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

Morphine self-administration decreases intrinsic excitability of accumbal medium spiny neurons and suppresses the innate immune system in male Wistar rats

INTRODUCTION

Morphine alleviates severe pain but is addictive and associated with weakened immune system. Interestingly, the immunosuppressive effects have been linked to central circuits including the nucleus accumbens shell (NAc), suggesting that there might be a direct link between reward processing in the NAc and weakened immune system. The overall aim with this study was to assess the impact displayed by morphine self-administration on neuroplasticity in the NAc shell and circulating white blood cells.

METHODS

Wistar rats received morphine injections over ten days, and locomotor activity was monitored. Next, morphine self-administration, and relapse drinking after forced abstinence, were assessed. Lastly, electrophysiological recordings were conducted in the NAc ex vivo to define neurophysiological adaptations, and hematological analysis were conducted in parallel.

RESULTS

While ten days of morphine injections were not sufficient to affect morphine self-administration, behavioral sensitization to the locomotor stimulatory properties of morphine was observed and further correlated with the amount of morphine consumed following forced abstinence. Electrophysiological slice recordings demonstrated no effect on excitatory neurotransmission, but the intrinsic excitability of NAc neurons was significantly depressed compared to water drinking controls. In addition, hematological analysis demonstrated a significant decline in the number of white blood cells, especially monocytes and neutrophils, while erythrocytes were not affected. The amount of circulating white blood cells further correlated with morphine intake, but not with neurophysiological parameters.

CONCLUSION

The data presented here demonstrates that morphine self-administration produces accumbal neuroplasticity and biological transformations that could contribute to the addictive and immunosuppressive properties of morphine.

Methadone and Buprenorphine as Medication for Addiction Treatment Diversely Affect Inflammation and Craving Depending on Their Doses

Buprenorphine and methadone are widely used as medication for addiction treatment (MAT) in patients with opioid use disorders. However, there is no compelling evidence of their impact on the immune-endocrine response. Therefore, the aim of this study was to examine the effects of the aforementioned medications on craving and on biomarkers of inflammation and cortisol, approaching the dose issue concurrently. Sixty-six patients (thirty-four under methadone and thirty-two under buprenorphine) who had just entered a MAT program and were stabilized with the suitable administered doses after a two-week process were divided into four groups based on medication dose (i.e., methadone high dose, buprenorphine high dose, methadone medium dose, and buprenorphine medium dose). The heroin craving questionnaire for craving assessment was completed, and the blood biomarkers were measured on Days 1 and 180. According to the results, high doses of both medications were accompanied by low levels of craving, cortisol, and inflammation on Day 1, and no alterations were observed on Day 180. On the contrary, medium doses reduced the tested psychosocial and biochemical parameters in terms of time, indicating a positive action for the patients. Concludingly, modifications in MAT doses are needed soon after the stabilization process to prevent inflammation and avoid relapse, thus helping opioid-addicted patients toward rehabilitation.

Methamphetamine-mediated astrocytic pyroptosis and neuroinflammation involves miR-152-NLRP6 inflammasome signaling axis

Methamphetamine is a widely abused drug associated with significant neuroinflammation and neurodegeneration, mainly through the activation of glial cells and neurons in the central nervous system. This study investigates the role of the astrocyte-specific NOD-like receptor family pyrin domain-containing protein 6 (NLRP6) inflammasome in methamphetamine-induced astrocytic pyroptosis and neuroinflammation. Our findings demonstrate that methamphetamine exposure induces NLRP6-dependent pyroptosis, astrocyte activation, and the release of proinflammatory cytokines in mouse primary astrocytes. Gene silencing of NLRP6 reduces methamphetamine-induced pyroptosis and proinflammatory cytokines release. We also identified miR-152 as a critical upstream regulator of NLRP6, which is downregulated in methamphetamine-exposed astrocytes. Overexpression of miR-152 decreases NLRP6 expression, mitigating methamphetamine-induced pyroptosis and inflammation. In vivo and ex vivo studies in methamphetamine-exposed mice confirmed these results and showed that methamphetamine induces anxiety-like, cognitive impairment, and depression-like behavior, further linking astrocyte-specific NLRP6 signaling to methamphetamine-induced neuroinflammation. This study highlights the potential of targeting the NLRP6 inflammasome in astrocytes as a therapeutic approach to alleviate methamphetamine-induced central nervous system pathology. Further research is warranted to explore clinical applications and identify therapeutic targets for methamphetamine-related neurological disorders.

The interaction between central and peripheral immune systems in methamphetamine use disorder: current status and future directions

Methamphetamine (METH) use disorder (MUD) is characterized by compulsive drug-seeking behavior and substantial neurotoxicity, posing a considerable burden on individuals and society. Traditionally perceived as a localized central nervous system disorder, recent preclinical and clinical studies have elucidated that MUD is a multifaceted disorder influenced by various biological systems, particularly the immune system. Emerging evidence suggests that both central and peripheral immune responses play a crucial role in the initiation and persistence of MUD. Conceptualizing it as a systemic immune process prompts significant inquiries regarding the mechanisms of communication between peripheral and central compartments. Also, whether this intercommunication could serve as diagnostic biomarkers or therapeutic targets. This review begins by offering an overview of mechanistic studies pertaining to the neuroimmune and peripheral immune systems. Finally, future directions are suggested through the integration of innovative technologies and multidimensional data to promote the translation of basic mechanistic research into clinical diagnostic and therapeutic interventions.

Influence of cocaine use reduction on markers of immune function

This study determined the effects of reduced cocaine use on immune function. Treatment seeking participants with Cocaine Use Disorder enrolled in a 12-week contingency management trial to reduce cocaine use. Participants were randomly assigned 1:1:1 to High Value Reinforcers (i.e., $55/negative urine sample) for cocaine abstinence (n = 41), Low Value Reinforcers (i.e., $13/negative urine sample) for cocaine abstinence (n = 33) or Non-Contingent Control (n = 33). Immune measures were collected at 6-week intervals. The High Value group had greatest use reductions, increased erythema and IL-6 and decreased IL-10 and CCL5, suggesting an activated immune response. Cocaine use reduction may promote changes in immune health.

Substance Addiction Rehabilitation Drugs

The relapse rate of substance abusers is high, and addiction rehabilitation adjunct drugs need to be developed urgently. There have been numerous reports on blocking the formation of substance addiction, but studies on drugs that can alleviate withdrawal symptoms are very limited. Both the dopamine transporter (DAT) hypothesis and D3 dopamine receptor (D3R) hypothesis are proposed. DAT activators reduce the extracellular dopamine level, and D3R antagonists reduce the neuron's sensitivity to dopamine, both of which may exacerbate the withdrawal symptoms subsequently. The D3R partial agonist SK608 has biased signaling properties via the G-protein-dependent pathway but did not induce D3R desensitization and, thus, may be a promising drug for the withdrawal symptoms. Drugs for serotoninergic neurons or GABAergic neurons and anti-inflammatory drugs may have auxiliary effects to addiction treatments. Drugs that promote structural synaptic plasticity are also discussed.

Impaired extinction of cocaine seeking in HIV-infected mice is accompanied by peripheral and central immune dysregulation

Substance use disorders (SUDs) are highly comorbid with HIV infection, necessitating an understanding of the interactive effects of drug exposure and HIV. The relationship between HIV infection and cocaine use disorder is likely bidirectional, with cocaine use directly impacting immune function while HIV infection alters addiction-related behavior. To better characterize the neurobehavioral and immune consequences of HIV infection and cocaine exposure, this study utilizes a humanized mouse model to investigate the outcomes of HIV-1 infection on cocaine-related behaviors in a conditioned place preference (CPP) model, and the interactive effects of cocaine and HIV infection on peripheral and central nervous system inflammation. HIV infection selectively impairs cocaine CPP extinction without effecting reinstatement or cocaine seeking under conflict. Behavioral alterations are accompanied by immune changes in HIV infected mice, including increased prefrontal cortex astrocyte immunoreactivity and brain-region specific effects on microglia number and reactivity. Peripheral immune system changes are observed in human cytokines, including HIV-induced reductions in human TNFα, and cocaine and HIV interactions on GM-CSF levels. Together these data provide new insights into the unique neurobehavioral outcomes of HIV infection and cocaine exposure and how they interact to effect immune responses.

Relationship between sphingolipids-mediated neuroinflammation and alcohol use disorder

BACKGROUND

Alcohol use disorder is a chronic recurrent encephalopathy, and its pathogenesis has not been fully understood. Among possible explanations, neuroinflammation caused by the disorders of brain central immune signaling has been identified as one possible mechanism of alcohol use disorder. As the basic components of cells and important bioactive molecules, sphingolipids are essential in regulating many cellular activities. Recent studies have shown that sphingolipids-mediated neuroinflammation may be involved in the development of alcohol use disorder.

METHODS

PubMed databases were searched for literature on sphingolipids and alcohol use disorder (alcohol abuse, alcohol addiction, alcohol dependence, and alcohol misuse) including evidence of the relationship between sphingolipids-mediated neuroinflammation and alcohol use disorder (formation, withdrawal, treatment).

RESULTS

Disorders of sphingolipid metabolism, including the different types of sphingolipids and regulatory enzyme activity, have been found in patients with alcohol use disorder as well as animal models, which in turn cause neuro-inflammation in the central nervous system. Thus, these disorders may also be an important mechanism in the development of alcohol use disorder in patients. In addition, different sphingolipids may have different or even reverse effects on alcohol use disorder.

CONCLUSIONS

The sphingolipids-mediated neuroinflammation plays an important role in the development of alcohol use disorder. This review proposes a potential approach to prevent and treat alcohol use disorders by manipulating sphingolipid metabolism.

Modafinil, an atypical CNS stimulant?

Modafinil is a central nervous system stimulant approved for the treatment of narcolepsy and sleep disorders. Due to its wide range of biochemical actions, modafinil has been explored for other potential therapeutic uses. Indeed, it has shown promise as a therapy for cognitive disfunction resulting from neurologic disorders like ADHD, and as a smart drug in non-medical settings. The mechanism(s) of actions underlying the therapeutic efficacy of this agent remains largely elusive. Modafinil is known to inhibit the dopamine transporter, thus decreasing dopamine reuptake following neuronal release, an effect shared by addictive psychostimulants. However, modafinil is unique in that only a few cases of dependence on this drug have been reported, as compared to other psychostimulants. Moreover, modafinil has been tested, with some success, as a potential therapeutic agent to combat psychostimulant and other substance use disorders. Modafinil has additional, but less understood, actions on other neurotransmitter systems (GABA, glutamate, serotonin, norepinephrine, etc.). These interactions, together with its ability to activate selected brain regions, are likely one of the keys to understand its unique pharmacology and therapeutic activity as a CNS stimulant. In this chapter, we outline the pharmacokinetics and pharmacodynamics of modafinil that suggest it has an "atypical" CNS stimulant profile. We also highlight the current approved and off label uses of modafinil, including its beneficial effects as a treatment for sleep disorders, cognitive functions, and substance use disorders.

Focal mu-opioid receptor activation promotes neuroinflammation and microglial activation in the mesocorticolimbic system: Alterations induced by inflammatory pain

Microglia participates in the modulation of pain signaling. The activation of microglia is suggested to play an important role in affective disorders that are related to a dysfunction of the mesocorticolimbic system (MCLS) and are commonly associated with chronic pain. Moreover, there is evidence that mu-opioid receptors (MORs), expressed in the MCLS, are involved in neuroinflammatory events, although the way by which they do it remains to be elucidated. In this study, we propose that MOR pharmacological activation within the MCLS activates and triggers the local release of proinflammatory cytokines and this pattern of activation is impacted by the presence of systemic inflammatory pain. To test this hypothesis, we used in vivo microdialysis coupled with flow cytometry to measure cytokines release in the nucleus accumbens and immunofluorescence of IBA1 in areas of the MCLS on a rat model of inflammatory pain. Interestingly, the treatment with DAMGO, a MOR agonist locally in the nucleus accumbens, triggered the release of the IL1α, IL1β, and IL6 proinflammatory cytokines. Furthermore, MOR pharmacological activation in the ventral tegmental area (VTA) modified the levels of IBA1-positive cells in the VTA, prefrontal cortex, the nucleus accumbens and the amygdala in a dose-dependent way, without impacting mechanical nociception. Additionally, MOR blockade in the VTA prevents DAMGO-induced effects. Finally, we observed that systemic inflammatory pain altered the IBA1 immunostaining derived from MOR activation in the MSCLS. Altogether, our results indicate that the microglia-MOR relationship could be pivotal to unravel some inflammatory pain-induced comorbidities related to MCLS dysfunction.

Microglia NLRP3 Inflammasome and Neuroimmune Signaling in Substance Use Disorders

During the last decade, substance use disorders (SUDs) have been increasingly recognized as neuroinflammation-related brain diseases. Various types of abused drugs (cocaine, methamphetamine, alcohol, opiate-like drugs, marijuana, etc.) can modulate the activation status of microglia and neuroinflammation levels which are involved in the pathogenesis of SUDs. Several neuroimmune signaling pathways, including TLR/NF-кB, reactive oxygen species, mitochondria dysfunction, as well as autophagy defection, etc., have been implicated in promoting SUDs. Recently, inflammasome-mediated signaling has been identified as playing critical roles in the microglia activation induced by abused drugs. Among the family of inflammasomes, NOD-, LRR-, and pyrin-domain-containing protein 3 (NLRP3) serves the primary research target due to its abundant expression in microglia. NLRP3 has the capability of integrating multiple external and internal inputs and coordinately determining the intensity of microglia activation under various pathological conditions. Here, we summarize the effects of abused drugs on NLRP3 inflammasomes, as well as others, if any. The research on this topic is still at an infant stage; however, the readily available findings suggest that NLRP3 inflammasome could be a common downstream effector stimulated by various types of abused drugs and play critical roles in determining abused-drug-mediated biological effects through enhancing glia-neuron communications. NLRP3 inflammasome might serve as a novel target for ameliorating the development of SUDs.

Challenges and future trends in wearable closed-loop neuromodulation to efficiently treat methamphetamine addiction

Achieving abstinence from drugs is a long journey and can be particularly challenging in the case of methamphetamine, which has a higher relapse rate than other drugs. Therefore, real-time monitoring of patients' physiological conditions before and when cravings arise to reduce the chance of relapse might help to improve clinical outcomes. Conventional treatments, such as behavior therapy and peer support, often cannot provide timely intervention, reducing the efficiency of these therapies. To more effectively treat methamphetamine addiction in real-time, we propose an intelligent closed-loop transcranial magnetic stimulation (TMS) neuromodulation system based on multimodal electroencephalogram-functional near-infrared spectroscopy (EEG-fNIRS) measurements. This review summarizes the essential modules required for a wearable system to treat addiction efficiently. First, the advantages of neuroimaging over conventional techniques such as analysis of sweat, saliva, or urine for addiction detection are discussed. The knowledge to implement wearable, compact, and user-friendly closed-loop systems with EEG and fNIRS are reviewed. The features of EEG and fNIRS signals in patients with methamphetamine use disorder are summarized. EEG biomarkers are categorized into frequency and time domain and topography-related parameters, whereas for fNIRS, hemoglobin concentration variation and functional connectivity of cortices are described. Following this, the applications of two commonly used neuromodulation technologies, transcranial direct current stimulation and TMS, in patients with methamphetamine use disorder are introduced. The challenges of implementing intelligent closed-loop TMS modulation based on multimodal EEG-fNIRS are summarized, followed by a discussion of potential research directions and the promising future of this approach, including potential applications to other substance use disorders.