Neurons of the superior nucleus of the medial habenula and ependymal cells express IL-18 in rat CNS

Neuroinflammation and Post-Stroke Depression: Focus on the Microglia and Astrocytes

Post-stroke depression (PSD), a frequent and disabling complication of stroke, has a strong impact on almost thirty percent of stroke survivors. The pathogenesis of PSD is not completely clear so far. Neuroinflammation following stroke is one of underlying mechanisms that involves in the pathophysiology of PSD and plays an important function in the development of depression and is regarded as a sign of depression. During the neuroinflammation after ischemic stroke onset, both astrocytes and microglia undergo a series of morphological and functional changes and play pro-inflammatory or anti-inflammatory effect in the pathological process of stroke. Importantly, astrocytes and microglia exert dual roles in the pathological process of PSD due to the phenotypic transformation. We summarize the latest evidence of neuroinflammation involving in PSD in this review, focus on the phenotypic transformation of microglia and astrocytes following ischemic stroke and reveal the dual roles of both microglia and astrocytes in the PSD via modulating the neuroinflammation.

The Neuroanatomy of the Habenular Complex and Its Role in the Regulation of Affective Behaviors

The habenular complex is a diencephalic structure divided into the medial and lateral divisions that lie within the epithalamus of most vertebrates. This brain structure, whose activities are mainly regulated via inputs/outputs from and to the stria medullaris and the fasciculus retroflexus, plays a significant role in the modulation of anti-reward behaviors in both the rodent and human brain. Such anti-reward circuits are regulated by dopaminergic and serotonergic projections with several other subcortical and cortical regions; therefore, it is plausible that impairment to this key subcortical structure or its connections contributes to the pathogenesis of affective disorders. Current literature reveals the existence of structural changes in the habenula complex in individuals afflicted by such disorders; however, there is a need for more comprehensive investigations to elucidate the underlying neuroanatomical connections that underpin disease development. In this review article, we aim to provide a comprehensive view of the neuroanatomical differences between the rodent and human habenular complex, the main circuitries, and provide an update on the emerging roles of this understudied subcortical structure in the control of affective behaviors, with special emphasis to morbid conditions of the affective sphere.

Circuits regulating pleasure and happiness - focus on potential biomarkers for circuitry including the habenuloid complex

INTRODUCTION

The multiplicity and complexity of the neuronal connections in the central nervous system make it difficult to disentangle circuits that play an essential role in the development or treatment of (neuro)psychiatric disorders. By choosing the evolutionary development of the forebrain as a starting point, a certain order in the connections can be created. The dorsal diencephalic connection (DDC) system can be applied for the development of biomarkers that can predict treatment response.

MATERIALS AND METHODS

After providing a brief introduction to the theory, we examined neuroanatomical publications on the connectivity of the DDC system. We then searched for neurochemical components that are specific for the habenula.

RESULTS AND DISCUSSION

The best strategy to find biomarkers that reflect the function of the habenular connection is to use genetic variants of receptors, transporters or enzymes specific to this complex. By activating these with probes and measuring the response in people with different functional genotypes, the usefulness of biomarkers can be assessed.

CONCLUSIONS

The most promising biomarkers in this respect are those linked to activation or inhibition of the nicotine receptor, dopamine D4 receptor, μ-opioid receptor and also those of the functioning of habenular glia cells (astrocytes and microglia).

IL-1α and TNF-α as an inducer for ROS-mediated NLRP1/NLRP3 inflammasomes activation in mononuclear blood cells from individuals with chronic insomnia disorder

BACKGROUND

There are some evidence that cytokines may play an important role in sleep deprivation; however, the underlying mechanisms are still unknown. So, the present study aim to evaluate the relationship between NLRP1 and NLRP3 inflammasomes activation of blood cells and serum levels of cytokines in individuals with chronic insomnia disorder (CID).

METHODS

Blood samples were collected from 24 individuals with CID and 24 healthy volunteers. The inflammasomes activation was evaluated using real time PCR of NLRP1, NLRP3, ASC, and Caspase-1; western blot of NLRP1 and NLRP3; caspase-1 activity assay; and serum levels of IL-1β, IL-18 and other cytokines using enzyme-linked immunosorbent assay (ELISA). ROS generation in blood cells were detected by flow cytometry assay. As well, MRI scans were obtained on a Siemens Magnetom Avanto 1.5 T MRI whole body scanner using an 8-channel head coil.

RESULTS

We found the increased activity of NLRP1 and NLRP3 inflammasomes in blood cells; the increased serum levels of pro-inflammatory cytokines; and the decreased serum levels of IL-10 and TGF-β in individuals with CID. We observed significant correlation between increased serum concentration of IL-1β and the severity of insomnia in individuals with CID. The levels of ROS in blood cells was found to be correlated with IL-1α and TNF-α concentrations in serums from individuals with CID. Moreover, the included individuals with CID demonstrated the increased right-cerebellum-cortex and lateral ventricle MD bilaterally compared to controls.

CONCLUSIONS

This study provided new insights on the pathogenesis of CID and the effects of cytokines on inflammasome activation.

Crystal structure of the Toll/interleukin-1 receptor (TIR) domain of IL-1R10 provides structural insights into TIR domain signaling

The Toll/interleukin-1 receptor (TIR) domains are key innate immune signaling modules. Here, we present the crystal structure of the TIR domain of human Interleukin-1 receptor 10 (IL-1R10), also called IL-1RAPL2. It is similar to that of IL-1R9 (IL-1RAPL1) but shows significant structural differences to those from Toll-like receptors (TLRs) and the adaptor proteins MAL and MyD88. Interactions of TIR domains in their respective crystals and the higher-order assemblies (MAL and MyD88) reveal the presence of a common 'BCD surface', suggesting its functional significance. We also show that the TIR domains of IL-1R10 and IL-1R9 lack NADase activity, consistent with their structures. Our study provides a foundation for unraveling the functions of IL-1R9 and IL-1R10.

Roles of Ependymal Cells in the Physiology and Pathology of the Central Nervous System

Ependymal cells are indispensable components of the central nervous system (CNS). They originate from neuroepithelial cells of the neural plate and show heterogeneity, with at least three types that are localized in different locations of the CNS. As glial cells in the CNS, accumulating evidence demonstrates that ependymal cells play key roles in mammalian CNS development and normal physiological processes by controlling the production and flow of cerebrospinal fluid (CSF), brain metabolism, and waste clearance. Ependymal cells have been attached to great importance by neuroscientists because of their potential to participate in CNS disease progression. Recent studies have demonstrated that ependymal cells participate in the development and progression of various neurological diseases, such as spinal cord injury and hydrocephalus, raising the possibility that they may serve as a potential therapeutic target for the disease. This review focuses on the function of ependymal cells in the developmental CNS as well as in the CNS after injury and discusses the underlying mechanisms of controlling the functions of ependymal cells.

Addiction-related neuroadaptations following chronic nicotine exposure

The addiction-relevant molecular, cellular, and behavioral actions of nicotine are derived from its stimulatory effects on neuronal nicotinic acetylcholine receptors (nAChRs) in the central nervous system. nAChRs expressed by dopamine-containing neurons in the ventral midbrain, most notably in the ventral tegmental area (VTA), contribute to the reward-enhancing properties of nicotine that motivate the use of tobacco products. nAChRs are also expressed by neurons in brain circuits that regulate aversion. In particular, nAChRs expressed by neurons in the medial habenula (mHb) and the interpeduncular nucleus (IPn) to which the mHb almost exclusively projects regulate the "set-point" for nicotine aversion and control nicotine intake. Different nAChR subtypes are expressed in brain reward and aversion circuits and nicotine intake is titrated to maximally engage reward-enhancing nAChRs while minimizing the recruitment of aversion-promoting nAChRs. With repeated exposure to nicotine, reward- and aversion-related nAChRs and the brain circuits in which they are expressed undergo adaptations that influence whether tobacco use will transition from occasional to habitual. Genetic variation that influences the sensitivity of addiction-relevant brain circuits to the actions of nicotine also influence the propensity to develop habitual tobacco use. Here, we review some of the key advances in our understanding of the mechanisms by which nicotine acts on brain reward and aversion circuits and the adaptations that occur in these circuits that may drive addiction to nicotine-containing tobacco products.

Mechanisms of Nicotine Addiction

Tobacco smoking results in more than five million deaths each year and accounts for ∼90% of all deaths from lung cancer.³ Nicotine, the major reinforcing component of tobacco smoke, acts in the brain through the neuronal nicotinic acetylcholine receptors (nAChRs). The nAChRs are allosterically regulated, ligand-gated ion channels consisting of five membrane-spanning subunits. Twelve mammalian α subunits (α2-α10) and three β subunits (β2-β4) have been cloned. The predominant nAChR subtypes in mammalian brain are those containing α4 and β2 subunits (denoted as α4β2* nAChRs). The α4β2* nAChRs mediate many behaviors related to nicotine addiction and are the primary targets for currently approved smoking cessation agents. Considering the large number of nAChR subunits in the brain, it is likely that nAChRs containing subunits in addition to α4 and β2 also play a role in tobacco smoking. Indeed, genetic variation in the CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the α5, α3, and β4 nAChR subunits, respectively, has been shown to increase vulnerability to tobacco dependence and smoking-associated diseases including lung cancer. Moreover, mice, in which expression of α5 or β4 subunits has been genetically modified, have profoundly altered patterns of nicotine consumption. In addition to the reinforcing properties of nicotine, the effects of nicotine on appetite, attention, and mood are also thought to contribute to establishment and maintenance of the tobacco smoking habit. Here, we review recent insights into the behavioral actions of nicotine, and the nAChR subtypes involved, which likely contribute to the development of tobacco dependence in smokers.

Interleukin-18 from neurons and microglia mediates depressive behaviors in mice with post-stroke depression

Post-stroke depression (PSD) is a common and serious complication that is affecting one thirds of stroke patients which leaves them with a poor quality of life, high mortality rate, high recurrent rate, and slow recovery. Recent studies showed that serum interleukin-18 (IL-18) level is a biomarker for patients with PSD. However, the role of IL-18 in the pathology of PSD is still unclear. In this study, we demonstrated that the IL-18 level in the ischemic brain significantly increased in mice with depression-like behaviors that were caused by the combined use of chronic spatial restraint stress and middle cerebral artery occlusion. Interestingly, IL-18 expression was mainly found in neurons at early phase and in microglia at a later phase. Injection of the exogenous IL-18 into the amygdala, but not the hippocampus or the striatum caused severe depression-like behaviors. On the contrary, the blockage of endogenous IL-18 by IL-18 binding protein, a specific antagonist of IL-18, repressed depressive phenotypes in SIR mice. IL-18 KO mice exhibited the resistance to spatial restraint stress and cerebral ischemia injury. Finally, we found that IL-18 mediated depressive behaviors by the interaction of IL-18 receptor and NKCC1, a sodium-potassium chloride co-transporter that is related to GABAergic inhibition. Administration of NKCC1 antagonist bumetanide exerted a therapeutic effect on the in IL-18-induced depressive mice. In conclusion, we demonstrated that increased IL-18 in the brain causes depression-like behaviors by promoting the IL-18 receptor/NKCC1 signaling pathway. Targeting IL-18 and its downstream pathway is a promising strategy for the prevention and treatment of PSD.

The contribution of glial cells to Huntington's disease pathogenesis

Glial cells play critical roles in the normal development and function of neural circuits, but in many neurodegenerative diseases, they become dysregulated and may contribute to the development of brain pathology. In Huntington's disease (HD), glial cells both lose normal functions and gain neuropathic phenotypes. In addition, cell-autonomous dysfunction elicited by mutant huntingtin (mHTT) expression in specific glial cell types is sufficient to induce both pathology and Huntington's disease-related impairments in motor and cognitive performance, suggesting that these cells may drive the development of certain aspects of Huntington's disease pathogenesis. In support of this imaging studies in pre-symptomatic HD patients and work on mouse models have suggested that glial cell dysfunction occurs at a very early stage of the disease, prior to the onset of motor and cognitive deficits. Furthermore, selectively ablating mHTT from specific glial cells or correcting for HD-induced changes in their transcriptional profile rescues some HD-related phenotypes, demonstrating the potential of targeting these cells for therapeutic intervention. Here we review emerging research focused on understanding the involvement of different glial cell types in specific aspects of HD pathogenesis. This work is providing new insight into how HD impacts biological functions of glial cells in the healthy brain as well as how HD induced dysfunction in these cells might change the way they integrate into biological circuits.

The Posterior Perforated Substance: A Brain Mystery Wrapped in an Enigma

BACKGROUND

There is a dearth of published information on the posterior perforated substance as compared to the anterior perforated substance. We managed to glean facts about the posterior perforated substance that can serve as a landmark for surgical operations in the adjacent regions of the midbrain and the vessels passing through it. Moreover, the posterior perforated substance contains the interpeduncular nucleus responsible for the mental state of the individual.

OBJECTIVES

1) To describe the topography of the blood vessels supplying the posterior perforated substance area from the surgical point of view; 2) to investigate the functions of the interpeduncular nucleus.

METHODS

We assembled and analyzed results from source databases by Elsevier, NCBI MedLine, Scopus, Scholar. Google and Embase. Each article was studied in detail for practically useful information about the posterior perforated substance.

RESULTS

The P1-segment perforating branches of the posterior cerebral artery supply the posterior perforated substance. This area is especially vulnerable in the case of vascular pathologies. The posterior communicating artery can block the surgeon's view and impede maneuverability of the tool in the area of the posterior perforated substance, which may be addressed using the separation technique, which can lead to positive results. In addition, the medial habenula-interpeduncular nucleus in the posterior perforated substance is associated with various addictions and psychiatric conditions.

CONCLUSION

The posterior perforated substance area is of great interest for surgical interventions. Future studies of the interpeduncular nucleus anticipate the development of drugs to affect different types of dependencies and some mental diseases.

Enteric Nervous System-Derived IL-18 Orchestrates Mucosal Barrier Immunity

Mucosal barrier immunity is essential for the maintenance of the commensal microflora and combating invasive bacterial infection. Although immune and epithelial cells are thought to be the canonical orchestrators of this complex equilibrium, here, we show that the enteric nervous system (ENS) plays an essential and non-redundant role in governing the antimicrobial protein (AMP) response. Using confocal microscopy and single-molecule fluorescence in situ mRNA hybridization (smFISH) studies, we observed that intestinal neurons produce the pleiotropic cytokine IL-18. Strikingly, deletion of IL-18 from the enteric neurons alone, but not immune or epithelial cells, rendered mice susceptible to invasive Salmonella typhimurium (S.t.) infection. Mechanistically, unbiased RNA sequencing and single-cell sequencing revealed that enteric neuronal IL-18 is specifically required for homeostatic goblet cell AMP production. Together, we show that neuron-derived IL-18 signaling controls tissue-wide intestinal immunity and has profound consequences on the mucosal barrier and invasive bacterial killing.

Transcriptomic Characterization of the Human Habenula Highlights Drug Metabolism and the Neuroimmune System

Due to size and accessibility, most information about the habenula is derived from rodent studies. To better understand the molecular signature of the habenula we characterized the genes that have high expression in the habenula. We compared anatomical expression profiles of three normal adult human brains and four fetal brains. We used gene set enrichment analyses to determine if genes annotated to specific molecular functions, cellular components, and biological processes are enriched in the habenula. We also tested gene sets related to depression and addiction to determine if they uniquely involve the habenula. As expected, we observed high habenular expression of GPR151, nicotinic cholinergic receptors, and cilia-associated genes (medial division). Genes identified in genetic studies of smoking and associated with nicotine response were enriched in the habenula. Genes associated with major depressive disorder did not have enriched expression in the habenula but genes negatively correlated with hedonic well-being were, providing a link to anhedonia. We observed enrichment of genes associated with diseases that are comorbid with addictions (hematopoiesis, thrombosis, liver cirrhosis, pneumonia, and pulmonary fibrosis) and depression (rheumatoid arthritis, multiple sclerosis, and kidney disease). These inflammatory diseases mark a neuroimmune signature that is supported by genes associated with mast cells, acute inflammatory response, and leukocyte migration. We also found enrichment of cytochrome p450 genes suggesting the habenula is uniquely sensitive to endogenous and xenobiotic compounds. Our results suggest the habenula receives negative reward signals from immune and drug processing molecules. This is consistent with the habenular role in the "anti-reward" system and suggests it may be a key bridge between autoimmune disorders, drug use, and psychiatric diseases.

The family of the interleukin-1 receptors

The extracellular forms of the IL-1 cytokines are active through binding to specific receptors on the surface of target cells. IL-1 ligands bind to the extracellular portion of their ligand-binding receptor chain. For signaling to take place, a non-binding accessory chain is recruited into a heterotrimeric complex. The intracellular approximation of the Toll-IL-1-receptor (TIR) domains of the 2 receptor chains is the event that initiates signaling. The family of IL-1 receptors (IL-1R) includes 10 structurally related members, and the distantly related soluble protein IL-18BP that acts as inhibitor of the cytokine IL-18. Over the years the receptors of the IL-1 family have been known with many different names, with significant confusion. Thus, we will use here a recently proposed unifying nomenclature. The family includes several ligand-binding chains (IL-1R1, IL-1R2, IL-1R4, IL-1R5, and IL-1R6), 2 types of accessory chains (IL-1R3, IL-1R7), molecules that act as inhibitors of signaling (IL-1R2, IL-1R8, IL-18BP), and 2 orphan receptors (IL-1R9, IL-1R10). In this review, we will examine how the receptors of the IL-1 family regulate the inflammatory and anti-inflammatory functions of the IL-1 cytokines and are, more at large, involved in modulating defensive and pathological innate immunity and inflammation. Regulation of the IL-1/IL-1R system in the brain will be also described, as an example of the peculiarities of organ-specific modulation of inflammation.

Blocking p38 Signaling Reduces the Activation of Pro-inflammatory Cytokines and the Phosphorylation of p38 in the Habenula and Reverses Depressive-Like Behaviors Induced by Neuroinflammation

Increasing evidence has demonstrated that neuroinflammation contributes to the development of depressive-like behaviors, in both animal models and human patients; however, the brain areas and signaling pathways involved are still elusive. Recent studies have suggested novel roles of the habenula in the onset of depression and other psychiatric disorders; however, there is no evidence for whether the habenula has a function in neuroinflammation-induced depression. Using an animal model of depression, which is induced by the repeated central administration of lipopolysaccharide (LPS), we examined whether cytokine expression and p38 signal activation in the habenula were involved in the depressive-like behaviors. Body weight, saccharin preference test, and tail suspension test were used to measure depressive-like behaviors. Immunohistochemistry, quantitative-polymerase chain reaction (q-PCR), and western blot were used to measure the expression of tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10), and the phosphorylation of p38 in the habenula. The results showed that central LPS administration induced depressive-like behaviors, characterized by anhedonia in the saccharin preference test and increased immobility in the tail suspension test. Central LPS administration also significantly increased the p-p38 level in microglial cells and increased TNF-α expression in the habenula. Treatment with fluoxetine, a widely prescribed antidepressant, or SB203580, a p38-specific inhibitor, reversed the depressive-like behaviors, normalized the alterations in p-p38 and TNF-α levels and increased the levels of the anti-inflammatory cytokine IL-10 in the habenula. The present findings suggest that the habenula is involved in the pathophysiology of behavioral depression induced by neuroinflammation, and the p38 pathway may serve as a novel mechanism-based target for the treatment of inflammation-related depression.

The Proinflammatory Cytokine Interleukin 18 Regulates Feeding by Acting on the Bed Nucleus of the Stria Terminalis

The proinflammatory cytokine IL-18 has central anorexigenic effects and was proposed to contribute to loss of appetite observed during sickness. Here we tested in the mouse the hypothesis that IL-18 can decrease food intake by acting on neurons of the bed nucleus of the stria terminalis (BST), a component of extended amygdala recently shown to influence feeding via its projections to the lateral hypothalamus (LH). We found that both subunits of the heterodimeric IL-18 receptor are highly expressed in the BST and that local injection of recombinant IL-18 (50 ng/ml) significantly reduced c-fos activation and food intake for at least 6 h. Electrophysiological experiments performed in BST brain slices demonstrated that IL-18 strongly reduces the excitatory input on BST neurons through a presynaptic mechanism. The effects of IL-18 are cell-specific and were observed in Type III but not in Type I/II neurons. Interestingly, IL-18-sensitve Type III neurons were recorded in the juxtacapsular BST, a region that contains BST-LH projecting neurons. Reducing the excitatory input on Type III GABAergic neurons, IL-18 can increase the firing of glutamatergic LH neurons through a disinhibitory mechanism. Imbalance between excitatory and inhibitory activity in the LH can induce changes in food intake. Effects of IL-18 were mediated by the IL-18R because they were absent in neurons from animals null for IL-18Rα (Il18ra(-/-)), which lack functional IL-18 receptors. In conclusion, our data show that IL-18 may inhibit feeding by inhibiting the activity of BST Type III GABAergic neurons.

SIGNIFICANCE STATEMENT

Loss of appetite during sickness is a common and often debilitating phenomenon. Although proinflammatory cytokines are recognized as mediators of these anorexigenic effects, their mechanism and sites of action remain poorly understood. Here we show that interleukin 18, an anorexigenic cytokine, can act on neurons of the bed nucleus of the stria terminalis to reduce food intake via the IL-18 receptor. The findings identify a site and a mode of action that indicate targets for the treatment of cachexia or other eating disorders.

The medial habenula and interpeduncular nucleus circuitry is critical in addiction, anxiety, and mood regulation

Abstinence from chronic use of addictive drugs triggers an aversive withdrawal syndrome that compels relapse and deters abstinence. Many features of this syndrome are common across multiple drugs, involving both affective and physical symptoms. Some of the network signaling underlying withdrawal symptoms overlaps with activity that is associated with aversive mood states, including anxiety and depression. Given these shared features, it is not surprising that a particular circuit, the dorsal diencephalic conduction system, and the medial habenula (MHb) and interpeduncular nucleus (IPN), in particular, have been identified as critical to the emergence of aversive states that arise both as a result and, independently, of drug addiction. As the features of this circuit continue to be characterized, the MHb-IPN axis is emerging as a viable target for therapeutics to aid in the treatment of addiction to multiple drugs of abuse as well as mood-associated disorders. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

NLRP3 inflammasome-driven pathways in depression: Clinical and preclinical findings

Over the past three decades, an intricate interaction between immune activation, release of pro-inflammatory cytokines and changes in brain circuits related to mood and behavior has been described. Despite extensive efforts, questions regarding when inflammation becomes detrimental or how we can target the immune system to develop new therapeutic strategies for the treatment of psychiatric disorders remain unresolved. In this context, novel aspects of the neuroinflammatory process activated in response to stressful challenges have recently been documented in major depressive disorder (MDD). The Nod-like receptor pyrin containing 3 inflammasome (NLRP3) is an intracellular multiprotein complex responsible for a number of innate immune processes associated with infection, inflammation and autoimmunity. Recent data have demonstrated that NLRP3 activation appears to bridge the gap between immune activation and metabolic danger signals or stress exposure, which are key factors in the pathogenesis of psychiatric disorders. In this review, we discuss both preclinical and clinical evidence that links the assembly of the NLRP3 complex and the subsequent proteolysis and release of the pro-inflammatory cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18) in chronic stress models and patients with MDD. Importantly, we also focus on the therapeutic potential of targeting the NLRP3 inflammasome complex to improve stress resilience and depressive symptoms.

Postnatal changes of interleukin-18 receptor immunoreactivity in neurons of the retrosplenial cortex in wild-type and interleukin-18 knock out mice

Interleukin-18 (IL-18), which is involved in the inflammatory response, is also found in the cerebral cortex. IL-18 receptor-immunoreactive (IL-18R-ir) neurons are present in layer V of the retrosplenial cortex (RSC). In the adult IL-18 knock out (KO) mice, no IL-18R-ir neurons but many degenerated neurons are present in layer V of the RSC, suggesting that any changes in the neurons of layer V have occurred during postnatal development. We examined changes of IL-18R expression during postnatal development. In the wild-type mice, many IL-18R-ir neurons were present in layers II, III and VI of the RSC in 2-week-old mice, whereas they were sparsely observed in only layer III in 3-week-old mice. No IL-18R-ir neurons were present in 4- and 5-week-old mice. In older than 6-week-old mice, many IL-18R-ir neurons were present in layers V and VI. The IL-18KO mice showed IL-18R-ir neurons in layers II, III and VI at 2-weeks-old, and a few in layer III at 3-week-old mice, similar to that in the wild-type mice. No IL-18R-ir neurons were found in mice older than 4 weeks of age. Thus, IL-18 or IL-18R seem to be involved in the construction of neural circuits corresponding to events after 3-weeks of age.

The histone deacetylase inhibitor, sodium butyrate, exhibits neuroprotective effects for ischemic stroke in middle-aged female rats

Background

Sodium butyrate (NaB) is a histone deacetylase (HDAC) inhibitor exhibiting anti-inflammatory and neuroprotective effects in a rat ischemic model of stroke as well as a myocardial ischemia model. Although clinical evidence shows that older women are at higher risk for stroke occurrence and greater stroke severity, no studies have evaluated the effectiveness of NaB either in females or in older animals.

Methods

To determine the effects of NaB on stroke in older females, acyclic middle-aged Sprague-Dawley female rats (9–11 months old, constant diestrus) were subject to middle cerebral artery occlusion (MCAo) by intracerebral injection of recombinant endothelin-1. Rats were treated with NaB (300 mg/kg, i.p.) at 6 and 30 h following ET-1 injection. Animals were sacrificed at the early (2 days) or late (5 days) acute phase after MCAo. Serum and tissue lysates were collected for biochemical analyses.

Results

NaB treatment reduced infarct volume and ameliorated sensory motor impairment in middle-aged female rats, when measured at 2 and 5 days post MCAo. At the early acute phase (2 days post stroke), NaB treatment decreased brain lipid peroxides, and reduced serum levels of GFAP, a surrogate marker of blood-brain barrier (BBB) permeability. NaB also reduced expression of the inflammatory cytokine IL-1beta in circulation and IL-18 in the ischemic hemisphere. At the late acute phase (5 days post stroke), NaB treatment further suppressed MCAo-induced increase of IL-1beta, IL-17A, and IL-18 in brain lysates (cortex and striatum) from the ischemic hemisphere, and decreased ischemia-induced upregulation of IL-1beta and IL-18 in circulation, indicating a potent anti-inflammatory effect of the HDAC inhibitor. Moreover, NaB treatment also increased expression of IGF-1, a known neuroprotectant, in peripheral tissue including serum, liver, and spleen at the late acute phase.

Conclusions

These data provide the first evidence that delayed (>6 h) NaB treatment post-stroke is neuroprotective in older female rats. Additionally, these data also show that in addition to its well-known anti-inflammatory actions, NaB may exert a biphasic effect after stroke, operating initially to reduce BBB permeability and oxidative stress in the brain, and later, elevating IGF-1 expression in peripheral tissues.

Fine structure of interleukin 18 (IL-18) receptor-immunoreactive neurons in the retrosplenial cortex and its changes in IL18 knockout mice

Interleukin 18 (IL-18) participates in the inflammatory immune response of lymphocytes. Delay in learning or memory are common in the IL-18 knockout mouse. Many IL-18-immunoreactive neurons are found in the retrosplenial cortex (RSC) and the subiculum. These neurons also contain the IL-18 receptor. We determined the location and the ultrastructure of the IL-18 receptor-immunoreactive neurons in the RSC and observed changes in the IL-18 receptor-immunoreactive neurons of the IL-18 knockout mouse. The IL-18 receptor-immunoreactive neurons were found specifically in layer V of the granular RSC. They were medium-sized neurons with a light oval nucleus and had little cytoplasm with many free ribosomes, rough endoplasmic reticulum and many mitochondria, but no Nissl bodies. The number of axosomatic terminals was about six per section. The IL-18 receptor-immunoreactive neurons were not found in the RSC in the IL-18 knockout mouse at 5 or 9 weeks of age. However, many small electron-dense neurons were found in layer V. Both the nucleus and cytoplasm were electron-dense, but not necrotic. The mitochondria and rough endoplasmic reticulum were swollen. The IL-18 receptor-immunoreactive neurons were presumed to be degenerating. The degeneration of the IL18-receptor-immunoreactive neurons in the RSC may cause the abnormal behaviors of the IL-18 knockout mice.

Acute experimental changes in mood state regulate immune function in relation to central opioid neurotransmission: a model of human CNS-peripheral inflammatory interaction

Although evidence shows depressed moods enhance risk for somatic diseases, molecular mechanisms underlying enhanced somatic susceptibility are ill-defined. Knowledge of these molecular mechanisms will inform development of treatment and prevention strategies across comorbid depressive and somatic illnesses. Existing evidence suggests that interleukin-18 (IL-18; an IL-1 family cytokine) is elevated in depression and implicated in pathophysiology underlying comorbid medical illnesses. We previously identified strong associations between baseline IL-18 and μ-opioid receptor availability in major depressive disorder (MDD) volunteers. Combined with the evidence in animal models, we hypothesized that experimental mood induction would change IL-18, the extent proportional to opioid neurotransmitter release. Using the Velten technique in a [(11)C]carfentanil positron emission tomography neuroimaging study, we examined the impact of experimentally induced mood (sad, neutral) on plasma IL-18 and relationships with concurrent changes in the central opioid neurotransmission in 28 volunteers (healthy, MDD). Results showed mood induction impacted IL-18 (F2,25=12.2, P<0.001), sadness increasing IL-18 (T27=2.6, P=0.01) and neutral mood reducing IL-18 (T27=-4.1, P<0.001). In depressed volunteers, changes in IL-18 were more pronounced (F2,25=3.6, P=0.03) and linearly proportional to sadness-induced μ-opioid activation (left ventral pallidum, bilateral anterior cingulate cortices, right hypothalamus and bilateral amygdala). These data demonstrate that dynamic changes of a pro-inflammatory IL-1 superfamily cytokine, IL-18, and its relationship to μ-opioid neurotransmission in response to experimentally induced sadness. Further testing is warranted to delineate the role of neuroimmune interactions involving IL-18 in enhancing susceptibility to medical illness (that is, diabetes, heart disease and persistent pain states) in depressed individuals.

The Spinal Ependymal Layer in Health and Disease

Ependymal cells are epithelial support cells that line the central canal and ventricular cavities of the central nervous system, providing the interface between the cerebrospinal fluid and the parenchyma of the brain and spinal cord. The spinal ependymal layer (SEL) is composed of 3 main cell types: tanycytes, ependymocytes, and cerebrospinal fluid-contacting neurons. A fourth cell type, termed the supraependymal cell, is also occasionally described. Cells of the SEL show restricted proliferative capacity in health but display neural stem cell properties both in vitro and in vivo in various disease states. A growing body of literature is devoted to the regenerative roles of the SEL, particularly in the context of spinal cord injury, where mechanical damage to the spinal cord leads to a significant increase in SEL proliferation. SEL-derived cell progeny migrate to sites of injury within the injured spinal cord parenchyma and contribute primarily to glial scar formation. In additional to their role as endogenous neural stem cells, cells of the SEL may be an important source of cytokines and other cell signaling molecules, such as tumor necrosis factor, heat shock proteins, and various growth factors. The SEL has become of recent interest to neuroscience researchers because of its potential to participate in and respond to diseases affecting the spinal cord (eg, traumatic spinal cord injury) and neurodegenerative disease. The intimate association of the SEL with the cerebrospinal fluid makes intrathecal therapies a viable option, and recent studies highlight the potential promise of treatments that augment SEL responses to disease.

Possible involvement of TRPV1 and TRPV4 in nociceptive stimulation- induced nocifensive behavior and neuroendocrine response in mice

Members of the transient receptor potential (TRP) family of ion channels play important roles in inflammation and pain. Here, we showed that both TRPV1 and TRPV4 might contribute to biphasic nocifensive behavior and neuroendocrine response following a formalin test. We subcutaneously injected saline, formalin, or the TRPV4 agonist, 4α-phorbol 12,13-didecanoate (4α-PDD) into one hindpaw of wild-type (WT), TRPV1-deficient (Trpv1(-/-)), and TRPV4-deficient (Trpv4(-/-)) mice to investigate nocifensive behaviors (phase I [0-10 min] and phase II [10-60 min]) and Fos expression in the dorsal horn of the spinal cord and other brain regions related to pain, in the paraventricular nucleus (PVN), paraventricular nucleus of the thalamus, the medial habenular nucleus, the medial nucleus of the amygdala and capsular part of the central amygdala. Subcutaneous (s.c.) injection of formalin caused less nocifensive behavior in Trpv1(-/-) and Trpv4(-/-) mice than in WT mice during phase I. In phase II, however, formalin induced less nocifensive behavior only in the Trpv1(-/-) mice, but not in the Trpv4(-/-) mice, relative to WT mice. The number of Fos-like immunoreactive (LI) neurons in laminae I-II of the dorsal horn increased in all types of mice 90 min after s.c. injection of formalin; however, there was no difference in the other regions between saline- and formalin-treated mice. Furthermore, s.c. injection of 4α-PDD did not induce nociceptive behavior nor influence the number of Fos-LI neurons in the all above mentioned regions in any of the mice. These results suggest that TRPV4-mediated nociceptive information from the peripheral tissue excluding the spinal pathway might be involved the formalin behavioral response during phase I. Only TRPV1 might regulate the formalin behavioral response in peripheral neuron.

Affective and cognitive prefrontal cortex projections to the lateral habenula in humans

Anterior insula (AI) and dorsal ACC (dACC) are known to process information about pain, loss, adversities, bad, harmful or suboptimal choices and consequences that threaten survival or well-being. Also pregenual ACC (pgACC) is linked to loss and pain, being activated by sad thoughts and regrets. Lateral habenula (LHb) is stimulated by predicted and received pain, discomfort, aversive outcome, loss. Its chronic stimulation makes us feel worse/low and gradually stops us choosing and moving for the suboptimal or punished choices, by direct and indirect (via rostromedial tegmental nucleus, RMTg) inhibition of dorsal raphe nucleus (DRN) and VTA/SNc. The response selectivity of LHb neurons suggests their cortical input from affective and cognitive evaluative regions that make expectations about bad, unpleasant or suboptimal outcomes. Based on these facts I predicted direct dACC, pgACC and AI projections to LHb, which form part of an adversity processing circuit that learns to avoid bad outcomes by suppressing dopamine and serotonin signal. To test this connectivity I used Diffusion Tensor Imaging (DTI). I found dACC, pgACC, AI and caudolateral OFC (clOFC) projections to LHb. I predicted no corticohabenular projections from the reward processing regions: medial OFC (mOFC) and ventral ACC (vACC) because both respond most strongly to good, high valued stimuli and outcomes, inducing dopamine and serotonin release. This lack of LHb projections was confirmed for vACC and likely for mOFC. The surprising findings were the corticohabenular projections from the cognitive prefrontal cortex regions, known for flexible reasoning, planning and combining whatever information are relevant for reaching current goals. I propose that the prefrontohabenular projections provide a teaching signal for value-based choice behavior, to learn to deselect, avoid or inhibit the potentially harmful, low valued or wrong choices, goals, strategies, predictions and ways of doing things, to prevent bad or suboptimal consequences.

Interleukin-18 directly protects cortical neurons by activating PI3K/AKT/NF-κB/CREB pathways

Interleukin-18 (IL-18), a member of the IL-1 family of cytokines, was initially identified as an interferon (IFN)-γ-inducing factor. IL-18 is expressed in both immune and non-immune cells and participates in the adjustment of multitude cellular functions. Nonetheless, the effects of IL-18 on cortical neurons have not been explored. The present study was conducted to investigate the influence of IL-18 on rat primary cortical neurons and elucidate the underlying mechanisms. We proved that rrIL-18 increased the brain-derived neurotrophic factor (BDNF) expression in a time-dependent manner. Treatment with rrIL-18 (50 ng/ml) deactivated phosphatase and tensin homolog deleted on chromosome 10 (PTEN) by facilitating its phosphorylation, enhanced the expression of Phosphoinositide 3-OH kinase (PI3K) and p-Akt, standing for the activation of the PI3K/Akt pathway. As its pivotal downstream pathways, nuclear factor-kappa B (NF-κB), cAMP-responsive element binding protein (CREB)/Bcl-2 and glycogen synthase kinase-3β (GSK-3β) were examined in further steps. Our data revealed that rrIL-18 stimulated NF-κB activation, improved p-CREB and anti-apoptotic Bcl-2 expression levels. But rrIL-18 had little or no effect on GSK-3β pathway. Besides, rrIL-18 increased levels of BDNF and Bcl-2/Bax ratio and decreased cleaved caspase-3 expression to protect cortical neurons from damage induced by oxygen-glucose deprivation (OGD). These results in vitro showed the protection of IL-18 on cortical neurons. And this direct neuroprotective effect of IL-18 is crippled by PI3K inhibitor wortmannin.

The role of inflammasome in Alzheimer's disease

Alzheimer's disease (AD) is a chronic, progressive and irreversible neurodegenerative disease with clinical characteristics of memory loss, dementia and cognitive impairment. Although the pathophysiologic mechanism is not fully understood, inflammation has been shown to play a critical role in the pathogenesis of AD. Inflammation in the central nervous system (CNS) is characterized by the activation of glial cells and release of proinflammatory cytokines and chemokines. Accumulating evidence demonstrates that inflammasomes, which cleave precursors of interleukin-1β (IL-1β) and IL-18 to generate their active forms, play an important role in the inflammatory response in the CNS and in AD pathogenesis. Therefore, modulating inflammasome complex assembly and activation could be a potential strategy for suppressing inflammation in the CNS. This review aims to provide insight into the role of inflammasomes in the CNS, with respect to the pathogenesis of AD, and may provide possible clues for devising novel therapeutic strategies.

Interleukin-18 null mutation increases weight and food intake and reduces energy expenditure and lipid substrate utilization in high-fat diet fed mice

OBJECTIVE

The proinflammatory cytokine interleukin-18 (IL-18) putatively modulates food intake and energy metabolism, but the effects of IL-18 in high-fat diet fed animals are unknown. Whether IL-18 alters basal metabolic rate or metabolic processes of living is unknown. Here, we tested the hypothesis that IL-18 modulates weight gain, energy intake, whole-body energy expenditure, and utilization of lipid as a fuel substrate in high-fat diet fed mice.

METHODS

Food intake, whole-body metabolism, and motor activity of IL-18 knockout mice were compared to those of wildtype littermates; anorectic effects of intracerebroventricular IL-18 administration were compared between IL-18 receptor knockout, IL-18/IL-18R knockout and wildtype mice.

RESULTS

Chow-reared IL-18 knockout mice were overweight at 6 months of age and then gained excess weight on both low-fat and high-fat diets, ate more high-fat diet, and showed reduced whole-body energy expenditure and increased respiratory exchange ratios. Reductions in energy expenditure of IL-18 knockout mice were seen across fasting vs. feeding conditions, low- vs. high-fat diets, high vs. low levels of physical activity and times of day, suggesting actions on basal metabolic rate. The circadian amplitude of energy expenditure, but not respiratory exchange ratio, food intake, or motor activity, also was blunted in IL-18 knockout mice. Central IL-18 administration reduced high-fat diet intake in wildtype mice, but not in mice lacking the IL-18 receptor.

CONCLUSION

The loss-of-function results support the hypothesis that endogenous IL-18 suppresses appetite and promote energy expenditure and lipid fuel substrate utilization not only during sickness, but also in healthy adults consuming high-fat diets.

The medial habenula: still neglected

The habenula is a small, bilateral brain structure located at the dorsal end of the diencephalon. This structure sends projections to the dopaminergic striatum and receives inputs from the limbic forebrain, making the habenula a unique modulator of cross-talk between these brain regions. Despite strong interest in the habenula during the seventies and eighties (Herkenham and Nauta, 1977; Beckstead, 1979; Beckstead et al., 1979; Herkenham and Nauta, 1979; Caldecott-Hazard et al., 1988), interest waned due to lack of a clearly identifiable functional role. Following Matsumoto and Hikosaka's seminal work on the lateral habenula as a predictor of negative reward in monkeys, the habenula has undergone a resurgence of scientific interest. Matsumoto and Hikosaka demonstrated an increase in habenular neuron firing when monkeys did not receive an expected juice reward (Matsumoto and Hikosaka, 2007). Studies have shown that increased habenular activity inactivates dopaminergic cells in the Rostromedial Tegmental Nucleus (RMTg) through GABAergic mechanisms (Jhou et al., 2009a,b). Additional studies link habenular activity to the regulation of serotonin and norepinephrine, suggesting the habenula modulates multiple brain systems (Strecker and Rosengren, 1989; Amat et al., 2001). These discoveries ushered in a series of new studies that have refocused attention on the lateral habenula and the importance of this small brain structure (Bianco and Wilson, 2009; Jhou et al., 2009a; Matsumoto and Hikosaka, 2009; Sartorius et al., 2010; Savitz et al., 2011). Recently, Geisler and Trimble reviewed this renewed interest in: The Lateral Habenula: No Longer Neglected (Geisler and Trimble, 2008). While the lateral habenula (LHb) has been extensively studied, the anatomically and histochemically distinct medial habenula (MHb) remains largely understudied. This short review argues that the MHb is functionally important and should be studied more aggressively.

Habenula functional resting-state connectivity in pediatric CRPS

The habenula (Hb) is a small brain structure located in the posterior end of the medial dorsal thalamus and through medial (MHb) and lateral (LHb) Hb connections, it acts as a conduit of information between forebrain and brainstem structures. The role of the Hb in pain processing is well documented in animals and recently also in acute experimental pain in humans. However, its function remains unknown in chronic pain disorders. Here, we investigated Hb resting-state functional connectivity (rsFC) in patients with complex regional pain syndrome (CRPS) compared with healthy controls. Twelve pediatric patients with unilateral lower-extremity CRPS (9 females; 10-17 yr) and 12 age- and sex-matched healthy controls provided informed consent to participate in the study. In healthy controls, Hb functional connections largely overlapped with previously described anatomical connections in cortical, subcortical, and brainstem structures. Compared with controls, patients exhibited an overall Hb rsFC reduction with the rest of the brain and, specifically, with the anterior midcingulate cortex, dorsolateral prefrontal cortex, supplementary motor cortex, primary motor cortex, and premotor cortex. Our results suggest that Hb rsFC parallels anatomical Hb connections in the healthy state and that overall Hb rsFC is reduced in patients, particularly connections with forebrain areas. Patients' decreased Hb rsFC to brain regions implicated in motor, affective, cognitive, and pain inhibitory/modulatory processes may contribute to their symptomatology.

Functional integrity of the habenula is necessary for social play behaviour in rats

During post-weaning development, a marked increase in peer-peer interactions is observed in mammals, including humans, which is signified by the abundance of social play behaviour. Social play is highly rewarding, and known to be modulated through monoaminergic neurotransmission. Recently, the habenula has received widespread attention because of its role in the regulation of monoaminergic neurotransmission as well as in a variety of emotional and cognitive functions. Therefore, in the present study, we investigated the involvement of the habenula in social play behaviour. Using the neuronal activity maker c-fos, we showed that the habenula was activated after 24 h of social isolation in adolescent rats, and that a subsequent social play interaction reduced c-fos activity in the medial part of the lateral habenula. This suggested that habenula activity modulated the aversive properties of social isolation, which was alleviated by the positive effects of social play. Furthermore, after functional inactivation of the habenula, using a mixture of the GABA receptor agonists baclofen and muscimol, social play behaviour was markedly reduced, whereby responsiveness to play solicitation was more sensitive to habenula inactivation than play solicitation itself. Together, our data indicate an important role for the habenula in the processing of positive (i.e., social play behaviour) and negative (i.e., social isolation) social information in adolescent rats. Altered habenula function might therefore be related to the social impairments in childhood and adolescent psychiatric disorders such as autism, attention deficit/hyperactivity disorder and early-onset schizophrenia.

Aversive cues fail to activate fos expression in the asymmetric olfactory-habenula pathway of zebrafish

The dorsal habenular nuclei of the zebrafish epithalamus have become a valuable model for studying the development of left-right (L-R) asymmetry and its function in the vertebrate brain. The bilaterally paired dorsal habenulae exhibit striking differences in size, neuroanatomical organization, and molecular properties. They also display differences in their efferent connections with the interpeduncular nucleus (IPN) and in their afferent input, with a subset of mitral cells distributed on both sides of the olfactory bulb innervating only the right habenula. Previous studies have implicated the dorsal habenulae in modulating fear/anxiety responses in juvenile and adult zebrafish. It has been suggested that the asymmetric olfactory-habenula pathway (OB-Ha), revealed by selective labeling from an lhx2a:YFP transgene, mediates fear behaviors elicited by alarm pheromone. Here we show that expression of the fam84b gene demarcates a unique region of the right habenula that is the site of innervation by lhx2a:YFP-labeled olfactory axons. Upon ablation of the parapineal, which normally promotes left habenular identity; the fam84b domain is present in both dorsal habenulae and lhx2a:YFP-labeled olfactory bulb neurons form synapses on the left and the right side. To explore the relevance of the asymmetric olfactory projection and how it might influence habenular function, we tested activation of this pathway using odorants known to evoke behaviors. We find that alarm substance or other aversive odors, and attractive cues, activate fos expression in subsets of cells in the olfactory bulb but not in the lhx2a:YFP expressing population. Moreover, neither alarm pheromone nor chondroitin sulfate elicited fos activation in the dorsal habenulae. The results indicate that L-R asymmetry of the epithalamus sets the directionality of olfactory innervation, however, the lhx2a:YFP OB-Ha pathway does not appear to mediate fear responses to aversive odorants.

Molecular characterization of the subnuclei in rat habenula

The mammalian habenula is involved in regulating the activities of serotonergic and dopaminergic neurons. It consists of the medial and lateral habenulae, with each subregion having distinct neural connectivity. Despite the functional significance, manipulating neural activity in a subset of habenular pathways remains difficult because of the poor availability of molecular markers that delineate the subnuclear structures. Thus, we examined the molecular nature of neurons in the habenular subnuclei by analyzing the gene expressions of neurotransmitter markers. The results showed that different subregions of the medial habenula (MHb) use different combinations of neurotransmitter systems and could be categorized as either exclusively glutamatergic (superior part of MHb), both substance P-ergic and glutamatergic (dorsal region of central part of MHb), or both cholinergic and glutamatergic (inferior part, ventral region of central part, and lateral part of MHb). The superior part of the MHb strongly expressed interleukin-18 and was innervated by noradrenergic fibers. In contrast, the inferior part, ventral region of the central part, and lateral part of the MHb were peculiar in that acetylcholine and glutamate were cotransmitted from the axonal terminals. In contrast, neurons in the lateral habenula (LHb) were almost uniformly glutamatergic. Finally, the expressions of Htr2c and Drd2 seemed complementary in the medial LHb division, whereas they coincided in the lateral division, suggesting that the medial and lateral divisions of LHb show strong heterogeneity with respect to monoamine receptor expression. These analyses clarify molecular differences between subnuclei in the mammalian habenula that support their respective functional implications.

Molecular mechanisms underlying behaviors related to nicotine addiction

Tobacco smoking results in more than 5 million deaths each year and accounts for almost 90% of all deaths from lung cancer. Nicotine, the major reinforcing component of tobacco smoke, acts in the brain through the neuronal nicotinic acetylcholine receptors (nAChRs). The nAChRs are allosterically regulated, ligand-gated ion channels consisting of five membrane-spanning subunits. Twelve mammalian α subunits (α2-α10) and β subunits (β2-β4) have been cloned. The predominant nAChR subtypes in mammalian brain are those containing α4 and β2 subunits (denoted as α4β2* nAChRs). The α4β2* nAChRs mediate many behaviors related to nicotine addiction and are the primary targets for currently approved smoking cessation agents. Considering the large number of nAChR subunits in the brain, it is likely that nAChRs containing subunits in addition to α4 and β2 also play a role in tobacco smoking. Indeed, genetic variation in the CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the α5, α3, and β4 nAChR subunits, respectively, has been shown to increase vulnerability to tobacco dependence and smoking-associated diseases including lung cancer. Moreover, mice in which expression of α5 or β4 subunits has been genetically modified have profoundly altered patterns of nicotine consumption. In addition to the reinforcing properties of nicotine, the effects of nicotine on appetite, attention, and mood are also thought to contribute to establishment and maintenance of the tobacco smoking habit. Here we review recent insights into the behavioral actions of nicotine and the nAChRs subtypes involved, which likely contribute to the development of tobacco dependence in smokers.

Development of novel pharmacotherapeutics for tobacco dependence: progress and future directions

INTRODUCTION

The vast majority of tobacco smokers seeking to quit will relapse within the first month of abstinence. Currently available smoking cessation agents have limited utility in increasing rates of smoking cessation and in some cases there are notable safety concerns related to their use. Hence, there is a pressing need to develop safer and more efficacious smoking cessation medications.

METHODS

Here, we provide an overview of current efforts to develop new pharmacotherapeutic agents to facilitate smoking cessation, identified from ongoing clinical trials and published reports.

RESULTS

Nicotine is considered the major addictive agent in tobacco smoke, and the vast majority of currently available smoking cessation agents act by modulating nicotinic acetylcholine receptor (nAChR) signaling. Accordingly, there is much effort directed toward developing novel small molecule therapeutics and biological agents such as nicotine vaccines for smoking cessation that act by modulating nAChR activity. Our increasing knowledge of the neurobiology of nicotine addiction has revealed new targets for novel smoking cessation therapeutics. Indeed, we highlight many examples of novel small molecule drug development around non-nAChR targets. Finally, there is a growing appreciation that medications already approved for other disease indications could show promise as smoking cessation agents, and we consider examples of such repurposing efforts.

CONCLUSION

Ongoing clinical assessment of potential smoking cessation agents offers the promise of new effective medications. Nevertheless, much of our current knowledge of molecular mechanisms of nicotine addiction derived from preclinical studies has not yet been leveraged for medications development.

Pro-inflammatory interleukin-18 increases Alzheimer's disease-associated amyloid-β production in human neuron-like cells

Background

Alzheimer’s disease (AD) involves increased accumulation of amyloid-β (Aβ) plaques and neurofibrillary tangles as well as neuronal loss in various regions of the neocortex. Neuroinflammation is also present, but its role in AD is not fully understood. We previously showed increased levels of pro-inflammatory cytokine interleukin-18 (IL-18) in different regions of AD brains, where it co-localized with Aβ-plaques, as well as the ability of IL-18 to increase expression of glycogen synthase kinase-3β (GSK-3β) and cyclin dependent kinase 5, involved in hyperphosphorylation of tau-protein. Elevated IL-18 has been detected in several risk conditions for AD, including obesity, type-II diabetes, and cardiovascular diseases as well as in stress.

Methods

We differentiated SH-SY5Y neuroblastoma cells as neuron-like and exposed them to IL-18 for various times. We examined the protein levels of amyloid-β precursor protein (APP) and its processing products, its cleaving enzymes, involved in amyloidogenic processing of APP, and markers of apoptosis.

Results

IL-18 increased protein levels of the β-site APP-cleaving enzyme BACE-1, the N-terminal fragment of presenilin-1 and slightly presenilin enhancer 2, both of which are members of the γ-secretase complex, as well as Fe65, which is a binding protein of the C-terminus of APP and one regulator for GSK-3β. IL-18 also increased APP expression and phosphorylation, which preceded increased BACE-1 levels. Further, IL-18 altered APP processing, increasing Aβ40 production in particular, which was inhibited by IL-18 binding protein. Increased levels of soluble APPβ were detected in culture medium after the IL-18 exposure. IL-18 also increased anti-apoptotic bcl-xL levels, which likely counteracted the minor increase of the pro-apoptotic caspase-3. Lactate dehydrogenase activity in culture medium was unaffected.

Conclusions

The IL-18 induction of BACE-1, APP processing, and Aβ is likely to be linked to stress-associated adaptations in neurons during the course of normal functioning and development. However, in the course of wider changes in the aging brain, and particularly in AD, the effects of heightened or prolonged levels of IL-18 may contribute to the process of AD, including via increased Aβ.

The medial habenula contains a specific nonstellate subtype of astrocyte expressing the ectonucleotidase NTPDase2

ATP-mediated synaptic transmission represents the only transmitter-gated Ca(2+)-entry pathway in neurons of the rodent medial habenula. In addition to direct purinergic receptor-mediated synaptic inputs, the medial habenula contains purinergic systems that modulate synaptic transmission. Purinergic signaling is modulated or terminated by ectonucleotidase, nucleotide-hydrolyzing enzymes of the cell surface. Here we identify the major ectonucleotidase responsible for the hydrolysis of extracellular ATP in the mouse medial habenula as ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2), using immunostaining and enzyme histochemistry. Double labeling experiments reveal that the enzyme is expressed by astrocytes enwrapping the densely packed neurons and also the myelinated fiber bundles of the stria medullaris. NTPDase2 immunoreactivity is absent from the lateral habenula. The analysis of mice expressing enhanced green fluorescent protein under the promoter of glial fibrillary acidic protein revealed that the medial habenula harbors a highly polar type of astrocytes with very long laminar cellular processes, untypical for grey matter astrocytes. Its morphology strongly differs from that of the stellate astrocytes in the adjacent lateral habenula. Our results suggest that the mouse medial habenula contains a specific perineuronal nonstellate subtype of astrocyte that expresses the ectonucleotidase NTPDase2 and is in a strategic position to modulate purinergic transmission in this subnucleus.

Transcriptome analysis of the ependymal barrier during murine neurocysticercosis

BACKGROUND

Central nervous system (CNS) barriers play a pivotal role in the protection and homeostasis of the CNS by enabling the exchange of metabolites while restricting the entry of xenobiotics, blood cells and blood-borne macromolecules. While the blood-brain barrier and blood-cerebrospinal fluid barrier (CSF) control the interface between the blood and CNS, the ependyma acts as a barrier between the CSF and parenchyma, and regulates hydrocephalic pressure and metabolic toxicity. Neurocysticercosis (NCC) is an infection of the CNS caused by the metacestode (larva) of Taenia solium and a major cause of acquired epilepsy worldwide. The common clinical manifestations of NCC are seizures, hydrocephalus and symptoms due to increased intracranial pressure. The majority of the associated pathogenesis is attributed to the immune response against the parasite. The properties of the CNS barriers, including the ependyma, are affected during infection, resulting in disrupted homeostasis and infiltration of leukocytes, which correlates with the pathology and disease symptoms of NCC patients.

RESULTS

In order to characterize the role of the ependymal barrier in the immunopathogenesis of NCC, we isolated ependymal cells using laser capture microdissection from mice infected or mock-infected with the closely related parasite Mesocestoides corti, and analyzed the genes that were differentially expressed using microarray analysis. The expression of 382 genes was altered. Immune response-related genes were verified by real-time RT-PCR. Ingenuity Pathway Analysis (IPA) software was used to analyze the biological significance of the differentially expressed genes, and revealed that genes known to participate in innate immune responses, antigen presentation and leukocyte infiltration were affected along with the genes involved in carbohydrate, lipid and small molecule biochemistry. Further, MHC class II molecules and chemokines, including CCL12, were found to be upregulated at the protein level using immunofluorescence microscopy. This is important, because these molecules are members of the most significant pathways by IPA analyses.

CONCLUSION

Thus, our study indicates that ependymal cells actively express immune mediators and likely contribute to the observed immunopathogenesis during infection. Of particular interest is the major upregulation of antigen presentation pathway-related genes and chemokines/cytokines. This could explain how the ependyma is a prominent source of leukocyte infiltration into ventricles through the disrupted ependymal lining by way of pial vessels present in the internal leptomeninges in murine NCC.

A single intraperitoneal injection of endotoxin in rats induces long-lasting modifications in behavior and brain protein levels of TNF-α and IL-18

Background

Systemic inflammation might cause neuronal damage and sustain neurodegenerative diseases and behavior impairment, with the participation of pro-inflammatory cytokines, like tumor necrosis factor (TNF)-α and interleukin (IL)-18. However, the potential contribution of these cytokines to behavioral impairment in the long-term period has not been fully investigated.

Methods

Wistar rats were treated with a single intraperitoneal injection of LPS (5 mg/kg) or vehicle. After 7 days and 10 months, the animal behavior was evaluated by testing specific cognitive functions, as mnesic, discriminative, and attentional functions, as well as anxiety levels. Contextually, TNF-α and IL-18 protein levels were measured by ELISA in defined brain regions (that is, frontal cortex, hippocampus, striatum, cerebellum, and hypothalamus).

Results

Behavioral testing demonstrated a specific and persistent cognitive impairment characterized by marked deficits in reacting to environment modifications, possibly linked to reduced motivational or attentional deficits. Concomitantly, LPS induced a TNF-α increase in the hippocampus and frontal cortex (from 7 days onward) and cerebellum (only at 10 months). Interestingly, LPS treatment enhanced IL-18 expression in these same areas only at 10 months after injection.

Conclusions

Overall, these results indicate that the chronic neuroinflammatory network elicited by systemic inflammation involves a persistent participation of TNF-α accompanied by a differently regulated contribution of IL-18. This leads to speculation that, though with still unclear mechanisms, both cytokines might take part in long-lasting modifications of brain functions, including behavioral alteration.

Morphologic and immunohistochemical organization of the human habenular complex

The habenular complex (HbCpx) is a phylogenetically conserved brain structure located in the epithalamus of vertebrates. Despite its fundamental role in decision-making processes and the proposed link between habenular dysfunction and neuropsychiatric conditions, little is known about the structural and functional organization of the HbCpx in humans. The goal of this study was thus to provide a first systematic morphologic and immunohistochemical analysis of the human HbCpx to begin dissecting its nuclear and subnuclear organization. Our results confirmed that the human HbCpx is subdivided into medial (MHb) and lateral (LHb) nuclei, each showing a large degree of intranuclear morphologic heterogeneity. Analysis of serially stained sections using a combination of morphologic and immunohistochemical criteria allowed the distinction of five subnuclei in both the MHb and LHb. Overall, the observed subnuclear organization of the MHb in humans resembles the organization of subnuclei in the MHb of rats. The shape, relative size, and intranuclear organization of the LHb, however, show significant differences. The contribution of the LHb to the entire HbCpx is about five times larger in humans than in rats. Noteworthy, a dorsal domain of the LHb that contains afferent myelinated fibers from the stria medullaris and shows GABA-(B) -R(1) immunoreactive cells, appears substantially enlarged in humans when compared to rats. This feature seems to account for a large part of the relative growth in size of the LHb in humans and opens the intriguing possibility of an increased influence of limbic and striatal afferents into the LHb of humans.

Mapping pain activation and connectivity of the human habenula

The habenula, located in the posterior thalamus, is implicated in a wide array of functions. Animal anatomical studies have indicated that the structure receives inputs from a number of brain regions (e.g., frontal areas, hypothalamic, basal ganglia) and sends efferent connections predominantly to the brain stem (e.g., periaqueductal gray, raphe, interpeduncular nucleus). The role of the habenula in pain and its anatomical connectivity are well-documented in animals but not in humans. In this study, for the first time, we show how high-field magnetic resonance imaging can be used to detect habenula activation to noxious heat. Functional maps revealed significant, localized, and bilateral habenula responses. During pain processing, functional connectivity analysis demonstrated significant functional correlations between the habenula and the periaqueductal gray and putamen. Probabilistic tractography was used to assess connectivity of afferent (e.g., putamen) and efferent (e.g., periaqueductal gray) pathways previously reported in animals. We believe that this study is the first report of habenula activation by experimental pain in humans. Since the habenula connects forebrain structures with brain stem structures, we suggest that the findings have important implications for understanding sensory and emotional processing in the brain during both acute and chronic pain.

Expression and localization of IL-18 in the hypothalamic-pituitary-ovarian axis of non-pregnant, pregnant, and abortive rats

Cytokines present in the reproductive system play an important role both in the modulation of immune responses to infectious challenge and in the establishment and maintenance of pregnancy. Interleukin 18 (IL-18) has been regarded as an important regulator of innate and acquired immune response, but its expression and distribution in the hypothalamic-pituitary-ovarian axis remain unclear. In this paper, the expression and distribution of IL-18 in non-pregnant, pregnant, and early abortive rats were examined using an ultra-sensitive immunohistochemical streptavidin-peroxidase method, enzyme-linked immunosorbent assay, and reverse transcription-polymerase chain reaction. The results showed that IL-18 expression in the pituitary, in follicular ovaries, and in the corpus luteum of abortive rats were significantly lower than that of pregnant and non-pregnant rats. However, the staining of IL-18 in the hypothalamus, interstitial glands of the ovary, and uterus of abortive rats was strikingly stronger than those of the non-pregnant ones. IL-18 mRNA expression in rat uterus was detected in all groups, whereas IL-18 mRNA content in abortive rat uterus was significantly higher than in normal pregnant rats. Further, IL-18 in the peripheral blood serum of abortive rats was significantly lower than in same-period normal pregnant rats. The differential expression of IL-18 in early abortion suggests that IL-18 may be related to the underlying mechanisms of abortion.

Interleukin-18 expression in pig salivary glands and salivary content changes during acute immobilization stress

Interleukin-18 (IL-18) has recently been considered a promising marker of stress responses. In this study, to evaluate IL-18 as a noninvasive stress marker in pigs, we investigated the expression of IL-18 in porcine salivary glands and its presence in saliva, and its dynamics during acute immobilization stress in pigs. IL-18 mRNA was detected robustly in the pig salivary glands by RT-PCR. Immunohistochemical staining of IL-18 protein expression revealed that the expression patterns differed among the three types of salivary glands (parotid, submandibular, and sublingual gland). IL-18 was also detected in pig saliva by ELISA, and a diurnal rhythm with a peak in the afternoon was observed. The IL-18 concentration in saliva was significantly increased during a 60-min acute immobilization stress in thirteen 5-month-old pigs. These results are the first evidence of a stress-related change of IL-18 in pig saliva. Salivary IL-18 may thus become a useful noninvasive marker for the evaluation of acute stress in pigs.

The habenula: from stress evasion to value-based decision-making

Surviving in a world with hidden rewards and dangers requires choosing the appropriate behaviours. Recent discoveries indicate that the habenula plays a prominent part in such behavioural choice through its effects on neuromodulator systems, in particular the dopamine and serotonin systems. By inhibiting dopamine-releasing neurons, habenula activation leads to the suppression of motor behaviour when an animal fails to obtain a reward or anticipates an aversive outcome. Moreover, the habenula is involved in behavioural responses to pain, stress, anxiety, sleep and reward, and its dysfunction is associated with depression, schizophrenia and drug-induced psychosis. As a highly conserved structure in the brain, the habenula provides a fundamental mechanism for both survival and decision-making.

Constitutive and LPS-regulated expression of interleukin-18 receptor beta variants in the mouse brain

Interleukin (IL)-18 is a pro-inflammatory cytokine that is proposed to be involved in physiological as well as pathological conditions in the adult brain. IL-18 acts through a heterodimer receptor comprised of a subunit alpha (IL-18Rα) required for binding, and a subunit beta (IL-18Rβ) necessary for activation of signal transduction. We recently demonstrated that the canonical alpha binding chain, and its putative decoy isoform, are expressed in the mouse central nervous system (CNS) suggesting that IL-18 may act on the brain by directly binding its receptor. Considering that the co-expression of the beta chain seems to be required to generate a functional receptor and, a short variant of this chain has been described in rat and human brain, in this study we have extended our investigation to IL-18Rβ in mouse. Using a multi-methodological approach we found that: (1) a short splice variant of IL-18Rβ was expressed in the CNS even if at lower levels compared to the full-length IL-18Rβ variants, (2) the canonical IL-18Rβ is expressed in the CNS particularly in areas and nuclei belonging to the limbic system as previously observed for IL-18Rα and finally (3) we have also demonstrated that both IL-18Rβ isoforms are up-regulated in different brain areas three hours after a single lipopolysaccharide (LPS) injection suggesting that IL-18Rβ in the CNS might be involved in mediating the endocrine and behavioral effects of LPS. Our data highlight the considerable complexity of the IL-18 regulation activity in the mouse brain and further support an important central role for IL-18.