Microglial IL-1β progressively increases with duration of alcohol consumption

Chronic ethanol induces a pro-inflammatory switch in interleukin-1β regulation of GABAergic signaling in the medial prefrontal cortex of male mice

Neuroimmune pathways regulate brain function to influence complex behavior and play a role in several neuropsychiatric diseases, including alcohol use disorder (AUD). In particular, the interleukin-1 (IL-1) system has emerged as a key regulator of the brain's response to ethanol (alcohol). Here we investigated the mechanisms underlying ethanol-induced neuroadaptation of IL-1β signaling at GABAergic synapses in the prelimbic region of the medial prefrontal cortex (mPFC), an area responsible for integrating contextual information to mediate conflicting motivational drives. We exposed C57BL/6J male mice to the chronic intermittent ethanol vapor-2 bottle choice paradigm (CIE-2BC) to induce ethanol dependence, and conducted ex vivo electrophysiology and molecular analyses. We found that the IL-1 system regulates basal mPFC function through its actions at inhibitory synapses on prelimbic layer 2/3 pyramidal neurons. IL-1β can selectively recruit either neuroprotective (PI3K/Akt) or pro-inflammatory (MyD88/p38 MAPK) mechanisms to produce opposing synaptic effects. In ethanol naïve conditions, there was a strong PI3K/Akt bias leading to a disinhibition of pyramidal neurons. Ethanol dependence produced opposite IL-1 effects - enhanced local inhibition via a switch in IL-1β signaling to the canonical pro-inflammatory MyD88 pathway. Ethanol dependence also increased cellular IL-1β in the mPFC, while decreasing expression of downstream effectors (Akt, p38 MAPK). Thus, IL-1β may represent a key neural substrate in ethanol-induced cortical dysfunction. As the IL-1 receptor antagonist (kineret) is already FDA-approved for other diseases, this work underscores the high therapeutic potential of IL-1 signaling/neuroimmune-based treatments for AUD.

Oxytocin reverses ethanol consumption and neuroinflammation induced by social defeat in male mice

Oxytocin (OXT) modulates social interactions, attenuates stressful responses and can decrease drug-seeking and taking behaviors. In previous studies, we observed that social defeat (SD) induced a long-lasting increase in ethanol intake and neuroinflammation in male mice. We also know that OXT blocks the increase in cocaine reward induced by SD. Therefore, in the present study we aimed to evaluate the effect of 1 mg/kg of OXT administered 30 min before each episode of SD on ethanol consumption and the neuroinflammatory response in adult male mice. Three weeks after the last SD, mice underwent oral ethanol self-administration (SA) procedure, and striatal levels of the two chemokines CX3CL1 and CXCL12 were measured after the last SD and at the end of the ethanol SA. OXT administration blocked the increase in voluntary ethanol consumption observed in defeated mice, although it did not affect motivation for ethanol. An increase in the striatal levels of CX3CL1 and CXCL12 was observed in defeated animals immediately after the last defeat and after the ethanol SA. However, defeated mice treated with OXT did not show this increase in the neuroinflammatory response. In conclusion, OXT treatment can be a powerful therapeutic target to reduce the negative effects of social stress on ethanol consumption and the neuroinflammatory process.

Targeting neuroinflammation: The therapeutic potential of ω-3 PUFAs in substance abuse

Substance abuse is a chronic relapsing disorder that results in serious health and socioeconomic issues worldwide. Addictive drugs induce long-lasting morphologic and functional changes in brain circuits and account for the formation of compulsive drug-seeking and drug-taking behaviors. Yet, there remains a lack of reliable therapy. In recent years, accumulating evidence indicated that neuroinflammation was implicated in the development of drug addiction. Findings from both our and other laboratories suggest that ω-3 polyunsaturated fatty acids (PUFAs) are effective in treating neuroinflammation-related mental diseases, and indicate that they could exert positive effects in treating drug addiction. Thus, in the present review, we summarized and evaluated recently published articles reporting the neuroinflammation mechanism in drug addiction and the immune regulatory ability of ω-3 PUFAs. We also sought to identify some of the challenges ahead in the translation of ω-3 PUFAs into addiction treatment.

Curcumin treatment attenuates alcohol-induced alterations in a mouse model of foetal alcohol spectrum disorders

Alcohol exposure during development produces physical and mental abnormalities in the foetus that result in long-term molecular adjustments in the brain, which could underlie the neurobehavioural deficits observed in individuals suffering from foetal alcohol spectrum disorders. In this study, we assessed the effects of curcumin on cognitive impairments caused by prenatal and lactational alcohol exposure (PLAE). Furthermore, we examined whether curcumin could counteract the molecular alterations that may underlie these behavioural impairments. We focused on inflammatory and epigenetic mechanisms by analysing the expression of pro-inflammatory mediators, such as IL-6, TNF-α, and NF-κB, in the hippocampus and prefrontal cortex, as well as microglia and astrocyte activation in the dentate gyrus. We also assessed the activity of histone acetyltransferase in these brain areas. To model binge alcohol drinking, we exposed pregnant C57BL/6 mice to a 20% v/v alcohol solution during gestation and lactation, with limited access periods. We treated male offspring with curcumin during postnatal days (PD28-35) and then evaluated their behaviour in adulthood (PD60). Our results showed that curcumin treatment during the peri-adolescence period improved the anxiety and memory deficits observed in PLAE mice. At the molecular level, we found enhanced histone acetyltransferase activity in mice subjected to PLAE that curcumin treatment could not reverse to baseline levels. These mice also showed increased expression of pro-inflammatory mediators, which could be rescued by curcumin treatment. They also displayed astrogliosis and microglia activation. Our study provides further evidence to support the use of curcumin as a therapeutic agent for counteracting behavioural and molecular alterations induced by PLAE.

Environmental Signals on Microglial Function during Brain Development, Neuroplasticity, and Disease

Recent discoveries on the neurobiology of the immunocompetent cells of the central nervous system (CNS), microglia, have been recognized as a growing field of investigation on the interactions between the brain and the immune system. Several environmental contexts such as stress, lesions, infectious diseases, and nutritional and hormonal disorders can interfere with CNS homeostasis, directly impacting microglial physiology. Despite many encouraging discoveries in this field, there are still some controversies that raise issues to be discussed, especially regarding the relationship between the microglial phenotype assumed in distinct contexts and respective consequences in different neurobiological processes, such as disorders of brain development and neuroplasticity. Also, there is an increasing interest in discussing microglial–immune system cross-talk in health and in pathological conditions. In this review, we discuss recent literature concerning microglial function during development and homeostasis. In addition, we explore the contribution of microglia to synaptic disorders mediated by different neuroinflammatory outcomes during pre- and postnatal development, with long-term consequences impacting on the risk and vulnerability to the emergence of neurodevelopmental, neurodegenerative, and neuropsychiatric disorders.

Microglial alterations induced by psychoactive drugs: A possible mechanism in substance use disorder?

Recently, the xenobiotic hypothesis has implicated the immune system in targeting substances of abuse as foreign molecules and stimulating inflammatory responses. Microglial cells are the resident immune cells of the central nervous system and function in homeostatic surveillance. Microglial changes that are induced by exposure to substances of abuse appear to mediate in part the establishment of addiction and the persistence of drug-mediated biological and behavioral changes. In this context, interest in the study of drug-microglia interactions has increased recently. This review summarizes the most recent preclinical rodent and clinical studies on the interaction between microglia and various classes of drugs of abuse, such as ethanol, psychostimulants, and opioids. The principal biological mechanisms of the communication between substances of abuse and microglia will be described to consider putative mechanisms of the establishment of drug addiction and future potential targets for treating substance use disorder.

IL-1β expression is increased and regulates GABA transmission following chronic ethanol in mouse central amygdala

The interleukin-1 system (IL-1) is a prominent pro-inflammatory pathway responsible for the initiation and regulation of immune responses. Human genetic and preclinical studies suggest a critical role for IL-1β signaling in ethanol drinking and dependence, but little is known about the effects of chronic ethanol on the IL-1 system in addiction-related brain regions such as the central amygdala (CeA). In this study, we generated naïve, non-dependent (Non-Dep) and dependent (Dep) male mice using a paradigm of chronic-intermittent ethanol vapor exposure interspersed with two-bottle choice to examine 1) the expression of IL-1β, 2) the role of the IL-1 system on GABAergic transmission, and 3) the potential interaction with the acute effects of ethanol in the CeA. Immunohistochemistry with confocal microscopy was used to assess expression of IL-1β in microglia and neurons in the CeA, and whole-cell patch clamp recordings were obtained from CeA neurons to measure the effects of IL-1β (50 ng/ml) or the endogenous IL-1 receptor antagonist (IL-1ra; 100 ng/ml) on action potential-dependent spontaneous inhibitory postsynaptic currents (sIPSCs). Overall, we found that IL-1β expression is significantly increased in microglia and neurons of Dep compared to Non-Dep and naïve mice, IL-1β and IL-1ra bi-directionally modulate GABA transmission through both pre- and postsynaptic mechanisms in all three groups, and IL-1β and IL-1ra do not alter the facilitation of GABA release induced by acute ethanol. These data suggest that while ethanol dependence induces a neuroimmune response in the CeA, as indicated by increased IL-1β expression, this does not significantly alter the neuromodulatory role of IL-1β on synaptic transmission.

GINS complex subunit 2 (GINS2) plays a protective role in alcohol-induced brain injury

Acute alcohol intoxication is a central nervous system disease that accounts for a large number of hospital admissions. In the present study, we have explored the role of GINS complex subunit 2 (GINS2) in acute alcohol intoxication and alcohol-induced brain injury. We began by determining that GINS2 mRNA expression was significantly increased in the serum of patients with alcohol abuse. We then found that GINS2 is increased in mouse brains after alcohol consumption. To explore the role of GINS2 in alcohol-induced microglia function, we knocked down GINS2 in mouse microglia and then treated the cells with alcohol. Knockdown of GINS2 significantly increased alcohol-induced ROS production and the oxidative stress marker malondialdehyde. To explore if GINS2 is involved in alcohol-induced microglia apoptosis, we examined cell viability in GINS2 knockdown cells by TUNEL staining and caspase activity assays. Consistently, results showed that alcohol-induced cell apoptosis was promoted by knockdown of GINS2. Finally, we assessed expression levels of inflammatory factors in GINS2 knockdown microglial cells as well as the effects of GINS2 knockdown on NF-κB signalling. Inflammatory factors were stimulated by alcohol and further promoted by GINS2 knockdown, and GINS2 knockdown promoted alcohol-induced NF-κB activity in microglia.

Pharmacological blockade of fatty acid amide hydrolase (FAAH) by URB597 improves memory and changes the phenotype of hippocampal microglia despite ethanol exposure

Changes in endogenous cannabinoid homeostasis are associated with both ethanol-related neuroinflammation and memory decline. Extensive research is still required to unveil the role of endocannabinoid signaling activation on hippocampal microglial cells after ethanol exposure. Either microglial morphology, phenotype and recruitment may become notably altered after chronic alcohol-related neurodegeneration. Here, we evaluated the pharmacological effects of fatty-acid amide-hydrolase (FAAH) inhibitor URB597 (0.3 mg/kg), oleoylethanolamide (OEA, 10 mg/kg), arachidonoylethanolamide (AEA, 10 mg/kg), the CB1 receptor agonist ACEA (3 mg/kg) and the CB2 receptor agonist JWH133 (0.2 mg/kg) administered for 5 days in a rat model of subchronic (2 weeks) ethanol diet (11% v/v) exposure. URB597 turned to be the most effective treatment. URB597 increased microglial (IBA-1+) cell population, and changed morphometric features (cell area and perimeter, roughness, fractal dimension, lacunarity) associated with activated microglia in the hippocampus of ethanol-exposed rats. Regarding innate immune activity, URB597 specifically increased mRNA levels of toll-like receptor 4 (TLR4), glial fibrillary acidic protein (Gfap) and the chemokine stromal cell-derived factor 1 (SDF-1α/CXCL12), and elevated the cell population expressing the chemokine receptors CX3CR1, CCR2 and CCR4 in the ethanol-exposed rat hippocampus. Contrary to ethanol effect, URB597 reduced mRNA levels of Iba-1, Tnfα, IL-6 and the monocyte chemoattractant protein-1 (MCP-1/CCL2), as well as cell population expressing iNOS. URB597 effects on hippocampal immune system were accompanied by changes in short and long-term visual recognition memory. These results suggest that FAAH inhibition may modulates hippocampal microglial recruitment and activation that can be associated with improved hippocampal-dependent memory despite ethanol exposure.

Long-Term Depression Induced by Optogenetically Driven Nociceptive Inputs to Trigeminal Nucleus Caudalis or Headache Triggers

The peripheral trigeminovascular pathway mediates orofacial and craniofacial pain and projects centrally to the brainstem trigeminal nucleus caudalis (TNc). Sensitization of this pathway is involved in many pain conditions, but little is known about synaptic plasticity at its first central synapse. We have taken advantage of optogenetics to investigate plasticity selectively evoked at synapses of nociceptive primary afferents onto TNc neurons. Based on immunolabeling in the trigeminal ganglia, TRPV1-lineage neurons comprise primarily peptidergic and nonpeptidergic nociceptors. Optical stimulation of channelrhodopsin-expressing axons in the TRPV1/ChR2 mouse in TNc slices thus allowed us to activate a nociceptor-enriched subset of primary afferents. We recorded from lamina I/II neurons in acutely prepared transverse TNc slices, and alternately stimulated two independent afferent pathways, one with light-activated nociceptive afferents and the other with electrically-activated inputs. Low-frequency optical stimulation induced robust long-term depression (LTD) of optically-evoked EPSCs, but not of electrically-evoked EPSCs in the same neurons. Blocking NMDA receptors or nitric oxide synthase strongly attenuated LTD, whereas a cannabinoid receptor 1 antagonist had no effect. The neuropeptide PACAP-38 or the nitric oxide donors nitroglycerin or sodium nitroprusside are pharmacologic triggers of human headache. Bath application of any of these three compounds also persistently depressed optically-evoked EPSCs. Together, our data show that LTD of nociceptive afferent synapses on trigeminal nucleus neurons is elicited when the afferents are activated at frequencies consistent with the development of central sensitization of the trigeminovascular pathway.SIGNIFICANCE STATEMENT Animal models suggest that sensitization of trigeminovascular afferents plays a major role in craniofacial pain syndromes including primary headaches and trigeminal neuralgia, yet little is known about synaptic transmission and plasticity in the brainstem trigeminal nucleus caudalis (TNc). Here we used optogenetics to selectively drive a nociceptor-enriched population of trigeminal afferents while recording from superficial laminae neurons in the TNc. Low-frequency optical stimulation evoked robust long-term depression at TRPV1/ChR2 synapses. Moreover, application of three different headache trigger drugs also depressed TRPV1/ChR2 synapses. Synaptic depression at these primary afferent synapses may represent a newly identified mechanism contributing to central sensitization during headache.