Sex differences in response to oral amitriptyline in three animal models of depression in C57BL/6J mice

G protein-biased LPAR1 agonism of prototypic antidepressants: Implication in the identification of novel therapeutic target for depression

Prototypic antidepressants, such as tricyclic/tetracyclic antidepressants (TCAs), have multiple pharmacological properties and have been considered to be more effective than newer antidepressants, such as selective serotonin reuptake inhibitors, in treating severe depression. However, the clinical contribution of non-monoaminergic effects of TCAs remains elusive. In this study, we discovered that amitriptyline, a typical TCA, directly binds to the lysophosphatidic acid receptor 1 (LPAR1), a G protein-coupled receptor, and activates downstream G protein signaling, while exerting a little effect on β-arrestin recruitment. This suggests that amitriptyline acts as a G protein-biased agonist of LPAR1. This biased agonism was specific to TCAs and was not observed with other antidepressants. LPAR1 was found to be involved in the behavioral effects of amitriptyline. Notably, long-term infusion of mouse hippocampus with the potent G protein-biased LPAR agonist OMPT, but not the non-biased agonist LPA, induced antidepressant-like behavior, indicating that G protein-biased agonism might be necessary for the antidepressant-like effects. Furthermore, RNA-seq analysis revealed that LPA and OMPT have opposite patterns of gene expression changes in the hippocampus. Pathway analysis indicated that long-term treatment with OMPT activated LPAR1 downstream signaling (Rho and MAPK), whereas LPA suppressed LPAR1 signaling. Our findings provide insights into the mechanisms underlying the non-monoaminergic antidepressant effects of TCAs and identify the G protein-biased agonism of LPAR1 as a promising target for the development of novel antidepressants.

Assessing Dose- and Sex-Dependent Antinociceptive Effects of Cannabidiol and Amitriptyline, Alone and in Combination, and Exploring Mechanism of Action Involving Serotonin 1A Receptors

Inflammatory pain is caused by tissue hypersensitization and is a component of rheumatic diseases, frequently causing chronic pain. Current guidelines use a multimodal approach to pain and sociocultural changes have renewed interest in cannabinoid use, particularly cannabidiol (CBD), for pain. The tricyclic antidepressant amitriptyline (AT) is approved for use in pain-related syndromes, alone and within a multimodal approach. Therefore, we investigated sex- and dose-dependent effects of CBD and AT antinociception in the 2.5% formalin inflammatory pain model. Male and female C57BL/6J mice were pretreated with either vehicle, CBD (0.3-100 mg/kg), or AT (0.1-30 mg/kg) prior to formalin testing. In the acute phase, CBD induced antinociception after administration of 30-100 mg/kg in males and 100 mg/kg in females and in the inflammatory phase at doses of 2.5-100 mg/kg in males and 10-100 mg/kg in females. In the acute phase, AT induced antinociception at 10 mg/kg for all mice, and at 0.3 mg/kg in males and 3 mg/kg in female mice in the inflammatory phase. Combining the calculated median effective doses of CBD and AT produced additive effects for all mice in the acute phase and for males only in the inflammatory phase. Use of selective serotonin 1A receptor antagonist N-[2-[4-(2-methoxyphenyl)-1 piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY-100635) maleate (0.1 mg/kg) before co-administration of CBD and AT reversed antinociception in the acute and partially reversed antinociception in the inflammatory phase. Administration of AT was found to enhance cannabinoid receptor type 1mRNA expression only in female mice. These results suggest a role for serotonin and sex in mediating cannabidiol and amitriptyline-induced antinociception in inflammatory pain. SIGNIFICANCE STATEMENT: Inflammatory pain is an important component of both acute and chronic pain. We have found that cannabidiol (CBD) and amitriptyline (AT) show dose-dependent, and that AT additionally shows sex-dependent, antinociceptive effects in an inflammatory pain model. Additionally, the combination of CBD and AT was found to have enhanced antinociceptive effects that is partially reliant of serotonin 1A receptors and supports the use of CBD within a multimodal approach to pain.

Practical solutions for including sex as a biological variable (SABV) in preclinical neuropsychopharmacological research

Recently, many funding agencies have released guidelines on the importance of considering sex as a biological variable (SABV) as an experimental factor, aiming to address sex differences and avoid possible sex biases to enhance the reproducibility and translational relevance of preclinical research. In neuroscience and pharmacology, the female sex is often omitted from experimental designs, with researchers generalizing male-driven outcomes to both sexes, risking a biased or limited understanding of disease mechanisms and thus potentially ineffective therapeutics. Herein, we describe key methodological aspects that should be considered when sex is factored into in vitro and in vivo experiments and provide practical knowledge for researchers to incorporate SABV into preclinical research. Both age and sex significantly influence biological and behavioral processes due to critical changes at different timepoints of development for males and females and due to hormonal fluctuations across the rodent lifespan. We show that including both sexes does not require larger sample sizes, and even if sex is included as an independent variable in the study design, a moderate increase in sample size is sufficient. Moreover, the importance of tracking hormone levels in both sexes and the differentiation between sex differences and sex-related strategy in behaviors are explained. Finally, the lack of robust data on how biological sex influences the pharmacokinetic (PK), pharmacodynamic (PD), or toxicological effects of various preclinically administered drugs to animals due to the exclusion of female animals is discussed, and methodological strategies to enhance the rigor and translational relevance of preclinical research are proposed.

Effect of titanium dioxide nanoparticles administered during pregnancy on depression-like behavior in forced swimming and tail suspension tests in offspring mice

INTRODUCTION

Applications of engineered nanoparticles are rapidly increasing. Titanium dioxide nanoparticles (TiO₂ NPs) are used in many products including those produced by pigment and cosmetic manufacturers. The objective of this study was to investigate the effects of maternal exposure during pregnancy to TiO₂ NPs on depressive-like behavior in the first and second generation offspring.

MATERIALS AND METHODS

Forty female albino mice were placed into four groups for 2 weeks. Fertile males were then added to each cage by a ratio of two males to five females. After detection of pregnancy, the mice were transferred to separate cages. The study groups were divided into four groups: the first group, served as control, did not receive any treatment; the second group received injections of normal saline; groups 3 and 4 received, respectively, 50 and 100 µl of TiO₂ NP solution injections subcutaneously on days 3, 7, 10, and 14 after mating. Behavioral tests were conducted on postnatal days 21 and 40.

FINDINGS

Subcutaneous injection of 50 and 100 µl of TiO₂ NPs significantly (p < 0.05) increased the immobility time in the forced swimming test and tail suspension test (TST). No significant difference was observed in measured variables between groups receiving 50 and 100 µl of TiO₂ NPs. No significant difference was also found between male and female offspring. Depression-like behavior increased in the second generation of mice in the forced swim test and TST.

CONCLUSION

Prenatal exposure of mothers to TiO₂ NPs would increase depression-like behavior in neonatal mice.

Learned Immobility Produces Enduring Impairment of the HPA Axis Reactivity in Mice without Replicating the Broad Spectrum of Depressive-Like Phenotype

The forced swim stress test (FST) is widely used for screening pharmacological or non-pharmacological strategies with potential antidepressant activities. Recent data have suggested that repeated FST for five consecutive days (i.e., 5d-RFSS) could be used to generate a robust depressive-like phenotype in mice. However, the face, construct, and predictive validities of 5d-RFSS have been recently challenged. This study took advantage of recent findings showing that mice vulnerability to anxiety is enhanced when animals are stressed during the dark phase, to provide new insight into the relevance of this model. Our results showed a progressive increase in time of immobility in 5d-RFSS mice relative to control non-stressed animals (sham). Three weeks later, we noticed that 5d-RFSS mice injected with the vehicle compound (Veh) still exhibited a high level of immobility in the FST whereas this behavior was reversed by the antidepressant drug amitriptyline (AMI). However, 5d-RFSS/Veh and 5d-RFSS mice/AMI mice showed normal performances in the open field, the novelty suppressed feeding and the tail suspension tests. Despite this lack of generalized behavioral deficits, an impairment of different parameters characterizing the hypothalamic-pituitary-adrenal (HPA) axis reactivity was evidenced in 5d-RFSS mice/Veh but not in 5d-RFSS mice/AMI. Despite anomalies in the HPA axis, the activity of the central serotonergic system remained unaffected in 5d-RFSS mice relative to controls. From our results, it is suggested that learned immobility does not replicate the broad spectrum of depressive symptoms observed in other chronic models of depression such as the unpredictable chronic mild stress (UCMS) model, the chronic social defeat stress (CSDS) model or chronic corticosterone (CORT) exposure but its influence on the HPA axis is remarkable. Further experiments are warranted to makes this model suitable for modelling depression and therefore refine its translational applicability.

Xanthotoxin affects depression-related behavior and neurotransmitters content in a sex-dependent manner in mice

The present study aimed to evaluate xanthotoxin's influence on male and female Swiss mice's depression-like behaviors and investigate the potential mechanism of this effect. Naturally derived furanocoumarin (the Apiaceae family), xanthotoxin, administered acutely (12.5 mg/kg), diminished the immobility level in the forced swim test only in males. The immobility level was lower in females than males, which may be associated with a higher serotonin level in the female prefrontal cortex. A dose-dependent increase of serotonin and noradrenaline was reported in the reverse-phase ion-pair liquid chromatography in the female prefrontal cortex but not in the hippocampus. We suggest that xanthotoxin may exert antidepressant properties and affect males and females differently. The increasing level of serotonin in the male and female prefrontal cortex may underlie this effect.

Facilitating Granule Cell Survival and Maturation in Dentate Gyrus With Baicalin for Antidepressant Therapeutics

Baicalin isolated from Scutellaria baicalensis possesses antidepressant abilities through its relation to hippocampal neurogenesis. Current research has found that baicalin can promote the proliferation of hippocampal granule cells, however, the detailed mechanism of baicalin on the survival and maturation of hippocampal granule cells has yet to be sufficiently explored. The purpose of this study was to evaluate whether baicalin could facilitate the survival and maturation of hippocampal granule cells, and to explore its potential mechanism. The chronic corticosterone (CORT)-induced mouse model of depression was used to assess antidepressant-like effects of baicalin and to illuminate possible molecular mechanisms by which baicalin affects hippocampal neurogenesis. The survival and maturation of granule cells were measured by immunohistochemistry, immunofluorescence and Golgi staining. The expression of Phosphatidylinositol 3-kinase (PI3K)/Protein kinase B (AKT)/glycogen synthase kinase-3β (GSK3β)/β-catenin pathway related proteins were measured by western blot analysis. PI3K inhibitor LY292002 and AKT inhibitor Perifosine were administered to HT-22 cells to explore the relationship between the PI3K/AKT/GSK3β/β-catenin pathway and baicalin. The results of the study illustrated that baicalin significantly decreased chronic CORT-induced depressive-like behaviors and reduced serum corticosterone levels. In addition, baicalin (administered at 60 mg/kg) reversed chronic CORT-induced lesions on hippocampal granule cells. Moreover, baicalin significantly increased the phosphorylation rate of PI3K, AKT, GSK3β, and total β-catenin. The study found that administration of LY292002/Perifosine counteracted the effects of baicalin in HT-22 cells. These results demonstrate that baicalin can alleviate chronic CORT-induced depressive-like behaviors through promoting survival and maturation of adult-born hippocampal granule cells and exhibiting protective effect on hippocampal neuron morphology. We propose the underlying mechanisms involve the activation of the PI3K/AKT/GSK3β/β-catenin pathway.

The zebrafish tail immobilization (ZTI) test as a new tool to assess stress-related behavior and a potential screen for drugs affecting despair-like states

BACKGROUND

Affective disorders, especially depression and anxiety, are highly prevalent, debilitating mental illnesses. Animal experimental models are a valuable tool in translational affective neuroscience research. A hallmark phenotype of clinical and experimental depression, the learned helplessness, has become a key target for 'behavioral despair'-based animal models of depression. The zebrafish (Danio rerio) has recently emerged as a promising novel organism for affective disease modeling and CNS drug screening. Despite being widely used to assess stress and anxiety-like behaviors, there are presently no clear-cut despair-like models in zebrafish.

NEW METHOD

Here, we introduce a novel behavioral paradigm, the zebrafish tail immobilization (ZTI) test, as a potential tool to assess zebrafish despair-like behavior. Conceptually similar to rodent 'despair' models, the ZTI protocol involves immobilizing the caudal half of the fish body for 5 min, leaving the cranial part to move freely, suspended vertically in a small beaker with water.

RESULTS

To validate this model, we used exposure to low-voltage electric shock, alarm pheromone, selected antidepressants (sertraline and amitriptyline) and an anxiolytic drug benzodiazepine (phenazepam), assessing the number of mobility episodes, time spent 'moving', total distance moved and other activity measures of the cranial part of the body, using video-tracking. Both electric shock and alarm pheromone decreased zebrafish activity in this test, antidepressants increased it, and phenazepam was inactive. Furthermore, a 5-min ZTI exposure increased serotonin turnover, elevating the 5-hydroxyindoleacetic acid/serotonin ratio in zebrafish brain, while electric shock prior to ZTI elevated both this and the 3,4-dihydroxyphenylacetic acid/dopamine ratios. In contrast, preexposure to antidepressants sertraline and amitriptyline lowered both ratios, compared to the ZTI test-exposed fish.

COMPARISON WITH EXISTINGMETHOD(S)

The ZTI test is the first despair-like experimental model in zebrafish.

CONCLUSIONS

Collectively, this study suggests the ZTI test as a potentially useful protocol to assess stress-/despair-related behaviors, potentially relevant to CNS drug screening and behavioral phenotyping of zebrafish.

Preclinical sex differences in depression and antidepressant response: Implications for clinical research

Women suffer from depression and anxiety disorders more often than men, and as a result they receive antidepressants to a greater extent. Sex differences in antidepressant response in humans have been modestly studied, and results have been controversial. At the same time, preclinical studies on animal models of depression and antidepressant response have provided insights with regard to sex differences that could be useful for the design and interpretation of future clinical trials. This Mini-Review discusses such sex-differentiated findings with regard to the presentation of depression, endophenotypes, and antidepressant response. In particular, men and women differ in symptomatology of depression, and animal models of depression have revealed sex differences in behavioral indices. However, although in experimental studies behavioral indices and models are adjusted to identify sex differences properly, this is not the case in the use of depression rating scales in clinical studies. Accordingly, preclinical studies highlight the importance of sex differences at the baseline behavioral response and the underlying mechanisms that often converge after antidepressant treatment. This is also a neglected issue in human studies. Finally, preclinical research suggests that, in the quest for potential biomarkers for depression, sex should be an important factor to consider. Careful consideration of sex differences in preclinical research could facilitate and ameliorate the design and quality of clinical studies for disease biomarkers and novel fast-acting antidepressants that are so essential for both men and women suffering from depression. © 2016 Wiley Periodicals, Inc.

Ginsenoside Rg3 exerts anti-depressive effect on an NMDA-treated cell model and a chronic mild stress animal model

Depression is a common mental disorder and a leading cause of disability. At its most severe, it can lead to suicide. Recently, there has been growing interest in the application of natural herbs for the prevention and treatment of depression. In this report, we found that the ginsenoside active component Rg3 has an apparent antidepressant effect. In N-methyl-d-aspartic acid (NMDA)-treated HT22 murine hippocampal neuronal cells, Rg3 recovered proliferation and inhibited apoptosis by altering the cell cycle. More interestingly, Rg3 led to apparent physiological behavior change in a chronic mild stress model as seen in forced swim, tail suspension, and sucrose preference tests. This effect was mediated by the phosphorylation of cAMP response element binding protein (CREB) and brain-derived neurotrophic factor (BDNF) signaling. This study provides direct evidence to support the antidepressant effects of ginsenoside Rg3, potentially indicating its application in the treatment of clinical depression.

Sensitivity during the forced swim test is a key factor in evaluating the antidepressant effects of abscisic acid in mice

Abscisic acid (ABA), a crucial phytohormone, is distributed in the brains of mammals and has been shown to have antidepressant effects in the chronic unpredictable mild stress test. The forced swim test (FST) is another animal model that can be used to assess antidepressant-like behavior in rodents. Here, we report that the antidepressant effects of ABA are associated with sensitivities to the FST in mice. Based on mean immobility in the 5-min forced swim pre-test, ICR mice were divided into short immobility mice (SIM) and long immobility mice (LIM) substrains. FST was carried out 8 days after drug administration. Learned helplessness, as shown by increased immobility, was only observed in SIM substrain and could be prevented by an 8-day ABA treatment. Our results show that ABA has antidepressant effects in SIM substrain and suggest that mice with learned helplessness might be more suitable for screening potential antidepressant drugs.

Rodent models of treatment-resistant depression

Major depression is a prevalent and debilitating disorder and a substantial proportion of patients fail to reach remission following standard antidepressant pharmacological treatment. Limited efficacy with currently available antidepressant drugs highlights the need to develop more effective medications for treatment- resistant patients and emphasizes the importance of developing better preclinical models that focus on treatment- resistant populations. This review discusses methods to adapt and refine rodent behavioral models that are predictive of antidepressant efficacy to identify populations that show reduced responsiveness or are resistant to traditional antidepressants. Methods include separating antidepressant responders from non-responders, administering treatments that render animals resistant to traditional pharmacological treatments, and identifying genetic models that show antidepressant resistance. This review also examines pharmacological and non-pharmacological treatments regimes that have been effective in refractory patients and how some of these approaches have been used to validate animal models of treatment-resistant depression. The goals in developing rodent models of treatment-resistant depression are to understand the neurobiological mechanisms involved in antidepressant resistance and to develop valid models to test novel therapies that would be effective in patients that do not respond to traditional monoaminergic antidepressants.

HIV-1 Nef expression in microglia disrupts dopaminergic and immune functions with associated mania-like behaviors

BACKGROUND

Neuropsychiatric disorders during HIV/AIDS are common although the contribution of HIV-1 infection within the brain, and in particular individual HIV-1 proteins, to the development of these brain disorders is unknown. Herein, an in vivo transgenic mouse model was generated in which the HIV-1 Nef protein was expressed in microglia cells, permitting investigation of neurobehavioral phenotypes and associated cellular and molecular properties.

METHODS

Transgenic (Tg) mice that expressed full length HIV-1 nef under the control of the c-fms promoter and wildtype (Wt) littermates were investigated using different measures of neurobehavioral performance including locomotory, forced swim (FST), elevated plus maze (EPM) and T-maze tests. Host gene and transgene expression were assessed by RT-PCR, immunoblotting, enzymatic activity and immunohistochemistry. Biogenic amine levels were measured by HPLC with electrochemical detection.

RESULTS

Tg animals exhibited Nef expression in brain microglia and cultured macrophages. Tg males displayed hyperactive behaviors including augmented locomotor activity, decreased immobility in the FST and increased open-arm EPM exploration compared to Wt littermates (p<0.05). Tg animals showed increased CCL2 expression with concurrent IFN-α suppression in striatum compared with Wt littermates (p<0.05). Dopamine levels, MAO activity and the dopamine transporter (DAT) expression were reduced in the striatum of Tg animals (p<0.05).

CONCLUSIONS

HIV-1 Nef expression in microglia induced CCL2 expression together with disrupting striatal dopaminergic transmission, resulting in hyperactive behaviors which are observed in mania and other psychiatric comorbidities among HIV-infected persons. These findings emphasize the selective effects of individual viral proteins in the brain and their participation in neuropathogenesis.

Amitriptyline is efficacious in ameliorating muscle inflammation and depressive symptoms in the mdx mouse model of Duchenne muscular dystrophy

Mutations in the structural protein dystrophin underlie muscular dystrophies characterized by progressive deterioration of muscle function. Dystrophin-deficient mdx mice are considered a model for Duchenne muscular dystrophy (DMD). Individuals with DMD are also susceptible to mood disorders, such as depression and anxiety. Therefore, the study objectives were to investigate the effects of the tricyclic antidepressant amitriptyline on mood, learning, central cytokine expression and skeletal muscle inflammation in mdx mice. Amitriptyline-induced effects (10 mg kg(-1) daily s.c. injections, 25 days) on the behaviour of mdx mice were investigated using the open field arena and tail suspension tests. The effects of chronic amitriptyline treatment on inflammatory markers were studied in the muscle and plasma of mdx mice, and mood-associated monoamine and cytokine concentrations were measured in the amygdala, hippocampus, prefrontal cortex, striatum, hypothalamus and midbrain. The mdx mice exhibited increased levels of anxiety and depressive-like behaviour compared with wild-type mice. Amitriptyline treatment had anxiolytic and antidepressant effects in mdx mice associated with elevations in serotonin levels in the amygdala and hippocampus. Inflammation in mdx skeletal muscle tissue was also reduced following amitriptyline treatment as indicated by decreased immune cell infiltration of muscle and lower levels of the pro-inflammatory cytokines tumour necrosis factor-α and interleukin-6 in the forelimb flexors. Interleukin-6 mRNA expression was remarkably reduced in the amygdala of mdx mice by chronic amitriptyline treatment. Positive effects of amitriptyline on mood, in addition to its anti-inflammatory effects in skeletal muscle, may make it an attractive therapeutic option for individuals with DMD.

Individual differences and the characterization of animal models of psychopathology: a strong challenge and a good opportunity

Despite the development of valuable new techniques (i.e., genetics, neuroimage) for the study of the neurobiological substrate of psychiatric diseases, there are strong limitations in the information that can be gathered from human studies. It is thus critical to develop appropriate animal models of psychiatric diseases to characterize their putative biological bases and the development of new therapeutic strategies. The present review tries to offer a general perspective and several examples of how individual differences in animals can contribute to explain differential susceptibility to develop behavioral alterations, but also emphasizes methodological problems that can lead to inappropriate or over-simplistic interpretations. A critical analysis of the approaches currently used could contribute to obtain more reliable data and allow taking full advantage of new and sophisticated technologies. The discussion is mainly focused on anxiety-like and to a lower extent on depression-like behavior in rodents.

Synergistic effects of celecoxib and bupropion in a model of chronic inflammation-related depression in mice

This study was aimed to characterize the depression-like behaviour in the classical model of chronic inflammation induced by Complete Freund's Adjuvant (CFA). Male Swiss mice received an intraplantar (i.pl.) injection of CFA (50 µl/paw) or vehicle. Behavioural and inflammatory responses were measured at different time-points (1 to 4 weeks), and different pharmacological tools were tested. The brain levels of IL-1β and BDNF, or COX-2 expression were also determined. CFA elicited a time-dependent edema formation and mechanical allodynia, which was accompanied by a significant increase in the immobility time in the tail suspension (TST) or forced-swimming (FST) depression tests. Repeated administration of the antidepressants imipramine (10 mg/kg), fluoxetine (20 mg/kg) and bupropion (30 mg/kg) significantly reversed depression-like behaviour induced by CFA. Predictably, the anti-inflammatory drugs dexamethasone (0.5 mg/kg), indomethacin (10 mg/kg) and celecoxib (30 mg/kg) markedly reduced CFA-induced edema. The oral treatment with the analgesic drugs dipyrone (30 and 300 mg/kg) or pregabalin (30 mg/kg) significantly reversed the mechanical allodyinia induced by CFA. Otherwise, either dipyrone or pregabalin (both 30 mg/kg) did not significantly affect the paw edema or the depressive-like behaviour induced by CFA, whereas the oral treatment with dipyrone (300 mg/kg) was able to reduce the immobility time in TST. Noteworthy, CFA-induced edema was reduced by bupropion (30 mg/kg), and depression behaviour was prevented by celecoxib (30 mg/kg). The co-treatment with bupropion and celecoxib (3 mg/kg each) significantly inhibited both inflammation and depression elicited by CFA. The same combined treatment reduced the brain levels of IL-1β, as well as COX-2 immunopositivity, whilst it failed to affect the reduction of BDNF levels. We provide novel evidence on the relationship between chronic inflammation and depression, suggesting that combination of antidepressant and anti-inflammatory agents bupropion and celecoxib might represent an attractive therapeutic strategy for depression.

Acute psychological stress results in the rapid development of insulin resistance

In recent years, the roles of chronic stress and depression as independent risk factors for decreased insulin sensitivity and the development of diabetes have been increasingly recognized. However, an understanding of the mechanisms linking insulin resistance and acute psychological stress are very limited. We hypothesized that acute psychological stress may cause the development of insulin resistance, which may be a risk factor in developing type 2 diabetes. We tested the hypothesis in a well-established mouse model using 180 episodes of inescapable foot shock (IES) followed by a behavioral escape test. In this study, mice that received IES treatment were tested for acute insulin resistance by measuring glucose metabolism and insulin signaling. When compared with normal and sham mice, mice that were exposed to IES resulting in escape failure (defined as IES with behavioral escape failure) displayed elevated blood glucose levels in both glucose tolerance and insulin tolerance tests. Furthermore, mice with IES exposure and behavioral escape failure exhibited impaired hepatic insulin signaling via the insulin-induced insulin receptor/insulin receptor substrate 1/Akt pathway, without affecting similar pathways in skeletal muscle, adipose tissue, and brain. Additionally, a rise in the murine growth-related oncogene KC/GRO was associated with impaired glucose metabolism in IES mice, suggesting a mechanism by which psychological stress by IES may influence glucose metabolism. The present results indicate that psychological stress induced by IES can acutely alter hepatic responsiveness to insulin and affect whole-body glucose metabolism.

A benzodiazepine impairs the neurogenic and behavioural effects of fluoxetine in a rodent model of chronic stress

Antidepressant agents such as fluoxetine have been shown to produce neurogenic effects involving transcriptional and translational changes that direct molecular and cellular plasticity. These cellular and molecular events appear necessary to mediate the therapeutic effects of fluoxetine and may be generated through the ability for fluoxetine to regulate BDNF levels. Clinically, benzodiazepines are frequently used in combination with standard antidepressants both for initial treatment and maintenance therapy, especially when comorbid anxiety is present. However, very little is known regarding the consequence of combined treatment of benzodiazepines and antidepressant on the development of clinical effect. The current study therefore examined the effect of co-administration of fluoxetine and the benzodiazepine, diazepam, on hippocampal neurogenesis in the social isolation rodent model of chronic stress. We demonstrate that 9 weeks of social isolation induces a deficit in motivational behaviour with increased anxiety as well as impairment in hippocampal neurogenesis. This was parallelled by reduced BDNF levels in the hippocampus. While treatment with fluoxetine alone for 3 weeks restored anxiety behaviour as well as progenitor cell proliferation and the generation of new hippocampal neurons, this effect was prevented by co-administration with diazepam. This suggests that co-administering benzodiazepines with antidepressants could significantly delay or prevent the cellular and behavioural improvement needed by patients. These findings indicate the need for future clinical studies designed to investigate the combined effects of benzodiazepines and antidepressants in patients.

A rodent model of premenstrual dysphoria: progesterone withdrawal induces depression-like behavior that is differentially sensitive to classes of antidepressants

Premenstrual dysphoric disorder (PMDD) is characterized by a range of physical and affective symptoms including anxiety, irritability, anhedonia, social withdrawal and depression. We demonstrate robust and reproducible depression-like behavior during progesterone withdrawal (PWD) protocols with different methodological variables. Comparable immobility in the forced swim test was evident with different routes of administration (i.e. injections vs. implants), with and without exogenous estrogens in addition to progesterone, and in both single and multiple withdrawal paradigms. Furthermore, withdrawal from physiological doses of progesterone resulted in modest social withdrawal in the social preference test and anhedonia in the saccharin preference test without altering general activity levels or total liquid consumption. However, progesterone withdrawal did not alter serotonin levels in the cortex or hippocampus. Furthermore tryptophan depletion did not augment immobility during PWD. Neither fluoxetine nor duloxetine reduced depression-like behavior during PWD in the forced swim test. In contrast, the tricyclic antidepressant, amitriptyline, was effective in reducing the immobility in forced swim test. These data demonstrate that progesterone withdrawal is a reproducible model of PMDD in several critical behavioral domains. Furthermore, these data do not support alterations in serotonin levels in the etiology of hormonally induced depression.

Antidepressant-like properties of oral riluzole and utility of incentive disengagement models of depression in mice

RATIONALE

The neuroprotective agent riluzole has antidepressant-like properties in humans, but its mechanisms of action are unclear. Despite the increasing utility of transgenic and knockout mice in addressing such issues, previous studies aimed at characterizing biochemical mechanisms have been conducted in rats.

OBJECTIVES

We sought to optimize an oral riluzole administration protocol with antidepressant-like consequences in C57BL/6 mice, a common background strain in genetically modified mice.

METHODS

Riluzole (6-60 μg/ml) was dissolved in tap water and replaced regular drinking water for up to 3 weeks; sensitivity to tail suspension, forced swimming, and the locomotor response to extinction training in a model of "incentive disengagement" were tested. Peripheral and central effects of long-term 60-μg/ml treatment were also evaluated.

RESULTS

Riluzole had dose-dependent antidepressant-like effects in the forced swim test, and like chronic fluoxetine, exerted antidepressant-like actions in an adaptation of the "incentive disengagement" model at the highest concentration tested. This 60-μg/ml concentration also restored hippocampal brain-derived neuroptrophic factor (BDNF) expression after chronic corticosteroid exposure and increased glutamate glial transporter 1 (GLT-1, or EAAT2) expression without significantly affecting baseline locomotor activity, thymus and adrenal gland weights, or blood serum corticosterone. The lowest 6-μg/ml concentration increased locomotor activity, potentially consistent with an anxiolytic-like effect.

CONCLUSIONS

Riluzole's therapeutic potential for treating mood disorders may involve GLT-1 and BDNF, and we suggest this protocol could be used to further characterize its precise long-term biochemical mechanisms of action in animal models of depression.

Examining antidepressant drug response by smoking status: why is it important and how often is it done?

Despite an increasingly recognized relationship between depression and smoking, little is known about the degree to which treatment studies for depression consider the impact of smoking on outcomes. The aim of this study is to examine the extent to which smoking is considered in current antidepressant treatment research. We conducted a MEDLINE search of recent randomized clinical trials of pharmacotherapy for depression published between 1 January and 31 December 2007, and a search of current pharmacological intervention studies for depression using www.ClinicalTrials.gov. Only 5% of the 107 pharmacological trials for depression published in 2007 reported the smoking status of their samples. Two studies (1.9%) controlled for smoking in the analyses and no studies analyzed outcomes by smoking status. Excluding the eight studies of combined treatment for depression and nicotine dependence, no other study on www.ClinicalTrials.gov (total n = 920) reported an intention to analyze outcomes by smoking status. Emerging data link smoking and depression, however, little attention has been directed toward the effects of smoking on antidepressant treatment outcomes. Conducting research to understand how nicotine and smoking affect responsiveness to antidepressants would advance our understanding of the neurobiology of depression and the development of new and targeted treatments.

Behaviour of a genetic mouse model of depression in the learned helplessness paradigm

RATIONALE

H/Rouen (displaying a helpless phenotype in the tail suspension test) mice exhibiting features of depressive disorders and NH/Rouen (displaying non-helpless phenotype) mice were previously created through behavioural screening and selective breeding. Learned helplessness (LH), in which footshock stress induces a coping deficit, models some aspects of depression in rodents, but so far, fewer LH studies have been performed in mice than in rats.

OBJECTIVES

To study H/Rouen and NH/Rouen in the LH paradigm.

RESULTS

When CD1 mice were submitted to footshock with various training durations and shock intensities, the most suitable parameters to induce a behavioural deficit were 0.3 mA and four training sessions. A significantly longer latency to escape shocks was found in male H/Rouen mice compared to male NH/Rouen mice. On the other hand, once shocked, NH/Rouen mice showed more severe coping deficits than H/Rouen mice. In addition, a sub-chronic treatment with fluoxetine lacked efficacy in NH/Rouen mice, whereas it improved performances in H/Rouen mice. We also found that a shock reminder at day 8, subsequent to inescapable shocks, maintained helplessness for 20 days. Finally, female H/Rouen mice responded to chronic fluoxetine administration after 10 days of treatment, while a 20-day treatment was necessary to improve the behavioural deficit in H/Rouen male mice.

CONCLUSION

H/Rouen and NH/Rouen lines displayed different despair-related behaviour in the LH paradigm. Fluoxetine had beneficial effects after sub-chronic or chronic but not acute treatment of H/Rouen mice, thus providing a pharmacological validation of the protocols.

Neuropeptide Y-Y2 receptor knockout mice: influence of genetic background on anxiety-related behaviors

Neuropeptide Y (NPY) has been extensively studied in relation to anxiety and depression but of the seven NPY receptors known to date, it is not yet clear which one is mainly involved in mediating its effects in emotional behavior. Mice lacking the NPY-Y2 receptors were previously shown to be less anxious due to their improved ability to cope with stressful situations. In the present study, the behavioral phenotype including the response to challenges was analyzed in NPY-Y2 knockout (KO) mice backcrossed in to congenic C57BL/6 background. In the elevated plus-maze (EPM) and the forced swim test (FST), the anxiolytic-like or antidepressant-like phenotype of the NPY-Y2 KO mice could not be confirmed, although this study differs from the previous one only with regard to the genetic background of the mice. In addition, no differences in response to acute stress or to the antidepressant desipramine in the FST were detected between wild type (WT) and NPY-Y2 KO animals. These results suggest that the genetic background of the animals appears to have a strong influence on the behavioral phenotype of NPY-Y2 KO mice. Additionally, to further characterize the animals by their biochemical response to a challenge, the neurochemical changes induced by the anxiogenic compound yohimbine were measured in the medial prefrontal cortex (mPFC) of NPY-Y2 KO and compared to WT mice. Dopamine (DA) levels were significantly increased by yohimbine in the WT but unaffected in the KO mice, suggesting that NPY-Y2 receptor exerts a direct control over both the tonic and phasic release of DA and that, although the anxiety-like behavior of these NPY-Y2 KO mice is unaltered, there are clear modifications of DA dynamics. However, yohimbine led to a significant increase in noradrenaline (NA) concentration and a slight reduction in serotonin concentration that were identical for both phenotypes.

Peripheral BDNF produces antidepressant-like effects in cellular and behavioral models

Recent clinical studies demonstrate that serum levels of brain-derived neurotrophic factor (BDNF) are significantly decreased in patients with major depressive disorder (MDD) and that antidepressant treatments reverse this effect, indicating that serum BDNF is a biomarker of MDD. These findings raise the possibility that serum BDNF may also have effects on neuronal activity and behavior, but the functional significance of altered serum BDNF is unknown. To address this issue, we determined the influence of peripheral BDNF administration on depression- and anxiety-like behavior, including the forced swim test (FST), chronic unpredictable stress (CUS)/anhedonia, novelty-induced hypophagia (NIH) test, and elevated-plus maze (EPM). Furthermore, we examined adult hippocampal neurogenesis as well as hippocampal and striatal expression of BDNF, extracellular signal-regulated kinase (ERK) and cAMP response element-binding protein (CREB), in order to determine whether peripherally administered BDNF produces antidepressant-like cellular responses in the brain. Peripheral BDNF administration increased mobility in the FST, attenuated the effects of CUS on sucrose consumption, decreased latency in the NIH test, and increased time spent in the open arms of an EPM. Moreover, adult hippocampal neurogenesis was increased after chronic, peripheral BDNF administration. We also found that BDNF levels as well as expression of pCREB and pERK were elevated in the hippocampus of adult mice receiving peripheral BDNF. Taken together, these results indicate that peripheral/serum BDNF may not only represent a biomarker of MDD, but also have functional consequences on molecular signaling substrates, neurogenesis, and behavior.

Maternal separation with early weaning: a novel mouse model of early life neglect

Background

Childhood adversity is associated with increased risk for mood, anxiety, impulse control, and substance disorders. Although genetic and environmental factors contribute to the development of such disorders, the neurobiological mechanisms involved are poorly understood. A reliable mouse model of early life adversity leading to lasting behavioral changes would facilitate progress in elucidating the molecular mechanisms underlying these adverse effects. Maternal separation is a commonly used model of early life neglect, but has led to inconsistent results in the mouse.

Results

In an effort to develop a mouse model of early life neglect with long-lasting behavioral effects in C57BL/6 mice, we designed a new maternal separation paradigm that we call Maternal Separation with Early Weaning (MSEW). We tested the effects of MSEW on C57BL/6 mice as well as the genetically distinct DBA/2 strain and found significant MSEW effects on several behavioral tasks (i.e., the open field, elevated plus maze, and forced swim test) when assessed more than two months following the MSEW procedure. Our findings are consistent with MSEW causing effects within multiple behavioral domains in both strains, and suggest increased anxiety, hyperactivity, and behavioral despair in the MSEW offspring. Analysis of pup weights and metabolic parameters showed no evidence for malnutrition in the MSEW pups. Additionally, strain differences in many of the behavioral tests suggest a role for genetic factors in the response to early life neglect.

Conclusions

These results suggest that MSEW may serve as a useful model to examine the complex behavioral abnormalities often apparent in individuals with histories of early life neglect, and may lead to greater understanding of these later life outcomes and offer insight into novel therapeutic strategies.

Peripheral BDNF produces antidepressant-like effects in cellular and behavioral models

Recent clinical studies demonstrate that serum levels of brain-derived neurotrophic factor (BDNF) are significantly decreased in patients with major depressive disorder (MDD) and that antidepressant treatments reverse this effect, indicating that serum BDNF is a biomarker of MDD. These findings raise the possibility that serum BDNF may also have effects on neuronal activity and behavior, but the functional significance of altered serum BDNF is unknown. To address this issue, we determined the influence of peripheral BDNF administration on depression- and anxiety-like behavior, including the forced swim test (FST), chronic unpredictable stress (CUS)/anhedonia, novelty-induced hypophagia (NIH) test, and elevated-plus maze (EPM). Furthermore, we examined adult hippocampal neurogenesis as well as hippocampal and striatal expression of BDNF, extracellular signal-regulated kinase (ERK) and cAMP response element-binding protein (CREB), in order to determine whether peripherally administered BDNF produces antidepressant-like cellular responses in the brain. Peripheral BDNF administration increased mobility in the FST, attenuated the effects of CUS on sucrose consumption, decreased latency in the NIH test, and increased time spent in the open arms of an EPM. Moreover, adult hippocampal neurogenesis was increased after chronic, peripheral BDNF administration. We also found that BDNF levels as well as expression of pCREB and pERK were elevated in the hippocampus of adult mice receiving peripheral BDNF. Taken together, these results indicate that peripheral/serum BDNF may not only represent a biomarker of MDD, but also have functional consequences on molecular signaling substrates, neurogenesis, and behavior.

Recapitulation and reversal of a persistent depression-like syndrome in rodents

Alterations in multiple biological functions, such as transcription factor activity, are implicated in the neurobiology of depression, based primarily on the characterization of antidepressant efficacy in naïve rodents rather than on models that capture the protracted feelings of anhedonia and helplessness that typify depression. This unit presents rat and mouse models of depression that involve chronic oral exposure to the stress-associated adrenal hormone, corticosterone (CORT), resulting in anhedonic- and helplessness-like behaviors that are persistent yet reversible by chronic antidepressant treatment. Prior CORT exposure also chronically influences molecular targets hypothesized to contribute to negative mood. One example is phosphorylation of cAMP response element binding protein in the hippocampus and nucleus accumbens. Prior chronic CORT exposure provides an alternative method to chronic mild stress models of depression that is easily replicable and persists well beyond the CORT exposure period, thereby modeling the persistent depressive-like state in humans.

Sex-related differential response to clomipramine treatment in a rat model of depression

Research in affective disorders is often performed without considering sex differences, although women are predominantly affected. Consequently, the potential sex-dependent action of antidepressants remains elusive. We investigated whether Flinders sensitive line (FSL) of rats, a model of depression, would present sex-differentiated responses to antidepressant treatment. FSL and Sprague-Dawley rats were treated with clomipramine 10 mg/kg/day for 14 days. Subsequently, they were subjected to either a single session of the forced swim test or an estimation of serotonergic function in the prefrontal cortex, hippocampus, amygdala and hypothalamus. Male FSL displayed increased immobility duration, decreased active behaviours, increased serotonin tissue levels and a reduced serotonin turnover rate in most brain areas studied. Female FSL showed a distinct profile, consisting of decreased immobility latency, increased climbing duration, limited serotonergic deviations and no difference in the serotonin turnover rate in comparison with controls. Interestingly, despite baseline differences, clomipramine treatment reversed all relevant behavioural responses and increased the serotonin turnover rate in both sexes. However, the latter effect was remarkably more pronounced in females. It is concluded that, in this animal model of depression, chronic clomipramine treatment attenuated baseline sex differences in the phenotype while maintaining or intensifying the sex differentiation in the serotonergic endophenotype.

Erythropoietin induction by electroconvulsive seizure, gene regulation, and antidepressant-like behavioral effects

BACKGROUND

The neuroprotective and trophic actions of erythropoietin (EPO) have been tested in several animal models of insult, injury, and neurodegeneration. Recent studies in human volunteers demonstrated that EPO improves cognition and also elicits antidepressant effects. It is believed that the behavioral effects are mediated by EPO's trophic effect on neuronal systems. We therefore tested whether EPO is able to alter behavior and brain gene expression in rats.

METHODS

The expression of EPO and EPO receptor (EPOR) in multiple brain regions was examined by quantitative polymerase chain reaction, in situ hybridization, and immunohistochemistry. The regulation of EPO and the transcription factor hypoxia-induced factor-alpha (HIF1alpha) after electroconvulsive seizure (ECS) was investigated. Behavioral effects of EPO were tested in the rodent forced swimming and novelty-induced hypophagia (NIH) models. EPO gene profiles were obtained by microarray analysis of the hippocampus after intracerebroventricular infusion.

RESULTS

EPO and EPOR were widely expressed in the brain albeit at low levels. Highest level of EPO and EPOR were in the choroid plexus and striatum, respectively. Peripheral administration of EPO was sufficient to produce a robust antidepressant-like effect in the forced swim and NIH tests. Gene expression profiles revealed that EPO induces the expression of neurotrophic genes such as brain-derived neurotrophic factor, VGF (nonacronymic), and neuritin.

CONCLUSIONS

EPO is induced by ECS and independently exhibits antidepressant-like efficacy in the forced swim and NIH tests. EPO regulates the expression of genes implicated in antidepressant action and appears to be a candidate molecule for further testing in neuropsychiatry.

Reduced emotional and corticosterone responses to stress in mu-opioid receptor knockout mice

The detailed mechanisms of emotional modulation in the nervous system by opioids remain to be elucidated, although the opioid system is well known to play important roles in the mechanisms of analgesia and drug dependence. In the present study, we conducted behavioral tests of anxiety and depression and measured corticosterone concentrations in both male and female mu-opioid receptor knockout (MOP-KO) mice to reveal the involvement of mu-opioid receptors in stress-induced emotional responses. MOP-KO mice entered more and spent more time in the open arms of the elevated plus maze compared with wild-type mice. MOP-KO mice also displayed significantly decreased immobility in a 15 min tail-suspension test compared with wild-type mice. Similarly, MOP-KO mice exhibited significantly decreased immobility on days 2, 3, and 4 in a 6 min forced swim test conducted for 5 consecutive days. The increase in plasma corticosterone concentration induced by tail-suspension, repeated forced swim, or restraint stress was reduced in MOP-KO mice compared with wild-type mice. Corticosterone levels were not different between wild-type and MOP-KO mice before stress exposure. In contrast, although female mice tended to exhibit fewer anxiety-like responses in the tail-suspension test in both genotypes, no significant gender differences were observed in stress-induced emotional responses. These results suggest that MOPs play an important facilitatory role in emotional responses to stress, including anxiety- and depression-like behavior and corticosterone levels.

Estrogen receptor beta regulates the expression of tryptophan-hydroxylase 2 mRNA within serotonergic neurons of the rat dorsal raphe nuclei

Dysfunctions of the brain 5-HT system are often associated with affective disorders, such as depression. The raphe nuclei target the limbic system and most forebrain areas and constitute the main source of 5-HT in the brain. All 5-HT neurons express tryptophan hydroxylase-2 (TPH2), the brain specific, rate-limiting enzyme for 5-HT synthesis. Estrogen receptor (ER) beta agonists have been shown to attenuate anxiety- and despair-like behaviors in rodent models. Therefore, we tested the hypothesis that ER beta may contribute to the regulation of gene expression in 5-HT neurons of the dorsal raphe nuclei (DRN) by examining the effects of systemic and local application of the selective ER beta agonist diarylpropionitrile (DPN) on tph2 mRNA expression. Ovariectomized (OVX) female rats were injected s.c. with DPN or vehicle once daily for 8 days. In situ hybridization revealed that systemic DPN-treatment elevated basal tph2 mRNA expression in the caudal and mid-dorsal DRN. Behavioral testing of all animals in the open field (OF) and on the elevated plus maze (EPM) on days 6 and 7 of treatment confirmed the anxiolytic nature of ER beta activation. Another cohort of female OVX rats was stereotaxically implanted bilaterally with hormone-containing wax pellets flanking the DRN. Pellets contained 17-beta-estradiol (E), DPN, or no hormone. Both DPN and E significantly enhanced tph2 mRNA expression in the mid-dorsal DRN. DPN also increased tph2 mRNA in the caudal DRN. DPN- and E-treated rats displayed a more active stress-coping behavior in the forced-swim test (FST). No behavioral differences were found in the OF or on the EPM. These data indicate that ER beta acts at the level of the rat DRN to modulate tph2 mRNA expression and thereby influence 5-HT synthesis in DRN subregions. Our results also suggest that local activation of ER beta neurons in the DRN may be sufficient to decrease despair-like behavior, but not anxiolytic behaviors.

Cytisine-based nicotinic partial agonists as novel antidepressant compounds

Nicotine and other nicotinic agents are thought to regulate mood in human subjects and have antidepressant-like properties in animal models. Recent studies have demonstrated that blockade of nicotinic acetylcholine receptors (nAChRs) including those containing the beta2 subunit (beta2(*)), results in antidepressant-like effects. Previous studies have shown that cytisine, a partial agonist at alpha4/beta2(*) nAChRs, and a full agonist at alpha3/beta4(*) and alpha7 nAChRs, has antidepressant-like properties in several rodent models of antidepressant efficacy; however, it is not clear whether more selective partial agonists will also be effective in these models. We tested cytisine and two derivatives, 5-bromo-cytisine (5-Br-Cyt) and 3-(pyridin-3'-yl)-cytisine (3-pyr-Cyt) for their ability to act as a partial agonist of different nAChR subtypes and to show antidepressant-like activity in C57/BL6 mice in the tail suspension, the forced-swim, and the novelty-suppressed feeding tests. 3-pyr-Cyt was a partial agonist with very low efficacy at alpha4/beta2(*) nAChRS but had no agonist effects at other nAChRs normally targeted by cytisine, and it was effective in mouse models of antidepressant efficacy. Animals showed dose-dependent antidepressant-like effects in all three behavioral paradigms. 5-Br-Cyt was not effective in behavioral tests when administered peripherally, probably because of its inability to penetrate the blood-brain barrier, because it efficiently reduced immobility in the tail suspension test when administered intraventricularly. These results suggest that novel nicotinic partial agonists may provide new possibilities for development of drugs to treat mood disorders.

Genetic regulation of behavioral and neuronal responses to fluoxetine

Despite widespread use of antidepressants, the factors underlying the behavioral response to antidepressants are unknown. It has been shown that antidepressant treatment promotes the proliferation and survival of neurons in the adult hippocampus via enhanced serotonergic signaling, but it is unclear whether hippocampal neurogenesis is responsible for the behavioral response to antidepressants. Furthermore, a large subpopulation of patients fails to respond to antidepressant treatment due to presumed underlying genetic factors. In the present study, we have used the phenotypic and genotypic variability of inbred mouse strains to show that there is a genetic component to both the behavioral and neuronal effects of chronic fluoxetine treatment, and that this antidepressant induces an increase in hippocampal cell proliferation only in the strains that also show a positive behavioral response to treatment. Furthermore, the behavioral and neuronal responses are associated with an upregulation of genes known to promote neuronal proliferation and survival. These results suggest that inherent genetic predisposition to increased serotonin-induced neurogenesis may be a determinant of antidepressant efficacy.

Regionally specific regulation of ERK MAP kinase in a model of antidepressant-sensitive chronic depression

BACKGROUND

Elevated phosphorylation of neurotrophin-regulated transcription factors, such as cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB), in the hippocampus has been proposed as a common mediator of antidepressant (ADT) efficacy in otherwise naive rodents. The intracellular factors by which ADTs and glucocorticoids, causal factors in depression, regulate depression-like behavior remain unclear, but extracellular signal-regulated kinase 1/2 (ERK1/2), upstream of CREB, is a likely candidate.

METHODS

We explored the long-term consequences of glucocorticoid exposure and subsequent ADT treatment in a novel model of chronic depression. Motivated behaviors, immobility during tail suspension, and ERK1/2, known to be required for behavioral response to ADTs, were quantified.

RESULTS

Chronic corticosterone (CORT) increased immobility, decreased responding in an operant conditioning task of motivation, and selectively reduced phosphorylated ERK1/2 (pERK1/2) in the dentate gyrus. Behavioral and biochemical measures were restored to baseline by amitriptyline (AMI) treatment. Corticosterone regulated pERK1/2 on a time course that paralleled increases in heat shock proteins associated with depression and decreased tyrosine kinase receptor B (trkB) phosphorylation. Chronic AMI also produced regionally dissociable effects on pERK1/2 in CA1/CA3, amygdala, and striatum, but not prefrontal cortex.

CONCLUSIONS

Antidepressant efficacy in a motivational task and behavioral despair assay are associated with altered limbic pERK1/2, including restored pERK1/2 in the dentate gyrus after stress-related insult.

Antidepressant-like effects of psoralidin isolated from the seeds of Psoralea Corylifolia in the forced swimming test in mice

The antidepressant-like effects of psoralidin isolated from the seeds of Psoralea corylifolia were investigated in the forced swimming test (FST) in ICR strain of male mice. Psoralidin significantly decreased immobility time and increased swimming behavior without altering climbing behavior in the mouse FST after oral administration for 1 h or 3 consecutive days. Psoralidin did not affect locomotor activity in the open-field test. After a 3-day treatment, psoralidin significantly increased 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels in various brain regions, as well as, changed dopamine (DA) levels in striatum in mice exposed to FST. Psoralidin also ameliorated the elevations in serum corticotropin-releasing factor (CRF), adrenal corticotropin-releasing hormone (ACTH) and corticosterone concentrations induced by swimming stress in mice. These results suggested that psoralidin possessed potent antidepressant-like properties that were mediated via the monoamine neurotransmitter and the hypothalamic-pituitary-adrenal (HPA) axis systems.

Voluntary exercise produces antidepressant and anxiolytic behavioral effects in mice

Reports of beneficial effects of exercise on psychological health in humans are increasingly supported by basic research studies. Exercise is hypothesized to regulate antidepressant-related mechanisms and we therefore characterized the effects of chronic exercise in mouse behavioral paradigms relevant to antidepressant actions. Mice given free access to running wheels showed antidepressant-like behavior in learned helplessness, forced-swim (FST) and tail suspension paradigms. These responses were similar to responses of antidepressant drug-treated animals. When tested under conditions where locomotor activity was not altered, exercising mice also showed reduced anxiety compared to sedentary control mice. In situ hybridization analysis showed that BDNF mRNA was increased in specific subfields of hippocampus after wheel running. We chose one paradigm, the FST, in which to investigate a functional role for brain-derived neurotrophic factor (BDNF) in the behavioral response to exercise. We tested mice heterozygous for a deletion of the BDNF gene in the FST after wheel-running. Exercising wild-type mice showed the expected antidepressant-like behavioral response in the FST but exercise was ineffective in improving FST performance in heterozygous BDNF knockout mice. A possible functional contribution of a BDNF signaling pathway to FST performance in exercising mice was investigated using the specific MEK inhibitor PD184161 to block the MAPK signaling pathway. Subchronic administration of PD184161 to exercising mice blocked the antidepressant-like behavioral response seen in vehicle-treated exercising mice in the FST. In summary, chronic wheel-running exercise in mice results in antidepressant-like behavioral changes that may involve a BDNF related mechanism similar to that hypothesized for antidepressant drug treatment.

Behavioral effects of chronic fluoxetine in BALB/cJ mice do not require adult hippocampal neurogenesis or the serotonin 1A receptor

We previously reported that chronic, but not subchronic, treatment with the selective serotonin reuptake inhibitor (SSRI) fluoxetine altered behavior in the forced swimming test (FST) in BALB/cJ mice. We now use this model to investigate mechanisms underlying the delayed onset of the behavioral response to antidepressants, specifically (1) adult hippocampal neurogenesis and (2) expression of the 5-HT1A receptor. Here, we show data validating this model of chronic antidepressant action. We found the FST to be selectively responsive to chronic administration of the SSRI fluoxetine (18 mg/kg/day) and the tricyclic antidepressant desipramine (20 mg/kg/day), but not to the antipsychotic haloperidol (1 mg/kg/day) in BALB/cJ mice. The behavioral effects of fluoxetine emerged by 12 days of treatment, and were affected neither by ablation of progenitor cells of the hippocampus nor by genetic deletion of the 5-HT1A receptor. The effect of fluoxetine in the BALB/cJ mice was also neurogenesis-independent in the novelty-induced hypophagia test. We also found that chronic fluoxetine does not induce an increase in cell proliferation or the number of young neurons as measured by BrdU and doublecortin immunolabeling, respectively, in BALB/cJ mice. These data are in contrast to our previous report using a different strain of mice (129SvEvTac). In conclusion, we find that BALB/cJ mice show a robust response to chronic SSRI treatment in the FST, which is not mediated by an increase in new neurons in the hippocampus, and does not require the 5-HT1A receptor. These findings suggest that SSRIs can produce antidepressant-like effects via distinct mechanisms in different mouse strains.

Antidepressant-like effects of the histone deacetylase inhibitor, sodium butyrate, in the mouse

BACKGROUND

Chromatin remodeling, including changes in histone acetylation, might play a role in the pathophysiology and treatment of depression. We investigated whether the histone deacetylase inhibitor sodium butyrate (SB) administered as single drug or in combination with the selective serotonin reuptake inhibitor (SSRI) fluoxetine exerts antidepressant-like effects in mice.

METHODS

Mice (C57BL/6J) received injections of SB, fluoxetine, or a combination of both drugs either acutely or chronically for a period of 28 days and were subjected to a battery of tests to measure anxiety and behavioral despair. Histone acetylation and expression of brain-derived neurotrophic factor (BDNF) were monitored in hippocampus and frontal cortex.

RESULTS

Co-treatment with SB and fluoxetine resulted in a significant 20%-40% decrease in immobility scores in the tail suspension test (TST), a measure for behavioral despair, both acutely and chronically. In contrast, decreased immobility after single drug regimens was limited either to the acute (fluoxetine) or chronic (SB) paradigm. Systemic injection of SB induced short-lasting histone hyperacetylation in hippocampus and frontal cortex. Among the four treatment paradigms that resulted in improved immobility scores in the TST, three were associated with a transient, at least 50% increase in BDNF transcript in frontal cortex, whereas changes in hippocampus were less consistent.

CONCLUSIONS

The histone deacetylase inhibitor SB exerts antidepressant-like effects in the mouse. The therapeutic benefits and molecular actions of histone modifying drugs, including co-treatment with SSRIs and other newer generation antidepressant medications, warrant further exploration in experimental models.

Cytisine, a partial agonist of high-affinity nicotinic acetylcholine receptors, has antidepressant-like properties in male C57BL/6J mice

The nicotine in tobacco is thought to modulate neuronal systems regulating mood. Moreover, it appears possible that blockade rather than activation of beta2-containing (beta2*) nicotinic acetylcholine receptors (nAChRs) may lead to antidepressant-like effects. We used cytisine, a partial agonist of alpha4/beta2*nAChRs and a full agonist at alpha3/beta4*nAChRs, in several tests of antidepressant efficacy. Further, we used c-fos expression to identify potential neurobiological correlates of the antidepressant-like effects of cytisine. Cytisine had antidepressant-like effects in several animal models of antidepressant efficacy. In addition, immunohistochemical analyses indicated that cytisine could reduce c-fos immunoreactivity in the basolateral amygdala by approximately 50%. These data show that cytisine acts like classical antidepressants in rodent models of antidepressant efficacy. In addition, cytisine's ability to block alpha4/beta2*nAChRs may be responsible for its antidepressant-like properties, and these may be mediated through a reduction of neuronal activity in the basolateral amygdala. These studies also suggest that both antagonists and partial agonists of alpha4/beta2*nAChRs would be interesting targets for the development of novel antidepressant drugs.