Association between repeated unpredictable chronic mild stress (UCMS) procedures with a high fat diet: a model of fluoxetine resistance in mice

Prepulse inhibition can predict the motivational effects of cocaine in female mice exposed to maternal separation

The prepulse inhibition (PPI) of the startle response can identify the rodents that are more sensitive to the effects of cocaine. Mice with a lower PPI presented a higher vulnerability to the effects of cocaine and a higher susceptibility to developing a substance use disorder (SUD). Maternal separation with early weaning (MSEW) is a relevant animal model to induce motivational alterations throughout life. Nevertheless, only a few studies on females exist, even though they are more vulnerable to stress- and cocaine-related problems. Hence, the aim of the present study was to evaluate the ability of PPI to identify females with a greater vulnerability to the long-term consequences of early stress on the motivational effects of cocaine. Female mice underwent MSEW and were classified according to their high or low PPI. They were then assessed in the cocaine-induced locomotor sensitization test, the conditioned place preference paradigm or the operant self-administration paradigm. Additionally, they were also evaluated in the passive avoidance task, the tail-suspension and the splash tests. The results revealed that the females with lower PPI presented higher consequences of MSEW on the effects of cocaine and showed an increase in anhedonia-like behaviours. Our findings support that a PPI deficit could represent a biomarker of vulnerability to the effects of cocaine induced by MSEW.

Combination of electroconvulsive stimulation with ketamine or escitalopram protects the brain against inflammation and oxidative stress induced by maternal deprivation and is critical for associated behaviors in male and female rats

This study aimed at evaluating the treatment effects with ketamine, electroconvulsive stimulation (ECS), escitalopram, alone or in combination in adult rats of both sexes, subjected to the animal model of maternal deprivation (MD). All groups were subjected to the forced swimming test (FST), splash and open field tests. The prefrontal cortex (PFC), hippocampus and serum were collected to analyze oxidative stress and inflammatory parameters. MD induced depressive-like behavior in the FST test in males and reduced grooming time in male and female rats. The treatments alone or combined reversed depressive and anhedonic behavior in females. In males, all treatments increased grooming time, except for ECS + escitalopram + ketamine. MD increased lipid peroxidation and protein carbonylation, nitrite/nitrate concentration and myeloperoxidase activity in the PFC and hippocampus of males and females. However, the treatment's response was sex dependent. Catalase activity decreased in the PFC of males and the PFC and hippocampus of females, and most treatments were not able to reverse it. MD increased the inflammation biomarkers levels in the PFC and hippocampus of males and females, and most treatments were able to reverse this increase. In all groups, a reduction in the interleukin-10 levels in the PFC and hippocampus of female and male rats was observed. Our study shows different responses between the sexes in the patterns evaluated and reinforces the use of the gender variable as a biological factor in MDD related to early stress and in the response of the therapeutic strategies used.

High and fluctuating levels of ovarian hormones induce an anxiogenic effect, which can be modulated under stress conditions: Evidence from an assisted reproductive rodent model

Elevated levels of endogenous ovarian hormones are conditions commonly experienced by women undergoing assisted reproductive technologies (ART). Additionally, infertility-associated stress and treatment routines are factors that together may have a highly negative impact on female emotionality, which can be aggravated when several cycles of ART are needed to attempt pregnancy. This study aimed to investigate the effect of high and fluctuating levels of gonadal hormones induced by repeated ovarian stimulation on the stress response in rodents. To mimic the context of ART, female rats were exposed to an unpredictable chronic mild stress (UCMS) paradigm for four weeks. During this time, three cycles of ovarian stimulation (superovulation) (150 IU/Kg of PMSG and 75 IU/Kg of hCG) were applied, with intervals of two estrous cycles between them. The rats were distributed into four groups: Repeated Superovulation/UCMS; Repeated Superovulation/No Stress; Saline/UCMS; and Saline/No Stress. Anxiety-like and depressive-like behaviors were evaluated in a light-dark transition box and by splash test, respectively. Corticosterone, estradiol, progesterone, and biometric parameters were assessed. Data were analyzed using a two-way Generalized Linear Model (GzLM). Our results showed that repeated ovarian stimulation exerts by itself an expressive anxiogenic effect. Surprisingly, when high and fluctuating levels of ovarian hormones were combined with chronic stress, anxiety-like behavior was no longer observed, and a depressive-like state was not detected. Our findings suggest that females subjected to emotional overload induced by repeated ovarian stimulation and chronic stress seem to trigger the elaboration of adaptive coping strategies.

Therapeutic effect of Thymoquinone on behavioural response to UCMS and neuroinflammation in hippocampus and amygdala in BALB/c mice model

RATIONALE

Major depressive disorder is the leading cause of disability worldwide. The corticolimbic system plays a critical role in the emotional and cognitive aspects of major depressive disorder. Owing to the unsatisfactory efficacy of conventional antidepressants, there is a need to explore novel therapies.

OBJECTIVES

The current study aimed to explore the antidepressant potential of thymoquinone, a natural compound with anti-inflammatory activity, and propose its underlying mechanism of action in the unpredictable chronic mild stress (UCMS) mouse model.

METHODS

Coat state, forced swim test, elevated plus maze test, novelty suppressed feeding test and social interaction test were performed to quantify the behavioural shift induced by UCMS and the effect of thymoquinone and fluoxetine treatment. In addition, messenger RNA (mRNA) expression levels of inflammatory cytokines (IL-1β, IL-6 and TNF-α) and BDNF and NeuN were analysed by a quantitative real-time polymerase chain reaction in the hippocampus and amygdala of experimental and control groups.

RESULTS

UCMS significantly deteriorated coat state. Thymoquinone reinstated the resignation behaviour and latency to feed affected by UCMS. UCMS induced an increase in inflammatory cytokines (IL-1β, IL-6 and TNF-α) in the hippocampus and amygdala, which was decreased by thymoquinone. UCMS caused an increase in BDNF and NeuN mRNA levels in the amygdala while a decrease in the hippocampus. This opposite effect on BDNF was also compensated by thymoquinone; however, thymoquinone did not significantly change Ki67 and NeuN mRNA levels in the hippocampus.

CONCLUSIONS

Thymoquinone restored the behavioural changes induced by UCMS. In addition, the antidepressant effect of thymoquinone is in line with changes in inflammatory parameters and changes in BDNF in the hippocampus and amygdala.

Ketamine abrogates sensorimotor deficits and cytokine dysregulation in a chronic unpredictable mild stress model of depression

Major depressive disorder (MDD) is a serious mental disorder with influence across the functional systems of the body. The pathogenesis of MDD has been known to involve the alteration of normal body functions responsible for the normal inflammation processes within the CNS; this along with other effects results in the depreciation of the sensorimotor performance of the body. Ketamine hydrochloride, a novel antidepressant agent, has been used as a therapeutic agent to treat MDD with its efficacy stretching as far as enhancing sensorimotor performance and restoring normal cytokine levels of the CNS. While these therapeutic actions of ketamine may or may not be related, this study made use of chronic unpredictable mild stress (CUMS) to generate the mouse model of depression. The efficacy of ketamine as an antidepressant following sequential exposure and co-administrative treatment protocols of administration was evaluated using behavioural tests for sensorimotor performance and depressive-like behaviours. Its effect in managing CNS inflammation was assessed via the biochemical analysis of inflammatory cytokine levels in the cerebrum, spinal cord and cerebellum; and immunohistochemical demonstration of microglial activity in the corpus striatum and cerebellum. The sensorimotor performance which had been diminished by CUMS showed greater improvement under the sequential exposure regimen of ketamine. Ketamine was also efficacious in decreasing the level of inflammation with an evident reduction in microglial activation and pro-inflammatory cytokines in the studied regions, following CUMS exposure. Taken together, our study indicates that ketamine therapy can improve sensorimotor deficits co-morbid with a depressive disorder in parallel with modulation of the inflammatory system.

Involvement of oxidative pathways and BDNF in the antidepressant effect of carvedilol in a depression model induced by chronic unpredictable stress

RATIONALE

Depression is a severe psychiatric disorder with oxidative imbalance and neurotrophic deficits as underlying mechanisms.

OBJECTIVES

Based on the antioxidant effects of carvedilol (CARV), here, we aimed to evaluate CARV's effects against depression induced by the chronic unpredictable stress (CUS) model.

METHODS

Female Swiss mice were submitted to the CUS protocol for 21 days. Between days 15 and 22, the animals received CARV (5 or 10 mg/kg) or desvenlafaxine (DVS 10 mg/kg) orally. On the 22nd day, mice were subjected to behavioral tests to evaluate locomotion, depressive-like behavior (tail suspension test), motivation/self-care with the splash test (ST), social interaction, and working memory Y-maze test. The prefrontal cortex (PFC) and hippocampus were dissected to evaluate alterations of oxidative and brain-derived neurotrophic factor (BDNF).

RESULTS

The CUS model reduced locomotion and increased grooming latency, while it reduced the number of groomings in the ST. Both doses of CARV and DVS reverted these alterations. In addition, DVS and CARV reversed CUS model-induced working memory and social interaction deficits. The CUS model decreased hippocampal reduced glutathione (GSH), while DVS and CARV increased GSH in the PFC (CARV5) and hippocampus (CARV5 and 10). The CUS model increased nitrite and malondialdehyde (MDA) concentrations in both areas. All treatments reversed nitrite alterations, while CARV10 changed MDA levels in PFC and all treatments in the hippocampus. The CUS model reduced BDNF levels. CARV10 increased BDNF in the PFC, while both doses of CARV increased hippocampal levels of this neurotrophin.

CONCLUSIONS

CARV presents antidepressant-like effects comparable to those observed with DVS. In addition, it has an antioxidant effect and is capable of increasing BDNF brain concentrations. Further studies are needed to elucidate the mechanisms involved in the antidepressant effect of CARV.

A new experimental design to study inflammation-related versus non-inflammation-related depression in mice

Background

Major depressive disorder (MDD) represents a major public health concern, particularly due to its steadily rising prevalence and the poor responsiveness to standard antidepressants notably in patients afflicted with chronic inflammatory conditions, such as obesity. This highlights the need to improve current therapeutic strategies, including by targeting inflammation based on its role in the pathophysiology and treatment responsiveness of MDD. Nevertheless, dissecting the relative contribution of inflammation in the development and treatment of MDD remains a major issue, further complicated by the lack of preclinical depression models suitable to experimentally dissociate inflammation-related vs. inflammation-unrelated depression.

Methods

While current models usually focus on one particular MDD risk factor, we compared in male C57BL/6J mice the behavioral, inflammatory and neurobiological impact of chronic exposure to high-fat diet (HFD), a procedure known to induce inflammation-related depressive-like behaviors, and unpredictable chronic mild stress (UCMS), a stress-induced depression model notably renowned for its responsivity to antidepressants.

Results

While both paradigms induced neurovegetative, depressive-like and anxiety-like behaviors, inflammation and downstream neurobiological pathways contributing to inflammation-driven depression were specifically activated in HFD mice, as revealed by increased circulating levels of inflammatory factors, as well as brain expression of microglial activation markers and enzymes from the kynurenine and tetrahydrobiopterin (BH4) pathways. In addition, serotoninergic and dopaminergic systems were differentially impacted, depending on the experimental condition.

Conclusions

These data validate an experimental design suitable to deeply study the mechanisms underlying inflammation-driven depression comparatively to non-inflammatory depression. This design could help to better understand the pathophysiology of treatment resistant depression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02330-9.

Role of toll-like receptor 4 and sex in 6-hydroxydopamine-induced behavioral impairments and neurodegeneration in mice

Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive loss of the nigrostriatal dopaminergic neurons that are associated with motor alterations and non-motor manifestations (such as depression). Neuroinflammation is a process with a critical role in the pathogenesis of PD. In this regard, toll-like receptor 4 (TLR4) is a central mediator of immune response in PD. Moreover, there are gender-related differences in the incidence, prevalence, and clinical features of PD. Therefore, we aimed to elucidate the role of TLR4 in the sex-dependent response to dopaminergic denervation induced by 6-hydroxydopamine (6-OHDA) in mice. Female and male adult wildtype (WT) and TLR4 knockout (TLR4-/-) mice were administered with unilateral injection of 6-OHDA in the dorsal striatum, and non-motor and motor impairments were evaluated for 30 days, followed by biochemistry analysis in the substantia nigra pars compacta (SNc), dorsal striatum, and dorsoventral cortex. Early non-motor impairments (i.e., depressive-like behavior and spatial learning deficits) induced by 6-OHDA were observed in the male WT mice but not in male TLR4-/- or female mice. Motor alterations were observed after administration of 6-OHDA in both strains, and the lack of TLR4 was also related to motor commitment. Moreover, ablation of TLR4 prevented 6-OHDA-induced dopaminergic denervation and microgliosis in the SNc, selectively in female mice. These results reinforced the existence of sex-biased alterations in PD and indicated TLR4 as a promising therapeutic target for the motor and non-motor symptoms of PD, which will help counteract the neuroinflammatory and neurodegenerative processes.

Novel drug developmental strategies for treatment-resistant depression

Major depressive disorder is a leading cause of disability worldwide. Because conventional therapies are ineffective in many patients, novel strategies are needed to overcome treatment‐resistant depression (TRD). Limiting factors of successful drug development in the last decades were the lack of (1) knowledge of pathophysiology, (2) translational animal models and (3) objective diagnostic biomarkers. Here, we review novel drug targets and drug candidates currently investigated in Phase I–III clinical trials. The most promising approaches are inhibition of glutamatergic neurotransmission by NMDA and mGlu₅ receptor antagonists, modulation of the opioidergic system by κ receptor antagonists, and hallucinogenic tryptamine derivates. The only registered drug for TRD is the NMDA receptor antagonist, S‐ketamine, but add‐on therapies with second‐generation antipsychotics, certain nutritive, anti‐inflammatory and neuroprotective agents seem to be effective. Currently, there is an intense research focus on large‐scale, high‐throughput omics and neuroimaging studies. These results might provide new insights into molecular mechanisms and potential novel therapeutic strategies.

Suppression of PTRF Alleviates Post-Infectious Irritable Bowel Syndrome via Downregulation of the TLR4 Pathway in Rats

Background: Accumulating evidence suggests that the polymerase I and transcript release factor (PTRF), a key component of the caveolae structure on the plasma membrane, plays a pivotal role in suppressing the progression of colorectal cancers. However, the role of PTRF in the development of functional gastrointestinal (GI) disorders remains unclear. Post-infectious irritable bowel syndrome (PI-IBS) is a common functional GI disorder that occurs after an acute GI infection. Here, we focused on the role of PTRF in the occurrence of PI-IBS and investigated the underlying mechanisms. Methods: Lipopolysaccharide (LPS) (5 μg/ml) was used to induce inflammatory injury in human primary colonic epithelial cells (HCoEpiCs). Furthermore, a rat model of PI-IBS was used to study the role of PTRF. Intestinal sensitivity was assessed based on the fecal water content. A two-bottle sucrose intake test was used to evaluate behavioral changes. Furthermore, shRNA-mediated knockdown of PTRF was performed both in vitro and in vivo. We detected the expression of PTRF in colonic mucosal tissues through immunohistochemistry (IHC), western blotting (WB), and immunofluorescence (IF) analysis. Luciferase activity was quantified using a luciferase assay. Co-localization of PTRF and Toll-like receptor 4 (TLR4) was detected using IF analysis. The activation of the signaling pathways downstream of TLR4, including the iNOs, p38, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) pathways, was detected via WB. The levels of NO, IL-1β, IL-6, and TNF-α were measured using enzyme-linked immunosorbent assays. Results: LPS significantly induced PTRF expression and signaling downstream of TLR4, including p38, ERK, and JNK pathways, in HCoEpiCs. Moreover, shRNA-mediated knockdown of PTRF in HCoEpiCs significantly decreased the phosphorylation of JNK, ERK, and p38 and iNOS expression. In PI-IBS rats, the lack of PTRF not only reduced fecal water content and suppressed depressive behavior but also increased the body weight. Furthermore, we found a strong co-localization pattern for PTRF and TLR4. Consistently, the lack of PTRF impaired TLR4 signaling, as shown by the decreased levels of p-JNK, p-ERK, and p-p38, which are upstream factors involved in iNOS expression. Conclusion: PTRF promoted PI-IBS and stimulated TLR4 signaling both in vitro and in vivo. The results of this study not only enlighten the pathogenesis of PI-IBS but also help us understand the biological activity of PTRF and provide an important basis for the clinical treatment of PI-IBS by targeting PTRF.

Exposure to Vicarious Social Defeat Stress and Western-Style Diets During Adolescence Leads to Physiological Dysregulation, Decreases in Reward Sensitivity, and Reduced Antidepressant Efficacy in Adulthood

A dramatic increase in the prevalence of major depression and diet-related disorders in adolescents has been observed over several decades, yet the mechanisms underlying this comorbidity have only recently begun to be elucidated. Exposure to western-style diet (WSD), high in both fats (45% kcal) and carbohydrates (35% kcal): e.g., high fat diet (HFD), has been linked to the development of metabolic syndrome-like symptoms and behavioral dysregulation in rodents, as similarly observed in the human condition. Because adolescence is a developmental period highlighted by vulnerability to both stress and poor diet, understanding the mechanism(s) underlying the combined negative effects of WSDs and stress on mood and reward regulation is critical. To this end, adolescent male C57 mice were exposed to vicarious social defeat stress (VSDS), a stress paradigm capable of separating physical (PS) versus psychological/emotional (ES) stress, followed by normal chow (NC), HFD, or a separate control diet high in carbohydrates (same sucrose content as HFD) and low in fat (LFD), while measuring body weight and food intake. Non-stressed control mice exposed to 5 weeks of NC or HFD showed no significant differences in body weight or social interaction. Mice exposed to VSDS (both ES and PS) gain weight rapidly 1 week after initiation of HFD, with the ES-exposed mice showing significantly higher weight gain as compared to the HFD-exposed control mice. These mice also exhibited a reduction in saccharin preference, indicative of anhedonic-like behavior. To further delineate whether high fat was the major contributing factor to these deficits, LFD was introduced. The mice in the VSDS + HFD gained weight more rapidly than the VSDS + LFD group, and though the LFD-exposed mice did not gain weight as rapidly as the HFD-exposed mice, both the VSDS + LFD- and VSDS + HFD-exposed mice exhibited attenuated response to the antidepressant fluoxetine. These data show that diets high in both fats and carbohydrates are responsible for rapid weight gain and reduced reward sensitivity; and that while consumption of diet high in carbohydrate and low in fat does not lead to rapid weight gain, both HFD and LFD exposure after stress leads to reduced responsiveness to antidepressant treatment.

Models of Depression: Unpredictable Chronic Mild Stress in Mice

Major depression is a complex psychiatric disorder characterized by affective, cognitive, and physiological impairments that lead to maladaptive behavior. The high lifetime prevalence of this disabling condition, coupled with limitations of existing medications, make necessary the development of improved therapeutics. This requires animal models that allow investigation of key biological correlates of the disorder. Described in this article is the unpredictable chronic mild stress mouse model that can be used to screen for antidepressant drug candidates. Originally designed for rats, this model has been adapted for mice to capitalize on the advantages of this species as an experimental model, including inter-strain variability, which permits an exploration of the contribution of genetic background; the ability to create transgenic animals; and lower cost. Thus, because it combines genetic features and socio-environmental chronic stressful events, the unpredictable chronic mild stress model in mice is a relevant and valuable paradigm to gain insight into the etiological and developmental components of major depression, as well as to identify novel treatments for this condition. © 2021 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Unpredictable Chronic Mild Stress (UCMS) Test in Mice Basic Protocol 2: Assessment Of Self-Directed Activity And Anhedonia in Mice.

Caloric restriction or cafeteria diet from birth to adulthood increases the sensitivity to ephedrine in anxiety and locomotion in Wistar rats

INTRODUCTION

Obesity and undernutrition, consequences of malnutrition, have been linked to the development of mental illnesses. Both states have been linked to increased sensitivity to some drugs, but there are few data for this association considering drugs with noradrenergic-dopaminergic action.

OBJECTIVE

To evaluate the nutritional status of animals treated with either a caloric restriction (CR) or cafeteria (CAF) diet from birth and their behavior after ephedrine application.

METHODS

During the lactation period, 12 litters of Wistar rats (dam + 8 pups) were fed one of three diets: control (n = 4), CR (n = 4), and CAF (n = 4). After weaning, the males were placed in individual boxes and received the same diet as their respective dams. Nutritional assessments were performed after weaning and in adulthood. In adulthood, males received either saline or ephedrine (20 mg/kg) and underwent behavioral tests including the elevated plus-maze, open-field, and food intake tests.

RESULTS

The CR group exhibited higher serum high-density lipoprotein (HDL) levels and lower food and caloric intake, weight gain, and fat mass than the control group. The CAF group exhibited lower food intake and higher fat caloric intake, fat mass, and serum low-density lipoprotein (LDL), triglyceride, total cholesterol, and hepatic lipid levels than the control group. These results indicated that the CR and CAF groups had developed undernutrition and obesity, respectively. In the elevated plus-maze and open-field tests, the CR and CAF groups showed lower anxiety-like behaviors than the control group after ephedrine application. This result indicates that the animal's nutritional status (undernutrition or obesity) can enhance ephedrine sensitivity.

CONCLUSION

The CR group exhibited undernutrition, whereas the CAF group exhibited obesity. Ephedrine altered anxiety and locomotion in animals that received the CR and CAF diets in manner different than that observed in animals receiving the standard diet.

Neonatal resource scarcity alters maternal care and impacts offspring core temperature and growth in rats

Stressful experiences during childhood, including poverty and inconsistent parental care, can enhance vulnerability for worsened physical and mental health outcomes in adulthood. Using Sprague Dawley rats, the present study explored the impact of limited resource availability on maternal behavior and physiological and emotional behavior outcomes in the offspring. Early life adversity was induced by incorporating aspects of the limited bedding and nesting and scarcity models, wherein limited resource availability has previously been shown to provoke unpredictable or adverse maternal care respectively. In our hands, neonatal limited bedding (NLB) stress during postnatal days (P)2-9 altered maternal care, augmenting pup-directed behaviors and reducing self-directed behaviors, and modestly increased the frequency of transitions between discrete behaviors across consecutive timed observations. NLB-exposed pups had lower core body temperatures immediately following the stressful manipulation and exhibited decreased body weight gain across development. However, NLB exposure did not impact adult offspring's social or emotional behavior outcomes in the three-chamber social interaction, novelty-suppressed feeding, splash, or forced swim tests. These findings add to the literature demonstrating that early life adversity impacts maternal care in rodents and can disrupt certain metabolic and thermoregulatory outcomes in the offspring.

Increasing Adult Hippocampal Neurogenesis Promotes Resilience in a Mouse Model of Depression

Many studies evaluated the functional role of adult hippocampal neurogenesis (AHN) and its key role in cognitive functions and mood regulation. The effects of promoting AHN on the recovery of stress-induced symptoms have been well studied, but its involvement in stress resilience remains elusive. We used a mouse model enabling us to foster AHN before the exposure to unpredictable chronic mild stress (UCMS) to evaluate the potential protective effects of AHN on stress, assessing the depressive-like phenotype and executive functions. For this purpose, an inducible transgenic mouse model was used to delete the pro-apoptotic gene Bax from neural progenitors four weeks before UCMS, whereby increasing the survival of adult-generated neurons. Our results showed that UCMS elicited a depressive-like phenotype, highlighted by a deteriorated coat state, a higher immobility duration in the tail suspension test (TST), and a delayed reversal learning in a water maze procedure. Promoting AHN before UCMS was sufficient to prevent the development of stressed-induced behavioral changes in the TST and the water maze, reflecting an effect of AHN on stress resilience. Taken together, our data suggest that increasing AHN promotes stress resilience on some depressive-like symptoms but also in cognitive symptoms, which are often observed in MD.

Inhibition of mTOR signaling by genetic removal of p70 S6 kinase 1 increases anxiety-like behavior in mice

The mechanistic target of rapamycin (mTOR) is a ubiquitously expressed kinase that acts through two complexes, mTORC1 and mTORC2, to regulate protein homeostasis, as well as long lasting forms of synaptic and behavioral plasticity. Alteration of the mTOR pathway is classically involved in neurodegenerative disorders, and it has been linked to dysregulation of cognitive functions and affective states. However, information concerning the specific involvement of the p70 S6 kinase 1 (S6K1), a downstream target of the mTORC1 pathway, in learning and memory processes and in the regulation of affective states remains scant. To fill this gap, we exposed adult male mice lacking S6K1 to a battery of behavioral tests aimed at measuring their learning and memory capabilities by evaluating reference memory and flexibility with the Morris water maze, and associative memory using the contextual fear conditioning task. We also studied their anxiety-like and depression-like behaviors by, respectively, performing elevated plus maze, open field, light-dark emergence tests, and sucrose preference and forced swim tests. We found that deleting S6K1 leads to a robust anxious phenotype concomitant with associative learning deficits; these symptoms are associated with a reduction of adult neurogenesis and neuronal atrophy in the hippocampus. Collectively, these results provide grounds for the understanding of anxiety reports after treatments with mTOR inhibitors and will be critical for developing novel compounds targeting anxiety.

A selanylimidazopyridine (3-SePh-IP) reverses the prodepressant- and anxiogenic-like effects of a high-fat/high-fructose diet in mice

OBJECTIVE

While chronic feeding with high-fat or high-sugar diets is known related to obesity and type 2 diabetes, later data have indicated that it is also related to depression and anxiety appearance. In this regard, multi-target drugs raise considerable interest as promising therapeutic solutions to complex diseases. Considering the pharmacological effects of the imidazopyridine-derivative moiety imidazo[1,2-a]pyridine and the organoselenium molecules, the combination of both could be a feasible strategy to develop efficient drugs to handle obesity and related comorbidities, for example dyslipidemia and mood disorders.

METHODS

The antidepressant- and anxiolytic-like properties of a selanylimidazopyridine compound, 2-Phenyl-3-(phenylselanyl)imidazo[1,2-a]pyridine (3-SePh-IP), were evaluated on high-fat/high-fructose diet (HFFD)-fed female Swiss mice.

KEY FINDINGS

Our results showed that a short-term HFFD (16 days) could promote a significant body weight gain, hypercholesterolemia, glucose intolerance, and anxiety- and depressive-like behaviour in mice. Concomitant treatment with 3-SePh-IP (10 mg/kg; i.p.) attenuated the HFFD-induced increase in cholesterol levels and blunted the anxiety- and depressive-like behaviour in mice.

CONCLUSIONS

3-SePh-IP holds multimodal pharmacological properties, which provide a rationale for further studies, for example to assess the underlying mechanisms linked to its anxiolytic- and antidepressive-like activities.

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

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

Adult neurogenesis augmentation attenuates anhedonia and HPA axis dysregulation in a mouse model of chronic stress and depression

Major depressive disorder is a common debilitating mental health problem that represents one of the leading causes of disability. Up to date, the therapeutic targets and approaches are still limited. Adult hippocampal neurogenesis (AHN) has been proposed as a critical contributor to the pathophysiology and treatment of depression, altering the hippocampal control over stress response at network, neuroendocrine and behavioral levels. These findings together have suggested that manipulating AHN may be a promising therapeutic strategy for depression. To investigate this question, we assessed whether increasing adult neurogenesis would be sufficient to produce antidepressant-like effects at behavioral and neuroendocrine levels in a mouse model of depression; the unpredictable chronic mild stress (UCMS). For this purpose, we used a bi-transgenic mouse line (iBax) in which AHN increase was induced by deletion of the pro-apoptotic gene Bax from the neural progenitors following the tamoxifen-dependent action of CreERT2 recombinases. UCMS induced a syndrome that is reminiscent of depression-like states, including anhedonia (cookie test), physical changes (coat deterioration, reduced weight gain), anxiety-like behaviors (higher latency in the novelty-supressed feeding -NSF- test), passive stress-coping behaviors (immobility in the forced swim test -FST-) and a blunted hypothalamo-pituitary-adrenal (HPA) axis reactivity to acute stress in addition to AHN decrease. Tamoxifen injection reversed the AHN decrease as well as partly counteracted UCMS effects on the cookie test and HPA axis but not for the coat state, weight gain, NSF test and FST. Taken together, our results suggest that a strategy directing at increasing AHN may be able to alleviate some depression-related behavioral and neuroendocrine dimensions of UCMS, such as anhedonia and HPA axis reactivity deficits, but may be hardly sufficient to produce a complete recovery.

High-caloric or isocaloric maternal high-fat diets differently affect young-adult offspring behavior in anxiety-related tests and offspring sensitivity to acute fluoxetine

OBJECTIVE

to evaluate the influence of two maternal high-fat diets with different caloric contents on anxiety-like behavior in young-adult offspring and their sensitivity to acute fluoxetine.

METHODS

females Wistar rats were used and divided according to diet received during gestation and lactation: Control (CTR), high-fat/isocaloric (HI) and high-fat/high-caloric (HH). Offspring were subsequently divided into three subgroups according to acute administration of vehicle or fluoxetine (1 or 10 mg/kg). To assess animals' anxiety-like behaviors, three tests were used: open field (OF), elevated plus-maze (EPM) and free-exploratory paradigm (FEP).

RESULTS

In OF, HI and HH showed increased hyperactivity- and anxiety-related behaviors, HI being more hyperactive than HH. In response to fluoxetine, HI offspring decreased number of quadrants entered, decreased number of central entries and spent less time in rearing in peripheral areas, while HH offspring showed less time spent in rearing in the OF peripheral area. In EPM test, HI pups spent more time in closed arms than the HH pups. Fluoxetine decreased number of open arms entries for HI offspring and increased percentage of time spent in central area for HH animals. Maternal diet did not influence FEP test, neither HI nor HH presented a response after fluoxetine acute administration.

CONCLUSION

Maternal high-fat diets influence offspring anxiety-like behavior in state-anxiety tests but not in trait-anxiety test. Responsiveness to acute fluoxetine depended on maternal diet, dose and which behavioral tests were being evaluated.

Animal Models of Depression: What Can They Teach Us about the Human Disease?

Depression is apparently the most common psychiatric disease among the mood disorders affecting about 10% of the adult population. The etiology and pathogenesis of depression are still poorly understood. Hence, as for most human diseases, animal models can help us understand the pathogenesis of depression and, more importantly, may facilitate the search for therapy. In this review we first describe the more common tests used for the evaluation of depressive-like symptoms in rodents. Then we describe different models of depression and discuss their strengths and weaknesses. These models can be divided into several categories: genetic models, models induced by mental acute and chronic stressful situations caused by environmental manipulations (i.e., learned helplessness in rats/mice), models induced by changes in brain neuro-transmitters or by specific brain injuries and models induced by pharmacological tools. In spite of the fact that none of the models completely resembles human depression, most animal models are relevant since they mimic many of the features observed in the human situation and may serve as a powerful tool for the study of the etiology, pathogenesis and treatment of depression, especially since only few patients respond to acute treatment. Relevance increases by the fact that human depression also has different facets and many possible etiologies and therapies.

An in vitro screening method for probiotics with antidepressant-like effect using the enterochromaffin cell model

Certain probiotics can regulate the host's neurobehavioral function through the microbiota-gut-brain axis. However, screening these probiotics is mainly carried out in animal models, and is costly and inefficient. Herein, a putative enterochromaffin cell line (RIN14B) was used as an in vitro pre-screening model; 30 bacterial strains were tested for bacteria-stimulated tryptophan hydroxylase 1 gene (Tph1) expression and 5-hydroxytryptophan/5-hydroxytryptamine secretion. All strains were further validated for their neurobehavioral effects in chronic stress-induced depressive mice. Using partial least squares (PLS) modeling of in vitro and in vivo datasets, we found that the level of Tph1 mRNA in RIN14B significantly correlated with the performance of a forced swim test and sucrose preference test, and serum corticosterone level in chronically stressed mice. Four strains were identified as the best candidates among 30 strains using principal component analysis on all in vivo measures, and unsurprisingly, three of them could enhance Tph1 expression in RIN14B, which further proved that the RIN14B-based screening method (especially the detection of bacteria-stimulated Tph1 mRNA) has good predictive validity and screening efficiency for the strain's antidepressant-like capacity. Collectively, this study provides a novel in vitro method for screening probiotics (or other related bioproducts) with antidepressant-like potential.

Chronic stress followed by social isolation promotes depressive-like behaviour, alters microglial and astrocyte biology and reduces hippocampal neurogenesis in male mice

Unpredictable chronic mild stress (UCMS) is one of the most commonly used, robust and translatable models for studying the neurobiological basis of major depression. Although the model currently has multiple advantages, it does not entirely follow the trajectory of the disorder, whereby depressive symptomology can often present months after exposure to stress. Furthermore, patients with depression are more likely to withdraw in response to their stressful experience, or as a symptom of their depression, and, in turn, this withdrawal/isolation can further exacerbate the stressful experience and the depressive symptomology. Therefore, we investigated the effect(s) of 6 weeks of UCMS followed by another 6 weeks of social isolation (referred to as UCMSI), on behaviour, corticosterone stress responsivity, immune system functioning, and hippocampal neurogenesis, in young adult male mice. We found that UCMSI induced several behavioural changes resembling depression but did not induce peripheral inflammation. However, UCMSI animals showed increased microglial activation in the ventral dentate gyrus (DG) of the hippocampus and astrocyte activation in both the dorsal and ventral DG, with increased GFAP-positive cell immunoreactivity, GFAP-positive cell hypertrophy and process extension, and increased s100β-positive cell density. Moreover, UCMSI animals had significantly reduced neurogenesis in the DG and reduced levels of peripheral vascular endothelial growth factor (VEGF) - a trophic factor produced by astrocytes and that stimulates neurogenesis. Finally, UCMSI mice also had normal baseline corticosterone levels but a smaller increase in corticosterone following acute stress, that is, the Porsolt Swim Test. Our work gives clinically relevant insights into the role that microglial and astrocyte functioning, and hippocampal neurogenesis may play in the context of stress, social isolation and depression, offering a potentially new avenue for therapeutic target.

The peroxisome proliferator-activated receptor gamma (PPARγ) agonist, rosiglitazone, ameliorates neurofunctional and neuroinflammatory abnormalities in a rat model of Gulf War Illness

Background

Gulf War (GW) Illness (GWI) is a debilitating condition with a complex constellation of immune, endocrine and neurological symptoms, including cognitive impairment, anxiety and depression. We studied a novel model of GWI based on 3 known common GW exposures (GWE): (i) intranasal lipopolysaccharide, to which personnel were exposed during desert sand storms; (ii) pyridostigmine bromide, used as prophylaxis against chemical warfare; and (iii) chronic unpredictable stress, an inescapable element of war. We used this model to evaluate prophylactic treatment with the PPARγ agonist, rosiglitazone (ROSI).

Methods

Rats were subjected to the three GWE for 33 days. In series 1 and 2, male and female GWE-rats were compared to naïve rats. In series 3, male rats with GWE were randomly assigned to prophylactic treatment with ROSI (GWE-ROSI) or vehicle. After the 33-day exposures, three neurofunctional domains were evaluated: cognition (novel object recognition), anxiety-like behaviors (elevated plus maze, open field) and depression-like behaviors (coat state, sucrose preference, splash test, tail suspension and forced swim). Brains were analyzed for astrocytic and microglial activation and neuroinflammation (GFAP, Iba1, tumor necrosis factor and translocator protein). Neurofunctional data from rats with similar exposures were pooled into 3 groups: naïve, GWE and GWE-ROSI.

Results

Compared to naïve rats, GWE-rats showed significant abnormalities in the three neurofunctional domains, along with significant neuroinflammation in amygdala and hippocampus. There were no differences between males and females with GWE. GWE-ROSI rats showed significant attenuation of neuroinflammation and of some of the neurofunctional abnormalities.

Conclusion

This novel GWI model recapitulates critical neurofunctional abnormalities reported by Veterans with GWI. Concurrent prophylactic treatment with ROSI was beneficial in this model.

Disinhibition of somatostatin interneurons confers resilience to stress in male but not female mice

Chronic stress represents a vulnerability factor for anxiety and depressive disorders and has been widely used to model aspects of these disorders in rodents. Disinhibition of somatostatin (SST)-positive GABAergic interneurons in mice by deletion of γ2 GABAA receptors selectively from these cells (SSTCre:γ2f/f mice) has been shown to result in behavioral and biochemical changes that mimic the responses to antidepressant doses of ketamine. Here we explored the extent to which SSTCre:γ2f/f mice exhibit resilience to unpredictable chronic mild stress (UCMS). We found that male SSTCre:γ2f/f mice are resilient to UCMS-induced (i) reductions in weight gain, (ii) reductions in SST-immuno-positive cells in medial prefrontal cortex (mPFC), (iii) increases in phosphorylation of eukaryotic elongation factor 2 (eEF2) in mPFC, and (iv) increased anxiety in a novelty suppressed feeding test. Female SSTCre:γ2f/f mice were resilient to UCMS-induced reductions in SST-immuno-positive cells indistinguishably from males. However, in contrast to males, they showed no UCMS effects on weight gain independent of genotype. Moreover, in mPFC of female γ2f/f control mice, UCMS resulted in paradoxically reduced p-EF2 levels without stress effects in the SSTCre:γ2f/f mutants. Lastly, female SSTCre:γ2f/f mice showed increased rather than reduced UCMS induced anxiety compared to γ2f/f controls. Thus, disinhibition of SST interneurons results in behavioral resilience to UCMS selectively in male mice, along with cellular resilience of SST neurons to UCMS independent of sex. Thus, mechanisms underlying vulnerability and resilience to stress are sex specific and map to mPFC rather than hippocampus but appear unrelated to changes in expression of SST as a marker of corresponding interneurons.

Switching from high-fat feeding (HFD) to regular diet improves metabolic and behavioral impairments in middle-aged female mice

Obesity represents a risk factor for metabolic syndrome and cardiovascular and psychiatric disorders. Excessive caloric intake, particularly in dietary fats, is an environmental factor that contributes to obesity development. Thus, the observation that switching from long-standing dietary obesity to standard diet (SD) can ameliorate the high-fat diet-induced metabolic, memory, and emotionality-related impairments are particularly important. Herein we investigated whether switching from the high-fat diet (HFD) to SD could improve the metabolic and behavioral impairments observed in middle-aged females C57Bl/6 mice. During twelve weeks, the animals received a high-fat diet (61 % fat) or SD diet. After 12-weeks, the HFD group's diet was switched to SD for an additional four weeks. It was observed a progressive deleterious effect of HFD in metabolic and behavioral parameters in mice. After four weeks of HFD-feeding, the animals showed glucose intolerance and increased locomotor activity. A subsequent increase in the body mass gain, hyperglycemia, and depressive-like behavior was observed after eight weeks, and memory impairments after twelve weeks. After replacing the HFD to SD, it was observed an improvement of metabolic (loss of body mass, normal plasma glucose levels, and glucose tolerance) and behavioral (absence of memory and emotional alterations) parameters. These results demonstrate the temporal development of metabolic and behavioral impairments following HFD in middle-age female mice and provide new evidence that these alterations can be improved by switching back the diet to SD.

Cholesterol homeostasis: Researching a dialogue between the brain and peripheral tissues

Cholesterol homeostasis is a highly regulated process in human body because of its several functions underlying the biology of cell membranes, the synthesis of all steroid hormones and bile acids and the need of trafficking lipids destined to cell metabolism. In particular, it has been recognized that peripheral and central nervous system cholesterol metabolism are separated by the blood brain barrier and are regulated independently; indeed, peripherally, it depends on the balance between dietary intake and hepatic synthesis on one hand and its degradation on the other, whereas in central nervous system it is synthetized de novo to ensure brain physiology. In view of this complex metabolism and its relevant functions in mammalian, impaired levels of cholesterol can induce severe cellular dysfunction leading to metabolic, cardiovascular and neurodegenerative diseases. The aim of this review is to clarify the role of cholesterol homeostasis in health and disease highlighting new intriguing aspects of the cross talk between its central and peripheral metabolism.

Impact of different fructose concentrations on metabolic and behavioral parameters of male and female mice

Clinical evidence has shown that a high consumption of sugar-sweetened beverages is a risk factor for developing obesity and metabolic syndrome. There has also been increasing interest in the potential effects of high-fructose intake on behavior. The present study evaluated sex differences in behavioral and metabolic characteristics in response to chronic fructose intake in mice. Swiss mice (3-months-old) had access to tap water or fructose-water solution (at 15% or 30% w/v) ad libitum for nine weeks. After the 8 weeks, the mice were submitted to a battery of behavioral tests. A glucose tolerance test was performed one day after these behavioral tests, and the next day blood was collected for biochemical analysis. At a 15% concentration, fructose-intaking resulted in higher plasma cholesterol levels and glucose intolerance in mice that paralleled with a passive stress-coping behavior in the female mice and lower self-care behavior in the male and the female mice. At a 30% concentration, fructose-intaking resulted in higher body mass gain and higher plasma cholesterol and triglycerides levels in the male and the female mice, whereas glucose intolerance was more pronounced in the male mice. Spatial memory impairments and lower self-care behavior were observed in the male and the female mice, while passive stress-coping behavior was observed only in the female mice. Collectively, high-fructose intake induces metabolic and behavioral alterations in mice, with the males being more susceptible to glucose metabolism dysfunctions and the females to depressive-like endophenotypes.

Treadmill Exercise Buffers Behavioral Alterations Related to Ethanol Binge-Drinking in Adolescent Mice

The binge-drinking pattern of EtOH consumption, which is frequently observed in adolescents, is known to induce several neurobehavioral alterations, but protection strategies against these impairments remain scarcely explored. We aimed to study the protective role of treadmill physical exercise on the deficits caused after repeated cycles of binge-like EtOH exposure in the cognition, motivation, exploration, and emotion of C57BL/6J mice from adolescence to adulthood. Animals were divided into four groups: control group, exercised group, EtOH group, and exercised + EtOH group (20% in tap water). The exercise was performed for 20 min, 5 days/week at 20 cm/s. Then, animals were submitted to several behavioral tasks. Compared to binge-drinking mice, the exercised + EtOH group exhibited diminished anxiolytic-related behaviors in the elevated plus-maze, enhanced exploratory activity in the open field, reduced preference for alcohol odor when another rewarding stimulus was present (social stimulus) and lower latency to start self-cleaning behaviors in the sucrose splash test. In contrast, other measurements such as habituation learning and working memory were not improved by exercise. Besides, exercise was not able to reduce alcohol consumption across the weeks. In conclusion, physical activity during adolescence and early adulthood could buffer certain neurobehavioral alterations associated with binge-drinking, despite not reducing the quantity of consumed alcohol.

Sex differences in the role of atypical PKC within the basolateral nucleus of the amygdala in a mouse hyperalgesic priming model

Though sex differences in chronic pain have been consistently described in the literature, their underlying neural mechanisms are poorly understood. Previous work in humans has demonstrated that men and women differentially invoke distinct brain regions and circuits in coping with subjective pain unpleasantness. The goal of the present work was to elucidate the molecular mechanisms in the basolateral nucleus of the amygdala (BLA) that modulate hyperalgesic priming, a pain plasticity model, in males and females. We used plantar incision as the first, priming stimulus and prostaglandin E₂ (PGE₂) as the second stimulus. We sought to assess whether hyperalgesic priming can be prevented or reversed by pharmacologically manipulating molecular targets in the BLA of male or female mice. We found that administering ZIP, a cell-permeable inhibitor of aPKC, into the BLA attenuated aspects of hyperalgesic priming induced by plantar incision in males and females. However, incision only upregulated PKCζ/PKMζ immunoreactivity in the BLA of male mice, and deficits in hyperalgesic priming were seen only when we restricted our analysis to male Prkcz^-/- mice. On the other hand, intra-BLA microinjections of pep2m, a peptide that interferes with the trafficking and function of GluA2-containing AMPA receptors, a downstream target of aPKC, reduced mechanical hypersensitivity after plantar incision and disrupted the development of hyperalgesic priming in both male and female mice. In addition, pep2m treatment reduced facial grimacing and restored aberrant behavioral responses in the sucrose splash test in male and female primed mice. Immunofluorescence results demonstrated upregulation of GluA2 expression in the BLA of male and female primed mice, consistent with pep2m findings. We conclude that, in a model of incision-induced hyperalgesic priming, PKCζ/PKMζ in the BLA is critical for the development of hyperalgesic priming in males, while GluA2 in the BLA is crucial for the expression of both reflexive and affective pain-related behaviors in both male and female mice in this model. Our findings add to a growing body of evidence of sex differences in molecular pain mechanisms in the brain.

High-fat diet negatively impacts both metabolic and behavioral health in outbred heterogeneous stock rats

Obesity is influenced by genetics and diet and has wide ranging comorbidities, including anxiety and depressive disorders. Outbred heterogeneous stock (HS) rats are used for fine-genetic mapping of complex traits and may be useful for understanding gene by diet interactions. In this study, HS rats were fed diets containing 60% kcal from fat (high-fat diet, HFD) or 10% kcal from fat (low-fat diet, LFD) and tested for metabolic (study 1) and behavioral (study 2) outcomes. In study 1, we measured glucose tolerance, fasting glucose and insulin, fat pad weights and despair-like behavior in the forced swim test (FST). In study 2, we assessed anxiety-like (elevated plus maze, EPM; open field test, OFT) and despair-like/coping (splash test, SpT; and FST) behaviors. Body weight and food intake were measured weekly in both studies. We found negative effects of HFD on metabolic outcomes, including increased body weight and fat pad weights, decreased glucose tolerance, and increased fasting insulin. We also found negative effects of HFD on despair-like/coping and anxiety-like behaviors. These include increased immobility in the FST, decreased open arm time in the EPM, and increased movement and rest episodes and decreased rearing in the OFT. The diet-induced changes in EPM and OFT were independent of overall locomotion. Additionally, diet-induced changes in OFT behaviors were independent of adiposity, while adiposity was a confounding factor for EPM and FST behavior. This work establishes the HS as a model to study gene by diet interactions affecting metabolic and behavioral health.

Thymoquinone harbors protection against Concanavalin A-induced behavior deficit in BALB/c mice model

Global health estimates indicated approximately 322 million people living with depression. Rising cost of depressive illness treatment and non-responsiveness to existing therapies demand continued research to explore new and more potent therapies. Exploring the potential of natural compounds for their potent antidepressant potentials is becoming topic of interest for scientists. Anti-inflammatory activity of thymoquinone, the active ingredient of Nigella sativa, has been well documented. Current study tested thymoquinone for its antidepressant effect in a Concanavalin A (Con A)-induced depressive-like behavior in BALB/c mice. Thymoquinone successfully protected against Con A-induced behavioral despair and anxiety-like behavior. Reduced grooming behavior as a function of Con A treatment, was also reinstated. Underlying mechanism responsible for antidepressant activity of thymoquinone was analyzed by molecular docking. Thymoquinone interacts in halogen-binding pocket (HBP) of serotonin reuptake transporter indicating its potential as serotonin reuptake inhibitor. Results of current study anticipate thymoquinone as a potential antidepressant drug candidate. PRACTICAL APPLICATIONS: Black seeds of Nigella sativa are consumed with traditional and religious reference since centuries. Thymoquinone, active, and abundant component of Nigella sativa, has shown positive effects in multiple studies against arthritis, asthma, hepatic injury, neurodegeneration, and cancer owing to its immunomodulatory and anti-inflammatory attributes. Considering inflammation as one of central components involved in pathophysiology of major depressive disorder, thymoquinone has been evaluated in current study for its antidepressant potential. Positive results of current study propose thymoquinone as an affordable, natural antidepressant drug candidate with better safety profile than currently available antidepressant regimes. Thymoquinone might provide benefits against inflammation-related sickness behavior that is associated with poorer outcome of clinical depression, thus, paving the way for effective drug development against treatment-resistant depression.

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

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

Neuroprotective Role of Dietary Supplementation with Omega-3 Fatty Acids in the Presence of Basal Forebrain Cholinergic Neurons Degeneration in Aged Mice

As major components of neuronal membranes, omega-3 polyunsaturated fatty acids (n-3 PUFA) exhibit a wide range of regulatory functions. Recent human and animal studies indicate that n-3 PUFA may exert beneficial effects on aging processes. Here we analyzed the neuroprotective influence of n-3 PUFA supplementation on behavioral deficits, hippocampal neurogenesis, volume loss, and astrogliosis in aged mice that underwent a selective depletion of basal forebrain cholinergic neurons. Such a lesion represents a valid model to mimic a key component of the cognitive deficits associated with dementia. Aged mice were supplemented with n-3 PUFA or olive oil (as isocaloric control) for 8 weeks and then cholinergically depleted with mu-p75-saporin immunotoxin. Two weeks after lesioning, mice were behaviorally tested to assess anxious, motivational, social, mnesic, and depressive-like behaviors. Subsequently, morphological and biochemical analyses were performed. In lesioned aged mice the n-3 PUFA pre-treatment preserved explorative skills and associative retention memory, enhanced neurogenesis in the dentate gyrus, and reduced volume and VAChT levels loss as well as astrogliosis in hippocampus. The present findings demonstrating that n-3 PUFA supplementation before cholinergic depletion can counteract behavioral deficits and hippocampal neurodegeneration in aged mice advance a low-cost, non-invasive preventive tool to enhance life quality during aging.

Testing the Limits of Sex Differences Using Variable Stress

Depression is a chronic disease that affects nearly twice as many women as men, and symptoms can differ by sex. Preclinical models disproportionately use male subjects and test a single behavioral endpoint immediately at the cessation of stress. We conducted variable stress in male and female mice for 6, 28, and 56 days, and measured behavior with a battery chosen to match research domain criteria. To examine individual differences, we generated a composite z score to measure stress susceptibility across behavioral tests. We also tested behavior following a 30-day recovery period to evaluate the duration of the stress effects. Females, but not males, were susceptible to 6 days of variable stress when behavioral testing started 24 h later. If behavioral testing was conducted 30 days later both males and females expressed stress related behaviors. Males and females were stress susceptible to 28 days of variable stress and effects were long lasting. Both sexes habituated to 56 days of variable stress, but anxiety associated measures still showed persistence. Performance on specific behavioral tests was often different between individuals and between sexes, and not all stressed animals were susceptible to all tested behaviors. These studies confirm that behavioral sex differences are detected in response to variable stress, and reveal information about individual differences. Use of a test battery that measures varying endophenotypes can be combined into a single stress susceptibility score as a tool similar to the scales/inventories used for the study of depression in humans. We present these data with the goal of furthering the field's understanding sex differences and how they shape the biology of mood disorders.

Epigenetic intersection of BDNF Val66Met genotype with premenstrual dysphoric disorder transcriptome in a cross-species model of estradiol add-back

Premenstrual dysphoric disorder (PMDD) affects over 5% of women, with symptoms similar to anxiety and major depression, and is associated with differential sensitivity to circulating ovarian hormones. Little is known about the genetic and epigenetic factors that increase the risk to develop PMDD. We report that 17β-estradiol (E2) affects the behavior and the epigenome in a mouse model carrying a single-nucleotide polymorphism of the brain-derived neurotrophic factor gene (BDNF Val66Met), in a way that recapitulates the hallmarks of PMDD. Ovariectomized mice heterozygous for the BDNF Met allele (Het-Met) and their matched wild-type (WT) mice were administered estradiol or vehicle in drinking water for 6 weeks. Using the open field and the splash test, we show that E2 add-back induces anxiety-like and depression-like behavior in Het-Met mice, but not in WT mice. RNA-seq of the ventral hippocampus (vHpc) highlights that E2-dependent gene expression is markedly different between WT mice and Het-Met mice. Through a comparative whole-genome RNA-seq analysis between mouse vHpc and lymphoblastoid cell line cultures from control women and women with PMDD, we discovered common epigenetic biomarkers that transcend species and cell types. Those genes include epigenetic modifiers of the ESC/E(Z) complex, an effector of response to ovarian steroids. Although the BDNF Met genotype intersects the behavioral and transcriptional traits of women with PMDD, we suggest that these similarities speak to the epigenetic factors by which ovarian steroids produce negative behavioral effects.

Ovarian status dictates the neuroinflammatory and behavioral consequences of sub-chronic stress exposure in middle-aged female mice

Ovarian hormones influence the outcomes of stress exposure and are implicated in stress-related disorders including depression, yet their roles are often complex and seemingly contradictory. Importantly, depression and stress exposure are associated with immune dysregulation, and ovarian hormones have immunomodulatory properties. However, how ovarian hormones can influence the inflammatory outcomes of stress exposure is poorly understood. Here, we examined the effects of long-term ovariectomy on the behavioral and neuroinflammatory outcomes of sub-chronic stress exposure in middle-aged mice. Briefly, sham-operated and ovariectomized mice were assigned to non-stress groups or exposed to 6 days of variable stress. Mice were assessed on a battery of behavioral tests, and cytokine concentrations were quantified in the frontal cortex and hippocampus. In the frontal cortex, postsynaptic density protein-95 expression was examined as an index of excitatory synapse number and/or stability, and phosphorylated mitogen-activated protein kinases (MAPKs) were measured to explore potential cell signaling pathways elicited by stress exposure and/or ovarian hormones. Long-term ovariectomy modified the central cytokine profile by robustly reducing cytokine concentrations in the frontal cortex and modestly increasing concentrations in the hippocampus. Under non-stress conditions, long-term ovariectomy also reduced extracellular signal-regulated kinase (ERK) phosphoprotein expression in the frontal cortex and increased some measures of depressive-like behavior. The effects of sub-chronic stress exposure were however more pronounced in sham-operated mice. Notably, in sham-operated mice only, sub-chronic stress exposure increased IL-1β and IL-6:IL-10 ratio in the frontal cortex and hippocampus and reduced pERK1/2 expression in the frontal cortex. Further, although sub-chronic stress exposure increased anhedonia-like behavior regardless of ovarian status, it increased passive-coping behavior in sham-operated mice only. These data indicate that long-term ovariectomy has potent effects on the central cytokine milieu and dictates the neuroinflammatory and behavioral effects of sub-chronic stress exposure in middle-aged mice. These findings therefore suggest that the immunomodulatory properties of ovarian hormones are of relevance in the context of stress and possibly depression.

Animal models of major depression: drawbacks and challenges

Major depression is a leading contributor to the global burden of disease. This situation is mainly related to the chronicity and/or recurrence of the disorder, and to poor response to antidepressant therapy. Progress in this area requires valid animal models. Current models are based either on manipulating the environment to which rodents are exposed (during the developmental period or adulthood) or biological underpinnings (i.e. gene deletion or overexpression of candidate genes, targeted lesions of brain areas, optogenetic control of specific neuronal populations, etc.). These manipulations can alter specific behavioural and biological outcomes that can be related to different symptomatic and pathophysiological dimensions of major depression. However, animal models of major depression display substantial shortcomings that contribute to the lack of innovative pharmacological approaches in recent decades and which hamper our capabilities to investigate treatment-resistant depression. Here, we discuss the validity of these models, review putative models of treatment-resistant depression, major depression subtypes and recurrent depression. Furthermore, we identify future challenges regarding new paradigms such as those proposing dimensional rather than categorical approaches to depression.

Celecoxib, ibuprofen, and indomethacin alleviate depression-like behavior induced by interferon-alfa in mice

Background Interferon-α (IFNα) therapy causes psychiatric side effects, including depression that may result in poor compliance of therapy. It is important to find alternative therapies for the prevention of IFNα induced depression. Non-steroidal anti-inflammatory drugs (NSAIDs) have been useful in depressive disorder. Therefore the effects of celecoxib, ibuprofen, and indomethacin were evaluated following IFNα-induced depression in mice. Methods Male albino mice weighing 26 ± 2 g were used. Depression was induced by IFNα (16 × 105 IU/kg, SC) for six consecutive days. Animals were first subject to the locomotor test, then the splash test and finally the forced swimming test (FST) on the 7th day. The NSAIDs were administered (IP) either one single dose before the test, or simultaneously with IFNα. Results locomotor activity was only impaired by ibuprofen high dose (75 mg/kg), thus it was not further evaluated. Following IFNα therapy depression-like behaviors were observed; significant changes during the splash test (grooming time 24 ± 7 sec vs. control 63 ± 7 sec), the FST (immobility time 166  ± 15 sec vs. control 128  ± 6 sec), and sucrose preference reduced to 64 ± 0.8%. The NSAIDs noticeably reduced the immobility time in FST, while grooming time was increased. Celecoxib and indomethacin single doses were effective while ibuprofen showed better antidepressant effects when it was administered along with IFNα. Conclusions The NSAIDs were able to prevent IFNα induced depression in mice. NSAIDs administration with IFNα does not interfere with clinical benefit effects of IFNα and they could also be useful to prevent IFNα psychiatric side effects, thus further clinical trials are suggested.

The histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) alleviates depression-like behavior and normalizes epigenetic changes in the hippocampus during ethanol withdrawal

Withdrawal from chronic alcohol drinking can cause depression, leading to an inability to function in daily life and an increased risk for relapse to harmful drinking. Understanding the causes of alcohol withdrawal-related depression may lead to new therapeutic targets for treatment. Epigenetic factors have recently emerged as important contributors to both depression and alcohol use disorder (AUD). Specifically, acetylation of the N-terminal tails of histone proteins that package DNA into nucleosomes is altered in stress-induced models of depression and during alcohol withdrawal. The goal of this study was to examine depression-like behavior during alcohol withdrawal and associated changes in histone acetylation and expression of histone deacetylase 2 (HDAC2) in the hippocampus, a brain region critical for mood regulation and depression. Male Sprague-Dawley rats were treated with the Lieber-DeCarli ethanol liquid diet for 15 days and then underwent withdrawal. Rats were treated with the HDAC inhibitor, suberoylanilide hydroxamic acid (SAHA), during withdrawal and were tested for depression-like behavior. In a separate group of rats, the hippocampus was analyzed for mRNA and protein expression of HDAC2 and levels of histone H3 lysine 9 acetylation (H3K9ac) during chronic ethanol exposure and withdrawal. Rats undergoing ethanol withdrawal exhibited depression-like behavior and had increased HDAC2 and decreased H3K9ac levels in specific structures of the hippocampus. Treatment with SAHA during withdrawal ameliorated depression-like behavior and normalized changes in hippocampal HDAC2 and H3K9ac levels. These results demonstrate that ethanol withdrawal causes an altered epigenetic state in the hippocampus. Treatment with an HDAC inhibitor can correct this state and alleviate depression-like symptoms developed during withdrawal. Targeting histone acetylation may be a novel strategy to reduce ethanol withdrawal-induced depression.

Antidepressant-like activity of hyperforin and changes in BDNF and zinc levels in mice exposed to chronic unpredictable mild stress

Chronic unpredictable mild stress (CUMS) - a rodent model of depression mimics a variety of neurochemical and behavioral alterations similar to those seen in human depression. This study evaluated the antidepressant activity of hyperforin in the CUMS model using fluoxetine (FLX) as a reference drug. The antidepressant-like effects of hyperforin and FLX were evaluated in the tail suspension test (TST), forced swim test (FST), and splash test (SPT). CUMS induced an increase in immobility time in mice (pro-depressive effects) in the FST and TST. CUMS-induced changes were reversed by chronic treatment with hyperforin (2.5 and 5 mg/kg), as well as FLX (10 mg/kg). SPT results revealed a decrease in the frequency and duration of grooming in stressed mice. These effects were normalized by hyperforin (5 mg/kg) and FLX treatment. Hyperforin (2.5 mg/kg) only reversed the CUMS-induced deficits related to the frequency of grooming. CUMS also caused a decrease in zinc concentration in the frontal cortex (FC) and hippocampus (Hp) of mice; hyperforin (2.5 mg/kg) increased zinc concentration in the Hp of control rats. CUMS also induced a decrease in BDNF protein levels in the FC and Hp, while decreasing the pCREB/CREB ratio only in the Hp. Hyperforin (2.5 and 5 mg/kg) reversed the CUMS-induced reduction of BDNF only in the Hp. Our results demonstrate the antidepressant-like activity of hyperforin in the CUMS model in mice and the possible involvement of hippocampal BDNF/zinc alterations in this activity.

Metformin Promotes Anxiolytic and Antidepressant-Like Responses in Insulin-Resistant Mice by Decreasing Circulating Branched-Chain Amino Acids

Epidemiological studies indicate that insulin resistance (IR), a hallmark of type 2 diabetes, is associated with an increased risk of major depression. Here, we demonstrated that male mice fed a high-fat diet (HFD) exhibited peripheral metabolic impairments reminiscent of IR accompanied by elevated circulating levels of branched-chain amino acids (BCAAs), whereas both parameters were normalized by chronic treatment with metformin (Met). Given the role of BCAAs in the regulation of tryptophan influx into the brain, we then explored the activity of the serotonin (5-HT) system. Our results indicated that HFD-fed mice displayed impairment in the electrical activity of dorsal raphe 5-HT neurons, attenuated hippocampal extracellular 5-HT concentrations and anxiety, one of the most visible and early symptoms of depression. On the contrary, Met stimulated 5-HT neurons excitability and 5-HT neurotransmission while hindering HFD-induced anxiety. Met also promoted antidepressant-like activities as observed with fluoxetine. In light of these data, we designed a modified HFD in which BCAA dietary supply was reduced by half. Deficiency in BCAAs failed to reverse HFD-induced metabolic impairments while producing antidepressant-like activity and enhancing the behavioral response to fluoxetine. Our results suggest that Met may act by decreasing circulating BCAAs levels to favor serotonergic neurotransmission in the hippocampus and promote antidepressant-like effects in mice fed an HFD. These findings also lead us to envision that a diet poor in BCAAs, provided either alone or as add-on therapy to conventional antidepressant drugs, could help to relieve depressive symptoms in patients with metabolic comorbidities.SIGNIFICANCE STATEMENT Insulin resistance in humans is associated with increased risk of anxiodepressive disorders. Such a relationship has been also found in rodents fed a high-fat diet (HFD). To determine whether insulin-sensitizing strategies induce anxiolytic- and/or antidepressant-like activities and to investigate the underlying mechanisms, we tested the effects of metformin, an oral antidiabetic drug, in mice fed an HFD. Metformin reduced levels of circulating branched-chain amino acids, which regulate tryptophan uptake within the brain. Moreover, metformin increased hippocampal serotonergic neurotransmission while promoting anxiolytic- and antidepressant-like effects. Moreover, a diet poor in these amino acids produced similar beneficial behavioral property. Collectively, these results suggest that metformin could be used as add-on therapy to a conventional antidepressant for the comorbidity between metabolic and mental disorders.

Peritoneal endometriosis induces time-related depressive- and anxiety-like alterations in female rats: involvement of hippocampal pro-oxidative and BDNF alterations

Endometriosis is a gynecological condition affecting 10% of women in reproductive age. High rates of depression and anxiety are observed in these patients. The mechanisms underlying endometriosis-induced behavioral alterations are still elusive. Animal models provide a useful tool to study the temporal sequence and biological pathways involved in this disease and comorbid states. Here, we sought to characterize time-related behavioral alterations in rats submitted to endometriosis model (EM) induced by peritoneal auto-transplantation of uterine tissues weekly for three weeks. Corticosterone stress reactivity, oxidative stress markers - reduced glutathione (GSH), lipid peroxidation, activity of superoxide dismutase (SOD) and myeloperoxidase (MPO) - and brain-derived-neurotrophic factor (BDNF) levels in the hippocampus were also evaluated. We observed a progressive increase in anxiety-like behavior from 14th to 21st days post-EM. Despair-like behavior was observed from the 14th day post-EM on, while anhedonia and apathetic-like behaviors accompanied by increased corticosterone stress response were detected on 21 days post-EM. Increased pain sensitivity was observed from the 7th day post-EM and was accompanied by increased endometrioma weight. The pro-oxidative alterations, decreased GSH and increased SOD activity were observed on 21 days post-EM, except for lipid peroxidation that was altered from the 14th day. Decreased BDNF also occurred on the 21st day. Therefore, this study demonstrates that EM is related to several features of clinical depression and proposes the contribution of hippocampal oxidative state and neurotrophic support for the emergence of these changes. Our results support the use of this model as a useful tool to test new strategies for endometriosis-related neuropsychiatric symptoms.

Silymarin and silymarin nanoparticles guard against chronic unpredictable mild stress induced depressive-like behavior in mice: involvement of neurogenesis and NLRP3 inflammasome

BACKGROUND

The neuropathology of depression is quite complex. Thus, treatment failures are frequent with current antidepressants, raising the need for more effective ones.

AIMS

This study aimed to investigate the influence of silymarin on depressive-like behavior induced by chronic unpredictable mild stress (CUMS) and explore the underlying mechanisms.

METHODS

Silymarin was formulated as nanostructured lipid carriers (a lipid-based type of nanoparticle with the advantages of physical stability, good release profile, and targeted delivery). Mice were subjected to CUMS paradigm during 14 days. During this period, mice received silymarin (200 mg/kg, p.o.) per se or in its nanoparticle form or fluoxetine (10 mg/kg, p.o.). On the 15th day behavioral and biochemical parameters were analyzed.

RESULTS

Oral administration of silymarin (200 mg/kg), particularly in its nanoparticulate form, exerted an antidepressant-like effect, comparable with fluoxetine in mice, as demonstrated in the behavioral despair tests. Silymarin also reversed prefrontal cortical and hippocampal CUMS-induced oxidative stress and neuroinflammation. Furthermore, silymarin augmented neurotransmitter levels, enhanced neurogenesis and inhibited nod-like receptor protein 3 inflammasome activation. Silymarin nanoparticles were superior to silymarin in certain parameters probably due to significantly higher brain silybinin (the major active component of silymarin) concentration by 12.46 fold in the group administered silymarin nanoparticles compared with the mice which were administered silymarin per se.

CONCLUSIONS

The antidepressant-like effect of silymarin can be attributed to its antioxidant and anti-inflammatory effects as well as increased neurogenesis in the prefrontal cortex and hippocampus, which delineates silymarin, especially in nanoparticle form, as a promising strategy for treatment of depression.

Sustained corticosterone rise in the prefrontal cortex is a key factor for chronic stress-induced working memory deficits in mice

Exposure to prolonged, unpredictable stress leads to glucocorticoids-mediated long-lasting neuroendocrine abnormalities associated with emotional and cognitive impairments. Excessive levels of serum glucocorticoids (cortisol in humans, corticosterone in rodents) contribute notably to deficits in working memory (WM), a task which heavily relies on functional interactions between the medial prefrontal cortex (PFC) and the dorsal hippocampus (dHPC). However, it is unknown whether stress-induced increases in plasma corticosterone mirror corticosterone levels in specific brain regions critical for WM. After a 6 week-UCMS exposure, C57BL/6 J male mice exhibited increased anxiety- and depressive-like behaviors when measured one week later and displayed WM impairments timely associated with increased plasma corticosterone response. In chronically stressed mice, basal phosphorylated/activated CREB (pCREB) was markedly increased in the PFC and the CA1 area of the dHPC and WM testing did not elicit any further increase in pCREB in the two regions. Using microdialysis samples from freely-moving mice, we found that WM testing co-occurred with a rapid and sustained increase in corticosterone response in the PFC while there was a late, non-significant rise of corticosterone in the dHPC. The results also show that non-stressed mice injected with corticosterone (2 mg/kg i.p.) before WM testing displayed behavioral and molecular alterations similar to those observed in stressed animals while a pre-WM testing metyrapone injection (35 mg/kg i.p.), a corticosterone synthesis inhibitor, prevented the effects of UCMS exposure. Overall, the abnormal regional increase of corticosterone concentrations mainly in the PFC emerges as a key factor of enduring WM dysfunctions in UCMS-treated animals.

VGF and its C-terminal peptide TLQP-62 in ventromedial prefrontal cortex regulate depression-related behaviors and the response to ketamine

Patients with major depressive disorder (MDD) often have structural and functional deficits in the ventromedial prefrontal cortex (vmPFC), but the underlying molecular pathways are incompletely understood. The neuropeptide precursor VGF (non-acronymic) plays a critical role in depression and antidepressant efficacy in hippocampus and nucleus accumbens, however its function in vmPFC has not been investigated. Here, we show that VGF levels were reduced in Brodmann area 25 (a portion of human vmPFC) of MDD patients and in mouse vmPFC following chronic restraint stress (CRS), and were increased by ketamine in mouse vmPFC. VGF overexpression in vmPFC prevented behavioral deficits induced by CRS, and VGF knockdown in vmPFC increased susceptibility to subchronic variable stress (SCVS) and reduced ketamine's antidepressant efficacy. Acute intra-vmPFC TLQP-62 infusion induced behavioral phenotypes that mimic those produced by antidepressant drug treatment. These antidepressant-like effects were sustained for 7 days and were abolished by local Bdnf gene ablation, or pretreatment with xestospongin C, an inhibitor of IP₃-mediated Ca²⁺ release, or SKF96365, an inhibitor of store-operated and TRPC channel-mediated Ca²⁺ entry. In conclusion, VGF in the vmPFC regulates susceptibility to stress and the antidepressant response to ketamine. TLQP-62 infusion produces sustained antidepressant responses that require BDNF expression and calcium mobilization in vmPFC.