Do antidepressants promote neurogenesis in adult hippocampus? A systematic review and meta-analysis on naive rodents

Synaptic Vesicle 2A (SV2A) Positron Emission Tomography (PET) Imaging as a Marker of Therapeutic Response in a Mouse Model of Depression

In this preclinical pilot study, we used [11C]UCB-J PET imaging to monitor the synaptic modulation in depression and after fluoxetine. PET imaging was performed in a validated mouse model of depression/anxiety (CORT model), and the effect of 5-week treatment with fluoxetine was tested. Depression/anxiety phenotype and antidepressant action of fluoxetine were confirmed using the novelty-suppressed feeding test, previously validated in the CORT model. PET data showed significant decreases of volume of distribution (V T) of [11C]UCB-J in most brain regions of CORT mice compared with controls. After 5 weeks of fluoxetine, a trend toward restoration of V T values to control levels was observed, although it reached significance only in the olfactory bulb. These preliminary data support the use of [11C]UCB-J PET imaging and the CORT model to study the synaptic modulation of antidepressants. It provides excellent translational opportunities to study the relationship between synaptic plasticity and the clinical efficacy of antidepressants.

Biomarkers of cognitive and memory decline in psychotropic drug users

Psychotropic drugs are vital in psychiatry, aiding in the management of mental health disorders. Their use requires an understanding of their pharmacological properties, therapeutic applications, and potential side effects. Ongoing research aims to improve their efficacy and safety. Biomarkers play a crucial role in understanding and predicting memory decline in psychotropic drug users. A comprehensive understanding of biomarkers, including neuroimaging, biochemical, genetic, and cognitive assessments, is essential for developing targeted interventions and preventive strategies. In this narrative review, we performed a comprehensive search on PubMed and Google using review-specific terms. Clinicians should use a multifaceted approach, including neurotransmitter analysis, neurotrophic factors, miRNA profiling, and cognitive tasks for early intervention and personalized treatment. Anxiolytics' mechanisms involve various neurotransmitter systems and emerging targets. Research on biomarkers for memory decline in anxiolytic users can lead to early detection and intervention, enhancing clinical practices and aligning with precision medicine. Mood stabilizer users can benefit from early detection of memory decline through RNA, neurophysiological, and inflammatory biomarkers, promoting timely interventions. Performance-enhancing drugs may boost athletic performance in the short term, but their long-term health risks and ethical issues make their use problematic. Long-term use of psychotropic performance enhancers in athletes shows changes in biomarkers of cognitive decline, necessitating ongoing monitoring and intervention strategies. Understanding these genetic influences on memory decline helps pave the way for personalized approaches to prevent or mitigate cognitive deterioration, emphasizing the importance of genetic screening and early interventions based on an individual's genetic profile. Future research should focus on refining these biomarkers and protective measures against cognitive deterioration. Overall, a comprehensive understanding of biomarkers in psychotropic drug users is essential for developing targeted interventions and preventive strategies.

Efficacy and Safety of Sovateltide in Patients with Acute Cerebral Ischaemic Stroke: A Randomised, Double-Blind, Placebo-Controlled, Multicentre, Phase III Clinical Trial

BACKGROUND AND OBJECTIVES

Sovateltide (Tycamzzi™), an endothelin-B (ET-B) receptor agonist, increases cerebral blood flow, has anti-apoptotic activity, and promotes neural repair following cerebral ischaemic stroke. The objectives of this study were to evaluate the efficacy and safety of sovateltide in adult participants with acute cerebral ischaemic stroke.

METHODS

This was a randomised, double-blind, placebo-controlled, multicentre, Phase III clinical trial of sovateltide in participants with cerebral ischaemic stroke receiving standard of care (SOC) in India. Patients aged 18-78 years presenting up to 24 h after the onset of symptoms with radiologic confirmation of ischaemic stroke and a National Institutes of Health Stroke Scale score (NIHSS) of ≥ 6 were enrolled. Patients with recurrent stroke, receiving endovascular therapy, or with intracranial haemorrhage were excluded. The study drug (saline or sovateltide [0.3 µg/kg] was administered intravenously in three doses at 3 ± 1 h intervals on Days 1, 3, and 6, and follow-up was 90 days). The Multivariate Imputation by Chained Equations (MICE) was used to impute the missing assessments on the endpoints. An unpaired t-test, two-way analysis of variance with Tukey's multiple comparison test, and the Chi-square test were used for the statistical analysis. The objective was to determine at Day 90 (1) the number of patients with a modified Rankin Scale score (mRS) 0-2, and (2) the number of patients with an NIHSS 0-5 at 90 days.

RESULTS

Patients were randomised with 80 patients in the sovateltide and 78 in the control group. Patients received the investigational drug at about 18 h of stroke onset in both control and sovateltide groups. The median NIHSS at randomisation was 10.00 (95% CI 9.99-11.65) in the control group and 9.00 (95% CI 9.11-10.46) in the sovateltide group. Seventy patients completed the 90-day follow-up in the control group and 67 in the sovateltide group. The proportion of intention-to-treat (ITT) patients with mRS 0-2 score at Day 90 post-randomisation was 22.67% higher (odds ratio [OR] 2.75, 95% CI 1.37-5.57); similarly, the proportion of patients with NIHSS score of 0-5 at Day 90 was 17.05% more (OR 2.67, 95% CI 1.27-5.90) in the sovateltide group than in the control group. An improvement of ≥ 2 points on the mRS was observed in 51.28% and 72.50% of patients in the control and sovateltide groups, respectively (OR 2.50, 95% CI 1.29-4.81). Seven of 78 patients (8.97%) in the control group and 7 of 80 (8.75%) in the sovateltide group developed intracranial haemorrhage (ICH). The adverse events were not related to sovateltide.

CONCLUSIONS

The sovateltide group had a greater number of cerebral ischaemic stroke patients with lower mRS and NIHSS scores at 90 days post-treatment than the control group. This trial supported the regulatory approval of sovateltide in India, but a multinational RESPECT-ETB trial will be conducted for US approval.

TRIAL REGISTRATION

Clinical Trials Registry, India (CTRI/2019/09/021373) and the United States National Library of Medicine, ClinicalTrials.gov (NCT04047563).

Semen Cuscutae flavonoids activated the cAMP-PKA-CREB-BDNF pathway and exerted an antidepressant effect in mice

Background

Semen Cuscutae flavonoids (SCFs) constitute a class of metabolites of Semen Cuscutae, a botanical drug that was recently found to have an anti-depression effect. This study aimed to evaluate the anti-depression effects of SCFs in chronic unpredictable mild stress (CUMS)-induced mice and to interrogate the underlying mechanisms.

Materials and methods

The CUMS mice were used for assessing the effects of SCFs treatments on depression. Mice were randomly divided into five groups. Four groups were subjected to the CUMS induction and concomitantly administered orally with either the vehicle or with a high-, medium-, and low-dose of SCFs, once per day for 4 weeks. One group was kept untreated as a control. The mice were then assessed for their statuses of a number of depression-related parameters, including body weight, food intake, sucrose preference test (SPT), open field test (OFT), tail suspension test (TST), and forced swim test (FST). In addition, a day after the completion of these tests, biopsies from the hippocampus were harvested and used to perform metabolomics by HPLC-MS/MS and to assess the levels of cAMP by ELISA and the levels of PKA, CREB, p-CREB, and BDNF by Western blot analyses.

Results

SCFs resulted in significant increases in both body weight and food intake and in the amelioration of the depressive-like behaviors in CUMS mice. A high-dose SCFs treatment led to significant alterations in 72 metabolites, of which 26 were identified as potential biomarkers for the SCFs treatment. These metabolites are associated with lipid, amino acid, and nucleotide metabolism. Among 26 metabolites, cAMP was positively correlated with body weight, SPT, OFT-total distance, and OFT-central residence time, while negatively correlated with immobility time in TST and FST, linking a change in cAMP with the SCFs treatment and the significant improvement in depressive symptoms in CUMS mice. Further analyses revealed that the levels of cAMP, PKA, CREB, p-CREB, and BDNF were reduced in the hippocampus of CUMS mice but were all increased following the SCFs treatments.

Conclusion

SCFs could ameliorate hippocampal metabolic disturbances and depressive behaviors and cause the activation of the cAMP-PKA-CREB-BDNF signaling pathway in the hippocampus of CUMS mice.

PERK inhibitor (ISRIB) improves depression-like behavior by inhibitions of HPA-axis over-activation in mice exposed to chronic restraint stress

Stressful life event is closely associated with depression, thus strategies that blunt or prevent the negative effect stress on the brain might benefits for the treatment of depression. Although previous study showed the role of protein kinase R (PKR)-like ER kinase (PERK) in inflammation related depression, its involvement in the neuropathology of chronic stress induced depression is still unknown. We tried to explore whether block the PERK pathway would alleviate the animals' depression-like behavior induced by chronic restraint stress (CRS) and investigate the underlying mechanism. The CRS-exposed mice exhibited depression-like behavior, including anhedonia in the sucrose preference test (SPT), and increased immobility time in tail suspension test (TST) and forced swim test (FST). ISRIB administration for 2 weeks significantly improved the depression-like behavior in male mice exposed to CRS, which was manifested by markedly increasing the sucrose preference and reducing the immobility time in the FST and TST. However, we observed that exposure to the same dose of ISRIB in CRS female mice only showed improved anhedonia-like deficits,leaving unaltered improvement in the FST and TST. Mechanically, we found that ISRIB reversed the hypothalamic-pituitary-adrenal (HPA) axis hyperactivity, indicating decreased levels of serum corticosterone, reduced hippocampal glucocorticoidreceptor (GR) expression and expression of FosB in hypothalamic paraventricularnucleus (PVN), which was accompanied by preserved hippocampal neurogenesis. The present findings further expand the potential role of ER stress in depression and provide important details for a therapeutic path forward for PERK inhibitors in mood disorders.

Group differences in OXT methylation between patients with Major Depressive Disorder and healthy controls: A pre-registered replication study

Depression is linked to stress which leaves traces in the epigenetic signature of genes. The oxytocin system is implicated in allostatic processes promoting adaption to environmental stressors. Interactions of the oxytocin system with the environment, e.g., methylation of the gene coding for oxytocin (OXT), are candidates for the investigation of the biological underpinnings of depression. Recently, we found hypomethylation of OXT in patients with Major Depressive Disorder (MDD) compared to healthy controls (HC). Since the replicability of findings is a key point of criticism in (epi‑)genetic research, we aimed to confirm our previous findings in a pre-registered study (data was stored in a database prior to pre-registration) within a new sample of n = 85 patients with MDD and n = 85 HC. We investigated OXT DNA-methylation in peripheral blood samples, stressful life events and depression severity. In accordance with our previous study, we found hypomethylation of OXT in patients with MDD compared to HC. Methylation was not associated with stressful life events. Patients reported significantly more stressful life events compared to HC. Our study revealed that hypomethylation of OXT can be demonstrated in a reproducible fashion and provides further evidence for the involvement of the oxytocin system in depression.

Significance of the anterior cingulate cortex in neurogenesis plasticity: Connections, functions, and disorders across postnatal and adult stages

The anterior cingulate cortex (ACC) is a complex and continually evolving brain region that remains a primary focus of research due to its multifaceted functions. Various studies and analyses have significantly advanced our understanding of how the ACC participates in a wide spectrum of memory and cognitive processes. However, despite its strong connections to brain areas associated with hippocampal and olfactory neurogenesis, the functions of the ACC in regulating postnatal and adult neurogenesis in these regions are still insufficiently explored. Investigating the intricate involvement of the ACC in neurogenesis could enhance our comprehension of essential aspects of brain plasticity. This involvement stems from its complex circuitry with other relevant brain regions, thereby exerting both direct and indirect impacts on the neurogenesis process. This review sheds light on the promising significance of the ACC in orchestrating postnatal and adult neurogenesis in conditions related to memory, cognitive behavior, and associated disorders.

A complex relation between levels of adult hippocampal neurogenesis and expression of the immature neuron marker doublecortin

We investigated the mechanisms underlying the effects of the antidepressant fluoxetine on behavior and adult hippocampal neurogenesis (AHN). After confirming our earlier report that the signaling molecule β-arrestin-2 (β-Arr2) is required for the antidepressant-like effects of fluoxetine, we found that the effects of fluoxetine on proliferation of neural progenitors and survival of adult-born granule cells are absent in the β-Arr2 knockout (KO) mice. To our surprise, fluoxetine induced a dramatic upregulation of the number of doublecortin (DCX)-expressing cells in the β-Arr2 KO mice, indicating that this marker can be increased even though AHN is not. We discovered two other conditions where a complex relationship occurs between the number of DCX-expressing cells compared to levels of AHN: a chronic antidepressant model where DCX is upregulated and an inflammation model where DCX is downregulated. We concluded that assessing the number of DCX-expressing cells alone to quantify levels of AHN can be complex and that caution should be applied when label retention techniques are unavailable.

The role of the circadian system in the etiology of depression

Circadian rhythms have evolved in almost all organisms enabling them to anticipate alternating changes in the environment. As a consequence, the circadian clock controls a broad range of bodily functions including appetite, sleep, activity and cortisol levels. The circadian clock synchronizes itself to the external world mainly by environmental light cues and can be disturbed by a variety of factors, including shift-work, jet-lag, stress, ageing and artificial light at night. Interestingly, mood has also been shown to follow a diurnal rhythm. Moreover, circadian disruption has been associated with various mood disorders and patients suffering from depression have irregular biological rhythms in sleep, appetite, activity and cortisol levels suggesting that circadian rhythmicity is crucially involved in the etiology and pathophysiology of depression. The aim of the present review is to give an overview and discuss recent findings in both humans and rodents linking a disturbed circadian rhythm to depression. Understanding the relation between a disturbed circadian rhythm and the etiology of depression may lead to novel therapeutic and preventative strategies.

Perceived antidepressant efficacy associated with reduced negative and enhanced neutral mnemonic discrimination

Introduction

While antidepressants are one of the first-line treatments for depression, the mechanisms underlying antidepressant action are unclear. Furthermore, the extent to which antidepressants impact emotional and cognitive dysfunction in depression requires more fine-grained approaches toward measuring these impacts in humans. Depression is associated with emotion and mood dysregulation in addition to cognitive deficits. Depressed individuals experience general memory impairment as well as a negativity bias in episodic memory, where negative events are better remembered than positive or neutral events. One potential mechanism hypothesized to underlie the negativity bias in memory is dysfunctional hippocampal pattern separation, in which depressed individuals tend to show impaired general pattern separation but enhanced negative pattern separation. Mnemonic discrimination tasks have been designed to tax hippocampal pattern separation in humans and provide a powerful approach to develop a mechanistic account for cognitive dysfunction in depression. While antidepressants have been examined primarily in rodent models in the context of hippocampal pattern separation, this has yet to be examined in humans.

Methods

Here, we investigated how antidepressant usage and their perceived efficacy was associated with emotional mnemonic discrimination, given our prior work indicating a negativity bias for mnemonic discrimination in individuals with greater depressive symptoms.

Results

We found that individuals who reported a greater improvement in their depressive symptoms after taking antidepressants (responders) showed reduced negative and enhanced neutral mnemonic discrimination compared to those with little to no improvement (non-responders). Perceived antidepressant efficacy was the strongest predictor of a reduction in the negativity bias for mnemonic discrimination, even when controlling for current depressive symptoms, antidepressant type, and other relevant factors.

Discussion

These results suggest that antidepressants, when effective, can shift memory dynamics toward healthy function.

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.

Early life adversity shapes neural circuit function during sensitive postnatal developmental periods

Early life adversity (ELA) is a major risk factor for mental illness, but the neurobiological mechanisms by which ELA increases the risk for future psychopathology are still poorly understood. Brain development is particularly malleable during prenatal and early postnatal life, when complex neural circuits are being formed and refined through an interplay of excitatory and inhibitory neural input, synaptogenesis, synaptic pruning, myelination, and neurogenesis. Adversity that influences these processes during sensitive periods of development can thus have long-lasting and pervasive effects on neural circuit maturation. In this review, we will discuss clinical and preclinical evidence for the impact of ELA on neural circuit formation with a focus on the early postnatal period, and how long-lasting impairments in these circuits can affect future behavior. We provide converging evidence from human and animal studies on how ELA alters the functional development of brain regions, neural circuits, and neurotransmitter systems that are crucial for cognition and affective behavior, including the hippocampus, the hypothalamus-pituitary-adrenal (HPA) axis, neural networks of fear responses and cognition, and the serotonin (5-HT) system. We also discuss how gene-by-environment (GxE) interactions can determine individual differences in susceptibility and resilience to ELA, as well as molecular pathways by which ELA regulates neural circuit development, for which we emphasize epigenetic mechanisms. Understanding the molecular and neurobiological mechanisms underlying ELA effects on brain function and psychopathology during early postnatal sensitive periods may have great potential to advance strategies to better treat or prevent psychiatric disorders that have their origin early in life.

Pre-weaning fluoxetine exposure caused anti-depressant like behavior at adulthood via perturbing tryptophan metabolism in rats

The perinatal depression exposes the child to antidepressants during vulnerable window of development, which can chronically impact the mental wellbeing of new born. Active pharmaceuticals are not tested for this long term neurobehavioral aspect of toxicity during drug development process. Keeping this in view, the current study was designed to study the effect of pre-weaning fluoxetine exposure on depression-like behavior of the offspring upon attaining adulthood using FST (Forced swim test). Additionally, the brain tryptophan, 5-HT (5-hydroxytryptamine) and its metabolite 5-HIAA (5-hydroxyindoleacetic acid) levels were quantified using Enzyme linked Immunosorbent Assay (ELISA), while expression of SERT (serotonin receptor), 5-HT1A receptor, TPH (tryptophan hydroxylase) genes were monitored using qPCR. Our data showed that pre-weaning fluoxetine (10, 50 or 100 mg/kg) exposure decreased depression-like behavior. The 5-HT and 5-HIAA levels showed declining trend. However, the 5-HT synthetic precursor i.e. tryptophan levels were found to be significantly elevated in both brain and plasma as compared to control rats. The gene expression study did not reveal any significant alterations as compared to control. In conclusion, the present study demonstrate that pre-weaning fluoxetine exposure decreased depression-like behavior upon adulthood via perturbing tryptophan metabolism.

A Review of Ocular Complications Associated with Medications Used for Anxiety, Depression, and Stress

This review of commonly prescribed psychotropic drugs aims to update the clinician on possible ophthalmic side effects that may include dry eye, diplopia, mydriasis, and cataracts. This review summarizes our current knowledge of known ocular side effects of psychotropic drugs based on reviews, case reports, case-control studies, a case series, and cross-sectional observational studies reported in the recent literature. The review covers disorders related to depression, anxiety, and stress which are commonly encountered within society and can have debilitating impacts on an individual's quality of life that may require chronic therapeutic management. The main medications used in the treatment and management of these conditions typically target receptors, metabolic enzymes, or transport pumps that alter the pre- and/or post-synaptic levels of neurotransmitters such as serotonin, norepinephrine, dopamine, gamma-aminobutyric acid, and opioids to improve mood and/or relieve pain and anxiety. Novel non-therapeutic options are undergoing clinical trials, and some patients may seek alternative therapies or have associated substance abuse issues to alleviate their symptoms. This review summarizes some of the clinical signs of depression and the main therapeutic options and their reported ocular side effects which may be pertinent today given the rise in use of psychotropic medications used to manage depression, anxiety, and stress.

Different depression: motivational anhedonia governs antidepressant efficacy in Huntington's disease

Depression is more common in neurodegenerative diseases such as Huntington's disease than the general population. Antidepressant efficacy is well-established for depression within the general population: a recent meta-analysis showed serotonin norepinephrine reuptake inhibitors, tricyclic antidepressants and mirtazapine outperformed other antidepressants. Despite the severe morbidity, antidepressant choice in Huntington's disease is based on Class IV evidence. We used complementary approaches to determine treatment choice for depression in Huntington's disease: propensity score analyses of antidepressant treatment outcome using the ENROLL-HD data set, and a dissection of the cognitive mechanisms underlying depression in Huntington's disease using a cognitive battery based on the Research Domain Criteria for Depression. Study 1 included ENROLL-HD 5486 gene-positive adult patients started on an antidepressant medication for depression. Our outcome measures were depression (Hospital Anxiety and Depression Scale or Problem Behaviours Assessment 'Depressed Mood' item) at first follow-up (primary outcome) and all follow-ups (secondary outcome). The intervention was antidepressant class. We used Svyglm&Twang in R to perform propensity scoring, using known variables (disease progression, medical comorbidity, psychiatric morbidity, sedatives, number of antidepressants, demographics and antidepressant contraindications) to determine the probability of receiving different antidepressants (propensity score) and then included the propensity score in a model of treatment efficacy. Study 2 recruited 51 gene-positive adult patients and 26 controls from the South Wales Huntington's Disease Management Service. Participants completed a motor assessment, in addition to measures of depression and apathy, followed by tasks measuring consummatory anhedonia, motivational anhedonia, learning from reward and punishment and reaction to negative outcome. We used generalised linear models to determine the association between task performance and depression scores. Study 1 showed selective serotonin reuptake inhibitors outperformed serotonin norepinephrine reuptake inhibitors on the primary outcome (P = 0.048), whilst both selective serotonin reuptake inhibitors (P = 0.00069) and bupropion (P = 0.0045) were superior to serotonin norepinephrine reuptake inhibitors on the secondary outcome. Study 2 demonstrated an association between depression score and effort for reward that was not explained by apathy. No other mechanisms were associated with depression score. We found that selective serotonin reuptake inhibitors and bupropion outperform serotonin norepinephrine reuptake inhibitors at alleviating depression in Huntington's disease. Moreover, motivational anhedonia appears the most significant mechanism underlying depression in Huntington's disease. Bupropion is improves motivational anhedonia and has a synergistic effect with selective serotonin reuptake inhibitors. This work provides the first large-scale, objective evidence to determine treatment choice for depression in Huntington's disease, and provides a model for determining antidepressant efficacy in other neurodegenerative diseases.

A Baldwin interpretation of adult hippocampal neurogenesis: from functional relevance to physiopathology

Hippocampal adult neurogenesis has been associated to many cognitive, emotional, and behavioral functions and dysfunctions, and its status as a selected effect or an "appendix of the brain" has been debated. In this review, we propose to understand hippocampal neurogenesis as the process underlying the "Baldwin effect", a particular situation in evolution where fitness does not rely on the natural selection of genetic traits, but on "ontogenetic adaptation" to a changing environment. This supports the view that a strong distinction between developmental and adult hippocampal neurogenesis is made. We propose that their functions are the constitution and the lifelong adaptation, respectively, of a basic repertoire of cognitive and emotional behaviors. This lifelong adaptation occurs through new forms of binding, i.e., association or dissociation of more basic elements. This distinction further suggests that a difference is made between developmental vulnerability (or resilience), stemming from dysfunctional (or highly functional) developmental hippocampal neurogenesis, and adult vulnerability (or resilience), stemming from dysfunctional (or highly functional) adult hippocampal neurogenesis. According to this hypothesis, developmental and adult vulnerability are distinct risk factors for various mental disorders in adults. This framework suggests new avenues for research on hippocampal neurogenesis and its implication in mental disorders.

Dose-dependent opposite effects of nortriptyline on affective-like behavior in adolescent rats: Comparison with adult rats

Antidepressant drugs elicit different behavioral and neurochemical responses with age. In fact, the use of antidepressants during adolescence is associated with an increased risk of suicidal thinking, being the best pharmacological treatment during this critical period a matter of constant debate in terms of its risk-benefit outcome. In this regard, the present study compared the effects of nortriptyline (3-10 mg/kg, 7 days) on regulating different aspects of affective-like behavior by screening adolescent and adult Sprague-Dawley rats through several consecutive tests (forced-swim, open field, sucrose preference). Brains were later collected to evaluate hippocampal neurogenesis and mBDNF protein content as potential molecular correlates of the observed behavioral responses. The main results in adolescent rats showed that nortriptyline induced dose-dependent opposite effects: while 3 mg/kg decreased immobility and increased mBDNF (indicative of an antidepressant-like response), 10 mg/kg decreased exploratory time in the open field and mBDNF (suggestive of an anxiogenic-like response). These effects were not associated with changes in neurogenesis regulation. In adult rats, nortriptyline failed to modulate affective-like behavior or the neuroplasticity markers evaluated at the doses tested. In conclusion, clear behavioral and neurochemical differences were observed between adolescent and adult rats in response to nortriptyline treatment. Interestingly, while nortriptyline displayed an antidepressant-like potential at the lowest dose examined in adolescence, a higher dose shifted these results towards a negative outcome, thus reinforcing the need to extreme caution when considering this treatment for our younger population.

Cell Cycle Regulation of Hippocampal Progenitor Cells in Experimental Models of Depression and after Treatment with Fluoxetine

Changes in adult hippocampal cell proliferation and genesis have been largely implicated in depression and antidepressant action, though surprisingly, the underlying cell cycle mechanisms are largely undisclosed. Using both an in vivo unpredictable chronic mild stress (uCMS) rat model of depression and in vitro rat hippocampal-derived neurosphere culture approaches, we aimed to unravel the cell cycle mechanisms regulating hippocampal cell proliferation and genesis in depression and after antidepressant treatment. We show that the hippocampal dentate gyrus (hDG) of uCMS animals have less proliferating cells and a decreased proportion of cells in the G2/M phase, suggesting a G1 phase arrest; this is accompanied by decreased levels of cyclin D1, E, and A expression. Chronic fluoxetine treatment reversed the G1 phase arrest and promoted an up-regulation of cyclin E. In vitro, dexamethasone (DEX) decreased cell proliferation, whereas the administration of serotonin (5-HT) reversed it. DEX also induced a G1-phase arrest and decreased cyclin D1 and D2 expression levels while increasing p27. Additionally, 5-HT treatment could partly reverse the G1-phase arrest and restored cyclin D1 expression. We suggest that the anti-proliferative actions of chronic stress in the hDG result from a glucocorticoid-mediated G1-phase arrest in the progenitor cells that is partly mediated by decreased cyclin D1 expression which may be overcome by antidepressant treatment.

Reviving through human hippocampal newborn neurons

Recent contradictory data has renewed discussion regarding the existence of adult hippocampal neurogenesis (AHN) in humans, i.e., the continued production of new neurons in the brain after birth. The present review revisits the debate of AHN in humans from a historical point of view in the face of contradictory evidence, analyzing the methods employed to investigate this phenomenon. Thus, to date, of the 57 studies performed in humans that we reviewed, 84% (48) concluded in favor of the presence of newborn neurons in the human adult hippocampus. Besides quality of the tissue (such as postmortem intervals below 26hours as well as tissue conservation and fixation), considerations for assessing and quantify AHN in the human brain require the use of stereology and toxicological analyses of clinical data of the patient.

WS6 Induces Adult Hippocampal Neurogenesis in Correlation to its Antidepressant Effect on the Alleviation of Depressive-like Behaviors of Rats

Major depressive disorder (MDD) is one of the most common psychiatric disorders. However, the effective drugs for MDD have not yet been developed. WS6 is originally designed with a similar structure as Resveratrol and Pterostilbene. The present study aims to investigate the neuroprotective and ameliorating effects of WS6 treatment in a rat model of chronic unpredictable mild stress (CUMS) induced depression. The results show that CUMS is effective in producing depressive-like behavior in rats as indicated by decreased responses in the locomotor activity, sucrose preference test and increased immobility time. However, WS6 treatment significantly ameliorated these behavioral alterations associated with CUMS-induced depression. Moreover, the reduction in neurogenesis, GABAergic neurons, dendrite complexity, spine density and synaptic plasticity-associate protein 95 (PSD95) by CUMS can be reversed by treatment with WS6. Taken together, this study highlights the neuroprotective and antidepressant-like effects of WS6 against CUMS-induced depression, and suggest a possible mechanism for this protection via changes in neurogenesis within the hippocampus. These finding reveal the therapeutic protection of WS6 for use in clinical trials in the treatment of neuronal deterioration in MDD.

Stress-Associated Molecular and Cellular Hippocampal Mechanisms Common for Epilepsy and Comorbid Depressive Disorders

The review discusses molecular and cellular mechanisms common to the temporal lobe epileptogenesis/epilepsy and depressive disorders. Comorbid temporal lobe epilepsy and depression are associated with dysfunction of the hypothalamic-pituitary-adrenocortical axis. Excessive glucocorticoids disrupt the function and impair the structure of the hippocampus, a brain region key to learning, memory, and emotions. Selective vulnerability of the hippocampus to stress, mediated by the reception of glucocorticoid hormones secreted during stress, is the price of the high functional plasticity and pleiotropy of this limbic structure. Common molecular and cellular mechanisms include the dysfunction of glucocorticoid receptors, neurotransmitters, and neurotrophic factors, development of neuroinflammation, leading to neurodegeneration and loss of hippocampal neurons, as well as disturbances in neurogenesis in the subgranular neurogenic niche and formation of aberrant neural networks. These glucocorticoid-dependent processes underlie altered stress response and the development of chronic stress-induced comorbid pathologies, in particular, temporal lobe epilepsy and depressive disorders.

Association between lifetime depression history, hippocampal volume and memory in non-amnestic mild cognitive impairment

Hippocampal subfield volume loss in older adults with amnestic mild cognitive impairment (aMCI) and depression history are associated with amyloid beta and tau pathology, thereby increasing the risk for Alzheimer's disease (AD). However, no studies have exclusively examined distinct alterations in hippocampal subfields in non-amnestic MCI (naMCI) in relation to depression history. Here, we used both longitudinal and transverse hippocampal segmentation methods using the automated FreeSurfer software to examine whether a lifetime depression history is associated with differences in hippocampal head/body/tail (H/B/T) and key subfield volumes (CA1, subiculum, dentate gyrus) in older adults with naMCI. Further, we explored whether differences in hippocampal H/B/T and subfield volumes were associated with structured and unstructured verbal encoding and retention, comparing those with and without a depression history. The naMCI with a depression history group demonstrated larger or relatively preserved right CA1 volumes, which were associated with better unstructured verbal encoding and as well as structured verbal memory retention. This association between memory encoding and hippocampal CA1 and total head volume was significantly different to those with no depression history. The relationship between right CA1 volume and memory retention was also moderated by depression history status F (5,143) = 7.84, p < 0.001, R²  = 0.22. Those participants taking antidepressants had significantly larger hippocampal subiculum (p = 0.008), and right hippocampal body (p = 0.004) and better performance on structured encoding (p = 0.011) and unstructured memory retention (p = 0.009). These findings highlight the importance of lifetime depression history and antidepressant use on the hippocampus and encoding and memory retention in naMCI.

Involvement of dopamine D2 and glutamate NMDA receptors in the antidepressant-like effect of amantadine in mice

The present study investigated the pharmacological mechanisms of the antidepressant-like effects of amantadine in mice and their influence on hippocampal neurogenesis. To improve the translational validity of preclinical results, reproducibility across laboratories and replication in other animal models and species are crucial. Single amantadine administration at doses of 50 and 75 mg/kg resulted in antidepressant-like effects in mice in the tail suspension test (TST), reflected by an increase in immobility time. The effects of amantadine were seen at doses that did not alter locomotor activity. The tyrosine hydroxylase inhibitor α-methyl-ρ-tyrosine did not influence the anti-immobility effect of amantadine in the TST. Pretreatment with the α₁ adrenergic receptor antagonist prazosin, β adrenergic receptor antagonist propranolol, α₂ adrenergic receptor antagonist yohimbine, and α₂ adrenergic receptor agonist clonidine did not alter the antidepressant-like effect of amantadine. However, amantadine's effect was blocked by the dopamine D₂ receptor antagonist haloperidol and glutamate receptor agonist N-methyl-D-aspartate (NMDA). Repeated amantadine administration (50 mg/kg) also exerted an antidepressant-like effect, paralleled by an increase in hippocampal neurogenesis. The present results demonstrate that the antidepressant-like effects of amantadine may be mediated by its actions on D₂ and NMDA receptors and likely involve hippocampal neurogenesis.

Do changes in microglial status underlie neurogenesis impairments and depressive-like behaviours induced by psychological stress? A systematic review in animal models

Stress may have a negative effect on mental health and is the primary environmental risk factor in the aetiology of depression. Nevertheless, the neurobiological mechanisms underlying this mood disorder remain poorly characterized. The hippocampus is a target structure of the adverse effects of stress, and hippocampal neurogenesis plays a crucial role. However, we do not know the mechanisms by which stress impacts neurogenesis. Recent studies indicate that changes in neuroinflammation, primarily via microglial cells, may play an essential role in this process. However, the relationship between stress, microglial changes, and alterations in neurogenesis and their involvement in the development of depression is poorly characterized. For this reason, this systematic review aims to synthesise and evaluate current studies that have investigated the relationship between these variables. Taken together, the revised data, although not entirely conclusive, seem to suggest that microglial changes induced by psychological stress regulate neurogenesis and in turn may be responsible for the development of depressive-like behaviours, but other factors that influence these stressful experiences should not be dismissed.

Assessment of Paroxetine Molecular Interactions with Selected Monoamine and γ-Aminobutyric Acid Transporters

Thus far, many hypotheses have been proposed explaining the cause of depression. Among the most popular of these are: monoamine, neurogenesis, neurobiology, inflammation and stress hypotheses. Many studies have proven that neurogenesis in the brains of adult mammals occurs throughout life. The generation of new neurons persists throughout adulthood in the mammalian brain due to the proliferation and differentiation of adult neural stem cells. For this reason, the search for drugs acting in this mechanism seems to be a priority for modern pharmacotherapy. Paroxetine is one of the most commonly used antidepressants. However, the exact mechanism of its action is not fully understood. The fact that the therapeutic effect after the administration of paroxetine occurs after a few weeks, even if the levels of monoamine are rapidly increased (within a few minutes), allows us to assume a neurogenic mechanism of action. Due to the confirmed dependence of depression on serotonin, norepinephrine, dopamine and γ-aminobutyric acid levels, studies have been undertaken into paroxetine interactions with these primary neurotransmitters using in silico and in vitro methods. We confirmed that paroxetine interacts most strongly with monoamine transporters and shows some interaction with γ-aminobutyric acid transporters. However, studies of the potency inhibitors and binding affinity values indicate that the neurogenic mechanism of paroxetine's action may be determined mainly by its interactions with serotonin transporters.

Chronic central modulation of LPA/LPA receptors-signaling pathway in the mouse brain regulates cognition, emotion, and hippocampal neurogenesis

Several studies have demonstrated that lysophosphatidic acid (LPA) acts through its LPA receptors in multiple biological and behavioral processes, including adult hippocampal neurogenesis, hippocampal-dependent memory, and emotional regulation. However, analyses of the effects have typically involved acute treatments, and there is no information available regarding the effect of the chronic pharmacological modulation of the LPA/LPA receptors-signaling pathway. Thus, we analyzed the effect of the chronic (21 days) and continuous intracerebroventricular (ICV) infusion of C18:1 LPA and the LPA1-3 receptor antagonist Ki16425 in behavior and adult hippocampal neurogenesis. Twenty-one days after continuous ICV infusions, mouse behaviors in the open field test, Y-maze test and forced swimming test were assessed. In addition, the hippocampus was examined for c-Fos expression and α-CaMKII and phospho-α-CaMKII levels. The current study demonstrates that chronic C18:1 LPA produced antidepressant effects, improved spatial working memory, and enhanced adult hippocampal neurogenesis. In contrast, chronic LPA1-3 receptor antagonism disrupted exploratory activity and spatial working memory, induced anxiety and depression-like behaviors and produced an impairment of hippocampal neurogenesis. While these effects were accompanied by an increase in neuronal activation in the DG of C18:1 LPA-treated mice, Ki16425-treated mice showed reduced neuronal activation in CA3 and CA1 hippocampal subfields. Treatment with the antagonist also induced an imbalance in the expression of basal/activated α-CaMKII protein forms. These outcomes indicate that the chronic central modulation of the LPA receptors-signaling pathway in the brain regulates cognition and emotion, likely comprising hippocampal-dependent mechanisms. The use of pharmacological modulation of this pathway in the brain may potentially be targeted for the treatment of several neuropsychiatric conditions.

Adult Hippocampal Neurogenesis and Alzheimer's Disease: Novel Application of Mesenchymal Stem Cells and their Role in Hippocampal Neurogenesis

The neurogenesis can occur in two regions of the adult mammalian brain throughout the lifespan: the subgranular zone of the hippocampal dentate gyrus, and the subventricular zone of the lateral ventricle. The proliferation and maturation of neural progenitor cells are tightly regulated through intrinsic and extrinsic factors. The integration of maturated cells into the circuitry of the adult hippocampus emphasizes the importance of adult hippocampal neurogenesis in learning and memory. There is a large body of evidence demonstrating that alteration in the neurogenesis process in the adult hippocampus results in an early event in the course of Alzheimer's disease (AD). In AD condition, the number and maturation of neurons declines progressively in the hippocampus. Innovative therapies are required to modulate brain homeostasis. Mesenchymal stem cells (MSCs) hold an immense potential to regulate the neurogenesis process, and are currently tested in some brain-related disorders, such as AD. Therefore, the aim of this review is to discuss the use of MSCs to regulate endogenous adult neurogenesis and their significant impact on future strategies for the treatment of AD.

Protocol for systematic review and meta-analysis of the evidence linking hippocampal neurogenesis to the effects of antidepressants on mood and behaviour

OBJECTIVE

Studies in rodents associated the deficits of adult hippocampal neurogenesis with behavioural anomalies which may be reversed by antidepressant treatments. A previous systematic review (SR) and meta-analysis (MA) indicated a hierarchy within the proneurogenic effects of different antidepressants in naive rodents. The present review aims to evaluate a more comprehensive sample of studies investigating the links between the effects of different antidepressants and adult hippocampal neurogenesis.

SEARCH STRATEGY SCREENING ANNOTATION DATA MANAGEMENT

Protocols were planned following Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols guidelines. Searches in Embase, Medline, Scopus and Web of Science followed by screening with inclusion/exclusion criteria will provide relevant publications. First SR will summarise the effects of antidepressants on adult hippocampal neurogenesis on different laboratory rodents. Second SR will summarise the correlations between neurogenic and behavioural effects of antidepressants while the third will focus on cause-effect relationships between them. If feasible, data will be analysed by pairwise or network random-effect or multivariate MA to determine the direction, magnitude, significance and heterogeneity (I2) of the estimated effect sizes on global or subgroup levels. Funnel plotting, Egger regression, 'trim and fill' will be used to estimate the risk of publication bias. Quality assessment of the included publications will be performed by applying adapted CAMARADES, Syrcles' risk of bias or CINeMA tools.

REPORTING

Find a preliminary version of this protocol at the Open Science Framework (https://osf.io/gmsvd/). Data extraction has already started. Results shall be published in a peer-reviewed journal. Due to the continuous production in the field, the implementation of a 'living SR' is intended.

Benefits of animal models to understand the pathophysiology of depressive disorders

Major depressive disorder (MDD) is a potentially life-threatening mental disorder imposing severe social and economic burden worldwide. Despite the existence of effective antidepressant treatment strategies the exact pathophysiology of the disease is still unknown. Large number of animal models of MDD have been developed over the years, but all of them suffer from significant shortcomings. Despite their limitations these models have been extensively used in academic research and drug development. The aim of this review is to highlight the benefits of animal models of MDD. We focus here on recent experimental data where animal models were used to examine current theories of this complex disease. We argue, that despite their evident imperfections, these models provide invaluable help to understand cellular and molecular mechanisms contributing to the development of MDD. Furthermore, animal models are utilized in research to find clinically useful biomarkers. We discuss recent neuroimaging and microRNA studies since these investigations yielded promising candidates for biomarkers. Finally, we briefly summarize recent progresses in drug development, i.e. the FDA approval of two novel antidepressant drugs: S-ketamine and brexanolone (allopregnanolone). Deeper understanding of the exact molecular and cellular mechanisms of action responsible for the antidepressant efficacy of these rapid acting drugs could aid us to design further compounds with similar effectiveness, but less side effects. Animal studies are likely to provide valuable help in this endeavor.

β2 and α2 adrenergic receptors mediate the proneurogenic in vitro effects of norquetiapine

Positive modulation of adult hippocampal neurogenesis may contribute to the therapeutic effects of clinically relevant antidepressant drugs, including atypical antipsychotics. Quetiapine, an antipsychotic which represents a therapeutic option in patients who are resistant to classical antidepressants, promotes adult hippocampal neurogenesis in preclinical studies. Norquetiapine, the key active metabolite of quetiapine in humans, has a distinctive receptor profile than the parent compound. The drug is indeed a high affinity norepinephrine transporter inhibitor and such activity has been proposed to contribute to its antidepressant effect. At present, no information is available on the effects of norquetiapine on adult neurogenesis. We extensively investigated the activity of quetiapine and norquetiapine on adult murine neural stem/progenitor cells and their progeny. Additionally, selective antagonists for β₂/α₂ adrenergic receptors allowed us to evaluate if these receptors could mediate quetiapine and norquetiapine effects. We demonstrated that both drugs elicit in vitro proneurogenic effects but also that norquetiapine had distinctive properties which may depend on its ability to inhibit norepinephrine transporter and involve β₂/α₂ adrenergic receptors. Animal care and experimental procedures were approved by the Institutional Animal Care and Use Committees (IACUC) at University of Piemonte Orientale, Italy (approval No. 1033/2015PR) on September 29, 2015.

Long-Term Effect of Post-traumatic Stress in Adolescence on Dendrite Development and H3K9me2/BDNF Expression in Male Rat Hippocampus and Prefrontal Cortex

Exposure to a harsh environment in early life increases in the risk of post-traumatic stress disorder (PTSD) of an individual. Brain derived neurotrophic factor (BDNF) plays an important role in neurodevelopment in developmental stages. Both chronic and traumatic stresses induce a decrease in the level of BDNF and reduce neural plasticity, which is linked to the pathogenesis of PTSD. Also, studies have shown that stress alters the epigenetic marker H3K9me2, which can bind to the promoter region of the Bdnf gene and reduce BDNF protein level. However, the long-term effects of traumatic stress during adolescence on H3K9me2, BDNF expression and dendrite development are not well-known. The present study established a model of PTSD in adolescent rats using an inescapable foot shock (IFS) procedure. Anxiety-like behaviors, social interaction behavior and memory function were assessed by the open field test, elevated plus maze test, three-chamber sociability test and Morris water maze test. In addition, neuronal development and H3K9me2/BDNF expression in hippocampus (HIP) and prefrontal cortex (PFC) were evaluated by Golgi staining, western blotting, qRT-PCR analysis and CHIP-qPCR analysis. Additionally, the Unc0642, a small molecule inhibitor of histone methyltransferase (EHMT2) was used for intervention. The results showed that the IFS procedure induced the PTSD-like behaviors in rats, resulted in fewer dendrite branches and shorter dendrite length in CA1 of HIP and PFC, increased H3K9me2 level and decreased BDNF expression in HIP and PFC. Also, although all the changes can persist to adulthood, Unc0642 administration relieved most of alterations. Our study suggests that traumatic stress in adolescence leads to immediate and long-term mental disorders, neuronal morphological changes, lower BDNF level and increased H3K9me2 level in the HIP and PFC, indicating that H3K9me2/BDNF dysfunction plays a key role in pathogenesis of PTSD.