Rat behavior after chronic variable stress and partial lesioning of 5-HT-ergic neurotransmission: effects of citalopram

A study of roflumilast treatment on functional and structural changes in hippocampus in depressed Adult male Wistar rats

Depression is a common stress disability disorder that affects higher mental functions including emotion, cognition, and behavior. It may be mediated by inflammatory cytokines that interfere with neuroendocrine function, and synaptic plasticity. Therefore, reductions in inflammation might contribute to treatment response. The current study aims to evaluate the role of Protein Kinase (PKA)- cAMP response element-binding protein (CREB)- brain derived neurotropic factor (BDNF) signaling pathway in depression and the effects of roflumilast (PDE4 inhibitor) as potential antidepressant on the activity of the PKA-CREB-BDNF signaling pathway, histology, and pro-inflammatory cytokine production. Forty Adult male Wistar rats were divided into 4 groups: Control group, Positive Control group: similar to the controls but received Roflumilast (3 mg / kg / day) by oral gavage for the last 4 weeks of the experiment, Depressed group which were exposed to chronic stress for 6 weeks, and Roflumilast-treated group which were exposed to chronic stress for 6 weeks and treated by Roflumilast (3 mg / kg / day) by oral gavage for the last 4 weeks of the experiment. The depressed group showed significant increase in immobility time with significant decrease in swimming and struggling times, significant decrease in hippocampal PKA, CERB, BDNF, Dopamine, Cortisone, and Superoxide dismutase while hippocampal Phosphodiesterase-E4, Interleukin-6, and Malondialdhyde levels were significantly elevated. These findings were significantly reversed upon Roflumilast treatment. Therefore, it could be concluded that depression is a neurodegenerative inflammatory disease and oxidative stress plays a key role in depression. Roflumilast treatment attenuated the depression behavior in rats denoting its neuroprotective, and anti-inflammatory effects.

Prophylactic administration of rosmarinic acid ameliorates depression-associated cardiac abnormalities in Wistar rats: Evidence of serotonergic, oxidative, and inflammatory pathways

Psychiatric disorders and associated cardiac comorbidities have increased the risk of mortality worldwide. Researchers reported that depression increases the possibility of future cardiac abnormalities by approximately 30%. Therefore, there is an unmet need to develop therapeutic interventions to treat depression and associated cardiac abnormalities. The present study was conducted to evaluate the prophylactic effect of rosmarinic acid (RA) against chronic unpredictable stress (CUS)-induced depression associated cardiac abnormalities in Wistar rats. The CUS paradigm, which comprised several stressors, was employed for 40 days to induce depressive-like behavior and associated cardiac abnormalities in rats. Along with CUS, RA at a dose of 25 and 50 mg/kg was administered orally to two groups of animals for 40 days. Behavioral tests (forced swim test and sucrose consumption test) and molecular biomarkers (corticosterone and serotonin) were performed. Electrocardiography was performed before CUS (Day 0), Day 20, and Day 40 to study electrocardiogram parameters. Furthermore, changes in body weight, organ weight, tissue lipid peroxidation, glutathione, catalase, cTn-I, MMP-2, and proinflammatory cytokines (TNF-α and IL-6) were estimated. Our results showed that RA treatment caused a reduction in immobility period, adrenal hyperplasia, corticosterone level, tissue lipid peroxidation, cTn-I, MMP-2, proinflammatory cytokines, and QRS complex duration, while an increase in sucrose consumption, brain serotonin level, T-wave width, glutathione, and catalase activity as compared with the CUS-control group. The results of our study proved that RA administration ameliorates CUS-induced depression-associated cardiac abnormalities in rats via serotonergic, oxidative, and inflammatory pathways.

Plasticity in mental health: A network theory

Plasticity is the ability to modify brain and behavior, ultimately promoting an amplification of the impact of the context on the individual's mental health. Thus, plasticity is not beneficial per se but its value depends on contextual factors, such as the quality of the living environment. High plasticity is beneficial in a favorable environment, but can be detrimental in adverse conditions, while the opposite applies to low plasticity. Resilience and vulnerability are not univocally associated to high or low plasticity. Consequently, individuals should undergo different preventive and therapeutic strategies according to their plasticity levels and living conditions. Here, an operationalization of plasticity relying on network theory is proposed: the strength of the connection among the network elements defining the individual, such as its symptoms, is a measure of plasticity. This theoretical framework represents a promising tool to investigate research questions related to changes in neural structure and activity and in behavior, and to improve therapeutic strategies for psychiatric disorders, such as major depression.

Selecting antidepressants according to a drug-by-environment interaction: A comparison of fluoxetine and minocycline effects in mice living either in enriched or stressful conditions

Selective serotonin reuptake inhibitors (SSRIs) are the first-line treatment for major depressive disorder. It has been recently proposed that these drugs, by enhancing neural plasticity, amplify the influences of the living conditions on mood. Consequently, SSRI outcome depends on the quality of the environment, improving symptomatology mainly in individuals living in favorable conditions. In adverse conditions, drugs with a different mechanism of action might have higher efficacy. The antibiotic minocycline, with neuroprotective and anti-inflammatory properties, has been recently proposed as a novel potential antidepressant treatment. To explore the drug-by-environment interaction, we compared the effects on depressive-like behavior and neural plasticity of the SSRI fluoxetine and minocycline in enriched and stressful conditions. We first exposed C57BL/6 adult female mice to 14 days of chronic unpredictable mild stress to induce a depressive-like profile. Afterward, mice received vehicle, fluoxetine, or minocycline for 21 days, while exposed to either enriched or stressful conditions. During the first five days, fluoxetine led to an improvement in enrichment but not in stress. By contrast, minocycline led to an improvement in both conditions. After 21 days, all groups showed a significant improvement in enrichment while fluoxetine worsened the depressive like behavior in stress. The effects of the drugs on neural plasticity, measured as long-term potentiation, were also environment-dependent. Overall, we show that the environment affects fluoxetine but not minocycline outcome, indicating that the latter represents a potential alternative to SSRIs to treat depressed patients living in adverse conditions. From a translation perspective, our finding call for considering the drug-by-environment interaction to select the most effective pharmacological treatment.

Shaping therapeutic trajectories in mental health: Instructive vs. permissive causality

We are currently facing the challenge of improving treatments for psychiatric disorders such as major depression. Notably, antidepressants have an incomplete efficacy, mostly due to our limited knowledge of their action. Here we present a theoretical framework that considers the distinction between instructive and permissive causality, which allows formalizing and disentangling the effects exerted by different therapeutic strategies commonly used in psychiatry. Instructive causality implies that an action determines a specific effect while permissive causality allows an action to take effect or not. We posit that therapeutic strategies able to improve the quality of the living environment or the ability to face it, including changes in lifestyle and psychotherapeutic interventions, rely mainly on instructive causality and thus shape the individual's ability to face the psychopathology and build resilience. By contrast, pharmacological treatments, such as selective serotonin reuptake inhibitors, act primarily through a permissive causality: they boost neural plasticity, i.e. the ability of the brain to change itself, and therefore allow for instructive interventions to produce beneficial effects or not. The combination of an instructive and a permissive action represents the most promising approach since the quality of the living environment can shape the path leading to mental health while drug treatment can increase the likelihood of achieving such a goal.

Natural Psychoplastogens As Antidepressant Agents

Increasing prevalence and burden of major depressive disorder presents an unavoidable problem for psychiatry. Existing antidepressants exert their effect only after several weeks of continuous treatment. In addition, their serious side effects and ineffectiveness in one-third of patients call for urgent action. Recent advances have given rise to the concept of psychoplastogens. These compounds are capable of fast structural and functional rearrangement of neural networks by targeting mechanisms previously implicated in the development of depression. Furthermore, evidence shows that they exert a potent acute and long-term positive effects, reaching beyond the treatment of psychiatric diseases. Several of them are naturally occurring compounds, such as psilocybin, N,N-dimethyltryptamine, and 7,8-dihydroxyflavone. Their pharmacology and effects in animal and human studies were discussed in this article.

TLR4 signaling modulation of PGC1-α mediated mitochondrial biogenesis in the LPS-Chronic mild stress model: Effect of fluoxetine and pentoxiyfylline

AIM

The addition of repeated lipopolysaccharide (LPS) to chronic mild stress was recently proposed in our lab as an alternative model of depression, highlighting the possible interaction between stress and immune-inflammatory pathways in predisposing depression. Given that CMS-induced depressive behavior was previously related to impaired hippocampal energy metabolism and mitochondrial dysfunction, our current study aimed to investigate the interplay between toll-like receptor 4 (TLR4) signaling and peroxisome proliferator-activated receptor gamma coactivators-1-alpha (PGC1-α) as a physiological regulator of energy metabolism and mitochondrial biogenesis in the combined LPS/CMS model.

MAIN METHODS

Male Wistar rats were exposed to either LPS (50 μg/kg i.p.) over 2 weeks, CMS protocol for 4 weeks or LPS over 2 weeks followed by 4 weeks of CMS (LPS/CMS). Three additional groups of rats were exposed to LPS/CMS protocol and treated with either pentoxifylline (PTX), fluoxetine (FLX) or a combination of both. Rats were examined for behavioral, neurochemical, gene expression and mitochondrial ultra-structural changes.

KEY FINDINGS

LPS/CMS increased the expression of TLR4 and its downstream players; MyD88, NFκB and TNF-α along with an escalation in hippocampal-energy metabolism and p-AMPK. Simultaneously LPS/CMS attenuated the expression of PGC1-α/NRF1/Tfam and mt-DNA. The antidepressant (AD) 'FLX', the TNF-α inhibitor 'PTX' and their combination ameliorated the LPS/CMS-induced changes. Interestingly, all the aforementioned changes induced by the LPS/CMS combined model were significantly less than those induced by CMS alone.

SIGNIFICANCE

Blocking the TLR4/NFκB signaling enhanced the activation of the PGC1-α/NRF1/Tfam and mt-DNA content independent on the activation of the energy-sensing kinase AMPK.

Behavioral effects of toll-like receptor-4 antagonist 'eritoran' in an experimental model of depression: role of prefrontal and hippocampal neurogenesis and γ-aminobutyric acid/glutamate balance

Depression is the disease of the modern era. The lack of response to the available antidepressants, which were developed on the basis of the monoaminergic deficit hypothesis of depression, has encouraged scientists to think about new mechanisms explaining the pathogenesis of depression. In this context, the inflammatory theory has emerged to clarify many aspects of depression that the previous theories have failed to explain. Toll-like receptor-4 (TLR-4) has a regulatory role in the brain's immune response to stress, and its activation is suggested to play a pivotal role in the pathophysiology of depression. In this study, we tested eritoran (ERI), a TLR-4 receptor-4 antagonist, as a potential antidepressant. We investigated the effect of long-term administration of ERI in three different doses on behavioral changes, hippocampal and prefrontal cortex (PFC) neurogenesis, and γ-aminobutyric acid (GABA)/glutamate balance in male Wistar rats exposed to chronic restraint stress (CRS). Long-term administration of ERI ameliorated CRS-induced depressive-like symptoms and hypothalamic-pituitary-adrenal axis hyperactivity alongside reducing levels of hippocampal and PFC inflammatory cytokines, restoring GABA and glutamate balance, and enhancing PFC and hippocampal neurogenesis, by increasing BDNF gene and protein expression in a dose-dependent manner. The results demonstrate an antidepressant-like activity of ERI in Wistar rats exposed to CRS, which may be largely mediated by its ability to reduce neuroinflammation, increase BDNF, and restore GABA/glutamate balance in prefrontal cortex and hippocampus. Nonetheless, further studies are needed to characterize the mechanism of the antidepressant effect of ERI.

The contribution of the locus coeruleus-norepinephrine system in the emergence of defeat-induced inflammatory priming

Exposure to psychosocial stress is known to precipitate the emergence of stress related psychiatric disorders such as depression and anxiety. While mechanisms by which this occurs remain largely unclear, recent evidence points towards a causative role for inflammation. Neurotransmitters, such as norepinephrine (NE), are capable of regulating expression of proinflammatory cytokines and thus may contribute to the emergence of stress-related disorders. The locus coeruleus (LC) is the major source of norepinephrine (NE) to the brain and therefore the current study utilized N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4), an LC selective noradrenergic neurotoxin, to determine the discrete involvement of the LC-NE system in social defeat-induced inflammation in LC projection regions including the central amygdala (CeA), dorsal raphe (DR) and plasma. In the current study, rats were exposed to brief social defeat or control manipulations on 5 consecutive days. To determine whether a history of social defeat enhanced or "primed" the inflammatory response to a subsequent defeat exposure, all rats regardless of stress history were exposed to an acute social defeat challenge immediately preceeding tissue collection. As anticipated, prior history of social defeat primed inflammatory responses in the plasma and CeA while neuroinflammation in the DR was markedly reduced. Notably, DSP-4 treatment suppressed stress-induced circulating inflammatory cytokines independent of prior stress history. In contrast, neuroinflammation in the CeA and DR were greatly augmented selectively in DSP-4 treated rats with a history of social defeat. Together these data highlight the dichotomous nature of NE in stress-induced inflammatory priming in the periphery and the brain and directly implicate the LC-NE system in these processes.

Insights into the potential antidepressant mechanisms of cilostazol in chronically restraint rats: impact on the Nrf2 pathway

Ample evidence has pointed to a close link between oxidative stress, mitochondrial dysfunction, and depression. Nuclear factor-erythroid 2-related factor-2 (Nrf2) is a master regulator of cellular redox homeostasis and affects mitochondrial function. Nrf2 holds promise for depression prevention and treatment. This study aimed to investigate the potential prophylactic antidepressant effect of cilostazol and the contribution of the Nrf2 pathway toward the putative neuroprotection. The behavioral and neurochemical effects of concomitant treatment of oral cilostazol at doses of 7.5, 15, and 30 mg/kg/day in Wistar rats exposed to chronic restraint stress (CRS) for 4 weeks were assayed. Cilostazol prevented CRS-induced depressive-like behavior shown in sucrose-preference, forced-swimming, and open-field tests, and hypothalamus-pituitary-adrenal axis hyperactivity (adrenal gland weight and serum corticosterone). Cilostazol prevented CRS-induced increase in hippocampal lipid peroxidation and 8-hydroxy-2'-deoxyguanosine, and a decrease in antioxidant activities (glutathione level, superoxide dismutase, and catalase). Western blot and PCR showed that cilostazol favorably modulated the Nrf2 protein and heme oxygenase-1 and NAD(P)H: quinone oxidoreductase-1 gene expression in the hippocampus of CRS rats. Cilostazol also prevented the decrease in the hippocampal activities of mitochondrial respiratory enzyme complexes I-IV. These behavioral and biochemical findings indicated the potential prophylactic antidepressant effect and mechanism of cilostazol by preventing oxidative stress by activation of redox defense mechanisms mediated through the Nrf2 pathway and restoring mitochondrial dysfunction.

Combined Fluoxetine and Metformin Treatment Potentiates Antidepressant Efficacy Increasing IGF2 Expression in the Dorsal Hippocampus

An increasing number of studies show that selective serotonin reuptake inhibitors (SSRIs) exert their therapeutic action, at least in part, by amplifying the influence of the living environment on mood. As a consequence, when administered in a favorable environment, SSRIs lead to a reduction of symptoms, but in stressful conditions, they show limited efficacy. Therefore, novel therapeutic approaches able to neutralize the influence of the stressful environment on treatment are needed. The aim of our study was to test whether, in a mouse model of depression, the combined administration of SSRI fluoxetine and metformin, a drug able to improve the metabolic profile, counteracts the limited efficacy of fluoxetine alone when administered in stressful conditions. Indeed, metabolic alterations are associated to both the onset of major depression and the antidepressant efficacy. To this goal, adult C57BL/6 male mice were exposed to stress for 6 weeks; the first two weeks was aimed at generating a mouse model of depression. During the remaining 4 weeks, mice received one of the following treatments: vehicle, fluoxetine, metformin, or a combination of fluoxetine and metformin. We measured liking- and wanting-type anhedonia as behavioral phenotypes of depression and assessed the expression levels of selected genes involved in major depressive disorder and antidepressant response in the dorsal and ventral hippocampus, which are differently involved in the depressive symptomatology. The combined treatment was more effective than fluoxetine alone in ameliorating the depressive phenotype after one week of treatment. This was associated to an increase in IGF2 mRNA expression and enhanced long-term potentiation, specifically in the dorsal hippocampus, at the end of treatment. Overall, the present results show that, when administered in stressful conditions, the combined fluoxetine and metformin treatment may represent a more effective approach than fluoxetine alone in a short term. Finally, our findings highlight the relevance of polypharmacological strategy as effective interventions to increase the efficacy of the antidepressant drugs currently available.

Animal models of depression: pros and cons

Animal models of depression are certainly needed but the question in the title has been raised owing to the controversies in the interpretation of the readout in a number of tests, to the perceived lack of progress in the development of novel treatments and to the expressed doubts in whether animal models can offer anything to make a true breakthrough in understanding the neurobiology of depression and producing novel drugs against depression. Herewith, it is argued that if anything is wrong with animal models, including those for depression, it is not about the principle of modelling complex human disorder in animals but in the way the tests are selected, conducted and interpreted. Further progress in the study of depression and in developing new treatments, will be supported by animal models of depression if these were more critically targeted to drug screening vs. studies of underlying neurobiology, clearly stratified to vulnerability and pathogenetic models, focused on well-defined endophenotypes and validated for each setting while bearing the existing limits to validation in mind. Animal models of depression need not to rely merely on behavioural readouts but increasingly incorporate neurobiological measures as the understanding of depression as human brain disorder advances. Further developments would be fostered by cross-fertilizinga translational approach that is bidirectional, research on humans making more use of neurobiological findings in animals.

Antidepressant-like actions by silencing of neuronal ELAV-like RNA-binding proteins HuB and HuC in a model of depression in male mice

Currently available antidepressant drugs often fail to achieve full remission and patients might evolve to treatment resistance, showing the need to achieve a better therapy of depressive disorders. Increasing evidence supports that post-transcriptional regulation of gene expression is important in neuronal development and survival and a relevant role is played by RNA binding proteins (RBP). To explore new therapeutic strategies, we investigated the role of the neuron-specific ELAV-like RBP (HuB, HuC, HuD) in a mouse model of depression. In this study, a 4-week unpredictable chronic mild stress (UCMS) protocol was applied to mice to induce a depressive-like phenotype. In the last 2 weeks of the UCMS regimen, silencing of HuB, HuC or HuD was performed by using specific antisense oligonucleotides (aODN). Treatment of UCMS-exposed mice with anti-HuB and anti-HuC aODN improved both anhedonia and behavioural despair, used as measures of depressive-like behaviour, without modifying the response of stressed mice to an anxiety-inducing environment. On the contrary, HuD silencing promoted an anxiolytic-like behaviour in UCMS-exposed mice without improving depressive-like behaviours. The antidepressant-like phenotype of anti-HuB and anti-HuC mice was not shown concurrently with the promotion of adult hippocampal neurogenesis in the dentate gyrus, and no increase in the BDNF and CREB content was detected. Conversely, in the CA3 hippocampal region, projection area of newly born neurons, HuB and HuC silencing increased the number of BrdU/NeuN positive cells. These results give the first indication of a role of nELAV in the modulation of emotional states in a mouse model of depression.

Metformin potentiates cognitive and antidepressant effects of fluoxetine in rats exposed to chronic restraint stress and high fat diet: potential involvement of hippocampal c-Jun repression

Several hypotheses link high fat diet (HFD) with the pathophysiology of depression and its response to antidepressants. This study aimed to determine the effect of metformin (MET) on the cognitive and antidepressant activity of fluoxetine (FLU) through its effect on c-Jun expression. Behavioral, cognitive function, biochemical, and histopathological studies were performed in non-HFD- and HFD-fed rats exposed to chronic restraint stress (CRS). Stressed group showed cognitive impairment, depressive-like symptoms, disturbed glucose homeostasis and lipid profile, reduced adiponectin level, brain-derived neurotrophic factor (BDNF) expression, and increased corticosterone and c-Jun. All these were aggravated by HFD. MET, FLU and their combination produced significant improvement in lipid profile with significant increase in adiponectin and BDNF expression. Corticosterone, body weight and insulin resistance showed significant decrease in the treated groups. Moreover, there was a significant decrease in hippocampal c Jun expression. There was a significant preferable effect toward the combination. Conclusion, MET may decrease the refractoriness to FLU and improves the cognition in individuals who are fed on HFD.

The potential benefit of combined versus monotherapy of coenzyme Q10 and fluoxetine on depressive-like behaviors and intermediates coupled to Gsk-3β in rats

As a part of the serotoninergic dysfunction implicated in neurobiology of depression, evidence has focused on serotonin (5-HT) receptors downstream signaling intermediates including glycogen synthase kinase-3β (GSK-3β), cAMP response element binding protein (CREB) and brain derived neurotrophic factor (BDNF). Our team previously reported that coenzyme Q10 (CoQ10) exerted antidepressant-like effect in rats exposed to chronic unpredictable mid stress (CUMS) via elevating serotonin levels. However, the effect of CoQ10 has not been elucidated in downstream signaling molecules mediating 5HT receptors' effect involved in depressive disorder hitherto. In the present study, we focused on 5-HT_1A and 5-HT_2A receptors (activation of 5-HT_1A receptor and inhibition of 5-HT_2A receptors reduce depressive like-behaviors). We investigated the role of these 5-HT receptors and their linked GSK-3β signaling intermediates as an underlying mechanism of CoQ10 as monotherapy or combined with fluoxetine, a selective serotonin reuptake inhibitor, to alleviate depressive-like phenotype. Effects of CoQ10 (100mg/kg/day) or/and fluoxetine (10mg/kg/day) were determined on 5-HT_1A, 5-HT_2A receptors mRNA expression, GSK-3β and phosphorylated (p)GSK-3β, CREB, pCREB and BDNF protein expression in rats subjected to CUMS for 6weeks. CUMS rats exhibited obvious depressive-like behaviors (anhedonia-like behavior, negative alterations in social interaction, open field and forced swimming tests) with increased corticosterone and adrenal glands weight, decreased hippocampal levels of pGSK-3β, pCREB and BDNF protein expressions. Additionally, they exhibited decreased hippocampal 5-HT_1A and increased 5-HT_2A receptor mRNA expression. CoQ10 or fluoxetine significantly attenuated the behavioral and neurochemical alterations in stressed rats with more significance with combined treatment. These findings imply that CoQ10 or/and fluoxetine attenuated CUMS-induced depressive-like behavior partly through modulating dysfunctional regulation of post-serotonergic receptor signaling pathway focusing on GSK-3β, CREB and BDNF.

Fluoxetine effects on molecular, cellular and behavioral endophenotypes of depression are driven by the living environment

Selective serotonin reuptake inhibitors (SSRIs) represent the most common treatment for major depression. However, their efficacy is variable and incomplete. In order to elucidate the cause of such incomplete efficacy, we explored the hypothesis positing that SSRIs may not affect mood per se but, by enhancing neural plasticity, render the individual more susceptible to the influence of the environment. Consequently, SSRI administration in a favorable environment promotes a reduction of symptoms, whereas in a stressful environment leads to a worse prognosis. To test such hypothesis, we exposed C57BL/6 mice to chronic stress in order to induce a depression-like phenotype and, subsequently, to fluoxetine treatment (21 days), while being exposed to either an enriched or a stressful condition. We measured the most commonly investigated molecular, cellular and behavioral endophenotypes of depression and SSRI outcome, including depression-like behavior, neurogenesis, brain-derived neurotrophic factor levels, hypothalamic-pituitary-adrenal axis activity and long-term potentiation. Results showed that, in line with our hypothesis, the endophenotypes investigated were affected by the treatment according to the quality of the living environment. In particular, mice treated with fluoxetine in an enriched condition overall improved their depression-like phenotype compared with controls, whereas those treated in a stressful condition showed a distinct worsening. Our findings suggest that the effects of SSRI on the depression- like phenotype is not determined by the drug per se but is induced by the drug and driven by the environment. These findings may be helpful to explain variable effects of SSRI found in clinical practice and to device strategies aimed at enhancing their efficacy by means of controlling environmental conditions.

Hemokinin-1 mediates anxiolytic and anti-depressant-like actions in mice

The tachykinin NK1 receptor was suggested to be involved in psychiatric disorders, but its antagonists have failed to be effective as antidepressants in clinical trials. Hemokinin-1 (HK-1), the newest tachykinin, is present in several brain regions and activates the NK1 receptor similarly to substance P (SP), but acts also through other mechanisms. Therefore, we investigated the roles of the Tac4 gene-derived HK-1 in comparison with SP and neurokinin A (NKA) encoded by the Tac1 gene, as well as the NK1 receptor in anxiety and depression-like behaviors in mice. Mice lacking SP/NKA, HK-1 or the NK1 receptor (Tac1^-/-, Tac4^-/-, Tacr1^-/-, respectively) compared to C57Bl/6 wildtypes (WT), and treatment with the NK1 antagonist CP99994 were used in the experiments. Anxiety was evaluated in the light-dark box (LDB) and the elevated plus maze (EPM), locomotor activity in the open field (OFT) tests. Hedonic behavior was assessed in the sucrose preference test (SPT), depression-like behavior in the tail suspension (TST) and forced swim (FST) tests. FST-induced neuronal responsiveness was evaluated with Fos immunohistochemistry in several stress-related brain regions. In the LDB, Tac4^-/- mice spent significantly less, while Tacr1^-/- and CP99994-treated mice spent significantly more time in the lit compartment. In the EPM only Tac4^-/- showed reduced time in the open arms, but no difference was observed in any other groups. In the OFT Tac4^-/- mice showed significantly reduced, while Tac1^-/- and Tacr1^-/- animals increased motility than the WTs, but CP99994 had no effect. NK1^-/- consumed markedly more, while Tac4^-/- less sucrose solution compared to WTs. In the TST and FST, Tac4^-/- mice showed significantly increased immobility. However, depression-like behavior was decreased both in cases of genetic deletion and pharmacological blockade of the NK1 receptor. FST-induced neuronal activation in different nuclei involved in behavioral and neuroendocrine stress responses was significantly reduced in the brain of Tac4 ^-/- mice. Our results provide the first evidence for an anxiolytic and anti-depressant-like actions of HK-1 through a presently unknown target-mediated mechanism. Identification of its receptor and/or signaling pathways might open new perspectives for anxiolytic and anti-depressant therapies.

Middle-range exploratory activity in adult rats suggests higher resilience to chronic social defeat

OBJECTIVE

Stressful life events play an important role in the aetiology of human mood disorders and are frequently modelled by chronic social defeat (SD) in rodents. Exploratory phenotype in rats is a stable trait that is likely related to inter-individual differences in reactivity to stress. The aim of the study was to confirm that low levels of exploratory activity (LE) are, in rodents, a risk factor for passive stress coping, and to clarify the role of medium (ME) and high (HE) exploratory disposition in the sensitivity to SD.

METHODS

We examined the effect of SD on male Wistar rats with LE, ME, and HE activity levels as measured in the exploration box. After SD, the rats were evaluated in social preference, elevated zero maze, and open-field tests. Brain tissue levels of monoamines were measured by high-performance liquid chromatography.

RESULTS

Rats submitted to SD exhibited lower weight gain, higher sucrose consumption, showed larger stress-induced hyperthermia, lower levels of homovanillic acid in the frontal cortex, and higher levels of noradrenaline in the amygdala and hippocampus. Open-field, elevated zero maze, and social preference tests revealed the interaction between stress and phenotype, as only LE-rats were further inhibited by SD. ME-rats exhibited the least reactivity to stress in terms of changes in body weight, stress-induced hyperthermia, and sucrose intake.

CONCLUSION

Both low and high novelty-related activity, especially the former, are associated with elevated sensitivity to social stress. This study shows that both tails of a behavioural dimension can produce stress-related vulnerability.

The effects of antidepressants "fluoxetine and imipramine" on vascular abnormalities and Toll like receptor-4 expression in diabetic and non-diabetic rats exposed to chronic stress

Several studies reveal that diabetes doubles the odds of comorbid depression with evidence of a pro-inflammatory state underlying its vascular complications. Indeed, little information is available about vascular effects of antidepressant drugs in diabetes.

METHOD

We investigated the effect of chronic administration of fluoxetine "FLU" and imipramine "IMIP" on behavioral, metabolic and vascular abnormalities in diabetic and non-diabetic rats exposed to chronic restraint stress (CRS).

RESULTS

Both diabetes and CRS induced depressive-like behavior which was more prominent in diabetic/depressed rats; this was reversed by chronic treatment with FLU and IMIP in a comparable manner. Diabetic and non-diabetic rats exposed to CRS exhibited abnormalities in glucose homeostasis, lipid profile and vascular function, manifested by decreased endothelium-dependent relaxation, increased systolic blood pressure and histopathological atherosclerotic changes. Vascular and metabolic dysfunctions were associated with significant increase in aortic expression of TLR-4, and pro-inflammatory cytokines (TNF-α and IL-1ß). FLU ameliorated these metabolic, vascular and inflammatory abnormalities, while IMIP induced either no change or even worsening of some parameters.

CONCLUSION

FLU has favorable effect over IMIP on metabolic, vascular and inflammatory aberrations associated with DM and CRS in Wistar rats, clarifying the preference of FLU over IMIP in management of comorbid depression in diabetic subjects.

Behavioral effects of nicotinic antagonist mecamylamine in a rat model of depression: prefrontal cortex level of BDNF protein and monoaminergic neurotransmitters

Several studies have pointed to the nicotinic acetylcholine receptor (nAChR) antagonists, such as mecamylamine (MEC), as a potential therapeutic target for the treatment of depression. The present study evaluated the behavioral and neurochemical effects of chronic administration of MEC (1, 2, and 4 mg/kg/day, intraperitoneally (i.p.)) in Wistar rats exposed to chronic restraint stress (CRS, 4 h × 6 W). MEC prevented CRS-induced depressive-like behavior via increasing sucrose preference, body weight, and forced swim test (FST) struggling and swimming while reducing immobility in FST and hypothalamic-pituitary-adrenal (HPA) axis hyperactivity (adrenal gland weight and serum corticosterone). At the same time, MEC amended CRS-induced anxiety as indicated by decreasing central zone duration in open field test and increasing active interaction duration. Additionally, MEC modulated the prefrontal cortex (PFC) level of brain-derived neurotrophic factor (BDNF), 5-hydroxy tryptamine (5-HT), and norepinephrine (NE). In conclusion, the present data suggest that MEC possesses antidepressant and anxiolytic-like activities in rats exposed to CRS. These behavioral effects may be in part mediated by reducing HPA axis hyperactivity and increasing PFC level of BDNF and monoamines. Accordingly, these findings further support the hypothesis that nAChRs blockade might afford a novel promising strategy for pharmacotherapy of depression.

Lipopolysaccharide repeated challenge followed by chronic mild stress protocol introduces a combined model of depression in rats: reversibility by imipramine and pentoxifylline

OBJECTIVES

The present study examined the effect of combined exposure to repeated challenge using low doses of lipopolysaccharide (LPS) and chronic mild stress (CMS) together. This combined exposure is thought to expose the animals to more realistic challenges, testable on different levels (behavioral, neurochemical, immunohistochemical and gene expression). The role of glial cells was examined, as well. Additionally, the effects of chronic administration of the tricyclic antidepressant imipramine and the anti-TNF-α pentoxyphylline were investigated.

METHODS

Wistar rats were exposed to either repeated LPS (50μg/kg i.p.) over 2weeks, CMS protocol for 4weeks or LPS over 2weeks then 4weeks of CMS. Two groups of rats were exposed to LPS/CMS protocol and treated with either imipramine or pentoxifylline. Rats were examined for behavioral, neurochemical and gene expression changes.

RESULTS

Animals exposed to LPS/CMS elaborated depressive-like symptoms with significant increase in both serum corticosterone and TNF-α levels compared to those in the saline, LPS or CMS groups. Hippocampal kynurenine/tryptophan ratio and TNF-α gene expression showed significant increase in the LPS/CMS model compared to those in saline, LPS or CMS groups. The immunohistochemical findings scrutinized the topography of the examined effects. Chronic treatment with imipramine or pentoxifylline significantly ameliorated the behavioral, neurochemical, immunohistochemical and TNF-α gene expression changes induced by the LPS/CMS protocol.

CONCLUSION

This study gave a clue to the neurobiological processes underlying, at least, the subtypes of depressive disorders. It highlighted the possible interactions between stress and immune-inflammatory pathways in the pathogenesis of depression and suggested a new animal model of depression that addresses these pathways.

Deuterium content of water increases depression susceptibility: the potential role of a serotonin-related mechanism

Environmental factors can significantly affect disease prevalence, including neuropsychiatric disorders such as depression. The ratio of deuterium to protium in water shows substantial geographical variation, which could affect disease susceptibility. Thus the link between deuterium content of water and depression was investigated, both epidemiologically, and in a mouse model of chronic mild stress. We performed a correlation analysis between deuterium content of tap water and rates of depression in regions of the USA. Next, we used a 10-day chronic stress paradigm to test whether 2-week deuterium-depleted water treatment (91 ppm) affects depressive-like behavior and hippocampal SERT. The effect of deuterium-depletion on sleep electrophysiology was also evaluated in naïve mice. There was a geographic correlation between a content of deuterium and the prevalence of depression across the USA. In the chronic stress model, depressive-like features were reduced in mice fed with deuterium-depleted water, and SERT expression was decreased in mice treated with deuterium-treated water compared with regular water. Five days of predator stress also suppressed proliferation in the dentate gyrus; this effect was attenuated in mice fed with deuterium-depleted water. Finally, in naïve mice, deuterium-depleted water treatment increased EEG indices of wakefulness, and decreased duration of REM sleep, phenomena that have been shown to result from the administration of selective serotonin reuptake inhibitors (SSRI). Our data suggest that the deuterium content of water may influence the incidence of affective disorder-related pathophysiology and major depression, which might be mediated by the serotoninergic mechanisms.

Alarin-induced antidepressant-like effects and their relationship with hypothalamus-pituitary-adrenal axis activity and brain derived neurotrophic factor levels in mice

Alarin is a newly identified member of the galanin family of peptides. Galanin has been shown to exert regulatory effects on depression. Similar to galanin in distribution, alarin is also expressed in the medial amygdala and hypothalamus, i.e., regions interrelated with depression. However, it remains a puzzle whether alarin is involved in depression. Accordingly, we established the depression-like mouse model using behavioral tests to ascertain the possible involvement of alarin, with fluoxetine as a positive control. With the positive antidepressant-like effects of alarin, we further examined its relationship to HPA axis activity and brain-derived neurotrophic factor (BDNF) levels in different brain areas in a chronic unpredictable mild stress (CUMS) paradigm. In the acute studies, alarin produced a dose-related reduction in the immobility duration in tail suspension test (TST) in mice. In the open-field test, intracerebroventricular (i.c.v.) injection of alarin (1.0 nmol) did not impair locomotion or motor coordination in the treated mice. In the CUMS paradigm, alarin administration (1.0 nmol, i.c.v.) significantly improved murine behaviors (FST and locomotor activity), which was associated with a decrease in corticotropin-releasing hormone (CRH) mRNA levels in the hypothalamus, as well as a decline in serum levels of CRH, adrenocorticotropic hormone (ACTH) and corticosterone (CORT), all of which are key hormones of the HPA axis. Furthermore, alarin upregulated BDNF mRNA levels in the prefrontal cortex and hippocampus. These findings suggest that alarin may potentiate the development of new antidepressants, which would be further secured with the identification of its receptor(s).

Behavioural, metabolic, and endothelial effects of the TNF-α suppressor thalidomide on rats subjected to chronic mild stress and fed an atherogenic diet

There is accumulating evidence suggesting that depression is a risk factor for cardiovascular diseases. This study aimed to examine the hypothesis that the proinflammatory cytokine TNF-α would partially explain the link between depression and atherosclerotic endothelial changes. Rats were distributed among 6 groups: (i) control group; (ii) group subjected to chronic mild stress (CMS); (iii) group fed a cholesterol–cholic acid–thiouracil (CCT diet); and (iv) CMS group fed the CCT diet and treated with the vehicle for 8 weeks. The last 2 groups were subjected to CMS–CCT and received thalidomide (THAL) or imipramine (IMIP). Rats were assessed behaviorally (sucrose preference, open field, and forced-swimming tests). TNF-α protein was assessed from the serum, aorta, and liver. Aortic TNF-α gene expression (assessed using RT–PCR), serum lipid profile, and insulin levels were measured. Endothelial function was assessed in isolated aortic rings. The THAL and IMIP groups showed ameliorated CMS–CCT-related behavioral changes. CMS–CCT-induced metabolic and endothelial dysfunctions were improved in the THAL group but were worsened in the IMIP group. RT–PCR showed a significant reduction of aortic TNF-α mRNA expression in the THAL and IMIP treatment groups. These data paralleled the findings for aortic immunohistochemistry. The THAL group, but not the IMIP group, showed improved CMS–CCT-induced changes in the vascular reactivity of the aortic rings. Thus, TNF-α provides a target link between depression, metabolic syndrome, and endothelial dysfunction. This could open a new therapeutic approach to address the comorbidities of depression.

Revealing the cerebral regions and networks mediating vulnerability to depression: oxidative metabolism mapping of rat brain

The large variety of available animal models has revealed much on the neurobiology of depression, but each model appears as specific to a significant extent, and distinction between stress response, pathogenesis of depression and underlying vulnerability is difficult to make. Evidence from epidemiological studies suggests that depression occurs in biologically predisposed subjects under impact of adverse life events. We applied the diathesis-stress concept to reveal brain regions and functional networks that mediate vulnerability to depression and response to chronic stress by collapsing data on cerebral long term neuronal activity as measured by cytochrome c oxidase histochemistry in distinct animal models. Rats were rendered vulnerable to depression either by partial serotonergic lesion or by maternal deprivation, or selected for a vulnerable phenotype (low positive affect, low novelty-related activity or high hedonic response). Environmental adversity was brought about by applying chronic variable stress or chronic social defeat. Several brain regions, most significantly median raphe, habenula, retrosplenial cortex and reticular thalamus, were universally implicated in long-term metabolic stress response, vulnerability to depression, or both. Vulnerability was associated with higher oxidative metabolism levels as compared to resilience to chronic stress. Chronic stress, in contrast, had three distinct patterns of effect on oxidative metabolism in vulnerable vs. resilient animals. In general, associations between regional activities in several brain circuits were strongest in vulnerable animals, and chronic stress disrupted this interrelatedness. These findings highlight networks that underlie resilience to stress, and the distinct response to stress that occurs in vulnerable subjects.

A new stress model, a scream sound, alters learning and monoamine levels in rat brain

Most existing animal models for stress involve the simultaneous application of physical and psychological stress factors. In the current study, we described and used a novel psychological stress model (scream sound stress). To study the validity of it, we carried out acute and chronic scream sound stress. First, adult Sprague-Dawley (SD) rats were randomly divided into white noise, stress and background groups. The white noise group and stress group were treated with white noise and scream sound for 4h in the morning respectively. Compared with white noise and background groups, exposure to acute scream sound increased corticosterone (CORT) level and decreased latency in Morris water maze (MWM) test. The levels of noradrenaline (NE), dopamine (DA), 5-hydroxytryptamine (5-HT), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were altered in the striatum, hypothalamus and hippocampus of stress rats. Second, adult SD rats were randomly divided into background and stress groups, which were treated with scream sound for three weeks. Exposure to chronic scream sound suppressed body weight gain, increased corticosterone (CORT) level, influenced the morphology of adrenal gland, improved spleen and thymus indices, and decreased latency in MWM test. NE, DA, DOPAC, HVA and 5-HIAA levels were also altered in the brain of stress rats. Our results suggested that scream sound, as a novel stressor, facilitated learning ability, as well as altered monoamine levels in the rat brain. Moreover, scream sound is easy to apply and can be applied in more animals at the same time.

Escitalopram alters gene expression and HPA axis reactivity in rats following chronic overexpression of corticotropin-releasing factor from the central amygdala

We have previously demonstrated that viral-mediated overexpression of corticotropin-releasing factor (CRF) within the central nucleus of the amygdala (CeA) reproduces many of the behavioral and endocrine consequences of chronic stress. The present experiment sought to determine whether administration of the selective serotonin reuptake inhibitor (SSRI) escitalopram reverses the adverse effects of CeA CRF overexpression. In a 2×2 design, adult male rats received bilateral infusions of a control lentivirus or a lentivirus in which a portion of the CRF promoter is used to drive increased expression of CRF peptide. Four weeks later, rats were then implanted with an Alzet minipump to deliver vehicle or 10mg/kg/day escitalopram for a 4-week period of time. The defensive withdrawal (DW) test of anxiety and the sucrose-preference test (SPT) of anhedonia were performed both before and after pump implantation. Additional post-implant behavioral tests included the elevated plus maze (EPM) and social interaction (SI) test. Following completion of behavioral testing, the dexamethasone/CRF test was performed to assess HPA axis reactivity. Brains were collected and expression of HPA axis-relevant transcripts were measured using in situ hybridization. Amygdalar CRF overexpression increased anxiety-like behavior in the DW test at week eight, which was only partially prevented by escitalopram. In both CRF-overexpressing and control groups, escitalopram decreased hippocampal CRF expression while increasing hypothalamic and hippocampal expression of the glucocorticoid receptor (GR). These gene expression changes were associated with a significant decrease in HPA axis reactivity in rats treated with escitalopram. Interestingly, escitalopram increased the rate of weight gain only in rats overexpressing CRF. Overall these data support our hypothesis that amygdalar CRF is critical in anxiety-like behavior; because the antidepressant was unable to reverse behavioral manifestations of CeA CRF-OE. This may be a potential animal model to study treatment-resistant psychopathologies.

Enhanced antidepressant-like effects of electroacupuncture combined with citalopram in a rat model of depression

Currently, antidepressants are the dominative treatment for depression, but they have limitations in efficacy and may even produce troublesome side effects. Electroacupuncture (EA) has been reported to have therapeutic benefits in the treatment of depressive disorders. The present study was conducted to determine whether EA could enhance the antidepressant efficacy of a low dose of citalopram (an SSRI antidepressant) in the chronic unpredictable stress-induced depression model rats. Here, we show that a combined treatment with 2 Hz EA and 5 mg/kg citalopram for three weeks induces a significant improvement in depressive-like symptoms as detected by sucrose preference test, open field test, and forced swimming test, whereas these effects were not observed with either of the treatments alone. Further investigations revealed that 2 Hz EA plus 5 mg/kg citalopram produced a remarkably increased expression of BDNF and its receptor TrkB in the hippocampus compared with those measured in the vehicle group. Our findings suggest that EA combined with a low dose of citalopram could produce greater therapeutic effects, thereby, predictive of a reduction in drug side effects.

Neonatal handling prevents anxiety-like symptoms in rats exposed to chronic mild stress: behavioral and oxidative parameters

This study investigated the influence of neonatal handling on behavioral and biochemical consequences of chronic mild stress (CMS) in adulthood. Male rat pups were submitted to daily tactile stimulation (TS) or maternal separation (MS), from postnatal day 1 (PND1) to postnatal day 21 (PND21), for 10 min/day. In adulthood, half the number of animals were exposed to CMS for 3 weeks and submitted to behavioral testing, including sucrose preference (SP), elevated plus maze (EPM), and defensive burying tasks (DBTs), followed by biochemical assessments. CMS reduced SP, increased anxiety in EPM and DBT, and increased adrenal weight. In addition, CMS decreased plasma vitamin C (VIT C) levels and increased protein carbonyl (PC) levels, catalase (CAT) activity in hippocampus and cortex, and superoxide dismutase (SOD) levels in cortex. In contrast, both forms of neonatal handling were able to prevent reduction in SP, anxiety behavior in DBT, and CMS-induced adrenal weight increase. Furthermore, they were also able to prevent plasma VIT C reduction, hippocampal PC levels increase, CAT activity increase in hippocampus and cortex, and SOD levels increase in cortex following CMS. Only TS was able to prevent CMS-induced anxiety symptoms in EPM and PC levels in cortex. Taken together, these findings show the protective role of neonatal handling, especially TS, which may enhance ability to cope with stressful situations in adulthood.

Antidepressant treatment outcome depends on the quality of the living environment: a pre-clinical investigation in mice

Antidepressants represent the standard treatment for major depression. However, their efficacy is variable and incomplete. A growing number of studies suggest that the environment plays a major role in determining the efficacy of these drugs, specifically of selective serotonin reuptake inhibitors (SSRI). A recent hypothesis posits that the increase in serotonin levels induced by SSRI may not affect mood per se, but enhances neural plasticity and, consequently, renders the individual more susceptible to the influence of the environment. Thus, SSRI administration in a favorable environment would lead to a reduction of symptoms, while in a stressful environment might lead to a worse prognosis. To test this hypothesis, we treated C57BL/6 adult male mice with chronic fluoxetine while exposing them to either (i) an enriched environment, after exposure to a chronic stress period aimed at inducing a depression-like phenotype, or (ii) a stressful environment. Anhedonia, brain BDNF and circulating corticosterone levels, considered endophenotypes of depression, were investigated. Mice treated with fluoxetine in an enriched condition improved their depression-like phenotype compared to controls, displaying higher saccharin preference, higher brain BDNF levels and reduced corticosterone levels. By contrast, when chronic fluoxetine administration occurred in a stressful condition, mice showed a more distinct worsening of the depression-like profile, displaying a faster decrease of saccharin preference, lower brain BDNF levels and increased corticosterone levels. Our findings suggest that the effect of SSRI on depression-like phenotypes in mice is not determined by the drug per se but is induced by the drug and driven by the environment. These findings may be helpful to explain variable effects of SSRI found in clinical practice and to device strategies aimed at enhancing their efficacy by means of controlling environmental conditions.

Coenzyme Q10 displays antidepressant-like activity with reduction of hippocampal oxidative/nitrosative DNA damage in chronically stressed rats

Multiple evidences suggest that depression is accompanied by an induction of oxidative/nitrosative stress (O&NS) pathways and by a reduced antioxidant status. Coenzyme Q10 (CoQ10) is an essential cofactor in the mitochondrial electron transport pathway and has a powerful antioxidant capacity.

METHODS

This study investigated the effect of chronic treatment with CoQ10 (25, 50, 100 and 150 mg/kg/day, i.p. for 3 weeks) on depressive-like behavior and hippocampal, O&NS, and DNA damage, induced by chronic restraint stress (CRS), an experimental model of depression, in rats.

RESULTS

CoQ10 showed a significant antidepressant effect, as evidenced by amelioration of CRS-induced behavioral aberrations in forced swimming and open field tests, elevated corticosterone level and body weight loss. Moreover, CoQ10 dose-dependently restored the hippocampal catalase, glutathione peroxidase and reduced glutathione and decreased the hippocampal malondialdehyde, nitric oxide and 8-hydroxy-2'-deoxyguanosine levels, which indicated a potential protective effect of CoQ10 against hippocampal O&NS lipid peroxidation and DNA damage.

CONCLUSION

CoQ10 possesses antidepressant activity and can protect against CRS-induced hippocampal DNA damage which could be mediated in part by maintaining mitochondrial function and its well documented antioxidant properties. Therefore, CoQ10 may have a potential therapeutic value for the management of depressive disorders. However, further research, is still required to characterize the mechanism of the antidepressant effect of CoQ10 and extend these results before the safe application in humans.

Long-lasting effects of chronic rTMS to treat chronic rodent model of depression

Repetitive transcranial magnetic stimulation (rTMS) has been demonstrated in the pre-clinical and clinical settings to have an antidepressant effect. However, studies on the long-lasting effect of rTMS, especially when the effect is measured after treatment has ceased for a few weeks is lacking. We examined this question in a chronic unpredicted mild stress (CUMS) rat model of depression. We gave 3 weeks of high frequency (15 Hz) rTMS, venlafaxine, or these two treatments combined to a modified CUMS paradigm, and then investigated the prolonged effect of treatments. Behavioral testing (sucrose preference test, open field test, forced swimming test, novelty suppressed feeding test), plasma hormone level, hippocampal BrdU labeling, and amount of related neurotropic factors were used to assess the effects of stress and treatments. Long-term chronic rTMS significantly reversed andehonic-like behavior, increased hippocampus cell proliferation, BDNF protein level, phosphorylation of ERK1/2 compared with CUMS rats two weeks after the cessation of rTMS treatment. However, the changes in plasma hormone level were not sustained for that amount of time. Venlafaxine had no interaction with the physical stimulation. Our results suggest that high frequency rTMS has long-lasting effects, which may have some relationship with neuroplasticity.

Effect of Mimosa pudica (Linn.) extract on anxiety behaviour and GABAergic regulation of 5-HT neuronal activity in the mouse

Mimosa pudica (Linn.) (M. pudica L.) is a plant used in some countries to treat anxiety and depression. In the present study we investigated the effects of an aqueous extract of M. pudica L. on mouse anxiety-like behaviour using the elevated T maze, and on regulation of dorsal raphe nucleus (DRN) 5-hydroxytryptamine (5-HT) neuronal activity using an in-vitro mouse brain slice preparation. Acute treatment with M. pudica L. extract had an anxiolytic effect on behaviour in the elevated T maze, specifically on inhibitory avoidance behaviour. Acute application of the extract alone had no effect on the activity of DRN 5-HT neurones. However, when co-applied with the GABA(A) receptor agonist THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol), the extract enhanced the inhibitory effect of the THIP on DRN 5-HT neurones. These observed effects of M. pudica L. on both behaviour and GABA modulation of 5-HT neuronal activity are similar to the effects of diazepam, the established anxiolytic and positive modulator of the GABA(A) receptor. This study suggests that the aqueous extract of M. pudica L. contains a positive modulator of GABA(A) receptor function and provides impetus for further investigation of the neuropharmacologically active constituents of the extract.

Animal models of depression vulnerability

The rapid increase in the number of proposed animal models of depression reflects the dissatisfaction with our current state of knowledge on neurobiology of depression and unsuccessful drug development. Results obtained with even the best validated models can be difficult to compare. Because evidence from epidemiological studies suggests that depression occurs in biologically predisposed subjects under the impact of adverse life events, increasing attempts have been made to use the diathesis-stress concept in animal models. In this way, factors underpinning vulnerability to depression have been identified by measuring behavioural traits analogous to facets of human personality, or created by inducing neurochemical lesions. Stressful interventions administered prenatally, in early life or in adulthood have been combined with other vulnerability factors including genetic changes. As a result, several putative animal models of endophenotypes of depression or depression vulnerability have been proposed. Diathesis-stress models may aid in separating adaptive and maladaptive strategies in coping with stress, and understanding the relevant neurobiology. Studies comparing effects of stress on males and females should reveal to which extent the pathogenetic processes leading to depression can be specific to sex/gender.

Exposure to repeated maternal aggression induces depressive-like behavior and increases startle in adult female rats

The stress response is a multifaceted physiological reaction that engages a wide range of systems. Animal studies examining stress and the stress response employ diverse methods as stressors. While many of these stressors are capable of inducing a stress response in animals, a need exists for an ethologically relevant stressor for female rats. The purpose of the current study was to use an ethologically relevant social stressor to induce behavioral alterations in adult female rats. Adult (postnatal day 90) female Wistar rats were repeatedly exposed to lactating Long Evans female rats to simulate chronic stress. After six days of sessions, intruder females exposed to defeat were tested in the sucrose consumption test, the forced swim test, acoustic startle test, elevated plus maze, and open field test. At the conclusion of behavioral testing, animals were restrained for 30 min and trunk blood was collected for assessment of serum hormones. Female rats exposed to maternal aggression exhibited decreased sucrose consumption, and impaired coping behavior in the forced swim test. Additionally, female rats exposed to repeated maternal aggression exhibited an increased acoustic startle response. No changes were observed in female rats in the elevated plus maze or open field test. Serum hormones were unaltered due to repeated exposure to maternal aggression. These data indicate the importance of the social experience in the development of stress-related behaviors: an acerbic social experience in female rats precipitates the manifestation of depressive-like behaviors and an enhanced startle response.

Activating effects of chronic variable stress in rats with different exploratory activity: association with dopamine d(1) receptor function in nucleus accumbens

BACKGROUND/AIMS

Rats display persistent behavioural phenotypes of low (LE) versus high (HE) exploratory activity in the exploration box paradigm. LE rats that prefer passive coping strategies show differential dopaminergic activity in the striatum. The main hypothesis of this study was that chronic variable stress (CVS) would have a higher impact on LE rats.

METHODS

Animals were submitted to a CVS regimen lasting 32 days that was followed by a behavioural test battery. The functional states of their dopamine D(1) and D(2) receptors were measured in the striatum and nucleus accumbens (NAcc). Cerebral oxidative metabolism was assessed via cytochrome c oxidase histochemistry in 65 brain regions.

RESULTS

CVS decreased weight gain, to a higher extent in LE rats, and lowered the sucrose preference after the first week, but habituation to the anhedonic effect had developed by the end of the experiment. CVS did not change the behavioural phenotypes initially assigned. No effect of stress on D(2) receptor function was found. Chronically stressed animals exhibited higher levels of social interaction and D(1) receptor-mediated cAMP accumulation in the NAcc, but not in the striatum. CVS was associated with higher oxidative metabolism levels in the anteroventral thalamus, median raphe nuclei and central periaqueductal grey matter. These changes after stress did not depend upon the exploratory phenotype.

CONCLUSION

This study revealed changes in brain biochemistry after habituation to CVS that might be implicated in successful adaptation to chronic stress.

Behavioral effects of chronic adolescent stress are sustained and sexually dimorphic

Evidence suggests that women are more susceptible to stress-related disorders than men. Animal studies demonstrate a similar female sensitivity to stress and have been used to examine the underlying neurobiology of sex-specific effects of stress. Although our understanding of the sex-specific effects of chronic adolescent stress has grown in recent years, few studies have reported the effects of adolescent stress on depressive-like behavior. The purpose of this study was to determine if a chronic mixed modality stressor (consisting of isolation, restraint, and social defeat) during adolescence (PND 37-49) resulted in differential and sustained changes in depressive-like behavior in male and female Wistar rats. Female rats exposed to chronic adolescent stress displayed decreased sucrose consumption, hyperactivity in the elevated plus maze, decreased activity in the forced swim test, and a blunted corticosterone response to an acute forced swim stress compared to controls during both adolescence (PND 48-57) and adulthood (PND 96-104). Male rats exposed to chronic adolescent stress did not manifest significant behavioral changes at either the end of adolescence or in adulthood. These data support the proposition that adolescence may be a stress sensitive period for females and exposure to stress during adolescence results in behavioral effects that persist in females. Studies investigating the sex-specific effects of chronic adolescent stress may lead to a better understanding of the sexually dimorphic incidence of depressive and anxiety disorders in humans and ultimately improve prevention and treatment strategies.

Brain responses to chronic social defeat stress: effects on regional oxidative metabolism as a function of a hedonic trait, and gene expression in susceptible and resilient rats

Chronic social defeat stress, a depression model in rats, reduced struggling in the forced swimming test dependent on a hedonic trait-stressed rats with high sucrose intake struggled less. Social defeat reduced brain regional energy metabolism, and this effect was also more pronounced in rats with high sucrose intake. A number of changes in gene expression were identified after social defeat stress, most notably the down-regulation of Gsk3b and Map1b. The majority of differences were between stress-susceptible and resilient rats. Conclusively, correlates of inter-individual differences in stress resilience can be identified both at gene expression and oxidative metabolism levels.