Chronic Restraint Stress Inhibits the Response to a Second Hit in Adult Male Rats : A Role for BDNF Signaling

Depression is a recurrent disorder, with about 50% of patients experiencing relapse. Exposure to stressful events may have an adverse impact on the long-term course of the disorder and may alter the response to a subsequent stressor. Indeed, not all the systems impaired by stress may normalize during symptoms remission, facilitating the relapse to the pathology. Hence, we investigated the long-lasting effects of chronic restraint stress (CRS) and its influence on the modifications induced by the exposure to a second hit on brain-derived neurotrophic factor (BDNF) signaling in the prefrontal cortex (PFC). We exposed adult male Sprague Dawley rats to 4 weeks of CRS, we left them undisturbed for the subsequent 3 weeks, and then we exposed animals to one hour of acute restraint stress (ARS). We found that CRS influenced the release of corticosterone induced by ARS and inhibited the ability of ARS to activate mature BDNF, its receptor Tropomyosin receptor kinase B (TRKB), and their associated intracellular cascades: the TRKB-PI3K-AKT), the MEK-MAPK/ERK, and the Phospholipase C \u3b3 (PLC\u3b3) pathways, positively modulated by ARS in non-stressed animals. These results suggest that CRS induces protracted and detrimental consequences that interfere with the ability of PFC to cope with a challenging situation

Modulatory activity of chronic treatment with the antidepressant agomelatine on LPS-induced inflammatory response in the rat ventral hippocampus: a genome wide analysis

Given the large body of clinical and preclinical evidence suggesting that the activation of the inflammatory/immune system may contribute to depression pathogenesis, several studies reported that antidepressant drugs have immunoregulatory effects. Accordingly, the aim of the present work was to assess the anti-inflammatory properties of chronic agomelatine treatment with an unbiased genome-wide approach by using the well-established microarray technique. Adult male Sprague-Dawley rats received agomelatine or vehicle for 21 days before being challenged with an acute injection of LPS or saline 16h after the last drug administration. Animals were sacrificed 2h after the immune challenge and the ventral hippocampus was dissected and processed for microarray analysis. The administration of LPS induced the transcription of genes mainly associated with the inflammatory response. Conversely, chronic treatment with agomelatine modulated 105 transcripts belonging to different signaling pathways such as the one of the phospholipase C and the pathway of the chemokine receptor CXCR4, which may contribute to potential neuroprotective effects of the antidepressant. From the transcripts found significantly modulated in the animals treated with agomelatine and challenged with LPS, the antidepressant was able to prevent the LPS-induced modulation of 91 genes with respect to the control group and of 52 genes with respect to animals treated only with LPS. An intersection analysis showed that some transcripts induced by LPS on which the pre-treatment with agomelatine has a large effect of normalization. In summary, we have highlighted the transcriptional profile of a chronic treatment with agomelatine in the rat ventral hippocampus both in basal condition and in condition of acute inflammation, identifying genes and pathways associated to its anti-inflammatory properties that might represent potential new targets for pharmacological intervention of depression associated to inflammation

Genome-wide analysis of LPS-induced inflammatory response in the rat ventral hippocampus: modulatory activity of chronic treatment with the antidepressant agomelatine

Growing evidence suggests that the activation of the immune/inflammatory system may be associated with depression pathogenesis and, in line with this observation, several studies mainly focused on pro-inflammatory cytokines reported that antidepressant drugs have immunoregulatory effects. However, given the complexity of the inflammatory response, which implies the integration of different mechanisms triggered by various systems, the aim of the present work was to assess the anti-inflammatory properties of the antidepressant agomelatine with an unbiased genome-wide approach by using the microarray technique. Specifically, we analyzed the gene expression profile of the ventral hippocampus, a cerebral area relevant for depression, of adult rats chronically treated with the antidepressant before to receive a systemic injection of lipopolysaccharide (LPS) in comparison with animals treated with saline. To this aim, adult male Sprague-Dawley rats received agomelatine or vehicle for 21 days before being challenged with an acute injection of LPS or saline 16 h after the last drug administration. Animals were sacrificed 2 h after the immune challenge and the ventral hippocampus was dissected and processed for RNA extraction. Transcriptomic analysis was performed using Affymetrix\uae Array and the results were analyzed with Partek Genomics Suite and with Ingenuity Pathway Analyses software. We found that LPS administration induced the transcription of 284 genes mainly associated with pathways related to inflammation. Conversely, chronic treatment with agomelatine alone modulated 105 transcripts belonging to different pathways in saline-treated rats, like the phospolipase C and the CXCR4 pathways. Moreover, the drug was able to prevent the LPS-induced modulation of 91 genes with respect to the control group and of 52 genes with respect to animals treated only with LPS. An intersection analysis between these two lists of genes led to the identification of some transcripts induced by LPS on which agomelatine has the larger effect of normalization. In summary, by using a genome-wide approach, we have highlighted the transcriptional profile of a chronic treatment with agomelatine both at basal state -identifying genes and pathways related to the basal effects of the antidepressant- and in condition of acute inflammation - identifying genes and pathways associated to its anti-inflammatory properties. These genes/pathways might represent potential new targets for pharmacological intervention of depression associated to inflammation

Genome-wide analysis of LPS-induced inflammatory response in the rat ventral hippocampus: Modulatory activity of the antidepressant agomelatine

Objectives: Several studies reported that antidepressant drugs have immune-regulatory effects by acting on specific inflammatory mediators. However, considering the highly complex nature of the inflammatory response, we have adopted an unbiased genome-wide strategy to investigate the immune-regulatory activity of the antidepressant agomelatine in modulating the response to an acute inflammatory challenge. Methods: Microarray analysis was used to identify genes modulated in the ventral hippocampus of adult rats chronically treated with agomelatine (40\u2009mg/kg, os) before being challenged with a single injection of lipopolysaccharide (LPS; 250\u2009\u3bcg/kg, i.p.). Results: The administration of LPS induced the transcription of 284 genes mainly associated with pathways related to the immune/inflammatory system. Agomelatine modulated pathways not only connected to its antidepressant activity, but was also able to prevent the activation of genes induced by LPS. Further comparisons between gene lists of the diverse experimental groups led to the identification of a few transcripts modulated by LPS on which agomelatine has the larger effect of normalisation. Among them, we found the pro-inflammatory cytokine Il-1\u3b2 and, interestingly, the metabotropic glutamatergic transporter Grm2. Conclusions: These results are useful to better characterise the association between depression and inflammation, revealing new potential targets for pharmacological intervention for depression associated to inflammation

Lipopolysaccharide does not affect sucrose intake in stress-resilient rats: potential contribution of microglia

Stressful events during life may expose a subject to the development or the exacerbation of major depression, however even if this disease occurs in a significant percentage of stress-exposed subjects, most of them are able to successfully cope with the adverse situation and avoid such psychopathology. In addition, stress exposure strongly influences inflammatory events in the periphery and in the central nervous system (CNS), with an impact on behavioral alterations. In the CNS, microglia -brain tissue-resident macrophages- display stress-responsive properties; in particular, the detrimental effects caused by chronic stress may be driven by a dysregulation of this cellular population through the production of pro-inflammatory mediators. On these bases, the purpose of our study was to deepen our knowledge on the molecular mechanisms underpinning stress resilience. We exposed adult male rats to two weeks of chronic mild stress, before being challenged with Lipopolysaccharide (LPS, i.p. 250microg/kg) and sacrificed 24h or 6 days after the immune challenge. Behavioural alterations were monitored through the sucrose consumption test to evaluate the insurgence of anhedonic-like phenotype and to identify stress resilient rats. We measured the expression of pro-inflammatory cytokines (IL1beta, IL6, TNF-alpha), toll-like receptor 4 and markers of microglia activation (CD11b, Iba1, CX3CR1 and its ligand CX3CL1) in the rat prefrontal cortex, dorsal and ventral hippocampus (brain area involved in stress response and in the aetiology of depression). Interestingly, LPS worsened the sucrose intake in sham animals, but not in non-anhedonic rats; moreover, these behavioural effects seemed to be related to alterations in the expression of inflammatory mediators and markers of microglia activation, thus suggesting a potential role of these cells in the mechanisms of stress resilience

Colony-stimulating factor 1 receptor blockade prevents fractionated whole-brain irradiation-induced memory deficits

Background: Primary central nervous system (CNS) neoplasms and brain metastases are routinely treated with whole-brain radiation. Long-term survival occurs in many patients, but their quality of life is severely affected by the development of cognitive deficits, and there is no treatment to prevent these adverse effects. Neuroinflammation, associated with activation of brain-resident microglia and infiltrating monocytes, plays a pivotal role in loss of neurological function and has been shown to be associated with acute and long-term effects of brain irradiation. Colony-stimulating factor 1 receptor (CSF-1R) signaling is essential for the survival and differentiation of microglia and monocytes. Here, we tested the effects of CSF-1R blockade by PLX5622 on cognitive function in mice treated with three fractions of 3.3 Gy whole-brain irradiation. Methods: Young adult C57BL/6J mice were given three fractions of 3.3 Gy whole-brain irradiation while they were on diet supplemented with PLX5622, and the effects on periphery monocyte accumulation, microglia numbers, and neuronal functions were assessed. Results: The mice developed hippocampal-dependent cognitive deficits at 1 and 3 months after they received fractionated whole-brain irradiation. The impaired cognitive function correlated with increased number of periphery monocyte accumulation in the CNS and decreased dendritic spine density in hippocampal granule neurons. PLX5622 treatment caused temporary reduction of microglia numbers, inhibited monocyte accumulation in the brain, and prevented radiation-induced cognitive deficits. Conclusions: Blockade of CSF-1R by PLX5622 prevents fractionated whole-brain irradiation-induced memory deficits. Therapeutic targeting of CSF-1R may provide a new avenue for protection from radiation-induced memory deficits

Differential Neuroinflammatory Response in Male and Female Mice: A Role for BDNF

A growing body of evidence supports the close relationship between major depressive disorder (MDD), a severe psychiatric disease more common among women than men, and alterations of the immune/inflammatory system. However, despite the large number of studies aimed at understanding the molecular bases of this association, a lack of information exists on the potential cross-talk between systems known to be involved in depression and components of the inflammatory response, especially with respect to sex differences. Brain-derived neurotrophic factor (BDNF) is a neurotrophin with a well-established role in MDD etiopathology: it is altered in depressed patients as well as in animal models of the disease and its changes are restored by antidepressant drugs. Interestingly, this neurotrophin is also involved in the inflammatory response. Indeed, it can be secreted by microglia, the primary innate immune cells in the central nervous system whose functions may be in turn regulated by BDNF. With these premises, in this study, we investigated the reciprocal impact of BDNF and the immune system by evaluating the neuroinflammatory response in male and female BDNF-heterozygous mutant mice acutely treated with the cytokine-inducer lipopolysaccharide (LPS). Specifically, we assessed the potential onset of an LPS-induced sickness behavior as well as changes of inflammatory mediators in the mouse hippocampus and frontal cortex, with respect to both genotype and sex. We found that the increased inflammatory response induced by LPS in the brain of male mice was independent of the genotype, whereas in the female, it was restricted to the heterozygous mice with no changes in the wild-type group, suggestive of a role for BDNF in the sex-dependent effect of the inflammatory challenge. Considering the involvement of both BDNF and neuroinflammation in several psychiatric diseases and the diverse incidence of such pathologies in males and females, a deeper investigation of the mechanisms underlying their interaction may have a critical translational relevance

Effect of the antidepressant agomelatine on the IL-6 pathway in rats exposed to chronic mild stress: role of suppressor of cytokine signaling 3 SOCS3

Major depression (MD) is a debilitating disorder whose treatment is being challenged by the high rate of failure and relapse of the pathology. Among the molecular systems thought to be involved in the MD etiology and in the mechanism of action of antidepressant drugs, inflammation has emerged as an important actor. In particular, increased levels of pro-inflammatory cytokines have been observed in the plasma and cerebrospinal fluid of depressed patients and, among these inflammatory mediators, interleukin (IL-) 6 has been recently proposed to play a crucial role (Fonseka et al., 2015). IL-6 triggers a peculiar pathway comprising the JAK/STAT signaling proteins and characterized by a specific negative feedback loop exerted by the cytoplasmic protein SOCS3 (Suppressor Of Cytokine Signalling-3). We have recently demonstrated that a seven weeks lasting chronic mild stress (CMS) paradigm, able to induce a depressive-like phenotype, up-regulates the expression of different pro-inflammatory cytokines in the rat brain. In this scenario, the pharmacological treatment with the antidepressant agomelatine during the last 5 weeks of stress (daily i.p., 40mg/kg) was able to normalize not only the pathologic phenotype but also the inflammatory state (Rossetti et al 2015). With these premises, the aim of the present work was to further investigate the mechanisms underpinning the anti-inflammatory activity of agomelatine by evaluating the impact of the drug on IL-6 pathway in the prefrontal cortex of rats exposed to CMS. As expected, stress was able to activate the IL-6 cascade, including SOCS3 gene and protein expression and JAK1/STAT3 phosphorylation, without any suppressive effect of SOCS3 on the feedback-loop inhibition. On the contrary, chronic treatment with agomelatine was able not only to normalize the stress-induced activation of IL-6 signaling, but also to induce SOCS3 transcription and translation under basal conditions. To better understand how agomelatine modulates IL-6 pathway, we deepened our analyses measuring the nuclear phosphorylation of STAT3 at Ser727, the activation of MAP-kinases, and STAT3-mediated gene expression of molecules involved in the control of apoptosis (i.e. Bcl-XL, Casp1, Casp3). The results show that in both non-stressed and stressed animals agomelatine is inducing SOCS3 expression by different mechanisms, but with a common potential neuroprotective effect. Furthermore, given the potentiality of IL-6 signaling as target of antidepressant treatment and the key protective activity of agomelatine on this system, probably through SOCS3, this data suggest that SOCS3 modulation might be a valuable target for new drug development

The activation of the immune/inflammatory system is associated with the stress-induced anhedonia in rats: effect of pharmacological intervention

Major depression (MD) is a common psychiatric disorder that represents a leading cause of disability in the world. It is known that this complex disease originates from the interaction between many factors of different nature -a genetic background of susceptibility, biological, social and environmental stimuli- that act in concert leading to the development of the illness. Despite the increased knowledge of MD neurobiology, an effective improvement in the overall impact of pharmacotherapy is still lacking, possibly because a number of systems that are affected in mood disorders may not be adequately modulated by pharmacological treatments. Currently there is strong evidence that depression involves alterations of the immune/inflammatory system. In particular MD shows an elevated comorbidity with cancer, rheumatoid arthritis, cardiovascular and neurodegenerative diseases, all characterized by inflammatory alterations. Moreover, the treatment of Hepatitis C virus with IFN\uf061 predisposes to the development of clinically significant depression. On these bases, the purpose of our study was to analyze the cerebral expression of several mediators of the immune/inflammatory system in an animal model of depression based on the environmental component of the disease -the rat exposed to chronic mild stress (CMS)-, to elucidate the role of inflammation on the generation of the anhedonic phenotype and to evaluate the ability of pharmacological intervention in modulating the behavioral-associated inflammatory alterations. To this aim, rats exposed to CMS for two weeks were tested with the sucrose consumption test to assess the insurgence of an anhedonic phenotype, then molecular analyses were carried out on dorsal, ventral hippocampus and on prefrontal cortex, three brain regions mainly involved in the etiology of depression. Afterward a group of anhedonic animals underwent to five further weeks of CMS with a parallel treatment with the tricyclic antidepressant imipramine and the atipical antipsychotic lurasidone. At the end of the treatment, molecular analyses on inflammatory mediators were conducted. Our findings indicate that the stress-induced anhedonic phenotype is associated to an altered expression of specific mediators of immune/inflammatory system and that pharmacological treatment is not only able to normalize the anhedonic phenotype, but also inflammatory changes. These data suggest that the immune/inflammatory alterations are not a merely consequence of stress exposure, but they may contribute to the subject\u2019s vulnerability to depression and support the idea that this system may serve as a viable therapeutic target for more effective antidepressant drugs