TLR3 activation with poly I:C exacerbates escalated alcohol consumption in dependent male C57BL/6J mice

Toll-like receptor 7: A novel neuroimmune target to reduce excessive alcohol consumption

Toll-like receptors (TLRs) are a family of innate immune receptors that recognize molecular patterns in foreign pathogens and intrinsic danger/damage signals from cells. TLR7 is a nucleic acid sensing endosomal TLR that is activated by single-stranded RNAs from microbes or by small noncoding RNAs that act as endogenous ligands. TLR7 signals through the MyD88 adaptor protein and activates the transcription factor interferon regulatory factor 7 (IRF7). TLR7 is found throughout the brain and is highly expressed in microglia, the main immune cells of the brain that have also been implicated in alcohol drinking in mice. Upregulation of TLR7 mRNA and protein has been identified in postmortem hippocampus and cortex from AUD subjects that correlated positively with lifetime consumption of alcohol. Similarly, Tlr7 and downstream signaling genes were upregulated in rat hippocampal and cortical slice cultures after chronic alcohol exposure and in these regions after chronic binge-like alcohol treatment in mice. In addition, repeated administration of the synthetic TLR7 agonists imiquimod (R837) or resiquimod (R848) increased voluntary alcohol drinking in different rodent models and produced sustained upregulation of IRF7 in the brain. These findings suggest that chronic TLR7 activation may drive excessive alcohol drinking. In the brain, this could occur through increased levels of endogenous TLR7 activators, like microRNAs and Y RNAs. This review explores chronic TLR7 activation as a pathway of dysregulated neuroimmune signaling in AUD and the endogenous small RNA ligands in the brain that could perpetuate innate immune responses and escalate alcohol drinking.

The effect of rifampicin on expression of the toll-like receptor system genes in the forebrain cortex of rats prenatally exposed to alcohol

Ethanol causes long-term changes in the toll-like receptor (TLR) system, promoting activation of neuroinflammation pathways. Alcohol use during pregnancy causes neuroinflammatory processes in the fetus; this can lead to the development of symptoms of fetal alcohol spectrum disorder (FASD). Our study has shown that prenatal alcohol exposure (PAE) induced long-term changes in the TLR system genes (Tlr3, Tlr4, Ticam, Hmgb1, cytokine genes) in the forebrain cortex of rat pups. Administration of rifampicin (Rif), which can reduce the level of pro-inflammatory mediators in various pathological conditions of the nervous system, normalized the altered expression level of the studied TLR system genes. This suggests that Rif can prevent the development of persistent neuroinflammatory events in the forebrain cortex of rat pups caused by dysregulation in the TLR system.

The Role of Toll and Nonnuclear NF-κB Signaling in the Response to Alcohol

An understanding of neuroimmune signaling has become central to a description of how alcohol causes addiction and how it damages people with an AUD. It is well known that the neuroimmune system influences neural activity via changes in gene expression. This review discusses the roles played by CNS Toll-like receptor (TLR) signaling in the response to alcohol. Also discussed are observations in Drosophila that show how TLR signaling pathways can be co-opted by the nervous system and potentially shape behavior to a far greater extent and in ways different than generally recognized. For example, in Drosophila, TLRs substitute for neurotrophin receptors and an NF-κB at the end of a TLR pathway influences alcohol responsivity by acting non-genomically.

A review on the reciprocal interactions between neuroinflammatory processes and substance use and misuse, with a focus on alcohol misuse

Background: The last decade has witnessed a surge of findings implicating neuroinflammatory processes as pivotal players in substance use disorders. The directionality of effects began with the expectation that the neuroinflammation associated with prolonged substance misuse contributes to long-term neuropathological consequences. As the literature grew, however, it became evident that the interactions between neuroinflammatory processes and alcohol and drug intake were reciprocal and part of a pernicious cycle in which disease-relevant signaling pathways contributed to an escalation of drug intake, provoking further inflammation-signaling and thereby exacerbating the neuropathological effects of drug misuse.Objectives: The goal of this review and its associated special issue is to provide an overview of the emergent findings relevant to understanding these reciprocal interactions. The review highlights the importance of preclinical and clinical studies in testing and validation of immunotherapeutics as viable targets for curtailing substance use and misuse, with a focus on alcohol misuse.Methods: A narrative review of the literature on drug and neuroinflammation was conducted, as well as articles published in this Special Issue on Alcohol- and Drug-induced Neuroinflammation: Insights from Pre-clinical Models and Clinical Research.Results: We argue that (a) demographic variables and genetic background contribute unique sensitivity to drug-related neuroinflammation; (b) co-morbidities between substance use disorders and affect dysfunction may share common inflammation-related signatures that predict the efficacy of immunotherapeutic drugs; and (c) examination of polydrug interactions with neuroinflammation is a critical area where greater research emphasis is needed.Conclusions: This review provides an accessible and example-driven review of the relationship between drug misuse, neuroinflammatory processes, and their resultant neuropathological outcomes.

[Ginsenosides affect the system of Toll-like receptors in the brain of rats under conditions of long-term alcohol withdrawal]

Long-term alcohol consumption causes the development of neuroinflammation in various brain structures. One of the mechanisms involved in this process is the increased activity of TLR-signaling intracellular pathways. Studies confirm the ability of ginseng extract or its individual ginsenosides to reduce the increased activity of TLR-signaling pathways. The aim of our study was to study the effect of the amount of ginsenosides obtained from the extract of the Panax japonicus cell line on the state of the TLR-signaling system in the nucleus accumbens and hippocampus of the rat brain in a model of long-term alcohol consumption during alcohol withdrawal. The results of the study showed that ginsenosides were able to make changes in the TLR signaling system, which has been altered by long-term alcohol consumption. A significant effect of ginsenosides on the level of TLR3 and TLR4 mRNA in the nucleus accumbens was found, while in the hippocampus, ginsenosides significantly affected the level of TLR7 mRNA. The effect of ginsenosides on the level of mRNA of transcription factors and cytokines involved in TLR-signaling was evaluated. Thus, results of our study confirm that ginsenosides are able to influence the state of TLR-signaling pathways, but this effect is multidirectional in relation to different brain structures. In the future, it seems interesting to evaluate the role of individual ginsenosides in relation to genes of TLR-signaling, as well as the effect of ginsenosides on other brain structures.