The Effect of Serotonin-Targeting Antidepressants on Neurogenesis and Neuronal Maturation of the Hippocampus Mediated via 5-HT1A and 5-HT4 Receptors

Flibanserin conquers murine depressive pseudodementia by amending HPA axis, maladaptive inflammation and AKT/GSK/STAT/BDNF trajectory: Center-staging of the serotonergic/adrenergic circuitry

Depressive pseudodementia (DPD) is a debilitating cognitive dysfunction that accompanies major and/or frequent depressive attacks. DPD has gained significant research attention owing to its negative effects on the patients' quality of life and productivity. This study tested the procognitive potential of Flibanserin (FBN), the serotonin (5HT) receptor modulator, against propranolol (PRP), as β/5HT1A receptors blocker. Serving this purpose, female Wistar Albino rats were subjected to chronic unpredictable stress (CUS) and subsequently treated with FBN only (3 mg/kg/day, p.o), PRP only (10 mg/kg/day, p.o), or PRP followed by FBN, using the same doses. FBN ameliorated the behavioral/cognitive alterations and calmed the hypothalamic-pituitary-adrenal (HPA) axis storm by reducing the levels of stress-related hormones, viz, corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), corticosterone (CORT) parallel to epinephrine (EPI) hyperstimulation. The maladaptive inflammatory response, comprising of interleukin (IL)-1β/6, and tumor necrosis factor (TNF)-α, was consequently blunted. This was contemporaneous to the partial restoration of the protein kinase-B (AKT)/glycogen synthase kinase (GSK)3β/signal transducer and activator of transcription (STAT)-3 survival trajectory and the reinstatement of the levels of brain derived neurotrophic factor (BDNF). Microscopically, FBN repaired the hippocampal architecture and lessened CD68/GFAP immunoreactivity. Pre-administration of PRP partially abolished FBN effect along the estimated parameters, except for 5HT2A receptor expression and epinephrine level, to prove 5HT1A receptor as a fulcrum initiator of the investigated pathway, while its sole administration worsened the underlying condition. Ultimately, these findings highlight the immense procognitive potential of FBN, offering a new paradigm for halting DPD advancement via synchronizing adrenergic/serotonergic circuitry.

Selective knockdown of GABAA-α2 subunit in the dorsal dentate gyrus in adulthood induces anxiety, learning and memory deficits and impairs synaptic plasticity

Animal studies and clinical trials suggest that maintenance of gamma-aminobutyric acid (GABA)-ergic activity may be crucial in coping with stressful conditions, anxiety and mood disorders. Drugs highly efficient in promoting anxiolysis were shown to activate this system, particularly via the α2-subunit of type A receptors (GABAA α2). Given the high expression of GABAA α2 in the dentate gyrus (DG) sub-field of the hippocampus, we sought to examine whether manipulation of the α2 subunit in this area will evoke changes in emotional behaviour, memory and learning as well as in synaptic plasticity. We found that knockdown of GABAAα2 receptor specifically in the dorsal DG of rats caused increased anxiety without affecting locomotor activity. Spatial memory and learning in the Morris water maze were also impaired in GABAAα2 receptor knocked down rats, an effect accompanied by alterations in synaptic plasticity, as assessed by long-term potentiation in the DG. Our findings provide further support to the notion that emotional information processing in the hippocampus may be controlled, at least in part, via the inhibitory GABAA α2 receptor subunit, opening a potential avenue for early interventions from pre- puberty into adulthood, as a strategy for controlling anxiety-related psychopathology.

Psilocybin for dementia prevention? The potential role of psilocybin to alter mechanisms associated with major depression and neurodegenerative diseases

Major depression is an established risk factor for subsequent dementia, and depression in late life may also represent a prodromal state of dementia. Considering current challenges in the clinical development of disease modifying therapies for dementia, the focus of research is shifting towards prevention and modification of risk factors to alter the neurodegenerative disease trajectory. Understanding mechanistic commonalities underlying affective symptoms and cognitive decline may reveal biomarkers to aid early identification of those at risk of progressing to dementia during the preclinical phase of disease, thus allowing for timely intervention. Adult hippocampal neurogenesis (AHN) is a phenomenon that describes the birth of new neurons in the dentate gyrus throughout life and it is associated with spatial learning, memory and mood regulation. Microglia are innate immune system macrophages in the central nervous system that carefully regulate AHN via multiple mechanisms. Disruption in AHN is associated with both dementia and major depression and microgliosis is a hallmark of several neurodegenerative diseases. Emerging evidence suggests that psychedelics promote neuroplasticity, including neurogenesis, and may also be immunomodulatory. In this context, psilocybin, a serotonergic agonist with rapid-acting antidepressant properties has the potential to ameliorate intersecting pathophysiological processes relevant for both major depression and neurodegenerative diseases. In this narrative review, we focus on the evidence base for the effects of psilocybin on adult hippocampal neurogenesis and microglial form and function; which may suggest that psilocybin has the potential to modulate multiple mechanisms of action, and may have implications in altering the progression from major depression to dementia in those at risk.

The Serotonin 4 Receptor Subtype: A Target of Particular Interest, Especially for Brain Disorders

In recent years, particular attention has been paid to the serotonin 4 receptor, which is well expressed in the brain, but also peripherally in various organs. The cerebral distribution of this receptor is well conserved across species, with high densities in the basal ganglia, where they are expressed by GABAergic neurons. The 5-HT4 receptor is also present in the cerebral cortex, hippocampus, and amygdala, where they are carried by glutamatergic or cholinergic neurons. Outside the central nervous system, the 5-HT4 receptor is notably expressed in the gastrointestinal tract. The wide distribution of the 5-HT4 receptor undoubtedly contributes to its involvement in a plethora of functions. In addition, the modulation of this receptor influences the release of serotonin, but also the release of other neurotransmitters such as acetylcholine and dopamine. This is a considerable asset, as the modulation of the 5-HT4 receptor can therefore play a direct or indirect beneficial role in various disorders. One of the main advantages of this receptor is that it mediates a much faster antidepressant and anxiolytic action than classical selective serotonin reuptake inhibitors. Another major benefit of the 5-HT4 receptor is that its activation enhances cognitive performance, probably via the release of acetylcholine. The expression of the 5-HT4 receptor is also altered in various eating disorders, and its activation by the 5-HT4 agonist negatively regulates food intake. Additionally, although the cerebral expression of this receptor is modified in certain movement-related disorders, it is still yet to be determined whether this receptor plays a key role in their pathophysiology. Finally, there is no longer any need to demonstrate the value of 5-HT4 receptor agonists in the pharmacological management of gastrointestinal disorders.

The Influence of Maternal Hypoxia and Buspirone during Pregnancy on Cognitive Abilities and a Stress Response in Adult Male Offspring

Spatial learning, memory, and reactivity of the hypothalamic-pituitary-adrenocortical system (HPA axis) were studied in adult male rats, whose mothers during pregnancy were subjected to acute moderate normobaric hypoxia, or repeated injections of buspirone, an agonist of type 1A serotonergic receptors (5HT1A), or their combination. Prenatal treatment with buspirone in rats with prenatal hypoxia impaired learning ability during the first day of 5-day training. A decrease in the effectiveness of long-term memory in comparison with short-term memory was revealed in two groups of rats: prenatal treatment with buspirone in combination with hypoxia and injection of physiological saline without hypoxia. The effectiveness of long-term memory and the level of corticosterone in response to stress did not differ between the groups, which can indicate adaptation of the 5HT1A receptor and the HPA axis to the prenatal buspirone and normobaric hypoxia during ontogeny.

Whole-brain structural and functional neuroimaging of individuals who attempted suicide and people who did not: A systematic review and exploratory coordinate-based meta-analysis

Suicide is the cause of death of approximately 800,000 people a year. Despite the relevance of this behaviour, risk assessment tools rely on clinician experience and subjective ratings. Given that previous suicide attempts are the single strongest predictors of future attempts, we designed a systematic review and coordinate-based meta-analysis to demonstrate whether neuroimaging features can help distinguish individuals who attempted suicide from subjects who did not. Out of 5,659 publications from PubMed, Scopus, and Web of Science, we summarised 102 experiments and meta-analysed 23 of them. A cluster in the right superior temporal gyrus, a region implicated in emotional processing, might be functionally hyperactive in individuals who attempted suicide. No statistically significant differences in brain morphometry were evidenced. Furthermore, we used JuSpace to show that this cluster is enriched in 5-HT1A heteroreceptors in the general population. This exploratory meta-analysis provides a putative neural substrate linked to previous suicide attempts. Heterogeneity in the analytical techniques and weak or absent power analysis of the studies included in this review currently limit the applicability of the findings, the replication of which should be prioritised.

Abnormalities of Hippocampal Subfield and Amygdalar Nuclei Volumes and Clinical Correlates in Behavioral Variant Frontotemporal Dementia with Obsessive-Compulsive Behavior-A Pilot Study

(1) Background: The hippocampus (HP) and amygdala are essential structures in obsessive-compulsive behavior (OCB); however, the specific role of the HP in patients with behavioral variant frontotemporal dementia (bvFTD) and OCB remains unclear. (2) Objective: We investigated the alterations of hippocampal and amygdalar volumes in patients with bvFTD and OCB and assessed the correlations of clinical severity with hippocampal subfield and amygdalar nuclei volumes in bvFTD patients with OCB. (3) Materials and methods: Eight bvFTD patients with OCB were recruited and compared with eight age- and sex-matched healthy controls (HCs). Hippocampal subfield and amygdalar nuclei volumes were analyzed automatically using a 3T magnetic resonance image and FreeSurfer v7.1.1. All participants completed the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), Neuropsychiatric Inventory (NPI), and Frontal Behavioral Inventory (FBI). (4) Results: We observed remarkable reductions in bilateral total hippocampal volumes. Compared with the HCs, reductions in the left hippocampal subfield volume over the cornu ammonis (CA)1 body, CA2/3 body, CA4 body, granule cell layer, and molecular layer of the dentate gyrus (GC-ML-DG) body, molecular layer of the HP body, and hippocampal tail were more obvious in patients with bvFTD and OCB. Right subfield volumes over the CA1 body and molecular layer of the HP body were more significantly reduced in bvFTD patients with OCB than in those in HCs. We observed no significant difference in amygdalar nuclei volume between the groups. Among patients with bvFTD and OCB, Y-BOCS score was negatively correlated with left CA2/3 body volume (τb = -0.729, p < 0.001); total NPI score was negatively correlated with left GC-ML-DG body (τb = -0.648, p = 0.001) and total bilateral hippocampal volumes (left, τb = -0.629, p = 0.002; right, τb = -0.455, p = 0.023); and FBI score was negatively correlated with the left molecular layer of the HP body (τb = -0.668, p = 0.001), CA4 body (τb = -0.610, p = 0.002), and hippocampal tail volumes (τb = -0.552, p < 0.006). Mediation analysis confirmed these subfield volumes as direct biomarkers for clinical severity, independent of medial and lateral orbitofrontal volumes. (5) Conclusions: Alterations in hippocampal subfield volumes appear to be crucial in the pathophysiology of OCB development in patients with bvFTD.

Pathophysiological Aspects and Therapeutic Armamentarium of Alzheimer's Disease: Recent Trends and Future Development

Alzheimer's disease (AD) is the primary cause of dementia and is characterized by the death of brain cells due to the accumulation of insoluble amyloid plaques, hyperphosphorylation of tau protein, and the formation of neurofibrillary tangles within the cells. AD is also associated with other pathologies such as neuroinflammation, dysfunction of synaptic connections and circuits, disorders in mitochondrial function and energy production, epigenetic changes, and abnormalities in the vascular system. Despite extensive research conducted over the last hundred years, little is established about what causes AD or how to effectively treat it. Given the severity of the disease and the increasing number of affected individuals, there is a critical need to discover effective medications for AD. The US Food and Drug Administration (FDA) has approved several new drug molecules for AD management since 2003, but these drugs only provide temporary relief of symptoms and do not address the underlying causes of the disease. Currently, available medications focus on correcting the neurotransmitter disruption observed in AD, including cholinesterase inhibitors and an antagonist of the N-methyl-D-aspartate (NMDA) receptor, which temporarily alleviates the signs of dementia but does not prevent or reverse the course of AD. Research towards disease-modifying AD treatments is currently underway, including gene therapy, lipid nanoparticles, and dendrimer-based therapy. These innovative approaches aim to target the underlying pathological processes of AD rather than just managing the symptoms. This review discusses the novel aspects of pathogenesis involved in the causation of AD of AD and in recent developments in the therapeutic armamentarium for the treatment of AD such as gene therapy, lipid nanoparticles, and dendrimer-based therapy, and many more.

Stress circuitry: mechanisms behind nervous and immune system communication that influence behavior

Inflammatory processes are increased by stress and contribute to the pathology of mood disorders. Stress is thought to primarily induce inflammation through peripheral and central noradrenergic neurotransmission. In healthy individuals, these pro-inflammatory effects are countered by glucocorticoid signaling, which is also activated by stress. In chronically stressed individuals, the anti-inflammatory effects of glucocorticoids are impaired, allowing pro-inflammatory effects to go unchecked. Mechanisms underlying this glucocorticoid resistance are well understood, but the precise circuits and molecular mechanisms by which stress increases inflammation are not as well known. In this narrative review, we summarize the mechanisms by which chronic stress increases inflammation and contributes to the onset and development of stress-related mood disorders. We focus on the neural substrates and molecular mechanisms, especially those regulated by noradrenergic signaling, that increase inflammatory processes in stressed individuals. We also discuss key knowledge gaps in our understanding of the communication between nervous and immune systems during stress and considerations for future therapeutic strategies. Here we highlight the mechanisms by which noradrenergic signaling contributes to inflammatory processes during stress and how this inflammation can contribute to the pathology of stress-related mood disorders. Understanding the mechanisms underlying crosstalk between the nervous and immune systems may lead to novel therapeutic strategies for mood disorders and/or provide important considerations for treating immune-related diseases in individuals suffering from stress-related disorders.

Antidepressant effects of p-coumaric acid isolated from Vaccinium bracteatum leaves extract on chronic restraint stress mouse model and antagonism of serotonin 6 receptor in vitro

BACKGROUND

Vaccinium bracteatum Thunb. leaves (VBL) are used in traditional herbal medicines to treat various biological diseases. p-coumaric acid (CA), the main active component of VBL, has neuroprotective effects against corticosterone-induced damage in vitro. However, the effects of CA on immobility induced by chronic restraint stress (CRS) in a mouse model and 5-HT receptor activity have not been investigated.

HYPOTHESIS/PURPOSE

We investigated the antagonistic effects of VBL, NET-D1602, and the three components of Gαs protein-coupled 5-HT receptors. Additionally, we identified the effects and mechanism of action of CA, the active component of NET-D1602, in the CRS-exposed model.

METHODS

For in vitro analyses, we used 1321N1 cells stably expressing human 5-HT₆ receptors and CHO-K1 expressing human 5-HT₄ or 5-HT₇ receptors cell lines to study the mechanism of action. For in vivo analyses, CRS-exposed mice were orally administered CA (10, 50, or 100 mg/kg) daily for 21 consecutive days. The effects of CA were analyzed by assessing behavioral changes using a forced swim test (FST), measuring levels of hypothalamic-pituitary-adrenal (HPA) axis-related hormones in ntial therapeutic effects as 5-HT6 receptor antagonists for neurodegenerative diseases and depressioserum, and acetylcholinesterase (AChE), monoamines, including 5-HT, dopamine, and norepinephrine, using enzyme-linked immunosorbent assay kits. The underlying molecular mechanisms of the serotonin transporter (SERT), monoamine oxidase A (MAO-A), and extracellular signal-regulated kinase (ERK)/protein kinase B (Akt)/mTORC1 signaling were detected using western blotting.

RESULTS

CA was confirmed to be an active component in the antagonistic effects of NET-D1602 on 5-HT₆ receptor activity through decreases in cAMP and ERK1/2 phosphorylation. Moreover, CRS-exposed mice treated with CA showed a significantly reduced immobility time in the FST. CA also significantly decreased corticosterone, corticotropin-releasing hormone (CRH), and adrenocorticotropic hormone (ACTH) levels. CA enhanced 5-HT, dopamine, and norepinephrine levels in the hippocampus (HC) and prefrontal cortex (PFC) but decreased MAO-A and SERT protein levels. Similarly, CA significantly upregulated the ERK, Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), Akt/mTOR/p70S6K/S6 signaling pathways in both HC and the PFC.

CONCLUSION

CA contained in NET-D1602 may play the antidepressant effects against CRS-induced depression-like mechanism and the selective antagonist effect of 5-HT₆ receptor.

Brain compartmentalization based on transcriptome analyses and its gene expression in Octopus minor

Coleoid cephalopods have a high intelligence, complex structures, and large brain. The cephalopod brain is divided into supraesophageal mass, subesophageal mass and optic lobe. Although much is known about the structural organization and connections of various lobes of octopus brain, there are few studies on the brain of cephalopod at the molecular level. In this study, we demonstrated the structure of an adult Octopus minor brain by histomorphological analyses. Through visualization of neuronal and proliferation markers, we found that adult neurogenesis occurred in the vL and posterior svL. We also obtained specific 1015 genes by transcriptome of O. minor brain and selected OLFM3, NPY, GnRH, and GDF8 genes. The expression of genes in the central brain showed the possibility of using NPY and GDF8 as molecular marker of compartmentation in the central brain. This study will provide useful information for establishing a molecular atlas of cephalopod brain.

5HT1AR-FGFR1 Heteroreceptor Complexes Differently Modulate GIRK Currents in the Dorsal Hippocampus and the Dorsal Raphe Serotonin Nucleus of Control Rats and of a Genetic Rat Model of Depression

The midbrain raphe serotonin (5HT) neurons provide the main ascending serotonergic projection to the forebrain, including hippocampus, which has a role in the pathophysiology of depressive disorder. Serotonin 5HT1A receptor (R) activation at the soma-dendritic level of serotonergic raphe neurons and glutamatergic hippocampal pyramidal neurons leads to a decrease in neuronal firing by activation of G protein-coupled inwardly-rectifying potassium (GIRK) channels. In this raphe-hippocampal serotonin neuron system, the existence of 5HT1AR-FGFR1 heteroreceptor complexes has been proven, but the functional receptor-receptor interactions in the heterocomplexes have only been investigated in CA1 pyramidal neurons of control Sprague Dawley (SD) rats. In the current study, considering the impact of the receptor interplay in developing new antidepressant drugs, the effects of 5HT1AR-FGFR1 complex activation were investigated in hippocampal pyramidal neurons and in midbrain dorsal raphe serotonergic neurons of SD rats and of a genetic rat model of depression (the Flinders Sensitive Line (FSL) rats of SD origin) using an electrophysiological approach. The results showed that in the raphe-hippocampal 5HT system of SD rats, 5HT1AR-FGFR1 heteroreceptor activation by specific agonists reduced the ability of the 5HT1AR protomer to open the GIRK channels through the allosteric inhibitory interplay produced by the activation of the FGFR1 protomer, leading to increased neuronal firing. On the contrary, in FSL rats, FGFR1 agonist-induced inhibitory allosteric action at the 5HT1AR protomer was not able to induce this effect on GIRK channels, except in CA2 neurons where we demonstrated that the functional receptor-receptor interaction is needed for producing the effect on GIRK. In keeping with this evidence, hippocampal plasticity, evaluated as long-term potentiation induction ability in the CA1 field, was impaired by 5HT1AR activation both in SD and in FSL rats, which did not develop after combined 5HT1AR-FGFR1 heterocomplex activation in SD rats. It is therefore proposed that in the genetic FSL model of depression, there is a significant reduction in the allosteric inhibition exerted by the FGFR1 protomer on the 5HT1A protomer-mediated opening of the GIRK channels in the 5HT1AR-FGFR1 heterocomplex located in the raphe-hippocampal serotonin system. This may result in an enhanced inhibition of the dorsal raphe 5HT nerve cell and glutamatergic hippocampal CA1 pyramidal nerve cell firing, which we propose may have a role in depression.

Dorsal Dentate Gyrus, a Key Regulator for Mood and Psychiatric Disorders

The dentate gyrus, a "gate" that controls the flow of information into the hippocampus, is critical for learning, memory, spatial navigation, and mood regulation. Several lines of evidence have demonstrated that deficits in dentate granule cells (DGCs) (e.g., loss of DGCs or genetic mutations in DGCs) contribute to the development of various psychiatric disorders, such as depression and anxiety disorders. Whereas ventral DGCs are believed to be critical for mood regulation, the functions of dorsal DGCs in this regard remain elusive. Here, we review the role of DGCs, in particular the dorsal DGCs, in the regulation of mood, their functional relationships with DGC development, and the contributions of dysfunctional DGCs to mental disorders.

Regulation of adult-born and mature neurons in stress response and antidepressant action in the dentate gyrus of the hippocampus

The dentate gyrus (DG) of the hippocampus has been implicated in the regulation of stress responses, and in the pathophysiology and treatment of depression. This review discusses the cellular changes caused by chronic stress and the cellular role of the DG in stress-induced behavioral changes and its antidepressant-like effects. Regarding adult-born neurogenic processes in the DG, chronic stress, such as repeated social defeat, suppresses cell proliferation during and immediately after stress; however, this effect is transient. The subsequent differentiation and survival processes are differentially regulated depending on the timing and sensitivity of stress. The activation of young adult-born neurons during stress contributes to stress resilience, while the transient increase in the survival of adult-born neurons after the cessation of stress seems to promote stress susceptibility. In mature granule neurons, the predominant cells in the DG, synaptic plasticity is suppressed by chronic stress. However, a group of mature granule neurons is activated by chronic stress. Chronic antidepressant treatment can transform mature granule neurons to a phenotype resembling that of immature neurons, characterized as "dematuration". Adult-born neurons suppress the activation of mature granule neurons during stress, indicating that local neural interactions within the DG are important for the stress response. Elucidating the stress-associated context- and timing-dependent cellular changes and functions in the DG will provide insights into stress-related psychiatric diseases.

Drugs and Endogenous Factors as Protagonists in Neurogenic Stimulation

Neurogenesis is a biological process characterized by new neurons formation from stem cells. For decades, it was believed that neurons only multiplied during development and in the postnatal period but the discovery of neural stem cells (NSCs) in mature brain promoted a revolution in neuroscience field. In mammals, neurogenesis consists of migration, differentiation, maturation, as well as functional integration of newborn cells into the pre-existing neuronal circuit. Actually, NSC density drops significantly after the first stages of development, however in specific places in the brain, called neurogenic niches, some of these cells retain their ability to generate new neurons and glial cells in adulthood. The subgranular (SGZ), and the subventricular zones (SVZ) are examples of regions where the neurogenesis process occurs in the mature brain. There, the potential of NSCs to produce new neurons has been explored by new advanced methodologies and in neuroscience for the treatment of brain damage and/or degeneration. Based on that, this review highlights endogenous factors and drugs capable of stimulating neurogenesis, as well as the perspectives for the use of NSCs for neurological and neurodegenerative diseases.

Sirtuin Type 1 Mediates the Antidepressant Effect of S-Ketamine in a Chronic Unpredictable Stress Model

BACKGROUND

Major depressive disorder (MDD) refers to a mental disease with complex pathogenesis and treatment mechanism. S-ketamine exhibited high effectiveness in treating MDD. However, the pharmacological activity of S-ketamine has not been reported yet.

MATERIALS AND METHODS

In this study, depression-like characteristics were induced by chronic unpredictable stress (CUS). After S-ketamine (15 mg/kg) was intraperitoneally injected, the behaviors of mice were tested by conducting open-field test, elevated plus maze test, tail suspension test, and forced swimming test. Bilateral injection of sirtuin type 1 (SIRT1) inhibitor EX-527 was injected into the medial prefrontal cortex (mPFC) to upregulate the SIRT1 expression. The expression of SIRT1 and brain-derived neurotrophic factor (BDNF) was detected by conducting Western blot and immunofluorescence assays. Meanwhile, the synaptic ultrastructure was detected by transmission electron microscopy.

RESULTS

In this study, the mice showed depression-like behavior in a series of behavioral tests. After the treatment with S-ketamine, the depression-like behavior stopped. Further, the synaptic ultrastructure in mPFC, including the decreased curvature of the post synaptic density and thinning of the postsynaptic density, improved after the S-ketamine treatment. Moreover, we found that S-ketamine had the possibility of spontaneous binding with SIRT1 at the molecular level and reversed CUS-induced SIRT1 reduction. Meanwhile, a positive relationship between SIRT1 and BDNF expression in mPFC and SIRT1 inhibitor limited the role of S-ketamine in reducing the depression-like behavior and increasing the BDNF level.

CONCLUSION

S-ketamine upregulated the SIRT1-mediated BDNF in mPFC and reversed the synaptic structural defects caused by CUS. SIRT1 is a mediator of S-ketamine in alleviating depression-like behavior.

Semen Sojae Praeparatum alters depression-like behaviors in chronic unpredictable mild stress rats via intestinal microbiota

A large number of Chinese medical books present that Semen Sojae Praeparatum, a fermented food, possesses antidepressant effect, but the mechanism of this antidepressant effect remains largely unknown. This study aimed to explore the effect of Semen Sojae Praeparatum on rats with chronic unpredictable mild stress (CUMS)-induced depression. The results showed that Semen Sojae Praeparatum improved depression-like behaviors (negative preference of sugar water and increased swimming immobility time and time spent in the dark zone) and effectively reduced cell morphological changes in the dentate gyrus of the hippocampus in CUMS rats. In addition, Semen Sojae Praeparatum significantly promoted the contents of norepinephrine (NE), 5-hydroxytryptamine (5-HT), brain-derived neurotrophic factor (BDNF), and gamma-aminobutyric acid (GABA) in the hippocampus and the content of BDNF in the serum (p < 0.05). 16S rRNA sequencing analysis results showed that Semen Sojae Praeparatum increased the abundance of genus Ruminococcaceae_UCG-008 and decreased those of genera Lactobacillus and Bacteroides. Genus Ruminococcaceae_UCG-008 was positively correlated with GABA and BDNF levels in the hippocampus; genus Lactobacillus had a positive correlation with 5-HT; and genus Bacteroides had negative correlations with 5-HT, BDNF, and NE. In addition, Semen Sojae Praeparatum considerably decreased the concentration of short-chain fatty acids (SCFAs). These results indicated that Semen Sojae Praeparatum fermented by Rhizopus chinensis 12 and Bacillus sp. DU-106 alleviated the neurotransmitter levels and structural changes in the neuronal morphology of the hippocampus associated with the modulation of gut microbiota and SCFAs. Therefore, this study confirmed that Semen Sojae Praeparatum could alter depression and provide a theoretical basis for the investigation of the relationship between the microbiota-gut-brain axis and antidepressant.

Antidepressant Like Effect of Ascorbic Acid in Mice: Possible Involvement of NO-sGC-cGMP Signaling

The present study was designed to determine the antidepressant like activity of ascorbic acid (AA) in mice. Further the influence of NO-sGC-cGMP signaling in the antidepressant like effect of AA in mice was determined. Male swiss albino mice were used in the present study. Mice in the control group received saline and fluoxetine (10 mg/kg, i.p.) was used as the standard antidepressant drug. AA (50, 100 and 150 mg/kg, i.p.) was administered to the mice and depression related behavior were determined using tail suspension test (TST) and forced swim test (FST). Further the whole brain nitrite and serotonin levels were also determined. It was observed that the administration of AA (100 mg/kg, i.p.) reversed the depression like behavior in mice in TST and FST. AA (100 mg/kg, i.p.) treatment decreased the level of nitrite and increased the level of serotonin in the brain of mice significantly as compared to control. Further the behavioral and neurochemical effect of AA (50 mg/kg, i.p) was studied in NO modulator [NO donor: L-Arginine (50 mg/kg, i.p); NO-sGC inhibitor: methylene blue (1 mg/kg, i.p.) and cGMP modulator: sildenafil (1 mg/kg, i.p.)] pretreated mice. It was observed that the pretreatment of NO donor and cGMP modulator counteracted the effect conferred by AA (50 mg/kg, i.p). While the pretreatment of NO-sGC inhibitor potentiated the effect conferred by AA (50 mg/kg, i.p). The present study suggested that the AA confer antidepressant like effect in mice and NO-sGC-cGMP signaling pathway influence the antidepressant like effect of AA in mice.

Neuroprotective Effects and Therapeutic Potential of Transcorneal Electrical Stimulation for Depression

Transcorneal electrical stimulation (TES) has emerged as a non-invasive neuromodulation approach that exerts neuroprotection via diverse mechanisms, including neurotrophic, neuroplastic, anti-inflammatory, anti-apoptotic, anti-glutamatergic, and vasodilation mechanisms. Although current studies of TES have mainly focused on its applications in ophthalmology, several lines of evidence point towards its putative use in treating depression. Apart from stimulating visual-related structures and promoting visual restoration, TES has also been shown to activate brain regions that are involved in mood alterations and can induce antidepressant-like behaviour in animals. The beneficial effects of TES in depression were further supported by its shared mechanisms with FDA-approved antidepressant treatments, including its neuroprotective properties against apoptosis and inflammation, and its ability to enhance the neurotrophic expression. This article critically reviews the current findings on the neuroprotective effects of TES and provides evidence to support our hypothesis that TES possesses antidepressant effects.

Relationship Between Interpersonal Depressive Symptoms and Reduced Amygdala Volume in People with Multiple Sclerosis: Considerations for Clinical Practice

Background

The lifetime prevalence of depression in people with multiple sclerosis (MS) is approximately 50% compared with around 15% in the general population. There is a relationship between depression and quality of life in people with MS and evidence that depression may contribute to disease progression.

Methods

This cross-sectional pilot study assessed the association between depression and regional brain atrophy, including amygdala and hippocampal volume. Forty-nine participants with MS recruited through a hospital MS clinic were administered the Center for Epidemiological Studies Depression Scale Revised (CESD-R) to investigate whether higher endorsements on the items depressive affect and interpersonal symptoms were associated with volumetric magnetic resonance imaging measurements of hippocampal and amygdala atrophy.

Results

Regression analysis revealed an association between depression-related interpersonal symptoms and right amygdala volume. No association was found between depression and hippocampal volume.

Conclusions

These results provide preliminary support for a unilateral, biologically based relationship between the right amygdala and characteristic interpersonal depressive symptoms expressed by people with MS and add to the growing body of literature implicating regional brain atrophy in MS-associated depression. Given that the interpersonal subcomponent of the CESD-R measures social functioning, and the neural networks in the amygdala are known to be implicated in processing social stimuli, this research suggests that targeted diagnosis and treatments for depression in people with MS may be particularly beneficial. Further confirmatory research of this relationship is required.

Hippocampal neuroanatomy in first episode psychosis: A putative role for glutamate and serotonin receptors

Disrupted serotonergic and glutamatergic signaling interact and contribute to the pathophysiology of schizophrenia, which is particularly relevant for the hippocampus where diverse expression of serotonin receptors is noted. Hippocampal atrophy is a well-established feature of schizophrenia, with select subfields hypothesized as particularly vulnerable due to variation in glutamate receptor densities. We investigated hippocampal anomalies in first-episode psychosis (FEP) in relation to receptor distributions by leveraging 4 sources of data: (1) ultra high-field (7-Tesla) structural neuroimaging, and (2) proton magnetic resonance spectroscopy (1H-MRS) of glutamate from 27 healthy and 41 FEP subjects, (3) gene expression data from the Allen Human Brain Atlas and (4) atlases of the serotonin receptor system. Automated methods delineated the hippocampus to map receptor density across subfields. We used gene expression data to correlate serotonin and glutamate receptor genes across the hippocampus. Measures of individual hippocampal shape-receptor alignment were derived through normative modelling and correlations to receptor distributions, termed Receptor-Specific Morphometric Signatures (RSMS). We found reduced hippocampal volumes in FEP, while CA4-dentate gyrus showed greatest reductions. Gene expression indicated 5-HT1A and 5-HT4 to correlate with AMPA and NMDA expression, respectively. Magnitudes of subfield volumetric reduction in FEP correlated most with 5-HT1A (R = 0.64, p = 4.09E-03) and 5-HT4 (R = 0.54, p = 0.02) densities as expected, and replicated using previously published data from two FEP studies. Right-sided 5-HT4-RSMS was correlated with MRS glutamate (R = 0.357, p = 0.048). We demonstrate a putative glutamate-driven hippocampal variability in FEP through a serotonin receptor-density gated mechanism, thus outlining a mechanistic interplay between serotonin and glutamate in determining the hippocampal morphology in schizophrenia.

5-HT Receptors and the Development of New Antidepressants

Serotonin modulates several physiological and cognitive pathways throughout the human body that affect emotions, memory, sleep, and thermal regulation. The complex nature of the serotonergic system and interactions with other neurochemical systems indicate that the development of depression may be mediated by various pathomechanisms, the common denominator of which is undoubtedly the disturbed transmission in central 5-HT synapses. Therefore, the deliberate pharmacological modulation of serotonergic transmission in the brain seems to be one of the most appropriate strategies for the search for new antidepressants. As discussed in this review, the serotonergic system offers great potential for the development of new antidepressant therapies based on the combination of SERT inhibition with different pharmacological activity towards the 5-HT system. The aim of this article is to summarize the search for new antidepressants in recent years, focusing primarily on the possibility of benefiting from interactions with various 5-HT receptors in the pharmacotherapy of depression.

Stress-Related Dysfunction of Adult Hippocampal Neurogenesis-An Attempt for Understanding Resilience?

Newborn neurons in the adult hippocampus are regulated by many intrinsic and extrinsic cues. It is well accepted that elevated glucocorticoid levels lead to downregulation of adult neurogenesis, which this review discusses as one reason why psychiatric diseases, such as major depression, develop after long-term stress exposure. In reverse, adult neurogenesis has been suggested to protect against stress-induced major depression, and hence, could serve as a resilience mechanism. In this review, we will summarize current knowledge about the functional relation of adult neurogenesis and stress in health and disease. A special focus will lie on the mechanisms underlying the cascades of events from prolonged high glucocorticoid concentrations to reduced numbers of newborn neurons. In addition to neurotransmitter and neurotrophic factor dysregulation, these mechanisms include immunomodulatory pathways, as well as microbiota changes influencing the gut-brain axis. Finally, we discuss recent findings delineating the role of adult neurogenesis in stress resilience.

Antidepressant and Anxiolytic-Like Effects of the Stem Bark Extract of Fraxinus rhynchophylla Hance and Its Components in a Mouse Model of Depressive-Like Disorder Induced by Reserpine Administration

There is an urgent need to find antidepressants that can be administered for long periods without inducing severe side effects to replace conventional antidepressants that control monoamine levels, such as tricyclic antidepressants (TCAs), monoamine oxidase inhibitors (MAOIs), and selective serotonin reuptake inhibitors (SSRI). We sought to determine the antidepressant effects of Fraxinus rhynchophylla Hance (F. rhynchophylla Hance, FX) and its components on a reserpine-induced mouse model. One hour after oral administration of FX (30, 50, and 100 mg/kg), esculin (50 mg/kg), esculetin (50 mg/kg), fraxin (50 mg/kg), and fluoxetine (20 mg/kg), reserpine was delivered intraperitoneally to mice. Behavioral experiments were conducted to measure anxiety and depressive-like behaviors after 10 days of administration. FX and its components increased the number of entries into the center of an open field as well as distance traveled within it and decreased immobility duration in the forced swim and tail suspension tests. Reserpine-induced increases in plasma corticosterone concentrations were attenuated by the administration of FX and its components, which were also found to decrease the reserpine-induced enhancement of mRNA levels of interleukin (IL)-12 p40, IL-6, and tumor necrosis factor (TNF)-α, pro-inflammatory cytokines. Finally, the diminished expressions of hippocampal phosphorylated cAMP response element-binding protein (pCREB) and brain-derived neurotrophic factor (BDNF) by reserpine were increased by FX and its components. Our results suggest that FX and its components regulate anxiety and depressive-like behaviors through stress hormones, immune regulation, and the activation of neuroprotective mechanisms, further supporting the potential of FX and its components as antidepressants.

Serotonin as a Mitogen in the Gastrointestinal Tract: Revisiting a Familiar Molecule in a New Role

Serotonin signaling is ubiquitous in the gastrointestinal (GI) system, where it acts as a neurotransmitter in the enteric nervous system (ENS) and influences intestinal motility and inflammation. Since its discovery, serotonin has been linked to cellular proliferation in several types of tissues, including vascular smooth muscle, neurons, and hepatocytes. Activation of serotonin receptors on distinct cell types has been shown to induce well-known intracellular proliferation pathways. In the GI tract, potentiation of serotonin signaling results in enhanced intestinal epithelial proliferation, and decreased injury from intestinal inflammation. Furthermore, activation of the type 4 serotonin receptor on enteric neurons leads to neurogenesis and neuroprotection in the setting of intestinal injury. It is not surprising that the mitogenic properties of serotonin are pronounced within the GI tract, where enterochromaffin cells in the intestinal epithelium produce 90% of the body's serotonin; however, these proliferative effects are attributed to increased serotonin signaling within the ENS compartment as opposed to the intestinal mucosa, which are functionally and chemically separate by virtue of the distinct tryptophan hydroxylase enzyme isoforms involved in serotonin synthesis. The exact mechanism by which serotonergic neurons in the ENS lead to intestinal proliferation are not known, but the activation of muscarinic receptors on intestinal crypt cells indicate that cholinergic signaling is essential to this signaling pathway. Further understanding of serotonin's role in mucosal and enteric nervous system mitogenesis may aid in harnessing serotonin signaling for therapeutic benefit in many GI diseases, including inflammatory bowel disease, malabsorptive conditions, and cancer.

Developmental Antecedents of Adult Macaque Neurogenesis: Early-Life Adversity, 5-HTTLPR Polymorphisms, and Adolescent Hippocampal Volume

INTRODUCTION

Attenuated adult hippocampal neurogenesis may manifest in affective symptomatology and/or resistance to antidepressant treatment. While early-life adversity and the short variant ('s') of the serotonin transporter gene's long polymorphic region (5-HTTLPR) are suggested as interacting risk factors for affective disorders, no studies have examined whether their superposed risk effectuates neurogenic changes into adulthood. Similarly, it is not established whether reduced hippocampal volume in adolescence, variously identified as a marker and antecedent of affective disorders, anticipates diminished adult neurogenesis. We investigate these potential developmental precursors of neurogenic alterations using a bonnet macaque model.

METHODS

Twenty-five male infant bonnet macaques were randomized to stressed [variable foraging demand (VFD)] or normative [low foraging demand (LFD)] rearing protocols and genotyped for 5-HTTLPR polymorphisms. Adolescent MRI brain scans (mean age 4.2y) were available for 14 subjects. Adult-born neurons were detected post-mortem (mean age 8.6y) via immunohistochemistry targeting the microtubule protein doublecortin (DCX). Models were adjusted for age and weight.

RESULTS

A putative vulnerability group (VG) of VFD-reared 's'-carriers (all 's/l') exhibited reduced neurogenesis compared to non-VG subjects. Neurogenesis levels were positively predicted by ipsilateral hippocampal volume normalized for total brain volume, but not by contralateral or raw hippocampal volume.

LIMITATIONS

No 's'-carriers were identified in LFD-reared subjects, precluding a 2×2 factorial analysis.

CONCLUSION

The 's' allele (with adverse rearing) and low adolescent hippocampal volume portend a neurogenic deficit in adult macaques, suggesting persistent alterations in hippocampal plasticity may contribute to these developmental factors' affective risk in humans.

Neuroimmunology of depression

Depression is one of the leading causes of disability worldwide and a major contributor to the global burden of disease, yet the cellular and molecular etiology of depression remain largely unknown. Major Depressive Disorder (MDD) is associated with a variety of chronic physical inflammatory and autoimmune disorders, and mood disorders may act synergistically with other medical disorders to worsen patient outcomes. Here, we outline the neuroimmune complement, explore the evidence for altered immune system function in MDD, and present some of the potential mechanisms by which immune cells and molecules may drive the onset and course of MDD. These include pro-inflammatory signaling, alterations in the hypothalamic-pituitary-adrenal axis, dysregulation of the serotonergic and noradrenergic neurotransmitter systems, neuroinflammation, and meningeal immune dysfunction. Finally, we discuss the interactions between current antidepressants and the immune system and propose the possibility of immunomodulatory drugs as potential novel antidepressant treatments.

Hippocampal regenerative medicine: neurogenic implications for addiction and mental disorders

Psychiatric illness is a prevalent and highly debilitating disorder, and more than 50% of the general population in both middle- and high-income countries experience at least one psychiatric disorder at some point in their lives. As we continue to learn how pervasive psychiatric episodes are in society, we must acknowledge that psychiatric disorders are not solely relegated to a small group of predisposed individuals but rather occur in significant portions of all societal groups. Several distinct brain regions have been implicated in neuropsychiatric disease. These brain regions include corticolimbic structures, which regulate executive function and decision making (e.g., the prefrontal cortex), as well as striatal subregions known to control motivated behavior under normal and stressful conditions. Importantly, the corticolimbic neural circuitry includes the hippocampus, a critical brain structure that sends projections to both the cortex and striatum to coordinate learning, memory, and mood. In this review, we will discuss past and recent discoveries of how neurobiological processes in the hippocampus and corticolimbic structures work in concert to control executive function, memory, and mood in the context of mental disorders.

A region of the brain called the hippocampus and its connections to other parts of the brain via what are called cortico-limbic structures are implicated in a variety of mental health disorders. These disorders can be accompanied by reduced hippocampal volume. Mi-Hyeon Jang, Doo-Sup Choi and colleagues at the Mayo Clinic College of Medicine and Science, Rochester, USA, review the role of hippocampal and cortico-limbic neurobiology in memory and mood in mental disorders. They focus particular attention on the role of neurogenesis, the production and growth of new nerve cells and connections. Disrupted neurogenesis in the adult hippocampus is implicated in conditions including addiction, depression, schizophrenia and related psychotic disorders. Learning more about neural regeneration in the hippocampus could yield insights into mental health conditions and open new avenues toward developing drug-based treatments.

Serotonin modulation of hippocampal functions: From anatomy to neurotherapeutics

The hippocampal region receives a dense serotoninergic innervation originating from both medial and dorsal raphe nuclei. This innervation regulates hippocampal activity through the activation of distinct receptor families that are expressed in excitatory and inhibitory neurons, terminals of several afferent neurotransmitter systems, and glial cells. Preclinical and clinical studies indicate that hippocampal dysfunctions are involved in learning and memory deficits, dementia, Alzheimer's disease, epilepsy and mood disorders such as anxiety, depression and post-traumatic syndrome disorder, whereas the hippocampus participates also in the therapeutic mechanisms of numerous medicines. Not surprisingly, several drugs acting via 5-HT mechanisms are efficacious to some extent in some diseases and the link between 5-HT and the hippocampus although clear remains difficult to untangle. For this reason, we review reported data concerning the distribution and the functional roles of the 5-HT receptors in the hippocampal region in health and disease. The impact of the 5-HT systems on the hippocampal function is such that the research of new 5-HT mechanisms and drugs is still very active. It concerns notably drugs acting at the 5-HT_1A,_2A,_2C,_4,6 receptor subtypes, in addition to the already existing drugs including the selective serotonin reuptake inhibitors.

Comprehensive Investigation of Metabolic Changes Occurring in the Rat Brain Hippocampus after Fluoxetine Administration Using Two Complementary In Vivo Techniques: Solid Phase Microextraction and Microdialysis

Fluoxetine is among the most prescribed antidepressant drugs worldwide. Nevertheless, limited information is known about its definitive mechanism. Although in vivo examinations performed directly in related brain structures can provide more realistic, and therefore more insightful, knowledge regarding the mechanisms and efficacy of this drug, only a few techniques are applicable for in vivo monitoring of metabolic alterations in the brain following an inducement. Among them, solid phase microextraction (SPME) and microdialysis (MD) have emerged as ideal in vivo tools for extraction of information from biosystems. In this investigation, we scrutinized the capabilities of SPME and MD to detect ongoing changes in the brain following acute fluoxetine administration. Sequential in vivo samples were collected simultaneously from male rats' hippocampi using SPME and MD before drug administration in order to establish a baseline; then samples were collected again following fluoxetine administration for an investigation of small molecule alterations. Our results indicate that MD provides more comprehensive information for polar compounds, while SPME provides superior information with respect to lipids and other medium level polar molecules. Interestingly, in the lipidomic investigation, all dysregulated features were found to be membrane lipids and associated compounds. Moreover, in the metabolomic investigations, dysregulation of hippocampal metabolite levels associated with fatty acid transportation and purine metabolisms were among the most notable findings. Overall, our evaluation of the obtained data corroborates that, when used in tandem, SPME and MD are capable of providing comprehensive information regarding the effect of fluoxetine in targeted brain structures and further elucidating this drug's mechanisms of action in the brain.

Psychological mechanisms and functions of 5-HT and SSRIs in potential therapeutic change: Lessons from the serotonergic modulation of action selection, learning, affect, and social cognition

Uncertainty regarding which psychological mechanisms are fundamental in mediating SSRI treatment outcomes and wide-ranging variability in their efficacy has raised more questions than it has solved. Since subjective mood states are an abstract scientific construct, only available through self-report in humans, and likely involving input from multiple top-down and bottom-up signals, it has been difficult to model at what level SSRIs interact with this process. Converging translational evidence indicates a role for serotonin in modulating context-dependent parameters of action selection, affect, and social cognition; and concurrently supporting learning mechanisms, which promote adaptability and behavioural flexibility. We examine the theoretical basis, ecological validity, and interaction of these constructs and how they may or may not exert a clinical benefit. Specifically, we bridge crucial gaps between disparate lines of research, particularly findings from animal models and human clinical trials, which often seem to present irreconcilable differences. In determining how SSRIs exert their effects, our approach examines the endogenous functions of 5-HT neurons, how 5-HT manipulations affect behaviour in different contexts, and how their therapeutic effects may be exerted in humans - which may illuminate issues of translational models, hierarchical mechanisms, idiographic variables, and social cognition.

Understanding the effects of chronic benzodiazepine use in depression: a focus on neuropharmacology

Benzodiazepines are frequently prescribed on an ongoing basis to individuals with depression, mainly to alleviate anxiety or insomnia, despite current guideline recommendations that continuous use should not exceed 4 weeks. Currently, there are no efficacy trials published beyond 8 weeks. Several antidepressant trials demonstrate that the concomitant use of a benzodiazepine is associated with poorer depressive outcomes and functional status; however, it is unclear why this is the case. Patients with depression receiving a benzodiazepine may reflect a more ill or high anxiety group, although even within anxiety disorders, the use of a benzodiazepine is associated with poorer outcomes. The neuroadaptive consequences of long-term benzodiazepine use may be a factor underlying these findings. Chronic benzodiazepine use results in decreased gamma-aminobutyric acid and monoaminergic function, as well as interference with neurogenesis, which are all purported to play a role in antidepressant efficacy. This review will discuss the oppositional neuropharmacological interactions between chronic benzodiazepine use and antidepressant mechanism of action, which could result in reduced antidepressant efficacy and function in depression.

eEF2/eEF2K Pathway in the Mature Dentate Gyrus Determines Neurogenesis Level and Cognition

Levels of adult neurogenesis in the dentate gyrus (DG) of the hippocampus are correlated with unique cognitive functions. However, the molecular pathways controlling it are poorly understood. Here, we found that the known physiological ways to enhance neurogenesis converged on the eEF2/eEF2K pathway via AMPK in the DG. Enhancing the elongation phase of mRNA translation in eEF2K-knockout (eEF2K-KO) mice induced the expression of neurogenesis-related proteins in the hippocampus. We thus tested the hypothesis that inducing eEF2K-KO in mature neurons of the DG controls neurogenesis. Indeed, both general eEF2K-KO and targeted KO in DG excitatory mature neurons resulted in enhanced neurogenesis levels and upregulation of neurogenesis-related proteins. Increased neurogenesis was correlated with enhanced performance in DG-dependent learning. Moreover, general and local eEF2K-KO in old mice rejuvenated the DG, paving the way for better mechanistic understanding of how neurogenesis is controlled in the mature DG and possible treatments for incurable aging-associated diseases.

Hippocampal mossy cell involvement in behavioral and neurogenic responses to chronic antidepressant treatment

Most antidepressants, including selective serotonin reuptake inhibitors (SSRIs), initiate their drug actions by rapid elevation of serotonin, but they take several weeks to achieve therapeutic onset. This therapeutic delay suggests slow adaptive changes in multiple neuronal subtypes and their neural circuits over prolonged periods of drug treatment. Mossy cells are excitatory neurons in the dentate hilus that regulate dentate gyrus activity and function. Here we show that neuronal activity of hippocampal mossy cells is enhanced by chronic, but not acute, SSRI administration. Behavioral and neurogenic effects of chronic treatment with the SSRI, fluoxetine, are abolished by mossy cell-specific knockout of p11 or Smarca3 or by an inhibition of the p11/AnxA2/SMARCA3 heterohexamer, an SSRI-inducible protein complex. Furthermore, simple chemogenetic activation of mossy cells using Gq-DREADD is sufficient to elevate the proliferation and survival of the neural stem cells. Conversely, acute chemogenetic inhibition of mossy cells using Gi-DREADD impairs behavioral and neurogenic responses to chronic administration of SSRI. The present data establish that mossy cells play a crucial role in mediating the effects of chronic antidepressant medication. Our results indicate that compounds that target mossy cell activity would be attractive candidates for the development of new antidepressant medications.

Antidepressant Drugs Correct the Imbalance Between proBDNF/p75NTR/Sortilin and Mature BDNF/TrkB in the Brain of Mice with Chronic Stress

Depression is a worldwide problem with a great social and economic burden in many countries. In our previous research, we found that the expression of proBDNF/p75NTR/sortilin is upregulated in patients with major depressive disorder. In addition, the treatment of proBDNF antibodies reversed both the depressive behaviors and the reduced BDNF mRNA detected in our rodent chronic stress models. Antidepressant drugs are usually only effective in a subpopulation of patients with major depression with a delayed time window of 2-4 weeks to exert their efficacy. The mechanism underlying such delayed response is not known. In this study, we hypothesize that antidepressant drugs exert their therapeutic effect by modulating proBDNF/p75NTR and mature BDNF/TrkB signaling pathways. To test the hypothesis, C57 mice were randomly divided into normal control, chronic unpredictable mild stress (CUMS), vehicle (VEH), fluoxetine (FLU), and clozapine (CLO) groups. Behavioral tests (sucrose preference, open field, and tail suspension tests) were performed before and after 4 weeks of CUMS. The gene and protein expression of proBDNF, the neurotrophin receptor (p75NTR), sortilin, and TrkB in the cortex and hippocampus were examined. At the protein level, CUMS induced a significant increase in proBDNF, p75NTR, and sortilin production while the TrkB protein level was found to be lower in the cortex and hippocampus compared with the control group. Consistently, at the mRNA level, p75NTR expression increased with reduced BDNF/TrkB mRNA in both cortex and hippocampus, while sortilin increased only in the hippocampus after CUMS. FLU and CLO treatments of CUMS mice reversed all protein and mRNA expression of the biomarkers in both cortex and hippocampus, except for sortilin mRNA in the cortex and proBDNF in the hippocampus, respectively. This study further confirms that the imbalance between proBDNF/p75NTR/sortilin and mBDNF/TrkB production is important in the pathogenesis of depression. It is likely that antidepressant FLU and antipsychotic CLO exert their antidepressant-like effect correcting the imbalance between proBDNF/p75NTR/sortilin and mBDNF/TrkB.

Peripheral adiponectin levels in anxiety, mood, trauma- and stressor-related disorders: A systematic review and meta-analysis

BACKGROUND

Anxiety, mood, trauma- and stressor-related disorders confer increased risk for metabolic disease. Adiponectin, a cytokine released by adipose tissue is associated with these disorders and obesity via inflammatory processes. Available data describing associations with mental disorders remain limited and conflicted.

METHODS

A systematic search was conducted for English, peer-reviewed articles from inception until February 2019 that assessed for serum or plasma adiponectin levels in adults with an anxiety, mood or trauma-related disorder. Diagnoses were determined by psychiatric interview, based on DSM-IV, DSM-5 or ICD-10 criteria. Analyses were performed using STATA 15 and Standardized mean difference (SMD) with 95% confidence interval was applied to pool the effect size of meta-analysis studies.

RESULTS

In total 65 eligible studies were included in the systematic review and 30 studies in this meta-analysis. 19,178 participants (11,262 females and 7916 males), comprising healthy adults and adults with anxiety, mood and trauma-related disorders, were included. Overall results indicated an inverse association between adiponectin levels and examined mental disorders. Specifically, patients with an anxiety disorder (SMD  = -1.18 µg/mL, 95% CI, -2.34; -0.01, p  = 0.047); trauma or stressor-related disorder (SMD  =  -0.34 µg/mL, 95% CI, -0.52; -0.17, p  = 0.0000) or bipolar disorder (SMD  =  -0.638 µg/mL, 95% CI, -1.16, -0.12, p  = 0.017) had significant lower adiponectin levels compared to healthy adults.

LIMITATIONS

Heterogeneity, potential publication bias, and lack of control for important potential confounders were significant limitations.

CONCLUSION

Peripheral adiponectin levels appear to be inversely associated with anxiety, mood, trauma- and stressor related disorders and may be a promising biomarker for diagnosis and disease monitoring.

Alzheimer's Disease and Its Potential Alternative Therapeutics

Alzheimer’s Disease (AD) is a chronic neurodegenerative disease that affects over 5 million individuals in the United States alone. Currently, there are only two kinds of pharmacological interventions available for symptomatic relief of AD; Acetyl Cholinesterase Inhibitors (AChEI) and N-methyl-D-aspartic Acid (NMDA) receptor antagonists and these drugs do not slow down or stop the progression of the disease. Several molecular targets have been implicated in the pathophysiology of AD, such as the tau (τ) protein, Amyloid-beta (Aβ), the Amyloid Precursor Protein (APP) and more and several responses have also been observed in the advancement of the disease, such as reduced neurogenesis, neuroinflammation, oxidative stress and iron overload. In this review, we discuss general features of AD and several small molecules across different experimental AD drug classes that have been studied for their effects in the context of the molecular targets and responses associated with the AD progression. These drugs include: Paroxetine, Desferrioxamine (DFO), N-acetylcysteine (NAC), Posiphen/-(−)Phenserine, JTR-009, Carvedilol, LY450139, Intravenous immunoglobulin G 10%, Indomethacin and Lithium Carbonate (Li₂CO₃).

Negr1 controls adult hippocampal neurogenesis and affective behaviors

Recent genome-wide association studies on major depressive disorder have implicated neuronal growth regulator 1 (Negr1), a GPI-anchored cell adhesion molecule in the immunoglobulin LON family. Although Negr1 has been shown to regulate neurite outgrowth and synapse formation, the mechanism through which this protein affects mood disorders is still largely unknown. In this research, we characterized Negr1-deficient (negr1^-/-) mice to elucidate the function of Negr1 in anxiety and depression. We found that anxiety- and depression-like behaviors increased in negr1^-/- mice compared with wild-type mice. In addition, negr1^-/- mice had decreased adult hippocampal neurogenesis compared to wild-type mice. Concurrently, both LTP and mEPSC in the dentate gyrus (DG) region were severely compromised in negr1^-/- mice. In our effort to elucidate the underlying molecular mechanisms, we found that lipocalin-2 (Lcn2) expression was decreased in the hippocampus of negr1^-/- mice compared to wild-type mice. Heterologous Lcn2 expression in the hippocampal DG of negr1^-/- mice rescued anxiety- and depression-like behaviors and restored neurogenesis and mEPSC frequency to their normal levels in these mice. Furthermore, we discovered that Negr1 interacts with leukemia inhibitory factor receptor (LIFR) and modulates LIF-induced Lcn2 expression. Taken together, our data uncovered a novel mechanism of mood regulation by Negr1 involving an interaction between Negr1 and LIFR along with Lcn2 expression.

Enhanced discriminative aversive learning and amygdala responsivity in 5-HT transporter mutant mice

Genetic variation in the human serotonin transporter (5-HTT) has been linked to altered fear learning but the data are inconsistent and the mechanism is unclear. The present study investigated conditioned aversive learning in 5-HTT knockout (KO) mice while simultaneously recording neural network activity (theta oscillations) and hemodynamic responses (tissue oxygen delivery) from the amygdala, a brain region necessary for forming fearful memories. Conditioned aversive learning was measured using a discrimination learning task in which one auditory cue was paired with foot-shock, whereas a second auditory cue was not. Compared with wild-type mice, 5-HTTKO mice exhibited faster discrimination learning. This effect was associated with stronger theta frequency oscillations and greater hemodynamic changes in the amygdala in response to both the emotionally relevant cues and the unconditioned foot-shock stimulus. Furthermore, hemodynamic responses to the unconditioned stimulus predicted behavioral discrimination performance the following day. Acute pharmacological 5-HTT blockade in wild-type mice produced a similar effect, to the extent that administration of citalopram during the fear conditioning sessions enhanced fear memory recall. Collectively, our data argue that loss of 5-HTT function enhances amygdala responsivity to aversive events and facilitates learning for emotionally relevant cues.

Increased Serotonin Transporter Expression in Huntington's Disease Patients Is Not Consistently Replicated in Murine Models

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) target the serotonin transporter (SERT) and are commonly prescribed for depression in Huntington's disease (HD) patients. However, SERT expression in HD has not been carefully evaluated in patients or mouse models.

OBJECTIVE

In this study, we investigated SERT levels in HD patients and HD mouse models.

METHODS

We obtained HD patient brain striatal samples and matched controls, as well as brain tissue from CAG140 and R6/2 mice. SERT mRNA and protein levels were analyzed using quantitative RT-PCR and immunoblotting.

RESULTS AND CONCLUSIONS

We found that SERT protein, but not mRNA is markedly increased in grade 4 HD patient striatal tissue. These findings suggest posttranscriptional or translational SERT dysregulation as a possible etiologic factor modulating psychopathology in HD. Interestingly, SERT expression is variable in mouse models of the disease. Increased SERT levels are demonstrated in the brain of CAG140 mice, a full-length knock-in mouse model of the disease, but not in the striatum of the R6/2 fragment murine model of the disease. Based on this parameter, the CAG140 huntingtin knock-in mouse model is more suitable than the R6/2 model for the study of serotonergic pathway pathology in Huntington's disease.

iPlasticity: Induced juvenile-like plasticity in the adult brain as a mechanism of antidepressants

The network hypothesis of depression proposes that mood disorders reflect problems in information processing within particular neural networks. Antidepressants (AD), including selective serotonin reuptake inhibitors (SSRI), function by gradually improving information processing within these networks. AD have been shown to induce a state of juvenile-like plasticity comparable to that observed during developmental critical periods: Such critical-period-like plasticity allows brain networks to better adapt to extrinsic and intrinsic signals. We have coined this drug-induced state of juvenile-like plasticity 'iPlasticity.' A combination of iPlasticity induced by chronic SSRI treatment together with training, rehabilitation, or psychotherapy improves symptoms of neuropsychiatric disorders and issues underlying the developmentally or genetically malfunctioning networks. We have proposed that iPlasticity might be a critical component of AD action. We have demonstrated that iPlasticity occurs in the visual cortex, fear erasure network, extinction of aggression caused by social isolation, and spatial reversal memory in rodent models. Chronic SSRI treatment is known to promote neurogenesis and to cause dematuration of granule cells in the dentate gyrus and of interneurons, especially parvalbumin interneurons enwrapped by perineuronal nets in the prefrontal cortex, visual cortex, and amygdala. Brain-derived neurotrophic factor (BDNF), via its receptor tropomyosin kinase receptor B, is involved in the processes of synaptic plasticity, including neurogenesis, neuronal differentiation, weight of synapses, and gene regulation of synaptic formation. BDNF can be activated by both chronic SSRI treatment and neuronal activity. Accordingly, the BDNF/tropomyosin kinase receptor B pathway is critical for iPlasticity, but further analyses will be needed to provide mechanical insight into the processes of iPlasticity.

Serotonin receptors in depression and anxiety: Insights from animal studies

Serotonin regulates many physiological processes including sleep, appetite, and mood. Thus, serotonergic system is an important target in the treatment of psychiatric disorders, such as major depression and anxiety. This natural neurotransmitter interacts with 7 families of its receptors (5-HT1-7), which cause a variety of pharmacological effects. Using genetically modified animals and selective or preferential agonists and antagonist, numerous studies demonstrated the involvement of almost all serotonin receptor subtypes in antidepressant- or anxiolytic-like effects. In this review, based on animal studies, we discuss the possible involvement of serotonin receptor subtypes in depression and anxiety.

Re-education begins at home: an overview of the discovery of in vivo-active small molecule modulators of endogenous stem cells

INTRODUCTION

Degenerative diseases, such as Alzheimer's disease, heart disease and arthritis cause great suffering and are major socioeconomic burdens. An attractive treatment approach is stem cell transplantation to regenerate damaged or destroyed tissues. However, this can be problematic. For example, donor cells may not functionally integrate into the host tissue. An alternative methodology is to deliver bioactive agents, such as small molecules, directly into the diseased tissue to enhance the regenerative potential of endogenous stem cells. Areas covered: In this review, the authors discuss the necessity of developing these small molecules to treat degenerative diseases and survey progress in their application as therapeutics. They describe both the successes and caveats of developing small molecules that target endogenous stem cells to induce tissue regeneration. This article is based on literature searches which encompass databases for biomedical research and clinical trials. These small molecules are also categorized per their target disease and mechanism of action. Expert opinion: The development of small molecules targeting endogenous stem cells is a high-profile research area. Some compounds have made the successful transition to the clinic. Novel approaches, such as modulating the stem cell niche or targeted delivery to disease sites, should increase the likelihood of future successes in this field.

Synaptic Ultrastructure Might Be Involved in HCN1-Related BDNF mRNA in Withdrawal-Anxiety After Ethanol Dependence

Withdrawal from ethanol dependence has been associated with heightened anxiety and reduced expression of Brain-derived neurotropic factor which promotes the synaptic transmission and plasticity of synapses. Hyperpolarization-activated cyclic nucleotide-gated channel 1 regulates expression; however, whether Hyperpolarization-activated cyclic nucleotide-gated channel 1-related Brain-derived neurotropic factor is involved in the synaptic ultrastructure that generates withdrawal-anxiety has been poorly perceived. Sprague-Dawley rats were treated with ethanol 3-9% (v/v) for a period of 21 days. Conditioned place preference and body weight were investigated during ethanol administration. Rats were subjected to behavioral testing and biochemical assessments after ethanol withdrawal, which was induced by abrupt discontinuation of the treatment. The results showed that the ethanol administration induced severe ethanol dependence behaviors, with higher body weight and more time in the ethanol-paired compartment. After withdrawal, rats had a higher total ethanol withdrawal score and explored less. Additionally, increased Hyperpolarization-activated cyclic nucleotide-gated channel 1 protein and gene expression and decreased Brain-derived neurotropic factor protein and gene expression were detected in the Ethanol group. Eventually, there was a negative correlation between the level of Brain-derived neurotropic factor mRNA and Hyperpolarization-activated cyclic nucleotide-gated channel 1 protein. Importantly, the synaptic ultrastructure changed in the Ethanol group, including increased synaptic cleft width and reduction in postsynaptic density thickness or synaptic curvature. The synthesis of the Brain-derived neurotropic factor mRNA could be down-regulated by higher Hyperpolarization-activated cyclic nucleotide-gated channel 1 protein expression. Changes in synaptic ultrastructure may be induced by lower Brain-derived neurotropic factor protein, which could be associated with the withdrawal-anxiety that is experiences after ethanol dependence.