CC-chemokine ligand 2 facilitates conditioned place preference to methamphetamine through the activation of dopamine systems

Pathological roles of bone marrow adipocyte-derived monocyte chemotactic protein-1 in type 2 diabetic mice

Type 2 diabetes mellitus (T2DM) has become a prevalent public health concern, with beta-cell dysfunction involved in its pathogenesis. Bone marrow adipose tissue (BMAT) increases in both the quantity and area in individuals with T2DM along with heightened monocyte chemotactic protein-1 (MCP-1) secretion. This study aims to investigate the influence and underlying mechanisms of MCP-1 originating from bone marrow adipocytes (BMAs) on systemic glucose homeostasis in T2DM. Initially, a substantial decrease in the proliferation and glucose-stimulated insulin secretion (GSIS) of islet cells was observed. Moreover, a comparative analysis between the control (Ctrl) group and db/db mice revealed significant alterations in the gene expression profiles of whole bone marrow cells, with a noteworthy upregulation of Mcp-1. And the primary enriched pathways included chemokine signaling pathway and AGE-RAGE signaling pathway in diabetic complications. In addition, the level of MCP-1 was distinctly elevated in BMA-derived conditional media (CM), leading to a substantial inhibition of proliferation, GSIS and the protein level of phosphorylated Akt (p-Akt) in Min6 cells. After blocking MCP-1 pathway, we observed a restoration of p-Akt and the proliferation of islet cells, resulting in a marked improvement in disordered glucose homeostasis. In summary, there is an accumulation of BMAs in T2DM, which secrete excessive MCP-1, exacerbating the abnormal accumulation of BMAs in the bone marrow cavity through paracrine signaling. The upregulated MCP-1, in turn, worsens glucose metabolism disorder by inhibiting the proliferation and insulin secretion of islet cells through an endocrine pathway. Inhibiting MCP-1 signaling can partially restore the proliferation and insulin secretion of islet cells, ultimately ameliorating glucose metabolism disorder. It's worth noting that to delve deeper into the impact of MCP-1 derived from BMAs on islet cells and its potential mechanisms, it is imperative to develop genetically engineered mice with conditional Mcp-1 knockout from BMAs.

Central and Peripheral Inflammation: A Common Factor Causing Addictive and Neurological Disorders and Aging-Related Pathologies

Many diseases and degenerative processes affecting the nervous system and peripheral organs trigger the activation of inflammatory cascades. Inflammation can be triggered by different environmental conditions or risk factors, including drug and food addiction, stress, and aging, among others. Several pieces of evidence show that the modern lifestyle and, more recently, the confinement associated with the COVID-19 pandemic have contributed to increasing the incidence of addictive and neuropsychiatric disorders, plus cardiometabolic diseases. Here, we gather evidence on how some of these risk factors are implicated in activating central and peripheral inflammation contributing to some neuropathologies and behaviors associated with poor health. We discuss the current understanding of the cellular and molecular mechanisms involved in the generation of inflammation and how these processes occur in different cells and tissues to promote ill health and diseases. Concomitantly, we discuss how some pathology-associated and addictive behaviors contribute to worsening these inflammation mechanisms, leading to a vicious cycle that promotes disease progression. Finally, we list some drugs targeting inflammation-related pathways that may have beneficial effects on the pathological processes associated with addictive, mental, and cardiometabolic illnesses.

Cyanidin prevents MDPV withdrawal-induced anxiety-like effects and dysregulation of cytokine systems in rats

Psychostimulant exposure and withdrawal cause neuroimmune dysregulation and anxiety that contributes to dependence and relapse. Here, we tested the hypothesis that withdrawal from the synthetic cathinone MDPV (methylenedioxypyrovalerone) produces anxiety-like effects and enhanced levels of mesocorticolimbic cytokines that are inhibited by cyanidin, an anti-inflammatory flavonoid and nonselective blocker of IL-17A signaling. For comparison, we tested effects on glutamate transporter systems that are also dysregulated during psychostimulant free period. Rats injected for 9 d with MDPV (1 mg/kg, IP) or saline were pretreated daily with cyanidin (0.5 mg/kg, IP) or saline, followed by behavioral testing on the elevated zero maze (EZM) 72 h after the last MDPV injection. MDPV withdrawal caused a reduction in time spent on the open arm of the EZM that was prevented by cyanidin. Cyanidin itself did not affect locomotor activity or time spent on the open arm, or cause aversive or rewarding effects in place preference experiments. MDPV withdrawal caused enhancement of cytokine levels (IL-17A, IL-1β, IL-6, TNF=α, IL-10, and CCL2) in the ventral tegmental area, but not amygdala, nucleus accumbens, or prefrontal cortex, that was prevented by cyanidin. During MDPV withdrawal, mRNA levels of glutamate aspartate transporter (GLAST) and glutamate transporter subtype 1 (GLT-1) in the amygdala were also elevated but normalized by cyanidin treatment. These results show that MDPV withdrawal induced anxiety, and brain-region specific dysregulation of cytokine and glutamate systems, that are both prevented by cyanidin, thus identifying cyanidin for further investigation in the context of psychostimulant dependence and relapse.

Neuroinflammatory Response in Reward-Associated Psychostimulants and Opioids: A Review

Substance abuse is one of the significant problems in social and public health worldwide. Vast numbers of evidence illustrate that motivational and reinforcing impacts of addictive drugs are primarily attributed to their ability to change dopamine signaling in the reward circuit. However, the roles of classic neurotransmitters, especially dopamine and neuromodulators, monoamines, and neuropeptides, in reinforcing characteristics of abused drugs have been extensively investigated. It has recently been revealed that central immune signaling includes cascades of chemokines and proinflammatory cytokines released by neurons and glia via downstream intracellular signaling pathways that play a crucial role in mediating rewarding behavioral effects of drugs. More interestingly, inflammatory responses in the central nervous system modulate the mesolimbic dopamine signaling and glutamate-dependent currents induced by addictive drugs. This review summarized researches in the alterations of inflammatory responses accompanied by rewarding and reinforcing properties of addictive drugs, including cocaine, methamphetamine, and opioids that were evaluated by conditioned place preference and self-administration procedures as highly common behavioral tests to investigate the motivational and reinforcing impacts of addictive drugs. The neuroinflammatory responses affect the rewarding properties of psychostimulants and opioids.

Role of Microglia in Psychostimulant Addiction

The use of psychostimulant drugs can modify brain function by inducing changes in the reward system, mainly due to alterations in dopaminergic and glutamatergic transmissions in the mesocorticolimbic pathway. However, the etiopathogenesis of addiction is a much more complex process. Previous data have suggested that microglia and other immune cells are involved in events associated with neuroplasticity and memory, which are phenomena that also occur in addiction. Nevertheless, how dependent is the development of addiction on the activity of these cells? Although the mechanisms are not known, some pathways may be involved. Recent data have shown psychoactive substances may act directly on immune cells, alter their functions and induce various inflammatory mediators that modulate synaptic activity. These could, in turn, be involved in the pathological alterations that occur in substance use disorder. Here, we extensively review the studies demonstrating how cocaine and amphetamines modulate microglial number, morphology, and function. We also describe the effect of these substances in the production of inflammatory mediators and a possible involvement of some molecular signaling pathways, such as the toll-like receptor 4. Although the literature in this field is scarce, this review compiles the knowledge on the neuroimmune axis that is involved in the pathogenesis of addiction, and suggests some pharmacological targets for the development of pharmacotherapy.

Claustral MeCP2 Regulates Methamphetamine-induced Conditioned Place Preference in Cynomolgus Monkey

The claustrum, a brain nucleus located between the cortex and the striatum, has recently been highlighted in drug-related reward processing. Methyl CpG-binding protein-2 (MeCP2) is a transcriptional regulator that represses or activates the expression of the target gene and has been known to have an important role in the regulation of drug addiction in the dopaminergic reward system. The claustrum is an important region for regulating reward processing where most neurons receive dopamine input; additionally, in this region, MeCP2 is also abundantly expressed. Therefore, here, we hypothesized that MeCP2 would be involved in drug addiction control in the Claustrum as well and investigated how claustral MeCP2 regulates drug addiction. To better understand the function of human claustral MeCP2, we established a non-human primate model of methamphetamine (METH) - induced conditioned place preference (CPP). After a habituation of two days and conditioning of ten days, the CPP test was conducted for three days. Interestingly, we confirmed that virus-mediated overexpression of MECP2 in the claustrum showed a significant reduction of METH-induced CPP in the three consecutive days during the testing period. Moreover, they showed a decrease in visit scores (frequency for visit) for the METH-paired room compared to the control group although the scores were statistically marginal. Taken together, we suggest that the claustrum is an important brain region associated with drug addiction, in which MeCP2 may function as a mediator in regulating the response to addictive drugs.

Epigenetic Regulatory Dynamics in Models of Methamphetamine-Use Disorder

Methamphetamine (METH)-use disorder (MUD) is a very serious, potentially lethal, biopsychosocial disease. Exposure to METH causes long-term changes to brain regions involved in reward processing and motivation, leading vulnerable individuals to engage in pathological drug-seeking and drug-taking behavior that can remain a lifelong struggle. It is crucial to elucidate underlying mechanisms by which exposure to METH leads to molecular neuroadaptive changes at transcriptional and translational levels. Changes in gene expression are controlled by post-translational modifications via chromatin remodeling. This review article focuses on the brain-region specific combinatorial or distinct epigenetic modifications that lead to METH-induced changes in gene expression.

Chemokines, cytokines and substance use disorders

Efficacious pharmacotherapies for the treatment of substance use disorders need to be expanded and improved. Non-neuronal cells, particularly astrocytes and microglia, have emerged as therapeutic targets for the development of pharmacotherapies to treat dependence and relapse that accompanies chronic drug use. Cytokines and chemokines are neuroimmune factors expressed in neurons, astrocytes, and microglia that demonstrate promising clinical utility as therapeutic targets for substance use disorders. In this review, we describe a role for cytokines and chemokines in the rewarding and reinforcing effects of alcohol, opioids, and psychostimulants. We also discuss emerging cytokine- and chemokine-based therapeutic strategies that differ from conventional strategies directed toward transporters and receptors within the dopamine, glutamate, GABA, serotonin, and GABA systems.

CXCR4 inhibition with AMD3100 attenuates amphetamine induced locomotor activity in adolescent Long Evans male rats

Adolescent psychostimulant abuse has been on the rise over the past decade. This trend has demonstrable ramifications on adolescent behavior and brain morphology, increasing risk for development of addiction during adolescence and in later adulthood. Neuroimmune substrates are implicated in the etiology of substance use disorders. To add to this body of work, the current study was developed to explore the role of a chemokine receptor, CXC Chemokine Receptor 4 (CXCR4), in the development of amphetamine (AMPH) sensitization. We targeted CXCR4 as it is implicated in developmental processes, dopaminergic transmission, neuroimmune responses, and the potentiation of psychostimulant abuse pathology. To evaluate the role of CXCR4 activity on the development of AMPH sensitization, a CXCR4 antagonist (Plerixafor; AMD3100) was administered to rats as a pretreatment variable. Specifically, adolescent Long Evans male rats (N = 37) were divided into four groups: (1) AMD3100 (IP, 4.0 mg/kg) + AMPH (IP, 4.0 mg/kg), (2) saline (SAL; 0.9% NaCl) + AMPH, (3) AMD3100 + SAL, and (4) SAL + SAL. Animals were first habituated to locomotor activity (LMA) chambers, then injected with a pretreatment drug (AMD3100 or SAL) followed by AMPH or SAL every other for four days. After a one-week withdrawal period, all animals were administered a low challenge dose of AMPH (IP, 1.0 mg/kg). AMPH-injected rats displayed significantly more locomotor activity compared to controls across all testing days. CXCR4 antagonism significantly attenuated AMPH-induced locomotor activity. On challenge day, AMD3100 pre-treated animals exhibited diminutive AMPH-induced locomotor activity compared to SAL pre-treated animals. Postmortem analyses of brain tissue revealed elevated CXCR4 protein levels in the striatum of all experimental groups. Our results implicate CXCR4 signaling in the development of AMPH sensitization and may represent an important therapeutic target for future research in psychostimulant abuse.

Aberrations in peripheral inflammatory cytokine levels in substance use disorders: a meta-analysis of 74 studies

AIMS

To characterize the peripheral inflammatory cytokine profile in people with substance use disorders (SUDs).

DESIGN

Systematic review and meta-analysis.

SETTING

Clinical studies that evaluated peripheral blood inflammatory cytokine levels in patients with SUDs and healthy controls PARTICIPANTS: SUD patients and healthy controls.

MEASUREMENTS

PubMed and Web of Science were systematically searched for relevant studies. Two investigators independently selected studies and extracted data. A total of 77 articles were included in the meta-analysis, containing 5649 patients with SUDs and 4643 healthy controls. Data were pooled using a random-effects model by the Comprehensive Meta-Analysis version 2 software.

FINDINGS

Concentrations of interleukin (IL)-6) in 32 studies, tumor necrosis factor (TNF)-α in 28 studies, IL-10 in 20 studies, IL-8 in 17 studies, C-reactive protein in 14 studies, IL-4 in 10 studies, IL-12 in seven studies, monocyte chemoattractant protein (MCP)-1 in 6 studies, TNF-receptor 2 (TNF-R2) in four studies and granulocyte-macrophage colony-stimulating factor (GM-CSF) in three studies were significantly higher in patients with SUDs compared with healthy controls, while concentrations of leptin in 14 studies were significantly lower in patients with SUDs compared with healthy controls. The findings were inconclusive for the associations between interferon-γ, IL-1β, IL-2, IL-1 receptor antagonist (IL-1RA), transforming growth factor (TGF)-β1, G-CSF, C-C motif chemokine 11, TGF-α and SUDs.

CONCLUSIONS

People with substance use disorders (SUDs) appear to have higher peripheral concentrations of IL-4, IL-6, IL-8, IL-10, IL-12, TNF-α, C-reactive protein, MCP-1, TNF-R2 and GM-CSF and lower peripheral concentrations of leptin than people without SUDs. This strengthens the view that SUD is accompanied by an inflammatory response.

Phenotyping CCL2 Containing Central Amygdala Neurons Controlling Alcohol Withdrawal-Induced Anxiety

Chemokines such as chemokine (C-C motif) ligand 2 (CCL2) play a role in several behaviors, including anxiety-like behavior, but whether neurons are an important source of CCL2 for behavior and how neuronal CCL2 may work to affect behavior are still debated. When a herpes simplex virus (HSV) vector was used to knockdown CCL2 mRNA in neurons of the central nucleus of the amygdala (CeA) in rats experiencing multiple withdrawals from low dose ethanol, anxiety-like behavior appeared in the social interaction task. To examine this finding further Fractalkine (CX3CL1), a chemokine that is often found to have an opposing function to CCL2 was measured in these rats. Both alcohol withdrawal and CCL2 knockdown increased the levels of the anti-inflammatory protein CX3CL1. The combination of alcohol withdrawal and CCL2 knockdown decreased CX3CL1 and may alter pro-inflammatory/anti-inflammatory balance, and thus highlights the potential importance of CCL2 and CCL2/CX3CL1 balance in anxiety. To find a mechanism by which neuronal chemokines like CCL2 could affect behavior, retrograde tracing with fluorescent nanobeads was done in two brain regions associated with anxiety the bed nucleus of the stria terminalis (BNST) and the ventral periaqueductal gray (VPAG). These studies identified CeA projection neurons to these brain regions that contain CCL2. To demonstrate that CCL2 can be transported via axons to downstream brain regions, the axonal transport blocker, colchicine, was given and 24 h later, the accumulation of CCL2 in CeA neuronal cell bodies was found. Finally, CCL2 in CeA neurons was localized to the synapse using confocal microscopy with enhanced resolution following deconvolution and electron microscopy, which along with the other evidence suggests that CCL2 may be transported down axons in CeA neurons and released from nerve terminals perhaps into brain regions like the BNST and VPAG to affect behaviors such as anxiety. These results suggest that neurons are an important target for chemokine research related to behavior.

Partial MHC/neuroantigen peptide constructs attenuate methamphetamine-seeking and brain chemokine (C-C motif) ligand 2 levels in rats

There are no medications that target the neurotoxic effects or reduce the use of methamphetamine. Recombinant T-cell receptor ligand (RTL) 1000 [a partial major histocompatibility complex (pMHC) class II construct with a tethered myelin peptide], addresses the neuroimmune effects of methamphetamine addiction by competitively inhibiting the disease-promoting activity of macrophage migration inhibitory factor to CD74, a key pathway involved in several chronic inflammatory conditions, including substance use disorders. We previously reported that RTL constructs improve learning and memory impairments and central nervous system (CNS) inflammation induced by methamphetamine in mouse models. The present study in Lewis rats evaluated the effects of RTL1000 on maintenance of self-administration and cue-induced reinstatement using operant behavioral methods. Post-mortem brain and serum samples were evaluated for the levels of inflammatory factors. Rats treated with RTL1000 displayed significantly fewer presses on the active lever as compared to rats treated with vehicle during the initial extinction session, indicating more rapid extinction in the presence of RTL1000. Immunoblotting of rat brain sections revealed reduced levels of the pro-inflammatory chemokine (C-C motif) ligand 2 (CCL2) in the frontal cortex of rats treated with RTL1000, as compared to vehicle. Post hoc analysis identified a positive association between the levels of CCL2 detected in the frontal cortex and the number of lever presses during the first extinction session. Taken together, results suggest that RTL1000 may block downstream inflammatory effects of methamphetamine exposure and facilitate reduced drug seeking-potentially offering a new strategy for the treatment of methamphetamine-induced CNS injury and neuropsychiatric impairments.

Cannabidiol modulates the expression of neuroinflammatory factors in stress- and drug-induced reinstatement of methamphetamine in extinguished rats

Methamphetamine (METH) is a highly potent and addictive psychostimulant that is frequently abused worldwide. Although the biggest challenge to the efficient treatment of drug dependence is relapse, its mechanism is completely unclear. Plenty of evidence suggests that inflammation contributes to drug-induced reward especially in brain regions that are involved in the reward system, but there is no document about relapse. Cannabidiol (CBD) is a nonpsychoactive cannabinoid that has powerful anti-inflammatory and immunosuppressive properties. A previous research in our laboratory has demonstrated that CBD prevents reinstatement of METH even in 24-hour rapid eye movement (REM) sleep-deprived (RSD) rats. The aim of this study was to assess whether CBD prevents reinstatement of METH through change of gene expression of cytokines such as interleukin-1β, interleukin-6, interleukin-10, and tumor necrosis factor α (TNF-α) in extinguished rats. Real-time polymerase chain reaction (PCR) was used in this research to assay gene expression of cytokines. We found that stress- and drug-induced reinstatement of METH enhanced mRNA expression of cytokines in the prefrontal cortex (PFC) and hippocampus. Furthermore, CBD treatment significantly reduced the mRNA expression of cytokines in the PFC and hippocampus, but CBD treatment in RSD rats increased expression of cytokines in the hippocampus. It seems that enhancement of cytokines leads to change in neurotransmission and so triggers reinstatement of METH.

Glial regulation of synaptic function in models of addiction

The glial regulation of synaptic function provides important modulation of the synaptic and behavioral changes induced by drugs of abuse. In some cases, this regulation is adaptive, reducing drug-induced change, and in other cases maladaptive, contributing to the induction or maintenance of these changes. Understanding the contribution of glia to addictive behaviors will be important to fully understand the development of addiction, and a critical entry into methods to potentially mitigate this affliction. This review will cover recent advances in elucidating the contribution of the major types of glia - microglia and astrocytes - to drug-induced synaptic plasticity.

Role of chemokines in Parkinson's disease

Parkinson's disease (PD) is a chronic progressive neurodegenerative disorder with an increasing incidence year by year, particularly as the population ages. The most common neuropathologic manifestation in patients with Parkinson's disease is dopamine neurons degeneration and loss in substantia nigra of middle brain. The main neurochemistry problem is the lack of the neurotransmitter dopamine. Clinically, PD patients may also have higher levels of glutamate, gamma-aminobutyric acid, acetylcholine and other neurotransmitters. At present, many data have shown that some chemokines are involved in regulating the release and transmission of neurotransmitters, and the growth and development of related neurons. In recent years, most of the studies relative to PD is based on immune and inflammatory mechanisms, and chemokines is also the focus on this mechanism. Chemokines are a class of cytokines that have definite chemotaxis effects on the different target cells. They might be involved in the pathogenesis of PD by inducing neuronal apoptosis and microglia activation. Clinical data has shown that the levels of chemokines in plasma and cerebrospinal fluid of PD patients have corresponding changes compared with the healthy persons. This review summarizes recent studies on chemokines and their receptors in Parkinson's disease: (i) to explore the role of chemokines in Parkinson's disease; (ii) to provide new indicators for clinical diagnosis of PD; (iii) to provide new targets for drug research and development in the treatment of Parkinson's disease.

Chemokine receptor CCR2 contributes to neuropathic pain and the associated depression via increasing NR2B-mediated currents in both D1 and D2 dopamine receptor-containing medium spiny neurons in the nucleus accumbens shell

Patients with neuropathic pain are usually accompanied by depression. Chemokine-mediated neuroinflammation is involved in a variety of diseases, including neurodegenerative diseases, depression, and chronic pain. The nucleus accumbens (NAc) is an important area in mediating pain sensation and depression. Here we report that spinal nerve ligation (SNL) induced upregulation of chemokine CCL2 and its major receptor CCR2 in both dopamine D1 and D2 receptor (D1R and D2R)-containing neurons in the NAc. Inhibition of CCR2 by shRNA lentivirus in the NAc shell attenuated SNL-induced pain hypersensitivity and depressive behaviors. Conversely, intra-NAc injection of CCL2-expressing lentivirus-induced nociceptive and depressive behaviors in naïve mice. Whole-cell patch clamp recording of D1R-positive or D2R-positive medium spiny neurons (MSNs) showed that SNL increased NMDA receptor (NMDAR)-mediated currents that are induced by stimulation of prefrontal cortical afferents to MSNs, which was inhibited by a CCR2 antagonist. Furthermore, Ccr2 shRNA also reduced NMDAR-mediated currents, and this reduction was mainly mediated via NR2B subunit. Consistently, NR2B, colocalized with CCR2 in the NAc, was phosphorylated after SNL and was inhibited by intra-NAc injection of Ccr2 shRNA. Furthermore, SNL or CCL2 induced ERK activation in the NAc. Inhibition of ERK by a MEK inhibitor reduced NR2B phosphorylation induced by SNL or CCL2. Finally, intra-NAc injection of NR2B antagonist or MEK inhibitor attenuated SNL-induced pain hypersensitivity and depressive behaviors. Collectively, these results suggest that CCL2/CCR2 signaling in the NAc shell is important in mediating neuropathic pain and depression via regulating NR2B-mediated NMDAR function in D1R- and D2R-containing neurons following peripheral nerve injury.

Role of MCP-1 and CCR2 in ethanol-induced neuroinflammation and neurodegeneration in the developing brain

Background

Neuroinflammation and microglial activation have been implicated in both alcohol use disorders (AUD) and fetal alcohol spectrum disorders (FASD). Chemokine monocyte chemoattractant protein 1 (MCP-1) and its receptor C-C chemokine receptor type 2 (CCR2) are critical mediators of neuroinflammation and microglial activation. FASD is the leading cause of mental retardation, and one of the most devastating outcomes of FASD is the loss of neurons in the central nervous system (CNS). The underlying molecular mechanisms, however, remain unclear. We hypothesize that MCP-1/CCR2 signaling mediates ethanol-induced neuroinflammation and microglial activation, which exacerbates neurodegeneration in the developing brain.

Methods

C57BL/6 mice and mice deficient of MCP-1 (MCP-1^−/−) and CCR2 (CCR2^−/−) were exposed to ethanol on postnatal day 4 (PD4). Neuroinflammation, and microglial activation, and neurodegeneration in the brain were evaluated by immunohistochemistry and immunoblotting. A neuronal and microglial co-culture system was used to evaluate the role of microglia and MCP-1/CCR2 signaling in ethanol-induced neurodegeneration. Specific inhibitors were employed to delineate the involved signaling pathways.

Results

Ethanol-induced microglial activation, neuroinflammation, and a drastic increase in the mRNA and protein levels of MCP-1. Treatment of Bindarit (MCP-1 synthesis inhibitor) and RS504393 (CCR2 antagonist) significantly reduced ethanol-induced microglia activation/neuroinflammation, and neuroapoptosis in the developing brain. MCP-1^−/− and CCR2^−/− mice were more resistant to ethanol-induced neuroapoptosis. Moreover, ethanol plus MCP-1 caused more neuronal death in a neuron/microglia co-culture system than neuronal culture alone, and Bindarit and RS504393 attenuated ethanol-induced neuronal death in the co-culture system. Ethanol activated TLR4 and GSK3β, two key mediators of microglial activation in the brain and cultured microglial cells (SIM-A9). Blocking MCP-1/CCR2 signaling attenuated ethanol-induced activation of TLR4 and GSK3β.

Conclusion

MCP-1/CCR2 signaling played an important role in ethanol-induced microglial activation/neuroinflammation and neurodegeneration in the developing brain. The effects may be mediated by the interaction among MCP-1/CCR2 signaling, TLR4, and GSK3β.

Chemokine CXCL1 is responsible for cocaine-induced reward in mice

Aim

We have previously demonstrated that upregulation of CC chemokines through dopamine receptor signaling in the prefrontal cortex (PFC) underlies methamphetamine (Meth)‐induced reward. Given the common pharmacological property of Meth and cocaine (Coca), which are highly addictive psychostimulants, we hypothesized that chemokines may also contribute to Coca‐induced reward. The aim of this study was to identify a key chemokine‐mediating Coca‐induced reward in mice.

Methods

The mRNA expression levels of chemokines were measured by reverse transcription‐quantitative polymerase chain reaction. Coca‐induced reward was evaluated by conditioned place preference test.

Results

We found that mRNA expression levels of CC chemokine ligand 2 (CCL2), CCL7, and CXC chemokine ligand 1 (CXCL1) were upregulated in the PFC after a single administration of Coca (20 mg/kg, s.c.). Upregulation of CXCL1, but not CCL2 and CCL7, mRNA in the PFC was also observed after repeated administration of Coca. A single administration of dopamine D1 receptor agonist SKF 81297 (10 mg/kg, s.c.), but not D2 receptor agonist sumanirole, upregulated CXCL1 mRNA in the PFC. Coca‐induced reward was attenuated by the pretreatment of SB 225002 (5 mg/kg, s.c.), a selective antagonist of CXC chemokine receptor 2 (CXCR2, cognate receptor for CXCL1).

Conclusions

Collectively, we identified CXCL1 as a key regulator in Coca‐induced reward and propose that pharmacological approach targeting CXCL1 could be a novel pharmacotherapy for Coca‐induced reward.

Upregulation of CXCL1 through dopamine D1 receptor signaling in the prefrontal cortex plays an important role in cocaine‐induced reward.

Maternal Overnutrition Programs Central Inflammation and Addiction-Like Behavior in Offspring

Obesity or maternal overnutrition during pregnancy and lactation might have long-term consequences in offspring health. Fetal programming is characterized by adaptive responses to specific environmental conditions during early life stages. Programming alters gene expression through epigenetic modifications leading to a transgenerational effect of behavioral phenotypes in the offspring. Maternal intake of hypercaloric diets during fetal development programs aberrant behaviors resembling addiction in offspring. Programming by hypercaloric surplus sets a gene expression pattern modulating axonal pruning, synaptic signaling, and synaptic plasticity in selective regions of the reward system. Likewise, fetal programming can promote an inflammatory phenotype in peripheral and central sites through different cell types such as microglia and T and B cells, which contribute to disrupted energy sensing and behavioral pathways. The molecular mechanism that regulates the central and peripheral immune cross-talk during fetal programming and its relevance on offspring's addictive behavior susceptibility is still unclear. Here, we review the most relevant scientific reports about the impact of hypercaloric nutritional fetal programming on central and peripheral inflammation and its effects on addictive behavior of the offspring.

Chemokines and 'bath salts': CXCR4 receptor antagonist reduces rewarding and locomotor-stimulant effects of the designer cathinone MDPV in rats

BACKGROUND AND PURPOSE

Little is known about how chemokine systems influence the behavioral effects of designer cathinones and psychostimulants. The chemokine CXCL12 and its principal receptor target, CXCR4, are of particular interest because CXCR4 activation enhances mesolimbic dopamine output that facilitates psychostimulant reward, reinforcement, and locomotor activation. Repeated cocaine enhances CXCL12 gene expression in the midbrain and produces conditioned place preference (CPP) that is inhibited by a CXCR4 antagonist. Yet, interactions between chemokines and synthetic cathinones remain elusive.

METHODS

We tested the hypothesis that an FDA-approved CXCR4 antagonist (AMD3100) inhibits MDPV-induced reward, locomotor activation and positive affective state in rats using a triad of behavioral assays (CPP, open field, and 50-kHz ultrasonic vocalizations [USVs]).

KEY RESULTS

AMD3100 (1, 2.5, 5, 10 mg/kg, ip) significantly reduced MDPV (2 mg/kg, ip)-evoked hyper-locomotion in a dose-related manner. AMD3100 (1, 5, 10 mg/kg) administered during CPP conditioning caused a significant, dose-dependent reduction of MDPV (2 mg/kg x 4 days) place preference. MDPV injection elicited significantly greater 50 kHz USVs in vehicle-pretreated rats but not in AMD3100-pretreated rats.

CONCLUSION AND IMPLICATION

A CXCR4 antagonist reduced the rewarding and locomotor-activating effects of MDPV. Our results identify the existence of chemokine/cathinone interactions and suggest the rewarding and stimulant effects of MDPV, similar to cocaine, require an active CXCL12/CXCR4 system.

Alpha-PVP induces the rewarding effect via activating dopaminergic neuron

A synthetic cathinone, 1-phenyl-2-(1-pyrrolidinyl)-1-pentanone (α-PVP), was occasionally found in the "bath salt" type of designer drugs, as an active ingredient. It has been reported that drivers who consumed α-PVP were in an excited state and incapable of controlling their behavior, causing traffic accidents. Despite its acute excitatory effects, there is no information on the psychological dependency elicited by α-PVP use. The purpose of the present study was to clarify whether the reward pathway is activated with repeated doses of α-PVP in experimental animals. Treatment of male C57BL/6j mice with α-PVP (25 mg/kg, i.p.), once a day, for 3 days significantly increased the conditioned place preference scores. Therefore, repeated doses of α-PVP were shown to induce palatability in mice. α-PVP increases extracellular dopamine levels in the nucleus accumbens shell immediately after administration. The number of cells immunopositive for phosphorylated cAMP-regulatory element binding protein (CREB) was significantly increased in the α-PVP-treated mice in our study. These results indicate that the administration of α-PVP activates the phosphorylation of CREB in the nucleus accumbens shell. Our results suggest that α-PVP stimulates the reward pathway by increasing the extracellular dopamine levels and CREB phosphorylation in the nucleus accumbens shell, eventually causing positive reinforcement in mice.

Upregulation of CCL7 and CCL2 in reward system mediated through dopamine D1 receptor signaling underlies methamphetamine-induced place preference in mice

We previously showed that the CC-chemokine ligand 2 (CCL2)-CC-chemokine receptor 2 (CCR2) system is responsible for conditioned place preference (CPP) by methamphetamine (Meth). In this study, we investigated the roles for other chemokines mediating Meth-induced CPP and the upstream factors upregulating chemokines in mice. We found that CCL7 mRNA level was upregulated in the prefrontal cortex (PFC) after Meth administration (3mg/kg, subcutaneous), and increased CCL7 immunoreactivity was localized to the PFC NeuN-positive neurons. Meth-induced CPP was blocked by the dopamine D1 receptor antagonist SCH 23390 but not by the D2 receptor antagonists raclopride or haloperidol. The D1 receptor agonist SKF 81297 alone elicited CPP, suggesting a critical role of D1 receptor signaling in Meth-induced reward. Consistent with these results, the Meth-induced upregulation of CCL7 and CCL2 were attenuated by SCH 23390, and a single administration of SKF 81297 upregulated mRNA expression levels of CCL7 and CCL2 in the PFC. Furthermore, Meth-induced CPP was prevented by INCB 3284, a selective antagonist of CCR2, a receptor that binds both CCL7 and CCL2. Collectively, we identified two CC-chemokines (i.e., CCL7 and CCL2) as key regulatory factors in Meth-induced reward. Pharmacological inhibitors of these chemokines may warrant development as novel therapeutics for ameliorating Meth addiction.

Midkine in the mouse ventral tegmental area limits ethanol intake and Ccl2 gene expression

Midkine (MDK) is a cytokine and neurotrophic factor that is more highly expressed in the brains of alcoholics and in mice predisposed to drink large amounts of ethanol, suggesting that MDK may regulate ethanol consumption. Here we measured ethanol consumption in male and female Mdk knockout (-/-) mice using the two-bottle choice and the drinking in the dark (DID) tests. We found that Mdk -/- mice consumed significantly more ethanol than wild-type controls in both tests. To determine if MDK acts in the ventral tegmental area (VTA) to regulate ethanol consumption, we delivered lentivirus expressing a Mdk shRNA into the VTA of male C57BL/6J mice to locally knockdown Mdk and performed the DID test. Mice expressing a Mdk shRNA in the VTA consumed more ethanol than mice expressing a control non-targeting shRNA, demonstrating that the VTA is one site in the brain through which MDK acts to regulate ethanol consumption. Since MDK also controls the expression of inflammatory cytokines in other organs, we examined gene expression of interleukin-1 beta (Il1b), tumor necrosis factor alpha (Tnfα) and the chemokine (C-C motif) ligand 2 (Ccl2) in the VTA of Mdk -/- mice and in mice expressing Mdk shRNA in the VTA. Expression of Ccl2 was elevated in the VTA of Mdk -/- mice and in mice expressing Mdk shRNA in the VTA. These results demonstrate that MDK functions in the VTA to limit ethanol consumption and levels of CCL2, a chemokine known to increase ethanol consumption.

TLR4 signaling in VTA dopaminergic neurons regulates impulsivity through tyrosine hydroxylase modulation

Alcohol dependence is a complex disorder that initiates with episodes of excessive alcohol drinking known as binge drinking, and has a 50-60% risk contribution from inherited susceptibility genes. Cognitive impulsivity is a heritable trait that may set the stage for transition to alcohol dependence but its role in the ethanol-seeking behavior and the involved genes are still poorly understood. We have previously shown that alcohol-preferring P rats have innately elevated levels of a neuronal Toll-like receptor 4 (TLR4) signal in the ventral tegmental area (VTA) that controls the initiation of excessive alcohol drinking. Here we report that TLR4 is localized in dopaminergic (TH+) neurons and it upregulates the expression of tyrosine hydroxylase (TH) through a cAMP-dependent protein kinase (PKA)/cyclic AMP response element binding protein (CREB) signal. P rats have higher impulsivity than wild-type (WT) rats and VTA infusion of a non-replicating Herpes simplex virus (HSV) vector for TLR4-specific small interfering RNA (siRNA; pHSVsiTLR4) inhibits both impulsivity and TLR4/TH expression. A scrambled siRNA vector does not affect gene expression or impulsivity. The data suggest that TLR4 signaling in VTA dopaminergic neurons controls impulsivity related to the regulation of TH expression, likely contributing to the initiation of alcohol drinking and its transition to alcohol dependence.

Cecal Ligation and Puncture Results in Long-Term Central Nervous System Myeloid Inflammation

Survivors of sepsis often experience long-term cognitive and functional decline. Previous studies utilizing lipopolysaccharide injection and cecal ligation and puncture in rodent models of sepsis have demonstrated changes in depressive-like behavior and learning and memory after sepsis, as well as evidence of myeloid inflammation and cytokine expression in the brain, but the long-term course of neuroinflammation after sepsis remains unclear. Here, we utilize cecal ligation and puncture with greater than 80% survival as a model of sepsis. We found that sepsis survivor mice demonstrate deficits in extinction of conditioned fear, but no acquisition of fear conditioning, nearly two months after sepsis. These cognitive changes occur in the absence of neuronal loss or changes in synaptic density in the hippocampus. Sepsis also resulted in infiltration of monocytes and neutrophils into the CNS at least two weeks after sepsis in a CCR2 independent manner. Cellular inflammation is accompanied by long-term expression of pro-inflammatory cytokine and chemokine genes, including TNFα and CCR2 ligands, in whole brain homogenates. Gene expression analysis of microglia revealed that while microglia do express anti-microbial genes and damage-associated molecular pattern molecules of the S100A family of genes at least 2 weeks after sepsis, they do not express the cytokines observed in whole brain homogenates. Our results indicate that in a naturalistic model of infection, sepsis results in long-term neuroinflammation, and that this sustained inflammation is likely due to interactions among multiple cell types, including resident microglia and peripherally derived myeloid cells.

Chronic Intracerebroventricular Infusion of Monocyte Chemoattractant Protein-1 Leads to a Persistent Increase in Sweetened Ethanol Consumption During Operant Self-Administration But Does Not Influence Sucrose Consumption in Long-Evans Rats

BACKGROUND

Among the evidence implicating neuroimmune signaling in alcohol use disorders are increased levels of the chemokine monocyte chemoattractant protein-1 (MCP-1) in the brains of human alcoholics and animal models of alcohol abuse. However, it is not known whether neuroimmune signaling can directly increase ethanol (EtOH) consumption, and whether MCP-1 is involved in that mechanism. We designed experiments to determine whether MCP-1 signaling itself is sufficient to accelerate or increase EtOH consumption. Our hypothesis was that increasing MCP-1 signaling by directly infusing it into the brain would increase operant EtOH self-administration.

METHODS

We implanted osmotic minipumps to chronically infuse either one of several doses of MCP-1 or vehicle into the cerebral ventricles (intracerebroventricular) of Long-Evans rats and then tested them in the operant self-administration of a sweetened EtOH solution for 8 weeks.

RESULTS

There was a significant interaction between dose of MCP-1 and sweetened EtOH consumed across the first 4 weeks (while pumps were flowing) and across the 8-week experiment. Animals receiving the highest dose of MCP-1 (2 μg/d) were the highest consumers of EtOH during weeks 3 through 8. MCP-1 did not influence the acquisition of self-administration (measured across the first 5 days), the motivation to consume EtOH (time to lever press or progressive ratio), withdrawal-induced anxiety, or the consumption of sucrose alone.

CONCLUSIONS

We provide novel evidence that neuroimmune signaling can directly increase chronic operant EtOH self-administration, and that this increase persists beyond the administration of the cytokine. These data suggest that EtOH-induced increases in MCP-1, or increases in MCP-1 due to various other neuroimmune mechanisms, may further promote EtOH consumption. Continued research into this mechanism, particularly using models of alcohol dependence, will help determine whether targeting MCP-1 signaling has therapeutic potential in the treatment of alcohol use disorders.

CRF-amplified neuronal TLR4/MCP-1 signaling regulates alcohol self-administration

Alcohol dependence is a complex disorder that initiates with episodes of excessive alcohol drinking known as binge drinking. It has a 50-60% risk contribution from inherited susceptibility genes; however, their exact identity and function are still poorly understood. We report that alcohol-preferring P rats have innately elevated levels of Toll-like receptor 4 (TLR4) and monocyte chemotactic protein-1 (MCP-1) that colocalize in neurons from the central nucleus of the amygdala (CeA) and ventral tegmental area (VTA). To examine the potential role of a TLR4/MCP-1 signal, we used Herpes Simplex Virus (HSV) vectors (amplicons) that retain in vivo neurotropism. Infusion of amplicons for TLR4 or MCP-1 siRNA into the CeA or VTA from the P rats inhibited target gene expression and blunted binge drinking. A similarly delivered amplicon for scrambled siRNA did not inhibit TLR4 or MCP-1 expression nor reduce binge drinking, identifying a neuronal TLR4/MCP-1 signal that regulates the initiation of voluntary alcohol self-administration. The signal was sustained during alcohol drinking by increased expression of corticotropin-releasing factor and its feedback regulation of TLR4 expression, likely contributing to the transition to alcohol dependence.