p38 MAPK Activation Elevates Serotonin Transport Activity via a Trafficking-independent, Protein Phosphatase 2A-dependent Process

Immune System Activation and Depression: Roles of Serotonin in the Central Nervous System and Periphery

Serotonin (5-hydroxytryptamine, 5-HT) has long been recognized as a key contributor to the regulation of mood and anxiety and is strongly associated with the etiology of major depressive disorder (MDD). Although more known for its roles within the central nervous system (CNS), 5-HT is recognized to modulate several key aspects of immune system function that may contribute to the development of MDD. Copious amounts of research have outlined a connection between alterations in immune system function, inflammation status, and MDD. Supporting this connection, peripheral immune activation results in changes in the function and/or expression of many components of 5-HT signaling that are associated with depressive-like phenotypes. How 5-HT is utilized by the immune system to effect CNS function and ultimately behaviors related to depression is still not well understood. This Review summarizes the evidence that immune system alterations related to depression affect CNS 5-HT signaling that can alter MDD-relevant behaviors and that 5-HT regulates immune system signaling within the CNS and periphery. We suggest that targeting the interrelationships between immune and 5-HT signaling may provide more effective treatments for subsets of those suffering from inflammation-associated MDD.

Role of Inflammation in Suicide: From Mechanisms to Treatment

Suicidal behavior is complex and manifests because of a confluence of diverse factors. One such factor involves dysregulation of the immune system, which has been linked to the pathophysiology of suicidal behavior. This review will provide a brief description of suicidality and discuss the contribution of upstream and downstream factors in the etiology of suicidal behavior, within the contextual framework of inflammation. The contribution of inflammatory conditions such as traumatic brain injury, autoimmune disorders, and infections to neuropsychiatric symptoms and suicidality is only beginning to be explored. We will summarize studies of inflammation in the etiology of suicide, and provide a neurobiological basis for different mechanisms by which inflammation might contribute to the pathophysiology. Finally, we will review treatments that affect upstream and downstream pathways related to inflammation in suicidality.

Inflammation Effects on Motivation and Motor Activity: Role of Dopamine

Motivational and motor deficits are common in patients with depression and other psychiatric disorders, and are related to symptoms of anhedonia and motor retardation. These deficits in motivation and motor function are associated with alterations in corticostriatal neurocircuitry, which may reflect abnormalities in mesolimbic and mesostriatal dopamine (DA). One pathophysiologic pathway that may drive changes in DAergic corticostriatal circuitry is inflammation. Biomarkers of inflammation such as inflammatory cytokines and acute-phase proteins are reliably elevated in a significant proportion of psychiatric patients. A variety of inflammatory stimuli have been found to preferentially target basal ganglia function to lead to impaired motivation and motor activity. Findings have included inflammation-associated reductions in ventral striatal neural responses to reward anticipation, decreased DA and DA metabolites in cerebrospinal fluid, and decreased availability, and release of striatal DA, all of which correlated with symptoms of reduced motivation and/or motor retardation. Importantly, inflammation-associated symptoms are often difficult to treat, and evidence suggests that inflammation may decrease DA synthesis and availability, thus circumventing the efficacy of standard pharmacotherapies. This review will highlight the impact of administration of inflammatory stimuli on the brain in relation to motivation and motor function. Recent data demonstrating similar relationships between increased inflammation and altered DAergic corticostriatal circuitry and behavior in patients with major depressive disorder will also be presented. Finally, we will discuss the mechanisms by which inflammation affects DA neurotransmission and relevance to novel therapeutic strategies to treat reduced motivation and motor symptoms in patients with high inflammation.

Therapeutic Implications of Brain-Immune Interactions: Treatment in Translation

A wealth of data has been amassed that details a complex, yet accessible, series of pathways by which the immune system, notably inflammation, can influence the brain and behavior. These data have opened the window to a diverse array of novel targets whose potential efficacy is tied to specific neurotransmitters and neurocircuits as well as specific behaviors. What is clear is that the impact of inflammation on the brain cuts across psychiatric disorders and engages dopaminergic and glutamatergic pathways that regulate motivation and motor activity as well as the sensitivity to threat. Given the ability to identify patient populations with increased inflammation, the precision of interventions can be further tuned, in conjunction with the ability to establish target engagement in the brain through the use of multiple neuroimaging strategies. After a brief overview of the mechanisms by which inflammation affects the brain and behavior, this review examines the extant literature on the efficacy of anti-inflammatory treatments, while forging guidelines for future intelligent clinical trial design. An examination of the most promising therapeutic strategies is also provided, along with some of the most exciting clinical trials that are currently being planned or underway.

The Development of Screening Methods to Identify Drugs to Limit ER Stress Using Wild-type and Mutant Serotonin Transporter

The function of the serotonin transporter (SERT) is regulated by its membrane trafficking. Previously, we showed that the C-terminus-deleted mutant of SERT (SERTΔCT) exhibited an aberrant membrane trafficking and subsequent retention at the endoplasmic reticulum (ER). In addition, we found that proteasome inhibitor-induced ER stress resulted in the impairment of SERT membrane trafficking and retention of SERT at the ER, an impairment very similar to that of SERTΔCT. Based on the result that the chemical chaperone 4-phnylbutulic acid (4-PBA), which relieves ER stress, accelerated the membrane trafficking and upregulated SERT activity, we hypothesized that drugs that facilitate the membrane trafficking of SERT would have potential therapeutic effects on an ER stress-related disease. In this study, we aimed to develop simple screening methods for such drugs using SERT. We first validated the serotonin uptake assay using fluorescent substrates. This simple and reliable assay method was useful for screening for drugs that affected the wild-type SERT but not SERTΔCT. In addition, we verified an assay focusing on the formation of SERTΔCT aggregates. The drugs 4-PBA and SKF-10047 facilitated the trafficking of SERT to the membrane and reduced SERTΔCT aggregates, indicating that the drugs with such characters could be potential candidates for ER stress relief. For both assays, we clarified the usefulness of a high-content screening microscope. These results could pave the way for high-throughput screening for such drugs.

Biochemical and physiological effects from exhaust emissions. A review of the relevant literature

Exhaust emissions are to date ranked among the most frequent causes of premature deaths worldwide. The combustion of fuels such as diesel, gasoline, and bio-blends provokes a series of pathophysiological responses in exposed subjects, which are associated with biochemical and immunological triggering. It is critical to understand these mechanisms, which are directly related to the levels of aerosol, liquid and gaseous components in fuel exhaust (e.g. nanoparticles, particulate matter, volatile compounds), so to cast attention on their toxicity and gradually minimize their use. This review reports findings in the recent literature concerning the biochemical and cellular pathways triggered during intoxication by exhaust emissions, and links these findings to pathophysiological responses such as inflammation and vasoconstriction. This study provides critical in vitro and in vivo data for the reduction of emissions in urban centers, with an emphasis on the prevention of exposure of groups such as children, the elderly, and other affected groups, and shows how the exposure to exhaust emissions induces mechanisms of pathogenesis related to cardiopulmonary pathologies and long-term diseases such as asthma, allergies, and cancer. This review summarizes the cellular and physiological responses of humans to exhaust emissions in a comprehensive fashion, and is important for legislative developments in fuel politics.

Kinase-dependent Regulation of Monoamine Neurotransmitter Transporters

Modulation of neurotransmission by the monoamines dopamine (DA), norepinephrine (NE), and serotonin (5-HT) is critical for normal nervous system function. Precise temporal and spatial control of this signaling in mediated in large part by the actions of monoamine transporters (DAT, NET, and SERT, respectively). These transporters act to recapture their respective neurotransmitters after release, and disruption of clearance and reuptake has significant effects on physiology and behavior and has been linked to a number of neuropsychiatric disorders. To ensure adequate and dynamic control of these transporters, multiple modes of control have evolved to regulate their activity and trafficking. Central to many of these modes of control are the actions of protein kinases, whose actions can be direct or indirectly mediated by kinase-modulated protein interactions. Here, we summarize the current state of our understanding of how protein kinases regulate monoamine transporters through changes in activity, trafficking, phosphorylation state, and interacting partners. We highlight genetic, biochemical, and pharmacological evidence for kinase-linked control of DAT, NET, and SERT and, where applicable, provide evidence for endogenous activators of these pathways. We hope our discussion can lead to a more nuanced and integrated understanding of how neurotransmitter transporters are controlled and may contribute to disorders that feature perturbed monoamine signaling, with an ultimate goal of developing better therapeutic strategies.

The Immune System and the Role of Inflammation in Perinatal Depression

Major depression during pregnancy is a common psychiatric disorder that arises from a complex and multifactorial etiology. Psychosocial stress, sex, hormones, and genetic vulnerability increase the risk for triggering mood disorders. Microglia and toll-like receptor 4 play a crucial role in triggering wide and varied stress-induced responses mediated through activation of the inflammasome; this leads to the secretion of inflammatory cytokines, increased serotonin metabolism, and reduction of neurotransmitter availability along with hypothalamic-pituitary-adrenal axis hyperactivity. Dysregulation of this intricate neuroimmune communication network during pregnancy modifies the maternal milieu, enhancing the emergence of depressive symptoms and negative obstetric and neuropsychiatric outcomes. Although several studies have clearly demonstrated the role of the innate immune system in major depression, it is still unclear how the placenta, the brain, and the monoaminergic and neuroendocrine systems interact during perinatal depression. Thus, in the present review we describe the cellular and molecular interactions between these systems in major depression during pregnancy, proposing that the same stress-related mechanisms involved in the activation of the NLRP3 inflammasome in microglia and peripheral myeloid cells in depressed patients operate in a similar fashion in the neuroimmune placenta during perinatal depression. Thus, activation of Toll-like receptor 2 and 4 signaling and the NLRP3 inflammasome in placental immune cells may promote a shift of the Th1/Th2 bias towards a predominant Th1/Th17 inflammatory response, associated with increased secretion of pro-inflammatory cytokines, among other secreted autocrine and paracrine mediators, which play a crucial role in triggering and/or exacerbating depressive symptoms during pregnancy.

Pathogenetic and Therapeutic Applications of Tumor Necrosis Factor-α (TNF-α) in Major Depressive Disorder: A Systematic Review

Major depressive disorder (MDD) is characterized by mood, vegetative, cognitive, and even psychotic symptoms and signs that can cause substantial impairments in quality of life and functioning. Up to now, the exact pathogenesis of MDD remains poorly understood. Recent research has begun to reveal that the pro-inflammatory cytokines, particularly, tumor necrosis factor-α (TNF-α), play an integral role in the pathophysiology of depressive disorders and the mechanism of antidepressant treatment. On the base of several observations: it is found that subsets of MDD patients have enhanced plasma levels TNF-α; antidepressant treatments had linked with the decline of TNF-α; central administration of TNF-α gives rise to sickness behavior which shares features with depression; and a blockade of it can ameliorate depressive symptomatology in animal models and clinical trials. In this review article, we focus on recent evidence linking TNF-α and MDD looking at data from animal and clinical studies, illustrating the pathophysiological role, susceptibility and its therapeutic application in depression. We conclude by discussing future directions for research, in particular the opportunities for the development of novel therapeutics that target TNF-α. This will be very important for designing preventative strategies and for the identification of new drug targets and preventative strategies.

Control of serotonin transporter phosphorylation by conformational state

Serotonin transporter (SERT) is responsible for reuptake and recycling of 5-hydroxytryptamine (5-HT; serotonin) after its exocytotic release during neurotransmission. Mutations in human SERT are associated with psychiatric disorders and autism. Some of these mutations affect the regulation of SERT activity by cGMP-dependent phosphorylation. Here we provide direct evidence that this phosphorylation occurs at Thr276, predicted to lie near the cytoplasmic end of transmembrane helix 5 (TM5). Using membranes from HeLa cells expressing SERT and intact rat basophilic leukemia cells, we show that agents such as Na(+) and cocaine that stabilize outward-open conformations of SERT decreased phosphorylation and agents that stabilize inward-open conformations (e.g., 5-HT, ibogaine) increased phosphorylation. The opposing effects of the inhibitors cocaine and ibogaine were each reversed by an excess of the other inhibitor. Inhibition of phosphorylation by Na(+) and stimulation by ibogaine occurred at concentrations that induced outward opening and inward opening, respectively, as measured by the accessibility of cysteine residues in the extracellular and cytoplasmic permeation pathways, respectively. The results are consistent with a mechanism of SERT regulation that is activated by the transport of 5-HT, which increases the level of inward-open SERT and may lead to unwinding of the TM5 helix to allow phosphorylation.

Kappa Opioid Receptor-Induced Aversion Requires p38 MAPK Activation in VTA Dopamine Neurons

The endogenous dynorphin-κ opioid receptor (KOR) system encodes the dysphoric component of the stress response and controls the risk of depression-like and addiction behaviors; however, the molecular and neural circuit mechanisms are not understood. In this study, we report that KOR activation of p38α MAPK in ventral tegmental (VTA) dopaminergic neurons was required for conditioned place aversion (CPA) in mice. Conditional genetic deletion of floxed KOR or floxed p38α MAPK by Cre recombinase expression in dopaminergic neurons blocked place aversion to the KOR agonist U50,488. Selective viral rescue by wild-type KOR expression in dopaminergic neurons of KOR(-/-) mice restored U50,488-CPA, whereas expression of a mutated form of KOR that could not initiate p38α MAPK activation did not. Surprisingly, while p38α MAPK inactivation blocked U50,488-CPA, p38α MAPK was not required for KOR inhibition of evoked dopamine release measured by fast scan cyclic voltammetry in the nucleus accumbens. In contrast, KOR activation acutely inhibited VTA dopaminergic neuron firing, and repeated exposure attenuated the opioid response. This adaptation to repeated exposure was blocked by conditional deletion of p38α MAPK, which also blocked KOR-induced tyrosine phosphorylation of the inwardly rectifying potassium channel (GIRK) subunit Kir3.1 in VTA dopaminergic neurons. Consistent with the reduced response, GIRK phosphorylation at this amino terminal tyrosine residue (Y12) enhances channel deactivation. Thus, contrary to prevailing expectations, these results suggest that κ opioid-induced aversion requires regulation of VTA dopaminergic neuron somatic excitability through a p38α MAPK effect on GIRK deactivation kinetics rather than by presynaptically inhibiting dopamine release.

SIGNIFICANCE STATEMENT

Kappa opioid receptor (KOR) agonists have the potential to be effective, nonaddictive analgesics, but their therapeutic utility is greatly limited by adverse effects on mood. Understanding how KOR activation produces dysphoria is key to the development of better analgesics and to defining how the endogenous dynorphin opioids produce their depression-like effects. Results in this study show that the aversive effects of κ receptor activation required arrestin-dependent p38α MAPK activation in dopamine neurons but did not require inhibition of dopamine release in the nucleus accumbens. Thus, contrary to the prevailing view, inhibition of mesolimbic dopamine release does not mediate the aversive effects of KOR activation and functionally selective κ opioids that do not activate arrestin signaling may be effective analgesics lacking dysphoric effects.

The Role of Dopamine in Inflammation-Associated Depression: Mechanisms and Therapeutic Implications

Studies investigating the impact of a variety of inflammatory stimuli on the brain and behavior have consistently reported evidence that inflammatory cytokines affect the basal ganglia and dopamine to mediate depressive symptoms related to motivation and motor activity. Findings have included inflammation-associated reductions in ventral striatal responses to hedonic reward, decreased dopamine and dopamine metabolites in cerebrospinal fluid, and decreased availability of striatal dopamine, all of which correlate with symptoms of anhedonia, fatigue, and psychomotor retardation. Similar relationships between alterations in dopamine-relevant corticostriatal reward circuitry and symptoms of anhedonia and psychomotor slowing have also been observed in patients with major depression who exhibit increased peripheral cytokines and other inflammatory markers, such as C-reactive protein. Of note, these inflammation-associated depressive symptoms are often difficult to treat in patients with medical illnesses or major depression. Furthermore, a wealth of literature suggests that inflammation can decrease dopamine synthesis, packaging, and release, thus sabotaging or circumventing the efficacy of standard antidepressant treatments. Herein, the mechanisms by which inflammation and cytokines affect dopamine neurotransmission are discussed, which may provide novel insights into treatment of inflammation-related behavioral symptoms that contribute to an inflammatory malaise.

A requirement of serotonergic p38α mitogen-activated protein kinase for peripheral immune system activation of CNS serotonin uptake and serotonin-linked behaviors

Alterations in central serotonin (5-hydroxytryptamine, 5-HT) neurotransmission and peripheral immune activation have been linked to multiple neuropsychiatric disorders, including depression, schizophrenia and autism. The antidepressant-sensitive 5-HT transporter (SERT, SLC6A4), a critical determinant of synaptic 5-HT inactivation, can be regulated by pro-inflammatory cytokine signaling. Systemic innate immune system activation via intraperitoneal lipopolysaccharide (LPS) injection rapidly elevates brain SERT activity and 5-HT clearance. Moreover, the pro-inflammatory cytokine interleukin (IL)-1β rapidly stimulates SERT activity in raphe nerve terminal preparations ex vivo, effects that are attenuated by pharmacological p38 MAPK inhibition. To establish a role of serotonergic p38α MAPK signaling in LPS/IL-1β-induced SERT regulation and attendant behavioral responses, we pursued studies in mice that afford conditional elimination of p38α MAPK in 5-HT neurons (p38α(5HT-)). We found p38α(5HT-) and control (p38α(5HT+)) littermates to be indistinguishable in viability and growth and to express equivalent levels of SERT protein and synaptosomal 5-HT transport activity. Consistent with pharmacological studies, however, IL-1β fails to increase SERT activity in midbrain synaptosomes prepared from p38α(5HT-) animals. Moreover, although LPS elevated plasma corticosterone and central/peripheral pro-inflammatory cytokines in p38α(5HT-) animals, elevations in midbrain SERT activity were absent nor were changes in depressive and anxiety-like behaviors observed. Our studies support an obligate role of p38α MAPK signaling in 5-HT neurons for the translation of immune activation to SERT regulation and 5-HT-modulated behaviors.

Integrin β3 Haploinsufficiency Modulates Serotonin Transport and Antidepressant-Sensitive Behavior in Mice

Converging lines of evidence have identified genetic interactions between the serotonin transporter (SERT) gene and ITGB3, which encodes the β3 subunit that forms the αIIbβ3 and αvβ3 integrin receptor complexes. Here we examine the consequences of haploinsufficiency in the mouse integrin β3 subunit gene (Itgb3) on SERT function and selective 5-hydroxytryptamine (5-HT) reuptake inhibitor (SSRI) effectiveness in vivo. Biochemical fractionation studies and immunofluorescent staining of murine brain slices reveal that αvβ3 receptors and SERTs are enriched in presynaptic membranes from several brain regions and that αvβ3 colocalizes with a subpopulation of SERT-containing synapses in raphe nuclei. Notably, we establish that loss of a single allele of Itgb3 in murine neurons is sufficient to decrease 5-HT uptake by SERT in midbrain synaptosomes. Pharmacological assays to elucidate the αvβ3-mediated mechanism of reduced SERT function indicate that decreased integrin β3 subunit expression scales down the population size of active SERT molecules and, as a consequence, lowers the effective dose of SSRIs. These data are consistent with the existence of a subpopulation of SERTs that are tightly modulated by integrin αvβ3 and significantly contribute to global SERT function at 5-HT synapses in the midbrain. Importantly, our screen of a normal human population for single nucleotide polymorphisms in human ITGB3 identified a variant associated with reductions in integrin β3 expression levels that parallel our mouse findings. Thus, polymorphisms in human ITGB3 may contribute to the differential responsiveness of select patients to SSRIs.

Depressive-like behavior induced by tumor necrosis factor-α is attenuated by m-trifluoromethyl-diphenyl diselenide in mice

A growing body of evidence associates activation of immune system with depressive symptoms. Accordingly, pro-inflammatory cytokines, such as tumor necrosis factor-α (TNF-α), have been shown to play a pivotal role in the pathophysiology of depression. The aim of this study was to evaluate the effectiveness of acute and subchronic treatments with (m-CF3-PhSe)2 to prevent the depressive-like behavior induced by intracerebroventricular injection of TNF-α in mice. TNF-α induced depressive-like behavior in the forced swimming test (FST) and tail suspension test (TST) (0.1 and 0.001 ƒg/5 μL/site, respectively) without changing locomotor activity, performed in the locomotor activity monitor (LAM). Acute (0.01-50 mg/kg; intragastric (i.g.); 30 min) and subchronic (0.01 and 0.1 mg/kg; i.g.; 14 days) treatments with (m-CF3-PhSe)2 at low doses were effective against the effect of TNF-α in the FST and TST. Nuclear factor-κB (NF-κB) and p38 mitogen-activated protein kinase (p38 MAPK), important proteins in TNF-activated signaling, were determined in the prefrontal cortex and hippocampus of mouse. TNF-α (0.1 ƒg/5 μL/site) increased NF-κB levels and p38 MAPK activation in both brain areas and acute (10 mg/kg; i.g.) and subchronic (0.01 mg/kg; i.g.) treatments with (m-CF3-PhSe)2 were effective in attenuating this increase. Although more studies are necessary to indicate this compound as a therapeutic alternative to depression, the antidepressant-like and anti-inflammatory effects of (m-CF3-PhSe)2 demonstrated herein may support it as an interesting molecule in the search for new drugs to treat depressive disorders that have been largely linked to immune process and inflammation.

Serotonin mediated immunoregulation and neural functions: Complicity in the aetiology of autism spectrum disorders

Serotonergic system has long been implicated in the aetiology of autism spectrum disorders (ASD), since platelet hyperserotonemia is consistently observed in a subset of autistic patients, who respond well to selective serotonin reuptake inhibitors. Apart from being a neurotransmitter, serotonin functions as a neurotrophic factor directing brain development and as an immunoregulator modulating immune responses. Serotonin transporter (SERT) regulates serotonin level in lymphoid tissues to ensure its proper functioning in innate and adaptive responses. Immunological molecules such as cytokines in turn regulate the transcription and activity of SERT. Dysregulation of serotonergic system could trigger signalling cascades that affect normal neural-immune interactions culminating in neurodevelopmental and neural connectivity defects precipitating behavioural abnormalities, or the disease phenotypes. Therefore, we suggest that a better understanding of the cross talk between serotonergic genes, immune systems and serotonergic neurotransmission will open wider avenues to develop pharmacological leads for addressing the core ASD behavioural deficits.

Toxoplasma gondii-induced neuronal alterations

The zoonotic pathogen Toxoplasma gondii infects over 30% of the human population. The intracellular parasite can persist lifelong in the CNS within neurons modifying their function and structure, thus leading to specific behavioural changes of the host. In recent years, several in vitro studies and murine models have focused on the elucidation of these modifications. Furthermore, investigations of the human population have correlated Toxoplasma seropositivity with changes in neurological functions; however, the complex underlying mechanisms of the subtle behavioural alteration are still not fully understood. The parasites are able to induce direct modifications in the infected cells, for example by altering dopamine metabolism, by functionally silencing neurons as well as by hindering apoptosis. Moreover, indirect effects of the peripheral immune system and alterations of the immune status of the CNS, observed during chronic infection, might also contribute to changes in neuronal connectivity and synaptic plasticity. In this review, we will provide an overview and highlight recent advances, which describe changes in the neuronal function and morphology upon T. gondii infection.

Akt-mediated regulation of antidepressant-sensitive serotonin transporter function, cell-surface expression and phosphorylation

The present study is focused on the cellular basis for Akt-mediated SERT regulation. SERT has been implicated in mood disorders. SERT is a primary target for antidepressants used in the therapeutic intervention of psychiatric disorders.

Role of nitric oxide in the behavioral and neurochemical effects of IB-MECA in zebrafish

RATIONALE

The adenosine A3 receptor and the nitric oxide (NO) pathway regulate the function and localization of serotonin transporters (SERTs). These transporters regulate extracellular serotonin levels, which are correlated with defensive behavior.

OBJECTIVE

The purpose of this study was to understand the role of the A3AR on anxiety and arousal models in zebrafish, and whether this role is mediated by the nitrergic modulation of serotonin uptake.

METHODS

The effects of IB-MECA (0.01 and 0.1 mg/kg) were assessed in a series of behavioral tasks in adult zebrafish, as well as on extracellular serotonin levels in vivo and serotonin uptake in brain homogenates. Finally, the interaction between IB-MECA and drugs blocking voltage-dependent calcium channels (VDCCs), NO synthase, and SERT was analyzed.

RESULTS

At the lowest dose, IB-MECA decreased bottom dwelling and scototaxis, while at the highest dose, it also decreased shoaling, startle probability, and melanophore responses. These effects were accompanied by an increase in brain extracellular serotonin levels. IB-MECA also concentration-dependently increased serotonin uptake in vitro. The effects of IB-MECA on extracellular 5-HT, scototaxis, and geotaxis were blocked by L-NAME, while only the effects on 5-HT and scototaxis were blocked by verapamil. In vitro, the increase in 5-HT uptake was dependent on VDCCs and NO. Finally, fluoxetine blocked the effect of IB-MECA on scototaxis, but not geotaxis.

CONCLUSION

These results suggest that the effect of IB-MECA on scototaxis are mediated by a VDCC-NO-SERT pathway. While NO seems to mediate the effects of IB-MECA on geotaxis, neither VDCCs nor SERT seems to be involved in this process.

Targeting human central nervous system protein kinases: An isoform selective p38αMAPK inhibitor that attenuates disease progression in Alzheimer's disease mouse models

The first kinase inhibitor drug approval in 2001 initiated a remarkable decade of tyrosine kinase inhibitor drugs for oncology indications, but a void exists for serine/threonine protein kinase inhibitor drugs and central nervous system indications. Stress kinases are of special interest in neurological and neuropsychiatric disorders due to their involvement in synaptic dysfunction and complex disease susceptibility. Clinical and preclinical evidence implicates the stress related kinase p38αMAPK as a potential neurotherapeutic target, but isoform selective p38αMAPK inhibitor candidates are lacking and the mixed kinase inhibitor drugs that are promising in peripheral tissue disease indications have limitations for neurologic indications. Therefore, pursuit of the neurotherapeutic hypothesis requires kinase isoform selective inhibitors with appropriate neuropharmacology features. Synaptic dysfunction disorders offer a potential for enhanced pharmacological efficacy due to stress-induced activation of p38αMAPK in both neurons and glia, the interacting cellular components of the synaptic pathophysiological axis, to be modulated. We report a novel isoform selective p38αMAPK inhibitor, MW01-18-150SRM (=MW150), that is efficacious in suppression of hippocampal-dependent associative and spatial memory deficits in two distinct synaptic dysfunction mouse models. A synthetic scheme for biocompatible product and positive outcomes from pharmacological screens are presented. The high-resolution crystallographic structure of the p38αMAPK/MW150 complex documents active site binding, reveals a potential low energy conformation of the bound inhibitor, and suggests a structural explanation for MW150’s exquisite target selectivity. As far as we are aware, MW150 is without precedent as an isoform selective p38MAPK inhibitor or as a kinase inhibitor capable of modulating in vivo stress related behavior.

STAT3 controls IL6-dependent regulation of serotonin transporter function and depression-like behavior

Experimental evidence suggests a role for the immune system in the pathophysiology of depression. A specific involvement of the proinflammatory cytokine interleukin 6 (IL6) in both, patients suffering from the disease and pertinent animal models, has been proposed. However, it is not clear how IL6 impinges on neurotransmission and thus contributes to depression. Here we tested the hypothesis that IL6-induced modulation of serotonergic neurotransmission through the STAT3 signaling pathway contributes to the role of IL6 in depression. Addition of IL6 to JAR cells, endogenously expressing SERT, reduced SERT activity and downregulated SERT mRNA and protein levels. Similarly, SERT expression was reduced upon IL6 treatment in the mouse hippocampus. Conversely, hippocampal tissue of IL6-KO mice contained elevated levels of SERT and IL6-KO mice displayed a reduction in depression-like behavior and blunted response to acute antidepressant treatment. STAT3 IL6-dependently associated with the SERT promoter and inhibition of STAT3 blocked the effect of IL6 in-vitro and modulated depression-like behavior in-vivo. These observations demonstrate that IL6 directly controls SERT levels and consequently serotonin reuptake and identify STAT3-dependent regulation of SERT as conceivable neurobiological substrate for the involvement of IL6 in depression.

Mesenchymal stem cells alleviate airway inflammation and emphysema in COPD through down-regulation of cyclooxygenase-2 via p38 and ERK MAPK pathways

Bone marrow-derived mesenchymal stem cells (MSCs) have been identified as one possible strategy for the treatment of chronic obstructive pulmonary disease (COPD). Our previous studies have demonstrated that MSC administration has therapeutic potential in airway inflammation and emphysema via a paracrine mechanism. We proposed that MSCs reverse the inflammatory process and restore impaired lung function through their interaction with macrophages. In our study, the rats were exposed to cigarette smoke (CS), followed by the administration of MSCs into the lungs for 5 weeks. Here we show that MSC administration alleviated airway inflammation and emphysema through the down-regulation of cyclooxygenase-2 (COX-2) and COX-2-mediated prostaglandin E2 (PGE2) production, possibly through the effect on alveolar macrophages. In vitro co-culture experiments provided evidence that MSCs down-regulated COX-2/PGE2 in macrophages through inhibition of the activation-associated phosphorylation of p38 MAPK and ERK. Our data suggest that MSCs may relieve airway inflammation and emphysema in CS-exposed rat models, through the inhibition of COX-2/PGE2 in alveolar macrophages, mediated in part by the p38 MAPK and ERK pathways. This study provides a compelling mechanism for MSC treatment in COPD, in addition to its paracrine mechanism.

Hypothalamic-pituitary-adrenal axis function during perinatal depression

Abnormal function of the hypothalamic-pituitary-adrenal (HPA) axis is an important pathological finding in pregnant women exhibiting major depressive disorder. They show high levels of cortisol pro-inflammatory cytokines, hypothalamic-pituitary peptide hormones and catecholamines, along with low dehydroepiandrosterone levels in plasma. During pregnancy, the TH2 balance together with the immune system and placental factors play crucial roles in the development of the fetal allograft to full term. These factors, when altered, may generate a persistent dysfunction of the HPA axis that may lead to an overt transfer of cortisol and toxicity to the fetus at the expense of reduced activity of placental 11β-hydroxysteroid dehydrogenase type 2. Epigenetic modifications also may contribute to the dysregulation of the HPA axis. Affective disorders in pregnant women should be taken seriously, and therapies focused on preventing the deleterious effects of stressors should be implemented to promote the welfare of both mother and baby.

Depression in cancer patients: Pathogenesis, implications and treatment (Review)

Depression is a common comorbidity in cancer cases, affecting >10% of patients. A cancer diagnosis is life-changing, and is a source of considerable psychological and emotional stress. Non-pathological sadness may be a normal response to a cancer diagnosis, however, stress beyond the coping mechanisms of patients may result in major depressive disorder. The current review, in addition to the obvious psychosocial elements of depression, explores its biological mechanisms, including tissue damage, inflammatory mediators and the chronic stress response, and how these immune and endocrine pathways may underlie depression in cancer. Possible iatrogenic causes of depression in cancer are also explored. There is a strong need to identify and treat depression in cancer patients in order to increase quality of life and reduce mortality. The most popular clinical and potential future biochemical screening tools for depression in cancer are briefly discussed. The interventions used will vary for every patient, but may include psychosocial therapies or pharmacotherapy; however, a paucity of research on the most effective management of depression in cancer means the optimal combination of therapies is unknown. Selection of antidepressants should be carefully considered, given the common side effects of chemotherapy (such as nausea), and the necessity to avoid serious interactions, including reducing the effectiveness of chemotherapeutic drugs. The possible link between the chronic stress response, which may predispose patients to depression, and the risk of mortality from cancer is also explored. The complex interactions between the endocrine, nervous and immune systems, which continue to be elucidated, may offer the opportunity for the development of more rapid and efficacious treatments for depression in cancer in the future.

The Neuro-Immune Pathophysiology of Central and Peripheral Fatigue in Systemic Immune-Inflammatory and Neuro-Immune Diseases

Many patients with systemic immune-inflammatory and neuro-inflammatory disorders, including depression, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's disease, cancer, cardiovascular disorder, Parkinson's disease, multiple sclerosis, stroke, and chronic fatigue syndrome/myalgic encephalomyelitis, endure pathological levels of fatigue. The aim of this narrative review is to delineate the wide array of pathways that may underpin the incapacitating fatigue occurring in systemic and neuro-inflammatory disorders. A wide array of immune, inflammatory, oxidative and nitrosative stress (O&NS), bioenergetic, and neurophysiological abnormalities are involved in the etiopathology of these disease states and may underpin the incapacitating fatigue that accompanies these disorders. This range of abnormalities comprises: increased levels of pro-inflammatory cytokines, e.g., interleukin-1 (IL-1), IL-6, tumor necrosis factor (TNF) α and interferon (IFN) α; O&NS-induced muscle fatigue; activation of the Toll-Like Receptor Cycle through pathogen-associated (PAMPs) and damage-associated (DAMPs) molecular patterns, including heat shock proteins; altered glutaminergic and dopaminergic neurotransmission; mitochondrial dysfunctions; and O&NS-induced defects in the sodium-potassium pump. Fatigue is also associated with altered activities in specific brain regions and muscle pathology, such as reductions in maximum voluntary muscle force, downregulation of the mitochondrial biogenesis master gene peroxisome proliferator-activated receptor gamma coactivator 1-alpha, a shift to glycolysis and buildup of toxic metabolites within myocytes. As such, both mental and physical fatigue, which frequently accompany immune-inflammatory and neuro-inflammatory disorders, are the consequence of interactions between multiple systemic and central pathways.

Kappa opioid receptor activation potentiates the cocaine-induced increase in evoked dopamine release recorded in vivo in the mouse nucleus accumbens

Behavioral stressors increase addiction risk in humans and increase the rewarding valence of drugs of abuse including cocaine, nicotine and ethanol in animal models. Prior studies have established that this potentiation of drug reward was mediated by stress-induced release of the endogenous dynorphin opioids and subsequent kappa opioid receptor (KOR) activation. In this study, we used in vivo fast scan cyclic voltammetry to test the hypothesis that KOR activation before cocaine administration might potentiate the evoked release of dopamine from ventral tegmental (VTA) synaptic inputs to the nucleus accumbens (NAc) and thereby increase the rewarding valence of cocaine. The KOR agonist U50488 inhibited dopamine release evoked by either medial forebrain bundle (MFB) or pedunculopontine tegmental nucleus (PPTg) activation of VTA inputs to the shell or core of the mouse NAc. Cocaine administration increased the dopamine response recorded in either the shell or core evoked by either MFB or PPTg stimulation. Administration of U50488 15 min before cocaine blocked the conditioned place preference (CPP) to cocaine, but only significantly reduced the effect of cocaine on the dopamine response evoked by PPTg stimulation to NAc core. In contrast, administration of U50488 60 min before cocaine significantly potentiated cocaine CPP and significantly increased the effects of cocaine on the dopamine response evoked by either MFB or PPTg stimulation, recorded in either NAc shell or core. Results of this study support the concept that stress-induced activation of KOR by endogenous dynorphin opioids may enhance the rewarding valence of drugs of abuse by potentiating the evoked dopamine response.

Mice genetically depleted of brain serotonin do not display a depression-like behavioral phenotype

Reductions in function within the serotonin (5HT) neuronal system have long been proposed as etiological factors in depression. Selective serotonin reuptake inhibitors (SSRIs) are the most common treatment for depression, and their therapeutic effect is generally attributed to their ability to increase the synaptic levels of 5HT. Tryptophan hydroxylase 2 (TPH2) is the initial and rate-limiting enzyme in the biosynthetic pathway of 5HT in the CNS, and losses in its catalytic activity lead to reductions in 5HT production and release. The time differential between the onset of 5HT reuptake inhibition by SSRIs (minutes) and onset of their antidepressant efficacy (weeks to months), when considered with their overall poor therapeutic effectiveness, has cast some doubt on the role of 5HT in depression. Mice lacking the gene for TPH2 are genetically depleted of brain 5HT and were tested for a depression-like behavioral phenotype using a battery of valid tests for affective-like disorders in animals. The behavior of TPH2(-/-) mice on the sucrose preference test, tail suspension test, and forced swim test and their responses in the unpredictable chronic mild stress and learned helplessness paradigms was the same as wild-type controls. While TPH2(-/-) mice as a group were not responsive to SSRIs, a subset responded to treatment with SSRIs in the same manner as wild-type controls with significant reductions in immobility time on the tail suspension test, indicative of antidepressant drug effects. The behavioral phenotype of the TPH2(-/-) mouse questions the role of 5HT in depression. Furthermore, the TPH2(-/-) mouse may serve as a useful model in the search for new medications that have therapeutic targets for depression that are outside of the 5HT neuronal system.

Inflammatory biomarker profiles of mental disorders and their relation to clinical, social and lifestyle factors

In the last few decades, mental health research has increasingly provided evidence supporting the role of inflammation in pathogenesis, course and treatment of mental disorders. With such a steep incline of research, resulting in a wealth of emerged findings, it has become difficult to follow developments within the field. The present review sets out to present the recent developments and to give an overview of the inflammatory profiles of depression, psychosis and bipolar disorder, as well as variations within these disorders. Moreover, mediating factors such as social environment and childhood experience are discussed, both in terms of their potential in elucidating the complex interface between the inflammation and other closely related biological systems, as well as the possibly confounding impact of various lifestyle factors. Whilst many issues in this fascinating area of research remain to be fully understood and elaborated, all current evidence suggests that inflammation plays a key role in mental disorders and may open up novel avenues for clinical treatment.

Signaling mechanisms involved in the acute effects of estradiol on 5-HT clearance

Estradiol was found previously to have an antidepressant-like effect and to block the ability of selective serotonin reuptake inhibitors (SSRIs) to have an antidepressant-like effect. The antidepressant-like effect of estradiol was due to estrogen receptor β (ERβ) and/or GPR30 activation, whereas estradiol's blockade of the effect of an SSRI was mediated by ERα. This study focuses on investigating signaling pathways as well as interacting receptors associated with these two effects of estradiol. In vivo chronoamperometry was used to measure serotonin transporter (SERT) function. The effect of local application of estradiol or selective agonists for ERα (PPT) or ERβ (DPN) into the CA3 region of the hippocampus of ovariectomized (OVX) rats on 5-hydroxytryptamine (5-HT) clearance as well as on the ability of fluvoxamine to slow 5-HT clearance was examined after selective blockade of signaling pathways or that of interacting receptors. Estradiol- or DPN-induced slowing of 5-HT clearance mediated by ERβ was blocked after inhibition of MAPK/ERK1/2 but not of PI3K/Akt signaling pathways. This effect also involved interactions with TrkB, and IGF-1 receptors. Estradiol's or PPT's inhibition of the fluvoxamine-induced slowing of 5-HT clearance mediated by ERα, was blocked after inhibition of either MAPK/ERK1/2 or PI3K/Akt signaling pathways. This effect involved interactions with the IGF-1 receptor and with the metabotropic glutamate receptor 1, but not with TrkB. This study illustrates some of the signaling pathways required for the effects of estradiol on SERT function, and particularly shows that ER subtypes elicit different as well as common signaling pathways for their actions.

Characterization of intracellular regions in the human serotonin transporter for phosphorylation sites

In the central nervous system, synaptic levels of the monoamine neurotransmitter serotonin are mainly controlled by the serotonin transporter (SERT), and drugs used in the treatment of various psychiatric diseases have SERT as primary target. SERT is a phosphoprotein that undergoes phosphorylation/dephosphorylation during transporter regulation by multiple pathways. In particular, activation and/or inhibition of kinases including PKC, PKG, p38MAPK, and CaMKII modulate SERT function and trafficking. The molecular mechanisms by which kinase activity is linked to SERT regulation are poorly understood, including the identity of specific phosphorylated residues. To elucidate SERT phosphorylation sites, we have generated peptides corresponding to the entire intracellular region of human SERT and performed in vitro phosphorylation assays with a panel of kinases suggested to be involved in SERT regulation or for which canonical phosphorylation sites are predicted. Peptide analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to identify and quantify site-specific phosphorylation. Five residues located in the N- and C-termini and in intracellular loop 1 and 2 were identified as phosphorylation sites; Ser149, Ser277, and Thr603 for PKC, Ser13 for CaMKII, and Thr616 for p38MAPK. Possible regulatory roles of these potential phosphoacceptors for SERT function and surface expression were investigated using phospho-mimicking and phosphodeficient mutations, coexpression of constitutively active kinases and pharmacological kinase induction in a heterologous expression system. Our results suggest that Ser277 is involved in an initial phase of PKC-mediated down-regulation of SERT. The five identified sites can guide future studies of direct links between SERT phosphorylation and regulatory processes.

Lipopolysaccharide increases degradation of central monoamines: an in vivo microdialysis study in the nucleus accumbens and medial prefrontal cortex of mice

Peripheral administration of lipopolysaccharide (LPS) in rodents induces anhedonia, i.e. the inability to experience pleasure. Recently, we reported that serotonin transporter (SERT) function is required for LPS-induced anhedonia. Less is known about the effect of LPS on the biological activity of dopamine transporters (DAT) and norepinephrine transporters (NET). Therefore, in vivo microdialysis was performed in the nucleus accumbens and medial prefrontal cortex of C57BL6/J mice exposed to saline or LPS (133 µg/kg i.p.). To investigate the possible involvement of different monoamine transporters, the triple reuptake inhibitor DOV 216,303 or saline was i.p. injected 30 min before the saline/LPS injection. The dose of LPS, shown to decrease responding for brain stimulation reward in mice, significantly increased extracellular levels of monoamine metabolites (5-HIAA, DOPAC and HVA) in the nucleus accumbens and medial prefrontal cortex. Remarkably, DOV 216,303 abolished LPS-induced DOPAC and HVA formation in the nucleus accumbens, suggesting that LPS increases DAT activity in this brain area. DOV 216,303 also inhibited LPS-induced DOPAC and HVA formation in the medial prefrontal cortex. Since DAT density is very low in this brain structure, reuptake of DA predominantly takes place via NET, suggesting that LPS increases DAT and NET activity in the medial prefrontal cortex. Furthermore, DOV 216,303 pretreatment prevented LPS-induced 5-HIAA formation only in the medial prefrontal cortex, indicating that LPS increases prefrontal SERT activity. In conclusion, the present findings suggest that peripheral LPS increases DAT activity in the nucleus accumbens and increases NET and SERT activity in the medial prefrontal cortex of mice.

Role of the serotonin transporter in pulmonary arterial hypertension

Pulmonary arterial hypertension is a disease in which pulmonary arterial pressure is raised, leading to right heart failure. Survival is poor despite current therapeutic strategies. The 'serotonin hypothesis of pulmonary arterial hypertension' arose in the 1960s following an 'epidemic' of pulmonary arterial hypertension in women taking the indirect serotinergic agonist aminorex as an anorexigen. In the 1980s, the hypothesis was revisited following the occurrence of pulmonary arterial hypertension associated with the use of fenfluramines as anorexigens; these are also indirect serotinergic agents. Research has identified changes in serotonin synthesis, serotonin receptor activation and serotonin uptake via the serotonin transporter in experimental and clinical pulmonary arterial hypertension. This review will discuss our current understanding of this serotonin hypothesis with particular reference to the role of the serotonin transporter.

Arrestin-mediated activation of p38 MAPK: molecular mechanisms and behavioral consequences

Studies of kappa opioid receptor signaling mechanisms during the last decade have demonstrated that agonist activation of the receptor results in Gβγ-dependent signaling and distinct arrestin-dependent signaling events. Gβγ-dependent signaling results in ion channel regulation causing neuronal inhibition, inhibition of transmitter release, and subsequent analgesic responses. In contrast, arrestin-dependent signaling events result in p38 MAPK activation and subsequent dysphoric and proaddictive behavioral responses. Resolution of these two branches of signaling cascades has enabled strategies designed to identify pathway-selective drugs that may have unique therapeutic utilities.

The SLC6 transporters: perspectives on structure, functions, regulation, and models for transporter dysfunction

The human SLC6 family is composed of approximately 20 structurally related symporters (co-transporters) that use the transmembrane electrochemical gradient to actively import their substrates into cells. Approximately half of the substrates of these transporters are amino acids, with others transporting biogenic amines and/or closely related compounds, such as nutrients and compatible osmolytes. In this short review, five leaders in the field discuss a number of currently important research themes that involve SLC6 transporters, highlighting the integrative role they play across a wide spectrum of different functions. The first essay, by Gary Rudnick, describes the molecular mechanism of their coupled transport which is being progressively better understood based on new crystal structures, functional studies, and modeling. Next, the question of multiple levels of transporter regulation is discussed by Reinhard Krämer, in the context of osmoregulation and stress response by the related bacterial betaine transporter BetP. The role of selected members of the human SLC6 family that function as nutrient amino acid transporters is then reviewed by François Verrey. He discusses how some of these transporters mediate the active uptake of (essential) amino acids into epithelial cells of the gut and the kidney tubule to support systemic amino acid requirements, whereas others are expressed in specific cells to support their specialized metabolism and/or growth. The most extensively studied members of the human SLC6 family are neurotransmitter reuptake transporters, many of which are important drug targets for the treatment of neuropsychiatric disorders. Randy Blakely discusses the role of posttranscriptional modifications of these proteins in regulating transporter subcellular localization and activity state. Finally, Dennis Murphy reviews how natural gene variants and mouse genetic models display consistent behavioral alterations that relate to altered extracellular neurotransmitter levels.

Immune dysregulation and autoimmunity in bipolar disorder: Synthesis of the evidence and its clinical application

OBJECTIVE

Increasing evidence suggests that inflammation and immune dysregulation play an important role in the pathogenesis of bipolar disorder. Because the brain can be affected by various autoimmune processes, it is possible that some psychiatric disorders may have an autoimmune basis.

METHOD

This article reviews the literature on peripheral and central immune dysregulation and autoimmunity in bipolar disorder. The mechanisms of the innate and adaptive immune systems in the pathophysiology of bipolar disorder are explored. The clinical features and pathogenesis of neuropsychiatric systemic lupus erythematosus, anti-NMDA encephalitis, and Hashimoto's encephalopathy are summarized.

RESULTS

Neuroinflammation and peripheral immune dysregulation may play a role in the pathophysiology of bipolar disorder. This involves a complex interaction between immune cells of the central nervous system and periphery resulting in cellular damage through mechanisms involving excitotoxicity, oxidative stress, and mitochondrial dysfunction. Neuropsychiatric systemic lupus erythematosus, anti-NMDA encephalitis, and Hashimoto's encephalopathy are important differentials for a psychiatrist to consider when suspecting autoimmune encephalopathy.

CONCLUSIONS

The link between immune dysregulation, autoimmunity, and bipolar disorder may be closer than previously thought. Psychiatrists should be vigilant for autoimmunity in presentations of bipolar disorder due to its high morbidity and therapeutic implications. Advances in neuroimaging and biomarker identification related to immune dysregulation and neuroinflammation will contribute to our knowledge of the pathophysiology of bipolar disorder.

Norepinephrine transporter heterozygous knockout mice exhibit altered transport and behavior

The norepinephrine (NE) transporter (NET) regulates synaptic NE availability for noradrenergic signaling in the brain and sympathetic nervous system. Although genetic variation leading to a loss of NET expression has been implicated in psychiatric and cardiovascular disorders, complete NET deficiency has not been found in people, limiting the utility of NET knockout mice as a model for genetically driven NET dysfunction. Here, we investigate NET expression in NET heterozygous knockout male mice (NET(+/-) ), demonstrating that they display an approximately 50% reduction in NET protein levels. Surprisingly, these mice display no significant deficit in NET activity assessed in hippocampal and cortical synaptosomes. We found that this compensation in NET activity was due to enhanced activity of surface-resident transporters, as opposed to surface recruitment of NET protein or compensation through other transport mechanisms, including serotonin, dopamine or organic cation transporters. We hypothesize that loss of NET protein in the NET(+/-) mouse establishes an activated state of existing surface NET proteins. The NET(+/-) mice exhibit increased anxiety in the open field and light-dark box and display deficits in reversal learning in the Morris water maze. These data suggest that recovery of near basal activity in NET(+/-) mice appears to be insufficient to limit anxiety responses or support cognitive performance that might involve noradrenergic neurotransmission. The NET(+/-) mice represent a unique model to study the loss and resultant compensatory changes in NET that may be relevant to behavior and physiology in human NET deficiency disorders.

A review of the serotonin transporter and prenatal cortisol in the development of autism spectrum disorders

The diagnosis of autism spectrum disorder (ASD) during early childhood has a profound effect not only on young children but on their families. Aside from the physical and behavioural issues that need to be dealt with, there are significant emotional and financial costs associated with living with someone diagnosed with ASD. Understanding how autism occurs will assist in preparing families to deal with ASD, if not preventing or lessening its occurrence.

Serotonin plays a vital role in the development of the brain during the prenatal and postnatal periods, yet very little is known about the serotonergic systems that affect children with ASD. This review seeks to provide an understanding of the biochemistry and physiological actions of serotonin and its termination of action through the serotonin reuptake transporter (SERT). Epidemiological studies investigating prenatal conditions that can increase the risk of ASD describe a number of factors which elevate plasma cortisol levels causing such symptoms during pregnancy such as hypertension, gestational diabetes and depression. Because cortisol plays an important role in driving dysregulation of serotonergic signalling through elevating SERT production in the developing brain, it is also necessary to investigate the physiological functions of cortisol, its action during gestation and metabolic syndromes.

Transforming growth factor-β1 impairs CFTR-mediated anion secretion across cultured porcine vas deferens epithelial monolayer via the p38 MAPK pathway

The goal of this study was to determine whether transforming growth factor-β1 (TGF-β1) affects epithelial cells lining the vas deferens, an organ that is universally affected in cystic fibrosis male patients. In PVD9902 cells, which are derived from porcine vas deferens epithelium, TGF-β1 exposure significantly reduced short-circuit current (Isc) stimulated by forskolin or a cell membrane-permeant cAMP analog, 8-pCPT-cAMP, suggesting that TGF-β1 affects targets of the cAMP signaling pathway. Electrophysiological results indicated that TGF-β1 reduces the magnitude of current inhibited by cystic fibrosis transmembrane conductance regulator (CFTR) channel blockers. Real-time RT-PCR revealed that TGF-β1 downregulates the abundance of mRNA coding for CFTR, while biotinylation and Western blot showed that TGF-β1 reduces both total CFTR and apical cell surface CFTR abundance. These results suggest that TGF-β1 causes a reduction in CFTR expression, which limits CFTR-mediated anion secretion. TGF-β1-associated attenuation of anion secretion was abrogated by SB431542, a TGF-β1 receptor I inhibitor. Signaling pathway studies showed that the effect of TGF-β1 on Isc was reduced by SB203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK). TGF-β1 exposure also increased the amount of phospho-p38 MAPK substantially. In addition, anisomycin, a p38 MAPK activator, mimicked the effect of TGF-β1, which further suggests that TGF-β1 affects PVD9902 cells through a p38 MAPK pathway. These observations suggest that TGF-β1, via TGF-β1 receptor I and p38 MAPK signaling, reduces CFTR expression to impair CFTR-mediated anion secretion, which would likely compound the effects associated with mild CFTR mutations and ultimately would compromise male fertility.

The role of immune genes in the association between depression and inflammation: a review of recent clinical studies

The role for dysregulation of the immune system in the pathogenesis of depressive disorder is well established, and emerging research suggests the role of an underlying genetic vulnerability. The purpose of this review is to summarize the existing literature on the genetic variants involved in neurobiological pathways associated with both immune activation and depression. Using PubMed, Scopus, The Cochrane Library, Embase, Ovid of Medline, PsycINFO and ISI web of Knowledge, we selected 52 papers which are relevant for this literature review. Findings across the literature suggest that functional allelic variants of genes for interleukin-1beta (IL)-1β, tumor necrosis factor-alpha (TNF-α) and C-reactive protein (CRP), as well as genetic variations affecting T-cell function, may increase the risk for depression. Moreover, single nucleotide polymorphisms (SNPs) in the IL-1β, IL-6 and IL-11 genes, and in those regulating T-cell function may be associated with reduced responsiveness to antidepressant therapy. There is also some evidence indicative of a role of genetic variants of the enzymes, Cyclo-oxygenase2 (COX-2) and Phospholipase2 (PLA2), in the aetiology of depression. Finally, SNPs in genes related to the serotonin pathway may play a fundamental role in the shared genetic liability to both immune activation and depressive symptoms. Our review confirms that genetic variants influence the biological mechanisms by which the innate immune system contributes to the development of depression. However, future studies are necessary to identify the molecular mechanisms underlying these associations.

Inflammatory cytokines in depression: neurobiological mechanisms and therapeutic implications

Mounting evidence indicates that inflammatory cytokines contribute to the development of depression in both medically ill and medically healthy individuals. Cytokines are important for development and normal brain function, and have the ability to influence neurocircuitry and neurotransmitter systems to produce behavioral alterations. Acutely, inflammatory cytokine administration or activation of the innate immune system produces adaptive behavioral responses that promote conservation of energy to combat infection or recovery from injury. However, chronic exposure to elevated inflammatory cytokines and persistent alterations in neurotransmitter systems can lead to neuropsychiatric disorders and depression. Mechanisms of cytokine behavioral effects involve activation of inflammatory signaling pathways in the brain that results in changes in monoamine, glutamate, and neuropeptide systems, and decreases in growth factors, such as brain-derived neurotrophic factor. Furthermore, inflammatory cytokines may serve as mediators of both environmental (e.g. childhood trauma, obesity, stress, and poor sleep) and genetic (functional gene polymorphisms) factors that contribute to depression's development. This review explores the idea that specific gene polymorphisms and neurotransmitter systems can confer protection from or vulnerability to specific symptom dimensions of cytokine-related depression. Additionally, potential therapeutic strategies that target inflammatory cytokine signaling or the consequences of cytokines on neurotransmitter systems in the brain to prevent or reverse cytokine effects on behavior are discussed.

Cytokine targets in the brain: impact on neurotransmitters and neurocircuits

Increasing attention has been paid to the role of inflammation in a host of illnesses including neuropsychiatric disorders such as depression and anxiety. Activation of the inflammatory response leads to release of inflammatory cytokines and mobilization of immune cells both of which have been shown to access the brain and alter behavior. The mechanisms of the effects of inflammation on the brain have become an area of intensive study. Data indicate that cytokines and their signaling pathways including p38 mitogen-activated protein kinase have significant effects on the metabolism of multiple neurotransmitters such as serotonin, dopamine, and glutamate through impact on their synthesis, release, and reuptake. Cytokines also activate the kynurenine pathway, which not only depletes tryptophan, the primary amino acid precursor of serotonin, but also generates neuroactive metabolites that can significantly influence the regulation of dopamine and glutamate. Through their effects on neurotransmitter systems, cytokines impact neurocircuits in the brain including the basal ganglia and anterior cingulate cortex, leading to significant changes in motor activity and motivation as well as anxiety, arousal, and alarm. In the context of environmental challenge from the microbial world, these effects of inflammatory cytokines on the brain represent an orchestrated suite of behavioral and immune responses that subserve evolutionary priorities to shunt metabolic resources away from environmental exploration to fighting infection and wound healing, while also maintaining vigilance against attack, injury, and further pathogen exposure. Chronic activation of this innate behavioral and immune response may lead to depression and anxiety disorders in vulnerable individuals.

The pro-inflammatory cytokine TNF-α regulates the activity and expression of the serotonin transporter (SERT) in astrocytes

Pro-inflammatory cytokines have been implicated in the precipitation of depression and related disorders, and the antidepressant sensitive serotonin transporter (SERT) may be a major target for immune regulation in these disorders. Here, we focus on astrocytes, a major class of immune competent cells in the brain, to examine the effects of pro-longed treatment with tumor necrosis factor-alpha (TNF-α) on SERT activity. We first established that high-affinity serotonin uptake into C6 glioma cells occurs through a SERT-dependent mechanism. Functional SERT expression is also confirmed for primary astrocytes. In both cell types, exposure to TNF-α resulted in a dose- and time-dependent increase in SERT-mediated 5-HT uptake, which was sustained for at least 48 h post-stimulation. Further analysis in primary astrocytes revealed that TNF-α enhanced the transport capacity (Vmax) of SERT-specific 5-HT uptake, suggesting enhanced transporter expression, consistent with our observation of an increase in SERT mRNA levels. We confirmed that in both, primary astrocytes and C6 glioma cells, treatment with TNF-α activates the p38 mitogen-activated protein kinase (MAPK) signaling pathway. Pre-treatment with the p38 MAPK inhibitor SB203580 attenuated the TNF-α mediated stimulation of 5-HT transport in both, C6 glioma and primary astrocytes. In summary, we show that SERT gene expression and activity in astrocytes is subject to regulation by TNF-α, an effect that is at least in part dependent on p38 MAPK activation.

A dialogue between the immune system and brain, spoken in the language of serotonin

Neuropsychiatric disorders have long been linked to both immune system activation and alterations in serotonin (5-HT) signaling. In the CNS, the contributions of 5-HT modulate a broad range of targets, most notably, hypothalamic, limbic and cortical circuits linked to the control of mood and mood disorders. In the periphery, many are aware of the production and actions of 5-HT in the gut but are unaware that the molecule and its receptors are also present in the immune system where evidence suggests they contribute to the both innate and adaptive responses. In addition, there is clear evidence that the immune system communicates to the brain via both humoral and neuronal mechanisms, and that CNS 5-HT neurons are a direct or indirect target for these actions. Following a brief primer on the immune system, we describe our current understanding of the synthesis, release, and actions of 5-HT in modulating immune function, including the expression of 5-HT biosynthetic enzymes, receptors, and transporters that are typically studied with respect to the roles in the CNS. We then orient our presentation to recent findings that pro-inflammatory cytokines can modulate CNS 5-HT signaling, leading to a conceptualization that among the many roles of 5-HT in the body is an integrated physiological and behavioral response to inflammatory events and pathogens. From this perspective, altered 5-HT/immune conversations are likely to contribute to risk for neurobehavioral disorders historically linked to compromised 5-HT function or ameliorated by 5-HT targeted medications, including depression and anxiety disorders, obsessive-compulsive disorder (OCD), and autism. Our review raises the question as to whether genetic variation impacting 5-HT signaling genes may contribute to maladaptive behavior as much through perturbed immune system modulation as through altered brain mechanisms. Conversely, targeting the immune system for therapeutic development may provide an important opportunity to treat mental illness.

The solute carrier 6 family of transporters

The solute carrier 6 (SLC6) family of the human genome comprises transporters for neurotransmitters, amino acids, osmolytes and energy metabolites. Members of this family play critical roles in neurotransmission, cellular and whole body homeostasis. Malfunction or altered expression of these transporters is associated with a variety of diseases. Pharmacological inhibition of the neurotransmitter transporters in this family is an important strategy in the management of neurological and psychiatric disorders. This review provides an overview of the biochemical and pharmacological properties of the SLC6 family transporters.

Stress produces aversion and potentiates cocaine reward by releasing endogenous dynorphins in the ventral striatum to locally stimulate serotonin reuptake

Activation of the dynorphin/κ-opioid receptor (KOR) system by repeated stress exposure or agonist treatment produces place aversion, social avoidance, and reinstatement of extinguished cocaine place preference behaviors by stimulation of p38α MAPK, which subsequently causes the translocation of the serotonin transporter (SERT, SLC6A4) to the synaptic terminals of serotonergic neurons. In the present study we extend those findings by showing that stress-induced potentiation of cocaine conditioned place preference occurred by a similar mechanism. In addition, SERT knock-out mice did not show KOR-mediated aversion, and selective reexpression of SERT by lentiviral injection into the dorsal raphe restored the prodepressive effects of KOR activation. Kinetic analysis of several neurotransporters demonstrated that repeated swim stress exposure selectively increased the V(max) but not K(m) of SERT without affecting dopamine transport or the high-capacity, low-affinity transporters. Although the serotonergic neurons in the dorsal raphe project throughout the forebrain, a significant stress-induced increase in cell-surface SERT expression was only evident in the ventral striatum, and not in the dorsal striatum, hippocampus, prefrontal cortex, amygdala, or dorsal raphe. Stereotaxic microinjections of the long-lasting KOR antagonist norbinaltorphimine demonstrated that local KOR activation in the nucleus accumbens, but not dorsal raphe, mediated this stress-induced increase in ventral striatal surface SERT expression. Together, these results support the hypothesis that stress-induced activation of the dynorphin/KOR system produces a transient increase in serotonin transport locally in the ventral striatum that may underlie some of the adverse consequences of stress exposure, including the potentiation of the rewarding effects of cocaine.