In the present studies, male and female mice were exposed to 14 or 28 days of chronic unpredictable stress (CUS) to assess molecular and cellular adaptations of microglia, astrocytes, and neurons in the medial PFC. Consistent with our recent work, male, but not female, mice displayed behavioral and cognitive deficits with corresponding perturbations of neuroimmune factors in the PFC after 14 days of CUS. Fluorescence-activated cell sorting and gene expression analyses revealed that CUS increased expression of select markers of phagocytosis in male PFC microglia. Confocal imaging in Thy1-GFP(M) mice showed that CUS reduced dendritic spine density, decreased GFAP immunolabeling, and increased microglia-mediated neuronal remodeling only in male mice. After 28 days of CUS, both male and female mice displayed behavioral and cognitive impairments. Interestingly, there were limited stress effects on neuroimmune factors and measures of microglial phagocytosis in the PFC of both sexes. Despite limited changes in neuroimmune function, reduced GFAP immunolabeling and dendritic spine deficits persisted in male mice. Further, GFAP immunolabeling and dendritic spine density remained unaltered in the PFC of females. These findings indicate that chronic stress causes sex-specific and temporally dynamic changes in microglial function which are associated with different neurobiological and behavioral adaptations. In all, these results suggest that microglia-mediated neuronal remodeling, astrocyte dystrophy, and synapse loss contribute to stress-induced PFC dysfunction and associated behavioral consequences in male mice.

Positive modulation of NMDA receptors by AGN-241751 exerts rapid antidepressant-like effects via excitatory neurons

Dysregulation of the glutamatergic system and its receptors in medial prefrontal cortex (mPFC) has been implicated in major depressive disorder. Recent preclinical studies have shown that enhancing NMDA receptor (NMDAR) activity can exert rapid antidepressant-like effects. AGN-241751, an NMDAR positive allosteric modulator (PAM), is currently being tested as an antidepressant in clinical trials, but the mechanism and NMDAR subunit(s) mediating its antidepressant-like effects are unknown. We therefore used molecular, biochemical, and electrophysiological approaches to examine the cell-type-specific role of GluN2B-containing NMDAR in mediating antidepressant-like behavioral effects of AGN-241751. We demonstrate that AGN-241751 exerts antidepressant-like effects and reverses behavioral deficits induced by chronic unpredictable stress in mice. AGN-241751 treatment enhances NMDAR activity of excitatory and parvalbumin-inhibitory neurons in mPFC, activates Akt/mTOR signaling, and increases levels of synaptic proteins crucial for synaptic plasticity in the prefrontal cortex. Furthermore, cell-type-specific knockdown of GluN2B-containing NMDARs in mPFC demonstrates that GluN2B subunits on excitatory, but not inhibitory, neurons are necessary for antidepressant-like effects of AGN-241751. Together, these results demonstrate antidepressant-like actions of the NMDAR PAM AGN-241751 and identify GluN2B on excitatory neurons of mPFC as initial cellular trigger underlying these behavioral effects.

Psychosocial Crowding Stress-Induced Changes in Synaptic Transmission and Glutamate Receptor Expression in the Rat Frontal Cortex

This study demonstrates how exposure to psychosocial crowding stress (CS) for 3, 7, and 14 days affects glutamate synapse functioning and signal transduction in the frontal cortex (FC) of rats. CS effects on synaptic activity were evaluated in FC slices of the primary motor cortex (M1) by measuring field potential (FP) amplitude, paired-pulse ratio (PPR), and long-term potentiation (LTP). Protein expression of GluA1, GluN2B mGluR1a/5, VGLUT1, and VGLUT2 was assessed in FC by western blot. The body’s response to CS was evaluated by measuring body weight and the plasma level of plasma corticosterone (CORT), adrenocorticotropic hormone (ACTH), and interleukin 1 beta (IL1B). CS 3 14d increased FP and attenuated LTP in M1, while PPR was augmented in CS 14d. The expression of GluA1, GluN2B, and mGluR1a/5 was up-regulated in CS 3d and downregulated in CS 14d. VGLUTs expression tended to increase in CS 7d. The failure to blunt the effects of chronic CS on FP and LTP in M1 suggests the impairment of habituation mechanisms by psychosocial stressors. PPR augmented by chronic CS with increased VGLUTs level in the CS 7d indicates that prolonged CS exposure changed presynaptic signaling within the FC. The CS bidirectional profile of changes in glutamate receptors’ expression seems to be a common mechanism evoked by stress in the FC.

How stress physically re-shapes the brain: Impact on brain cell shapes, numbers and connections in psychiatric disorders

Severe stress is among the most robust risk factors for the development of psychiatric disorders. Imaging studies indicate that life stress is integral to shaping the human brain, especially regions involved in processing the stress response. Although this is likely underpinned by changes to the cytoarchitecture of cellular networks in the brain, we are yet to clearly understand how these define a role for stress in human psychopathology. In this review, we consolidate evidence of macro-structural morphometric changes and the cellular mechanisms that likely underlie them. Focusing on stress-sensitive regions of the brain, we illustrate how stress throughout life may lead to persistent remodelling of the both neurons and glia in cellular networks and how these may lead to psychopathology. We support that greater translation of cellular alterations to human cohorts will support parsing the psychological sequalae of severe stress and improve our understanding of how stress shapes the human brain. This will remain a critical step for improving treatment interventions and prevention outcomes.

Synergistic inhibition of histone modifiers produces therapeutic effects in adult Shank3-deficient mice

Autism spectrum disorder (ASD) is a lifelong developmental disorder characterized by social deficits and other behavioral abnormalities. Dysregulation of epigenetic processes, such as histone modifications and chromatin remodeling, have been implicated in ASD pathology, and provides a promising therapeutic target for ASD. Haploinsufficiency of the SHANK3 gene is causally linked to ASD, so adult (3-5 months old) Shank3-deficient male mice were used in this drug discovery study. We found that combined administration of the class I histone deacetylase inhibitor Romidepsin and the histone demethylase LSD1 inhibitor GSK-LSD1 persistently ameliorated the autism-like social preference deficits, while each individual drug alone was largely ineffective. Another behavioral abnormality in adult Shank3-deficient male mice, heightened aggression, was also alleviated by administration of the dual drugs. Furthermore, Romidepsin/GSK-LSD1 treatment significantly increased transcriptional levels of NMDA receptor subunits in prefrontal cortex (PFC) of adult Shank3-deficient mice, resulting in elevated synaptic expression of NMDA receptors and the restoration of NMDAR synaptic function in PFC pyramidal neurons. These results have offered a novel pharmacological intervention strategy for ASD beyond early developmental periods.

Activation of dopaminergic VTA inputs to the mPFC ameliorates chronic stress-induced breast tumor progression

AIMS

Chronic stress plays an important role in promoting the progression and migration of cancers. However, little is known of any direct impact on tumor progression related to the regulation of emotion-related circuitry. The aim of this study was to explore the neural-circuit mechanisms underlying stress-induced progression of cancers and the impact of emotion-related regulation of circuitry on tumor growth.

METHODS

Optogenetic manipulation was applied to unpredictable chronic mild stress (UCMS)-treated mice bearing breast tumor cell. The stress-related hormones, tumor-related cytokines, the tyrosine hydroxylase (TH)-positive neurons and their fibers, dopamine receptor-positive cells, and anxiety level were measured using ELISA, immunohistochemical staining, fluorescence in situ hybridization, and behavioral test, respectively.

RESULTS

By investigating breast cancer mouse models with a chronic mild stress model, optogenetic stimulation, and behavioral analysis, we show that chronic stress induced anxiety-like behavior in mice and increased serum concentration of norepinephrine and corticosterone, hormones closely related to stress and anxiety. Optogenetic activation of VTA TH terminals in the mPFC rescued anxiety-like behavior induced by chronic stress. Chronic stress resulted in marked progression of breast tumors, and repetitive optogenetic activation of VTA TH terminals in the mPFC significantly attenuated stress-induced progression of breast cancers and reduced serum concentration of norepinephrine and corticosterone. Furthermore, there was a positive correlation between serum norepinephrine or corticosterone concentration and tumor size.

CONCLUSIONS

These findings indicate a positive role of an emotion regulation circuit on the progression of breast cancer and reveal a link between stress, emotion regulation, and the progression of breast cancers. Our findings provide new insights pertinent to therapeutic interventions in the treatment of breast cancers.

Modulation by chronic stress and ketamine of ionotropic AMPA/NMDA and metabotropic glutamate receptors in the rat hippocampus

Converging clinical and preclinical evidence has shown that dysfunction of the glutamate system is a core feature of major depressive disorder. In this context, the N-methyl-d-aspartate (NMDA) receptor antagonist ketamine has raised growing interest as fast acting antidepressant. Using the chronic mild stress (CMS) rat model of depression, performed in male rats, we aimed at analyzing whether hippocampal specific changes in subunit expression and regulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or NMDA ionotropic receptors and in metabotropic glutamate receptors could be associated with behavioral vulnerability/resilience to CMS. We also assessed whether acute ketamine (10 mg/kg) was able to dampen the alterations in CMS vulnerable animals. Although chronic stress and ketamine had no effect on ionotropic glutamate receptors mRNAs (expression, RNA editing and splicing), we found selective modulations in their protein expression, phosphorylation and localization at synaptic membranes. AMPA GluA2 expression at synaptic membranes was significantly increased only in CMS resilient rats (although a trend was found also in vulnerable animals), while its phosphorylation at Ser⁸⁸⁰ was higher in both CMS resilient and vulnerable rats, a change partially dampened by ketamine. In the hippocampus from all stressed groups, despite NMDA receptor expression levels were reduced in total extract, the levels of GluN2B-containing NMDA receptors were remarkably increased in synaptic membranes. Finally, mGlu2 underwent a selective downregulation in stress vulnerable animals, which was completely restored by acute ketamine. Overall, these results are in line with a hypofunction of activity-dependent glutamatergic synaptic transmission induced by chronic stress exposure in all the animals, as suggested by the alterations of ionotropic glutamate receptors expression and localization at synaptic level. At the same time, the selective modulation of mGlu2 receptor, confirms its previously hypothesized functional role in regulating stress vulnerability and, for the first time here, suggests a mGlu2 involvement in the fast antidepressant effect of ketamine.

Advances in novel molecular targets for antidepressants

Depression is the most common psychiatric illness affecting numerous people world-wide. The currently available antidepressant treatment presents low response and remission rates. Thus, new effective antidepressants need to be developed or discovered. Aiming to give an overview of novel possible antidepressant drug targets, we summarized the molecular targets of antidepressants and the underlying neurobiology of depression. We have also addressed the multidimensional perspectives on the progress in the psychopharmacological treatment of depression and on the new potential approaches with effective drug discovery.

An Update on Glutamatergic System in Suicidal Depression and on the Role of Esketamine

BACKGROUND

A research on mood disorder pathophysiology has hypothesized abnormalities in glutamatergic neurotransmission, by suggesting further investigation on glutamatergic N-methyl-Daspartate (NMDA) receptor modulators in treating Major Depressive Disorder (MDD). Esketamine (ESK), an NMDA receptor antagonist able to modulate glutamatergic neurotransmission has been recently developed as an intranasal formulation for treatment-resistant depression (TRD) and for rapid reduction of depressive symptomatology, including suicidal ideation in MDD patients at imminent risk for suicide.

OBJECTIVE

The present study aims at investigating recent clinical findings on research on the role of the glutamatergic system and ESK in treating suicidal depression in MDD and TRD.

METHODS

A systematic review was here carried out on PubMed/Medline, Scopus and the database on U.S. N.I.H. Clinical Trials (https://clinicaltrials.gov) and the European Medical Agency (EMA) (https://clinicaltrialsregister.eu) from inception until October 2019.

RESULTS

Intravenous infusion of ESK is reported to elicit rapid-acting and sustained antidepressant activity in refractory patients with MDD and TRD. In phase II studies, intranasal ESK demonstrated a rapid onset and a persistent efficacy in patients with TRD as well as in MDD patients at imminent risk for suicide. However, some data discrepancies have emerged in phase III studies.

CONCLUSION

The U.S. Food and Drug Administration (FDA) granted fast track and Breakthrough Therapy Designation to Janssen Pharmaceuticals®, Inc. for intranasal ESK in 2013 for treatment-resistant depression (TRD) and in 2016 for the treatment of MDD with an imminent risk of suicide. However, further studies should be implemented to investigate the long-term efficacy and safety of intranasal ESK.

Evidence for an Interaction Between NEDD4 and Childhood Trauma on Clinical Characters of Schizophrenia With Family History of Psychosis

Background: Neural precursor cell-expressed developmentally downregulated 4 (NEDD4) polymorphisms and childhood trauma (CT) are associated with schizophrenia. However, whether NEDD4 interacts with CT on symptoms of schizophrenia remains unknown. This study aimed to investigate the gene-environment interaction effect. Methods: We recruited 289 schizophrenia patients and 487 controls and genotyped rs2303579, rs3088077, rs7162435, rs11550869, and rs62043855 in their NEDD4 gene. Results: We found significant differences in the rs2303579 and rs3088077 between the two groups. Patients with the rs2303579 CC genotype had higher scores compared with other genotype (P = 0.026) in the test of positive schizophrenia syndrome scores, whereas patients with the rs3088077 TT (P = 0.037) and rs7162435 CC genotypes (P = 0.009) had higher scores compared with the other genotypes in the test of excitement factor. Patients with a family history of psychosis (FH+) reported higher negative scores (P = 0.012) than those without. Patients exposed to physical abuse (PA) reported a lower language learning and memory score (P = 0.017) and working memory score (P = 0.047) than those not. Patients exposed to sexual abuse (SA) reported a lower reasoning and problem-solving skills score (P = 0.025); those exposed to emotional neglect (EN) reported a lower social cognition score (P = 0.044); and those exposed to physical neglect reported a lower social cognition score (P = 0.036) but higher visual learning and memory score (P = 0.032). Rs3088077 could interact with EN to increase risk for schizophrenia. Optimal model rs62043855 × EA, rs3088077 × rs7162435 × rs11550869 × SA × EN and rs2303579 × rs7162435 × rs11550869 × rs62043855 × EA × PA could explain positive symptom, excitement symptom and working memory, respectively, in FH+ group. Conclusion: The study highlighted that the combined interaction of NEDD4 and CT may be associated with symptoms of schizophrenia especially for those with FH+.

Shisa6 mediates cell-type specific regulation of depression in the nucleus accumbens

Depression is the leading cause of disability and produces enormous health and economic burdens. Current treatment approaches for depression are largely ineffective and leave more than 50% of patients symptomatic, mainly because of non-selective and broad action of antidepressants. Thus, there is an urgent need to design and develop novel therapeutics to treat depression. Given the heterogeneity and complexity of the brain, identification of molecular mechanisms within specific cell-types responsible for producing depression-like behaviors will advance development of therapies. In the reward circuitry, the nucleus accumbens (NAc) is a key brain region of depression pathophysiology, possibly based on differential activity of D1- or D2- medium spiny neurons (MSNs). Here we report a circuit- and cell-type specific molecular target for depression, Shisa6, recently defined as an AMPAR component, which is increased only in D1-MSNs in the NAc of susceptible mice. Using the Ribotag approach, we dissected the transcriptional profile of D1- and D2-MSNs by RNA sequencing following a mouse model of depression, chronic social defeat stress (CSDS). Bioinformatic analyses identified cell-type specific genes that may contribute to the pathogenesis of depression, including Shisa6. We found selective optogenetic activation of the ventral tegmental area (VTA) to NAc circuit increases Shisa6 expression in D1-MSNs. Shisa6 is specifically located in excitatory synapses of D1-MSNs and increases excitability of neurons, which promotes anxiety- and depression-like behaviors in mice. Cell-type and circuit-specific action of Shisa6, which directly modulates excitatory synapses that convey aversive information, identifies the protein as a potential rapid-antidepressant target for aberrant circuit function in depression.

Glutamate and GABA Homeostasis and Neurometabolism in Major Depressive Disorder

Major depressive disorder (MDD) is a leading cause of distress, disability, and suicides. As per the latest WHO report, MDD affects more than 260 million people worldwide. Despite decades of research, the underlying etiology of depression is not fully understood. Glutamate and γ-aminobutyric acid (GABA) are the major excitatory and inhibitory neurotransmitters, respectively, in the matured central nervous system. Imbalance in the levels of these neurotransmitters has been implicated in different neurological and psychiatric disorders including MDD. ¹H nuclear magnetic resonance (NMR) spectroscopy is a powerful non-invasive method to study neurometabolites homeostasis in vivo. Additionally, ¹³C-NMR spectroscopy together with an intravenous administration of non-radioactive ¹³C-labeled glucose or acetate provides a measure of neural functions. In this review, we provide an overview of NMR-based measurements of glutamate and GABA homeostasis, neurometabolic activity, and neurotransmitter cycling in MDD. Finally, we highlight the impact of recent advancements in treatment strategies against a depressive disorder that target glutamate and GABA pathways in the brain.

Remodeling without destruction: non-proteolytic ubiquitin chains in neural function and brain disorders

Ubiquitination is a fundamental posttranslational protein modification that regulates diverse biological processes, including those in the CNS. Several topologically and functionally distinct polyubiquitin chains can be assembled on protein substrates, modifying their fates. The classical and most prevalent polyubiquitin chains are those that tag a substrate to the proteasome for degradation, which has been established as a major mechanism driving neural circuit deconstruction and remodeling. In contrast, proteasome-independent non-proteolytic polyubiquitin chains regulate protein scaffolding, signaling complex formation, and kinase activation, and play essential roles in an array of signal transduction processes. Despite being a cornerstone in immune signaling and abundant in the mammalian brain, these non-proteolytic chains are underappreciated in neurons and synapses in the brain. Emerging studies have begun to generate exciting insights about some fundamental roles played by these non-degradative chains in neuronal function and plasticity. In addition, their roles in a number of brain diseases are being recognized. In this article, we discuss recent advances on these nonconventional ubiquitin chains in neural development, function, plasticity, and related pathologies.

The Impact of FKBP5 Deficiency in Glucocorticoid Receptor Mediated Regulation of Synaptic Transmission in the Medial Prefrontal Cortex

Exposure to stress activates glucocorticoid receptors in the brain and facilitates the onset of multitude psychiatric disorders. It has been shown that FK506 binding protein 51 (FKBP5) expression increases during glucocorticoid receptor (GR) activation in various brain regions including the medial prefrontal cortex (mPFC). FKBP5 knockout (KO) mice are reported to be resilient to stress, however, it remains uninvestigated whether FKBP5 loss affects neurotransmission and if so, what the functional consequences are. Here, we examined the impact of FKBP5 deletion in synaptic transmission of the mPFC. We found that GR activation significantly decreased excitatory neurotransmission in the mPFC, which was completely abolished upon FKBP5 deletion, in consistent with behavioral resilience observed in FKBP5 KO mice. Even though FKBP5 loss has minimal impact on neural excitability, we found that FKBP5 deletion distorts the excitatory/inhibitory balance in the mPFC. Our study suggests that FKBP5 deficiency leads to the mPFC insensitive to GR activation and provides a neurophysiological explanation for how FKBP5 deficiency may mediate stress resilience.

AMPA receptors mediate the pro-cognitive effects of electrical and optogenetic stimulation of the medial prefrontal cortex in antidepressant non-responsive Wistar-Kyoto rats

BACKGROUND

The chronic mild stress (CMS) procedure is a widely used animal model of depression, and its application in Wistar-Kyoto (WKY) rats has been validated as a model of antidepressant-refractory depression. While not responding to chronic treatment with antidepressant drugs, WKY rats do respond to acute deep brain stimulation (DBS) of the medial prefrontal cortex (mPFC). In antidepressant-responsive strains there is evidence suggesting a role for AMPA subtype of glutamate receptor in the action mechanism of both antidepressants and DBS.

METHODS

Animals were subjected to CMS for 6 to 8 weeks; sucrose intake was monitored weekly and novel object recognition (NOR) test was conducted following recovery from CMS. Wistars were treated chronically with venlafaxine (VEN), while WKY were treated acutely with either DBS, optogenetic stimulation (OGS) of virally-transduced (AAV5-hSyn-ChR2-EYFP) mPFC or ventral hippocampus, or acute intra-mPFC injection of the AMPA receptor positive allosteric modulator CX-516. The AMPA receptor antagonist NBQX was administered, at identical sites in mPFC, immediately following the exposure trial in the NOR.

RESULTS

Sucrose intake and NOR were suppressed by CMS, and restored by VEN in Wistars and by DBS, OGS, or CX-516 in WKY. However, OGS of the ventral hippocampal afferents to mPFC was ineffective. A low dose of NBQX selectively blocked the procognitive effect of VEN, DBS and OGS.

CONCLUSIONS

These results suggest that activation of AMPA receptors in the mPFC represents a common pathway for the antidepressant effects of both conventional (VEN) and novel (DBS, OGS) antidepressant modalities, in both antidepressant responsive (Wistar) and antidepressant-resistant (WKY) rats.

Targeting histone K4 trimethylation for treatment of cognitive and synaptic deficits in mouse models of Alzheimer's disease

Epigenetic aberration is implicated in aging and neurodegeneration. Using postmortem tissues from patients with Alzheimer's disease (AD) and AD mouse models, we have found that the permissive histone mark H3K4me3 and its catalyzing enzymes are significantly elevated in the prefrontal cortex (PFC). Inhibiting H3K4-specific methyltransferases with the compound WDR5-0103 leads to the substantial recovery of PFC synaptic function and memory-related behaviors in AD mice. Among the up-regulated genes reversed by WDR5-0103 treatment in PFC of AD mice, many have the increased H3K4me3 enrichment at their promoters. One of the identified top-ranking target genes, Sgk1, which encodes serum and glucocorticoid-regulated kinase 1, is also significantly elevated in PFC of patients with AD. Administration of a specific Sgk1 inhibitor reduces hyperphosphorylated tau protein, restores PFC glutamatergic synaptic function, and ameliorates memory deficits in AD mice. These results have found a novel epigenetic mechanism and a potential therapeutic strategy for AD and related neurodegenerative disorders.

Effects of Blood Pressure on Cognitive Performance in Aging: A Systematic Review

Introduction: Cognitive functions play a crucial role in daily functioning. Unfortunately, some cognitive abilities decline in the process of healthy aging. An increasing body of evidence has highlighted the role of lifestyle habits and cardiovascular diseases, such as high blood pressure, in increasing the risk of cognitive decline. Surprisingly, although hypertension is a modifiable risk factor for cerebrovascular damage, the role of hypertension on cognitive impairment development is not still clear. Several key questions remain unresolved, and there are many inconsistent results in studies considering this topic. This review is aimed to systematically analyze the results found by the studies that investigated whether high blood pressure, in both hypertensive and healthy people, is related to cognitive performance. Furthermore, it points to evaluate the role of age in this relationship. Method: The review process was conducted according to the PRISMA statement. Restrictions were made, selecting the studies in English and published in peer-review journals, including at least one cognitive measure and blood pressure measurement. Studies that included participants with medical conditions, dementia, psychiatric disorders, strokes, and brain injury were excluded. Cross-sectional and longitudinal studies were analyzed separately. Finally, blood pressure measured at young life (18–39 years), midlife (age 40–64 years), elderly (65–74 years), and old age (≥75 years) were considered. Results: The review allows 68 studies to be selected, which include 154,935 participants. The results provided evidence of an adverse effect of exposure to high blood pressure on cognitive performance. High blood pressure in midlife was linked with poorer cognitive functioning; this evidence was found in cross-sectional and longitudinal studies. However, this association declines with increasing age and tends to become inconsistent. In older people, the relationship between blood pressure and cognitive performance is non-linear, highlighting a beneficial effect of high blood pressure on cognition. Conclusions: Despite some limitations, this review showed that cardiovascular and neuro-cognitive systems do not operate in isolation, but they are related. Blood pressure can be considered an early biomarker of cognitive impairment, and the necessity of early blood pressure measurement and control was underlined.

DNA Methyltransferase 3A Is Involved in the Sustained Effects of Chronic Stress on Synaptic Functions and Behaviors

Emerging evidence suggests that epigenetic mechanisms regulate aberrant gene transcription in stress-associated mental disorders. However, it remains to be elucidated about the role of DNA methylation and its catalyzing enzymes, DNA methyltransferases (DNMTs), in this process. Here, we found that male rats exposed to chronic (2-week) unpredictable stress exhibited a substantial reduction of Dnmt3a after stress cessation in the prefrontal cortex (PFC), a key target region of stress. Treatment of unstressed control rats with DNMT inhibitors recapitulated the effect of chronic unpredictable stress on decreased AMPAR expression and function in PFC. In contrast, overexpression of Dnmt3a in PFC of stressed animals prevented the loss of glutamatergic responses. Moreover, the stress-induced behavioral abnormalities, including the impaired recognition memory, heightened aggression, and hyperlocomotion, were partially attenuated by Dnmt3a expression in PFC of stressed animals. Finally, we found that there were genome-wide DNA methylation changes and transcriptome alterations in PFC of stressed rats, both of which were enriched at several neural pathways, including glutamatergic synapse and microtubule-associated protein kinase signaling. These results have therefore recognized the potential role of DNA epigenetic modification in stress-induced disturbance of synaptic functions and cognitive and emotional processes.

Stress-induced expression pattern of glutamate signaling genes associated with anhedonia

Chronic stress can predispose vulnerable individuals to mood disorders, including depression. Glutamate, one of the key participants in this process, may exert both pathological and therapeutic psycho-emotional effects. However, the role of expression of genes encoding proteins that provide glutamatergic signal is still unclear. In this study, we attempted to distinguish changes in expression of glutamatergic genes associated with stress-induced anhedonia, a core symptom of depression, from those related to other stress-related effects. For this, expression of genes was compared between rats after a short-term stress, which did not yet cause depressive-like symptoms, and animals exposed chronically to different stressors that produce anhedonia-like responses. The changes in gene expression induced by chronic restraint or forced swimming concomitantly with anhedonia development demonstrated similar for both stressors patterns. Main features of the expression patterns include the decrease in mRNA levels for AMPA and NMDA subunits in the midbrain and hippocampus that is consistent with the hypothesis that "monoamine (serotonin)-Glutamate/GABA long neural circuit" involved in mood regulation. The decrease in expression of these subunits in the midbrain may attenuate glutamatergic drive on the serotonergic neurons promoting a shift of excitation/inhibition balance between glutamate and GABA in the forebrain regions resulting in anhedonia. In general, changes in expression of multiple genes involved in glutamatergic neurotransmission in the forebrain and brainstem regions suggest that stress-induced anhedonia may result from the network dysfunction of this neurotransmitter system.

Depression-like behaviors induced by defective PTPRT activity through dysregulated synaptic functions and neurogenesis

PTPRT has been known to regulate synaptic formation and dendritic arborization of hippocampal neurons. PTPRT-/- null and PTPRT-D401A mutant mice displayed enhanced depression-like behaviors compared with wild-type mice. Transient knockdown of PTPRT in the dentate gyrus enhanced the depression-like behaviors of wild-type mice, whereas rescued expression of PTPRT ameliorated the behaviors of PTPRT-null mice. Chronic stress exposure reduced expression of PTPRT in the hippocampus of mice. In PTPRT-deficient mice the expression of GluR2 (also known as GRIA2) was attenuated as a consequence of dysregulated tyrosine phosphorylation, and the long-term potentiation at perforant-dentate gyrus synapses was augmented. The inhibitory synaptic transmission of the dentate gyrus and hippocampal GABA concentration were reduced in PTPRT-deficient mice. In addition, the hippocampal expression of GABA transporter GAT3 (also known as SLC6A11) was decreased, and its tyrosine phosphorylation was increased in PTPRT-deficient mice. PTPRT-deficient mice displayed reduced numbers and neurite length of newborn granule cells in the dentate gyrus and had attenuated neurogenic ability of embryonic hippocampal neural stem cells. In conclusion, our findings show that the physiological roles of PTPRT in hippocampal neurogenesis, as well as synaptic functions, are involved in the pathogenesis of depressive disorder.

Cumulative Effects of Social Stress on Reward-Guided Actions and Prefrontal Cortical Activity

BACKGROUND

When exposed to chronic social stress, animals display behavioral changes that are relevant to depressive-like phenotypes. However, the cascading relationship between incremental stress exposure and neural dysfunctions over time remains incompletely understood.

METHODS

We characterized the longitudinal effect of social defeat on goal-directed actions and prefrontal cortical activity in mice using a novel head-fixed sucrose preference task and two-photon calcium imaging.

RESULTS

Behaviorally, stress-induced loss of reward sensitivity intensifies over days. Motivational anhedonia, the failure to translate positive reinforcements into future actions, requires multiple sessions of stress exposure to become fully established. For neural activity, individual layer 2/3 pyramidal neurons in the cingulate and medial secondary motor subregions of the medial prefrontal cortex have heterogeneous responses to stress. Changes in ensemble activity differ significantly between susceptible and resilient mice after the first defeat session and continue to diverge following successive stress episodes before reaching persistent abnormal levels.

CONCLUSIONS

Collectively, these results demonstrate that the cumulative impact of an ethologically relevant stress can be observed at the level of cellular activity of individual prefrontal neurons. The distinct neural responses associated with resilience versus susceptibility suggests the hypothesis that the negative impact of social stress is neutralized in resilient animals, in part through an adaptive reorganization of prefrontal cortical activity.

Amelioration of autism-like social deficits by targeting histone methyltransferases EHMT1/2 in Shank3-deficient mice

Many of the genes disrupted in autism are identified as histone-modifying enzymes and chromatin remodelers, most prominently those that mediate histone methylation/demethylation. However, the role of histone methylation enzymes in the pathophysiology and treatment of autism remains unknown. To address this, we used mouse models of haploinsufficiency of the Shank3 gene (a highly penetrant monogenic autism risk factor), which exhibits prominent autism-like social deficits. We found that histone methyltransferases EHMT1 and EHMT2, as well as histone lysine 9 dimethylation (specifically catalyzed by EHMT1/2), were selectively increased in the prefrontal cortex (PFC) of Shank3-deficient mice and autistic human postmortem brains. Treatment with the EHMT1/2 inhibitor UNC0642 or knockdown of EHMT1/2 in PFC induced a robust rescue of autism-like social deficits in Shank3-deficient mice, and restored NMDAR-mediated synaptic function. Activity-regulated cytoskeleton-associated protein (Arc) was identified as one of the causal factors underlying the rescuing effects of UNC0642 on NMDAR function and social behaviors in Shank3-deficient mice. UNC0642 treatment also restored a large set of genes involved in neural signaling in PFC of Shank3-deficient mice. These results suggest that targeting histone methylation enzymes to adjust gene expression and ameliorate synaptic defects could be a potential therapeutic strategy for autism.

Chronic stress induces significant gene expression changes in the prefrontal cortex alongside alterations in adult hippocampal neurogenesis

Adult hippocampal neurogenesis is involved in stress-related disorders such as depression, posttraumatic stress disorders, as well as in the mechanism of antidepressant effects. However, the molecular mechanisms involved in these associations remain to be fully explored. In this study, unpredictable chronic mild stress in mice resulted in a deficit in neuronal dendritic tree development and neuroblast migration in the hippocampal neurogenic niche. To investigate molecular pathways underlying neurogenesis alteration, genome-wide gene expression changes were assessed in the prefrontal cortex, hippocampus and the hypothalamus alongside neurogenesis changes. Cluster analysis showed that the transcriptomic signature of chronic stress is much more prominent in the prefrontal cortex compared to the hippocampus and the hypothalamus. Pathway analyses suggested huntingtin, leptin, myelin regulatory factor, methyl-CpG binding protein and brain-derived neurotrophic factor as the top predicted upstream regulators of transcriptomic changes in the prefrontal cortex. Involvement of the satiety regulating pathways (leptin) was corroborated by behavioural data showing increased food reward motivation in stressed mice. Behavioural and gene expression data also suggested circadian rhythm disruption and activation of circadian clock genes such as Period 2. Interestingly, most of these pathways have been previously shown to be involved in the regulation of adult hippocampal neurogenesis. It is possible that activation of these pathways in the prefrontal cortex by chronic stress indirectly affects neuronal differentiation and migration in the hippocampal neurogenic niche via reciprocal connections between the two brain areas.

Repurposing of Drugs-The Ketamine Story

An intranasal formulation of esketamine, the S enantiomer of ketamine, in conjunction with an oral antidepressant, has been approved by the FDA for treating treatment-resistant major depressive disorder (TRD) in 2019, almost 50 years after it was approved as an intravenous anesthetic. In contrast to traditional antidepressants, ketamine shows a rapid (within 2 h) and sustained (∼7 days) antidepressant effect and has significant positive effects on antisuicidal ideation. Ketamine's antidepressant mechanism is predominantly mediated by the N-methyl-d-aspartate receptor (NMDA) receptor, although NMDA-independent mechanisms are not ruled out. At the neurocircuitry level, ketamine affects the brain's reward and mood circuitry located in the corticomesolimbic structures involving the hippocampus, nucleus accumbens, and prefrontal cortex. Repurposing of ketamine for treating TRD provided a new understanding of the pathophysiology of depression, a paradigm shift from monoamine to glutamatergic neurotransmission, thus making it a unique tool to investigate the brain and its complex neurocircuitries.

Facilitation of dopamine-dependent long-term potentiation in the medial prefrontal cortex of male rats follows the behavioral effects of stress

The effect of stress on animal behavior and brain activity has been attracting growing attention in the last decades. Stress dramatically affects several aspects of animal behavior, including motivation and cognitive functioning, and has been used to model human pathologies such as post-traumatic stress disorder. A key question is whether stress alters the plastic potential of synaptic circuits. In this work, we evaluated if stress affects dopamine (DA)-dependent synaptic plasticity in the medial prefrontal cortex (mPFC). On male adolescent rats, we characterized anxiety- and depressive-like behaviors using behavioral testing before and after exposure to a mild stress (elevated platform, EP). After the behavioral protocols, we investigated DA-dependent long-term potentiation (DA-LTP) and depression (DA-LTD) on acute slices of mPFC and evaluated the activation of DA-producing brain regions by western and dot blot analysis. We show that exposure to the EP stress enhances DA-LTP and that desipramine (DMI) treatment abolishes this effect. We also found that DA-LTD is not affected by EP stress unless when this is followed by DMI treatment. In addition, EP stress reduces anxiety, an effect abolished by both DMI and ketamine, while motivation is promoted by previous exposure to EP stress independently of pharmacological treatments. Finally, this form of stress reduces the expression of the early gene cFOS in the ventral tegmental area. These findings support the idea that mild stressors can promote synaptic plasticity in PFC through a dopaminergic mechanism, an effect that might increase the sensitivity of mPFC to subsequent stressful experiences.

Diazepam limits microglia-mediated neuronal remodeling in the prefrontal cortex and associated behavioral consequences following chronic unpredictable stress

Chronic stress induces neuronal atrophy and synaptic loss in the medial prefrontal cortex (PFC), and this leads to behavioral and cognitive impairments. Our recent findings indicate that microglia contribute to structural remodeling of neurons via increased colony-stimulating factor (CSF)-1 in the medial PFC. Other work shows that chronic stress induces aberrant neuronal activity in the medial PFC, and that neuronal hyperactivity increases CSF1 signaling and alters microglia function. Thus, the present studies were designed to examine the role of neuronal activity in stress-induced CSF1 signaling and microglia-mediated neuronal remodeling in the medial PFC. Additional analyses probed stress effects on the dorsal hippocampus (HPC), basolateral amygdala (BLA), and somatosensory cortex (SSCTX). Mice were exposed to chronic unpredictable stress (CUS) or handled intermittently as controls, and received daily injection of vehicle or diazepam (1 mg/kg). As anticipated, diazepam attenuated CUS-induced behavioral despair and cognitive impairments. Further studies showed that diazepam normalized Csf1 and C3 mRNA in the PFC, and prevented increases in Csf1r and Cd11b in frontal cortex microglia following CUS. Stress had no effect on neuroimmune gene expression in the HPC. Confocal imaging in Thy1-GFP(M) mice demonstrated that diazepam limited microglial engulfment of neuronal elements and blocked CUS-induced dendritic spine loss in the medial PFC. Altogether, these findings indicate that modulation of chronic stress-induced neuronal activity limits microglia-mediated neuronal remodeling in the medial PFC, and subsequent behavioral and cognitive consequences.

Alleviation of Depression by Glucagon-Like Peptide 1 Through the Regulation of Neuroinflammation, Neurotransmitters, Neurogenesis, and Synaptic Function

Depression has emerged as a major cause of mortality globally. Many studies have reported risk factors and mechanisms associated with depression, but it is as yet unclear how these findings can be applied to the treatment and prevention of this disorder. The onset and recurrence of depression have been linked to diverse metabolic factors, including hyperglycemia, dyslipidemia, and insulin resistance. Recent studies have suggested that depression is accompanied by memory loss as well as depressive mood. Thus, many researchers have highlighted the relationship between depressive behavior and metabolic alterations from various perspectives. Glucagon-like peptide-1 (GLP-1), which is secreted from gut cells and hindbrain areas, has been studied in metabolic diseases such as obesity and diabetes, and was shown to control glucose metabolism and insulin resistance. Recently, GLP-1 was highlighted as a regulator of diverse pathways, but its potential as the therapeutic target of depressive disorder was not described comprehensively. Therefore, in this review, we focused on the potential of GLP-1 modulation in depression.

Restoring tripartite glutamatergic synapses: A potential therapy for mood and cognitive deficits in Gulf War illness

Gulf War illness is associated with a combination of exposure to war-related chemical agents and traumatic stress. Currently, there are no effective treatments, and the pathophysiology remains elusive. Neurological problems are among the most commonly reported symptoms. In this study, we investigated the glutamatergic system in the hippocampi of mice exposed to war-related chemical agents and stress. Mice developed Gulf War illness-like symptoms, including mood deficits, cognitive impairments, and fatigue. They exhibited the following pathological changes in hippocampi: elevated extracellular glutamate levels, impaired glutamatergic synapses, astrocyte atrophy, loss of interneurons, and decreased neurogenesis. LDN/OSU-215111 is a small-molecule that can strengthen the structure and function of both the astrocytic processes and the glutamatergic synapses that together form the tripartite synapses. We found that LDN/OSU-215111 effectively prevented the development of mood and cognitive deficits in mice when treatment was implemented immediately following the exposure. Moreover, when symptoms were already present, LDN/OSU-215111 still significantly ameliorated these deficits; impressively, benefits were sustained one month after treatment cessation, indicating disease modification. LDN/OSU-215111 effectively normalized hippocampal pathological changes. Overall, this study provides strong evidence that restoration of tripartite glutamatergic synapses by LDN/OSU-215111 is a potential therapy for Gulf War illness.

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Exposure to Gulf War-related agents and stress causes long-term hippocampal glutamatergic synapses impairment.

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LDN/OSU-215111, a small-molecule that enhances tripartite synapses, normalizes hippocampal deficits in a mouse model of GWI.

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LDN/OSU-215111 effectively ameliorates mood deficits, cognitive impairments, and fatigue in a mouse model of GWI.

Chronic Restraint Stress Affects Network Oscillations in the Anterior Cingulate Cortex in Mice

The anterior cingulate cortex (ACC) is vulnerable to stress. Its dysfunction is observed in psychiatric disorders manifested as alterations in network oscillations. Mechanisms linking stress load to disturbed emotional-cognitive behaviors are of essential importance to further elucidate therapeutic strategies for psychiatric diseases. Here, we analyzed the effects of chronic restraint stress (CRS) load in juvenile mice on kainic acid (KA)-induced network oscillations in ACC slice preparations and on the forced swim test (FST). The immobility time (IT) was shortened at the beginning of the FST in CRS mice. Power spectral density (PSD) obtained from KA-induced oscillations in field potentials in the superficial layers of the ACC were altered in slices from the CRS mice. The PSD was decreased in CRS mice at the alpha (8-12 Hz), beta (13-30 Hz), low gamma (30-50 Hz), and high gamma (50-80 Hz) components. Noradrenaline increased the PSD of the theta (3-8 Hz) components in both the control and CRS groups, and also in alpha components only in the CRS group. Dopamine did not modulate the PSD of any frequency components in the control mice, whereas it enhanced the PSD of theta and alpha components in CRS mice. It was suggested that chronic stress load affects the dynamics of the network oscillations in the ACC with enhanced cathecolaminergic modulation.

Neuroprotective efficacy of different levels of high-frequency repetitive transcranial magnetic stimulation in mice with CUMS-induced depression: Involvement of the p11/BDNF/Homer1a signaling pathway

High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) is widely used to treat depression. However, the underlying mechanism has not been identified, and there is uncertainty regarding the optimal choice of stimulus parameters, especially stimulus frequency. Our previous study in mice demonstrated that 10-Hz HF-rTMS ameliorated depression by inducing expression of Homer1a and reducing excitability of cortical pyramidal cells. The aims of this study were to compare the effects of 15-Hz and 25-Hz HF-rTMS in a model of chronic unpredictable mild stress (CUMS)-induced depression and investigate its possible molecular mechanism. Male C57BL/6J mice were treated with CUMS for 28 days followed by 15-Hz and 25-Hz rTMS for 4 weeks. The sucrose preference, open field, forced swimming, and tail suspension tests were used to evaluate depression-like behaviors. Immunostaining was performed to measure neuronal loss and neurogenesis. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. Expression of synapse-related proteins and the effects of HF-rTMS on the signaling pathway were examined using Western blot. The results showed that both 15-Hz and 25-Hz rTMS had significant antidepressant effects; 15-Hz rTMS seemed to be more effective than 25-Hz rTMS in preventing neuronal loss and promoting neurogenesis, while 25-Hz rTMS was superior to 15-Hz rTMS in facilitating synaptic plasticity. We also found that 15-Hz and 25-Hz rTMS markedly increased expression of p11, BDNF, Homer1a, and p-trkB proteins. These findings suggest that 15-Hz and 25-Hz HF-rTMS could exert neuroprotective effects to different degrees via multiple perspectives, which at least in part involve the p11/BDNF/Homer1a pathway.

Chronic Stress-induced Behaviors Correlate with Exacerbated Acute Stress-induced Cingulate Cortex and Ventral Hippocampus Activation

Altered activity of corticolimbic brain regions is a hallmark of stress-related illnesses, including mood disorders, neurodegenerative diseases, and substance abuse disorders. Acute stress adaptively recruits brain region-specific functions for coping, while sustained activation under chronic stress may overwhelm feedback mechanisms and lead to pathological cellular and behavioral responses. The neural mechanisms underlying dysregulated stress responses and how they contribute to behavioral deficits are poorly characterized. Here, we tested whether prior exposure to chronic restraint stress (CRS) or unpredictable chronic mild stress (UCMS) in mice could alter functional response to acute stress and whether these changes are associated with chronic stress-induced behavioral deficits. More specifically, we assessed acute stress-induced functional activation indexed by c-Fos+ cell counts in 24 stress- and mood-related brain regions, and determined if changes in functional activation were linked to chronic stress-induced behavioral impairments, summarized across dimensions through principal component analysis (PCA). Results indicated that CRS and UCMS led to convergent physiological and anxiety-like deficits, whereas working and short-term memory were impaired only in UCMS mice. CRS and UCMS exposure exacerbated functional activation by acute stress in anterior cingulate cortex (ACC) area 24b and ventral hippocampal (vHPC) CA1, CA3, and subiculum. In dysregulated brain regions, levels of functional activation were positively correlated with principal components reflecting variance across behavioral deficits relevant to stress-related disorders. Our data supports an association between a dysregulated stress response, altered functional corticolimbic excitation/inhibition balance, and the expression of maladaptive behaviors.

Identification of a prefrontal cortex-to-amygdala pathway for chronic stress-induced anxiety

Dysregulated prefrontal control over amygdala is engaged in the pathogenesis of psychiatric diseases including depression and anxiety disorders. Here we show that, in a rodent anxiety model induced by chronic restraint stress (CRS), the dysregulation occurs in basolateral amygdala projection neurons receiving mono-directional inputs from dorsomedial prefrontal cortex (dmPFC→BLA PNs) rather than those reciprocally connected with dmPFC (dmPFC↔BLA PNs). Specifically, CRS shifts the dmPFC-driven excitatory-inhibitory balance towards excitation in the former, but not latter population. Such specificity is preferential to connections made by dmPFC, caused by enhanced presynaptic glutamate release, and highly correlated with the increased anxiety-like behavior in stressed mice. Importantly, low-frequency optogenetic stimulation of dmPFC afferents in BLA normalizes the enhanced prefrontal glutamate release onto dmPFC→BLA PNs and lastingly attenuates CRS-induced increase of anxiety-like behavior. Our findings thus reveal a target cell-based dysregulation of mPFC-to-amygdala transmission for stress-induced anxiety.

Antidepressant mechanisms of ketamine: Focus on GABAergic inhibition

There has been much recent progress in understanding of the mechanism of ketamine's rapid and enduring antidepressant effects. Here we review recent insights from clinical and preclinical studies, with special emphasis of ketamine-induced changes in GABAergic synaptic transmission that are considered essential for its antidepressant therapeutic effects. Subanesthetic ketamine is now understood to exert its initial action by selectively blocking a subset of NMDA receptors on GABAergic interneurons, which results in disinhibition of glutamatergic target neurons, a surge in extracellular glutamate and correspondingly elevated glutamatergic synaptic transmission. This surge in glutamate appears to be corroborated by the rapid metabolism of ketamine into hydroxynorketamine, which acts at presynaptic sites to disinhibit the release of glutamate. Preclinical studies indicate that glutamate-induced activity triggers the release of BDNF, followed by transient activation of the mTOR pathway and increased expression of synaptic proteins, along with functional strengthening of glutamatergic synapses. This drug-on phase lasts for approximately 2h and is followed by a period of days characterized by structural maturation of newly formed glutamatergic synapses and prominently enhanced GABAergic synaptic inhibition. Evidence from mouse models with constitutive antidepressant-like phenotypes suggests that this phase involves strengthened inhibition of dendrites by somatostatin-positive GABAergic interneurons and correspondingly reduced NMDA receptor-mediated Ca²⁺ entry into dendrites, which activates an intracellular signaling cascade that converges with the mTOR pathway onto increased activity of the eukaryotic elongation factor eEF2 and enhanced translation of dendritic mRNAs. Newly synthesized proteins such as BDNF may be important for the prolonged therapeutic effects of ketamine.

Glutamine Supplementation Prevents Chronic Stress-Induced Mild Cognitive Impairment

We recently reported that glutamine (Gln) supplementation protected glutamatergic neurotransmission from the harmful effects of chronic stress. Altered glutamatergic neurotransmission is one of the main causes of cognitive disorders. However, the cognitive enhancer function of Gln has not been clearly demonstrated thus far. Here, we evaluated whether and how Gln supplementation actually affects chronic stress-induced cognitive impairment. Using a chronic immobilization stress (CIS) mouse model, we confirmed that chronic stress induced mild cognitive impairment (MCI) and neuronal damage in the hippocampus. In contrast, Gln-supplemented mice did not show evidence of MCI. To investigate possible underlying mechanisms, we confirmed that CIS increased plasma corticosterone levels as well as brain and plasma levels of reactive oxygen/nitrogen species. CIS also increased levels of inducible nitric oxide synthase and NADPH oxidase subunits (p47^phox and p67^phox) in both the prefrontal cortex and CA1 region of the hippocampus. CIS decreased the number of synaptic puncta in the prefrontal cortex and hippocampus, but these effects were inhibited by Gln supplementation. Taken together, the present results suggest that Gln is an effective agent against chronic stress-induced MCI.

Repeated stress induces a pro-inflammatory state, increases amygdala neuronal and microglial activation, and causes anxiety in adult male rats

A link exists between immune function and psychiatric conditions, particularly depressive and anxiety disorders. Psychological stress is a powerful trigger for these disorders and stress influences immune state. However, the nature of peripheral immune changes after stress conflicts across studies, perhaps due to the focus on few measures of pro-inflammatory or anti-inflammatory processes. The basolateral amygdala (BLA) is critical for emotion, and plays an important role in the effects of stress on anxiety. As such, it may be a primary central nervous system (CNS) mediator for the effects of peripheral immune changes on anxiety after stress. Therefore, this study aimed to delineate the influence of stress on peripheral pro-inflammatory and anti-inflammatory aspects, BLA immune activation, and its impact on BLA neuronal activity. To produce a more encompassing view of peripheral immune changes, this study used a less restrictive approach to categorize and group peripheral immune changes. We found that repeated social defeat stress in adult male Sprague-Dawley rats increased the frequencies of mature T-cells positive for intracellular type 2-like cytokine and serum pro-inflammatory cytokines. Principal component analysis and hierarchical clustering was used to guide grouping of T-cells and cytokines, producing unique profiles. Stress shifted the balance towards a specific set that included mostly type 2-like T-cells and pro-inflammatory cytokines. Within the CNS component, repeated stress caused an increase of activated microglia in the BLA, increased anxiety-like behaviors across several assays, and increased BLA neuronal firing in vivo that was prevented by blockade of microglia activation. Because repeated stress can trigger anxiety states by actions in the BLA, and altered immune function can trigger anxiety, these results suggest that repeated stress may trigger anxiety-like behaviors by inducing a pro-inflammatory state in the periphery and the BLA. These results begin to uncover how stress may recruit the immune system to alter the function of brain regions critical to emotion.

Transcriptome analysis of rat dorsal hippocampal CA1 after an early life seizure induced by kainic acid

Seizures that occur during early development are associated with adverse neurodevelopmental outcomes. Causation and mechanisms are currently under investigation. Induction of an early life seizure by kainic acid (KA) in immature rats on post-natal day (P) 7 results in behavioral changes in the adult rat that reflect social and intellectual deficits without overt cellular damage. Our previous work also demonstrated increased expression of CA1 hippocampal long-term potentiation (LTP) and reduced desensitization of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type ionotropic glutamate receptors (AMPA-R) one week following a kainic acid induced seizure (KA-ELS). Here we used RNA sequencing (RNAseq) of mRNA from dorsal hippocampal CA1 to probe changes in mRNA levels one week following KA-ELS as a means to investigate the mechanisms for these functional changes. Ingenuity pathway analysis (IPA) confirmed our previous results by predicting an up-regulation of the synaptic LTP pathway. Differential gene expression results revealed significant differences in 7 gene isoforms. Additional assessments included AMPA-R splice variants and adenosine deaminase acting on RNA 2 (ADAR2) editing sites as a means to determine the mechanism for reduced AMPA-R desensitization. Splice variant analysis demonstrated that KA-ELS result in a small, but significant decrease in the "flop" isoform of Gria3, and editing site analysis revealed significant changes in the editing of a kainate receptor subunit, Grik2, and a serotonin receptor, Htr2c. While these specific changes may not account for altered AMPA-R desensitization, the differences indicate that KA-ELS alters gene expression in the hippocampal CA1 one week after the insult.