Astrocyte Dysfunction Induced by Alcohol in Females but Not Males

Sex differences in Huntington's disease from a neuroinflammation perspective

Huntington's disease (HD) is a debilitating neurodegenerative condition characterized by motor, cognitive and psychiatric abnormalities. Immune dysregulation, prominently featuring increased immune activity, plays a significant role in HD pathogenesis. In addition to the central nervous system (CNS), systemic innate immune activation and inflammation are observed in HD patients, exacerbating the effects of the Huntingtin (HTT) gene mutation. Recent attention to sex differences in HD symptom severity underscores the need to consider gender as a biological variable in neurodegenerative disease research. Understanding sex-specific immune responses holds promise for elucidating HD pathophysiology and informing targeted treatment strategies to mitigate cognitive and functional decline. This perspective will highlight the importance of investigating gender influence in HD, particularly focusing on sex-specific immune responses predisposing individuals to disease.

Treadmill Exercise Reshapes Cortical Astrocytic and Neuronal Activity to Improve Motor Learning Deficits Under Chronic Alcohol Exposure

Alcohol abuse induces various neurological disorders including motor learning deficits, possibly by affecting neuronal and astrocytic activity. Physical exercise is one effective approach to remediate synaptic loss and motor deficits as shown by our previous works. In this study, we unrevealed the role of exercise training in the recovery of cortical neuronal and astrocytic functions. Using a chronic alcohol injection mouse model, we found the hyperreactivity of astrocytes along with dendritic spine loss plus lower neuronal activity in the primary motor cortex. Persistent treadmill exercise training, on the other hand, improved neural spine formation and inhibited reactive astrocytes, alleviating motor learning deficits induced by alcohol exposure. These data collectively support the potency of endurance exercise in the rehabilitation of motor functions under alcohol abuse.

Estrogen signaling in the dorsal raphe regulates binge-like drinking in mice

Estrogens promote binge alcohol drinking and contribute to sex differences in alcohol use disorder. However, the mechanisms are largely unknown. This study aims to test if estrogens act on 5-hydroxytryptamine neurons in the dorsal raphe nucleus (5-HTDRN) to promote binge drinking. We found that female mice drank more alcohol than male mice in chronic drinking in the dark (DID) tests. This sex difference was associated with distinct alterations in mRNA expression of estrogen receptor α (ERα) and 5-HT-related genes in the DRN, suggesting a potential role of estrogen/ERs/5-HT signaling. In supporting this view, 5-HTDRN neurons from naïve male mice had lower baseline firing activity but higher sensitivity to alcohol-induced excitation compared to 5-HTDRN neurons from naïve female mice. Notably, this higher sensitivity was blunted by 17β-estradiol treatment in males, indicating an estrogen-dependent mechanism. We further showed that both ERα and ERβ are expressed in 5-HTDRN neurons, whereas ERα agonist depolarizes and ERβ agonist hyperpolarizes 5-HTDRN neurons. Notably, both treatments blocked the stimulatory effects of alcohol on 5-HTDRN neurons in males, even though they have antagonistic effects on the activity dynamics. These results suggest that ERs' inhibitory effects on ethanol-induced burst firing of 5-HTDRN neurons may contribute to higher levels of binge drinking in females. Consistently, chemogenetic activation of ERα- or ERβ-expressing neurons in the DRN reduced binge alcohol drinking. These results support a model in which estrogens act on ERα/β to prevent alcohol-induced activation of 5-HTDRN neurons, which in return leads to higher binge alcohol drinking.

Neuroimmune Activation and Microglia Reactivity in Female Rats Following Alcohol Dependence

The rates of alcohol use disorder among women are growing, yet little is known about how the female brain is affected by alcohol. The neuroimmune system, and specifically microglia, have been implicated in mediating alcohol neurotoxicity, but most preclinical studies have focused on males. Further, few studies have considered changes to the microglial phenotype when examining the effects of ethanol on brain structure and function. Therefore, we quantified microglial reactivity in female rats using a binge model of alcohol dependence, assessed through morphological and phenotypic marker expression, coupled with regional cytokine levels. In a time- and region-dependent manner, alcohol altered the microglial number and morphology, including the soma and process area, and the overall complexity within the corticolimbic regions examined, but no significant increases in the proinflammatory markers MHCII or CD68 were observed. The majority of cytokine and growth factor levels examined were similarly unchanged. However, the expression of the proinflammatory cytokine TNFα was increased, and the anti-inflammatory IL-10, decreased. Thus, female rats showed subtle differences in neuroimmune reactivity compared to past work in males, consistent with reports of enhanced neuroimmune responses in females across the literature. These data suggest that specific neuroimmune reactions in females may impact their susceptibility to alcohol neurotoxicity and other neurodegenerative events with microglial contributions.

Effect of menstrual cycle on rewarding properties of alcohol cues in women

OBJECTIVE

Compared with men, women are disproportionately affected by alcohol, including greater risks of behavioral impairment and relapse from abstinence-based treatments. One potential mechanism underlying this disparity is ovarian hormone fluctuations across menstrual cycle phases, particularly estradiol (E2). Preclinical and clinical studies have shown that E2 levels positively correlate with alcohol consumption, suggesting E2 modulates drinking. Rewarding properties of alcohol are thought to mediate this relationship. The present study tested the degree to which women report increased rewarding effects from alcohol and heightened attention to alcohol-related cues when E2 was elevated during the late follicular phase of the menstrual cycle.

METHOD

Fifty women aged 21-29 participated in a within-subjects placebo-controlled study examining how menstrual cycle phase alters the rewarding properties of alcohol and alcohol-associated cues when sober and intoxicated, as measured by their attentional bias toward alcohol-associated cues and subjective reports. Measures were obtained following 0.60 g/kg alcohol and placebo during the early follicular phase when E2 was low and the late follicular phase (i.e., ovulation) when E2 was elevated.

RESULTS

Attentional bias to alcohol-associated cues was greater during the late follicular phase in both sober and intoxicated states. Women reported rewarding effects from alcohol, but no effects of phase were observed.

CONCLUSIONS

The findings suggest that the rewarding properties of alcohol-associated cues might be enhanced during the late follicular phase of the menstrual cycle when E2 is elevated, possibly increasing the risk for excessive drinking in women during this phase. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Astrocyte Reactivity and Neurodegeneration in the Female Rat Brain Following Alcohol Dependence

Recent evidence suggests that alcohol use disorder (AUD) may manifest itself differently in women compared to men. Women experience AUDs on an accelerated timeline and may have certain regional vulnerabilities. In male rats, neuronal cell death and astrocyte reactivity are noted following induction of alcohol dependence in an animal model of an AUD. However, the regional and temporal patterns of neurodegeneration and astrocyte reactivity have yet to be fully examined in females using this model. Therefore, adult female rats were exposed to a 4-day binge model of alcohol dependence followed by different periods of abstinence. Histological markers for FluoroJade B, a label of degenerating neurons, and vimentin, a marker for reactive astrocytes, were utilized. The expression of these markers in cortical and limbic regions was quantified immediately after their last dose (e.g., T0), or 2, 7, and 14 days later. Significant neuronal cell death was noted in the entorhinal cortex and the hippocampus, similar to previous reports in males, but also in several cortical regions not previously observed. Vimentin immunoreactivity was noted in the same regions as previously reported, in addition to three novel regions. Vimentin immunoreactivity also occurred at earlier and later time points in some cortical and hippocampal regions. These data suggest that both neuronal cell death and astrocyte reactivity could be more widespread in females compared to males. Therefore, this study provides a framework for specific regions and time points which should be examined in future studies of alcohol-induced damage that include female rats.

Sex-dependent factors of alcohol and neuroimmune mechanisms

Excessive alcohol use disrupts neuroimmune signaling across various cell types, including neurons, microglia, and astrocytes. The present review focuses on recent, albeit limited, evidence of sex differences in biological factors that mediate neuroimmune responses to alcohol and underlying neuroimmune systems that may influence alcohol drinking behaviors. Females are more vulnerable than males to the neurotoxic and negative consequences of chronic alcohol drinking, reflected by elevations of pro-inflammatory cytokines and inflammatory mediators. Differences in cytokine, microglial, astrocytic, genomic, and transcriptomic evidence suggest females are more reactive than males to neuroinflammatory changes after chronic alcohol exposure. The growing body of evidence supports that innate immune factors modulate synaptic transmission, providing a mechanistic framework to examine sex differences across neurocircuitry. Targeting neuroimmune signaling may be a viable strategy for treating AUD, but more research is needed to understand sex-specific differences in alcohol drinking and neuroimmune mechanisms.

Heightened sensitivity to the disinhibiting effect of alcohol in women during the late follicular phase of the menstrual cycle

Compared with men, women are disproportionately affected by alcohol, including greater risks of physiological damage, behavioral impairment, and relapse. One likely mechanism underlying the sexual disparity in this vulnerability is the fluctuation of ovarian hormones, particularly estradiol (E2), across phases of the menstrual cycle. Several preclinical and clinical studies have shown that higher E2 levels positively correlate with drinking, suggesting E2 may play a significant role in modulating drinking. Inhibitory control also modulates drinking; when it is reduced or compromised by alcohol, the drinker's ability to stop the self-administration of alcohol could be impaired, leading to a binge episode. The present study aimed to examine the degree to which menstrual cycle phase can influence the disinhibiting effect of alcohol. Twenty-four healthy young adult women participated in a within-subjects placebo-controlled study of the acute disinhibiting effect of 0.60 g/kg alcohol over the course of two test sessions. A cued go/no-go task measured the disinhibiting effects of alcohol and placebo beverages during the early follicular phase of the cycle when E2 levels were low and the late follicular phase (i.e., ovulation) when E2 was elevated. Results showed that the disinhibiting effect of alcohol increased nearly twofold during the late follicular phase when E2 was elevated. These findings highlight the role of alcohol-induced disinhibition as a potential behavioral mechanism by which fluctuations in ovarian hormones as a function of the menstrual cycle contribute to increased risk for excessive alcohol use in women. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Ethanol-induced transcriptional and translational changes in Aldh1l1-Egfp/Rpl10a cortical astrocyte cultures

The role astrocytes play in brain development and function has garnered greater attention as the diversity of roles they are involved in has become apparent. We have previously shown that ethanol-exposed astrocytes alter neuronal neurite outgrowth in an in vitro co-culture system and that ethanol alters the astrocyte-produced extracellular matrix (ECM) in vitro, with similar alterations in vivo. In this study, we utilized the translating ribosome affinity purification (TRAP) procedure in Aldh1l1-EGFP/Rpl10a transgenic mouse primary cortical astrocyte cultures to transcriptionally and translationally profile the astrocyte response to ethanol. We found a large number of differences between the total RNA pool and the translating RNA pool, indicating that the transcriptional state of astrocytes may not always reflect the translational state of astrocytes. In addition, there was a considerable overlap between ethanol-dysregulated genes in the total RNA pool and the translating RNA pool. Comparisons to published datasets indicate the in vitro model used here is most similar to PD1 or PD7 in vivo cortical astrocytes, and the ethanol-regulated genes showed a significant overlap with models of chronic ethanol exposure in astrocytes, a model of third-trimester ethanol exposure in the hippocampus and cerebellum, and an acute model of ethanol exposure in the hippocampus. These findings will further our understanding of the effects of ethanol on astrocyte gene expression and protein translation and how these changes may alter brain development and support the use of in vitro astrocyte cultures as models of neonatal astrocytes.

iAstrocytes do not restrain T cell proliferation in vitro

The cross-talk between T cells and astrocytes occurring under physiological and, even more, neuroinflammatory conditions may profoundly impact the generation of adaptive immune responses in the nervous tissue. In this study, we used a standardized in vitro co-culture assay to investigate the immunomodulatory properties of astrocytes differing for age, sex, and species. Mouse neonatal astrocytes enhanced T cell vitality but suppressed T lymphocyte proliferation in response to mitogenic stimuli or myelin antigens, regardless of the Th1, Th2 or Th17 T cell phenotype. Studies comparing glia cells from adult and neonatal animals showed that adult astrocytes were more efficient in inhibiting T lymphocyte activation than neonatal astrocytes, regardless of their sex. Differently from primary cultures, mouse and human astrocytes derived from reprogrammed fibroblasts did not interfere with T cell proliferation. Overall, we describe a standardized astrocyte-T cell interaction in vitro assay and demonstrate that primary astrocytes and iAstrocytes may differ in modulating T cell function.

Acute and Chronic Ethanol Effects during Adolescence on Neuroimmune Responses: Consequences and Potential Pharmacologic Interventions

Heavy ethanol consumption during adolescence has been linked to neuroimmune response dysregulation and cognitive deficits in the developing adolescent brain. During adolescence, the brain is particularly susceptible to the pharmacological effects of ethanol that are induced by acute and chronic bouts of exposure. Numerous preclinical rodent model studies have used different ethanol administration techniques, such as intragastric gavage, self-administration, vapor, intraperitoneal, and free access, and while most models indicated proinflammatory neuroimmune responses in the adolescent brain, there are various factors that appear to influence this observation. This review synthesizes the most recent findings of the effects of adolescent alcohol use on toll-like receptors, cytokines, and chemokines, as well as the activation of astrocytes and microglia with an emphasis on differences associated with the duration of ethanol exposure (acute vs. chronic), the amount of exposure (e.g., dose or blood ethanol concentrations), sex differences, and the timing of the neuroimmune observation (immediate vs. persistent). Finally, this review discusses new therapeutics and interventions that may ameliorate the dysregulation of neuroimmune maladaptations after ethanol exposure.

Astrocyte expression in the extended amygdala of C57BL/6J mice is sex-dependently affected by chronic intermittent and binge-like ethanol exposure

Excessive ethanol drinking is a major problem within the United States, causing alterations in brain plasticity and neurocognitive function. Astrocytes are glial cells that regulate neurosynaptic plasticity, modulate neurochemicals, and monitor other homeostatic roles. Astrocytes have been found to play a part in modulating excessive ethanol consumption. The basolateral amygdala (BLA), central amygdala (CeA), and bed nucleus of the stria terminalis (BNST) are brain regions that process stress, anxiety, and reward; they are also implicated in modulating ethanol intake. Little is understood, however, about how astrocyte expression in each region is modulated by chronic and binge-like ethanol drinking patterns. In the present report, we utilized two separate animal models of excessive drinking: chronic intermittent ethanol (CIE) and "Drinking-in-the-dark" (DID). Following these paradigms, animal brains were processed through immunohistochemistry (IHC) and stained for glial fibrillary acidic protein (GFAP). Collected data illustrated a sex-dependent relationship between ethanol intake and GFAP immunoreactivity (IR) in the BLA and BNST, but not in the CeA. Specifically, CIE and DID ethanol drinking resulted in blunted GFAP-IR (specifically via GFAP-positive cell count) in the BLA and BNST, particularly in males. These findings may implicate sex-dependent ethanol-induced changes in BLA and BNST astrocytes, providing a potential therapeutic target for anxiety and stress disorders.

Implication of the PTN/RPTPβ/ζ Signaling Pathway in Acute Ethanol Neuroinflammation in Both Sexes: A Comparative Study with LPS

Binge drinking during adolescence increases the risk of alcohol use disorder, possibly by involving alterations of neuroimmune responses. Pleiotrophin (PTN) is a cytokine that inhibits Receptor Protein Tyrosine Phosphatase (RPTP) β/ζ. PTN and MY10, an RPTPβ/ζ pharmacological inhibitor, modulate ethanol behavioral and microglial responses in adult mice. Now, to study the contribution of endogenous PTN and the implication of its receptor RPTPβ/ζ in the neuroinflammatory response in the prefrontal cortex (PFC) after acute ethanol exposure in adolescence, we used MY10 (60 mg/kg) treatment and mice with transgenic PTN overexpression in the brain. Cytokine levels by X-MAP technology and gene expression of neuroinflammatory markers were determined 18 h after ethanol administration (6 g/kg) and compared with determinations performed 18 h after LPS administration (5 g/kg). Our data indicate that Ccl2, Il6, and Tnfa play important roles as mediators of PTN modulatory actions on the effects of ethanol in the adolescent PFC. The data suggest PTN and RPTPβ/ζ as targets to differentially modulate neuroinflammation in different contexts. In this regard, we identified for the first time important sex differences that affect the ability of the PTN/RPTPβ/ζ signaling pathway to modulate ethanol and LPS actions in the adolescent mouse brain.

Testing the consequences of alcohol, cannabis, and nicotine use on hippocampal volume: a quasi-experimental cotwin control analysis of young adult twins

BACKGROUND

Alcohol, cannabis, and nicotine use are highly comorbid and alarmingly prevalent in young adults. The hippocampus may be particularly sensitive to substance exposure. This remains largely untested in humans and familial risk may confound exposure effects. We extend prior work on alcohol and hippocampal volume in women by testing common and unique substance use effects and the potential moderating role of sex on hippocampal volume during emerging adulthood. A quasi-experimental cotwin control (CTC) design was used to separate familial risk from exposure consequences.

METHODS

In a population-based sample of 435 24-year-old same-sex twins (58% women), dimensional measures (e.g. frequency, amount) of alcohol, cannabis, and nicotine use across emerging adulthood were assessed. Hippocampal volume was assessed using MRI.

RESULTS

Greater substance use was significantly associated with lower hippocampal volume for women but not men. The same pattern was observed for alcohol, cannabis, and nicotine. CTC analyses provided evidence that hippocampal effects likely reflected familial risk and the consequence of substance use in general and alcohol and nicotine in particular; cannabis effects were in the expected direction but not significant. Within-pair mediation analyses suggested that the effect of alcohol use on the hippocampus may reflect, in part, comorbid nicotine use.

CONCLUSIONS

The observed hippocampal volume deviations in women likely reflected substance-related premorbid familial risk and the consequences of smoking and, to a lesser degree, drinking. Findings contribute to a growing body of work suggesting heightened risk among women toward experiencing deleterious effects of substance exposure on the still-developing young adult hippocampus.

The neuroimmune system - Where aging and excess alcohol intersect

As the percentage of the global population over age 65 grows, and with it a subpopulation of individuals with alcohol use disorder (AUD), understanding the effect of alcohol on the aged brain is of utmost importance. Neuroinflammation is implicated in both natural aging as well as alcohol use, and its role in alterations to brain morphology and function may be exacerbated in aging individuals who drink alcohol to excess. The neuroimmune response to alcohol in aging is complex. The few studies investigating this issue have reported heightened basal activity and either hypo- or hyper-reactivity to an alcohol challenge. This review of preclinical research will first introduce key players of the immune system, then explore changes in neuroimmune function with aging or alcohol alone, with discussion of vulnerable brain regions, changes in cytokines, and varied reactions of microglia and astrocytes. We will then consider different levels of alcohol exposure, relevant animal models of AUD, and neuroimmune activation by alcohol across the lifespan. By identifying key findings, challenges, and targets for future research, we hope to bring more attention and resources to this underexplored area of inquiry.

Differential Effects of Nicotine, Alcohol, and Coexposure on Neuroimmune-Related Protein and Gene Expression in Corticolimbic Brain Regions of Rats

Nicotine and alcohol co-use is extremely common and their use constitutes two of the most common causes of preventable death, yet the underlying biological mechanisms are largely understudied. Activation of neuroimmune toll-like receptors (TLRs) promotes the induction of proinflammatory cascades and increases alcohol intake in rodents, which further promotes TLRs in the brain; nicotine may decrease central proinflammatory signaling. The current studies sought to determine the effects of nicotine ± alcohol (alone or in combination) on circulating blood plasma and TLR protein/gene expression in addiction-associated corticolimbic brain regions, including the prefrontal cortex-prelimbic (mPFC-PL) and nucleus accumbens core (AcbC). Adult rats were treated with alcohol (0 or 2 g/kg, IG) and exposed to nicotine vapor (0 or 30 mg/mL solution) daily for 2, 14, or 28 days. Plasma studies indicated no effects of independent exposure or coexposure in males. Coexposure decreased plasma nicotine levels versus nicotine-only treated females, yet alcohol and cotinine concentrations were unchanged. By 28 days, the anti-inflammatory cytokine IL-13 was decreased in alcohol-only females. Divergent changes in TLR3 (but not TLR4) protein occurred for independent-drug exposed males (but not coexposure), with reductions in the mPFC-PL after 14 days and increases in the AcbC by 28 days. Gene expression following chronic coexposure suggests nicotine may regionally counteract alcohol-induced inflammation, including increased AcbC-TLR3/4/7 and several downstream markers in females and increased mPFC-PL-TLR3 and -STAT3 (but not IRF3) evident in males with exposure to either drug alone. These findings give further insight into the role of sex and the neuroimmune system in independent exposure and coexposure to nicotine ± alcohol.

Chronic Intermittent Ethanol Exposure Alters Behavioral Flexibility in Aged Rats Compared to Adult Rats and Modifies Protein and Protein Pathways Related to Alzheimer's Disease

Repeated excessive alcohol consumption increases the risk of developing cognitive decline and dementia. Hazardous drinking among older adults further increases such vulnerabilities. To investigate whether alcohol induces cognitive deficits in older adults, we performed a chronic intermittent ethanol exposure paradigm (ethanol or water gavage every other day 10 times) in 8-week-old young adult and 70-week-old aged rats. While spatial memory retrieval ascertained by probe trials in the Morris water maze was not significantly different between ethanol-treated and water-treated rats in both age groups after the fifth and tenth gavages, behavioral flexibility was impaired in ethanol-treated rats compared to water-treated rats in the aged group but not in the young adult group. We then examined ethanol-treatment-associated hippocampal proteomic and phosphoproteomic differences distinct in the aged rats. We identified several ethanol-treatment-related proteins, including the upregulations of the Prkcd protein level, several of its phosphosites, and its kinase activity and downregulation in the Camk2a protein level. Our bioinformatic analysis revealed notable changes in pathways involved in neurotransmission regulation, synaptic plasticity, neuronal apoptosis, and insulin receptor signaling. In conclusion, our behavioral and proteomic results identified several candidate proteins and pathways potentially associated with alcohol-induced cognitive decline in aged adults.

Sex-specific effects of adolescent intermittent ethanol exposure-induced dysregulation of hippocampal glial cells in adulthood

Adolescent alcohol abuse is a significant public health concern, with approximately 4.3 million U.S. adolescents reporting monthly binge drinking. Excessive ethanol consumption during adolescence has been linked to dysregulation of the neuroimmune system, particularly in the hippocampus. Because there are sex differences in both neuroimmune responses and ethanol's pharmacologic actions, this study tested whether there were disparate effects based on sex in glial cells and neurodegeneration in adulthood after the adolescent intermittent ethanol (AIE) model. Male and female adolescent Sprague-Dawley rats underwent AIE. In adulthood, immunohistochemical techniques were utilized to determine the effects of AIE on astrocytes and microglia, and Fluoro-Jade C (FJC) was used to assess neurodegeneration in the hippocampus. AIE exposure significantly increased astrocyte activation in the cornu ammonis 1 (CA1), CA2/3, and dentate gyrus (DG) in both male and female rats with no discernible sex differences in immunoreactivity. Likewise, the number of GFAP + cells was significantly increased by AIE across the hippocampus. In our microglial assessment, AIE only led to increased Iba1 immunoreactivity in the CA1 but not CA2/3 or DG regions. However, the number of Iba1+ cells was increased by AIE in both the CA1 and DG subregions. In the DG, the ethanol effect was observed in both sexes, but in the CA1, AIE-induced increased Iba1 cells were only observed in females. In regard to neurodegeneration, there were no persisting AIE effects on FJC + cells. These findings indicate that AIE alters hippocampal glial cells in adulthood, in the absence of active neurodegeneration. However, while AIE induced long-term elevation of astroglial measures in both males and females, persisting AIE-induced microglial activation was more sparse and sex-dependent. While the majority of these findings suggest that AIE has similar effects on glial morphology and number between males and females, additional work should determine whether there are molecular differences as well as innate sex differences in glial interaction with AIE's influence on glial functions in behavior.

From Synapses to Circuits, Astrocytes Regulate Behavior

Astrocytes are non-neuronal cells that regulate synapses, neuronal circuits, and behavior. Astrocytes ensheath neuronal synapses to form the tripartite synapse where astrocytes influence synapse formation, function, and plasticity. Beyond the synapse, recent research has revealed that astrocyte influences on the nervous system extend to the modulation of neuronal circuitry and behavior. Here we review recent findings on the active role of astrocytes in behavioral modulation with a focus on in vivo studies, primarily in mice. Using tools to acutely manipulate astrocytes, such as optogenetics or chemogenetics, studies reviewed here have demonstrated a causal role for astrocytes in sleep, memory, sensorimotor behaviors, feeding, fear, anxiety, and cognitive processes like attention and behavioral flexibility. Current tools and future directions for astrocyte-specific manipulation, including methods for probing astrocyte heterogeneity, are discussed. Understanding the contribution of astrocytes to neuronal circuit activity and organismal behavior will be critical toward understanding how nervous system function gives rise to behavior.

Human-Induced Pluripotent Stem Cell-Based Models for Studying Sex-Specific Differences in Neurodegenerative Diseases

The prevalence of neurodegenerative diseases is steadily increasing worldwide, and epidemiological studies strongly suggest that many of the diseases are sex-biased. It has long been suggested that biological sex differences are crucial for neurodegenerative diseases; however, how biological sex affects disease initiation, progression, and severity is not well-understood. Sex is a critical biological variable that should be taken into account in basic research, and this review aims to highlight the utility of human-induced pluripotent stem cells (iPSC)-derived models for studying sex-specific differences in neurodegenerative diseases, with advantages and limitations. In vitro systems utilizing species-specific, renewable, and physiologically relevant cell sources can provide powerful platforms for mechanistic studies, toxicity testings, and drug discovery. Matched healthy, patient-derived, and gene-corrected human iPSCs, from both sexes, can be utilized to generate neuronal and glial cell types affected by specific neurodegenerative diseases to study sex-specific differences in two-dimensional (2D) and three-dimensional (3D) human culture systems. Such relatively simple and well-controlled systems can significantly contribute to the elucidation of molecular mechanisms underlying sex-specific differences, which can yield effective, and potentially sex-based strategies, against neurodegenerative diseases.

Reactive, Adult Neurogenesis From Increased Neural Progenitor Cell Proliferation Following Alcohol Dependence in Female Rats

Hippocampal neurodegeneration is a consequence of excessive alcohol drinking in alcohol use disorders (AUDs), however, recent studies suggest that females may be more susceptible to alcohol-induced brain damage. Adult hippocampal neurogenesis is now well accepted to contribute to hippocampal integrity and is known to be affected by alcohol in humans as well as in animal models of AUDs. In male rats, a reactive increase in adult hippocampal neurogenesis has been observed during abstinence from alcohol dependence, a phenomenon that may underlie recovery of hippocampal structure and function. It is unknown whether reactive neurogenesis occurs in females. Therefore, adult female rats were exposed to a 4-day binge model of alcohol dependence followed by 7 or 14 days of abstinence. Immunohistochemistry (IHC) was used to assess neural progenitor cell (NPC) proliferation (BrdU and Ki67), the percentage of increased NPC activation (Sox2+/Ki67+), the number of immature neurons (NeuroD1), and ectopic dentate gyrus granule cells (Prox1). On day seven of abstinence, ethanol-treated females showed a significant increase in BrdU+ and Ki67+ cells in the subgranular zone of the dentate gyrus (SGZ), as well as greater activation of NPCs (Sox2+/Ki67+) into active cycling. At day 14 of abstinence, there was a significant increase in the number of immature neurons (NeuroD1+) though no evidence of ectopic neurogenesis according to either NeuroD1 or Prox1 immunoreactivity. Altogether, these data suggest that alcohol dependence produces similar reactive increases in NPC proliferation and adult neurogenesis. Thus, reactive, adult neurogenesis may be a means of recovery for the hippocampus after alcohol dependence in females.

Sex difference in the vulnerability to hippocampus plasticity impairment after binge-like ethanol exposure in adolescent rat: Is estrogen the key?

Binge drinking during adolescence induces memory impairments, and evidences suggest that females are more vulnerable than males. However, the reason for such a difference is unclear, whereas preclinical studies addressing this question are lacking. Here we tested the hypothesis that endogenous estrogen level (E2) may explain sex differences in the effects of ethanol on hippocampus plasticity, the cellular mechanism of memory. Long-term depression (LTD) in hippocampus slice of pubertal female rats was recorded 24 h after two ethanol binges (3 g/kg, i.p., 9 h apart). Neither the estrous cycle nor ethanol altered LTD. However, if ethanol was administered during proestrus (i.e., at endogenous E2 peak), LTD was abolished 24 h later, whereas NMDA-fEPSPs response to a GluN2B antagonist increased. The abolition of LTD was not observed in adult female rats. Exogenous E2 combined with ethanol replicated LTD abolition in pubertal, prepubertal female, and in pubertal male rats without changes in ethanol metabolism. In male rats, a higher dose of ethanol was required to abolish LTD at 24-h delay. In pubertal female rats, tamoxifen, an antagonist of estrogen receptors, blocked the impairing effects of endogenous and exogenous E2 on LTD, suggesting estrogen interacts with ethanol through changes in gene expression. In addition, tamoxifen prevented LTD abolition at 24 h but not at 48-h delay. In conclusion, estrogen may explain the increased vulnerability to ethanol-induced plasticity impairment seen in females compared with males. This increased vulnerability of female rats is likely due to changes in the GluN2B subunit that represent a common target between ethanol and estrogen.

The Effects of Alcohol and Cannabis Use on the Cortical Thickness of Cognitive Control and Salience Brain Networks in Emerging Adulthood: A Co-twin Control Study

BACKGROUND

Impairments in inhibitory control and its underlying brain networks (control/salience areas) are associated with substance misuse. Research often assumes a causal substance exposure effect on brain structure. This assumption remains largely untested, and other factors (e.g., familial risk) may confound exposure effects. We leveraged a genetically informative sample of twins aged 24 years and a quasi-experimental co-twin control design to separate alcohol or cannabis exposure effects during emerging adulthood from familial risk on control/salience network cortical thickness.

METHODS

In a population-based sample of 436 twins aged 24 years, dimensional measures of alcohol and cannabis use (e.g., frequency, density, quantity, intoxications) across emerging adulthood were assessed. Cortical thickness of control/salience network areas were assessed using magnetic resonance imaging and defined by a fine-grained cortical atlas.

RESULTS

Greater alcohol, but not cannabis, misuse was associated with reduced thickness of prefrontal (e.g., dorso/ventrolateral, right frontal operculum) and frontal medial cortices, as well as temporal lobe, intraparietal sulcus, insula, parietal operculum, precuneus, and parietal medial areas. Effects were predominately (pre)frontal and right lateralized. Co-twin control analyses suggested that the effects likely reflect both the familial predisposition to misuse alcohol and, specifically for lateral prefrontal, frontal/parietal medial, and right frontal operculum, an alcohol exposure effect.

CONCLUSIONS

This study provides novel evidence that alcohol-related reductions in cortical thickness of control/salience brain networks likely represent the effects of alcohol exposure and premorbid characteristics of the genetic predisposition to misuse alcohol. The dual effects of these two alcohol-related causal influences have important and complementary implications regarding public health and prevention efforts to curb youth drinking.

Chemogenetic manipulation of astrocytic signaling in the basolateral amygdala reduces binge-like alcohol consumption in male mice

Binge drinking is a common occurrence in the United States, but a high concentration of alcohol in the blood has been shown to have reinforcing and reciprocal effects on the neuroimmune system in both dependent and non-dependent scenarios. The first part of this study examined alcohol's effects on the astrocytic response in the central amygdala and basolateral amygdala (BLA) in a non-dependent model. C57BL/6J mice were given access to either ethanol, water, or sucrose during a "drinking in the dark" paradigm, and astrocyte number and astrogliosis were measured using immunohistochemistry. Results indicate that non-dependent consumption increased glial fibrillary acidic protein (GFAP) density but not the number of GFAP+ cells, suggesting that non-dependent ethanol is sufficient to elicit astrocyte activation. The second part of this study examined how astrocytes impacted behaviors and the neurochemistry related to alcohol using the chemogenetic tool, DREADDs (designer receptors exclusively activated by designer drugs). Transgenic GFAP-hM3Dq mice were administered clozapine N-oxide both peripherally, affecting the entire central nervous system (CNS), or directly into the BLA. In both instances, GFAP-Gq-signaling activation significantly reduced ethanol consumption and correlating blood ethanol concentrations. However, GFAP-Gq-DREADD activation throughout the CNS had more broad effects resulting in decreased locomotor activity and sucrose consumption. More targeted GFAP-Gq-signaling activation in the BLA only impacted ethanol consumption. Finally, a glutamate assay revealed that after GFAP-Gq-signaling activation glutamate concentrations in the amygdala were partially normalized to control levels. Altogether, these studies support the theory that astrocytes represent a viable target for alcohol use disorder therapies.

Role of glial cells in the generation of sex differences in neurodegenerative diseases and brain aging

Diseases and aging-associated alterations of the nervous system often show sex-specific characteristics. Glial cells play a major role in the endogenous homeostatic response of neural tissue, and sex differences in the glial transcriptome and function have been described. Therefore, the possible role of these cells in the generation of sex differences in pathological alterations of the nervous system is reviewed here. Studies have shown that glia react to pathological insults with sex-specific neuroprotective and regenerative effects. At least three factors determine this sex-specific response of glia: sex chromosome genes, gonadal hormones and neuroactive steroid hormone metabolites. The sex chromosome complement determines differences in the transcriptional responses in glia after brain injury, while gonadal hormones and their metabolites activate sex-specific neuroprotective mechanisms in these cells. Since the sex-specific neuroprotective and regenerative activity of glial cells causes sex differences in the pathological alterations of the nervous system, glia may represent a relevant target for sex-specific therapeutic interventions.

Binge-like ethanol drinking activates anaplastic lymphoma kinase signaling and increases the expression of STAT3 target genes in the mouse hippocampus and prefrontal cortex

Alcohol use disorder (AUD) has a complex pathogenesis, making it a difficult disorder to treat. Identifying relevant signaling pathways in the brain may be useful for finding new pharmacological targets to treat AUD. The receptor tyrosine kinase anaplastic lymphoma kinase (ALK) activates the transcription factor STAT3 in response to ethanol in cell lines. Here, we show ALK activation and upregulation of known STAT3 target genes (Socs3, Gfap and Tnfrsf1a) in the prefrontal cortex (PFC) and ventral hippocampus (HPC) of mice after 4 days of binge-like ethanol drinking. Mice treated with the STAT3 inhibitor stattic drank less ethanol than vehicle-treated mice, demonstrating the behavioral importance of STAT3. To identify novel ethanol-induced target genes downstream of the ALK and STAT3 pathway, we analyzed the NIH LINCS L1000 database for gene signature overlap between ALK inhibitor (alectinib and NVP-TAE684) and STAT3 inhibitor (niclosamide) treatments on cell lines. These genes were then compared with differentially expressed genes in the PFC of mice after binge-like drinking. We found 95 unique gene candidates, out of which 57 had STAT3 binding motifs in their promoters. We further showed by qPCR that expression of the putative STAT3 genes Nr1h2, Smarcc1, Smarca4 and Gpnmb were increased in either the PFC or HPC after binge-like drinking. Together, these results indicate activation of the ALK-STAT3 signaling pathway in the brain after binge-like ethanol consumption, identify putative novel ethanol-responsive STAT3 target genes, and suggest that STAT3 inhibition may be a potential method to reduce binge drinking in humans.

Astrocyte modulation of extinction impairments in ethanol-dependent female mice

Rates of alcohol use disorders are increasing in women, and there is growing evidence that both the cognitive and biological consequences of alcohol dependence are distinct in women as compared to men. Despite this, the neurobehavioral outcomes of chronic alcohol exposure are poorly characterized in women and female animals. In this study, we find that ethanol dependence impaired extinction of reward seeking in a food conditioned place preference task in female mice. At the same time point, ethanol-dependent females exhibited astrocytic dysregulation as indicated by a brain region-specific reduction in glial fibrillary acidic protein (GFAP) expression. Using a chemogenetic strategy, we demonstrate that modulating astrocyte function via chemogenetic activation of Gq-signaling in nucleus accumbens astrocytes transiently rescued extinction in ethanol-dependent females without impacting basal reward seeking. These findings identify astrocyte function as a potential target for the restoration of behavioral flexibility following chronic alcohol exposure in females.

Murine Models for the Study of Fetal Alcohol Spectrum Disorders: An Overview

Prenatal alcohol exposure is associated to different physical, behavioral, cognitive, and neurological impairments collectively known as fetal alcohol spectrum disorder. The underlying mechanisms of ethanol toxicity are not completely understood. Experimental studies during human pregnancy to identify new diagnostic biomarkers are difficult to carry out beyond genetic or epigenetic analyses in biological matrices. Therefore, animal models are a useful tool to study the teratogenic effects of alcohol on the central nervous system and analyze the benefits of promising therapies. Animal models of alcohol spectrum disorder allow the analysis of key variables such as amount, timing and frequency of ethanol consumption to describe the harmful effects of prenatal alcohol exposure. In this review, we aim to synthetize neurodevelopmental disabilities in rodent fetal alcohol spectrum disorder phenotypes, considering facial dysmorphology and fetal growth restriction. We examine the different neurodevelopmental stages based on the most consistently implicated epigenetic mechanisms, cell types and molecular pathways, and assess the advantages and disadvantages of murine models in the study of fetal alcohol spectrum disorder, the different routes of alcohol administration, and alcohol consumption patterns applied to rodents. Finally, we analyze a wide range of phenotypic features to identify fetal alcohol spectrum disorder phenotypes in murine models, exploring facial dysmorphology, neurodevelopmental deficits, and growth restriction, as well as the methodologies used to evaluate behavioral and anatomical alterations produced by prenatal alcohol exposure in rodents.

Sex-dependent effects of chronic intermittent voluntary alcohol consumption on attentional, not motivational, measures during probabilistic learning and reversal

Background

Forced alcohol (ethanol, EtOH) exposure has been shown to cause significant impairments on reversal learning, a widely-used assay of cognitive flexibility, specifically on fully-predictive, deterministic versions of this task. However, previous studies have not adequately considered voluntary EtOH consumption and sex effects on probabilistic reversal learning. The present study aimed to fill this gap in the literature.

Methods

Male and female Long-Evans rats underwent either 10 weeks of voluntary intermittent 20% EtOH access or water only (H2O) access. Rats were then pretrained to initiate trials and learn stimulus-reward associations via touchscreen response, and subsequently required to select between two visual stimuli, rewarded with probability 0.70 or 0.30. In the final phase, reinforcement contingencies were reversed.

Results

We found significant sex differences on several EtOH-drinking variables, with females reaching a higher maximum EtOH consumption, exhibiting more high-drinking days, and escalating their EtOH at a quicker rate compared to males. During early abstinence, EtOH drinkers (and particularly EtOH-drinking females) made more initiation omissions and were slower to initiate trials than H2O drinking controls, especially during pretraining. A similar pattern in trial initiations was also observed in discrimination, but not in reversal learning. EtOH drinking rats were unaffected in their reward collection and stimulus response times, indicating intact motivation and motor responding. Although there were sex differences in discrimination and reversal phases, performance improved over time. We also observed sex-independent drinking group differences in win-stay and lose-shift strategies specific to the reversal phase.

Conclusions

Females exhibit increased vulnerability to EtOH effects in early learning: there were sex-dependent EtOH effects on attentional measures during pretraining and discrimination phases. We also found sex-independent EtOH effects on exploration strategies during reversal. Future studies should aim to uncover the neural mechanisms for changes in attention and exploration in both acute and prolonged EtOH withdrawal.

Gender differences in the effects of cannabidiol on ethanol binge drinking in mice

The purpose of this study was to explore the effects of cannabidiol (CBD) on binge drinking and evaluate potential gender-related differences. To this aim, male and female C57BL/6J mice (n = 60 per sex) were exposed to the drinking in the dark (DID) model for 4 weeks (DID-1 to DID-4). Dose-response effects of CBD on the ethanol intake were tested by acute (day-4 of DID-3) or repeated administration (day-1 to 4 of DID-4) (experiment 1: CBD 15, 30, and 60 mg/kg, i.p.; experiment 2: CBD 90 mg/kg, i.p.). Finally, we analyzed the relative gene expression of tyrosine hydroxylase (TH) and μ-opioid receptor (OPRM1) and cannabinoid CB1 receptor (CB₁ r) in the ventral tegmental area (VTA) and in the nucleus accumbens (NAc), respectively, by real-time quantitative PCR. Females exhibited higher ethanol intake during each DID session. Interestingly, females also showed higher expression of TH and OPRM1, without any difference in CB₁ r. Only the acute administration of CBD at the highest dose (90 mg/kg) reduced significantly ethanol consumption in both sexes. Chronic CBD administration (30, 60 and 90 mg/kg) reduced ethanol intake in males, whereas in females a significant reduction was only achieved with the highest dose (90 mg/kg). Repeated administration with CBD (60 mg/kg) significantly reduced TH and OPRM1 in males. In addition, CBD (30 and 60 mg/kg) significantly reduced CB₁ r in males. No effect was observed in females. Taken together, these findings suggest that CBD may be of interest for treating binge-drinking patterns and that gender-related difference may affect the treatment outcome.

Time Course of Blood and Brain Cytokine/Chemokine Levels Following Adolescent Alcohol Exposure and Withdrawal in Rats

BACKGROUND

Adolescence is a critical period for neural development, and alcohol exposure during adolescence can lead to an elevated risk for health consequences as well as alcohol use disorders. Clinical and experimental data suggest that chronic alcohol exposure may produce immunomodulatory effects that can lead to the activation of pro-inflammatory cytokine pathways as well as microglial markers. The present study evaluated, in brain and blood, the effects of adolescent alcohol exposure and withdrawal on microglia and on the most representative pro- and anti-inflammatory cytokines and major chemokines that can contribute to the establishing of a neuroinflammatory environment.

METHODS

Wistar rats (males, n = 96) were exposed to ethanol (EtOH) vapors, or air control, for 5 weeks over adolescence (PD22-PD58). Brains and blood samples were collected at 3 time points: (i) after 35 days of vapor/air exposure (PD58); (ii) after 1 day of withdrawal (PD59), and (iii) 28 days after withdrawal (PD86). The ionized calcium-binding adapter molecule 1 (Iba-1) was used to index microglial activation, and cytokine/chemokine responses were analyzed using magnetic bead panels.

RESULTS

After 35 days of adolescent vapor exposure, a significant increase in Iba-1 immunoreactivity was seen in amygdala, frontal cortex, hippocampus, and substantia nigra. However, Iba-1 density returned to control levels at both 1 day and 28 days of withdrawal except in the hippocampus where Iba-1 density was significantly lower than controls. In serum, adolescent EtOH exposure induced a reduction in IL-13 and an increase in fractalkine at day 35. After 1 day of withdrawal, IL-18 was reduced, and IP-10 was elevated, whereas both IP-10 and IL-10 were elevated at 28 days following withdrawal. In the frontal cortex, adolescent EtOH exposure induced an increase in IL-1β at day 35, and 28 days of withdrawal, and IL-10 was increased after 28 days of withdrawal.

CONCLUSION

These data demonstrate that EtOH exposure during adolescence produces significant microglial activation; however, inflammatory markers seen in the blood appear to differ from those observed in the brain.

Rapid alterations in neuroimmune gene expression after acute ethanol: Timecourse, sex differences and sensitivity to cranial surgery

Prior work has established that that an acute ethanol challenge mimicking high intensity alcohol consumption increased IL-6 and suppressed IL-1β and TNFα mRNA in intoxication, with the opposite pattern seen in withdrawal. These experiments utilized Sprague-Dawley rats to further extend these results across time course (from 45 min to 6 h after ethanol), sex, and central versus peripheral expression. Furthermore, these data show that cannulation surgery may selectively modify the central neuroimmune response to ethanol. These findings highlight a unique plasticity of IL-6 that is specific to central structures and responsive to alterations by environmental factors.

Ethanol and Cytokines in the Central Nervous System

The innate immune system plays a critical role in the ethanol-induced neuroimmune response in the brain. Ethanol initiates the innate immune response via activation of the innate immune receptors Toll-like receptors (TLRs, e.g., TLR4, TLR3, TLR7) and NOD-like receptors (inflammasome NLRs) leading to a release of a plethora of chemokines and cytokines and development of the innate immune response. Cytokines and chemokines can have pro- or anti-inflammatory properties through which they regulate the immune response. In this chapter, we will focus on key cytokines (e.g., IL-1, IL-6, TNF-α) and chemokines (e.g., MCP-1/CCL2) that mediate the ethanol-induced neuroimmune responses. In this regard, we will use IL-1β, as an example cytokine, to discuss the neuromodulatory properties of cytokines on cellular properties and synaptic transmission. We will discuss their involvement through a set of evidence: (1) changes in gene and protein expression following ethanol exposure, (2) association of gene polymorphisms (humans) and alterations in gene expression (animal models) with increased alcohol intake, and (3) modulation of alcohol-related behaviors by transgenic or pharmacological manipulations of chemokine and cytokine systems. Over the last years, our understanding of the molecular mechanisms mediating cytokine- and chemokine-dependent regulation of immune responses has advanced tremendously, and we review evidence pointing to cytokines and chemokines serving as neuromodulators and regulators of neurotransmission.

Assessment of Extracellular Cytokines in the Hippocampus of the Awake Behaving Rat Using Large-Molecule Microdialysis Combined with Multiplex Arrays After Acute and Chronic Ethanol Exposure

BACKGROUND

Studies have demonstrated persistent changes in central nervous system (CNS) cytokine gene expression following ethanol (EtOH) exposure. However, the low endogenous expression and short half-lives of cytokines in the CNS have made cytokine protein detection challenging. The goal of these studies was to establish parameters for use of large-molecule microdialysis and sensitive multiplexing technology for the simultaneous detection of brain cytokines, corticosterone (CORT), and EtOH concentrations in the awake behaving rat.

METHODS

Adult (P75+) male Sprague Dawley rats that were either naïve to EtOH (Experiment 1) or had a history of adolescent chronic intermittent EtOH (CIE; Experiment 2) were given an acute EtOH challenge during microdialysis. Experiment 1 examined brain EtOH concentrations, CORT and a panel of neuroimmune analytes, including cytokines associated with innate and adaptive immunity. The natural time course of changes in these cytokines was compared to the effects of an acute 1.5 or 3.0 g/kg intraperitoneal (i.p.) EtOH challenge. In Experiment 2, rats with a history of adolescent CIE or controls exposed to vehicle were challenged with 3.0 g/kg i.p. EtOH during microdialysis in adulthood, and a panel of cytokines was examined in parallel with brain EtOH concentrations and CORT.

RESULTS

The microdialysis procedure itself induced a cytokine-specific response that replicated across studies, specifically a sequential elevation of interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), and IL-10. Surprisingly, acute EtOH did not significantly alter this course of cytokine fluctuations in the hippocampus. However, a history of adolescent CIE showed drastic effects on multiple neuroimmune analytes when rechallenged with EtOH as adults. Rats with a history of adolescent EtOH displayed a severely blunted neuroimmune response in adulthood, evinced by suppressed IL-1β, IL-10, and TNF-α.

CONCLUSIONS

Together, these findings provide a methodological framework for assessment of cytokine release patterns, their modulation by EtOH, and the long-lasting changes to neuroimmune reactivity evoked by a history of adolescent CIE.

Recurrent binge ethanol is associated with significant loss of dentate gyrus granule neurons in female rats despite concomitant increase in neurogenesis

Binge drinking is becoming increasingly common among American women and girls. We have previously shown significant cell loss, downregulation of neurotrophins and microgliosis in female rats after a single 4-day ethanol exposure. To determine whether recurrent binge exposure would produce similar effects, we administered ethanol (5 g/kg) or iso-caloric control diet once-weekly for 11 weeks to adult female rats. As we have previously shown exercise neuroprotection against binge-induced damage, half the rats were given access to exercise wheels. Blood ethanol concentration (BEC) did not differ between sedentary and exercised groups, nor did it change across time. Using stereology, we quantified the number and/or size of neurons in the medial prefrontal cortex (mPFC) and hippocampal dentate gyrus (DG), as well as the number and activation state of microglia. Binged sedentary rats had significant cell loss in the dentate gyrus, but exercise eliminated this effect. Compared to sedentary controls, sedentary binged rats and all exercised rats showed increased neurogenesis in the DG. Number and nuclear volume of neurons in the mPFC were not changed. In the hippocampus and mPFC, the number of microglia with morphology indicative of partial activation was increased by recurrent binge ethanol and decreased by exercise. In summary, we show significant binge-induced loss of DG granule neurons despite increased neurogenesis, suggesting an unsuccessful compensatory response. Although exercise eliminated cell loss, our results indicate that infrequent, but recurrent exposure to clinically relevant BEC is neurotoxic.

A comparison of hippocampal microglial responses in aged and young rodents following dependent and non-dependent binge drinking

Alcoholism is a highly visible and prevalent issue in the United States. Although binge-drinking is assumed to be a college-age problem, older adults (ages 65+) consume binge amounts of alcohol and have alcohol use disorders (AUDs). Moreover, individuals with alcohol dependence in their youth often continue to drink as they age. As such, this study tested the hypothesis that the effects of alcohol on hippocampal microglia are exacerbated in aged versus younger rodents in two AUD models. Briefly, adult (2-3 months) and aged (15+ months) Sprague-Dawley rats were administered alcohol or control diet using the Majchrowicz model to study alcohol-induced neurodegeneration. To study the effects of non-dependent binge consumption on microglia, adolescent (6-8 weeks) and aged (18+ months) C57/BL6N were subjected to the Drinking in the Dark paradigm. Microglia number and densitometry were assessed using immunohistochemistry. Hippocampal subregional and model/species-specific effects of alcohol were observed, but overall, aging did not appear to increase the alcohol-induced microglia reactivity as measured by Iba-1 densitometry. However, analysis of microglial counts revealed a significant decrease in the number microglia cells in both the alcohol-induced neurodegeneration and DID model across age groups. In the dentate gyrus, the loss of microglia was exacerbated by aging, particularly in mice after DID, non-dependent model. Using qRT-PCR, the persistence of alcohol and aging effects was assessed following the DID model. Allograft Inflammatory Factor 1 mRNA was increased in both young and aged mice by alcohol exposure; however, only in the aged mice did the alcohol effect persist. Overall, these data imply that the microglial response to alcohol is complex with evidence of depressed numbers of microglia but also increased reactivity with advanced age.

Neuroimmune signaling in alcohol use disorder

Alcohol use disorder (AUD) is a widespread disease with limited treatment options. Targeting the neuroimmune system is a new avenue for developing or repurposing effective pharmacotherapies. Alcohol modulates innate immune signaling in different cell types in the brain by altering gene expression and the molecular pathways that regulate neuroinflammation. Chronic alcohol abuse may cause an imbalance in neuroimmune function, resulting in prolonged perturbations in brain function. Likewise, manipulating the neuroimmune system may change alcohol-related behaviors. Psychiatric disorders that are comorbid with AUD, such as post-traumatic stress disorder, major depressive disorder, and other substance use disorders, may also have underlying neuroimmune mechanisms; current evidence suggests that convergent immune pathways may be involved in AUD and in these comorbid disorders. In this review, we provide an overview of major neuroimmune cell-types and pathways involved in mediating alcohol behaviors, discuss potential mechanisms of alcohol-induced neuroimmune activation, and present recent clinical evidence for candidate immune-related drugs to treat AUD.

Binge ethanol effects on prefrontal cortex neurons, spatial working memory and task-induced neuronal activation in male and female rats

Excessive alcohol intake is associated with a multitude of health risks, especially for women. Recent studies in animal models indicate that the female brain is more negatively affected by alcohol, compared to the male brain. Among other regions, excessive alcohol consumption damages the frontal cortex, an area important for many functions and decision making of daily life. The objective of the present study was to determine whether the medial prefrontal cortex (mPFC) in female rats is selectively vulnerable to alcohol-induced damage. In humans, loss of prefrontal grey matter resulting from heavy alcohol consumption has been documented, however this volume loss is not necessarily due to a decrease in the number of neurons. We therefore quantified both number and nuclear volume of mPFC neurons following binge alcohol, as well as performance and neuronal activation during a prefrontal-dependent behavioral task. Adult male and female Long-Evans rats were assigned to binge or control groups and exposed to ethanol using a well-established 4-day model of alcohol-induced neurodegeneration. Both males and females had significantly smaller average neuronal nuclei volumes than their respective control groups immediately following alcohol binge, but neither sex showed a decrease in neuron number. Binged rats of both sexes initially showed spatial working memory deficits. Although they eventually achieved control performance, binged rats of both sexes showed increased c-Fos labeling in the mPFC during rewarded alternation, suggesting decreased neural efficiency. Overall, our results substantiate prior evidence indicating that the frontal cortex is vulnerable to alcohol, but also indicate that sex-specific vulnerability to alcohol may be brain region-dependent.

Estradiol enhances ethanol reward in female mice through activation of ERα and ERβ

Alcohol use disorder (AUD) manifests differently in men and women, but little is known about sex differences in the brain's response to ethanol. It is known that the steroid hormone 17β-estradiol (E2) regulates voluntary ethanol consumption in female rodents. However, the role of E2 as a regulator of ethanol reward has not been investigated. In this study, we tested for the effects of E2 and agonists selective for the classical estrogen receptors, ERα and ERβ, on ethanol reward in ovariectomized (OVX) mice using the conditioned place preference (CPP) test. E2 enhanced ethanol CPP and, while specific activation of either receptor alone had no effect, co-activation of ERα and ERβ also enhanced ethanol CPP, suggesting that E2 enhances ethanol reward in female mice through actions at both ERα and ERβ. These results have implications for sex differences in the development of AUD, suggesting that women may find ethanol more rewarding than men because of higher circulating E2 levels.

Ovarian Hormones Contribute to High Levels of Binge-Like Drinking by Female Mice

BACKGROUND

Recently, the incidence of binge drinking by women has increased. Binge drinking is detrimental to women's health, yet the biological mechanisms that promote excessive drinking by women are not well understood. One method of assessing binge-like ethanol (EtOH) consumption in mice is the drinking in the dark (DID) test, in which mice drink sufficient EtOH to achieve intoxication. In this study, we directly compared male, female, and ovariectomized (OVX) mice for DID and tested whether 17β-estradiol (E2) contributes to DID. We also measured whether DID varies throughout the estrous cycle and whether repeated intermittent DID impacts the estrous cycle.

METHODS

Male, female, and OVX C57BL/6J mice were tested for DID for 2 hours per day on days 1 to 3 and for 4 hours on day 4 using a single bottle containing 20% EtOH. To measure the effects of E2 on DID, OVX mice were treated with estradiol benzoate (EB) or vehicle daily starting 2 weeks prior to the drinking test and throughout the DID procedure. In a separate group of experiments, EtOH consumption and estrous cycle phase were measured in freely cycling mice that were drinking EtOH or water 5 days per week for 2 or 6 weeks.

RESULTS

Female mice consumed more EtOH than male and OVX mice. Treatment with EB increased EtOH consumption by OVX mice compared with vehicle-treated controls. However, EtOH intake did not vary across the estrous cycle, nor did long-term DID alter the estrous cycle.

CONCLUSIONS

These results demonstrate that ovarian hormones, specifically E2, contribute to increased EtOH consumption by female mice in the DID test. Although ovarian hormones contribute to this behavior, EtOH consumption is not affected by estrous cycle phase in freely cycling mice. This study provides a framework for understanding the factors that contribute to binge drinking in females.

Investigation of Sex Differences in the Microglial Response to Binge Ethanol and Exercise

The female brain appears selectively vulnerable to the neurotoxic effects of alcohol, but the reasons for this are unclear. One possibility is an exaggerated neuroimmune response in the female brain, such that alcohol increases microglia number and reactivity to subsequent stimuli, such as exercise. It is important to better characterize the interactive neural effects of alcohol and exercise, as exercise is increasingly being used in the treatment of alcohol use disorders. The present study compared the number of microglia and evidence of their activation in alcohol-vulnerable regions of the brain (medial prefrontal cortex and hippocampus) in male and female rats following binge alcohol and/or exercise. Binge alcohol increased microglia number and morphological characteristics consistent with their activation in the female brain but not the male, regardless of exercise. Binge alcohol followed by exercise did increase the number of MHC II+ (immunocompetent) microglia in females, although the vast majority of microglia did not express MHC II. These results indicate that binge alcohol exerts sex-specific effects on microglia that may result in enhanced reactivity to a subsequent challenge and in part underlie the apparent selective vulnerability of the female brain to alcohol.

Sex differences in hippocampal damage, cognitive impairment, and trophic factor expression in an animal model of an alcohol use disorder

Compared to men, women disproportionally experience alcohol-related organ damage, including brain damage, and while men remain more likely to drink and to drink heavily, there is cause for concern because women are beginning to narrow the gender gap in alcohol use disorders. The hippocampus is a brain region that is particularly vulnerable to alcohol damage, due to cell loss and decreased neurogenesis. In the present study, we examined sex differences in hippocampal damage following binge alcohol. Consistent with our prior findings, we found a significant binge-induced decrement in dentate gyrus (DG) granule neurons in the female DG. However, in the present study, we found no significant decrement in granule neurons in the male DG. We show that the decrease in granule neurons in females is associated with both spatial navigation impairments and decreased expression of trophic support molecules. Finally, we show that post-binge exercise is associated with an increase in trophic support and repopulation of the granule neuron layer in the female hippocampus. We conclude that sex differences in alcohol-induced hippocampal damage are due in part to a paucity of trophic support and plasticity-related signaling in females.

The neuroimmune transcriptome and alcohol dependence: potential for targeted therapies

Transcriptome profiling enables discovery of gene networks that are altered in alcoholic brains. This technique has revealed involvement of the brain's neuroimmune system in regulating alcohol abuse and dependence, and has provided potential therapeutic targets. In this review, we discuss Toll-like-receptor pathways, hypothesized to be key players in many stages of the alcohol addiction cycle. The growing appreciation of the neuroimmune system's involvement in alcoholism has also led to consideration of crucial roles for glial cells, including astrocytes and microglia, in the brain's response to alcohol abuse. We discuss current knowledge and hypotheses on the roles that specific neuroimmune cell types may play in addiction. Current strategies for repurposing US FDA-approved drugs for the treatment of alcohol use disorders are also discussed.

p15(INK4b) regulates cell cycle signaling in hippocampal astrocytes of aged rats

BACKGROUND AND AIMS

Cyclin-dependent kinase inhibitor p15(INK4b) is thought to be an important player in regulating astrocytic cell cycle. However, little is known with regard to the expression of p15(INK4b) and its function in hippocampal astrocytes. This study evaluated the expression of p15(INK4b) and its function during different development stages in hippocampal astrocytes.

METHODS

In this study, we cultured hippocampal astrocytes from neonatal adult and aged rats. The expression of p15(INK4b) in neonatal, adult and aged astrocytes was examined. Short interfering RNA (siRNA) was then used to study the functional effects of p15(INK4b) down-regulation during cell cycle regulation.

RESULTS

We found the expression of p15(INK4b) in hippocampal astrocytes was detectable on postnatal day 7, was expressed at moderate levels in adult mice (9 months old) astrocytes and peaked in aged rat (24 months old) astrocytes. Incubation with siRNA significantly suppressed p15(INK4b) expression at the mRNA and protein levels in astrocytes. Down-regulation of p15(INK4b) increased [(3)H]-thymidine incorporation into DNA and allowed cells to pass the G0/G1-S checkpoint in aged but not in neonatal or adult astrocytes.

CONCLUSIONS

These observations suggest p15(INK4b) is expressed at a steady level in neonatal and adult rat hippocampal astrocytes with no effect on cell cycle regulation. Importantly, aged astrocyte cell cycle regulation was significantly affected by high expression levels of p15(INK4b) suggesting a role for p15(INK4b) in cell cycle regulation when it is expressed at high but not moderate or low levels in hippocampal astrocytes.

Disentangling the Role of Astrocytes in Alcohol Use Disorder

Several laboratories recently identified that astrocytes are critical regulators of addiction machinery. It is now known that astrocyte pathology is a common feature of ethanol (EtOH) exposure in both humans and animal models, as even brief EtOH exposure is sufficient to elicit long-lasting perturbations in astrocyte gene expression, activity, and proliferation. Astrocytes were also recently shown to modulate the motivational properties of EtOH and other strongly reinforcing stimuli. Given the role of astrocytes in regulating glutamate homeostasis, a crucial component of alcohol use disorder (AUD), astrocytes might be an important target for the development of next-generation alcoholism treatments. This review will outline some of the more prominent features displayed by astrocytes, how these properties are influenced by acute and long-term EtOH exposure, and future directions that may help to disentangle astrocytic from neuronal functions in the etiology of AUD.

A neurotoxic alcohol exposure paradigm does not induce hepatic encephalopathy

Alcohol abuse is associated with neurological dysfunction, brain morphological deficits and frank neurotoxicity. Although these disruptions may be a secondary effect due to hepatic encephalopathy, no clear evidence of causality is available. This study examined whether a 72h period of alcohol intoxication known to induce physical dependence, followed by a single withdrawal, was sufficient to induce signs of hepatic encephalopathy in male and female mice. Animals were continuously intoxicated via alcohol vapor inhalation, a procedure previously shown to induce significant neurotoxicity in female mice. At peak synchronized withdrawal (8h following the end of alcohol exposure), blood samples were taken and levels of several liver-regulated markers and brain swelling were characterized. Glutathione levels were also determined in the medial frontal cortex (mFC) and hippocampus. Results revealed elevated levels of cholesterol, albumin, alkaline phosphatase (ALP), alanine aminotransferase (ALT) and decreased levels of blood urea nitrogen and total bilirubin in alcohol-exposed male and female groups compared to controls. Brain water weight was not affected by alcohol exposure, though males tended to have slightly more water weight overall. Alcohol exposure led to reductions in tissue levels of glutathione in both the hippocampus and mFC which may indicate increased oxidative stress. Combined, these results suggest that hepatic encephalopathy does not appear to play a significant role in the neurotoxicity observed following alcohol exposure in this model.

Sex and the Lab: An Alcohol-Focused Commentary on the NIH Initiative to Balance Sex in Cell and Animal Studies

In May 2014, Dr. Francis Collins, the director of U.S. National Institutes of Health (NIH), and Dr. Janine Clayton, the director of the U.S. National Institutes of Health Office of Research on Women's Health, published a commentary in the journal Nature announcing new policies to ensure that preclinical research funded by the NIH considers both males and females. While these policies are still developing, they have already generated great interest by the scientific community and triggered both criticism and applause. This review provides a description and interpretation of the NIH guidelines, and it traces the history that led to their implementation. As expected, this NIH initiative generated some anxiety in the scientific community. The use of female animals in the investigation of basic mechanisms is perceived to increase variability in the results, and the use of both sexes has been claimed to slow the pace of scientific discoveries and to increase the cost at a time characterized by declining research support. This review discusses issues related to the study of sex as a biological variable (SABV) in alcohol studies and provides examples of how researchers have successfully addressed some of them. A practical strategy is provided to include both sexes in biomedical research while maintaining control of the research direction. The inclusion of sex as an important biological variable in experimental design, analysis, and reporting of preclinical alcohol research is likely to lead to a better understanding of alcohol pharmacology and the development of alcohol use disorder, may promote drug discovery for new pharmacotherapies by increasing scientific rigor, and may provide clinical benefit to women's health. This review aims to promote the understanding of the NIH's SABV guidelines and to provide alcohol researchers with a theoretical and practical framework for working with both sexes in preclinical research.

Fetal Alcohol Spectrum Disorders: An Overview from the Glia Perspective

Alcohol consumption during pregnancy can produce a variety of central nervous system (CNS) abnormalities in the offspring resulting in a broad spectrum of cognitive and behavioral impairments that constitute the most severe and long-lasting effects observed in fetal alcohol spectrum disorders (FASD). Alcohol-induced abnormalities in glial cells have been suspected of contributing to the adverse effects of alcohol on the developing brain for several years, although much research still needs to be done to causally link the effects of alcohol on specific brain structures and behavior to alterations in glial cell development and function. Damage to radial glia due to prenatal alcohol exposure may underlie observations of abnormal neuronal and glial migration in humans with Fetal Alcohol Syndrome (FAS), as well as primate and rodent models of FAS. A reduction in cell number and altered development has been reported for several glial cell types in animal models of FAS. In utero alcohol exposure can cause microencephaly when alcohol exposure occurs during the brain growth spurt a period characterized by rapid astrocyte proliferation and maturation; since astrocytes are the most abundant cells in the brain, microenchephaly may be caused by reduced astrocyte proliferation or survival, as observed in in vitro and in vivo studies. Delayed oligodendrocyte development and increased oligodendrocyte precursor apoptosis has also been reported in experimental models of FASD, which may be linked to altered myelination/white matter integrity found in FASD children. Children with FAS exhibit hypoplasia of the corpus callosum and anterior commissure, two areas requiring guidance from glial cells and proper maturation of oligodendrocytes. Finally, developmental alcohol exposure disrupts microglial function and induces microglial apoptosis; given the role of microglia in synaptic pruning during brain development, the effects of alcohol on microglia may be involved in the abnormal brain plasticity reported in FASD. The consequences of prenatal alcohol exposure on glial cells, including radial glia and other transient glial structures present in the developing brain, astrocytes, oligodendrocytes and their precursors, and microglia contributes to abnormal neuronal development, reduced neuron survival and disrupted brain architecture and connectivity. This review highlights the CNS structural abnormalities caused by in utero alcohol exposure and outlines which abnormalities are likely mediated by alcohol effects on glial cell development and function.

A Review on the Sex Differences in Organ and System Pathology with Alcohol Drinking

Hazardous consequences of alcohol consumption adversely influence overall health, specifically physical and mental health. Differences in alcohol consumption and manifestations in pathology have been observed between males and females, however research on understanding these differences is limited. Negative consequences of alcohol consumption have now been studied including sex as a significant factor. Some studies have shown differences in the severity of consequences of alcohol consumption between the sexes, both in the mental consequences and changes/ injury in various organ systems. Over time, reports in females on both the dynamics of drinking and on the hazardous consequences of alcohol consumption have grown, primarily because of more awareness, better observation, and the inclusion of sex as a factor in scientific investigations. This paper reviews role of sex differences in pathophysiological and behavioral consequences of alcohol drinking.