Impact of Prenatal and Subsequent Adult Alcohol Exposure on Pro-Inflammatory Cytokine Expression in Brain Regions Necessary for Simple Recognition Memory

The effects of moderate prenatal alcohol exposure on performance in object and spatial discrimination tasks by adult male rats

Exposure to alcohol during pregnancy produces Fetal Alcohol Spectrum Disorders, which in its most severe form is characterized by physical dysmorphology and neurobehavioral alterations. Moderate prenatal alcohol exposure (mPAE) is known to produce deficits in discrimination of spatial locations in adulthood. However, the impact of mPAE on higher-order sensory representations, such as discrimination of perceptually similar stimuli, is currently unknown. In the present study, we tested the hypothesis that mPAE would disrupt performance on hippocampal-sensitive tasks that require discrimination between perceptually similar objects or discrimination between spatial locations in a radial arm maze. Here we report that male mPAE rats exhibited intact performance on three types of object discrimination tasks: one in which rats discriminated between distinct toy objects, a second in which discrimination was made between distinct and similar LEGO objects, and a mnemonic similarity task in which rats discriminated between randomly presented LEGO objects that varied in similarity with a learned object. Although adult male mPAE rats performed similarly to control rats on all three object discrimination tasks, they showed deficits when tested in a radial arm maze spatial discrimination task. Specifically, male mPAE rats expressed a significantly higher number of working memory errors (returns to previously visited arms) and were more likely to use non-spatial strategies during training. Together, the findings of the present study support the conclusion that mPAE produces specific deficits in the online processing of spatial information and executing spatial navigation strategies, but spares the ability to discriminate between perceptually similar stimuli.

Extracellular vesicles from mesenchymal stem cells improve neuroinflammation and neurotransmission in hippocampus and cognitive impairment in rats with mild liver damage and minimal hepatic encephalopathy

BACKGROUND

Patients with steatotic liver disease may show mild cognitive impairment. Rats with mild liver damage reproduce this cognitive impairment, which is mediated by neuroinflammation that alters glutamate neurotransmission in the hippocampus. Treatment with extracellular vesicles (EV) from mesenchymal stem cells (MSC) reduces neuroinflammation and improves cognitive impairment in different animal models of neurological diseases. TGFβ in these EVs seems to be involved in its beneficial effects. The aim of this work was to assess if MSCs-EVs may improve cognitive impairment in rats with mild liver damage and to analyze the underlying mechanisms, assessing the effects on hippocampal neuroinflammation and neurotransmission. We also aimed to analyze the role of TGFβ in the in vivo effects of MSCs-EVs.

METHODS

Male Wistar rats with CCl4-induced mild liver damage were treated with EVs from unmodified MSC or with EVs derived from TGFβ-silenced MSCs and its effects on cognitive function and on neuroinflammation and altered neurotransmission in the hippocampus were analysed.

RESULTS

Unmodified MSC-EVs reversed microglia activation and TNFα content, restoring membrane expression of NR2 subunit of NMDA receptor and improved object location memory. In contrast, EVs derived from TGFβ-silenced MSCs did not induce these effects but reversed astrocyte activation, IL-1β content and altered GluA2 AMPA receptor subunit membrane expression leading to improvement of learning and working memory in the radial maze.

CONCLUSIONS

EVs from MSCs with TGFβ silenced induce different effects on behavior, neuroinflammation and neurotransmitter receptors alterations than unmodified MSC-EVs, indicating that the modification of TGFβ in the MSC-EVs has a notable effect on the consequences of the treatment. This work shows that treatment with MSC-EVs improves learning and memory in a model of mild liver damage and MHE in rats, suggesting that MSC-EVs may be a good therapeutic option to reverse cognitive impairment in patients with steatotic liver disease.

Prenatal alcohol exposure promotes NLRP3 inflammasome-dependent immune actions following morphine treatment and paradoxically prolongs nerve injury-induced pathological pain in female mice

BACKGROUND

Neuroimmune dysregulation from prenatal alcohol exposure (PAE) may contribute to neurological deficits associated with fetal alcohol spectrum disorders (FASD). PAE is a risk factor for developing peripheral immune and spinal glial sensitization and release of the proinflammatory cytokine IL-1β, which lead to neuropathic pain (allodynia) from minor nerve injury. Although morphine acts on μ-opioid receptors, it also activates immune receptors, TLR4, and the NLRP3 inflammasome that induces IL-1β. We hypothesized that PAE induces NLRP3 sensitization by morphine following nerve injury in adult mice.

METHODS

We used an established moderate PAE paradigm, in which adult PAE and non-PAE control female mice were exposed to a minor sciatic nerve injury, and subsequent allodynia was measured using the von Frey fiber test. In control mice with standard sciatic damage or PAE mice with minor sciatic damage, the effects of the NLRP3 inhibitor, MCC950, were examined during chronic allodynia. Additionally, minor nerve-injured mice were treated with morphine, with or without MCC950. In vitro studies examined the TLR4-NLRP3-dependent proinflammatory response of peripheral macrophages to morphine and/or lipopolysaccharide, with or without MCC950.

RESULTS

Mice with standard sciatic damage or PAE mice with minor sciatic damage developed robust allodynia. Blocking NLRP3 activation fully reversed allodynia in both control and PAE mice. Morphine paradoxically prolonged allodynia in PAE mice, while control mice with minor nerve injury remained stably non-allodynic. Allodynia resolved sooner in nerve-injured PAE mice without morphine treatment than in morphine-treated mice. MCC950 treatment significantly shortened allodynia in morphine-treated PAE mice. Morphine potentiated IL-1β release from TLR4-activated PAE immune cells, while MCC950 treatment greatly reduced it.

CONCLUSIONS

In female mice, PAE prolongs allodynia following morphine treatment through NLRP3 activation. TLR4-activated PAE immune cells showed enhanced IL-1β release with morphine via NLRP3 actions. Similar studies are needed to examine the adverse impact of morphine in males with PAE. These results are predictive of adverse responses to opioid pain therapeutics in individuals with FASD.

Prenatal alcohol exposure dysregulates spinal and circulating immune cell circular RNA expression in adult female rats with chronic sciatic neuropathy

Alcohol consumption during pregnancy is associated with Fetal Alcohol Spectrum Disorders (FASD) that results in a continuum of central nervous system (CNS) deficits. Emerging evidence from both preclinical and clinical studies indicate that the biological vulnerability to chronic CNS disease in FASD populations is driven by aberrant neuroimmune actions. Our prior studies suggest that, following minor nerve injury, prenatal alcohol exposure (PAE) is a risk factor for developing adult-onset chronic pathological touch sensitivity or allodynia. Allodynia in PAE rats occurs concurrently with heightened proinflammatory peripheral and spinal glial-immune activation. However, minor nerve-injured control rats remain non-allodynic, and corresponding proinflammatory factors are unaltered. A comprehensive molecular understanding of the mechanism(s) that underlie PAE-induced proinflammatory bias during adulthood remains elusive. Non-coding circular RNAs (circRNAs) are emerging as novel modulators of gene expression. Here, we hypothesized that PAE induces dysregulation of circRNAs that are linked to immune function under basal and nerve-injured conditions during adulthood. Utilizing a microarray platform, we carried out the first systematic profiling of circRNAs in adult PAE rats, prior to and after minor nerve injury. The results demonstrate a unique circRNA profile in adult PAE rats without injury; 18 circRNAs in blood and 32 spinal circRNAs were differentially regulated. Following minor nerve injury, more than 100 differentially regulated spinal circRNAs were observed in allodynic PAE rats. Bioinformatic analysis identified that the parental genes of these circRNAs are linked to the NF-κB complex, a central transcription factor for pain-relevant proinflammatory cytokines. Quantitative real-time PCR was employed to measure levels of selected circRNAs and linear mRNA isoforms. We have validated that circVopp1 was significantly downregulated in blood leukocytes in PAE rats, concurrent with downregulation of Vopp1 mRNA levels. Spinal circVopp1 levels were upregulated in PAE rats, regardless of nerve injury. Additionally, PAE downregulated levels of circItch and circRps6ka3, which are linked to immune regulation. These results demonstrate that PAE exerts long-lasting dysregulation of circRNA expression in blood leukocytes and the spinal cord. Moreover, the spinal circRNA expression profile following peripheral nerve injury is differentially modulated by PAE, potentially contributing to PAE-induced neuroimmune dysregulation.

Neuroimmune interactions with binge alcohol drinking in the cerebellum of IL-6 transgenic mice

The neuroimmune system of the brain, which is comprised primarily of astrocytes and microglia, regulates a variety of homeostatic mechanisms that underlie normal brain function. Numerous conditions, including alcohol consumption, can disrupt this regulatory process by altering brain levels of neuroimmune factors. Alcohol and neuroimmune factors, such as proinflammatory cytokines IL-6 and TNF-alpha, act at similar targets in the brain, including excitatory and inhibitory synaptic transmission. Thus, alcohol-induced production of IL-6 and/or TNF-alpha could be important contributing factors to the effects of alcohol on the brain. Recent studies indicate that IL-6 plays a role in alcohol drinking and the effects of alcohol on the brain activity following the cessation of alcohol consumption (post-alcohol period), however information on these topics is limited. Here we used homozygous and heterozygous female and male transgenic mice with increased astrocyte expression of IL-6 to examined further the interactions between alcohol and IL-6 with respect to voluntary alcohol drinking, brain activity during the post-alcohol period, IL-6 signal transduction, and expression of synaptic proteins. Wildtype littermates (WT) served as controls. The transgenic mice model brain neuroimmune status with respect to IL-6 in subjects with a history of persistent alcohol use. Results showed a genotype dependent reduction in voluntary alcohol consumption in the Drinking in the Dark protocol and in frequency-dependent relationships between brain activity in EEG recordings during the post-alcohol period and alcohol consumption. IL-6, TNF-alpha, IL-6 signal transduction partners pSTAT3 and c/EBP beta, and synaptic proteins were shown to play a role in these genotypic effects.

Choline Supplementation Alters Hippocampal Cytokine Levels in Adolescence and Adulthood in an Animal Model of Fetal Alcohol Spectrum Disorders

Alcohol (ethanol) exposure during pregnancy can adversely affect development, with long-lasting consequences that include neuroimmune, cognitive, and behavioral dysfunction. Alcohol-induced alterations in cytokine levels in the hippocampus may contribute to abnormal cognitive and behavioral outcomes in individuals with fetal alcohol spectrum disorders (FASD). Nutritional intervention with the essential nutrient choline can improve hippocampal-dependent behavioral impairments and may also influence neuroimmune function. Thus, we examined the effects of choline supplementation on hippocampal cytokine levels in adolescent and adult rats exposed to alcohol early in development. From postnatal day (PD) 4-9 (third trimester-equivalent), Sprague-Dawley rat pups received ethanol (5.25 g/kg/day) or sham intubations and were treated with choline chloride (100 mg/kg/day) or saline from PD 10-30; hippocampi were collected at PD 35 or PD 60. Age-specific ethanol-induced increases in interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), and keratinocyte chemoattractant/human growth-regulated oncogene (KC/GRO) were identified in adulthood, but not adolescence, whereas persistent ethanol-induced increases of interleukin-6 (IL-6) levels were present at both ages. Interestingly, choline supplementation reduced age-related changes in interleukin-1 beta (IL-1β) and interleukin-5 (IL-5) as well as mitigating the long-lasting increase in IFN-γ in ethanol-exposed adults. Moreover, choline influenced inflammatory tone by modulating ratios of pro- to -anti-inflammatory cytokines. These results suggest that ethanol-induced changes in hippocampal cytokine levels are more evident during adulthood than adolescence, and that choline can mitigate some effects of ethanol exposure on long-lasting inflammatory tone.

Choline Supplementation Modifies the Effects of Developmental Alcohol Exposure on Immune Responses in Adult Rats

Prenatal alcohol exposure can disrupt the development of numerous systems, including the immune system. Indeed, alterations in cytokine levels may contribute to the neuropathological, behavioral, and cognitive problems, and other adverse outcomes observed in individuals with fetal alcohol spectrum disorders. Importantly, supplementation with the essential nutrient choline can improve performance in hippocampal-dependent behaviors; thus, the present study examined the effects of choline on plasma and hippocampal cytokines in adult rats exposed to ethanol in early development. From postnatal day (PD) 4–9 (third trimester equivalent), pups received ethanol (5.25 g/kg/day) or Sham intubations. Subjects were treated with choline chloride (100 mg/kg/day) or saline from PD10–30. On PD60, plasma and hippocampal tissue was collected before and after an immune challenge (lipopolysaccharide (LPS); 50 ug/kg). Prior to the immune challenge, ethanol-exposed subjects showed an overall increase in hippocampal pro-inflammatory cytokines, an effect mitigated by choline supplementation. In contrast, in the plasma, choline reduced LPS-related increases in pro-inflammatory markers, particularly in ethanol-exposed subjects. Thus, early choline supplementation may modify both brain and peripheral inflammation. These results suggest that early choline can mitigate some long-term effects of ethanol exposure on hippocampal inflammation, which may contribute to improved hippocampal function, and could also influence peripheral immune responses that may impact overall health.

Adolescent neuroimmune function and its interaction with alcohol

Adolescence is an evolutionarily conserved developmental period associated with behavioral change, including increased risk-taking and alcohol use. Experimentation with alcohol typically begins in adolescence and transitions to binge-like patterns of consumption. Alcohol exposure during adolescence can alter normative changes in brain structure and function. Understanding mechanisms by which ethanol impacts neurodevelopmental processes is important for preventing and ameliorating the deleterious consequences of adolescent alcohol abuse. This review focuses on the neuroimmune system as a key contributor to ethanol-induced changes in adolescent brain and behavior. After brief review of neuroimmune system development, acute and chronic effects of ethanol on adolescent neuroimmune functioning are addressed. Comparisons between stress/immunological challenges and ethanol on adolescent neuroimmunity are reviewed, as cross-sensitization is relevant during adolescence. The mechanisms by which ethanol alters neuroimmune functioning are then discussed, as they may portend development of neuropathological consequences and thus increase vulnerability to subsequent challenges and potentiate addictive behaviors.

Ethanol: Toxicity and Dangers in Women of Child-Bearing Age

The World Health Organisation estimates that alcohol abuse by adults accounts for about 5% of global disease burden. Additionally, prenatal alcohol exposure (PAE) causes ‘fetal alcohol spectrum disorder’ (FASD). Depending on severity, FASD is characterised by low birth weight, small head size at birth and growth retardation. There are also facial features of narrow eyes, flat upper lip and midface and impaired fine motor skills, hearing loss, poor hand-eye coordination and cognitive impairment. World-wide, up to 10% of children may be affected by PAE. It is unclear what dose or pattern of drinking results in these damaging effects, but animal models suggest that high, acute doses of ethanol (‘binge drinking’) in early pregnancy can result in the facial changes of FASD, whilst sustained, lower dose intake in later pregnancy produces anxiety and depression-like symptoms and deficits of learning and memory. The mechanisms underlying the deleterious effects of PAE are also unresolved, but evidence exists of long-lasting damage due to oxidative stress, increases in inflammatory mediators and changes to the brain renin-angiotensin system. There is also evidence of epigenetic changes. There is a need to prevent or limit the potential adverse effects of ethanol on the unborn child. It is highly unlikely, however, that all sexually-active women of child-bearing age not using reliable contraception will abstain from alcohol. There is therefore a need to research methods of reducing ethanol toxicity for the unborn child and / or develop therapeutic strategies to reverse the deleterious effects of ethanol on the unborn child.

Environmental Enrichment During Adolescence Mitigates Cognitive Deficits and Alcohol Vulnerability due to Continuous and Intermittent Perinatal Alcohol Exposure in Adult Rats

Perinatal alcohol exposure affects ontogenic neurodevelopment, causing physical and functional long-term abnormalities with limited treatment options. This study investigated long-term consequences of continuous and intermittent maternal alcohol drinking on behavioral readouts of cognitive function and alcohol vulnerability in the offspring. The effects of environmental enrichment (EE) during adolescence were also evaluated. Female rats underwent continuous alcohol drinking (CAD)—or intermittent alcohol drinking paradigm (IAD), along pregestation, gestation, and lactation periods—equivalent to the whole gestational period in humans. Male offspring were reared in standard conditions or EE until adulthood and were then assessed for declarative memory in the novel object recognition test; spatial learning, cognitive flexibility, and reference memory in the Morris water maze (MWM); alcohol consumption and relapse by a two-bottle choice paradigm. Our data show that perinatal CAD decreased locomotor activity, exploratory behavior, and declarative memory with respect to controls, whereas perinatal IAD displayed impaired declarative memory and spatial learning and memory. Moreover, both perinatal alcohol-exposed offspring showed higher vulnerability to alcohol consummatory behavior than controls, albeit perinatal IAD rats showed a greater alcohol consumption and relapse behavior with respect to perinatal-CAD progeny. EE ameliorated declarative memory in perinatal CAD, while it mitigated spatial learning and reference memory impairment in perinatal-IAD progeny. In addition, EE decreased vulnerability to alcohol in both control and perinatal alcohol-exposed rats. Maternal alcohol consumption produces drinking pattern-related long-term consequences on cognition and vulnerability to alcohol in the offspring. However, increased positive environmental stimuli during adolescence may curtail the detrimental effects of developmental alcohol exposure.

Lingering Effects of Prenatal Alcohol Exposure on Basal and Ethanol-Evoked Expression of Inflammatory-Related Genes in the CNS of Adolescent and Adult Rats

Emerging data suggest that alcohol's effects on central inflammatory factors are not uniform across the lifespan. In particular, prenatal alcohol exposure (PAE) significantly alters steady-state levels of neuroimmune factors, as well as subsequent reactivity to later immune challenge. Thus, the current experiment investigated developmental sensitivities to, and long-lasting consequences of, PAE on ethanol-evoked cytokine expression in male and female adolescent and adult rats. Pregnant dams received either an ad libitum ethanol liquid diet (2.2% GD 6-8; 4.5% GD 9-10; 6.7% GD11-20; 35% daily calories from ethanol) or free-choice access to a control liquid diet and water. At birth, offspring were fostered to dams given free-choice access to the control liquid diet. Pups then matured until mid-adolescence [postnatal day (PD) 35] or adulthood (PD90), at which time they were challenged with either a binge-like dose of ethanol (4 g/kg; intragastrically) or tap water. During intoxication (3 h post-ethanol challenge), brains and blood were collected for assessment of neuroimmune gene expression (reverse transcription-polymerase chain reaction; RT-PCR) in the hippocampus, amygdala, and PVN, as well as for blood ethanol concentrations (BEC) and plasma corticosterone levels. Results revealed that rats challenged with ethanol at either PD35 or PD90 generally exhibited a characteristic cytokine signature of acute intoxication that we have previously reported: increased Il-6 and IkBα expression, with decreased Il-1β and Tnfα gene expression. With a few exceptions, this pattern of gene changes was observed in all three structures examined, at both ages of postnatal ethanol challenge, and in both sexes. While few significant effects of PAE were observed for ethanol-induced alterations in cytokine expression, there was a consistent (but nonsignificant) trend for PAE to potentiate the expression of Il-6 and IkBα in all groups except adult females. Although these data suggest that later-life ethanol challenge was a far greater driver of inflammatory signaling than PAE, the current results demonstrate PAE resulted in subtle long-term alterations in the expression of many key neuroinflammatory factors associated with NF-κB signaling. Such long-lasting impacts of PAE that may engender vulnerability to later environmental events triggering neuroinflammatory processes, such as chronic ethanol exposure or stress, could contribute to heightened vulnerability for PAE-related alterations and deficits.

Chronic alcohol-induced liver injury correlates with memory deficits: Role for neuroinflammation

Alcohol use disorder (AUD) affects over 15 million adults over age 18 in the United States, with estimated costs of 220 billion dollars annually - mainly due to poor quality of life and lost productivity, which in turn is intricately linked to cognitive dysfunction. AUD-induced neuroinflammation in the brain, notably the hippocampus, is likely to contribute to cognitive impairments. The neuroinflammatory mechanisms mediating the impact of chronic alcohol on the central nervous system, specifically cognition, require further study. We hypothesized that chronic alcohol consumption impairs memory and increases the inflammatory cytokines TNFα, IL6, MCP1, and IL1β in the hippocampus and prefrontal cortex regions in the brain. Using the chronic-binge Gao-NIAAA alcohol mouse model of liver disease, representative of the drinking pattern common to human alcoholics, we investigated behavioral and neuroinflammatory parameters. Our data show that chronic alcohol intake elevated peripheral and brain alcohol levels, induced serum alanine aminotransferase (ALT, a marker of liver injury), impaired memory and sensorimotor coordination, and increased inflammatory gene expression in the hippocampus and prefrontal cortex. Interestingly, serum ALT and hippocampal IL6 correlated with memory impairment, suggesting an intrinsic relationship between neuroinflammation, cognitive decline, and liver disease. Overall, our results point to a likely liver-brain functional partnership and suggest that future strategies to alleviate hepatic and/or neuroinflammatory impacts of chronic AUD may result in improved cognitive outcomes.

Role of P2 receptors in normal brain development and in neurodevelopmental psychiatric disorders

The purinergic signaling system, including P2 receptors, plays an important role in various central nervous system (CNS) disorders. Over the last few decades, a substantial amount of accumulated data suggest that most P2 receptor subtypes (P2X1, 2, 3, 4, 6, and 7, and P2Y₁, ₂, ₆, ₁₂, and ₁₃) regulate neuronal/neuroglial developmental processes, such as proliferation, differentiation, migration of neuronal precursors, and neurite outgrowth. However, only a few of these subtypes (P2X2, P2X3, P2X4, P2X7, P2Y₁, and P2Y₂) have been investigated in the context of neurodevelopmental psychiatric disorders. The activation of these potential target receptors and their underlying mechanisms mainly influence the process of neuroinflammation. In particular, P2 receptor-mediated inflammatory cytokine release has been indicated to contribute to the complex mechanisms of a variety of CNS disorders. The released inflammatory cytokines could be utilized as biomarkers for neurodevelopmental and psychiatric disorders to improve the early diagnosis intervention, and prognosis. The population changes in gut microbiota after birth are closely linked to neurodevelopmental/neuropsychiatric disorders in later life; thus, the dynamic expression and function of P2 receptors on gut epithelial cells during disease processes indicate a novel avenue for the evaluation of disease progression and for the discovery of related therapeutic compounds.

Moderate prenatal alcohol exposure impairs performance by adult male rats in an object-place paired-associate task

Memory impairments, including spatial and object processing, are often observed in individuals with Fetal Alcohol Spectrum Disorders. The neurobiological basis of memory deficits after prenatal alcohol exposure (PAE) is often linked to structural and functional alterations in the medial temporal lobe, including the hippocampus. Recent evidence suggests that the medial temporal lobe plays a critical role in processing high-order sensory stimuli such as complex objects and their associated locations in space. In the first experiment, we tested male rat offspring with moderate PAE in a medial temporal-dependent object-place paired-associate (OPPA) task. The OPPA task requires a conditional discrimination between an identical pair of objects presented at two spatial locations 180° opposite arms of a radial arm maze. Food reinforcement is contingent upon selecting the correct object of the pair for a given spatial location. Adult rats were given a total of 10 trials per day over 14 consecutive days of training. PAE male rats made significantly more errors than male saccharin (SACC) control rats during acquisition of the OPPA task. In Experiment 2, rats performed an object-discrimination task in which a pair of objects were presented in a single arm of the maze. Moderate PAE and SACC control rats exhibited comparable performance. The results suggest that moderate PAE rats can learn to discriminate objects, but are impaired when required to discriminate between objects on the basis of spatial location in the environment.

Lifelong Impacts of Moderate Prenatal Alcohol Exposure on Neuroimmune Function

In utero alcohol exposure is emerging as a major risk factor for lifelong aberrant neuroimmune function. Fetal alcohol spectrum disorder encompasses a range of behavioral and physiological sequelae that may occur throughout life and includes cognitive developmental disabilities as well as disease susceptibility related to aberrant immune and neuroimmune actions. Emerging data from clinical studies and findings from animal models support that very low to moderate levels of fetal alcohol exposure may reprogram the developing central nervous system leading to altered neuroimmune and neuroglial signaling during adulthood. In this review, we will focus on the consequences of low to moderate prenatal alcohol exposure (PAE) on neuroimmune interactions during early life and at different stages of adulthood. Data discussed here will include recent studies suggesting that while abnormal immune function is generally minimal under basal conditions, following pathogenic stimuli or trauma, significant alterations in the neuroimmune axis occur. Evidence from published reports will be discussed with a focus on observations that PAE may bias later-life peripheral immune responses toward a proinflammatory phenotype. The propensity for proinflammatory responses to challenges in adulthood may ultimately shape neuron–glial-immune processes suspected to underlie various neuropathological outcomes including chronic pain and cognitive impairment.

Sex Differences in Early Postnatal Microglial Colonization of the Developing Rat Hippocampus Following a Single-Day Alcohol Exposure

Microglia are involved in various homeostatic processes in the brain, including phagocytosis, apoptosis, and synaptic pruning. Sex differences in microglia colonization of the developing brain have been reported, but have not been established following alcohol insult. Developmental alcohol exposure represents a neuroimmune challenge that may contribute to cognitive dysfunction prevalent in humans with Fetal Alcohol Spectrum Disorders (FASD) and in rodent models of FASD. Most studies have investigated neuroimmune activation following adult alcohol exposure or following multiple exposures. The current study uses a single day binge alcohol exposure model (postnatal day [PD] 4) to examine sex differences in the neuroimmune response in the developing rat hippocampus on PD5 and 8. The neuroimmune response was evaluated through measurement of microglial number and cytokine gene expression at both time points. Male pups had higher microglial number compared to females in many hippocampal subregions on PD5, but this difference disappeared by PD8, unless exposed to alcohol. Expression of pro-inflammatory marker CD11b was higher on PD5 in alcohol-exposed (AE) females compared to AE males. After alcohol exposure, C-C motif chemokine ligand 4 (CCL4) was significantly increased in female AE pups on PD5 and PD8. Tumor necrosis factor-α (TNF-α) levels were also upregulated by AE in males on PD8. The results demonstrate a clear difference between the male and female neuroimmune response to an AE challenge, which also occurs in a time-dependent manner. These findings are significant as they add to our knowledge of specific sex-dependent effects of alcohol exposure on microglia within the developing brain.