Stimulation of chemokine CXC receptor 4 induces synaptic depression of evoked parallel fibers inputs onto Purkinje neurons in mouse cerebellum

Cellular, synaptic, and network effects of chemokines in the central nervous system and their implications to behavior

Accumulating evidence highlights chemokines as key mediators of the bidirectional crosstalk between neurons and glial cells aimed at preserving brain functioning. The multifaceted role of these immune proteins in the CNS is mirrored by the complexity of the mechanisms underlying its biological function, including biased signaling. Neurons, only in concert with glial cells, are essential players in the modulation of brain homeostatic functions. Yet, attempts to dissect these complex multilevel mechanisms underlying coordination are still lacking. Therefore, the purpose of this review is to summarize the current knowledge about mechanisms underlying chemokine regulation of neuron-glia crosstalk linking molecular, cellular, network, and behavioral levels. Following a brief description of molecular mechanisms by which chemokines interact with their receptors and then summarizing cellular patterns of chemokine expression in the CNS, we next delve into the sequence and mechanisms of chemokine-regulated neuron-glia communication in the context of neuroprotection. We then define the interactions with other neurotransmitters, neuromodulators, and gliotransmitters. Finally, we describe their fine-tuning on the network level and the behavioral relevance of their modulation. We believe that a better understanding of the sequence and nature of events that drive neuro-glial communication holds promise for the development of new treatment strategies that could, in a context- and time-dependent manner, modulate the action of specific chemokines to promote brain repair and reduce the neurological impairment.

Temporal Lobe Epilepsy: What do we understand about protein alterations?

During neuronal diseases, neuronal proteins get disturbed due to changes in the connections of neurons. As a result, neuronal proteins get disturbed and cause epilepsy. At the genetic level, many mutations may take place in proteins like axon guidance proteins, leucine-rich glioma inactivated 1 protein, microtubular protein, pore-forming, chromatin remodeling, and chemokine proteins which may lead toward temporal lobe epilepsy. These proteins can be targeted in the future for the treatment purpose of epilepsy. Novel avenues can be developed for therapeutic interventions by these new insights.

Interactions of neuroimmune signaling and glutamate plasticity in addiction

Chronic use of drugs of abuse affects neuroimmune signaling; however, there are still many open questions regarding the interactions between neuroimmune mechanisms and substance use disorders (SUDs). Further, chronic use of drugs of abuse can induce glutamatergic changes in the brain, but the relationship between the glutamate system and neuroimmune signaling in addiction is not well understood. Therefore, the purpose of this review is to bring into focus the role of neuroimmune signaling and its interactions with the glutamate system following chronic drug use, and how this may guide pharmacotherapeutic treatment strategies for SUDs. In this review, we first describe neuroimmune mechanisms that may be linked to aberrant glutamate signaling in addiction. We focus specifically on the nuclear factor-kappa B (NF-κB) pathway, a potentially important neuroimmune mechanism that may be a key player in driving drug-seeking behavior. We highlight the importance of astroglial-microglial crosstalk, and how this interacts with known glutamatergic dysregulations in addiction. Then, we describe the importance of studying non-neuronal cells with unprecedented precision because understanding structure-function relationships in these cells is critical in understanding their role in addiction neurobiology. Here we propose a working model of neuroimmune-glutamate interactions that underlie drug use motivation, which we argue may aid strategies for small molecule drug development to treat substance use disorders. Together, the synthesis of this review shows that interactions between glutamate and neuroimmune signaling may play an important and understudied role in addiction processes and may be critical in developing more efficacious pharmacotherapies to treat SUDs.

Enduring neuroimmunological consequences of developmental experiences: From vulnerability to resilience

The immune system is crucial for normal neuronal development and function (neuroimmune system). Both immune and neuronal systems undergo significant postnatal development and are sensitive to developmental programming by environmental experiences. Negative experiences from infection to psychological stress at a range of different time points (in utero to adolescence) can permanently alter the function of the neuroimmune system: given its prominent role in normal brain development and function this dysregulation may increase vulnerability to psychiatric illness. In contrast, positive experiences such as exercise and environmental enrichment are protective and can promote resilience, even restoring the detrimental effects of negative experiences on the neuroimmune system. This suggests the neuroimmune system is a viable therapeutic target for treatment and prevention of psychiatric illnesses, especially those related to stress. In this review we will summarise the main cells, molecules and functions of the immune system in general and with specific reference to central nervous system development and function. We will then discuss the effects of negative and positive environmental experiences, especially during development, in programming the long-term functioning of the neuroimmune system. Finally, we will review the sparse but growing literature on sex differences in neuroimmune development and response to environmental experiences.

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The immune system is essential for development and function of the central nervous system (neuroimmune system)

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Environmental experiences can permanently alter neuroimmune function and associated brain development

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Altered neuroimmune function following negative developmental experiences may play a role in psychiatric illnesses

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Positive experiences can promote resilience and rescue the effects of negative experiences on the neuroimmune system

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The neuroimmune system is therefore a viable therapeutic target for preventing and treating psychiatric illnesses

Multi-omics analysis suggests enhanced epileptogenesis in the Cornu Ammonis 3 of the pilocarpine model of mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is a chronic neurological disorder characterized by the occurrence of seizures, and histopathological abnormalities in the mesial temporal lobe structures, mainly hippocampal sclerosis (HS). We used a multi-omics approach to determine the profile of transcript and protein expression in the dorsal and ventral hippocampal dentate gyrus (DG) and Cornu Ammonis 3 (CA3) in an animal model of MTLE induced by pilocarpine. We performed label-free proteomics and RNAseq from laser-microdissected tissue isolated from pilocarpine-induced Wistar rats. We divided the DG and CA3 into dorsal and ventral areas and analyzed them separately. We performed a data integration analysis and evaluated enriched signaling pathways, as well as the integrated networks generated based on the gene ontology processes. Our results indicate differences in the transcriptomic and proteomic profiles among the DG and the CA3 subfields of the hippocampus. Moreover, our data suggest that epileptogenesis is enhanced in the CA3 region when compared to the DG, with most abnormalities in transcript and protein levels occurring in the CA3. Furthermore, our results show that the epileptogenesis in the pilocarpine model involves predominantly abnormal regulation of excitatory neuronal mechanisms mediated by N-methyl D-aspartate (NMDA) receptors, changes in the serotonin signaling, and neuronal activity controlled by calcium/calmodulin-dependent protein kinase (CaMK) regulation and leucine-rich repeat kinase 2 (LRRK2)/WNT signaling pathways.

Neuroimmunological effects of early life experiences

Exposure to adverse experiences during development increases the risk of psychiatric illness later in life. Growing evidence suggests a role for the neuroimmune system in this relationship. There is now substantial evidence that the immune system is critical for normal brain development and behaviour, and responds to environmental perturbations experienced early in life. Severe or chronic stress results in dysregulated neuroimmune function, concomitant with abnormal brain morphology and function. Positive experiences including environmental enrichment and exercise exert the opposite effect, promoting normal brain and immune function even in the face of early life stress. The neuroimmune system may therefore provide a viable target for prevention and treatment of psychiatric illness. This review will briefly summarise the neuroimmune system in brain development and function, and review the effects of stress and positive environmental experiences during development on neuroimmune function. There are also significant sex differences in how the neuroimmune system responds to environmental experiences early in life, which we will briefly review.

Chemokines: Key Molecules that Orchestrate Communication among Neurons, Microglia and Astrocytes to Preserve Brain Function

In the CNS, chemokines and chemokine receptors are involved in pleiotropic physiological and pathological activities. Several evidences demonstrated that chemokine signaling in the CNS plays key homeostatic roles and, being expressed on neurons, glia and endothelial cells, chemokines mediate the bidirectional cross-talk among parenchymal cells. An efficient communication between neurons and glia is crucial to establish and maintain a healthy brain environment which ensures normal functionality. Glial cells behave as active sensors of environmental changes induced by neuronal activity or detrimental insults, supporting and exerting neuroprotective activities. In this review we summarize the evidence that chemokines (CXCL12, CX3CL1, CXCL16 and CCL2) modulate neuroprotective processes upon different noxious stimuli and participate to orchestrate neurons-microglia-astrocytes action to preserve and limit brain damage. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

The Role of Chemokines in the Pathophysiology of Major Depressive Disorder

Major depressive disorder (MDD) is a debilitating condition, whose high prevalence and multisymptomatic nature set its standing as a leading contributor to global disability. To better understand this psychiatric disease, various pathophysiological mechanisms have been proposed, including changes in monoaminergic neurotransmission, imbalance of excitatory and inhibitory signaling in the brain, hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, and abnormalities in normal neurogenesis. While previous findings led to a deeper understanding of the disease, the pathogenesis of MDD has not yet been elucidated. Accumulating evidence has confirmed the association between chronic inflammation and MDD, which is manifested by increased levels of the C-reactive protein, as well as pro-inflammatory cytokines, such as Interleukin 1 beta, Interleukin 6, and the Tumor necrosis factor alpha. Furthermore, recent findings have implicated a related family of cytokines with chemotactic properties, known collectively as chemokines, in many neuroimmune processes relevant to psychiatric disorders. Chemokines are small (8-12 kDa) chemotactic cytokines, which are known to play roles in direct chemotaxis induction, leukocyte and macrophage migration, and inflammatory response propagation. The inflammatory chemokines possess the ability to induce migration of immune cells to the infection site, whereas their homeostatic chemokine counterparts are responsible for recruiting cells for their repair and maintenance. To further support the role of chemokines as central elements to healthy bodily function, recent studies suggest that these proteins demonstrate novel, brain-specific mechanisms including the modulation of neuroendocrine functions, chemotaxis, cell adhesion, and neuroinflammation. Elevated levels of chemokines in patient-derived serum have been detected in individuals diagnosed with major depressive disorder, bipolar disorder, and schizophrenia. Furthermore, despite the considerable heterogeneity of experimental samples and methodologies, existing biomarker studies have clearly demonstrated the important role of chemokines in the pathophysiology of psychiatric disorders. The purpose of this review is to summarize the data from contemporary experimental and clinical studies, and to evaluate available evidence for the role of chemokines in the central nervous system (CNS) under physiological and pathophysiological conditions. In light of recent results, chemokines could be considered as possible peripheral markers of psychiatric disorders, and/or targets for treating depressive disorders.

Systemic inflammation induces anxiety disorder through CXCL12/CXCR4 pathway

It is evidenced that inflammation is involved in the pathogenesis of anxiety disorder, as well as the dysfunction of glutamate neurotransmission in the central nervous system (CNS). Chemokine CXCL12 has been reported taking part in the regulation of neurotransmitter release, however, the roles of CXCL12 in the development of anxiety are still unclear. In this study, we found that intraperitoneal (i.p) injection of lipopolysaccharide (LPS) induced anxiety-like behaviors in adult mice as measured by elevated plus-maze test (EPM) and open field test (OFT). Astrocytes were responsible for CXCL12 induction upon LPS challenge in hippocampus and amygdala, and microinjection of CXCL12 into amygdala induced mice anxiety-like behaviors. AMD3100, which is an antagonist for CXCL12 receptor CXCR4, prevented the anxiety behaviors induced by microinjection of CXCL12 into amygdala as well as injection i.p of LPS. Knockdown of CXCR4 expression in neurons using short hairpin RNAs (shRNAs) significantly blocked anxiety behaviors mediated by CXCL12 i.c injection. Furthermore, AMD3100 or shCXCR4 prevented the impairment of nesting ability induced by CXCL12 in mice. Whole-cell patch-clamp recordings in the neurons of basolateral amygdala (BLA) revealed that CXCL12 enhanced glutamatergic transmission by increasing sEPSC frequency in the amygdala. AMD3100 inhibited the excitatory glutamatergic neural transmission and involved in the development of anxiety through CXCR4. These findings provide direct evidence that alterations of CXCL12 in BLA play critical roles in the development of anxiety induced by systemic inflammation and that CXCR4 may be a potential therapeutic target for inflammation-induced anxiety.

CXCL12 impairs the acquisition and extinction of auditory fear conditioning in rats via crosstalk with GABAergic system

OBJECTIVE

Chemokines, such as CXCL12, are signaling molecules playing an important role in immune regulations. Chemokine upsurge has also been associated with neuroinflammatory conditions characterized with cognitive impairments. Recently, some in-vitro data suggests that CXCL12 is a potential neuromodulator and interacts with GABAergic system, but, so far, whether these effects translate into alterations in neural and behavioral functions has not been investigated.

METHODS

In the present study, we used auditory fear conditioning as a model to define the contribution of CXCL12/CXCR4 on fear-related cognitive disorders. We microinjected different dosages of CXCL12 into the bilateral amygdala of rats to investigate their behavioral effects on the acquisition and extinction of conditioned fear memory. Moreover, we pretreated the rats with the selective CXCR4 receptor antagonist (AMD3100), GABAA antagonist (bicuculline) and GABAB antagonist (CGP55845) to examine whether the CXCL12 induced changes could be reversed.

RESULTS

We found that intra-amygdala infusion of CXCL12 impaired the acquisition and extinction of conditioned fear response. Pretreatment with AMD3100, rescued the CXCL12 induced impairments, indicating that CXCL12 produced the effects by activating CXCR4 receptors. Furthermore, both bicuculline and CGP55845 prevented CXCL12 from impairing the rat's ability of conditioned learning, indicating a crosstalk between CXCL12/CXCR4 and GABAergic system.

CONCLUSION

Our data suggest that the chemokine CXCL12 is able to regulate neurotransmitter mechanisms involved in associative learning functions, and the effect of GABAergic agents on CXCL12/CXCR4 may be new therapeutic potentials for neuroinflammatory diseases.

CXCL12/CXCR4 signaling pathway regulates cochlear development in neonatal mice

Chemotactic cytokines (chemokines) are a highly conserved class of secreted signaling molecules that are important in various cellular processes. CXC chemokine ligand 12 (CXCL12) and its receptor, CXC chemokine receptor 4 (CXCR4) have been previously reported to be crucial for the establishment of neural networks in different neuronal systems. However, it is unclear whether the CXCL12/CXCR4 signaling pathway regulates the development of the cochlea. The current study investigated the effects of the CXCL12/CXCR4 signaling pathway on cochlear development in neonatal mice. The expression levels of CXCL12 and CXCR4 were detected using immunofluorescence, reverse transcription‑quantitative polymerase chain reaction and western blot analysis demonstrating that CXCL12 and CXCR4 expression were significantly increased during cochlear development in neonatal mice. Treatment of spiral ganglion neurons with CXCL12 significantly decreased the protein expression levels of caspase‑3 and cleaved caspase‑3, indicating that CXCL12/CXCR4 signaling increased cell survival of spiral ganglion neurons. Furthermore, CXCL12 treatment significantly increased the number and length of neurites extending from spiral ganglion neurons. By contrast, the in vitro effects of CXCL12 were significantly abrogated by AMD100, a CXCR4 antagonist. Additionally, inhibiting CXCL12/CXCR4 signaling in neonatal mice significantly reduced the cell number and altered the morphology of spiral ganglion neurons in vivo. Thus, the present study indicates that the CXCL12/CXCR4 signaling pathway is important during the development of cochleae in neonatal mice.

Chemokines and the hippocampus: a new perspective on hippocampal plasticity and vulnerability

The hippocampus is critical for several aspects of learning and memory and is unique among other cortical regions in structure, function and the potential for plasticity. This remarkable region recapitulates development throughout the lifespan with enduring neurogenesis and well-characterized plasticity. The structure and traits of the hippocampus that distinguish it from other brain regions, however, may be the same reasons that this important brain region is particularly vulnerable to insult and injury. The immune system within the brain responds to insult and injury, and the hippocampus and the immune system are extensively interconnected. Immune signaling molecules, cytokines and chemokines (chemotactic cytokines), are well known for their functions during insult or injury. They are also increasingly implicated in normal hippocampal neurogenesis (e.g., CXCR4 on newborn neurons), cellular plasticity (e.g., interleukin-6 in LTP maintenance), and learning and memory (e.g., interleukin-1β in fear conditioning). We provide evidence from the small but growing literature that neuroimmune interactions and immune signaling molecules, especially chemokines, may be a primary underlying mechanism for the coexistence of plasticity and vulnerability within the hippocampus. We also highlight the evidence that the hippocampus exhibits a remarkable resilience in response to diverse environmental events (e.g., enrichment, exercise), which all may converge onto common neuroimmune mechanisms.

Tetramethylpyrazine (TMP) protects cerebral neurocytes and inhibits glioma by down regulating chemokine receptor CXCR4 expression

The survival in patients with malignant gliomas still remains limited and novel treatment strategies are urgently needed. Tetramethylpyrazine (TMP) extracted from the Chinese herb Chuanxiong, has been suggested to have a therapeutic potential towards glioma primarily through its neural protection activity. However, the exact mechanisms correlating TMP's antitumor function and neural protection have not been yet elucidated. Thus, this study aimed to investigate TMP's molecular target in tumor inhibition and neural protection. The primary cultured cerebral neurocytes were treated with 100 μM TMP for 14 days in vitro. We found TMP can effectively promote neurons survival, compared to controls. TMP effectively inhibits H2O2-induced rise of [Ca(2+)]i and glutamate releasing in cerebral neurocytes, compared to controls. In addition, we verify previous results that TMP significantly decreases the migration and proliferation of C6 glioma cells. Using glioma-neuronal co-culturing system, we further confirm TMP bioactivity in inhibition of glioma cells and protection of cerebral neurocytes. More importantly, our study demonstrates that the expression of chemokine receptor, CXCR4, which plays a key role in tumor development and various neurodegenerative diseases, is significantly decreased in both cerebral neurocytes and C6 glioma cells with TMP treatment, cultured alone or co-cultured. Compared with CXCR4 antagonist, AMD3100, TMP is more effective on glioma inhibition and neural protection. Glutamate concentration in medium of co-culturing system was lower after treatment with 100 μM TMP. Therefore, our findings suggest that TMP-mediated suppression of C6 gliomas and neural protection involves inhibition of CXCR4 expression. Thus, this study provides new insights into TMP's therapeutic potential in the treatment of malignant gliomas.

Towards Alzheimer's root cause: ECSIT as an integrating hub between oxidative stress, inflammation and mitochondrial dysfunction. Hypothetical role of the adapter protein ECSIT in familial and sporadic Alzheimer's disease pathogenesis

Here we postulate that the adapter protein evolutionarily conserved signalling intermediate in Toll pathway (ECSIT) might act as a molecular sensor in the pathogenesis of Alzheimer's disease (AD). Based on the analysis of our AD-associated protein interaction network, ECSIT emerges as an integrating signalling hub that ascertains cell homeostasis by the specific activation of protective molecular mechanisms in response to signals of amyloid-beta or oxidative damage. This converges into a complex cascade of patho-physiological processes. A failure to repair would generate severe mitochondrial damage and ultimately activate pro-apoptotic mechanisms, promoting synaptic dysfunction and neuronal death. Further support for our hypothesis is provided by increasing evidence of mitochondrial dysfunction in the disease etiology. Our model integrates seemingly controversial hypotheses for familial and sporadic forms of AD and envisions ECSIT as a biomarker to guide future therapies to halt or prevent AD.

Exploring the genomic basis of pharmacoresistance in epilepsy: an integrative analysis of large-scale gene expression profiling studies on brain tissue from epilepsy surgery

Some patients with pharmacoresistant epilepsy undergo therapeutic resection of the epileptic focus. At least 12 large-scale microarray studies on brain tissue from epilepsy surgery have been published over the last 10 years, but they have failed to make a significant impact upon our understanding of pharmacoresistance, because (1) doubts have been raised about their reproducibility, (2) only a small number of the gene expression changes found in each microarray study have been independently validated and (3) the results of different studies have not been integrated to give a coherent picture of the genetic changes involved in epilepsy pharmacoresistance. To overcome these limitations, we (1) assessed the reproducibility of the microarray studies by calculating the overlap between lists of differentially regulated genes from pairs of microarray studies and determining if this was greater than would be expected by chance alone, (2) used an inter-study cross-validation technique to simultaneously verify the expression changes of large numbers of genes and (3) used the combined results of the different microarray studies to perform an integrative analysis based on enriched gene ontology terms, networks and pathways. Using this approach, we respectively (1) demonstrate that there are statistically significant overlaps between the gene expression changes in different publications, (2) verify the differential expression of 233 genes and (3) identify the biological processes, networks and genes likely to be most important in the development of pharmacoresistant epilepsy. Our analysis provides novel biologically plausible candidate genes and pathways which warrant further investigation to assess their causal relevance.

Regulation of neuronal ferritin heavy chain, a new player in opiate-induced chemokine dysfunction

The heavy chain subunit of ferritin (FHC), a ubiquitous protein best known for its iron-sequestering activity as part of the ferritin complex, has recently been described as a novel inhibitor of signaling through the chemokine receptor CXCR4. Levels of FHC as well as its effects on CXCR4 activation increase in cortical neurons exposed to mu-opioid receptor agonists such as morphine, an effect likely specific to neurons. Major actions of CXCR4 signaling in the mature brain include a promotion of neurogenesis, activation of pro-survival signals, and modulation of excitotoxic pathways; thus, FHC up-regulation may contribute to the neuronal dysfunction often associated with opiate drug abuse. This review summarizes our knowledge of neuronal CXCR4 function, its regulation by opiates and the role of FHC in this process, and known mechanisms controlling FHC production. We speculate on the mechanism involved in FHC regulation by opiates and offer FHC as a new target in opioid-induced neuropathology.

Interactions between chemokine and mu-opioid receptors: anatomical findings and electrophysiological studies in the rat periaqueductal grey

Opioids have immunomodulatory functions and may alter susceptibility to immune disorders. Behavioral studies also indicate that chemokines, molecules expressed by immune cells, block opioid-induced analgesia in the periaqueductal grey (PAG). Bi-directional heterologous desensitization of opioid and chemokine receptors has been described in cell systems. We report the anatomical and functional interactions of chemokine receptors with the mu-opioid receptor (MOR) in the rat brain. The chemokine receptors, CXCR4 and CX3CR1, as well as their chemokine substrates, CXCL12 and CX3CL1, are widely expressed in the central nervous system (CNS). Immunohistochemical techniques were utilized to investigate MOR-CXCR4 and MOR-CX3CR1 receptor colocalization in multiple brain areas. Our results demonstrate co-expression of these receptors on individual neurons in several regions including cingulate cortex, hippocampus, and PAG, suggesting functional receptor interactions. Whole-cell patch-clamp recordings of PAG neurons in a rat brain slice preparation were used to examine morphine or chemokine (CXCL12, CX3CL1) effects alone, or in combination on neuronal membrane properties. Morphine (10 μM) hyperpolarized and reduced input resistance of PAG neurons. CXCL12 and CX3CL1 (10 nM) had no impact on either parameter. In the presence of CXCL12, morphine's electrophysiological effects were blocked in all neurons examined, whereas with CX3CL1, morphine's effects were blocked in 57% of neurons studied. The data provide electrophysiological evidence for MOR-CXCR4 and MOR-CX3CR1 heterologous desensitization in the PAG at the single-cell level. These interactions may contribute to the limited utility of opioid analgesics for inflammatory pain treatment and supports chemokines as neuromodulators.

CXCR4-mediated glutamate exocytosis from astrocytes

The role of astrocytes as structural and metabolic support for neurons is known since the beginning of the last century. Because of their strategic localization between neurons and capillaries they can monitor and control the level of synaptic activity by providing energetic metabolites to neurons and remove excess of neurotransmitters. During the last two decades number of papers further established that the astrocytic plasma-membrane G-protein coupled receptors (GPCR) can sense external inputs (such as the spillover of neurotransmitters) and transduce them as intracellular calcium elevations and release of chemical transmitters such as glutamate. The chemokine CXCR4 receptor is a GPCR widely expressed on glial cells (especially astrocytes and microglia). Activation of the astrocytic CXCR4 by its natural ligand CXCL12 (or SDF1 alpha) results in a long chain of intracellular and extracellular events (including the release of the pro-inflammatory cytokine TNFalpha and prostanglandins) leading to glutamate release. The emerging role of CXCR4-CXCL12 signalling axis in brain physiology came from the recent observation that glutamate in astrocytes is released via a regulated exocytosis process and occurs with a relatively fast time-scale, in the order of few hundred milliseconds. Taking into account that astrocytes are electrically non-excitable and thus exocytosis rely only on a signalling pathway that involves the release Ca(2+) from the internal stores, these results suggested a close relationship between sites of Ca(2+) release and those of fusion events. Indeed, a recent observation describes structural sub-membrane microdomains where fast ER-dependent calcium elevations occur in spatial and temporal correlation with fusion events.

The emerging role for chemokines in epilepsy

Epilepsy has been considered mainly a neuronal disease, without much attention to non-neuronal cells. In recent years growing evidence suggest that astrocytes, microglia, blood leukocytes and blood-brain barrier breakdown are involved in the pathogenesis of epilepsy. In particular, leukocyte-endothelium interactions and eventually subsequent leukocyte recruitment in the brain parenchyma seem to represent key players in the epileptogenic cascade. Chemokines are chemotactic factors controlling leukocyte migration under physiological and pathological conditions. In the light of recent advances in our understanding of the role of inflammation mechanisms in the pathogenesis of epilepsy, pro-inflammatory chemokines may play a critical role in epileptogenesis.

CX3CL1-induced modulation at CA1 synapses reveals multiple mechanisms of EPSC modulation involving adenosine receptor subtypes

We characterized the role of adenosine receptor (AR) subtypes in the modulation of glutamatergic neurotransmission by the chemokine fractalkine (CX3CL1) in mouse hippocampal CA1 neurons. CX(3)CL1 causes a reversible depression of excitatory postsynaptic current (EPSC), which is abolished by the A(3)R antagonist MRS1523, but not by A(1)R (DPCPX) or A(2A)R (SCH58261) antagonists. Consistently, CX3CL1-induced EPSC depression is absent in slices from A(3)R(-/-) but not A(1)R(-/-) or A(2A)R(-/-) mice. Further, A(3)R stimulation causes similar EPSC depression. In cultured neurons, CX3CL1-induced depression of AMPA current shows A(1)R-A(3)R pharmacology. We conclude that glutamatergic depression induced by released adenosine requires the stimulation of different ARs.

SDF-1alpha/CXCL12 enhances GABA and glutamate synaptic activity at serotonin neurons in the rat dorsal raphe nucleus

The serotonin (5-hydroxytryptamine; 5-HT) system has a well-characterized role in depression. Recent reports describe comorbidities of mood-immune disorders, suggesting an immunological component may contribute to the pathogenesis of depression as well. Chemokines, immune proteins which mediate leukocyte trafficking, and their receptors are widely distributed in the brain, mediate neuronal patterning, and modulate various neuropathologies. The purpose of this study was to investigate the neuroanatomical relationship and functional impact of the chemokine stromal cell-derived factor-1alpha/CXCL12 and its receptor, CXCR4, on the serotonin dorsal raphe nucleus (DRN) system in the rat using anatomical and electrophysiological techniques. Immunohistochemical analysis indicates that over 70% of 5-HT neurons colocalize with CXCL12 and CXCR4. At a subcellular level, CXCL12 localizes throughout the cytoplasm whereas CXCR4 concentrates to the outer membrane and processes of 5-HT neurons. CXCL12 and CXCR4 also colocalize on individual DRN cells. Furthermore, electrophysiological studies demonstrate CXCL12 depolarization of 5-HT neurons indirectly via glutamate synaptic inputs. CXCL12 also enhances the frequency of spontaneous inhibitory and excitatory postsynaptic currents (sIPSC and sEPSC). CXCL12 concentration-dependently increases evoked IPSC amplitude and decreases evoked IPSC paired-pulse ratio selectively in 5-HT neurons, effects blocked by the CXCR4 antagonist AMD3100. These data indicate presynaptic enhancement of GABA and glutamate release at 5-HT DRN neurons by CXCL12. Immunohistochemical analysis further shows CXCR4 localization to DRN GABA neurons, providing an anatomical basis for CXCL12 effects on GABA release. Thus, CXCL12 indirectly modulates 5-HT neurotransmission via GABA and glutamate synaptic afferents. Future therapies targeting CXCL12 and other chemokines may treat serotonin related mood disorders, particularly depression experienced by immune-compromised individuals.

Functional diversity of SDF-1 splicing variants

SDF-1 is ubiquitously expressed in vertebrate tissues in a constitutive manner. It performs an essential role in cell migration and proliferation as well as participates in tissue-specific physiological processes such as neuromodulation. It is also involved in many pathological processes including: HIV infection, metastatic malignancy, chronic inflammatory disorders and benign proliferative diseases. SDF-1 is mostly regulated at the splicing, and not transcriptional level. Different splicing variants share agonist potency to their cognate receptor, CXCR4, but are characterized by distinct properties. SDF-1alpha is the predominant isoform found in all organs, but undergoes rapid proteolysis in blood. SDF-1beta is more resistant to blood-dependent degradation, stimulates angiogenesis and is present in highly vascularized organs such as: the liver, spleen and kidneys. In contrast, SDF-1gamma is located in very active, less vascularized organs susceptible to infarction such as the heart and the brain. The understanding of the functional diversity of the different splicing variants will help in developing therapeutic strategies.

Chemokines and neuromodulation

Chemokines are not only mediators of the immune system and expressed in inflammatory situations. They are also constitutively expressed in the brain in both glial cells and neurons. Several recent evidence suggest that they can have a neurotransmitter/neuromodulatory role on brain functions similar to several neuropeptides reported so far. The aim of this short review is to illustrate that point using two chemokine systems, SDF-1/CXCL12 and its receptor CXCR4 and MCP-1/CCL2 and its receptor CCR2.

Multiple roles of chemokine CXCL12 in the central nervous system: a migration from immunology to neurobiology

Chemotactic cytokines (chemokines) have been traditionally defined as small (10-14kDa) secreted leukocyte chemoattractants. However, chemokines and their cognate receptors are constitutively expressed in the central nervous system (CNS) where immune activities are under stringent control. Why and how the CNS uses the chemokine system to carry out its complex physiological functions has intrigued neurobiologists. Here, we focus on chemokine CXCL12 and its receptor CXCR4 that have been widely characterized in peripheral tissues and delineate their main functions in the CNS. Extensive evidence supports CXCL12 as a key regulator for early development of the CNS. CXCR4 signaling is required for the migration of neuronal precursors, axon guidance/pathfinding and maintenance of neural progenitor cells (NPCs). In the mature CNS, CXCL12 modulates neurotransmission, neurotoxicity and neuroglial interactions. Thus, chemokines represent an inherent system that helps establish and maintain CNS homeostasis. In addition, growing evidence implicates altered expression of CXCL12 and CXCR4 in the pathogenesis of CNS disorders such as HIV-associated encephalopathy, brain tumor, stroke and multiple sclerosis (MS), making them the plausible targets for future pharmacological intervention.

Chemokines: a new class of neuromodulator?

Chemokines are not only found in the immune system or expressed in inflammatory conditions: they are constitutively present in the brain in both glial cells and neurons. Recently, the possibility has been raised that they might act as neurotransmitters or neuromodulators. Although the evidence is incomplete, emerging data show that chemokines have several of the characteristics that define neurotransmitters. Moreover, their physiological actions resemble those of neuromodulators in the sense that chemokines usually have few effects by themselves in basal conditions, but modify the induced release of neurotransmitters or neuropeptides. These findings, together with the pharmacological development of agonists and antagonists that are selective for chemokine receptors and can cross the blood-brain barrier, open a new era of research in neuroscience.

The chemokine stromal cell-derived factor-1/CXCL12 activates the nigrostriatal dopamine system

We recently demonstrated that dopaminergic (DA) neurons of the rat substantia nigra constitutively expressed CXCR4, receptor for the chemokine stromal cell-derived factor-1 (SDF-1)/CXCL12 (SDF-1). To check the physiological relevance of such anatomical observation, in vitro and in vivo approaches were used. Patch clamp recording of DA neurons in rat substantia nigra slices revealed that SDF-1 (10 nmol/L) induced: (i) a depolarization and increased action potential frequency; and (ii) switched the firing pattern of depolarized DA neurons from a tonic to a burst firing mode. This suggests that SDF-1 could increase DA release from neurons. Consistent with this hypothesis, unilateral intranigral injection of SDF-1 (50 ng) in freely moving rat decreased DA content and increased extracellular concentrations of DA and metabolites in the ipsilateral dorsal striatum, as shown using microdialysis. Furthermore, intranigral SDF-1 injection induced a contralateral circling behavior. These effects of SDF-1 were mediated via CXCR4 as they were abrogated by administration of a selective CXCR4 antagonist. Altogether, these data demonstrate that SDF-1, via CXCR4, activates nigrostriatal DA transmission. They show that the central functions of chemokines are not restricted, as originally thought, to neuroinflammation, but extend to neuromodulatory actions on well-defined neuronal circuits in non-pathological conditions.

Neuronal chemokines: versatile messengers in central nervous system cell interaction

Whereas chemokines are well known for their ability to induce cell migration, only recently it became evident that chemokines also control a variety of other cell functions and are versatile messengers in the interaction between a diversity of cell types. In the central nervous system (CNS), chemokines are generally found under both physiological and pathological conditions. Whereas many reports describe chemokine expression in astrocytes and microglia and their role in the migration of leukocytes into the CNS, only few studies describe chemokine expression in neurons. Nevertheless, the expression of neuronal chemokines and the corresponding chemokine receptors in CNS cells under physiological and pathological conditions indicates that neuronal chemokines contribute to CNS cell interaction. In this study, we review recent studies describing neuronal chemokine expression and discuss potential roles of neuronal chemokines in neuron-astrocyte, neuron-microglia, and neuron-neuron interaction.

Temporal mRNA profiles of inflammatory mediators in the murine 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). With the exception of a few rare familial forms of the disease, the precise molecular mechanisms underlying PD are unknown. Inflammation is a common finding in the PD brain, but due to the limitation of postmortem analysis its relationship to disease progression cannot be established. However, studies using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD have also identified inflammatory responses in the nigrostriatal pathway that precede neuronal degeneration in the SNpc. To assess the pathological relevance of these inflammatory responses and to identify candidate genes that might contribute to neuronal vulnerability, we used quantitative reverse-transcription polymerase chain reaction (qRT-PCR) to measure mRNA levels of 11 cytokine and chemokine encoding genes in the striatum of MPTP-sensitive (C57BL/6J) and MPTP-insensitive (Swiss Webster, SWR) mice following administration of MPTP. The mRNA levels of all 11 genes changed following MPTP treatment, indicating the presence of inflammatory responses in both strains. Furthermore, of the 11 genes examined only 3, interleukin 6 (Il-6), macrophage inflammatory protein 1 alpha/CC chemokine ligand 3 (Mip-1alpha/Ccl3) and macrophage inflammatory protein 1 beta/CC chemokine ligand 4 (Mip-1beta/Ccl4), were differentially regulated between C57BL/6J and SWR mice. In both mouse strains, the level of monocyte chemoattractant protein 1/CC chemokine ligand 2 (Mcp-1/Ccl2) mRNA was the first to increase following MPTP administration, and might represent a key initiating component of the inflammatory response. Using Mcp-1/Ccl2 knockout mice backcrossed onto a C57BL/6J background we found that MPTP-stimulated Mip-1alpha/Ccl3 and Mip-1beta/Ccl4 mRNA expression was significantly lower in the knockout mice; suggesting that Mcp-1/Ccl2 contributes to MPTP-enhanced expression of Mip-1alpha/Ccl3 and Mip-1beta/Ccl4. However, stereological analysis of SNpc neuronal loss in Mcp-1/Ccl2 knockout and wild-type mice showed no differences. These findings suggest that it is the ability of dopaminergic SNpc neurons to survive an inflammatory insult, rather than genetically determined differences in the inflammatory response itself, that underlie the molecular basis of MPTP resistance.

Chemokine fractalkine/CX3CL1 negatively modulates active glutamatergic synapses in rat hippocampal neurons

We examined the effects of the chemokine fractalkine (CX3CL1) on EPSCs evoked by electrical stimulation of Schaffer collaterals in patch-clamped CA1 pyramidal neurons from rat hippocampal slices. Acute application of CX3CL1 caused a sustained reduction of EPSC amplitude, with partial recovery after washout. CX3CL1-induced EPSC depression is postsynaptic in nature, because paired-pulse ratio was maintained, amplitude distribution of spontaneous excitatory postsynaptic currents shifted to lower values, and whole-cell current responses to AMPA were reversibly inhibited. EPSC depression by CX3CL1 is mediated by CX3CL1 receptor (CX3CR1), because CX3CL1 was unable to influence EPSC amplitude in CA1 pyramidal neurons from CX3CR1 knock-out mice. CX3CL1-induced depression of both EPSC and AMPA current was not observed in the absence of afferent fiber stimulation or AMPA receptor activation, respectively, indicating the requirement of sustained receptor activity for its development. Findings obtained from hippocampal slices, cultured hippocampal neurons, and transfected human embryonic kidney cells indicate that a Ca2+-, cAMP-, and phosphatase-dependent process is likely to modulate CX3CL1 effects because of the following: (1) CX3CL1-induced depression was antagonized by intracellular BAPTA, 8Br-cAMP, phosphatase inhibitors, and pertussis toxin (PTX); (2) CX3CL1 inhibited forskolin-induced cAMP formation sensitive to PTX; and (3) CX3CL1 inhibited forskolin-induced Ser845 GluR1 phosphorylation, which was sensitive to PTX and dependent on Ca2+ and phosphatase activity. Together, these findings indicate that CX3CL1 negatively modulates AMPA receptor function at active glutamatergic synapses through cell-signaling pathways by influencing the balance between kinase and phosphatase activity.

The chemokine SDF-1/CXCL12 modulates the firing pattern of vasopressin neurons and counteracts induced vasopressin release through CXCR4

Chemokines play a key role in inflammation. They are expressed not only in neuroinflammatory conditions, but also constitutively by different cell types, including neurons in the normal brain, suggesting that they may act as modulators of neuronal functions. Here, we investigated a possible neuroendocrine role of the chemokine stromal cell-derived factor 1 (SDF-1)/CXCL12. We demonstrated the colocalization of SDF-1 and its receptor CXCR4 with arginine vasopressin (AVP) in the magnocellular neurons of the supraoptic nucleus (SON) and the paraventricular hypothalamic nucleus and on AVP projections to the neurohypophysis. Electrophysiological recordings of SON neurons demonstrated that SDF-1 affects the electrical activity of AVP neurons through CXCR4, resulting in changes in AVP release. We observed that SDF-1 can blunt the autoregulation of AVP release in vitro and counteract angiotensin II-induced plasma AVP release in vivo. Furthermore, a short-term physiological increase in AVP release induced by enhanced plasma osmolarity, which was produced by the administration of 1 M NaCl i.p., was similarly blocked by central injection of SDF-1 through CXCR4. A change in water balance by long-term salt loading induced a decrease in both SDF-1 and CXCR4 parallel to that of AVP immunostaining in SON. From these data, we demonstrate that chemokine actions in the brain are not restricted to inflammatory processes. We propose to add to the known autoregulation of AVP on its own neurons, a second autocrine system induced by SDF-1 able to modulate central AVP neuronal activity and release.

The cerebellar-hypothalamic circuits: potential pathways underlying cerebellar involvement in somatic-visceral integration

The cerebellum has been considered only as a classical subcortical center for motor control. However, accumulating experimental and clinical evidences have revealed that the cerebellum also plays an important role in cognition, for instance, in learning and memory, as well as in emotional behavior and in nonsomatic activities, such as visceral and immunological responses. Although it is not yet clear through which pathways such cerebellar nonsomatic functions are mediated, the direct bidirectional connections between the cerebellum and the hypothalamus, a high autonomic center, have recently been demonstrated in a series of neuroanatomical investigations on a variety of mammals and indicated to be potential pathways underlying the cerebellar autonomic modulation. The direct hypothalamocerebellar projections originate from the widespread hypothalamic nuclei/areas and terminate in both the cerebellar cortex as multilayered fibers and the cerebellar nuclei. Immunohistochemistry studies have offered fairly convincing evidence that some of these projecting fibers are histaminergic. It has been suggested that through their excitatory effects on cerebellar cortical and nuclear cells mediated by metabotropic histamine H(2) and/or H(1) receptors, the hypothalamocerebellar histaminergic fibers participate in cerebellar modulation of somatic motor as well as non-motor responses. On the other hand, the direct cerebellohypothalamic projections arise from all cerebellar nuclei (fastigial, anterior and posterior interpositus, and dentate nuclei) and reach almost all hypothalamic nuclei/areas. Neurophysiological and neuroimaging studies have demonstrated that these connections may be involved in feeding, cardiovascular, osmotic, respiratory, micturition, immune, emotion, and other nonsomatic regulation. These observations provide support for the hypothesis that the cerebellum is an essential modulator and coordinator for integrating motor, visceral and behavioral responses, and that such somatic-visceral integration through the cerebellar circuitry may be fulfilled by means of the cerebellar-hypothalamic circuits.

Viewing chemokines as a third major system of communication in the brain

There is irrefutable proof that opioids and other classes of centrally acting drugs have profound effects on the immune system. Evidence is mounting that products of the immune system, such as chemokines, can reciprocally alter the actions of these drugs and the endogenous ligands for their receptors. Chemokines are a family of small (8 to 12 kDa) proteins involved in cellular migration and intercellular communication. With a few exceptions, they act on more than one receptor. Although the chemokines and their G protein-coupled receptors are located in both glia and neurons throughout the brain, they are not uniformly distributed. They are found in such brain areas as the hypothalamus, nucleus accumbens, limbic system, hippocampus, thalamus, cortex, and cerebellum. Among the chemokines differentially localized in brain neurons and glia are CCL2/MCP-1, CXCL12/SDF-1alpha, CX3CL1/fractalkine, CXCL10/IP 10, CCL3/MIP-1alpha, and CCL5/RANTES. Functional roles for the chemokine system, composed of the chemokine ligands and their receptors, have been suggested in brain development and heterologous desensitization. The system can alter the actions of neuronally active pharmacological agents such as opioids and cannabinoids and interact with neurotransmitter systems. In this review, we propose that the endogenous chemokine system in the brain acts in concert with the neurotransmitter and neuropeptide systems to govern brain function. It can thus be thought of as the third major system in the brain.

Mice deficient in the chemokine receptor CXCR4 exhibit impaired limb innervation and myogenesis

The chemokine CXCL12/SDF-1 and its receptor CXCR4 regulate the development and the function of the hematopoietic system and control morphogenesis of distinct brain areas. Here, we demonstrate that inactivation of CXCR4 results in a massive loss of spinal cord motoneurons and dorsal root ganglion neurons and, subsequently, in a reduced innervation of the developing mouse fore- and hindlimbs. However, only the death of sensory neurons seems to be a direct consequence of receptor inactivation as suggested by the observations that DRG neurons, but not motoneurons, of wild-type animals express CXCR4 and respond to CXCL12 with an increase in cell survival. In contrast, the increased death of motoneurons in CXCR4-deficient animals seems to result from impaired limb myogenesis and a subsequent loss of muscle-derived neurotrophic support. In summary, our findings unravel a previously unrecognized complex role of CXCL12/CXCR4 in the control of limb neuromuscular development.

Constitutive expression of CCR2 chemokine receptor and inhibition by MCP-1/CCL2 of GABA-induced currents in spinal cord neurones

In the CNS, immune-like competent cells (microglia and astrocytes) were first described as potential sites of chemokine synthesis, but more recent evidence has indicated that neurones might also express chemokines and their receptors. The aim of the present work was to investigate further, both in vivo and in vitro, CC Chemokine Family Receptor 2 (CCR2) expression and functionality in rat spinal cord neurones. First, we demonstrated by RT-PCR and western blot analysis that CCR2 mRNA and protein were present in spinal extracts. Furthermore, we showed by immunolabelling that CCR2 was exclusively expressed by neurones in spinal sections of healthy rat. Finally, to test the functionality of CCR2, we used primary cultures of rat spinal neurones. In this model, similar to what was observed in vivo, CCR2 mRNA and protein were expressed by neurones. Cultured neurones stimulated with Monocyte Chemoattractant Protein-1 (MCP-1)/CCL2, the best characterized CCR2 agonist, showed activation of the Akt pathway. Finally, patch-clamp recording of cultured spinal neurones was used to investigate whether MCP-1/CCL2 could modulate their electrophysiological properties. MCP-1 alone did not affect the electrical properties of spinal neurones, but potently and efficiently inhibited GABA(A)-mediated GABAergic responses in these neurones. These data constitute the first demonstration of a modulatory role of MCP-1 on GABAergic neurotransmission and contribute to our understanding of the roles of CCR2 and MCP-1/CCL2 in spinal cord physiology, in particular with respect to nociceptive transmission, as well as the implication of this chemokine in neuronal adaptation or dysfunction during neuropathy.

Complex effects of stromal cell-derived factor-1 alpha on melanin-concentrating hormone neuron excitability

Stromal cell-derived factor 1alpha (SDF-1alpha), a chemoattractant for leucocytes and neurons, and its receptor, CXCR4 are expressed in subsets of neurons of specific brain areas. In rat lateral hypothalamic area (LHA) we show, using immunocytochemistry, that CXCR4 is localized within melanin-concentrating hormone (MCH)-expressing neurons, mainly involved in feeding behaviour regulation. We investigated whether SDF-1alpha may control MCH neuronal activity. Patch-clamp recordings in rat LHA slices revealed multiple effects of SDF-1alpha on the membrane potential of MCH neurons, indirect through glutamate/GABA release and direct through GIRK current activation. Moreover, SDF-1alpha at 0.1-1 nM decreased peak and discharge frequency of action potential evoked by current pulses. These effects were further confirmed in voltage-clamp experiments, SDF-1alpha depressing both potassium and sodium currents. At 10 nM, however, SDF-1alpha increased peak and discharge frequency of action potential evoked by current pulses. Using a specific CXCR4 antagonist, we demonstrated that only the depressing effect on AP discharge was mediated through CXCR4 while the opposite effect was indirect. Together, our studies reveal for the first time a direct effect of SDF-1alpha on voltage-dependent membrane currents of neurons in brain slices and suggest that this chemokine may regulate MCH neuron activity.

The chemokine CXCL10 modulates excitatory activity and intracellular calcium signaling in cultured hippocampal neurons

In this study, we provide evidence for direct modulatory effects of the chemokine, CXCL10, on the physiology of hippocampal neurons maintained in primary culture. CXCL10 elicited a rise in intracellular Ca2+ and enhanced both spontaneous and evoked electrical activity of hippocampal neurons. CXCL10-induced elevations in intracellular Ca2+ were associated with an increase in neuronal firing and an alteration in the relationship between the evoked Ca2+ signal and neuronal activity. The effects of CXCL10 were not accompanied by a shift in resting membrane potential (RMP) or input resistance. Expression of the CXCR3 chemokine receptor supports a direct effect of CXCL10 on hippocampal neurons.

Acute exposure to CXC chemokine ligand 10, but not its chronic astroglial production, alters synaptic plasticity in mouse hippocampal slices

Brain levels of CXC chemokine ligand 10 (CXCL10) are elevated in a number of neuropathological conditions. To determine its impact on neuronal function, we measured synaptic transmission and plasticity in hippocampal slices prepared from transgenic (TG) mice with chronic astroglial production of CXCL10. We also tested the acute effect of recombinant CXCL10 applied to slices from normal C57Bl/6J mice, CXCL10 TG mice and CXCR3 knock out (KO) mice. Chronic production of CXCL10 did not alter synaptic plasticity. By contrast, exogenous CXCL10 (10 ng/ml) significantly inhibited long-term potentiation (LTP) in slices from normal C57Bl/6J mice and CXCL10 TG. The effect was probably receptor-mediated because CXCL10-induced inhibition of LTP was not observed in CXCR3 KO mice. Our findings suggest that acute exposure to CXCL10 alters synaptic plasticity via CXCR3 in mouse hippocampus.

Highly regionalized distribution of stromal cell-derived factor-1/CXCL12 in adult rat brain: constitutive expression in cholinergic, dopaminergic and vasopressinergic neurons

The stromal cell-derived factor-1 (SDF-1)/CXCL12 and its receptor CXCR4 are key modulators of immune functions. In the nervous system, SDF-1/CXCL12 is crucial for neuronal guidance in developing brain, intercellular communication and the neuropathogenesis of acquired immunodeficiency syndrome. However, cerebral functions of SDF-1/CXCL12 in adult brain are poorly understood. The understanding of its role in the adult brain needs a detailed neuroanatomical mapping of SDF-1/CXCL12. By dual immunohistochemistry we demonstrate that this chemokine is constitutively expressed not only in astrocytes and microglia but also in neurons, in discrete neuroanatomical regions. Indeed, neuronal expression of SDF-1/CXCL12 is mainly found in cerebral cortex, substantia innominata, globus pallidus, hippocampus, paraventricular and supraoptic hypothalamic nuclei, lateral hypothalamus, substantia nigra and oculomotor nuclei. Moreover, we provide the first evidence that SDF-1/CXCL12 is constitutively expressed in cholinergic neurons in the medial septum and substantia innominata and in dopaminergic neurons in substantia nigra pars compacta and the ventral tegmental area. Interestingly we also show, for the first time, a selective co-localization of SDF-1/CXCL12 with vasopressin-expressing neurons in the supraoptic and paraventricular hypothalamic nuclei. In addition, in the lateral hypothalamic area, SDF-1/CXCL12 was found to be located on melanin concentrating hormone-expressing neurons. Altogether, these original data suggest that SDF-1/CXCL12 could be a modulatory neuropeptide regulating both central cholinergic and dopaminergic systems. In addition, a key role for SDF-1/CXCL12 in neuroendocrine regulation of vasopressin-expressing neurons represents an exciting new field of research.

Signalling pathways involved in the chemotactic activity of CXCL12 in cultured rat cerebellar neurons and CHP100 neuroepithelioma cells

We compared the signal transduction pathways activated by stromal cell-derived factor-1 (CXCL12) chemokine in two different cell systems: primary cultures of rat cerebellar granule neurons (CGN) and human neuroepithelioma CHP100 cells. Both cell types express functional CXC chemokine receptor 4 (CXCR4), which is coupled both to extracellular signal-regulated kinase (ERK) and Akt phosphorylation pathways. The activation of ERK shows different dependency on the phosphatidylinositol 3-kinase (PI3-K) pathway and different sensitivity to pertussis toxin (PTX) treatment, indicative of coupling to different G proteins in the two cell systems considered. We demonstrate that the inhibition of either the ERK kinase or the PI3-K pathways blocks the CXCL12 induced-chemotaxis in CHP100 cells; while only PI3-K activity is stringently necessary for CGN migration.

CXC chemokine receptors in the central nervous system: Role in cerebellar neuromodulation and development

Chemokines and their receptors are constitutively present in the central nervous system (CNS), expressed in neurons and glial cells. Much evidence suggests that, beyond their involvement in neuroinflammation, these proteins play a role in neurodevelopment and neurophysiological signaling. The goal of this review is to summarize recent information concerning expression, signaling, and function of CXC chemokine receptor in the CNS, with the main focus on the developmental and neuromodulatory actions of chemokines in the cerebellum.