Animal models of major depression: drawbacks and challenges

Exploring the contribution of the dopaminergic and noradrenergic systems in the antidepressant-like action of 1-(2-(4-(4-ethylphenyl)-1H-1,2,3-triazol-1-yl)phenyl)ethanone in mice

1-(2-(4-(4-ethylphenyl)-1H-1,2,3-triazol-1-yl)phenyl)ethanone (ETAP) is a novel hybrid compound containing 1,2,3-triazole and acetophenone. It exhibits antidepressant-like effects in male mice, linked to modulation of serotonergic receptors and monoamine oxidase A (MAO-A) inhibition. This study aimed to evaluate the involvement of the dopaminergic and noradrenergic systems, as well as MAO-B activity inhibition, in the antidepressant-like effect of ETAP in male mice, and to evaluate the antidepressant-like effect of ETAP in female mice. Male mice were treated with different dopaminergic and noradrenergic receptors antagonists 15 min before administering ETAP (1 mg/kg, intragastrically, i.g.). The tail suspension test (TST) was performed 30 minutes later. Different male mice were treated with ETAP (1 mg/kg, i.g.), and 30 minutes later, were euthanized to assess MAO-B activity in the prefrontal cortex and hippocampus. To evaluate the antidepressant-like of ETAP in female mice, ETAP (1 mg/kg, i.g.) was administered, followed by the TST and the forced swimming test (FST) 30 minutes later. The dopaminergic antagonists haloperidol (0.05 mg/kg, intraperitoneally, i.p.), SCH23390 (0.01 mg/kg, subcutaneously, s.c.), and sulpiride (50 mg/kg, i.p.), as well the noradrenergic antagonists prazosin (1 mg/kg, i.p.), yohimbine (1 mg/kg, i.p.), and propranolol (2 mg/kg, i.p.), prevented the antidepressant-like effect of ETAP in the TST. MAO-B activity was unaffected by ETAP in both the prefrontal cortex and hippocampus. ETAP (1 mg/kg, i.g.) induced a significant antidepressant-like effect in female mice in the TST and FST. These findings provide valuable insights into the antidepressant-like effect of ETAP, highlighting its potential for developing more effective depression treatments.

Ashwagandha (Withania somnifera (L.) dunal) root extract containing withanolide a alleviates depression-like behavior in mice by enhancing the brain-derived neurotrophic factor pathway under unexpected chronic mild stress

ETHNOPHARMACOLOGICAL RELEVANCE

Ashwagandha (Withania somnifera (L.) Dunal) root or whole-plant extracts are used to treat anxiety, insomnia, and other nervous system disturbances.

AIM OF THE STUDY

We evaluated the neuroprotective and antidepressant effects of ashwagandha root extract (ARE) on corticosterone-exposed HT-22 cells and unpredictable chronic mild stress (UCMS)-challenged mice.

MATERIALS AND METHODS

The neuroprotective properties of ARE containing withanolide A were assessed in HT-22 cells subjected to corticosterone-induced oxidative stress. Additionally, the effects of ARE on depression-like behavior, stress-related hormones, and inflammatory cytokine levels were evaluated in a mouse model of UCMS.

RESULTS

In HT-22 cells, ARE (100 and 200 μg/mL) and its constituent, withanolide A (1.56 and 3.12 μg/mL), mitigated corticosterone-induced increases in MAO activity, ROS, and MDA levels. Treatment also reversed corticosterone-induced reductions in BDNF, TrkB, p-AKT, p-ERK, and p-CREB and normalized Nrf2 and Keap1 levels, thereby elevating HO-1 expression. In UCMS mice, ARE improved behavioral outcomes, increased sucrose preference, and reduced immobility in the forced swimming test while enhancing activity in the open field test and elevated plus maze. ARE decreased the levels of stress hormones (corticotropin-releasing hormone, adrenocorticotropic hormone, and corticosterone) and increased the levels of neurotransmitters (L-DOPA, 5-HTP, and serotonin). Histological analysis revealed that ARE reduced hippocampal cell loss. Additionally, ARE (60 and 100 mg/kg) restored decreased levels of p-AKT, p-ERK, and p-CREB and lowered inflammation-related proteins (Cox2, iNOS, IL-6, IL-1β, TNF-α).

CONCLUSION

These results indicate that ARE containing withanolide A exhibits notable neuroprotective and antidepressant properties.

Microglial-Biomimetic Memantine-Loaded Polydopamine Nanomedicines for Alleviating Depression

Depression is a common psychiatric disorder, and monoamine-based antidepressants as first-line therapy remain ineffective in some patients. The synergistic modulation of neuroinflammation and neuroplasticity could be a major strategy for treating depression. In this study, an inflammation-targeted microglial biomimetic system, PDA-Mem@M, is reported for treating depression. Microglial membrane-coated nanoparticles penetrate the blood-brain barrier and facilitate microglial targeting. Subsequently, owing to the excellent free radical-scavenging capacity, PDA-Mem@M attenuate the brain inflammatory microenvironment. After on-demand release from the nanoparticles, memantine increases the expression of brain-derived neurotrophic factors and reverses the loss of synaptic dendritic spines. Further, in vivo studies demonstrate that PDA-Mem@M effectively alleviate depression-like behaviors to a greater extent than memantine or polydopamine nanoparticles (PDA) monotherapy. This synergistic strategy, with satisfactory biosafety and strong anti-inflammatory and synaptic plasticity restoration effects, is conducive to advances in depression therapy.

Seltorexant for major depressive disorder

INTRODUCTION

Preclinical and clinical pharmacologic evidence indicates that orexin systems are relevant to sleep-wake cycle regulation and dimensions of reward and cognition, providing the basis for hypothesizing that they may be effective as therapeutics in mental disorders. Due to the limited efficacy and tolerability profiles of existing treatments for Major Depressive Disorder (MDD), investigational compounds in novel treatment classes are needed; seltorexant, an orexin receptor antagonist, is a potential new treatment currently under investigation.

AREAS COVERED

Mechanisms implicated in MDD, including reward and sleep, are first overviewed. Then, the safety, tolerability, and efficacy profiles of seltorexant and the wider context of orexin receptor antagonism for depression are discussed in focus. Preclinical and clinical data are also discussed. PubMed, Medline, Cochrane Library, Embase, Scopus, and Web of Science were systematically searched from inception to 10 October 2024, in accordance with PRISMA guidelines.

EXPERT OPINION

Early clinical evidence suggests that seltorexant is effective in treating MDD, both in individuals diagnosed with insomnia and those not, although greater antidepressant effects are observed in individuals with severe sleep disturbance. Results from large phase III clinical trials are needed to confirm efficacy and safety.

Investigating amygdala nuclei volumes in military personnel with post-traumatic stress disorder, major depressive disorder, and adjustment disorder: A retrospective cross-sectional study using clinical routine data

BACKGROUND

Post-traumatic Stress Disorder (PTSD), Major Depressive Disorder (MDD), and Adjustment Disorder (AdjD) are highly prevalent among military personnel, often presenting diagnostic challenges due to overlapping symptoms and reliance on self-reporting. The amygdala, particularly the basolateral complex involved in fear-related memory formation and extinction recall, plays a crucial role in emotional processing. Abnormalities in these amygdala nuclei are implicated in PTSD and may distinguish it from other disorders like MDD and AdjD, where these mechanisms are less central. Investigating structural differences in specific amygdala nuclei could enhance diagnostic precision and inform targeted interventions.

GOAL

This study aimed to explore volumetric differences in amygdala nuclei among patients with PTSD, MDD, comorbid PTSD and MDD (PTSD+MDD), and AdjD using routine clinical MRI data. We hypothesized that patients with PTSD would exhibit distinct amygdala nuclei volumes compared to those with MDD or AdjD. Additionally, we examined the influence of symptom duration, prior medication, and psychotherapeutic experience on amygdala volumes.

METHODS

We conducted a retrospective cross-sectional study with 185 military personnel (162 men, 23 women) diagnosed with PTSD (n = 50), MDD (n = 70), PTSD+MDD (n = 38), and AdjD (n = 27). High-resolution T1-weighted MRI scans were obtained using a 3T Siemens Skyra scanner. Amygdala subfields were automatically segmented and volumetrized using FreeSurfer software. Analysis of covariance (ANCOVA) models compared amygdala nuclei volumes across diagnostic groups, controlling for estimated total intracranial volume (eTIV), age, and gender. Exploratory analyses included symptom duration, medication use, and prior psychotherapy as additional covariates. Sensitivity analyses further examined the impact of depressive episode type (first vs. recurrent), severity (mild, moderate, severe), and AdjD symptom duration.

RESULTS

The main analyses revealed no significant differences in the volumes of the basolateral and medial amygdala nuclei among the PTSD, MDD, PTSD+MDD, and AdjD groups. Exploratory analyses did not identify significant associations between amygdala volumes and symptom duration, medication use, or prior psychotherapy. Sensitivity analyses also showed no significant volumetric differences related to depressive episode type, severity, or AdjD symptom duration.

CONCLUSION

Our findings suggest that, within this military population, amygdala nuclei volumes measured using routine clinical MRI data do not significantly differ among patients with PTSD, MDD, PTSD+MDD, and AdjD. This indicates that structural amygdala volumetry alone may not suffice to distinguish between these stress-related disorders in clinical settings. The study highlights the complexity of diagnosing overlapping mental health conditions and underscores the need for comprehensive approaches that integrate neuroimaging with clinical assessments. Future research should include healthy control groups, consider additional brain regions and functional connectivity, and employ longitudinal designs to better understand the temporal dynamics of amygdala changes and their relation to symptomatology.

Depression unveiled: Insights into etiology and animal models for behavioral assessment, exploring the multifactorial nature and treatment of depression

Over the past century, significant shifts in daily living have led to an increased prevalence of mental disorders, often linked to hormonal imbalances. Among these, anxiety and depression stand out as prevalent diagnoses, particularly in industrialized nations. Depression, according to the DSM-5, is a heterogeneous condition that affects emotional, cognitive, and physical functioning, with symptoms including insomnia, sexual dysfunction, and weight changes. Cognitive theories of depression highlight its impact on judgment, decision-making, thinking, and focus. Depression's multifaceted nature means that no two patients experience identical symptoms, risk factors, or treatment responses. The COVID-19 pandemic has exacerbated mental health issues, with social isolation, restricted contact, and altered daily routines contributing to increased anxiety and depression, especially among adolescents and young adults. The pandemic's psychological toll underscores the need for effective treatment strategies for mental disorders. The physical manifestations of major depressive disorder (MDD) are associated with a heightened risk of developing various medical conditions, including metabolic disorders, cardiovascular disease, stroke, epilepsy, and dementia. This review provides a comprehensive exploration of depression and anxiety, covering their different types, epidemiology, potential causes, diagnostic criteria, and available treatment options. It delves into the role of pharmacological interventions and examines recent advancements to enhance therapeutic outcomes. Additionally, the review assesses the therapeutic potential of drugs, offering insights into their efficacy in treating these complex mental health disorders. By targeting the multifactorial etiology of depression through drug repurposing and new drug development, researchers aim to enhance treatment efficacy and achieve better outcomes for patients with depression.

Early psilocybin intervention alleviates behavioral despair and cognitive impairment in stressed Wistar rats

Chronic stress exerts profound effects on mental health, contributing to disorders such as depression, anxiety, and cognitive impairment. This study examines the potential of psilocybin to alleviate behavioral despair and cognitive deficits in a rodent model of chronic stress, focusing on the interplay between the Hypothalamic-Pituitary-Adrenal (HPA) axis and the Endocannabinoid System (ECS). Twenty-two male Wistar rats were divided into control and stress groups. Animals within the stress group were exposed to predator odor and chronic social instability to induce chronic stress, and were either sham treated, or given psilocybin. Behavioral assessments were conducted using the Open Field Test, Sucrose Preference Test, Novel Object Recognition, Elevated Plus Maze, and Forced Swimming Test to evaluate locomotion, anhedonia, memory, anxiety, and behavioral despair, respectively. Blood and brain samples were analyzed for biochemical markers. Results indicated that psilocybin significantly reduced stress-induced behavioral despair and cognitive impairments, likely through ECS-mediated downregulation of the HPA axis. These findings suggest that early intervention with psilocybin has sustained beneficial effects on stress-related behavioral and cognitive disturbances, underscoring its potential as a novel therapeutic approach for stress-related mental health disorders.

Lipopolysaccharide preconditioning disrupts the behavioral and molecular response to restraint stress in male mice

Major depressive disorder (MDD) is a complex neuropsychiatric disorder potentially influenced by factors such as stress and inflammation. Chronic stress can lead to maladaptive brain changes that may trigger immune hyperactivation, contributing to MDD's pathogenesis. While the involvement of inflammation in MDD is well established, the effects of inflammatory preconditioning in animals subsequently exposed to chronic stress remain unclear. This study aimed to investigate the impact of inflammatory preconditioning on behavioral, biochemical, and molecular changes in adult male Swiss mice subjected to chronic restraint stress (CRS). The mice received a single injection of lipopolysaccharide (LPS) 24 h before thefirst CRS and performed 6 h daily for 28 days. Behavioral tests were conducted 24 h after the last CRS, across 4 days, and euthanasia followed 24 h after the final tests. Results indicated that only the LPS + CRS group exhibited depressive- and anxiety-like behaviors, accompanied by demotivation and apathy. Biochemical and molecular analyses revealed anoxidative imbalance in the hippocampus, marked by elevated H2O2 levels and MPO activity. In the prefrontal cortex, theLPS + CRS group demonstrated a central inflammatory imbalance, with reduced IL-10 levels, increased Iba1 gene expression, and decreased Gfap and Bdnf gene expression. A trend toward elevated IL-17 levels was also observed at the peripheral level. These findings indicate that inflammatory preconditioning contributes significantly to behaviors phenotypically associated with MDD. Furthermore, the study suggests that these behavioral changes are linked to a dysfunctional immune response and impaired neuroplasticity.

Secure attachment to caregiver prevents adult depressive symptoms in a sex-dependent manner: A translational study

Although clinically relevant, evidence for a protective effect of early secure attachment against the development of depressive symptoms in adulthood is still inconsistent. This study used a translational approach to overcome this limitation. The analysis of a non-clinical adult population revealed a moderating effect of secure attachment on depressive symptoms in women only. Thus, we tested the causal link between early attachment with caregiver and adult depressive-like phenotypes in a mouse model of early adversities that is especially effective in females. Repeated cross fostering (RCF) in the first postnatal days prevented the development of pups' secure attachment with the caregiver as tested in a rodent version of the "strange situation"-the standard human test-induced depressive-like behaviors and altered activity of the ventral tegmental area dopamine neurons in adulthood. Finally, a stable alternative caregiver during the RCF experience prevented all these effects, modeling human "earned attachment."

Dynamic human gut microbiome and immune shifts during an immersive psychosocial intervention program

BACKGROUND

Although depression is a leading cause of disability worldwide, the pathophysiological mechanisms underlying this disorder-particularly those involving the gut microbiome-are poorly understood.

METHOD

To investigate, we conducted a community-based observational study to explore complex associations between changes in the gut microbiome, cytokine levels, and depression symptoms in 52 participants (Mage = 49.56, SD = 13.31) receiving an immersive psychosocial intervention. A total of 142 multi-omics samples were collected from participants before, during, and three months after the nine-day inquiry-based stress reduction program.

RESULTS

Results revealed that depression was associated with both an increased presence of putatively pathogenic bacteria and reduced microbial beta-diversity. Following the intervention, we observed reductions in neuroinflammatory cytokines and improvements in several mental health indicators. Interestingly, participants with a Prevotella-dominant microbiome showed milder symptoms when depressed, along with a more resilient microbiome and more favorable inflammatory cytokine profile, including reduced levels of CXCL-1.

CONCLUSIONS

These findings reveal a potentially protective link between the Prevotella-dominant microbiome and depression, as evidenced by a reduced pro-inflammatory environment and fewer depressive symptoms. These insights, coupled with observed improvements in neuroinflammatory markers and mental health from the intervention, may highlight potential avenues for microbiome-targeted therapies for managing depression.

Depression like-behavior and memory loss induced by methylglyoxal is associated with tryptophan depletion and oxidative stress: a new in vivo model of neurodegeneration

BACKGROUND

Depression and memory loss are prevalent neurodegenerative disorders, with diabetic patients facing an elevated risk of brain dysfunction. Methylglyoxal (MGO) formation, which is heightened in diabetes owing to hyperglycemia and gut dysbiosis, may serve as a critical link between diabetes and brain diseases. Despite the high prevalence of MGO, the precise mechanisms underlying MGO-induced depression and memory loss remain unclear.

RESULTS

We investigated the effect of MGO stress on depression like-behavior and memory loss to elucidate the potential interplay between MGO-induced tryptophan (Trp) metabolism impairment and oxidative stress in the brain. It demonstrates that MGO induces depression-like behavior in mice, as confirmed by the OFT, TST, FST, SPT, and EPM behavioral tests. MGO led to the depletion of Trp and related neurotransmitters as 5-HT, EPI, and DA in the mouse brain. Additionally, MGO reduced the cell count in the DG, CA1, and CA3 hippocampal regions and modulated TPH2 levels in the brain. Notably, co-treatment with MGO and Trp mirrored the effects observed after Trp-null treatment in neurons, including reduced TPH1 and TPH2 levels and inhibition of neuronal outgrowth. Furthermore, MGO significantly altered the expression of key proteins associated with neurodegeneration, such as p-Tau, p-GSK-3β, APP, oAβ, BDNF, NGF, and p-TrkB. Concurrently, MGO activated MAPKs through ROS induction, triggering a redox imbalance by downregulating Nrf-2, Ho-1, TXNRD1, Trx, Sirt-3, and Sirt-5 expression levels, NAD+, and CAT activity in the mouse brain. This led to an accelerated neuroinflammatory response, as evidenced by increased expression of Iba-1, p-NF-κB, and the secretion of IL-6 and TNF-α. Importantly, Trp treatment ameliorated MGO-induced depression like-behavior and memory loss in mice and markedly mitigated increased expression of p-Tau, APP, p-ERK1/2, p-pJNK, and p-NF-κB in the brain. Likewise, Trp treatment also induced the expression of MGO detoxifying factors GLO-I and GLO-II and CAT activity, suggesting the induction of an antioxidant system and reduced inflammation by inhibiting IL-6 and TNF-α secretion.

CONCLUSIONS

Our data revealed that MGO-induced depression like-behavior and memory deficits resulted from disturbances in Trp, 5-HT, BDNF, and NGF levels, increased p-Tau and APP expression, neuroinflammation, and impaired redox status (Nrf-2/Ho-1/TXNRD1/Sirt3/5) in the brain.

The chronic unpredictable mild stress (CUMS) Paradigm: Bridging the gap in depression research from bench to bedside

Depression is a complicated neuropsychiatric condition with an incompletely understoodetiology, making the discovery of effective therapies challenging. Animal models have been crucial in improving our understanding of depression and enabling antidepressant medication development. The CUMS model has significant face validity since it induces fundamental depression symptoms in humans, such as anhedonia, behavioral despair, anxiety, cognitive impairments, and changes in sleep, food, and social behavior. Its construct validity is demonstrated by the dysregulation of neurobiological systems involved in depression, including monoaminergic neurotransmission, the hypothalamic-pituitary-adrenal axis, neuroinflammatory processes, and structural brain alterations. Critically, the model's predictive validity is demonstrated by the reversal of CUMS-induced deficits following treatment with clinically effective antidepressants such as selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, tricyclic antidepressants, and monoamine oxidase inhibitors. This review comprehensivelyassesses the multifarious depressive-like phenotypes in the CUMS model using behavioral paradigms like sucrose preference, forced swim, tail suspension, elevated plus maze, and novel object recognition tests. It investigates the neurobiological mechanisms that underlie CUMS-induced behaviors, including signaling pathways involving tumor necrosis factor-alpha, brain-derived neurotrophic factor and its receptor TrkB, cyclooxygenase-2, glycogen synthase kinase-3 beta, and the kynurenine pathway. This review emphasizes the CUMS model's importance as a translationally relevant tool for unraveling the complex mechanisms underlying depression and facilitating the development of improved and targeted interventions for this debilitating neuropsychiatric disorder by providing a comprehensive overview of its validity, behavioral assessments, and neurobiological underpinnings.

Mild traumatic brain injury gives rise to chronic depression-like behavior and associated alterations in glutamatergic protein expression

Mild traumatic brain injury (mTBI) is known to result in chronic somatic, cognitive, and emotional symptoms. Depression is commonly reported among individuals suffering from persistent concussion symptoms; however, the underlying mechanisms are not understood. The glutamatergic system has recently been linked with mTBI and depression due to reports of similar changes in expression of glutamatergic proteins. Using a closed-head controlled cortical impact (cCCI) model in adult male rats (n = 8/group), this study investigated the emergence of self-care deficits and changes in social interaction behaviors at four, eight and twelve weeks post-injury. Western blotting was used to assess associated changes in expression of glutamate transporters and N-methyl-D-aspartate (NMDA) receptor subunits at twelve weeks. Splash test results revealed deficits in self-care behaviors beginning at eight weeks, which continued through twelve weeks in the injury group. Injured animals also exhibited decreased preference for social novelty at four weeks and loss of desire for social interaction as a whole by twelve weeks. GluN1 was increased in injured animals compared to shams in the frontal cortex and amygdala, while decreased GLT-1 was observed in the hippocampus. Linear regression was performed to evaluate relationships between behavioral and molecular variables; the results suggested that injury affects these relationships in a region-dependent manner. Together, these results suggest that the development of chronic depression-like behavior was associated with changes in glutamatergic protein expression. Deeper investigations into how injury influences glutamatergic synaptic protein expression are needed, as this has the potential to affect circuit-level neurotransmission that drives depression-like behavior following mTBI.

Integrated Long Noncoding RNA and Messenger RNA Expression Analysis Identifies Molecules Specifically Associated With Resiliency and Susceptibility to Depression and Antidepressant Response

Background

Depression involves maladaptive processes impairing an individual's ability to interface with the environment appropriately. Long noncoding RNAs (lncRNAs) are gaining traction for their role in higher-order brain functioning. Recently, we reported that lncRNA coexpression modules may underlie abnormal responses to stress in rats showing depression-like behavior. The current study explored the global expression regulation of lncRNAs and messenger RNAs (mRNAs) in the hippocampus of rats showing susceptibility (learned helplessness [LH]) or resiliency (non-LH) to depression and fluoxetine response to LH (LH+FLX).

Methods

Multiple comparison analysis was performed with an analysis of variance via the aov and summary function in the R platform to identify the differential expression of mRNAs and lncRNAs among LH, non-LH, tested control, and LH+FLX groups. Weighted gene coexpression network analysis was used to identify distinctive modules and pathways associated with each phenotype. A machine learning analysis was conducted to screen the critical target genes. Based on the combined analysis, the regulatory effects of lncRNAs on mRNA expression were explored.

Results

Multiple comparison analyses revealed differentially expressed mRNAs and lncRNAs with each phenotype. Integrated bioinformatics analysis identified novel transcripts, specific modules, and regulatory pairs of mRNA-lncRNA in each phenotype. In addition, the machine learning approach predicted lncRNA-regulated Spp2 and Olr25 genes in developing LH behavior, whereas joint analysis of mRNA-lncRNA pairs identified Mboat7, Lmod1, I l 18, and Rfx5 genes in depression-like behavior and Adam6 and Tpra1 in antidepressant response.

Conclusions

The study shows a novel role for lncRNAs in the development of specific depression phenotypes and in identifying newer targets for therapeutic development.

The TrkC-PTPσ complex governs synapse maturation and anxiogenic avoidance via synaptic protein phosphorylation

The precise organization of pre- and postsynaptic terminals is crucial for normal synaptic function in the brain. In addition to its canonical role as a neurotrophin-3 receptor tyrosine kinase, postsynaptic TrkC promotes excitatory synapse organization through interaction with presynaptic receptor-type tyrosine phosphatase PTPσ. To isolate the synaptic organizer function of TrkC from its role as a neurotrophin-3 receptor, we generated mice carrying TrkC point mutations that selectively abolish PTPσ binding. The excitatory synapses in mutant mice had abnormal synaptic vesicle clustering and postsynaptic density elongation, more silent synapses, and fewer active synapses, which additionally exhibited enhanced basal transmission with impaired release probability. Alongside these phenotypes, we observed aberrant synaptic protein phosphorylation, but no differences in the neurotrophin signaling pathway. Consistent with reports linking these aberrantly phosphorylated proteins to neuropsychiatric disorders, mutant TrkC knock-in mice displayed impaired social responses and increased avoidance behavior. Thus, through its regulation of synaptic protein phosphorylation, the TrkC-PTPσ complex is crucial for the maturation, but not formation, of excitatory synapses in vivo.

Prolactin mitigates chronic stress-induced maladaptive behaviors and physiology in ovariectomized female rats

Stress is a major risk factor for several neuropsychiatric disorders in women, including postpartum depression. During the postpartum period, diminished ovarian hormone secretion increases susceptibility to developing depressive symptoms. Pleiotropic peptide hormones, like prolactin, are markedly released during lactation and suppress hypothalamic-pituitary-adrenal axis responses in women and acute stress-induced behavioral responses in female rodents. However, the effects of prolactin on chronic stress-induced maladaptive behaviors remain unclear. Here, we used chronic variable stress to induce maladaptive physiology in ovariectomized female rats and concurrently administered prolactin to assess its effects on several depression-relevant behavioral, endocrine, and neural characteristics. We found that chronic stress increased sucrose anhedonia and passive coping in saline-treated, but not prolactin-treated rats. Prolactin treatment did not alter stress-induced thigmotaxis, corticosterone (CORT) concentrations, hippocampal cell activation or survival. However, prolactin treatment reduced basal CORT concentrations and increased dopaminergic cells in the ventral tegmental area. Further, prolactin-treated rats had reduced microglial activation in the ventral hippocampus following chronic stress exposure. Together, these data suggest prolactin mitigates chronic stress-induced maladaptive behaviors and physiology in hypogonadal females. Moreover, these findings imply neuroendocrine-immune mechanisms by which peptide hormones confer stress resilience during periods of low ovarian hormone secretion.

Validation of a non-food or water motivated effort-based foraging task as a measure of motivational state in male mice

Disorders of motivation such as apathy syndrome are highly prevalent across neurological disorders but do not yet have an agreed treatment approach. The use of translational behavioural models can provide a route through which to meaningfully screen novel drug targets. Methods that utilise food deprivation in contrived environments may lack the sensitivity to detect deficits in self-initiated behaviour, and may have limited translation to normal behaviour. Animals monitored in more naturalistic environments may display more ethologically-relevant behaviours of greater translational value. Here, we aimed to validate a novel, non-food or water motivated effort-based foraging task as a measure of motivational state in mice. In this task, the mouse can freely choose to exert effort to forage nesting material and shuttle it back to a safe and enclosed environment. The amount of nesting material foraged is used as a readout of motivational state. Acute dopaminergic modulation with haloperidol, amphetamine and methylphenidate, and two phenotypic models known to induce motivational deficits (healthy ageing and chronic administration of corticosterone) were used to validate this task. Consistent with other effort-based decision-making tasks we find that foraging behaviour is sensitive to acute modulation of dopaminergic transmission. We find that both phenotypic models induce differing deficits in various aspects of foraging behaviour suggesting that the task may be used to parse different behavioural profiles from distinct disease phenotypes. Thus, without requiring extended training periods or physiological deprivation, this task may represent a refined and translational preclinical measure of motivation.

Identifying dysfunctional cell types and circuits in animal models for psychiatric disorders with calcium imaging

A central goal of neuroscience is to understand how the brain transforms external stimuli and internal bodily signals into patterns of activity that underlie cognition, emotional states, and behavior. Understanding how these patterns of activity may be disrupted in mental illness is crucial for developing novel therapeutics. It is well appreciated that psychiatric disorders are complex, circuit-based disorders that arise from dysfunctional activity patterns generated in discrete cell types and their connections. Recent advances in large-scale, cell-type specific calcium imaging approaches have shed new light on the cellular, circuit, and network-level dysfunction in animal models for psychiatric disorders. Here, we highlight a series of recent findings over the last ~10 years from in vivo calcium imaging studies that show how aberrant patterns of activity in discrete cell types and circuits may underlie behavioral deficits in animal models for several psychiatric disorders, including depression, anxiety, autism spectrum disorders, and schizophrenia. These advances in calcium imaging in pre-clinical models demonstrate the power of cell-type-specific imaging tools in understanding the underlying dysfunction in cell types, activity patterns, and neural circuits that may contribute to disease and provide new blueprints for developing more targeted therapeutics and treatment strategies.

Paroxetine Loaded Nanostructured Lipid Carriers Based In-situ Gel for Brain Delivery via Nasal Route for Enhanced Anti-Depressant Effect: In Vitro Prospect and In Vivo Efficacy

This study focused on developing a thermosensitive gel with nanostructured lipid carriers (NLCs) loaded with paroxetine (PAR) to enhance the treatment and management of depression via nasal administration. Micro emulsion technique was utilized for the PAR-NLCs preparation. The acetyl alcohol and oleic acid were used in the ratio of 76:24. In the NLCs Tween 40, Span40 and Myrj 52 were used as a surfactant. The NLCs were then added into Poloxamer mixture to get thermosensitive NLCs based gel. Characterization, in vitro and in vivo studies were performed to check the efficiency of formulation in drug delivery. The entrapment efficiency of optimized PAR-NLCs was about 90%. The particle size, zeta potential and PDI were 155 ± 1.4 nm, -25.9 ± 0.5 mV, and 0.12 ± 0.01 respectively. The optimized gel showed a gelling temperature of 31.50 ± 0.50°C and a gelling time of 1 ± 0.12 s with a pH of 6, suitable for nasal administration. The in vitro release assay of PAR-NLC-gel showed a cumulative release of about 59% in the first 6 h after comparison with PAR-NLCs which showed almost 100%release. In vivo studies included forced swim test and tail suspension tests showed significant potential for treating depression when compared to PAR-NLCs. PAR-NLCs and NLCs based gel enhanced the tissue architecture and suppressed the expression of TNF-α in brain cortex from histological and immunohistochemical analysis. PAR- NLCs gel-based delivery system can prove to be an effective delivery system for brain targeting through nose for the better management of depression.

Extremely Low-Frequency Electromagnetic Field (ELF-EMF) Increases Mitochondrial Electron Transport Chain Activities and Ameliorates Depressive Behaviors in Mice

Compromised mitochondrial electron transport chain (ETC) activities are associated with depression in humans and rodents. However, the effects of the enhancement of mitochondrial ETC activities on depression remain elusive. We recently reported that an extremely low-frequency electromagnetic field (ELF-EMF) of as low as 10 μT induced hormetic activation of mitochondrial ETC complexes in human/mouse cultured cells and mouse livers. Chronic social defeat stress (CSDS) for 10 consecutive days caused behavioral defects mimicking depression in mice, and using an ELF-EMF for two to six weeks ameliorated them. CSDS variably decreased the mitochondrial ETC proteins in the prefrontal cortex (PFC) in 10 days, which were increased by an ELF-EMF in six weeks. CSDS had no effect on the mitochondrial oxygen consumption rate in the PFC in 10 days, but using an ELF-EMF for six weeks enhanced it. CSDS inactivated SOD2 by enhancing its acetylation and increased lipid peroxidation in the PFC. In contrast, the ELF-EMF activated the Sirt3-FoxO3a-SOD2 pathway and suppressed lipid peroxidation. Furthermore, CSDS increased markers for mitophagy, which was suppressed by the ELF-EMF in six weeks. The ELF-EMF exerted beneficial hormetic effects on mitochondrial energy production, mitochondrial antioxidation, and mitochondrial dynamics in a mouse model of depression. We envisage that an ELF-EMF is a promising therapeutic option for depression.

Psychedelics and Consciousness: Expanding the Horizons of Mind and Therapy

Psychedelics have long been recognized not only for their profound impact on human consciousness but also for their potential therapeutic applications. This perspective explores the multifaceted relationship between psychedelics and consciousness, emphasizing their capacity to alter sensory perceptions, disrupt self-referential thought processes, and catalyze profound spiritual and existential experiences. As research advances, psychedelics are being integrated into therapeutic settings, challenging existing psychiatric models and offering new insights into the complex nature of consciousness and mental health. This emerging paradigm marks the need for careful regulation and ethical considerations in the therapeutic use of psychedelics, promising a more holistic approach to mental health disorders.

Neuroinflammation in osteoarthritis: From pain to mood disorders

Osteoarthritis (OA) is the most common form of musculoskeletal disease, and its prevalence is increasing due to the aging of the population. Chronic pain is the most burdensome symptom of OA that significantly lowers patients' quality of life, also due to its frequent association with emotional comorbidities, such as anxiety and depression. In recent years, both chronic pain and mood alterations have been linked to the development of neuroinflammation in the peripheral nervous system, spinal cord and supraspinal brain areas. Thus, mechanisms at the basis of the development of the neuroinflammatory process may indicate promising targets for novel treatment for pain and affective comorbidities that accompany OA. In order to assess the key role of neuroinflammation in the maintenance of chronic pain and its potential involvement in development of psychiatric components, the monoiodoacetate (MIA) model of OA in rodents has been used and validated. In the present commentary article, we aim to summarize up-to-date results achieved in this experimental model of OA, focusing on glia activation and cytokine production in the sciatic nerve, dorsal root ganglia (DRGs), spinal cord and brain areas. The association of a neuroinflammatory state with the development of pain and anxiety- and depression-like behaviors are discussed. Results suggest that cells and molecules involved in neuroinflammation may represent novel targets for innovative pharmacological treatments of OA pain and mood comorbidities.

Lung-brain crosstalk: Behavioral disorders and neuroinflammation in septic survivor mice

Although studies have suggested an association between lung infections and increased risk of neuronal disorders (e.g., dementia, cognitive impairment, and depressive and anxious behaviors), its mechanisms remain unclear. Thus, an experimental mice model of pulmonary sepsis was developed to investigate the relationship between lung and brain inflammation. Male Swiss mice were randomly assigned to either pneumosepsis or control groups. Pneumosepsis was induced by intratracheal instillation of Klebsiella pneumoniae, while the control group received a buffer solution. The model's validation included assessing systemic markers, as well as tissue vascular permeability. Depression- and anxiety-like behaviors and cognitive function were assessed for 30 days in sepsis survivor mice, inflammatory profiles, including cytokine levels (lungs, hippocampus, and prefrontal cortex) and microglial activation (hippocampus), were examined. Pulmonary sepsis damaged distal organs, caused peripheral inflammation, and increased vascular permeability in the lung and brain, impairing the blood-brain barrier and resulting in bacterial dissemination. After sepsis induction, we observed an increase in myeloperoxidase activity in the lungs (up to seven days) and prefrontal cortex (up to 24 h), proinflammatory cytokines in the hippocampus and prefrontal cortex, and percentage of areas with cells positive for ionized calcium-binding adaptor molecule 1 (IBA-1) in the hippocampus. Also, depression- and anxiety-like behaviors and changes in short-term memory were observed even 30 days after sepsis induction, suggesting a crosstalk between inflammatory responses of lungs and brain.

Psilocybin restrains activity-based anorexia in female rats by enhancing cognitive flexibility: contributions from 5-HT1A and 5-HT2A receptor mechanisms

Psilocybin has shown promise for alleviating symptoms of depression and is currently in clinical trials for the treatment of anorexia nervosa (AN), a condition that is characterised by persistent cognitive inflexibility. Considering that enhanced cognitive flexibility after psilocybin treatment is reported to occur in individuals with depression, it is plausible that psilocybin could improve symptoms of AN by breaking down cognitive inflexibility. A mechanistic understanding of the actions of psilocybin is required to tailor the clinical application of psilocybin to individuals most likely to respond with positive outcomes. This can only be achieved using incisive neurobiological approaches in animal models. Here, we use the activity-based anorexia (ABA) rat model and comprehensively assess aspects of reinforcement learning to show that psilocybin (post-acutely) improves body weight maintenance in female rats and facilitates cognitive flexibility, specifically via improved adaptation to the initial reversal of reward contingencies. Further, we reveal the involvement of signalling through the serotonin (5-HT) 1 A and 5-HT2A receptor subtypes in specific aspects of learning, demonstrating that 5-HT1A antagonism negates the cognitive enhancing effects of psilocybin. Moreover, we show that psilocybin elicits a transient increase and decrease in cortical transcription of these receptors (Htr2a and Htr1a, respectively), and a further reduction in the abundance of Htr2a transcripts in rats exposed to the ABA model. Together, these findings support the hypothesis that psilocybin could ameliorate cognitive inflexibility in the context of AN and highlight a need to better understand the therapeutic mechanisms independent of 5-HT2A receptor binding.

SIRT1 Coordinates Transcriptional Regulation of Neural Activity and Modulates Depression-Like Behaviors in the Nucleus Accumbens

BACKGROUND

Major depression and anxiety disorders are significant causes of disability and socioeconomic burden. Despite the prevalence and considerable impact of these affective disorders, their pathophysiology remains elusive. Thus, there is an urgent need to develop novel therapeutics for these conditions. We evaluated the role of SIRT1 in regulating dysfunctional processes of reward by using chronic social defeat stress to induce depression- and anxiety-like behaviors. Chronic social defeat stress induces physiological and behavioral changes that recapitulate depression-like symptomatology and alters gene expression programs in the nucleus accumbens, but cell type-specific changes in this critical structure remain largely unknown.

METHODS

We examined transcriptional profiles of D1-expressing medium spiny neurons (MSNs) lacking deacetylase activity of SIRT1 by RNA sequencing in a cell type-specific manner using the RiboTag line of mice. We analyzed differentially expressed genes using gene ontology tools including SynGO and EnrichR and further demonstrated functional changes in D1-MSN-specific SIRT1 knockout (KO) mice using electrophysiological and behavioral measurements.

RESULTS

RNA sequencing revealed altered transcriptional profiles of D1-MSNs lacking functional SIRT1 and showed specific changes in synaptic genes including glutamatergic and GABAergic (gamma-aminobutyric acidergic) receptors in D1-MSNs. These molecular changes may be associated with decreased excitatory and increased inhibitory neural activity in Sirt1 KO D1-MSNs, accompanied by morphological changes. Moreover, the D1-MSN-specific Sirt1 KO mice exhibited proresilient changes in anxiety- and depression-like behaviors.

CONCLUSIONS

SIRT1 coordinates excitatory and inhibitory synaptic genes to regulate the GABAergic output tone of D1-MSNs. These findings reveal a novel signaling pathway that has potential for the development of innovative treatments for affective disorders.

State of the Art in Sub-Phenotyping Midbrain Dopamine Neurons

Dopaminergic neurons in the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNpc) comprise around 75% of all dopaminergic neurons in the human brain. While both groups of dopaminergic neurons are in close proximity in the midbrain and partially overlap, development, function, and impairments in these two classes of neurons are highly diverse. The molecular and cellular mechanisms underlying these differences are not yet fully understood, but research over the past decade has highlighted the need to differentiate between these two classes of dopaminergic neurons during their development and in the mature brain. This differentiation is crucial not only for understanding fundamental circuitry formation in the brain but also for developing therapies targeted to specific dopaminergic neuron classes without affecting others. In this review, we summarize the state of the art in our understanding of the differences between the dopaminergic neurons of the VTA and the SNpc, such as anatomy, structure, morphology, output and input, electrophysiology, development, and disorders, and discuss the current technologies and methods available for studying these two classes of dopaminergic neurons, highlighting their advantages, limitations, and the necessary improvements required to achieve more-precise therapeutic interventions.

Neurobiological mechanisms of electroconvulsive therapy for depression: Insights into hippocampal volumetric increases from clinical and preclinical studies

Depression is a highly prevalent and disabling psychiatric disorder. The hippocampus, which plays a central role in mood regulation and memory, has received considerable attention in depression research. Electroconvulsive therapy (ECT) is the most effective treatment for severe pharmacotherapy-resistant depression. Although the working mechanism of ECT remains unclear, recent magnetic resonance imaging (MRI) studies have consistently reported increased hippocampal volumes following ECT. The clinical implications of these volumetric increases and the specific cellular and molecular significance are not yet fully understood. This narrative review brings together evidence from animal models and human studies to provide a detailed examination of hippocampal volumetric increases following ECT. In particular, our preclinical MRI research using a mouse model is consistent with human findings, demonstrating a marked increase in hippocampal volume following ECT. Notable changes were observed in the ventral hippocampal CA1 region, including dendritic growth and increased synaptic density at excitatory synapses. Interestingly, inhibition of neurogenesis did not affect the ECT-related hippocampal volumetric increases detected on MRI. However, it remains unclear whether these histological and volumetric changes would be correlated with the clinical effect of ECT. Hence, future research on the relationships between cellular changes, ECT-related brain volumetric changes, and antidepressant effect could benefit from a bidirectional translational approach that integrates human and animal models. Such translational research may provide important insights into the mechanisms and potential biomarkers associated with ECT-induced hippocampal volumetric changes, thereby advancing our understanding of ECT for the treatment of depression.

Lycopene alleviates BCG-induced depressive phenotypes in mice by disrupting 5-HT3 receptor - IDO1 interplay in the brain

The 5-HT3 receptor and indoleamine 2,3-dioxygenase 1 (IDO1) enzyme play a crucial role in the pathogenesis of depression as their activation reduces serotonin contents in the brain. Since molecular docking analysis revealed lycopene as a potent 5-HT3 receptor antagonist and IDO1 inhibitor, we hypothesized that lycopene might disrupt the interplay between the 5-HT3 receptor and IDO1 to mitigate depression. In mice, the depression-like phenotypes were induced by inoculating Bacillus Calmette-Guerin (BCG). Lycopene (intraperitoneal; i.p.) was administered alone or in combination with 5-HT3 receptor antagonist ondansetron (i.p.) or IDO1 inhibitor minocycline (i.p.), and the behavioral screening was performed by the sucrose preference test, open field test, tail suspension test, and splash test which are based on the different principles. Further, the brains were subjected to the biochemical analysis of serotonin and its precursor tryptophan by the HPLC. The results showed depression-like behavior in BCG-inoculated mice, which was reversed by lycopene administration. Moreover, prior treatment with ondansetron or minocycline potentiated the antidepressant action of lycopene. Minocycline pretreatment also enhanced the antidepressant effect of ondansetron indicating the regulation of IDO1 activity by 5-HT3 receptor-triggered signaling. Biochemical analysis of brain samples revealed a drastic reduction in the levels of tryptophan and serotonin in depressed animals, which were restored following treatment with lycopene and its combination with ondansetron or minocycline. Taken together, the data from molecular docking, behavioral experiments, and biochemical estimation suggest that lycopene might block the 5-HT3 receptor and consequently inhibit the activity of IDO1 to ameliorate BCG-induced depression in mice.

Corticosterone disrupts spatial working memory during retention testing when highly taxed, which positively correlates with depressive-like behavior in middle-aged, ovariectomized female rats

Major Depressive Disorder affects 8.4 % of the U.S. population, particularly women during perimenopause. This study implemented a chronic corticosterone manipulation (CORT, a major rodent stress hormone) using middle-aged, ovariectomized female rats to investigate depressive-like behavior, anxiety-like symptoms, and cognitive ability. CORT (400 μg/ml, in drinking water) was administered for four weeks before behavioral testing began and continued throughout all behavioral assessments. Compared to vehicle-treated rats, CORT significantly intensified depressive-like behaviors: CORT decreased sucrose preference, enhanced immobility on the forced swim test, and decreased sociability on a choice task between a novel conspecific female rat and an inanimate object. Moreover, CORT enhanced anxiety-like behavior on a marble bury task by reducing time investigating tabasco-topped marbles. No effects were observed on novelty suppressed feeding or the elevated plus maze. For spatial working memory using an 8-arm radial arm maze, CORT did not alter acquisition but disrupted performance during retention. CORT enhanced the errors committed during the highest working memory load following a delay and during the last trial requiring the most items to remember; this cognitive metric positively correlated with a composite depressive-like score to reveal that as depressive-like symptoms increased, cognitive performance worsened. This protocol allowed for the inclusion of multiple behavioral assessments without stopping the CORT treatment needed to produce a MDD phenotype and to assess a battery of behaviors. Moreover, that when middle-age was targeted, chronic CORT produced a depressive-like phenotype in ovariectomized females, who also comorbidly expressed aspects of anxiety and cognitive dysfunction.

Identifying the most crucial factors associated with depression based on interpretable machine learning: a case study from CHARLS

Background

Depression is one of the most common mental illnesses among middle-aged and older adults in China. It is of great importance to find the crucial factors that lead to depression and to effectively control and reduce the risk of depression. Currently, there are limited methods available to accurately predict the risk of depression and identify the crucial factors that influence it.

Methods

We collected data from 25,586 samples from the harmonized China Health and Retirement Longitudinal Study (CHARLS), and the latest records from 2018 were included in the current cross-sectional analysis. Ninety-three input variables in the survey were considered as potential influential features. Five machine learning (ML) models were utilized, including CatBoost and eXtreme Gradient Boosting (XGBoost), Gradient Boosting decision tree (GBDT), Random Forest (RF), Light Gradient Boosting Machine (LightGBM). The models were compared to the traditional multivariable Linear Regression (LR) model. Simultaneously, SHapley Additive exPlanations (SHAP) were used to identify key influencing factors at the global level and explain individual heterogeneity through instance-level analysis. To explore how different factors are non-linearly associated with the risk of depression, we employed the Accumulated Local Effects (ALE) approach to analyze the identified critical variables while controlling other covariates.

Results

CatBoost outperformed other machine learning models in terms of MAE, MSE, MedAE, and R2metrics. The top three crucial factors identified by the SHAP were r4satlife, r4slfmem, and r4shlta, representing life satisfaction, self-reported memory, and health status levels, respectively.

Conclusion

This study demonstrates that the CatBoost model is an appropriate choice for predicting depression among middle-aged and older adults in Harmonized CHARLS. The SHAP and ALE interpretable methods have identified crucial factors and the nonlinear relationship with depression, which require the attention of domain experts.

Mouse Model of Parkinson's Disease with Bilateral Dorsal Striatum Lesion with 6-Hydroxydopamine Exhibits Cognitive Apathy-like Behavior

Among the symptoms of Parkinson's disease (PD), apathy comprises a set of behavioral, affective, and cognitive features that can be classified into several subtypes. However, the pathophysiology and brain regions that are involved in these different apathy subtypes are still poorly characterized. We examined which subtype of apathy is elicited in a mouse model of PD with 6-hydroxydopamine (6-OHDA) lesions and the behavioral symptoms that are exhibited. Male C57/BL6J mice were allocated to sham (n = 8) and 6-OHDA (n = 13) groups and locally injected with saline or 4 µg 6-OHDA bilaterally in the dorsal striatum. We then conducted motor performance tests and apathy-related behavioral experiments. We then pathologically evaluated tyrosine hydroxylase (TH) immunostaining. The 6-OHDA group exhibited significant impairments in motor function. In the behavioral tests of apathy, significant differences were observed between the sham and 6-OHDA groups in the hole-board test and novelty-suppressed feeding test. The 6-OHDA group exhibited impairments in inanimate novel object preference, whereas social preference was maintained in the three-chamber test. The number of TH+ pixels in the caudate putamen and substantia nigra compacta was significantly reduced in the 6-OHDA group. The present mouse model of PD predominantly showed dorsal striatum dopaminergic neuronal loss and a decrease in novelty seeking as a symptom that is related to the cognitive apathy component.

Reserpine-induced rat model for depression: Behavioral, physiological and PET-based dopamine receptor availability validation

BACKGROUND

Reserpine (RES), a Vesicular Monoamine Transporter 2 (VMAT2) inhibitor agent, has been used in preclinical research for many years to create animal models for depression and to test experimental antidepressant strategies. Nevertheless, evidence of the potential use and validity of RES as a chronic pharmacological model for depression is lacking, and there are no comprehensive studies of the behavioral effects in conjunction with molecular outcomes.

METHODS

Experiment 1. Following baseline behavior testing sensitive to depression-like phenotype and locomotion (Phase 1), 27 Sprague-Dawley (SD) rats received i.p. either vehicle solution (0.0 mg/kg), low (0.2 mg/kg) or high (0.8 mg/kg) RES dose for 20 days using a pre-determined schedule and reassessed for behavioral phenotypes (Phase 2). After 10 days washout period, and a final behavioral assessment (Phase 3), the brains were collected 16 days after the last injection for mRNA-expression assessment. Experiment 2. In a similar timetable as in Experiment 1 but without the behavioral testing, 12 SD rats underwent repetitive dopamine D2/3 receptor PET scanning with [18F]DMFP following each Phase. The binding potential (BPND) of [18F]DMFP was quantified by kinetic analysis as a marker of striatal D2/3R availability. Weight and welfare were monitored throughout the study.

RESULTS

Significant, dose-dependent weight loss and behavioral deficits including both motor (hypo-locomotion) and non-motor behavior (anhedonia, mild anxiety and reduced exploration) were found for both the low and high dose groups with significant decrease in D2R mRNA expression in the accumbal region for the low RES group after Phase 3. Both RES treated groups showed substantial increase in [18F]DMFP BPND (in line with dopamine depletion) during Phase 2 and 3 compared to baseline and Controls.

CONCLUSIONS

The longitudinal design of the study demonstrated that chronic RES administration induced striatal dopamine depletion that persisted even after the wash-out period. However, the behavior phenotype observed were transient. The data suggest that RES administration can induce a rodent model for depression with mild face validity.

Repetitive transcranial magnetic stimulation (rTMS) for depressive-like symptoms in rodent animal models

Repetitive transcranial magnetic stimulation (rTMS) emerged as a non-invasive brain stimulation technique in the treatment of psychiatric disorders. Both preclinical and clinical studies as well as systematic reviews provide a heterogeneous picture, particularly concerning the stimulation protocols used in rTMS. Here, we present a review of rTMS effects in rodent models of depressive-like symptoms with the aim to identify the most relevant factors that lead to an increased therapeutic success. The influence of different factors, such as the stimulation parameters (stimulus frequency and intensity, duration of stimulation, shape and positioning of the coil), symptom severity and individual characteristics (age, species and genetic background of the rodents), on the therapeutic success are discussed. Accumulating evidence indicates that rTMS ameliorates a multitude of depressive-like symptoms in rodent models, most effectively at high stimulation frequencies (≥5 Hz) especially in adult rodents with a pronounced pathological phenotype. The therapeutic success of rTMS might be increased in the future by considering these factors and using more standardized stimulation protocols.

The complex role of the chemokine CX3CL1/Fractalkine in major depressive disorder: A narrative review of preclinical and clinical studies

Evidence suggests that neuroinflammation exhibits a dual role in the pathogenesis of major depressive disorder (MDD), both potentiating the onset of depressive symptoms and developing as a consequence of them. Our narrative review focuses on the role of the chemokine fractalkine (FKN) (also known as CX3CL1), which has gained increasing interest for its ability to induce changes to microglial phenotypes through interaction with its corresponding receptor (CX3CR1) that may impact neurophysiological processes relevant to MDD. Despite this, there is a lack of a clear understanding of the role of FKN in MDD. Overall, our review of the literature shows the involvement of FKN in MDD, both in preclinical models of depression, and in clinical studies of depressed patients. Preclinical studies (N = 8) seem to point towards two alternative hypotheses for FKN's role in MDD: a) FKN may drive pro-inflammatory changes to microglia that contribute towards MDD pathogenesis; or b) FKN may inhibit pro-inflammatory changes to microglia, thereby exerting a protective effect against MDD pathogenesis. Evidence for a) primarily derives from preclinical chronic stress models of depression in mice, whereas for b) from preclinical inflammation models of depression. Whereas, in humans, clinical studies (N = 4) consistently showed a positive association between FKN and presence of MDD, however it is not clear whether FKN is driving or moderating MDD pathogenesis. Future studies should aim for larger and more controlled clinical cohorts, in order to advance our understanding of FKN role both in the context of stress and/or inflammation.

Synergy between psychological impact and biochemical manifestation of stress among the COVID-19 pandemic-affected population

Objective

Due to the COVID-19 pandemic, many countries around the world experienced an unprecedented increase in stress in the general population. Even after normal life has been reestablished, the new normal is punctuated by severely impacted vulnerable groups. Stress-associated symptoms display an intricate relationship with biochemical modulations, which coordinate the stress response. Identifying these biochemical factors is inherent to deciphering the mode of treatment needed to diminish the health-care gap resulting from the pandemic.

Methods

We applied psychological measures using the perceived stress (PS) and COVID-19 anxiety (CA) scales and preventive health behavior (PHB) to evaluate stress in the general population. Biochemical markers of stress, that is, total antioxidant capacity (TAC), thiobarbituric acid reactive substances (TBARS), cortisol, and C-reactive protein (CRP) were tested in the serum samples of the participants. Statistical analysis was carried out using SPSS version 22.0.

Results

Stress scores for PS, CA, and PHB indicate the prevalence of moderate-to-high stress among participants, and a correlation between psychological stress and biochemical correlates, TAC, TBARS, cortisol, and CRP. Serum concentrations of TBARS, Cortisol, and CRP were found to be significantly increased, while the TAC was decreased across all stress types and levels. Our findings demonstrate a positive correlation between PS, CA, PHB TBARS, cortisol, and CRP and a strong negative correlation with TAC.

Conclusion

The results of this study will help in tailoring targeted interventions and preventive regimes to mitigate COVID-19-associated anxiety and stress disorders prevailing even after the actual pandemic has subsided.

A new mouse model of depression induced by chronic restraint stress combined with lipopolysaccharide

The aim of this study was to establish a multi-factor-induced depression model in mice within a relatively short period, specifically through the combination of intraperitoneal injection of lipopolysaccharide (LPS) and chronic restraint stress (CRS), and to evaluate the differences in depressive-like behaviors among three different strains of mice, seeking mouse strains more suitable for this combined model. The mice of each strain were randomly divided into the normal group and model group. The mice in the model group received a single intraperitoneal injection of LPS once daily (1 mg/kg/d for 7 days) and subsequent CRS for 6 h, to induce depression, while the mice in the normal group received no treatment. Behavioral tests: sucrose preference test (SPT), open field test (OFT), forced swim test (FST), and tail suspension test (TST) were conducted to assess depressive-like behaviors in the mice. Data analysis showed that there were significant intergroup differences in depressive-like behaviors in ICR and C57BL/6 J mice, while KM mice exhibited minor differences with relatively high deviation in individual behavioral score. This study indicated that the combined depression mouse model could successfully induce significant depressive-like behaviors in ICR and C57BL/6 J mice.

Amygdala-specific changes in Cacna1c, Nfat5, and Bdnf expression are associated with stress responsivity in mice: A possible mechanism for psychiatric disorders

The CACNA1C gene encodes the alpha-1c subunit of the Cav1.2 calcium channel, a regulator of neuronal calcium influx involved in neurotransmitter release and synaptic plasticity. Genetic data show a role for CACNA1C in depressive symptoms underlying different psychiatric diagnoses. However, the mechanisms involved still require further exploration. This study aimed to investigate sex and region-specific changes in the Cacna1c gene and behavioral outcomes in mice exposed to chronic stress. Moreover, we evaluated the Nuclear factor of activated T-cells 5 (Nfat5) and the Brain-derived neurotrophic factor (Bdnf) as potential upstream and downstream Cacna1c targets and their correlation in stressed mice and humans with depression. Male and female Swiss mice were exposed to chronic unpredictable stress (CUS) for 21 days. Animal-integrated emotionality was assessed using the sucrose splash test, the tail suspension, the open-field test, and the elevated-plus-maze. Gene expression analysis was performed in the amygdala, prefrontal cortex, and hippocampus. Human data for in silico analysis was obtained from the Gene Expression Omnibus. CUS-induced impairment in integrated emotional regulation was observed in males. Gene expression analysis showed decreased levels of Cacna1c and Nfat5 and increased levels of Bdnf transcripts in the amygdala of stressed male mice. In contrast, there were no major changes in behavioral responses or gene expression in female mice after stress. The expression of the three genes was significantly correlated in the amygdala of mice and humans. The strong and positive correlation between Canac1c and Nfat5 suggests a potential role for this transcription factor in Canac1c expression. These changes could impact amygdala reactivity and emotional responses, making them a potential target for psychiatric intervention.

Dynamic Human Gut Microbiome and Immune Shifts During an Immersive Psychosocial Therapeutic Program

Background

Depression is a leading cause of disability worldwide yet its underlying factors, particularly microbial associations, are poorly understood.

Methods

We examined the longitudinal interplay between the microbiome and immune system in the context of depression during an immersive psychosocial intervention. 142 multi-omics samples were collected from 52 well-characterized participants before, during, and three months after a nine-day inquiry-based stress reduction program.

Results

We found that depression was associated with both an increased presence of putatively pathogenic bacteria and reduced microbial beta-diversity. Following the intervention, we observed reductions in neuroinflammatory cytokines and improvements in several mental health indicators. Interestingly, participants with a Prevotella-dominant microbiome showed milder symptoms when depressed, along with a more resilient microbiome and more favorable inflammatory cytokine profile, including reduced levels of CXCL-1.

Conclusions

Our findings reveal a protective link between the Prevotella-dominant microbiome and depression, associated with a less inflammatory environment and moderated symptoms. These insights, coupled with observed improvements in neuroinflammatory markers and mental health from the intervention, highlight potential avenues for microbiome-targeted therapies in depression management.

Immediate and long-term electrophysiological biomarkers of antidepressant-like behavioral effects after subanesthetic ketamine and medial prefrontal cortex deep brain stimulation treatment

Introduction

Both ketamine (KET) and medial prefrontal cortex (mPFC) deep brain stimulation (DBS) are emerging therapies for treatment-resistant depression, yet our understanding of their electrophysiological mechanisms and biomarkers is incomplete. This study investigates aperiodic and periodic spectral parameters, and the signal complexity measure sample entropy, within mPFC local field potentials (LFP) in a chronic corticosterone (CORT) depression model after ketamine and/or mPFC DBS.

Methods

Male rats were intraperitoneally administered CORT or vehicle for 21 days. Over the last 7 days, animals receiving CORT were treated with mPFC DBS, KET, both, or neither; then tested across an array of behavioral tasks for 9 days.

Results

We found that the depression-like behavioral and weight effects of CORT correlated with a decrease in aperiodic-adjusted theta power (5-10 Hz) and an increase in sample entropy during the administration phase, and an increase in theta peak frequency and a decrease in the aperiodic exponent once the depression-like phenotype had been induced. The remission-like behavioral effects of ketamine alone correlated with a post-treatment increase in the offset and exponent, and decrease in sample entropy, both immediately and up to eight days post-treatment. The remission-like behavioral effects of mPFC DBS alone correlated with an immediate decrease in sample entropy, an immediate and sustained increase in low gamma (20-50 Hz) peak width and aperiodic offset, and sustained improvements in cognitive function. Failure to fully induce remission-like behavior in the combinatorial treatment group correlated with a failure to suppress an increase in sample entropy immediately after treatment.

Conclusion

Our findings therefore support the potential of periodic theta parameters as biomarkers of depression-severity; and periodic low gamma parameters and cognitive measures as biomarkers of mPFC DBS treatment efficacy. They also support sample entropy and the aperiodic spectral parameters as potential cross-modal biomarkers of depression severity and the therapeutic efficacy of mPFC DBS and/or ketamine. Study of these biomarkers is important as objective measures of disease severity and predictive measures of therapeutic efficacy can be used to personalize care and promote the translatability of research across studies, modalities, and species.

Repeated Sulforaphane Treatment Reverses Depressive-like Behavior and Exerts Antioxidant Effects in the Olfactory Bulbectomy Model in Mice

Growing evidence suggests that activators of nuclear factor erythroid-derived 2-like 2 (Nrf2), such as sulforaphane, may represent promising novel pharmacological targets for conditions related to oxidative stress, including depressive disorder. Therefore, we conducted a study to explore the behavioral and biochemical effects of repeated (14 days) sulforaphane (SFN) treatment in the olfactory bulbectomy (OB) animal model of depression. An open field test (OFT), splash test (ST), and spontaneous locomotor activity test (LA) were used to assess changes in depressive-like behavior and the potential antidepressant-like activity of SFN. The OB model induced hyperactivity in mice during the OFT and LA as well as a temporary loss of self-care and motivation in the ST. The repeated administration of SFN (10 mg/kg) effectively reversed these behavioral changes in OB mice across all tests. Additionally, a biochemical analysis revealed that SFN (10 mg/kg) increased the total antioxidant capacity in the frontal cortex and serum of the OB model. Furthermore, SFN (10 mg/kg) significantly enhanced superoxide dismutase activity in the serum of OB mice. Overall, the present study is the first to demonstrate the antidepressant-like effects of repeated SFN (10 mg/kg) treatment in the OB model and indicates that these benefits may be linked to improved oxidative status.

Astroglial Dysfunctions in Mood Disorders and Rodent Stress Models: Consequences on Behavior and Potential as Treatment Target

Astrocyte dysfunctions have been consistently observed in patients affected with depression and other psychiatric illnesses. Although over the years our understanding of these changes, their origin, and their consequences on behavior and neuronal function has deepened, many aspects of the role of astroglial dysfunction in major depressive disorder (MDD) and post-traumatic stress disorder (PTSD) remain unknown. In this review, we summarize the known astroglial dysfunctions associated with MDD and PTSD, highlight the impact of chronic stress on specific astroglial functions, and how astroglial dysfunctions are implicated in the expression of depressive- and anxiety-like behaviors, focusing on behavioral consequences of astroglial manipulation on emotion-related and fear-learning behaviors. We also offer a glance at potential astroglial functions that can be targeted for potential antidepressant treatment.

A scoping review of the effects of mushroom and fungus extracts in rodent models of depression and tests of antidepressant activity

One of the most important developments in psychopharmacology in the past decade has been the emergence of novel treatments for mood disorders, such as psilocybin for treatment-resistant depression. Psilocybin is most commonly found in different species of mushroom; however, the literature on mushroom and fungus extracts with potential antidepressant activity extends well beyond just psilocybin-containing mushrooms, and includes both psychedelic and non-psychedelic species. In the current review, we systematically review the preclinical literature on mushroom and fungus extracts, and their effects of animal models of depression and tests of antidepressant activity. The PICO structure, PRISMA checklist and the Cochrane Handbook for systematic reviews of intervention were used to guide the search strategy. A scoping search was conducted in electronic databases PubMed, CINAHL, Embase and Web of Science. The literature search identified 50 relevant and suitable published studies. These included 19 different species of mushrooms, as well as seven different species of other fungi. Nearly all studies reported antidepressant-like effects of treatment with extracts. Treatments were most commonly delivered orally, in both acute and chronically administered studies to predominantly male rodents. Multiple animal models of depression were used, the most common being unpredictable chronic mild stress, while the tail suspension test and forced swim test were most frequently used as standalone antidepressant screens. Details on each experiment with mushroom and fungus species are discussed in detail, while an evaluation is provided of the strengths and weaknesses of these studies.

Environmental enrichment and the combined interventions of EE and metformin enhance hippocampal neuron survival and hippocampal-dependent memory in type 2 diabetic rats under stress through the BDNF-TrkB signaling pathways

BACKGROUND

Type 2 diabetes (T2D) with depression causes severe cognitive impairments. The devastating conditions will further compromise the overall quality of life. The overconsumption of high-fat and high-sucrose (HFS) diet is one of the modifiable risk factors for T2D, depression, and cognitive impairments. Thus, it is essential to identify effective therapeutic strategies to overcome the cognitive impairments in T2D with depression. We proposed environmental enrichment (EE) which encompasses social, cognitive, and physical components as the alternative treatment for such impairments. We also investigated the potential neuroprotective properties of the antidiabetic drug metformin. This study aimed to investigate the effects of EE and metformin interventions on hippocampal neuronal death, and hippocampal-dependent memory impairment in T2D rats under stress.

METHODS

Thirty-two male rats (200-250 g) were divided into four groups: C group (standard diet + conventional cage), DS group [HFS-induced T2D + restraint stress (RS)], DSE group [HFS-induced T2D + RS + EE] and DSEM group [HFS + RS + EE + metformin]. Serum corticosterone (CORT) was measured to evaluate stress levels. The serum Free Oxygen Radicals Testing (FORT) and Free Oxygen Radicals Defence Test (FORD) were measured to evaluate the systemic oxidative status (OS). Serum brain-derived neurotrophic factor (BDNF) and T-maze tasks were performed to evaluate cognitive functions. Rats were humanely sacrificed to collect brains for histological, morphometric, and hippocampal gene expression studies.

RESULTS

The CORT and the serum FORT levels in the DSE and DSEM groups were lower than in the DS group. Meanwhile, the serum BDNF, T-maze scores, histological, and morphometric analysis were improved in the DSE and DSEM groups than in the DS group. These findings supported that EE and the combined interventions of EE and metformin had neuroprotective properties. The hippocampal gene expression analysis revealed that the DSE and DSEM groups showed improved regulation of BDNF-TrkB signalling pathways, including the BDNF/TrkB binding, PI3K - Akt pathway, Ras-MAPK pathway, PLCγ-Ca2+ pathway, and CREB transcription.

CONCLUSION

EE and the combined interventions of EE and metformin improved hippocampal neuron survival and hippocampal-dependent memory in T2D rats under stress by enhancing gene expression regulation of neurogenesis and synaptic plasticity.

Cannabidiol Treatment Shows Therapeutic Efficacy in a Rodent Model of Social Transfer of Pain in Pair-Housed Male Mice

Introduction: Prosocial behavior refers to sharing emotions and sensations such as pain. Accumulated data indicate that cannabidiol (CBD), a nonpsychotomimetic component of the Cannabis sativa plant, attenuates hyperalgesia, anxiety, and anhedonic-like behavior. Nevertheless, the role of CBD in the social transfer of pain has never been evaluated. In this study, we investigated the effects of acute systemic administration of CBD in mice that cohabited with a conspecific animal suffering from chronic constriction injury. Furthermore, we assessed whether repeated CBD treatment decreases hypernociception, anxiety-like behavior, and anhedonic-like responses in mice undergoing chronic constriction injury and whether this attenuation would be socially transferred to the partner. Materials and Methods: Male Swiss mice were Housed in pairs for 28 days. On the 14th day of living together, animals were then divided into two groups: cagemate nerve constriction (CNC), in which one animal of each partner was subjected to sciatic nerve constriction; and cagemate sham (CS), subjected to the same surgical procedure but without suffering nerve constriction. In Experiments 1, 2, and 3 on day 28 of living together, the cagemates (CNC and CS) animals received a single systemic injection (intraperitoneally) of vehicle or CBD (0.3, 1, 10, or 30 mg/kg). After 30 min, the cagemates were subjected to the elevated plusmaze followed by exposure to the writhing and sucrose splash tests. For chronic treatment (Exp. 4), sham and chronic constriction injury animals received a repeated systemic injection (subcutaneous) of vehicle or CBD (10 mg/kg) for 14 days after the sciatic nerve constriction procedure. On days 28 and 29 sham and chronic constriction injury animals and their cagemates were behaviorally tested. Results and Conclusion: Acute CBD administration attenuated anxiety-like behavior, pain hypersensitivity, and anhedonic-like behavior in cagemates that cohabited with a pair in chronic pain. In addition, repeated CBD treatment reversed the anxiety-like behavior induced by chronic pain and enhanced the mechanical withdrawal thresholds in Von Frey filaments and the grooming time in the sucrose splash test. Moreover, repeated CBD treatment effects were socially transferred to the chronic constriction injury cagemates.

Optogenetic behavioral studies in depression research: A systematic review

Optogenetics has made substantial contributions to our understanding of the mechanistic underpinnings of depression. This systematic review employs quantitative analysis to investigate the impact of optogenetic stimulation in mice and rats on behavioral alterations in social interaction, sucrose consumption, and mobility. The review analyses optogenetic behavioral studies using standardized behavioral tests to detect behavioral changes induced via optogenetic stimulation in stressed or stress-naive mice and rats. Behavioral changes were evaluated as either positive, negative, or not effective. The analysis comprises the outcomes of 248 behavioral tests of 168 studies described in 37 articles, including negative and null results. Test outcomes were compared for each behavior, depending on the animal cohort, applied type of stimulation and the stimulated neuronal circuit and cell type. The presented synthesis contributes toward a comprehensive picture of optogenetic behavioral research in the context of depression.

Intranasal delivery of paroxetine: A preclinical study on pharmacokinetics, depressive-like behaviour, and neurochemical sex differences

Treatment of major depressive disorder remains a major unmet clinical need. Given the advantages of intranasal administration for targeted brain delivery, the present study aimed at investigating the pharmacokinetics of paroxetine, after its intranasal instillation and assessing its potential therapeutic effect on female and male mice subjected to unpredictable chronic mild stress (UCMS) protocol. IN administration revealed direct nose-to-brain paroxetine delivery but dose- and sex-dependent differences. Pharmacokinetics was nonlinear and paroxetine concentrations were consistently higher in plasma and brain of male mice. Additionally, UCMS decreased animal preference for sucrose in both male and female mice following acute (p < 0.01) and chronic stress (p < 0.05), suggesting anhedonia. Both male and female mice exhibited depressive-like behavior in the forced swimming test. UCMS females displayed a significantly longer immobility time and shorter climbing time than the control group (p < 0.05), while no differences were found between male mice. Two weeks of paroxetine intranasal administration reduced immobility time and lengthened climbing and swimming time, approaching values similar to those observed in the healthy control group. The therapeutic effect was stronger on female mice. Importantly, melatonin plasma levels were significantly decreased in female mice following UCMS (p < 0.05), while males exhibited heightened corticosterone levels. On the other hand, treatment with IN paroxetine significantly increased corticosterone and melatonin levels in both sexes compared to healthy mice (p < 0.05). Intranasal paroxetine delivery undoubtedly ameliorated the behavioral despair, characteristic of depressive-like animals. Despite its efficiency in male and female mice subjected to UCMS, females were more prone to this novel therapeutic strategy.

Repeated cannabidiol treatment affects neuroplasticity and endocannabinoid signaling in the prefrontal cortex of the Flinders Sensitive Line (FSL) rat model of depression

Delayed therapeutic responses and limited efficacy are the main challenges of existing antidepressant drugs, thereby incentivizing the search for new potential treatments. Cannabidiol (CBD), non-psychotomimetic component of cannabis, has shown promising antidepressant effects in different rodent models, but its mechanism of action remains unclear. Herein, we investigated the antidepressant-like effects of repeated CBD treatment on behavior, neuroplasticity markers and lipidomic profile in the prefrontal cortex (PFC) of Flinders Sensitive Line (FSL), a genetic animal model of depression, and their control counterparts Flinders Resistant Line (FRL) rats. Male FSL animals were treated with CBD (10 mg/kg; i.p.) or vehicle (7 days) followed by Open Field Test (OFT) and the Forced Swimming Test (FST). The PFC was analyzed by a) western blotting to assess markers of synaptic plasticity and cannabinoid signaling in synaptosome and cytosolic fractions; b) mass spectrometry-based lipidomics to investigate endocannabinoid levels (eCB). CBD attenuated the increased immobility observed in FSL, compared to FRL in FST, without changing the locomotor behavior in the OFT. In synaptosomes, CBD increased ERK1, mGluR5, and Synaptophysin, but failed to reverse the reduced CB1 and CB2 levels in FSL rats. In the cytosolic fraction, CBD increased ERK2 and decreased mGluR5 expression in FSL rats. Surprisingly, there were no significant changes in eCB levels in response to CBD treatment. These findings suggest that CBD effects in FSL animals are associated with changes in synaptic plasticity markers involving mGluR5, ERK1, ERK2, and synaptophysin signaling in the PFC, without increasing the levels of endocannabinoids in this brain region.

Immunotherapy for depression: Recent insights and future targets

Depression stands as a prominent contributor to global disability, entailing an elevated risk of suicide. Substantial evidence supports the notion that immune dysregulation may play a role in the development of depression and impede responses to antidepressant treatments. Immune dysregulation may cause depression in susceptible individuals through raising inflammatory responses. Differences in immune cell types and the release of pro-inflammatory mediators are observed in the blood and cerebrospinal fluid of patients with major depressive disorder, which is associated with neuroimmune dysfunction. Therefore, the interaction of peripheral and central immune targets in depression needs to be understood. Urgent attention is required for the development of innovative therapeutics directed at modulating immune responses for the treatment of depression. This review delineates the immune mechanisms involved in the pathogenesis of depression, assesses the therapeutic potential of immune system targeting for depression treatment, and deliberates on the merits and constraints of employing immunotherapy in the management of depression.

Social stress-induced depressive-like symptoms and changes in gut microbial and lipidomic profiles are prevented by pharmacological inhibition of FAAH activity in male rats

Pharmacological inhibition of fatty acid amide hydrolase (FAAH) activity has antidepressant-like effects in preclinical models of stress. In this study, we investigated whether the antidepressant-like effects of FAAH inhibition are associated with corresponding changes in gut microbial and lipidomic profiles, which are emerging as critical components in the pathophysiology of depression. Adult male Wistar rats experienced five weeks of repeated social defeat or control procedure and were treated with the FAAH inhibitor URB694 (0.3 mg/kg/day, i.p.) or vehicle starting from the third week. Repeated social defeat induced the emergence of depressive-like behavioral (sucrose preference reduction and passive coping behaviors in the forced swim test) and neuroendocrine (increased corticosterone levels) changes, which were prevented by URB694 treatment. Repeated social defeat also provoked a significant variation in gut microbiota (changes in the relative abundance of 14 bacterial taxa) and lipidic (e.g., glycerophospholipids) composition. These stress-induced changes were prevented by URB694 treatment. These findings indicate that inhibition of FAAH activity with URB694 blocks the co-occurrence of depressive-like behavioral and neuroendocrine changes and alterations in gut microbial and lipid composition in rats exposed to repeated social defeat. In conclusion, these results suggest that the gut microbiota-lipid crosstalk may represent a novel biological target for FAAH inhibitors to enhance stress resilience.

Long-term enhancements in antidepressant efficacy and neurogenesis: Effects of intranasal co-administration of neuropeptide Y 1 receptor (NPY1R) and galanin receptor 2 (GALR2) agonists in the ventral hippocampus

This study evaluates the sustained antidepressant-like effects and neurogenic potential of a 3-day intranasal co-administration regimen of galanin receptor 2 (GALR2) agonist M1145 and neuropeptide Y Y1 receptor (NPY1R) agonist [Leu31, Pro34]NPY in the ventral hippocampus of adult rats, with outcomes analyzed 3 weeks post-treatment. Utilizing the forced swimming test (FST), we found that this co-administration significantly enhances antidepressant-like behaviors, an effect neutralized by the GALR2 antagonist M871, highlighting the synergistic potential of these neuropeptides in modulating mood-related behaviors. In situ proximity ligation assay (PLA) indicated a significant increase in GALR2/NPYY1R heteroreceptor complexes in the ventral hippocampal dentate gyrus, suggesting a molecular basis for the behavioral outcomes observed. Moreover, proliferating cell nuclear antigen (PCNA) immunolabeling revealed increased cell proliferation in the subgranular zone of the dentate gyrus, specifically in neuroblasts as evidenced by co-labeling with doublecortin (DCX), without affecting quiescent neural progenitors or astrocytes. The study also noted a significant uptick in the number of DCX-positive cells and alterations in dendritic morphology in the ventral hippocampus, indicative of enhanced neuronal differentiation and maturation. These morphological changes highlight the potential of these agonists to facilitate the functional integration of new neurons into existing neural circuits. By demonstrating the long-lasting effects of a brief, 3-day intranasal administration of GALR2 and NPY1R agonists, our findings contribute significantly to the understanding of neuropeptide-mediated neuroplasticity and herald novel therapeutic strategies for the treatment of depression and related mood disorders, emphasizing the therapeutic promise of targeting neurogenesis and neuronal maturation processes.