Ghrelin alleviates anxiety- and depression-like behaviors induced by chronic unpredictable mild stress in rodents

Evaluating the impact of metabolic and cognitive stress on ghrelin and nesfatin-1 hormones in patients with diabetes and diabetic depression

Nesfatin-1 and ghrelin, initially recognised as hormones involved in regulating energy, have emerged as crucial players with vital functions in various human body systems. In this study, we conducted a comparative assessment of nesfatin-1 and ghrelin responses in individuals experiencing metabolic stress due to diabetes, those with depressive diabetes characterised by both metabolic and mental stress, and healthy controls. We collected blood samples from a total of 90 participants, consisting of 30 people with type II diabetes mellitus (DM), 30 people with type II DM and major depressive disorders, and 30 healthy individuals. Diabetes was diagnosed based on glycated haemoglobin (HbA1c) levels, while depression was assessed using DSM-V criteria. Insulin resistance (HOMA-IR) was calculated, and serum ghrelin and nesfatin-1 levels were measured using ELISA kits. We observed statistically significant decreases in nesfatin-1 and ghrelin levels in the diabetic group (p < 0.0001). However, in the depressive diabetic group, nesfatin-1 levels increased significantly, while ghrelin levels decreased further. The nesfatin-1 to ghrelin ratio decreased in the diabetic group but increased significantly in the depressive diabetic group (p < 0.0001). Nesfatin-1 and ghrelin hormones exhibit parallel impacts in response to metabolic stress, but nesfatin-1 demonstrates contrasting actions compared to ghrelin when mental stress is added to metabolic stress. The findings of this study suggest that nesfatin-1 and ghrelin hormones may play active roles as protective, prognostic, and even etiological factors in various stress situations, particularly those involving mental stress, in addition to their known functions in regulating energy.

Pogostemon cablin essential oil affects anxiety- and depressive-like behaviors and the gut microbiota in chronic unpredictable mild stress model rats

The gut microbiota is thought to be an important factor that influences brain processes and behaviors through the gut-brain axis. Pogostemon cablin is used in traditional Chinese medicine (TCM) to treat gastrointestinal symptoms. Patchouli essential oil (PCO), the main active agent in P. cablin, is used in aromatherapy for stress relief. The aim of our study was to investigate the effects of orally administered PCO on anxiety- and depressive-like behaviors and the gut microbiota. We constructed a rat model of chronic unpredictable mild stress (CUMS) and explored the anxiolytic- and antidepressant-like effects of PCO using the open field test (OFT) and forced swim test (FST). Changes in the abundance of the gut microbiota, short-chain fatty acids (SCFAs), and other related molecules were assessed to determine the role of the gut microbiota. Our results showed that CUMS induced an anxiety-like phenotype in the OFT, which was reversed by PCO, and that PCO also significantly mitigated the depression-like behaviors caused by CUMS in the FST. Furthermore, we found that PCO increased the relative abundances of several probiotics, including Bacteroides and Blautia, and decreased the relative abundances of Ruminococcus_1 and Ruminococcus_2, which were increased by CUMS. Regarding SCFAs, the metabolites of the gut microbiota, PCO increased the concentration of propionic acid and decreased that of caproic acid. Finally, PCO restored the serotonin (5-hydroxytryptamine, 5-HT) level in the hippocampus, which had been decreased by CUMS. The results of this study suggested that PCO can improve stress-related anxiety- and depression-like behaviors and might exert its effects on the central nervous system through interactions with the gut microbiota.

Genetic Variants Associated with Suicide Risk in the Mexican Population: A Systematic Literature Review

Suicide is defined as the action of harming oneself with the intention of dying. It is estimated that worldwide, one person dies by suicide every 40 s, making it a major health problem. Studies in families have suggested that suicide has a genetic component, so the search for genetic variants associated with suicidal behavior could be useful as potential biomarkers to identify people at risk of suicide. In Mexico, some studies of gene variants related to neurotransmission and other important pathways have been carried out and potential association of variants located in the following genes has been suggested: SLC6A4, SAT-1, TPH-2, ANKK1, GSHR, SCARA50, RGS10, STK33, COMT, and FKBP5. This systematic review shows the genetic studies conducted on the Mexican population. This article contributes by compiling the existing information on genetic variants and genes associated with suicidal behavior, in the future could be used as potential biomarkers to identify people at risk of suicide.

A comparative analysis of depressive-like behavior: Exploring sex-related differences and insights

Profiling the variability related to the estrous cycle is essential for assessing depressive-like behavior and screening drugs. This study compares circulating plasma corticosterone levels [CORT] and behavioral alterations in mice exposed to sucrose preference, forced swimming, and tail suspension tests (SPT, FST, and TST, respectively). While SPT exposure did not significantly alter [CORT], FST and TST showed notable changes. Mice in the TST exhibited increased movement and decreased immobility time compared to FST, suggesting a lower likelihood of depressive-like behavior in male mice. Notably, during the proestrus phase, female mice displayed the highest tendency for depressive-like behavior and elevated [CORT], but similar response to antidepressants (imipramine and fluoxetine). The inherent stress of the FST and TST tasks appears to influence [CORT] as well as depressant and antidepressant effects. These comparisons provide valuable insights for further behavioral phenotyping, model sensitivity assessment, and deepen our neurobiological understanding of depression in the context of drug screening.

Male mice engaging differently in emotional eating present distinct plasmatic and neurological profiles

Objective: Stressed individuals tend to turn to calorie-rich food, also known as 'comfort food' for the temporary relief it provides. The emotional eating drive is highly variable among subjects. Using a rodent model, we explored the plasmatic and neurobiological differences between 'high and low emotional eaters' (HEE and LEE).Methods: 40 male mice were exposed for 5 weeks to a protocol of unpredictable chronic mild stress. Every 3 or 4 days, they were submitted to a 1-h restraint stress, immediately followed by a 3-h period during which a choice between chow and chocolate sweet cereals was proposed. The dietary intake was measured by weighing. Plasmatic and neurobiological characteristics were compared in mice displaying high vs low intakes.Results: Out of 40 mice, 8 were considered as HEE because of their high post-stress eating score, and 8 as LEE because of their consistent low intake. LEE displayed higher plasma corticosterone and lower levels of NPY than HEE, but acylated and total ghrelin were similar in both groups. In the brain, the abundance of NPY neurons in the arcuate nucleus of the hypothalamus was similar in both groups, but was higher in the ventral hippocampus and the basal lateral amygdala of LEE. The lateral hypothalamus LEE had also more orexin (OX) positive neurons. Both NPY and OX are orexigenic peptides and mood regulators.Discussion: Emotional eating difference was reflected in plasma and brain structures implicated in emotion and eating regulation. These results concur with the psychological side of food consumption.

Pharmacological inhibition of histone deacetylases ameliorates cognitive impairment after intracerebral hemorrhage with epigenetic alteration in the hippocampus

OBJECTIVES

Post-stroke cognitive impairment (PSCI) interferes with neurorehabilitation in patients with stroke. Epigenetic regulation of the hippocampus has been targeted to ameliorate cognitive function. In particular, the acetylation level of histones is modulated by exercise, a potent therapy for patients with stroke.

MATERIALS AND METHODS

We examined the effects of exercise and pharmacological inhibition of histone deacetylase (HDAC) using sodium butyrate (NaB) on cognitive function and epigenetic factors in the hippocampus after intracerebral hemorrhage (ICH) to seek beneficial neuronal conditioning against PSCI. Forty rats were randomly assigned to five groups: sham, control, NaB, exercise, and NaB plus exercise groups (n=8 in each group). Except for those in the sham group, all rats underwent stereotaxic ICH surgery with a microinjection of collagenase solution. Intraperitoneal administration of NaB (300 mg/kg) and treadmill exercise (11 m/min for 30 min) were conducted for approximately 4 weeks starting 3 days post-surgery.

RESULTS

ICH reduced cognitive function, as detected by the object location test, accompanied by enhanced activity of HDACs. Although exercise did not modulate HDAC activity or cognitive function, repetitive NaB administration increased HDAC activity and ameliorated cognitive impairment induced by ICH.

CONCLUSIONS

This study suggests that pharmacological treatment with an HDAC inhibitor could potentially present an enriched epigenetic platform in the hippocampus and ameliorate PSCI for neurorehabilitation following ICH.

Research trends in the field of the gut-brain interaction: Functional dyspepsia in the spotlight – An integrated bibliometric and science mapping approach

Objectives

This study aims to perform a bibliometric analysis of functional dyspepsia (FD), which includes visualizing bibliographic information, in order to identify prevailing study themes, topics of interest, contributing journals, countries, institutions, and authors as well as co-citation patterns.

Methods

The Web of Science™ Core Collection Database was used to retrieve all peer-reviewed scientific publications related to FD research. The validated search terms were entered into the “title” and “author keywords” fields, and the results were sorted by publication year from 2006 to 2022. There were no restrictions on language. On 12 February 2023, a manual export of the complete metadata for each original publication and review article was performed. CiteSpace was used to reveal co-authorship, publication, and co-citation patterns to find prominent authors, organizations, countries, and journals in FD research as well as to identify author keywords with strong citation bursts, which could indicate an emerging research area. VOSviewer was used to build the co-occurrence indicator (co-word) to identify the main author keywords on which previous studies focused and to induce clustered scientific landscape for two consecutive periods to identify intriguing areas for future research.

Results

A search of the database retrieved 2,957 documents. There was a wave-like pattern in the number of publications until 2017, after which there was a spike in publication volume. The USA, China, and Japan provided the majority of contributions. In terms of institution, Mayo Clin, Univ Newcastle, and Katholieke Univ Leuven were found to be the prolific institutions. Additionally, the results indicate that eastern Asian researchers contributed significantly to the global knowledge of literature that led other countries; however, Canada, the USA, Australia, England, and Germany were found to have the highest degree of betweenness centrality. Nicholas J. Talley, Jan Tack, Gerald Holtmann, Michael Camilleri, Ken Haruma, and Paul Moayyedi occupied the top positions based on productivity and centrality indicators. Six thematic clusters emerged (Helicobacter pylori infection; pathophysiological mechanisms of FD; extraintestinal co-morbidities and overlap syndromes associated with FD; herbal medicine in FD; diabetic gastroparesis; and dietary factors in FD). “Acupuncture,” “duodenal eosinophilia,” “gut microbiota,” and others were among the author keywords with rising prevalence.

Conclusion

In FD research, eastern Asian countries have established themselves as major contributors with the highest publishing productivity; however, research has primarily been driven by North America, Europe, and Australia, where cooperation is generally more active and highly influential scientific results are produced. Our analysis suggests that increased investments, training of human resources, improved infrastructures, and expanded collaborations are essential to improving the quality of FD research in Asia. The emerging author keyword analysis suggests that eosinophil-mast cell axis, gut microbiota, mental disorders, and acupuncture are the key areas that attract researchers’ attention as future research boulevards. There is a highly skewed distribution of research output across Asia, with most focus on complementary and alternative medicine (CAM) coming from Chinese, Japanese, and South Korean centers. However, CAM remains an underexplored area of research in the context of FD, and it deserves greater research efforts in order to obtain quality scientific evidence. Furthermore, we propose that the research framework of CAM should not be limited to dysmotility; rather, it could be interpreted within a more holistic context that includes the brain-gut-microbiota axis, as well as novel concepts such as duodenitis, increased mucosal permeability, and infiltration and activation of eosinophils and mast cells, among others. Overall, we provided bibliometrics-based overviews of relevant literature to researchers from different backgrounds and healthcare professionals to provide an in-depth overview of major trends in FD research.

Glucocorticoids, stress and eating: The mediating role of appetite-regulating hormones

Disrupted hormonal appetite signaling plays a crucial role in obesity as it may lead to uncontrolled reward-related eating. Such disturbances can be induced not only by weight gain itself but also by glucocorticoid overexposure, for example, due to chronic stress, disease, or medication use. However, the exact pathways are just starting to be understood. Here, we present a conceptual framework of how glucocorticoid excess may impair hormonal appetite signaling and, consequently, eating control in the context of obesity. The evidence we present suggests that counteracting glucocorticoid excess can lead to improvements in appetite signaling and may therefore pose a crucial target for obesity prevention and treatment. In turn, targeting hormonal appetite signals may not only improve weight management and eating behavior but may also decrease detrimental effects of glucocorticoid excess on cardio-metabolic outcomes and mood. We conclude that gaining a better understanding of the relationship between glucocorticoid excess and circulating appetite signals will contribute greatly to improvements in personalized obesity prevention and treatment.

Ghrelin receptor agonist MK0677 and overnight fasting do not rescue deficient fear extinction in 129S1/SvImJ mice

The hunger hormone ghrelin has been implicated in the modulation of anxiety- and fear-related behaviors in rodents and humans, while its dysregulation may be associated with psychiatric illness. Along these lines, the ghrelin system has been suggested as a potential target to facilitate fear extinction, which is the main mechanism underlying cognitive behavioral therapy. So far, this hypothesis has not been tested in individuals that have difficulties to extinguish fear. Thus, we investigated pharmacological (ghrelin receptor agonist MK0677) and non-pharmacological (overnight fasting) strategies to target the ghrelin system in the 129S1/SvImJ (S1) mouse strain, which models the endophenotype of impaired fear extinction that has been associated with treatment resistance in anxiety and PTSD patients. MK0677 induced food intake and overnight fasting increased plasma ghrelin levels in S1 mice, suggesting that the ghrelin system is responsive in the S1 strain. However, neither systemic administration of MK0677 nor overnight fasting had an effect on fear extinction in S1 mice. Similarly, our groups previously reported that both interventions did not attenuate fear in extinction-competent C57BL/6J mice. In summary, our findings are in contrast to several studies reporting beneficial effects of GHSR agonism and overnight fasting on fear- and anxiety-related behaviors in rodents. Rather, our data agree with accumulating evidence of divergent behavioral effects of ghrelin system activation and underscore the hypothesis that potential benefits of targeting the ghrelin system in fear extinction may be dependent on factors (e.g., previous stress exposure) that are not yet fully understood.

The associations of gut microbiota, endocrine system and bone metabolism

Gut microbiota is of great importance in human health, and its roles in the maintenance of skeletal homeostasis have long been recognized as the "gut-bone axis." Recent evidence has indicated intercorrelations between gut microbiota, endocrine system and bone metabolism. This review article discussed the complex interactions between gut microbiota and bone metabolism-related hormones, including sex steroids, insulin-like growth factors, 5-hydroxytryptamine, parathyroid hormone, glucagon-like peptides, peptide YY, etc. Although the underlying mechanisms still need further investigation, the regulatory effect of gut microbiota on bone health via interplaying with endocrine system may provide a new paradigm for the better management of musculoskeletal disorders.

Comparative evaluation of natural neuroprotectives and their combinations on chronic immobilization stress-induced depression in experimental mice

The present study evaluates the potential of neuroprotective phytochemicals-rutin (R), resveratrol (Res), 17β-estradiol (17β-E2), and their different combinations against chronic immobilization stress (CIS)-induced depression-like behaviour in male albino mice. Here, the mice were exposed to stress via immobilization of their four limbs under a restrainer for 6 h daily until 7 days of the induction after 30 min of respective drug treatment in different mice groups. The result found the protective effect of these phytoconstituents and their combinations against CIS-induced depression due to their ability to suppress oxidative stress, restore mitochondria, HPA-axis modulation, neurotransmitter level, stress hormones, and inflammatory markers. Also, the combination drug regimens of these phytoconstituents showed synergistic results in managing the physiological and biochemical features of depression. Thus, these neuroprotective could be utilized well in combination to manage depression-like symptoms during episodic stress. Furthermore, such results could be well justified when administered in polyherbal formulation with these neuroprotective as major components. In addition, an advanced study can be designed at the molecular and epigenetics level using a formulation based on these neuroprotective.

Minocycline, a classic antibiotic, exerts psychotropic effects by normalizing microglial neuroinflammation-evoked tryptophan-kynurenine pathway dysregulation in chronically stressed male mice

The dysregulation of tryptophan-kynurenine pathway (TKP) is extensively involved in the pathophysiology of Alzheimer's disease, depression, and neurodegenerative disorders. Minocycline, a classic antibiotic, may exert psychotropic effects associated with the modulation of TKP. In this study, we examined the effects of minocycline in improving behaviour and modulating TKP components in chronically stressed male mice. Following repeated treatment with 22.5 mg/kg and 45 mg/kg minocycline for 27 days, the stressed mice particularly with higher dose displayed significant improvement on cognitive impairment, depression- and anxiety-like behaviour. Minocycline suppressed stress-induced overexpression of pro-inflammatory cytokines and restored anti-inflammatory cytokines. Chronic stress dramatically suppressed blood and prefrontal cortical levels of the primary substrate tryptophan (TRP), the neuroprotective metabolite kynurenic acid (KYNA), and KYNA/KYN ratio, but increased the intermediate kynurenine (KYN), 3-hydroxykynurenine (3-HK), KYN/TRP ratio, and the neurotoxic metabolite quinolinic acid (QUIN). Minocycline partially or completely reversed changes in these components. Minocycline also inhibited stress-induced overexpression of QUIN-related enzymes, indoleamine 2, 3-dioxygenase 1(iDO-1), kynureninase (KYNU), kynurenine 3-monooxygenase (KMO), 3-hydroxyanthranilate 3,4-dioxygenase (3-HAO), but rescued the decreased expression of kynurenine aminotransferase (KAT) in brain regions. Behavioral improvements were correlated with multiple TKP metabolites and enzymes. These results suggest that the psychotropic effects of minocycline are mainly associated with the restoration of biodistribution of the primary substrate in the brain and normalization of neuroinflammation-evoked TKP dysregulation.

Isorhynchophylline ameliorates stress-induced emotional disorder and cognitive impairment with modulation of NMDA receptors

Introduction

Isorhynchophylline is one of the main active ingredients from Uncaria rhynchophylla, the effects and mechanisms of isorhynchophylline on stress-induced emotional disorders and cognitive impairment remain unclear.

Methods

Long-term potentiation (LTP) in vivo was used for synaptic plasticity evaluation; chronic unpredictable mild stress (CUMS) model was used to evaluate the effect of isorhynchophylline on stress induced emotional disorders and cognitive impairment; sucrose preference test (SPT), open field test (OFT), and elevated plus maze (EPM) were used to evaluate emotional disorders; morris water maze (MWM) test was used to evaluate cognitive impairment; Western blotting (WB) was used to the expression of proteins; high performance liquid chromatography (HPLC) was used to quantify neurotransmitters; Nissl staining was used to identify pathological changes induced by stress.

Results

In this study, we found that isorhynchophylline improved corticosterone-induced in vivo LTP impairment significantly, indicating positive effects on stress. Therefore, 28-day CUMS model was adopted to evaluate the anti-stress effects of isorhynchophylline. The results showed that isorhynchophylline improved CUMS-induced weight loss, anxiety- and depression-like behaviors, and spatial memory impairment. Isorhynchophylline reduced CUMS-induced corticosterone elevation. N-methyl-D-aspartic acid (NMDA) receptors play an important role in the process of emotion and memory. Glutamate and the expression of GluN2B increased in the CUMS mice, while D-serine and the expression of serine racemase (SR) decreased significantly, and isorhynchophylline restored these changes to normal level.

Conclusion

These results indicated that isorhynchophylline ameliorated stress-induced emotional disorders and cognitive impairment, modulating NMDA receptors might be one of the underlying mechanisms.

Potential of Heterogeneous Compounds as Antidepressants: A Narrative Review

Depression is a globally widespread disorder caused by a complicated interplay of social, psychological, and biological factors. Approximately 280 million people are suffering from depression worldwide. Traditional frontline antidepressants targeting monoamine neurotransmitters show unsatisfactory effects. The development and application of novel antidepressants for dissimilar targets are on the agenda. This review characterizes the antidepressant effects of multiple endogenous compounds and/or their targets to provide new insight into the working mechanism of antidepressants. We also discuss perspectives and challenges for the generation of novel antidepressants.

Stress-induced myelin damage in the hippocampal formation in a rat model of depression

BACKGROUND

According to previous studies, myelin damage may be involved in the occurrence of depression. However, to date, no study has quantitatively investigated the changes in myelinated fibers and myelin sheaths in the hippocampal formation (HF) and hippocampal subfields in the context of depression.

METHODS

Male Sprague-Dawley (SD) rats (aged 4-5 weeks) were evenly divided into the control group and chronic unpredictable stress (CUS) group. Behavioral tests were performed, and then changes in myelinated fibers and myelin ultrastructure in hippocampal subfields in depression model rats were investigated using modern stereological methods and transmission electron microscopy techniques.

RESULTS

After a four-week CUS protocol, CUS rats showed depressive-like and anxiety-like behaviors. The total length and total volume of myelinated fibers were reduced in the CA1 region and DG in the CUS group compared with the control group. The total volumes of myelin sheaths and axons in the CA1 region but not in the DG were significantly lower in the CUS group than in the control group. The decrease in the total length of myelinated nerve fibers in the CA1 region in CUS rats was mainly due to a decrease in the length of myelinated fibers with a myelin sheath thickness of 0.15 μm-0.20 μm.

LIMITATIONS

The exact relationship between the degeneration of myelin sheaths and depression-like, anxiety-like behaviors needs to be further investigated.

CONCLUSIONS

CUS induces depression- and anxiety-like behaviors, and the demyelination in the CA1 region induced by 4 weeks of CUS might be an important structural basis for these behaviors.

The liver X receptors agonist GW3965 attenuates depressive-like behaviors and suppresses microglial activation and neuroinflammation in hippocampal subregions in a mouse depression model

Liver X receptors (LXRs) have recently been reported to be novel and potential targets for the reversal of depressive-like behaviors, but the mechanism remains unclear. Hippocampal neuroinflammation and impairment of the normal structure and function of microglia are closely associated with depression. To investigate the effects of LXRs agonist (GW3965) on neuroinflammation and microglia in the hippocampal formation of mice with chronic unpredictable stress (CUS)-induced depression, depressive-like behaviors were evaluated by behavioral tests, hippocampal LXRs gene expression were evaluated by qRT-PCR, the protein expression levels of interleukin-1β, tumor necrosis factor-α, inducible nitric oxide synthase, nuclear factor kappa B, and cluster of differentiation 206 were estimated by western blotting, modern stereological methods were used to precisely quantify the total number of microglia in each hippocampal subregion, and immunofluorescence was used to detect the density of activated microglia and the morphology of microglia. We found that GW3965 alleviated the depressive-like behavior induced by CUS, reversed the decrease in hippocampal LXRα and LXRβ induced by CUS, increased the protein expression of pro-inflammatory factors, and decreased the protein expression of antiinflammatory factors induced by CUS. Moreover, CUS intervention significantly increased the number of microglia in the CA1 region, CA2/3 region, and dentate gyrus and the density of activated microglia in the CA2/3 region and dentate gyrus and significantly decreased the endpoints of microglial branches and process length of microglia in the dentate gyrus, while 4 weeks of injections with GW3965 reversed these changes. These findings suggest that regulating the number, activated state, and morphology of microglia in hippocampal subregions might be an important basis for the antidepressant effects of LXRs.

Hyperbaric oxygen improves depression-like behaviors in chronic stress model mice by remodeling gut microbiota and regulating host metabolism

AIMS

There is growing evidence that the gut microbiota plays a significant part in the pathophysiology of chronic stress. The dysbiosis of the gut microbiota closely relates to dysregulation of microbiota-host cometabolism. Composition changes in the gut microbiota related to perturbations in metabolic profiles are vital risk factors for disease development. Hyperbaric oxygen therapy is commonly applied as an alternative or primary therapy for various diseases. Therefore, a metabolic and gut bacteria perspective is essential to uncover possible mechanisms of chronic stress and the therapeutic effect of hyperbaric oxygenation. We determined that there were significantly disturbed metabolites and disordered gut microbiota between control and chronic stress group. The study aims to offer further information on the interactions between host metabolism, gut microbiota, and chronic stress.

METHODS

At present, chronic unpredictable mild stress is considered the most widespread method of modeling chronic stress in animals, so we used a chronic unpredictable mild stress mouse model to characterize changes in the metabolome and microbiome of depressed mice by combining 16S rRNA gene sequencing and UHPLC-MS/MS-based metabolomics. Pearson's correlation-based clustering analysis was performed with above metabolomics and fecal microbiome data to determine gut microbiota-associated metabolites.

RESULTS

We found that 18 metabolites showed a significant correlation with campylobacterota. Campylobacterota associated metabolites were significantly enriched mainly in the d-glutamate and d-glutamine metabolism. Hyperoxia treatment may improve depression-like behaviors in chronic stress model mice through regulating the disrupted metabolites.

CONCLUSIONS

Hyperbaric oxygen improves depression-like behaviors in chronic stress model mice by remodeling Campylobacterota associated metabolites.

Molecular Mechanisms and Health Benefits of Ghrelin: A Narrative Review

Ghrelin, an endogenous brain-gut peptide, is secreted in large quantities, mainly from the stomach, in humans and rodents. It can perform the biological function of activating the growth hormone secretagogue receptor (GHSR). Since its discovery in 1999, ample research has focused on promoting its effects on the human appetite and pleasure-reward eating. Extensive, in-depth studies have shown that ghrelin is widely secreted and distributed in tissues. Its role in neurohumoral regulation, such as metabolic homeostasis, inflammation, cardiovascular regulation, anxiety and depression, and advanced cancer cachexia, has attracted increasing attention. However, the effects and regulatory mechanisms of ghrelin on obesity, gastrointestinal (GI) inflammation, cardiovascular disease, stress regulation, cachexia treatment, and the prognosis of advanced cancer have not been fully summarized. This review summarizes ghrelin's numerous effects in participating in a variety of biochemical pathways and the clinical significance of ghrelin in the regulation of the homeostasis of organisms. In addition, potential mechanisms are also introduced.

Abnormal prostate microbiota composition is associated with experimental autoimmune prostatitis complicated with depression in rats

Background

Microbiota play essential roles in the pathogenesis of prostatitis and depression. However, the changes in prostate microbiota have not yet been explored in rats with prostatitis/depression. This study aimed to investigate the changes of prostate microbiota in rats with prostatitis/depression.

Methods

Rats with experimental autoimmune prostatitis (EAP) complicated with depression were constructed through injection of rat prostate antigen with immunoadjuvants followed by application of chronic unpredictable mild stress (CUMS). The rats were subjected to inflammatory factor detection and behavioral testing to confirm the establishment of the model. Subsequently, the prostate microbiota was assayed in the rats and compared by 16S rRNA gene sequencing.

Results

A rat model of EAP complicated with depression was established and confirmed by increases in IL-1β, IL-6, and TNF-α as well as the occurrence of depressive‐like behaviors. EAP/CUMS significantly altered the richness, evenness, and composition of prostate microbiota. Forty-six taxonomic biomarkers for prostate microbiota were enriched in rats with EAP/depression and exhibited statistically significant and biologically consistent differences. Metabolomics profiling revealed that EAP/depression was associated with reductive acetyl coenzyme A pathway, L-lysine fermentation to acetate and butanoate, protein N-glycosylation and purine nucleobases degradation I, which is regulated by DCE29, Nocardioes, Helicobacter and Dorea.

Conclusion

Findings from the study demonstrate the existence of abnormal prostate microbiota in EAP complicated with depression and may be helpful in the treatment of comorbid diseases of prostatitis and depression.

Ghrelin and Obestatin in Adolescent Patients with Anorexia Nervosa: Is There an Association with Disordered Eating, Depression, and Obsessive-Compulsive Symptoms?

Anorexia nervosa (AN) is an eating disorder characterized by restrictive eating and significant weight loss. In the course of AN, changes are observed in appetite regulation, including orexigenic ghrelin and potentially anorexigenic obestatin. The study aimed to determine if any changes in serum ghrelin and obestatin levels during treatment of AN are observed, while investigating the correlations between these peptides and the severity of disturbed eating attitudes, depression, and anxiety. Thirty adolescent inpatients with AN (examined twice: before hospitalization treatment AN-BT and after treatment AN-AT) and thirty healthy age- and height-matched girls (CG) participated in the study. Anthropometric, serum ghrelin and obestatin concentrations and psychometric evaluations (Eating Attitudes Test 26 Item-EAT-26, Beck Depression Inventory-BDI, Hamilton Depression Rating Scale-HDRS, and Yale Brown Obsessive-Compulsive Scale-Y-BOCS) were performed. The study revealed significantly higher ghrelin and obestatin levels in AN-BT than in AN-AT. A trend toward lower levels during treatment provided partial normalizations. Analyzing correlations in the AN-BT vs. CG group, correlations of peptides with EAT-26, BDI, and HDRS scores were detected. These results suggest a potential role for ghrelin and obestatin in the context of defense mechanisms regulating appetite and body weight in the course of AN and in terms of psychopathological changes co-occurring with this eating disorder.

Effect of Epigallocatechin-3-gallate on Stress-Induced Depression in a Mouse Model: Role of Interleukin-1β and Brain-Derived Neurotrophic Factor

Epigallocatechin 3-gallate (EGCG) is a natural polyphenolic antioxidant in green tea leaves with well-known health-promoting properties. However, the influence of EGCG on a chronic animal model of depression remains to be fully investigated, and the details of the molecular and cellular changes are still unclear. Therefore, the present study aimed to investigate the antidepressant effect of EGCG in mice subjected to chronic unpredictable mild stress (CUMS). After eight consecutive weeks of CUMS, the mice were treated with EGCG (200 mg/kg b.w.) by oral gavage for two weeks. A forced swimming test (FST) was used to assess depressive symptoms. EGCG administration significantly alleviated CUMS-induced depression-like behavior in mice. EGCG also effectively decreased serum interleukin-1β (IL-1β) and increased the mRNA expression levels of brain-derived neurotrophic factor (BDNF) in the hippocampal CA3 region of CUMS mice. Furthermore, electron microscopic examination of CA3 neurons in CUMS mice showed morphological features of apoptosis, loss or disruption of the myelin sheath, and degenerating synapses. These neuronal injuries were diminished with the administration of EGCG. The treatment effect of EGCG in CUMS-induced behavioral alterations was comparable with that of clomipramine hydrochloride (Anafranil), a tricyclic antidepressant drug. In conclusion, our study demonstrates that the antidepressive action of EGCG involves downregulation of serum IL-1β, upregulation of BDNF mRNA in the hippocampus, and reduction of CA3 neuronal lesions.

Activation of liver X receptors protects oligodendrocytes in CA3 of stress-induced mice

Depression is a complex disorder that is associated with various structural abnormalities. Oligodendrocyte (OL) dysfunction is associated with the pathogenesis of depression and the promotion of hippocampal oligodendrocyte maturation and myelination could be a novel therapeutic strategy for ameliorating depressive behaviors. Recent studies have shown that activation of liver X receptors (LXRs) by GW3965 improves depressive phenotypes, but the effects of GW3965 on OL function and myelination in the hippocampus of depression remain relatively unclear. To address this issue, we investigated the effects of GW3965 on mature OL in the hippocampus and on the myelin sheaths of mice subjected to chronic unpredictable stress (CUS). Behavioral tests were performed to assess depressive behaviors. Then, the number of mature OLs (CC1⁺) in each hippocampal subregion was precisely quantified with immunohistochemical and stereological methods, and the density of newborn mature OLs (BrdU⁺/Olig2⁺/CC1⁺ cells) in each hippocampal subregion was quantified with immunofluorescence. In addition, myelin basic protein (MBP) staining intensity in the cornu ammonis 3 (CA3) region was assessed by using immunofluorescence. We found that both the number of CC1⁺ OLs and the density of BrdU⁺/Olig2⁺/CC1⁺ cells were obviously decreased in each hippocampal subregion of mice subjected to CUS, and 4 weeks of GW3965 treatment reversed these effects only in the CA3 region. Furthermore, the decreased MBP expression in the CA3 region of mice subjected to CUS was ameliorated by GW3965 treatment. Collectively, these results suggested that improvement of OL maturation and enhancement of myelination may be structural mechanisms underlying the antidepressant effects of LXR agonists.

Repeated testing modulates chronic unpredictable mild stress effects in male rats

Depression is a highly prevalent, debilitating mental disorder. Chronic unpredictable mild stress (CUMS) is the most widely applied model to study this affliction in rodents. While studies incorporating CUMS prior to an intervention often require long-lasting stress effects that persist after exposure is ceased, the longevity of these effects is rarely studied. Additionally, it is unclear whether behavioural assessments can be performed before and after interventions without repeated testing effects. In rats, we investigated CUMS effects on components of depressive-like behaviour both acutely after stress cessation and after a recovery period, as well as effects of repeated testing. We observed acute disruptions of the circadian locomotor rhythm and a reduced sucrose preference immediately after CUMS exposure. While circadian locomotor rhythm effects persisted up until four weeks after stress cessation, independently of repeated testing, sucrose preference effects did not. Interestingly, CUMS animals tested once after a recovery period of four weeks showed reduced anxiety-like behaviour in the open field and elevated plus maze compared to their control group and repeatedly-tested CUMS animals. These findings suggest that distinct CUMS-induced components of depressive-like behaviour are affected differentially by recovery time and repeated testing; these aspects should be considered carefully in future study designs.

Rapamycin Attenuates Anxiety and Depressive Behavior Induced by Helicobacter pylori in Association with Reduced Circulating Levels of Ghrelin

Background. Helicobacter pylori (H. pylori) infection is closely associated with depression and development of neuroinflammation. The aim of this study is to explore the relationship between H. pylori, depression, and circulating levels of ghrelin. Methods. Mice were randomly divided into three groups: healthy control group (gavaged sterile saline and injected with saline, $n=8$ ); H. pylori+saline group (gavaged H. pylori and injected with saline, $n=8$ ); and H. pylori+rapa group (gavaged H. pylori and injected with rapamycin, $n=8$ ). Open field test (OFT), sucrose preference test (SPT), forced swim test (FST), and tail suspension test (TST) were used for anxiety and depressive behavior test. Western blotting was utilized to assess mTOR, p-mTOR, and GSMD expression, and serum ghrelin levels were estimated using ELISA. Results. In the OFT, the control mice moved more and exhibited a increase in crossing number relative to the H. pylori+saline mice (all $P<0.05$ ). Increased quantity of fecal boli can be indicative of increased anxiety and emotionality of the subject animal. H. pylori+saline mice exhibited an increase in fecal boli when compared to control mice and H. pylori+rapa mice ( $P<0.05$ ). H. pylori infected mice decreasing the expression of ghrelin. The protein levels of p-mTOR/mTOR in the gastric antrum mTOR signaling activation and low-level ghrelin in H. pylori-infect mice compared to those in control mice (all P <0.001). Compared with single H. pylori infection, mTOR inhibitors increased the ghrelin secretion of H. pylori infection to a certain extent ( $P<0.05$ ). The protein levels of GSDMD expression significantly increase in hippocampus of H. pylori-infected mice ( $P<0.001$ ). Rapamycin treatment inhibited expression of GSDMD in H. pylori-infected mice ( $P<0.05$ ). Conclusions. H. pylori infection is associated with increased expression of mTOR and decreased circulating levels of ghrelin. Elevated pyroptosis in the brain and anxiety- and depressed-like behaviors occur when ghrelin levels are suppressed.

Gene expression profiling reveals candidate biomarkers and probable molecular mechanisms in chronic stress

Chronic stress refers to nonspecific systemic reactions under the over-stimulation of different external and internal factors for a long time. Previous studies confirmed that chronic psychological stress had a negative effect on almost all tissues and organs. We intended to further identify potential gene targets related to the pathogenesis of chronic stress-induced consequences involved in different diseases. In our study, mice in the model group lived under the condition of chronic unpredictable mild stress (CUMS) until they expressed behaviors like depression which were supposed to undergo chronic stress. We applied high-throughput RNA sequencing to assess mRNA expression and obtained transcription profiles in lung tissue from CUMS mice and control mice for analysis. In view of the prediction of high-throughput RNA sequences and bioinformatics software, and mRNA regulatory network was constructed. First, we conducted differentially expressed genes (DEGs) and obtained 282 DEGs between CUMS (group A) and the control model (group B). Then, we conducted functional and pathway enrichment analyses. In general, the function of upregulated regulated DEGs is related to immune and inflammatory responses. PPI network identified several essential genes, of which ten hub genes were related to the T cell receptor signaling pathway. qRT-PCR results verified the regulatory network of mRNA. The expressions of CD28, CD3e, and CD247 increased in mice with CUMS compared with that in control. This illustrated immune pathways are related to the pathological molecular mechanism of chronic stress and may provide information for identifying potential biomarkers and early detection of chronic stress.

How Microbes Affect Depression: Underlying Mechanisms via the Gut-Brain Axis and the Modulating Role of Probiotics

Accumulating evidence suggests that the gut microbiome influences the brain functions and psychological state of its host via the gut-brain axis, and gut dysbiosis has been linked to several mental illnesses, including major depressive disorder (MDD). Animal experiments have shown that a depletion of the gut microbiota leads to behavioral changes, and is associated with pathological changes, including abnormal stress response and impaired adult neurogenesis. Short-chain fatty acids such as butyrate are known to contribute to the up-regulation of brain-derived neurotrophic factor (BDNF), and gut dysbiosis causes decreased levels of BDNF, which could affect neuronal development and synaptic plasticity. Increased gut permeability causes an influx of gut microbial components such as lipopolysaccharides, and the resultant systemic inflammation may lead to neuroinflammation in the central nervous system. In light of the fact that gut microbial factors contribute to the initiation and exacerbation of depressive symptoms, this review summarizes the current understanding of the molecular mechanisms involved in MDD onset, and discusses the therapeutic potential of probiotics, including butyrate-producing bacteria, which can mediate the microbiota-gut-brain axis.

Oral administration of Lactococcus lactis WHH2078 alleviates depressive and anxiety symptoms in mice with induced chronic stress

Depression is a mood disorder with a high prevalence rate globally, which is associated with abnormalities in 5-hydroxytryptamine (5-HT) metabolism. Emerging evidence suggests that certain probiotics that modulate 5-HT metabolism confer beneficial effects on depression. In this study, in vitro enterochromaffin RIN14B cells were used for screening potential antidepressant probiotic Lactococcus lactis strains. The L. lactis strain WHH2078 increased to high levels the 5-HT precursor 5-hydroxytryptophan (5-HTP) and the expression of tryptophan hydroxylase 1 (Tph1), which converts tryptophan to 5-HTP in RIN14B cells. The oral administration of WHH2078 (1 × 10⁹ CFU mL^-1) in mice with induced chronic unpredictable mild stress (CUMS) for 5 weeks significantly ameliorated depressive and anxiety-like behaviors in the tail suspension test, forced swim test, sucrose preference test, and open field test. Besides, WHH2078 significantly reduced the serum corticosterone level and restored the central levels of 5-HT, 5-HTP, and brain-derived neurotrophic factor in CUMS-induced mice. Moreover, WHH2078 also reversed the 5-HTP levels in the serum and colon, accompanied by an upregulation in colonic Tph1 gene expression. Using 16S rRNA high-throughput sequencing of feces, WHH2078 was shown to improve the CUMS-induced gut microbial dysbiosis, through restoring alpha diversity and the abundances of Firmicutes and Bacteroidetes. In summary, these results indicate that WHH2078 can alleviate rodent depressive and anxiety-like behaviors in response to CUMS, which is associated with the improvement of 5-HT metabolism and modulation of the gut microbiome composition. Therefore, supplementation of the L. lactis strain WHH2078 with antidepressant properties may serve as a promising therapeutic strategy for chronic stress-induced depression.

Ghrelin mediated regulation of neurosynaptic transmitters in depressive disorders

Ghrelin is a peptide released by the endocrine cells of the stomach and the neurons in the arcuate nucleus of the hypothalamus. It modulates both peripheral and central functions. Although ghrelin has emerged as a potent stimulator of growth hormone release and as an orexigenic neuropeptide, the wealth of literature suggests its involvement in the pathophysiology of affective disorders including depression. Ghrelin exhibits a dual role through the advancement and reduction of depressive behavior with nervousness in the experimental animals. It modulates depression-related signals by forming neuronal networks with various neuropeptides and classical neurotransmitter systems. The present review emphasizes the integration and signaling of ghrelin with other neuromodulatory systems concerning depressive disorders. The role of ghrelin in the regulation of neurosynaptic transmission and depressive illnesses implies that the ghrelin system modulation can yield promising antidepressive therapies.

•

Ghrelin is the orexigenic type of neuropeptide.

•

It binds with the growth hormone secretagogue receptor (GHSR).

•

GHSR is ubiquitously present in the various brain regions.

•

Ghrelin is involved in the regulation of depression-related behavior.

•

The review focuses on the neurotransmission and signaling of ghrelin in neuropsychiatric and depressive disorders.

Electroacupuncture Ameliorates Depression-Like Behaviour in Rats by Enhancing Synaptic Plasticity via the GluN2B/CaMKII/CREB Signalling Pathway

Background

Hippocampal synaptic plasticity during the pathological process of depression has received increasing attention. Hippocampal neuron atrophy and the reduction in synaptic density induced by chronic stress are important pathological mechanisms of depression. Electroacupuncture (EA) exerts beneficial effects on depression, but the mechanism is unclear. This study explored the effect of EA on synaptic plasticity and the potential mechanism.

Methods

Forty-eight SD rats were randomly divided into the control, chronic unpredictable mild stress (CUMS), EA, and fluoxetine (FLX) groups, and each group consisted of 12 rats. The sucrose preference test, open field test, and forced swimming test were used for the evaluation of depression-like behaviour, and Golgi and Nissl staining were used for the assessment of synaptic plasticity. Western blotting and immunofluorescence were conducted to detect proteins related to synaptic plasticity and to determine their effects on signalling pathways.

Results

We found that CUMS led to depression-like behaviours, including a reduced preference for sucrose, a prolonged immobility time, and reduced exploration activity. The dendritic spine densities and neuron numbers and the protein levels of MAP-2, PSD-95, and SYN were decreased in the hippocampi of rats with CUMS-induced depression, and these trends were reversed by EA. The molecular mechanism regulating this plasticity may involve the GluN2B/CaMKII/CREB signalling pathway.

Conclusion

These results suggest that EA can improve depression-like behaviour and hippocampal plasticity induced by CUMS, and the mechanism may be related to the GluN2B/CaMKII/CREB pathway.

Potential gut-brain mechanisms behind adverse mental health outcomes of bariatric surgery

Bariatric surgery induces sustained weight loss and metabolic benefits via notable effects on the gut-brain axis that lead to alterations in the neuroendocrine regulation of appetite and glycaemia. However, in a subset of patients, bariatric surgery is associated with adverse effects on mental health, including increased risk of suicide or self-harm as well as the emergence of depression and substance use disorders. The contributing factors behind these adverse effects are not well understood. Accumulating evidence indicates that there are important links between gut-derived hormones, microbial and bile acid profiles, and disorders of mood and substance use, which warrant further exploration in the context of changes in gut-brain signalling after bariatric surgery. Understanding the basis of these adverse effects is essential in order to optimize the health and well-being of people undergoing treatment for obesity.

Gut Hormones as Potential Therapeutic Targets or Biomarkers of Response in Depression: The Case of Motilin

Recent research has identified the gut–brain axis as a key mechanistic pathway and potential therapeutic target in depression. In this paper, the potential role of gut hormones as potential treatments or predictors of response in depression is examined, with specific reference to the peptide hormone motilin. This possibility is explored through two methods: (1) a conceptual review of the possible links between motilin and depression, including evidence from animal and human research as well as clinical trials, based on a literature search of three scientific databases, and (2) an analysis of the relationship between a functional polymorphism (rs2281820) of the motilin (MLN) gene and cross-national variations in the prevalence of depression based on allele frequency data after correction for potential confounders. It was observed that (1) there are several plausible mechanisms, including interactions with diet, monoamine, and neuroendocrine pathways, to suggest that motilin may be relevant to the pathophysiology and treatment of depression, and (2) there was a significant correlation between rs2281820 allele frequencies and the prevalence of depression after correcting for multiple confounding factors. These results suggest that further evaluation of the utility of motilin and related gut peptides as markers of antidepressant response is required and that these molecular pathways represent potential future mechanisms for antidepressant drug development.

Assessing the role of ghrelin and the enzyme ghrelin O-acyltransferase (GOAT) system in food reward, food motivation, and binge eating behavior

The peripheral peptide hormone ghrelin is a powerful stimulator of food intake, which leads to body weight gain and adiposity in both rodents and humans. The hormone, thus, increases the vulnerability to obesity and binge eating behavior. Several studies have revealed that ghrelin's functions are due to its interaction with the growth hormone secretagogue receptor type 1a (GHSR1a) in the hypothalamic area; besides, ghrelin also promotes the reinforcing properties of hedonic food, acting at extra-hypothalamic sites and interacting with dopaminergic, cannabinoid, opioid, and orexin signaling. The hormone is primarily present in two forms in the plasma and the enzyme ghrelin O-acyltransferase (GOAT) allows the acylation reaction which causes the transformation of des-acyl-ghrelin (DAG) to the active form acyl-ghrelin (AG). DAG has been demonstrated to show antagonist properties; it is metabolically active, and counteracts the effects of AG on glucose metabolism and lipolysis, and reduces food consumption, body weight, and hedonic feeding response. Both peptides seem to influence the hypothalamic-pituitary-adrenal (HPA) axis and the corticosterone/cortisol level that drive the urge to eat under stressful conditions. These findings suggest that DAG and inhibition of GOAT may be targets for obesity and bingeing-related eating disorders and that AG/DAG ratio may be an important potential biomarker to assess the risk of developing maladaptive eating behaviors.

Chronic stress accelerates the process of gastric precancerous lesions in rats

Background: Gastrointestinal cancers account for 20% of all deaths worldwide. Gastric cancer (GC) patients are susceptible to psychological change, especially depression which is commonly induced by chronic stress. Gastric precancerous lesions (GPL) is an important prodromal stage in the occurrence of gastric cancer. Chronic stress influences the prognosis of GC and may influence the process of GPL as well. Methods: Sixty SD rats were randomly divided into a control group, GPL group, and GPL+CUMS group. In the GPL group, 200μg/mL N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) free drinking method combined with intermittent fasting was applied to establish the GPL animal model. Based on this, we combined the GPL rats with chronic unpredicted mild stress (CUMS) to establish a comprehensive model. We then evaluated their behavior by open field tests and sucrose preference tests. We tested the IL-6, IL-10, TNF-α, Ghrelin, Leptin and Somatostatin (SS) levels in serum and observed the expression of Ghrelin and Gastrokine 2(GKN2) in the gastric mucosa of rats with tumors by immunofluorescence. Results: Our results showed that GPL and GPL+CUMS rats all displayed a significantly decreased total distance and mean velocity traveled in the open field test. The percentages of sucrose preference were significantly decreased in the GPL+CUMS group compared to the control group. In addition, IL-6 and TNF-α were significantly increased in both the GPL and GPL+CUMS groups. Furthermore, the GPL+CUMS group showed significantly increased TNF-α levels in serum compared to the GPL rats. Our results showed that the expression of NF-κB, p53, and BCL-2 were significantly increased while BAX was reduced in the GPL and GPL+CUMS groups. Moreover, Ghrelin and Leptin levels in serum were significantly decreased in the GPL and GPL+CUMS groups. SS levels in serum were significantly increased in the GPL+CUMS group. Additionally, we found that the GPL+CUMS rats with tumors not only had strong expression of GKN2 on the luminal side and the lamina propria of the gastric mucosa and tumor, but also had expression of Ghrelin on the luminal side of the gastric mucosa. The areas that showed strong expression of GKN2 and Ghrelin, are all located around the blood vessels in the tumor. Conclusions: GPL rats under chronic stress would aggravate the conditions of GPL, shorten the process of GPL, and increase the risk of tumorigenesis. In addition, the close monitoring of the mental health of cancer survivors and precancerous lesion patients is suggested to be of great significance in the prevention and treatment of cancer.

Preliminary evidence of acylated ghrelin association with depression severity in postmenopausal women

We have previously shown increased depression and anxiety scores in postmenopausal overweight women, when compared to overweight premenopausal women. The mechanisms responsible for these alterations are not understood. Although ghrelin involvement in mood modulation has been suggested, its role is still ambiguous and has not been evaluated in postmenopause. Here we investigated the association of ghrelin with depression and anxiety symptoms in postmenopausal women. Fifty-five postmenopausal women with depression symptoms, who were not in use of hormones or antidepressants, were included in the study. Depression symptoms were evaluated by Beck's Depression Inventory (BDI) and Patient Health Questionnaire-9 (PHQ-9) and anxiety symptoms were evaluated by Beck's Anxiety Inventory (BAI). Women were allocated into three groups, according to BDI classification of mild, moderate, or severe depression symptoms. Anthropometric, biochemical and hormonal parameters were analyzed. Total and acylated ghrelin levels were higher in the severe depression than in the mild depression group. Multivariate regression analyses showed positive associations of BDI scores with acylated ghrelin and BMI, and of PHQ-9 scores with acylated ghrelin and homeostasis model assessment of insulin resistance (HOMA-IR). BAI scores associated positively with waist-to-hip ratio. To the best of our knowledge, this is the first demonstration of an association between acylated ghrelin and the severity of depression symptoms in postmenopausal women. This association may reflect either a physiological response aimed at fighting against depression symptoms or a causal factor of this mental disorder.

The Ghrelin/Growth Hormone Secretagogue Receptor System Is Involved in the Rapid and Sustained Antidepressant-Like Effect of Paeoniflorin

Major depressive disorder (MDD) is a debilitating mental illness affecting people worldwide. Although significant progress has been made in the development of therapeutic agents to treat this condition, fewer than half of all patients respond to currently available antidepressants, highlighting the urgent need for the development of new classes of antidepressant drugs. Here, we found that paeoniflorin (PF) produced rapid and sustained antidepressant-like effects in multiple mouse models of depression, including the forced swimming test and exposure to chronic mild stress (CMS). Moreover, PF decreased the bodyweight of mice without affecting food intake and glucose homeostasis, and also reduced the plasma levels of total ghrelin and the expression of ghrelin O-acyltransferase in the stomach; however, the plasma levels of ghrelin and the ghrelin/total ghrelin ratio were unaffected. Furthermore, PF significantly increased the expression of growth hormone secretagogue receptor 1 alpha (GHSR1α, encoded by the Ghsr gene) in the intestine, whereas the levels of GHSR1α in the brain were only marginally downregulated following subchronic PF treatment. Finally, the genetic deletion of Ghsr attenuated the antidepressant-like effects of PF in mice exposed to CMS. These results suggested that increased GHSR1α expression in the intestine mediates the antidepressant-like effects of PF. Understanding peripheral ghrelin/GHSR signaling may provide new insights for the screening of antidepressant drugs that produce fast-acting and sustained effects.

Electroacupuncture may alleviate behavioral defects via modulation of gut microbiota in a mouse model of Parkinson's disease

OBJECTIVE

Parkinson's disease (PD) is a chronic neurodegenerative disease involving non-motor symptoms, of which gastrointestinal disorders are the most common. In light of recent results, intestinal dysfunction may be involved in the pathogenesis of PD. Electroacupuncture (EA) has shown potential effects, although the underlying mechanism remains mostly unknown. We speculated that EA could relieve the behavioral defects of PD, and that this effect would be associated with modulation of the gut microbiota.

METHODS

Mice were randomly divided into three groups: control, PD + MA (manual acupuncture), and PD + EA. MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) was used to establish the mouse model of PD. Rotarod performance tests, open field tests, and pole tests were carried out to assess motor deficiencies. Immunohistochemistry was conducted to examine the survival of dopaminergic neurons. 16S ribosomal RNA (rRNA) gene sequencing was applied to investigate the alterations of the gut microbiome. Quantitative real-time polymerase chain reaction (PCR) was performed to characterize the messenger RNA (mRNA) levels of pro-inflammatory and anti-inflammatory cytokines.

RESULTS

We found that EA was able to alleviate the behavioral defects in the rotarod performance test and pole test, and partially rescue the significant loss of dopaminergic neurons in the substantia nigra (SN) chemically induced by MPTP in mice. Moreover, the PD + MA mice showed a tendency toward decreased intestinal microbial alpha diversity, while EA significantly reversed it. The abundance of Erysipelotrichaceae was significantly increased in PD + MA mice, and the alteration was also reversed by EA. In addition, the pro-inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-α were substantially increased in the SN of PD + MA mice, an effect that was reversed by EA.

CONCLUSION

These results suggest that EA may alleviate behavioral defects via modulation of gut microbiota and suppression of inflammation in the SN of mice with PD, which provides new insights into the pathogenesis of PD and its treatment.

Pathophysiology linking depression and type 2 diabetes: Psychotherapy, physical exercise, and fecal microbiome transplantation as damage control

Diabetes increases the likelihood of developing depression and vice versa. Research on this bidirectional association has somewhat managed to delineate the interplay among implicated physiological processes. Still, further exploration is required in this context. This review addresses the comorbidity by investigating suspected common pathophysiological mechanisms. One such factor is psychological stress which disturbs the hypothalamic-pituitary-adrenal axis causing hormonal imbalance. This includes elevated cortisol levels, a common biomarker of both depression and diabetes. Disrupted insulin signaling drives the hampered neurotransmission of serotonin, dopamine, and norepinephrine. Also, adipokine hormones such as adiponectin, leptin, and resistin and the orexigenic hormone, ghrelin, are involved in both depression and T2DM. This disarray further interferes with physiological processes encompassing sleep, the gut-brain axis, metabolism, and mood stability. Behavioral coping mechanisms, such as unhealthy eating, mediate disturbed glucose homeostasis, and neuroinflammation. This is intricately linked to oxidative stress, redox imbalance, and mitochondrial dysfunction. However, interventions such as psychotherapy, physical exercise, fecal microbiota transplantation, and insulin-sensitizing agents can help to manage the distressing condition. The possibility of glucagon-like peptide 1 possessing a therapeutic role has also been discussed. Nonetheless, there stands an urgent need for unraveling new correlating targets and biological markers for efficient treatment.

A new understanding of GHSR1a--independent of ghrelin activation

Growth hormone secretagogue receptor 1a (GHSR1a), a member of the G protein-coupled receptor (GPCR) family, is a functional receptor of ghrelin. The expression levels and activities of GHSR1a are affected by various factors. In past years, it has been found that the ghrelin-GHSR1a system can perform biological functions such as anti-inflammation, anti-apoptosis, and anti-oxidative stress. In addition to mediating the effect of ghrelin, GHSR1a also has abnormally high constitutive activity; that is, it can still transmit intracellular signals without activation of the ghrelin ligand. This constitutive activity affects brain functions, growth and development of the body; therefore, it has profound impacts on neurodegenerative diseases and some other age-related diseases. In addition, GHSR1a can also form homodimers or heterodimers with other GPCRs, affecting the release of neurotransmitters, appetite regulation, cell proliferation and insulin release. Therefore, further understanding of the constitutive activities and dimerization of GHSR1a will enable us to better clarify the characteristics of GHSR1a and provide more therapeutic targets for drug development. Here, we focus on the roles of GHSR1a in various biological functions and provide a comprehensive summary of the current research on GHSR1a to provide broader therapeutic prospects for age-related disease treatment.

Vitamin C protects against chronic social isolation stress-induced weight gain and depressive-like behavior in adult male rats

Objective. Considering the importance of ghrelin in stress-induced hyperphagia and a role of antioxidants in decreasing body weight, in the present study, the effect of vitamin C (VitC) on ghrelin secretion and food intake following chronic social isolation (CIS) was evaluated in rats.Methods. Thirty two male Wistar rats (200-220g) were randomly divided into: control, VitC, CIS, and CIS + VitC groups. Animals received VitC (500 mg/kg/day)/saline by gavage for 3 weeks. For 24 h cumulative and post 18-20 h fasting food intake, fasting plasma ghrelin level, and body weight were measured. Gastric histopathology was also evaluated.Results. Results showed a marked increase in fasting plasma ghrelin and food intake in stressed rats compared to controls. VitC prevented the increases in stressed rats. Histological assessment indicated a positive effect of VitC on gastric glandular cells compared to control, an effect that might partially be a reason of significant increase of plasma ghrelin levels in VitC rats. Elevated plasma ghrelin in VitC group was even higher than that one in stressed group, whereas there were no significant changes in the food intake. Assessment of the percentage of changes in body weight during 21 days showed a significant increase in stressed rats compared to controls. Vitamin C treatment prevented this increase. Stressed rats also displayed depression-like behavior as indicated by sucrose test, whereas VitC ameliorated it.Conclusions. The data of the present study indicate that VitC may overcome ghrelin-induced hyperphagia and improve the abnormal feeding and depressive behavior in CIS rats.

Western Diet: Implications for Brain Function and Behavior

The Western diet (WD) pattern characterized by high daily intake of saturated fats and refined carbohydrates often leads to obesity and overweight, and it has been linked to cognitive impairment and emotional disorders in both animal models and humans. This dietary pattern alters the composition of gut microbiota, influencing brain function by different mechanisms involving the gut-brain axis. In addition, long-term exposure to highly palatable foods typical of WD could induce addictive-like eating behaviors and hypothalamic-pituitary-adrenal (HPA) axis dysregulation associated with chronic stress, anxiety, and depression. In turn, chronic stress modulates eating behavior, and it could have detrimental effects on different brain regions such as the hippocampus, hypothalamus, amygdala, and several cortical regions. Moreover, obesity and overweight induce neuroinflammation, causing neuronal dysfunction. In this review, we summarize the current scientific evidence about the mechanisms and factors relating WD consumption with altered brain function and behavior. Possible therapeutic interventions and limitations are also discussed, aiming to tackle and prevent this current pandemic.

THE INTRIGUING LIGAND-DEPENDENT AND LIGAND-INDEPENDENT ACTIONS OF THE GROWTH HORMONE SECRETAGOGUE RECEPTOR ON REWARD-RELATED BEHAVIORS

The growth hormone secretagogue receptor (GHSR) is a G-protein-coupled receptor (GPCR) highly expressed in the brain, and also in some peripheral tissues. GHSR activity is evoked by the stomach-derived peptide hormone ghrelin and abrogated by the intestine-derived liver-expressed antimicrobial peptide 2 (LEAP2). In vitro, GHSR displays ligand-independent actions, including a high constitutive activity and an allosteric modulation of other GPCRs. Beyond its neuroendocrine and metabolic effects, cumulative evidence shows that GHSR regulates the activity of the mesocorticolimbic pathway and modulates complex reward-related behaviors towards different stimuli. Here, we review current evidence indicating that ligand-dependent and ligand-independent actions of GHSR enhance reward-related behaviors towards appetitive stimuli and drugs of abuse. We discuss putative neuronal networks and molecular mechanisms that GHSR would engage to modulate such reward-related behaviors. Finally, we briefly discuss imaging studies showing that ghrelin would also regulate reward processing in humans. Overall, we conclude that GHSR is a key regulator of the mesocorticolimbic pathway that influences its activity and, consequently, modulates reward-related behaviors via ligand-dependent and ligand-independent actions.

The Good, the Bad and the Unknown Aspects of Ghrelin in Stress Coping and Stress-Related Psychiatric Disorders

Ghrelin is a peptide hormone released by specialized X/A cells in the stomach and activated by acylation. Following its secretion, it binds to ghrelin receptors in the periphery to regulate energy balance, but it also acts on the central nervous system where it induces a potent orexigenic effect. Several types of stressors have been shown to stimulate ghrelin release in rodents, including nutritional stressors like food deprivation, but also physical and psychological stressors such as foot shocks, social defeat, forced immobilization or chronic unpredictable mild stress. The mechanism through which these stressors drive ghrelin release from the stomach lining remains unknown and, to date, the resulting consequences of ghrelin release for stress coping remain poorly understood. Indeed, ghrelin has been proposed to act as a stress hormone that reduces fear, anxiety- and depression-like behaviors in rodents but some studies suggest that ghrelin may - in contrast - promote such behaviors. In this review, we aim to provide a comprehensive overview of the literature on the role of the ghrelin system in stress coping. We discuss whether ghrelin release is more than a byproduct of disrupted energy homeostasis following stress exposure. Furthermore, we explore the notion that ghrelin receptor signaling in the brain may have effects independent of circulating ghrelin and in what way this might influence stress coping in rodents. Finally, we examine how the ghrelin system could be utilized as a therapeutic avenue in stress-related psychiatric disorders (with a focus on anxiety- and trauma-related disorders), for example to develop novel biomarkers for a better diagnosis or new interventions to tackle relapse or treatment resistance in patients.

Panaxynol attenuates CUMS-induced anxiety and depressive-like behaviors via regulating neurotransmitters, synapses and the HPA axis in mice

Panaxynol (PAL, also called falcarinol) is widely found in plants of the Umbelliferae family, among which carrots are rich in PAL, so it is proved to be edible. PAL has neuroprotective effects and other pharmacological activities. This study aimed to explore the effects and mechanisms of action of PAL on chronic unpredictable mild stress (CUMS)-induced anxiety and depression in mice. The effects of PAL on behavioral activities in mice were first assessed by a CUMS-induced depression model. The secretion levels of monoamine neurotransmitters and hypothalamic-pituitary-adrenal (HPA) axis-related hormones were measured by ELISA. Western blotting was used to analyze the expression of glucocorticoid receptor (GR), glutamate receptor 1 (GluR1) and synapse-associated protein in the hippocampus. The behavioral experiment results showed that PAL can improve exploratory behavior and activities in mice. Meanwhile, PAL can significantly activate the release of 5-HT/5-HIAA and DA/HVA in the hippocampus. It inhibits the expression of adrenocorticotropic hormone (ACTH), corticosterone (CORT) and corticotrophin-releasing hormone (CRH) in serum and the hypothalamus. The contents of GR, glutamate receptor 1 (GluR1), postsynaptic density-95 (PSD95) and synapsin I protein in the hippocampus significantly increased. Studies have found that PAL can inhibit the hyperfunction of the HPA axis, which may be achieved by regulating HPA axis hormones and GR. Meanwhile, PAL promotes the release of 5-HT and DA in the hippocampus and improves synaptic plasticity in the hippocampus, allowing neurotransmitters to function more effectively. Therefore, PAL may improve anxiety and depression-like effects in mice through the abovementioned effects.

Both ghrelin deletion and unacylated ghrelin overexpression preserve muscles in aging mice

Sarcopenia, the decline in muscle mass and functionality during aging, might arise from age-associated endocrine dysfunction. Ghrelin is a hormone circulating in both acylated (AG) and unacylated (UnAG) forms with anti-atrophic activity on skeletal muscle. Here, we show that not only lifelong overexpression of UnAG (Tg) in mice, but also the deletion of ghrelin gene (Ghrl KO) attenuated the age-associated muscle atrophy and functionality decline, as well as systemic inflammation. Yet, the aging of Tg and Ghrl KO mice occurs with different dynamics: while old Tg mice seem to preserve the characteristics of young animals, Ghrl KO mice features deteriorate with aging. However, young Ghrl KO mice show more favorable traits compared to WT animals that result, on the whole, in better performances in aged Ghrl KO animals. Treatment with pharmacological doses of UnAG improved muscle performance in old mice without modifying the feeding behavior, body weight, and adipose tissue mass. The antiatrophic effect on muscle mass did not correlate with modifications of protein catabolism. However, UnAG treatment induced a strong shift towards oxidative metabolism in muscle. Altogether, these data confirmed and expanded some of the previously reported findings and advocate for the design of UnAG analogs to treat sarcopenia.

Effects of sex and age on parental motivation in adult virgin California mice

Female mammals often demonstrate a rapid initiation of maternal responsiveness immediately after giving birth, as a result of neuroendocrine changes that occur during pregnancy and parturition. However, fathers and virgins of some species may display infant care similar to that performed by mothers but without experiencing these physiological events. In biparental species, in which both mothers and fathers care for their offspring, both sex and age may affect parental motivation, even in adult virgins. We examined the effects of sex and age on parental motivation in the California mouse, a monogamous, biparental rodent. We compared parental motivation of male and female virgins in both mid- and old adulthood using two new tests - a T-maze test and a rain test - as well as in standard parental-behavior tests. Adult virgin males were more parentally motivated than adult virgin females in both the T-maze test and the parental-behavior test, but parental motivation did not differ markedly between middle-aged and older adults of either sex. These findings suggest that sex differences in parental motivation in adult virgins are similar to those observed in other biparental rodents, and indicate that the T-maze test may be useful for evaluating parental motivation in this species.

Rapid and Prolonged Antidepressant-like Effect of Crocin Is Associated with GHSR-Mediated Hippocampal Plasticity-related Proteins in Mice Exposed to Prenatal Stress

Prenatal stress (PNS) has a prolonged and adverse effect on offspring, leading to a significantly increased vulnerability to developing depression in their later life. Traditional therapies have delayed onset and limited efficacy; thus, it remains an urgent need to find novel medications with fast-onset and high-efficacy potentials. Crocin, with its structure clearly examined, has shown antidepressant-like effects. However, few studies extensively investigated its effect especially in mice exposed to PNS. Using an established PNS model, we tested whether crocin could have a rapid and persistent antidepressant-like effect in PNS mice. Growth hormone secretagogue receptor (GHSR) and phosphoinositide 3-kinase (PI3K) inhibitors were used to test their effects in antidepressant-like effect of crocin. Hippocampal GHSR-PI3K signaling was examined both in PNS mice treated with a single dose of crocin and in combination of GHSR inhibitor. PNS mice showed depression-like behaviors at juvenile and adulthood, and crocin induced an instant and persistent antidepressant-like response in PNS mice in a dose-dependent manner. Moreover, crocin increased the expression of hippocampal synaptic plasticity-associated proteins through the restoration of GHSR-PI3K signaling. Inhibitions of both GHSR and PI3K abolished the effect of crocin in alleviating depressive-like behaviors. More importantly, GHSR inhibitor JMV2959 blocked the enhanced expression of hippocampal plasticity-related proteins induced by crocin. The present study demonstrated that crocin induced a fast-onset and prolonged antidepressant effect in PNS mice and suggested that GHSR-PI3K signaling may play a key role in crocin's effect at least partially by a restoration of hippocampal synaptic plasticity-associated proteins.

Rapid anti-depressant-like effects of ketamine and other candidates: Molecular and cellular mechanisms

Major depressive disorder takes at least 3 weeks for clinical anti‐depressants, such as serotonin selective reuptake inhibitors, to take effect, and only one‐third of patients remit. Ketamine, a kind of anaesthetic, can alleviate symptoms of major depressive disorder patients in a short time and is reported to be effective to treatment‐resistant depression patients. The rapid and strong anti‐depressant‐like effects of ketamine cause wide concern. In addition to ketamine, caloric restriction and sleep deprivation also elicit similar rapid anti‐depressant‐like effects. However, mechanisms about the rapid anti‐depressant‐like effects remain unclear. Elucidating the mechanisms of rapid anti‐depressant effects is the key to finding new therapeutic targets and developing therapeutic patterns. Therefore, in this review we summarize potential molecular and cellular mechanisms of rapid anti‐depressant‐like effects based on the pre‐clinical and clinical evidence, trying to provide new insight into future therapy.

Optimization of food deprivation and sucrose preference test in SD rat model undergoing chronic unpredictable mild stress

BACKGROUND

The chronic unpredictable mild stress (CUMS) model has long been considered the best model for exploring the pathophysiological mechanisms underlying depression. However, there are no widely recognised standards for strategies for modeling and for behavioral testing. The present study aimed to optimize the protocols for food deprivation and the sucrose preference test (SPT) for the CUMS model.

METHODS

We first evaluated the effects of different long periods of food deprivation on the body weight of Sprague Dawley (SD) rats by testing food deprivation for 24 hours (8:00-8:00+), food deprivation for 12 hours during the daytime (8:00-20:00) and food deprivation for 12 hours at night (20:00-8:00+). Next, we established a SD rat CUMS model with 15 different stimulations, and used body weight measurement, SPT, forced swim test (FST), open field test (OFT) and Morris water maze (MWM) test to verify the success of the modeling. In the SPT, consumption of sucrose and pure water within 1 and 12 hours was measured.

RESULTS

Twelve hours of food deprivation during the daytime (8:00-20:00) had no effect on body weight, while 12 hours of food deprivation at night (20:00-8:00+) and 24 hours of food deprivation (8:00-8:00+) significantly reduced the mean body weight of the SD rats. When SPT was used to verify the successful establishment of the CUMS rat model, sucrose consumption measured within 12 hours was less variable than that measured within 1 hour.

CONCLUSIONS

Twelve hours of food deprivation in the daytime (8:00-20:00) may be considered a mild stimulus for the establishment of a CUMS rat model. Measuring sucrose consumption over 12 hours is recommended for SPT.