Adolescent Alcohol Exposure Produces Protracted Cognitive-Behavioral Impairments in Adult Male and Female Rats

Alcohol Consumption During Adolescence Alters the Cognitive Function in Adult Male Mice by Persistently Increasing Levels of DUSP6

Binge alcohol drinking during adolescence has long-term effects on the adult brain that alter brain structure and behaviors, but the underlying mechanisms remain poorly understood. Extracellular signal-regulated kinase (ERK) is involved in the synaptic plasticity and pathological brain injury by regulating the expression of cyclic adenosine monophosphate response element binding protein (CREB) and brain-derived neurotrophic factor (BDNF). Dual-specificity phosphatase 6 (DUSP6) is a critical effector that dephosphorylates ERK1/2 to control the basal tone, amplitude, and duration of ERK signaling. To explore DUSP6 as a regulator of ERK signaling in the mPFC and its impact on long-term effects of alcohol, a male mouse model of adolescent intermittent alcohol (AIA) exposure was established. Behavioral experiments showed that AIA did not affect anxiety-like behavior or sociability in adulthood, but significantly damaged new object recognition and social recognition memory. Molecular studies further found that AIA reduced the levels of pERK-pCREB-BDNF-PSD95/NR2A involved in synaptic plasticity, while DUSP6 was significantly increased. Intra-mPFC infusion of AAV-DUSP6-shRNA restored the dendritic spine density and postsynaptic density thickness by reversing the level of p-ERK and its downstream molecular expression, and ultimately repaired adult cognitive impairment caused by chronic alcohol exposure during adolescence. These findings indicate that AIA exposure inhibits ERK-CREB-BDNF-PSD95/NR2A by increasing DUSP6 in the mPFC in adulthood that may be associated with long-lasting cognitive deficits.

Sex-dependent responses to high concentration of binge ethanol in spleen of adolescent F344 rats

BACKGROUND

We previously reported that binge ethanol induces atrophy of the spleen, a key immune organ, in adolescent male F344 rats. Because there are significant sex effects in immune function, we investigated whether binge ethanol exerts sex-dependent effects on the spleen, including producing splenic atrophy.

METHODS

We gave F344 rats ethanol (4.8 g/kg/day; 52% w/v; i.g.) on postnatal days [PND] 36 ~ 38 and sacrificed them on PND 39 for spleen collection. We performed immunophenotyping analysis of splenic cells and examined the expression of 158 genes related to alcohol metabolism, epigenetic modification, and immune regulation in the spleens of adolescent (PND 39) male and female rats.

RESULTS

Following a 3-day ethanol exposure, a loss of body weight, and absolute and relative spleen weight, was seen only in male adolescent rats. Ethanol altered the relative proportions of lymphocyte subtypes in both sexes with different patterns. We also found that 3-day ethanol exposure induced sex-dependent gene expression changes in spleen. Among the 158 genes studied, the expression of only three genes was significantly increased in female rats. However, the expression of 30 genes was significantly increased/decreased in male rats. Female rats had greater expression of alcohol metabolizing enzyme genes in the spleen under physiological conditions and when stimulated by binge ethanol. The genes are involved in epigenetic modification were differentially expressed in a sex-dependent manner.

CONCLUSION

We found that male adolescent rats were more sensitive to binge ethanol than female rats. Differential expression of the genes related to alcohol metabolism and epigenetic modification (of DNA methyltransferase and histone deacetylases) between the sexes could account for the observed sex-dependent responses to binge ethanol in adolescent rats.

Chronic Ethanol Exposure Produces Persistent Impairment in Cognitive Flexibility and Decision Signals in the Striatum

Lack of cognitive flexibility is a hallmark of substance use disorders and has been associated with drug-induced synaptic plasticity in the dorsomedial striatum (DMS). Yet the possible impact of altered plasticity on real-time striatal neural dynamics during decision-making is unclear. Here, we identified persistent impairments induced by chronic ethanol (EtOH) exposure on cognitive flexibility and striatal decision signals. After a substantial withdrawal period from prior EtOH vapor exposure, male, but not female, rats exhibited reduced adaptability and exploratory behavior during a dynamic decision-making task. Reinforcement learning models showed that prior EtOH exposure enhanced learning from rewards over omissions. Notably, neural signals in the DMS related to the decision outcome were enhanced, while those related to choice and choice-outcome conjunction were reduced, in EtOH-treated rats compared to the controls. These findings highlight the profound impact of chronic EtOH exposure on adaptive decision-making, pinpointing specific changes in striatal representations of actions and outcomes as underlying mechanisms for cognitive deficits.

Epigenetic regulation of microglia and neurons by proinflammatory signaling following adolescent intermittent ethanol (AIE) exposure and in human AUD

Adolescent alcohol drinking is linked to high rates of adult alcohol problems and alcohol use disorder (AUD). The Neurobiology of Alcohol Drinking in Adulthood (NADIA) consortium adolescent intermittent ethanol (AIE) models adolescent binge drinking, followed by abstinent maturation to adulthood to determine the persistent AIE changes in neurobiology and behavior. AIE increases adult alcohol drinking and preference, increases anxiety and reward seeking, and disrupts sleep and cognition, all risks for AUD. In addition, AIE induces changes in neuroimmune gene expression in neurons and glia that alter neurocircuitry and behavior. HMGB1 is a unique neuroimmune signal released from neurons and glia by ethanol that activates multiple proinflammatory receptors, including Toll-like receptors (TLRs), that spread proinflammatory gene induction. HMGB1 expression is increased by AIE in rat brain and in post-mortem human AUD brain, where it correlates with lifetime alcohol consumption. HMGB1 activation of TLR increase TLR expression. Human AUD brain and rat brain following AIE show increases in multiple TLRs. Brain regional differences in neurotransmitters and cell types impact ethanol responses and neuroimmune gene induction. Microglia are monocyte-like cells that provide trophic and synaptic functions, that ethanol proinflammatory signals sensitize or "prime" during repeated drinking cycles, impacting neurocircuitry. Neurocircuits are differently impacted dependent upon neuronal-glial signaling. Acetylcholine is an anti-inflammatory neurotransmitter. AIE increases HMGB1-TLR4 signaling in forebrain, reducing cholinergic neurons by silencing multiple cholinergic defining genes through upregulation of RE-1 silencing factor (REST), a transcription inhibitor known to regulate neuronal differentiation. HMGB1 REST induction reduces cholinergic neurons in basal forebrain and cholinergic innervation of hippocampus. Adult brain hippocampal neurogenesis is regulated by a neurogenic niche formed from multiple cells. In vivo AIE and in vitro studies find ethanol increases HMGB1-TLR4 signaling and other proinflammatory signaling as well as reducing trophic factors, NGF, and BDNF, coincident with loss of the cholinergic synapse marker vChAT. These changes in gene expression-transcriptomes result in reduced adult neurogenesis. Excitingly, HMGB1 antagonists, anti-inflammatories, and epigenetic modifiers like histone deacetylase inhibitors restore trophic the neurogenesis. These findings suggest anti-inflammatory and epigenetic drugs should be considered for AUD therapy and may provide long-lasting reversal of psychopathology.

Adolescent intermittent ethanol exposure alters adult exploratory and affective behaviors, and cerebellar Grin2b expression in C57BL/6J mice

Binge drinking is one of the most common patterns (more than 90%) of alcohol consumption by young people. During adolescence, the brain undergoes maturational changes that influence behavioral control and affective behaviors, such as cerebellar brain volume and function in adulthood. We investigated long-term impacts of adolescent binge ethanol exposure on affective and exploratory behaviors and cerebellar gene expression in adult male and female mice. Further, the cerebellum is increasingly recognized as a brain region integrating a multitude of behaviors that span from the traditional primary sensory-motor to affective functions, such as anxiety and stress reactivity. Therefore, we investigated the persistent effects of adolescent intermittent ethanol (AIE) on exploratory and affective behaviors and began to elucidate the role of the cerebellum in these behaviors through excitatory signaling gene expression. We exposed C57BL/6J mice to AIE or air (control) vapor inhalation from postnatal day 28-42. After prolonged abstinence (>34 days), in young adulthood (PND 77+) we assessed behavior in the open field, light/dark, tail suspension, and forced swim stress tests to determine changes in affective behaviors including anxiety-like, depressive-like, and stress reactivity behavior. Excitatory signaling gene mRNA levels of fragile X messenger ribonucleoprotein (FMR1), glutamate receptors (Grin2a, Grin2b and Grm5) and excitatory synaptic markers (PSD-95 and Eaat1) were measured in the cerebellum of adult control and AIE-exposed mice. AIE-exposed mice showed decreased exploratory behaviors in the open field test (OFT) where both sexes show reduced ambulation, however only females exhibited a reduction in rearing. Additionally, in the OFT, AIE-exposed females also exhibited increased anxiety-like behavior (entries to center zone). In the forced swim stress test, AIE-exposed male mice, but not females, spent less time immobile compared to their same-sex controls, indicative of sex-specific changes in stress reactivity. Male and female AIE-exposed mice showed increased Grin2b (Glutamate Ionotropic Receptor NMDA Type Subunit 2B) mRNA levels in the cerebellum compared to their same-sex controls. Together, these data show that adolescent binge-like ethanol exposure altered both exploratory and affective behaviors in a sex-specific manner and modified cerebellar Grin2b expression in adult mice. This indicates the cerebellum may serve as an important brain region that is susceptible to long-term molecular changes after AIE.

Therapeutic role of mesenchymal stem cell-derived extracellular vesicles in neuroinflammation and cognitive dysfunctions induced by binge-like ethanol treatment in adolescent mice

BACKGROUND

Extracellular vesicles (EVs) are heterogeneous membrane vesicles secreted by cells in extracellular spaces that play an important role in intercellular communication under both normal and pathological conditions. Mesenchymal stem cells (MSC) are anti-inflammatory and immunoregulatory cells capable of secreting EVs, which are considered promising molecules for treating immune, inflammatory, and degenerative diseases. Our previous studies demonstrate that, by activating innate immune receptors TLR4 (Toll-like receptor 4), binge-like ethanol exposure in adolescence causes neuroinflammation and neural damage.

AIMS

To evaluate whether the intravenous administration of MSC-derived EVs is capable of reducing neuroinflammation, myelin and synaptic alterations, and the cognitive dysfunction induced by binge-like ethanol treatment in adolescent mice.

MATERIALS & METHODS

MSC-derived EVs obtained from adipose tissue were administered in the tail vein (50 microg/dose, one weekly dose) to female WT adolescent mice treated intermittently with ethanol (3.0 g/kg) during two weeks.

RESULTS

MSC-derived EVs from adipose tissue ameliorate ethanol-induced up-regulation of inflammatory genes (e.g., COX-2, iNOS, MIP-1α, NF-κB, CX3CL1, and MCP-1) in the prefrontal cortex of adolescent mice. Notably, MSC-derived EVs also restore the myelin and synaptic derangements, and the memory and learning impairments, induced by ethanol treatment. Using cortical astroglial cells in culture, our results further confirm that MSC-derived EVs decrease inflammatory genes in ethanol-treated astroglial cells. This, in turn, confirms in vivo findings.

CONCLUSION

Taken together, these results provide the first evidence for the therapeutic potential of the MSC-derived EVs in the neuroimmune response and cognitive dysfunction induced by binge alcohol drinking in adolescence.

Adolescent intermittent alcohol exposure produces strain-specific cross-sensitization to nicotine and other behavioral adaptations in adulthood in C57BL/6J and DBA/2J mice

Adolescent alcohol exposure is associated with lasting behavioral changes in humans and in mice. Prior work from our laboratory and others have demonstrated that C57BL/6J and DBA/2J mice differ in sensitivity to some effects of acute alcohol exposure during adolescence and adulthood. However, it is unknown if these strains differ in cognitive, anxiety-related, and addiction-related long-term consequences of adolescent intermittent alcohol exposure. This study examined the impact of a previously validated adolescent alcohol exposure paradigm (2-3 g/kg, i.p., every other day PND 30-44) in C57BL/6J and DBA/2J male and female mice on adult fear conditioning, anxiety-related behavior (elevated plus maze), and addiction-related phenotypes including nicotine sensitivity (hypothermia and locomotor depression) and alcohol sensitivity (loss of righting reflex; LORR). Both shared and strain-specific long-term consequences of adolescent alcohol exposure were found. Most notably, we found a strain-specific alcohol-induced increase in sensitivity to nicotine's hypothermic effects during adulthood in the DBA/2J strain but not in the C57BL/6J strain. Conversely, both strains demonstrated a robust increased latency to LORR during adulthood after adolescent alcohol exposure. Thus, we observed strain-dependent cross-sensitization to nicotine and strain-independent tolerance to alcohol due to adolescent alcohol exposure. Several strain and sex differences independent of adolescent alcohol treatment were also observed. These include increased sensitivity to nicotine-induced hypothermia in the C57BL/6J strain relative to the DBA/2J strain, in addition to DBA/2J mice showing more anxiety-like behaviors in the elevated plus maze relative to the C57BL/6J strain. Overall, these results suggest that adolescent alcohol exposure results in altered adult sensitivity to nicotine and alcohol with some phenotypes mediated by genetic background.

Determining the neuronal ensembles underlying sex-specific social impairments following adolescent intermittent ethanol exposure

Binge drinking during adolescence can have behavioral and neurobiological consequences. We have previously found that adolescent intermittent ethanol (AIE) exposure produces sex-specific social alterations indexed via decreases of social investigation and/or social preference in rats. The prelimbic cortex (PrL) regulates social interaction, and alterations within the PrL resulting from AIE may contribute to social alterations. The current study sought to determine whether AIE-induced PrL dysfunction underlies decreases in social interaction evident in adulthood. We first examined social interaction-induced neuronal activation of the PrL and several other regions of interest (ROIs) implicated in social interaction. Adolescent male and female cFos-LacZ rats were exposed to water (control) or ethanol (4 g/kg, 25% v/v) via intragastric gavage every other day between postnatal day (P) 25 and 45 (total 11 exposures). Since cFos-LacZ rats express β-galactosidase (β-gal) as a proxy for Fos, activated cells that express of β-gal can be inactivated by Daun02. In most ROIs, expression of β-gal was elevated in socially tested adult rats relative to home cage controls, regardless of sex. However, decreased social interaction-induced β-gal expression in AIE-exposed rats relative to controls was evident only in the PrL of males. A separate cohort underwent PrL cannulation surgery in adulthood and was subjected to Daun02-induced inactivation. Inactivation of PrL ensembles previously activated by social interaction reduced social investigation in control males, with no changes evident in AIE-exposed males or females. These findings highlight the role of the PrL in male social investigation and suggest an AIE-associated dysfunction of the PrL that may contribute to reduced social investigation following adolescent ethanol exposure.

Adolescent Intermittent Ethanol Exposure Alters Adult Exploratory and Affective Behaviors, and Cerebellar Grin2B Expression in C57BL/6J Mice

Binge drinking is one of the most common patterns (more than 90%) of alcohol consumption by young people. During adolescence, the brain undergoes maturational changes that influence behavioral control and affective behaviors, such as cerebellar brain volume and function in adulthood. We investigated long-term impacts of adolescent binge ethanol exposure on affective and exploratory behaviors and cerebellar gene expression in adult male and female mice. Further, the cerebellum is increasingly recognized as a brain region integrating a multitude of behaviors that span from the traditional primary sensory-motor to affective functions, such as anxiety and stress reactivity. Therefore, we investigated the persistent effects of adolescent intermittent ethanol (AIE) on exploratory and affective behaviors and began to elucidate the role of the cerebellum in these behaviors through excitatory signaling gene expression. We exposed C57BL/6J mice to AIE or air (control) vapor inhalation from postnatal day 28-42. After prolonged abstinence (>34 days), in young adulthood (PND 77+) we assessed behavior in the open field, light/dark, tail suspension, and forced swim stress tests to determine changes in affective behaviors including anxiety-like, depressive-like, and stress reactivity behavior. Excitatory signaling gene mRNA levels of fragile X messenger ribonucleoprotein ( FMR1) , glutamate receptors ( Grin2a , Grin2B and Grm5 ) and excitatory synaptic markers (PSD-95 and Eaat1) were measured in the cerebellum of adult control and AIE-exposed mice. AIE-exposed mice showed decreased exploratory behaviors in the open field test (OFT) where both sexes show reduced ambulation, however only females exhibited a reduction in rearing. Additionally, in the OFT, AIE-exposed females also exhibited increased anxiety-like behavior (entries to center zone). In the forced swim stress test, AIE-exposed male mice, but not females, spent less time immobile compared to their same-sex controls, indicative of sex-specific changes in stress reactivity. Male and female AIE-exposed mice showed increased Grin2B (Glutamate Ionotropic Receptor NMDA Type Subunit 2B) mRNA levels in the cerebellum compared to their same-sex controls. Together, these data show that adolescent binge-like ethanol exposure altered both exploratory and affective behaviors in a sex-specific manner and modified cerebellar Grin2B expression in adult mice. This indicates the cerebellum may serve as an important brain region that is susceptible to long-term molecular changes after AIE.

Highlights

Adolescent intermittent ethanol (AIE) exposure decreased exploratory behavior in adult male and female mice.In females, but not males, AIE increased anxiety-like behavior.In males, but not females, AIE reduced stress reactivity in adulthood.These findings indicate sex differences in the enduring effects of AIE on exploratory and affective behaviors. Cerebellar Grin2B mRNA levels were increased in adulthood in both male and female AIE-exposed mice. These findings add to the small, but growing literature on behavioral AIE effects in mice, and establish cerebellar excitatory synaptic gene expression as an enduring effect of adolescent ethanol exposure.

Chronic intermittent ethanol exposure during adolescence produces sex- and age-dependent changes in anxiety and cognition without changes in microglia reactivity late in life

Binge-like ethanol exposure during adolescence has been shown to produce long lasting effects in animal models including anxiety-like behavior that can last into young adulthood and impairments in cognition that can last throughout most of the lifespan. However, little research has investigated if binge-like ethanol exposure during adolescence produces persistent anxiety-like behavior and concomitantly impairs cognition late in life. Furthermore, few studies have investigated such behavioral effects in both female and male rats over the lifespan. Finally, it is yet to be determined if binge-like ethanol exposure during adolescence alters microglia activation in relevant brain regions late in life. In the present study female and male adolescent rats were exposed to either 3.0 or 5.0 g/kg ethanol, or water control, in a chronic intermittent pattern before being tested in the elevated plus maze and open field task over the next ∼18 months. Animals were then trained in a spatial reference task via the Morris water maze before having their behavioral flexibility tested. Finally, brains were removed, sectioned and presumptive microglia activation determined using autoradiography for [3H]PK11195 binding. Males, but not females, displayed an anxiety-like phenotype initially following the chronic intermittent ethanol exposure paradigm which resolved in adulthood. Further, males but not females had altered spatial reference learning and impaired behavioral flexibility late in life. Conversely, [3H]PK11195 binding was significantly elevated in females compared to males late in life and the level of microglia activation interacted as a function of sex and brain regions, but there was no long-term outcome related to adolescent alcohol exposure. These data further confirm that binge-like ethanol exposure during adolescence produces alterations in behavior that can last throughout the lifespan. In addition, the data suggest that microglia activation late in life is not exacerbated by prior binge-like ethanol exposure during adolescence but the expression is sex- and brain region-dependent across the lifespan.

Determining the neuronal ensembles underlying sex-specific social impairments following adolescent intermittent ethanol exposure

Binge drinking during adolescence can have behavioral and neurobiological consequences. We have previously found that adolescent intermittent ethanol (AIE) exposure produces a sex-specific social impairment in rats. The prelimbic cortex (PrL) regulates social behavior, and alterations within the PrL resulting from AIE may contribute to social impairments. The current study sought to determine whether AIE-induced PrL dysfunction underlies social deficits in adulthood. We first examined social stimulus-induced neuronal activation of the PrL and several other regions of interest implicated in social behavior. Male and female cFos-LacZ rats were exposed to water (control) or ethanol (4 g/kg, 25% v/v) via intragastric gavage every other day between postnatal day (P) 25 and 45 (total 11 exposures). Since cFos-LacZ rats express β-galactosidase (β-gal) as a proxy for cFos, activated cells that express of β-gal can be inactivated by Daun02. β-gal expression in most ROIs was elevated in socially tested adult rats relative to home cage controls, regardless of sex. However, differences in social stimulus-induced β-gal expression between controls and AIE-exposed rats was evident only in the PrL of males. A separate cohort underwent PrL cannulation surgery in adulthood and were subjected to Daun02-induced inactivation. Inactivation of PrL ensembles previously activated by a social stimulus led to a reduction of social behavior in control males, with no changes evident in AIE-exposed males or females. These findings highlight the role of the PrL in male social behavior and suggest an AIE-associated dysfunction of the PrL may contribute to social deficits following adolescent ethanol exposure.

Adolescent binge ethanol impacts H3K36me3 regulation of synaptic genes

Adolescence is marked in part by the ongoing development of the prefrontal cortex (PFC). Binge ethanol use during this critical stage in neurodevelopment induces significant structural changes to the PFC, as well as cognitive and behavioral deficits that can last into adulthood. Previous studies showed that adolescent binge ethanol causes lasting deficits in working memory, decreases in the expression of chromatin remodeling genes responsible for the methylation of histone 3 lysine 36 (H3K36), and global decreases in H3K36 in the PFC. H3K36me3 is present within the coding region of actively-transcribed genes, and safeguards against aberrant, cryptic transcription by RNA Polymerase II. We hypothesize that altered methylation of H3K36 could play a role in adolescent binge ethanol-induced memory deficits. To investigate this at the molecular level, ethanol (4 g/kg, i.g.) or water was administered intermittently to adolescent mice. RNA-and ChIP-sequencing were then performed within the same tissue to determine gene expression changes and identify genes and loci where H3K36me3 was disrupted by ethanol. We further assessed ethanol-induced changes at the transcription level with differential exon-use and cryptic transcription analysis - a hallmark of decreased H3K36me3. Here, we found ethanol-induced changes to the gene expression and H3K36me3-regulation of synaptic-related genes in all our analyses. Notably, H3K36me3 was differentially trimethylated between ethanol and control conditions at synaptic-related genes, and Snap25 and Cplx1 showed evidence of cryptic transcription in males and females treated with ethanol during adolescence. Our results provide preliminary evidence that ethanol-induced changes to H3K36me3 during adolescent neurodevelopment may be linked to synaptic dysregulation at the transcriptional level, which may explain the reported ethanol-induced changes to PFC synaptic function.

Indomethacin restores loss of hippocampal neurogenesis and cholinergic innervation and reduces innate immune expression and reversal learning deficits in adult male and female rats following adolescent ethanol exposure

BACKGROUND

Adolescent intermittent ethanol (AIE) exposure causes long-term changes in the brain and behavior of adult male rodents, including persistent induction of innate immune pathways, reductions in hippocampal neurogenic and forebrain cholinergic neuronal markers, and reversal learning deficits. The current study tests the hypothesis that proinflammatory induction mediates AIE-induced (1) loss of adult neurogenesis (i.e., doublecortin (DCX) expressing immature neurons), (2) reductions in forebrain and hippocampal cholinergic markers, and (3) reversal learning deficits.

METHODS

Male and female rats underwent AIE (5.0 g/kg/day ethanol or water, i.g., 2 day-on/2 day-off from postnatal day (PND) 25-54), followed by a 2-week regimen of the anti-inflammatory compound indomethacin (4.0 g/kg/day, PND 56-69) or vehicle, after which one cohort was euthanized for immunohistochemical markers (PND 70) and the second underwent the Morris water maze to assess reversal learning.

RESULTS

AIE reduced adult (PND 70) DCX+ immunoreactivity (IR) and increased hippocampal expression of the innate immune signal's high-mobility group box protein 1 (HMGB1 + IR) and cyclooxygenase-2 (COX-2 + IR) in adult male and female rats. AIE also reduced choline acetyltransferase (ChAT+IR) in the basal forebrain and co-labeling of hippocampal vesicular acetylcholine transporter (VAChT+) cholinergic terminals on DCX + IR neurons. Indomethacin treatment after AIE restored molecular endpoints to control levels and rescued AIE-induced reversal learning deficits in the Morris water maze in both sexes. Of note, indomethacin produced several adverse effects selectively in control conditions, highlighting the uniquely beneficial effect of indomethacin in AIE rats.

CONCLUSIONS

These data suggest that in males and females, (1) AIE persistent neuroimmune induction mediates both the loss of adult hippocampal DCX and loss of basal forebrain cholinergic neurons and their innervation to hippocampal targets, and (2) anti-inflammatory indomethacin treatment following AIE that restores these persistent molecular pathologies also restores spatial reversal learning deficits.

Targeting Persistent Changes in Neuroimmune and Epigenetic Signaling in Adolescent Drinking to Treat Alcohol Use Disorder in Adulthood

Studies universally find early age of drinking onset is linked to lifelong risks of alcohol problems and alcohol use disorder (AUD). Assessment of the lasting effect of drinking during adolescent development in humans is confounded by the diversity of environmental and genetic factors that affect adolescent development, including emerging personality disorders and progressive increases in drinking trajectories into adulthood. Preclinical studies using an adolescent intermittent ethanol (AIE) exposure rat model of underage binge drinking avoid the human confounds and support lifelong changes that increase risks. AIE increases adult alcohol drinking, risky decision-making, reward-seeking, and anxiety as well as reductions in executive function that all increase risks for the development of an AUD. AIE causes persistent increases in brain neuroimmune signaling high-mobility group box 1 (HMGB1), Toll-like receptor, receptor for advanced glycation end products, and innate immune genes that are also found to be increased in human AUD brain. HMGB1 is released from cells by ethanol, both free and within extracellular vesicles, that act on neurons and glia, shifting transcription and cellular phenotype. AIE-induced decreases in adult hippocampal neurogenesis and loss of basal forebrain cholinergic neurons are reviewed as examples of persistent AIE-induced pathology. Both are prevented and reversed by anti-inflammatory and epigenetic drugs. Findings suggest AIE-increased HMGB1 signaling induces the RE-1 silencing transcript blunting cholinergic gene expression, shifting neuronal phenotype. Inhibition of HMGB1 neuroimmune signaling, histone methylation enzymes, and galantamine, the cholinesterase inhibitor, both prevent and reverse AIE pathology. These findings provide new targets that may reverse AUD neuropathology as well as other brain diseases linked to neuroimmune signaling. SIGNIFICANCE STATEMENT: Adolescent underage binge drinking studies find that earlier adolescent drinking is associated with lifelong alcohol problems including high levels of lifetime alcohol use disorder (AUD). Preclinical studies find the underage binge drinking adolescent intermittent ethanol (AIE) model causes lasting changes in adults that increase risks of developing adult alcohol problems. Loss of hippocampal neurogenesis and loss of basal forebrain cholinergic neurons provide examples of how AIE-induced epigenetic and neuroimmune signaling provide novel therapeutic targets for adult AUD.

[Binge drinking in the young population: Lost memory after initial ethanol exposure via neuroinflammation and epigenetic]

Binge drinking (BD) in young adults/adolescents can lead to cognitive deficits in the adult probably through neuroinflammation and epigenetic. However, the mode of action of alcohol during the initial exposure is less known while it may be the origin of the deficits seen in adults. Recent studies in adolescent rat hippocampus revealed that loss of memory occurred since the very first exposure to BD with similar mechanisms than those highlighted for longer alcohol exposure. Thus, initiation to BD in the young is responsible for cognitive deficits that will be probably entertained by repeated BD behavior. These kind of data may serve to reinforce the prevention campaigns towards the young population who practice BD.

Adolescent ethanol drinking promotes hyperalgesia, neuroinflammation and serotonergic deficits in mice that persist into adulthood

Adolescent alcohol use can permanently alter brain function and lead to poor health outcomes in adulthood. Emerging evidence suggests that alcohol use can predispose individuals to pain disorders or exacerbate existing pain conditions, but the underlying neural mechanisms are currently unknown. Here we report that mice exposed to adolescent intermittent access to ethanol (AIE) exhibit increased pain sensitivity and depressive-like behaviors that persist for several weeks after alcohol cessation and are accompanied by elevated CD68 expression in microglia and reduced numbers of serotonin (5-HT)-expressing neurons in the dorsal raphe nucleus (DRN). 5-HT expression was also reduced in the thalamus, anterior cingulate cortex (ACC) and amygdala as well as the lumbar dorsal horn of the spinal cord. We further demonstrate that chronic minocycline administration after AIE alleviated hyperalgesia and social deficits, while chemogenetic activation of microglia in the DRN of ethanol-naïve mice reproduced the effects of AIE on pain and social behavior. Chemogenetic activation of microglia also reduced tryptophan hydroxylase 2 (Tph2) expression and was negatively correlated with the number of 5-HT-immunoreactive cells in the DRN. Taken together, these results indicate that microglial activation in the DRN may be a primary driver of pain, negative affect, and 5-HT depletion after AIE.

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.

The Influence of Sex on Hippocampal Neurogenesis and Neurotrophic Responses on the Persistent Effects of Adolescent Intermittent Ethanol Exposure into Adulthood

In the United States, approximately 90% of alcohol consumed by adolescents is binge drinking. Binge-like ethanol exposure during adolescence promotes dysregulation of neurotrophic responses and neurogenesis in the hippocampus. These effects include changes in proliferation, regulation, differentiation, and maturation of neurons, and there is indication that such effects may be disproportionate between sexes. This study determined whether sex impacts neurotrophic responses and neurogenesis in adulthood after adolescent intermittent ethanol (AIE) exposure. To determine this, adolescent rats underwent AIE with ethanol (5 g/kg). In adulthood, animals were euthanized, and immunohistochemical techniques and ELISAs were utilized to determine AIE effects on sex-specific neurogenesis factors and neurotrophic markers, respectively. AIE exposure led to a significant decrease in neurogenesis in the dentate gyrus of the hippocampal formation indicated by reductions in the numbers of DCX+, SOX2+ and Ki-67+ cells in male and female AIE-exposed rats. Additionally, AIE increased markers for the pro-inflammatory cytokines, TNF-α and IL-1β, in the hippocampus into adulthood in male AIE-exposed rats only. No significant AIE-induced differences were observed in the anti-inflammatory cytokines, IL-10 and TGF-β, nor in the neurotrophic factors BDNF and GDNF. Altogether, our findings indicate that although AIE did not have a persistent effect on hippocampal neurotrophic levels, there was still a reduction in neurogenesis. The neurogenic impairment was not sex specific, but the neurogenic deficits in males may be attributed to an increase in pro-inflammatory cytokine expression. A persistent impairment in neurogenesis may have an impact on both behavioral maladaptations and neurodegeneration in adulthood.

Treadmill Exercise Prevents Cognitive Impairments in Adolescent Intermittent Ethanol Rats by Reducing the Excessive Activation of Microglia Cell in the Hippocampus

The excessive activation of microglia cell induced by adolescent intermittent ethanol (AIE) leads to neuroinflammation in the hippocampus. The endocannabinoid system plays a key role in the modulation of microglia activation. Accumulating evidence suggests that regular exercise improves learning and memory deficits in AIE models. The purpose of this study was to explore the effects of treadmill exercise intervention on the cognitive performance, activation of microglia cells and the expression of monoacylglycerol lipase (MAGL), cannabinoid receptor type 1 (CB1R) and cannabinoid receptor type 2 (CB2R) in the hippocampus of AIE rats. Here, we show that AIE rats exhibited cognitive impairments, whereas the treadmill exercise improves the cognitive performance in AIE rats. In order to explore the possible mechanisms for the exercise-induced attenuation of cognitive disorder, we examined the neuroinflammation in the hippocampus. We found that treadmill exercise led to the decrease in the level of proinflammatory cytokines (IL-1β, IL-6 and TNF-α) and the increase in the level of anti-inflammatory cytokine (IL-10). In addition, we found that treadmill exercise reduced the excessive activation of the microglia cell in the hippocampus of AIE rats. Finally, we found that AIE led to a decrease in the expression of CB1R and CB2R in the hippocampus; however, the treadmill exercise further decreased the expression of CB2R in the hippocampus of AIE rats. Our results suggest that treadmill exercise attenuates AIE-induced neuroinflammation and the excessive activation of hippocampus microglial cells, which may contribute to the exercise-induced improvement of cognitive performance in AIE rats.

Cholinergic REST-G9a gene repression through HMGB1-TLR4 neuroimmune signaling regulates basal forebrain cholinergic neuron phenotype

Lipopolysaccharide (LPS) and high-mobility group box 1 (HMGB1) are Toll-like receptor (TLR4) agonists that activate proinflammatory neuroimmune signaling linked to loss of basal forebrain cholinergic neurons (BFCNs) and cognitive deficits. Loss of choline acetyltransferase immunoreactive (ChAT + IR) BFCNs is generally interpreted as cell death, but recent in vivo studies find anti-inflammatory interventions restore adolescent ethanol exposure-induced persistent loss of adult ChAT + IR neurons and cognitive deficits, suggesting proinflammatory signaling-induced reversible gene repression of ChAT in BFCNs. Using an ex vivo Wistar rat basal forebrain slice culture (FSC) model to investigate TLR4 involvement in repression of the BFCN phenotype, we report that direct TLR4 activation with LPS decreases expression of multiple BFCN markers in the absence of observable neuronal loss or cell death. Inhibition of HMGB1 blunts while inhibition of TLR4 blocks the LPS-induced loss of ChAT + IR neurons. TLR4 activation induces the transcriptional repressor RE1-silencing transcription factor (REST) and the methyltransferase G9a while increasing repressive histone 3 lysine 9 dimethylation and REST occupancy at cholinergic gene promoters. G9a inhibitors both prevent and reverse the LPS-induced loss of ChAT + IR whereas siRNA inhibition of REST blocks the LPS-induced loss of ChAT + IR BFCNs. These data suggest in vivo HMGB1-TLR4 signaling in BFCNs leads to a reversible loss of the cholinergic neuron phenotype through epigenetic gene repressive mechanisms.

Object recognition tasks in rats: Does sex matter?

Novelty recognition tasks based on object exploration are frequently used for the evaluation of cognitive abilities and investigation of neurobiological and molecular aspects of memory in rodents. This is an interesting approach because variations of the object recognition tasks focus on different aspects of the memory events such as novelty, location, context, and combinations of these elements. Nevertheless, as in most animal neuroscience research, female subjects are underrepresented in object recognition studies. When studies include females, the particularities of this sex are not always considered. For example, appropriate controls for manipulations conducted exclusively in females (such as estrous cycle verification) are not included. In addition, interpretation of data is often based on standardizations conducted with male subjects. Despite that, females are frequently reported as deficient and unable to adequately perform some memory tests. Thus, our study aims to review studies that describe similarities and differences between male and female performances in the different variations of object recognition tasks. In summary, although females are commonly described with deficits and the articles emphasize sex differences, most published data reveal similar performances when sexes are compared.

Chronic Intermittent Ethanol Administration during Adolescence Produces Sex Dependent Impairments in Behavioral Flexibility and Survivability

Chronic intermittent ethanol exposure during adolescence produces behavioral impairments and neurobiological changes that can last into young adulthood. One such behavioral impairment is reduced behavioral flexibility, a behavioral impairment that has been correlated with the risk for increased ethanol intake. In the current study, we investigated if chronic intermittent ethanol exposure during adolescence alters cognition, including behavioral flexibility, over a 22-month testing period. Female and male rats were treated with either 3.0 g/kg or 5.0 g/kg ethanol via gavage in a chronic intermittent fashion during adolescence and then tested every 4 to 5 months on a series of cognitive measures in the Morris water maze. Chronic intermittent ethanol selectively impaired behavioral flexibility in both female and male rats, although the pattern of results was different as a function of sex. In addition, female, but not male, rats were impaired in a short-term relearning test. Finally, male rats administered ethanol during adolescence were significantly more likely to not survive the 22-month experiment compared to female rats administered ethanol during adolescence. The current results demonstrate that adolescence is a unique period of development where chronic intermittent ethanol exposure produces long-lasting, selective cognitive impairments across the lifespan.

Impact of adolescent intermittent ethanol exposure on interneurons and their surrounding perineuronal nets in adulthood

BACKGROUND

Binge alcohol exposure during adolescence results in long-lasting alterations in the brain and behavior. For example, adolescent intermittent ethanol (AIE) exposure in rodents results in long-term loss of functional connectivity among prefrontal cortex (PFC) and striatal regions as well as a variety of neurochemical, molecular, and epigenetic alterations. Interneurons in the PFC and striatum play critical roles in behavioral flexibility and functional connectivity. For example, parvalbumin (PV) interneurons are known to contribute to neural synchrony and cholinergic interneurons contribute to strategy selection. Furthermore, extracellular perineuronal nets (PNNs) that surround some interneurons, particularly PV+ interneurons, further regulate cellular plasticity. The effect of AIE exposure on the expression of these markers within the PFC is not well understood.

METHODS

The present study tested the hypothesis that AIE exposure reduces the expression of PV+ and choline acetyltransferase (ChAT)+ interneurons in the adult PFC and striatum and increases the related expression of PNNs (marked by binding of Wisteria floribunda agglutinin lectin) in adulthood. Male rats were exposed to AIE (5 g/kg/day, 2-days-on/2-days-off, i.e., P25 to P54) or water (CON), and brain tissue was harvested in adulthood (>P80). Immunohistochemistry and co-immunofluorescence were used to assess the expression of ChAT, PV, and PNNs within the adult PFC and striatum following AIE exposure.

RESULTS

ChAT and PV interneuron densities in the striatum and PFC were unchanged after AIE exposure. However, PNN density in the PFC of AIE-exposed rats was greater than in CON rats. Moreover, significantly more PV neurons were surrounded by PNNs in AIE-exposed subjects than controls in both PFC subregions assessed: orbitofrontal cortex (CON = 34%; AIE = 40%) and medial PFC (CON = 10%; AIE = 14%).

CONCLUSIONS

These findings indicate that, following AIE exposure, PV interneuron expression in the adult PFC and striatum is unaltered, while PNNs surrounding these neurons are increased. This increase in PNNs may restrict the plasticity of the ensheathed neurons, thereby contributing to impaired microcircuitry in frontostriatal connectivity and related behavioral impairments.

Impact of Adolescent Intermittent Ethanol Exposure on Social Investigation, Social Preference, and Neuronal Activation in cFos-LacZ Male and Female Rats

Adolescence is a sensitive developmental period during which alcohol use is often initiated and consumed in high quantities, often at binge or even high-intensity drinking levels. Our lab has repeatedly found that adolescent intermittent ethanol (AIE) exposure in rats results in long-lasting social impairments, specifically in males, however our knowledge of the neuronal underpinnings to this sex-specific effect of AIE is limited. The present study was designed to test whether social anxiety-like alterations in AIE-exposed males would be accompanied by alterations of neuronal activation across brain regions associated with social behavior, with AIE females demonstrating no social impairments and alterations in neuronal activation. Adolescent male and female cFos-LacZ transgenic rats on a Sprague-Dawley background were exposed to ethanol (4 g/kg, 25% v/v) or water via intragastric gavage every other day during postnatal days (P) 25–45 for a total of 11 exposures (n = 13 per group). Social behavior of adult rats was assessed on P70 using a modified social interaction test, and neuronal activation in brain regions implicated in social responding was assessed via β-galactosidase (β-gal) expression. We found that AIE exposure in males resulted in a significantly lower social preference coefficient relative to water-exposed controls, with no effect evident in females. Exposure-specific relationships between social behavior and neuronal activation were identified, with AIE eliminating correlations found in water controls related to social interaction, and eliciting negative correlations mainly in limbic regions in a sex-specific manner. AIE exposure in the absence of social testing was also found to differentially affect neural activity in the orbitofrontal cortex and central amygdala in males and females. These data suggest that AIE produces sex-specific social impairments that are potentially driven by differential neuronal activation states in regions important for social behavior, including the medial prefrontal and orbitofrontal cortices, nucleus accumbens, lateral septum, and central amygdala. Future studies should be focused on identification of specific neuronal phenotypes activated by interaction with a social partner in AIE-exposed subjects and their control counterparts.

Cholinergic and Neuroimmune Signaling Interact to Impact Adult Hippocampal Neurogenesis and Alcohol Pathology Across Development

Alcohol (ethanol) use and misuse is a costly societal issue that can affect an individual across the lifespan. Alcohol use and misuse typically initiates during adolescence and generally continues into adulthood. Not only is alcohol the most widely abused drug by adolescents, but it is also one of the most widely abused drugs in the world. In fact, high rates of maternal drinking make developmental ethanol exposure the most preventable cause of neurological deficits in the Western world. Preclinical studies have determined that one of the most consistent effects of ethanol is its disruption of hippocampal neurogenesis. However, the severity, persistence, and reversibility of ethanol’s effects on hippocampal neurogenesis are dependent on developmental stage of exposure and age at assessment. Complicating the neurodevelopmental effects of ethanol is the concurrent development and maturation of neuromodulatory systems which regulate neurogenesis, particularly the cholinergic system. Cholinergic signaling in the hippocampus directly regulates hippocampal neurogenesis through muscarinic and nicotinic receptor actions and indirectly regulates neurogenesis by providing anti-inflammatory regulatory control over the hippocampal environmental milieu. Therefore, this review aims to evaluate how shifting maturational patterns of the cholinergic system and its regulation of neuroimmune signaling impact ethanol’s effects on adult neurogenesis. For example, perinatal ethanol exposure decreases basal forebrain cholinergic neuron populations, resulting in long-term developmental disruptions to the hippocampus that persist into adulthood. Exaggerated neuroimmune responses and disruptions in adult hippocampal neurogenesis are evident after environmental, developmental, and pharmacological challenges, suggesting that perinatal ethanol exposure induces neurogenic deficits in adulthood that can be unmasked under conditions that strain neural and immune function. Similarly, adolescent ethanol exposure persistently decreases basal forebrain cholinergic neuron populations, increases hippocampal neuroimmune gene expression, and decreases hippocampal neurogenesis in adulthood. The effects of neither perinatal nor adolescent ethanol are mitigated by abstinence whereas adult ethanol exposure-induced reductions in hippocampal neurogenesis are restored following abstinence, suggesting that ethanol-induced alterations in neurogenesis and reversibility are dependent upon the developmental period. Thus, the focus of this review is an examination of how ethanol exposure across critical developmental periods disrupts maturation of cholinergic and neuroinflammatory systems to differentially affect hippocampal neurogenesis in adulthood.

Long-term consequences of alcohol use in early adolescent mice: Focus on neuroadaptations in GR, CRF and BDNF

Our aim was to assess the cognitive and emotional state, as well as related-changes in the glucocorticoid receptor (GR), the corticotropin-releasing factor (CRF) and the brain-derived neurotrophic factor (BDNF) expression of adolescent C57BL/6J male mice after a 5-week two-bottle choice protocol (postnatal day [pd]21 to pd52). Additionally, we wanted to analyse whether the behavioural and neurobiological effects observed in late adolescence (pd62) lasted until adulthood (pd84). Behavioural testing revealed that alcohol during early adolescence increased anxiety-like and compulsive-related behaviours, which was maintained in adulthood. Concerning cognition, working memory was only altered in late adolescent mice, whereas object location test performance was impaired in both ages. In contrast, novel object recognition remained unaltered. Immunohistochemical analysis showed that alcohol during adolescence diminished BDNF+ cells in the cingulate cortex, the hippocampal CA1 layer and the central amygdala. Regarding hypothalamic-pituitary-adrenal axis (HPA) functioning, alcohol abuse increased the GR and CRF expression in the hypothalamic paraventricular nucleus and the central amygdala. Besides this, GR density was also higher in the prelimbic cortex and the basolateral amygdala, regardless of the animals' age. Our findings suggest that adolescent alcohol exposure led to long-term behavioural alterations, along with changes in BDNF, GR and CRF expression in limbic brain areas involved in stress response, emotional regulation and cognition.

Study on the autophagy-related mechanism of puerarin in improving the cognitive impairment induced by alcohol in female mice

PRIMARY OBJECTIVE

This study aimed to investigate the effects of low-, medium-, and high-dose puerarin on cognitive impairment induced by 50% alcohol in mice and revealed the role of autophagy-related signaling pathways (mTOR and JNK pathways) in this process.

RESEARCH DESIGN

The alcohol-induced brain injury model was treated with different concentrations of puerarin. The cognitive function of mice was evaluated by the behavioral test, and the changes of target proteins in hippocampus of each experimental group were detected.

METHODS AND PROCEDURES

40 female Kunming mice were randomly divided into 5 groups. The cognitive ability of mice was tested by Morris water maze, the morphological changes in the CA1 area of hippocampus were observed by HE staining, and the target proteins in hippocampus were measured by WB and IHC.

MAIN OUTCOMES AND RESULTS

Compared with the 50% alcohol group, the expression of p-mTOR/mTOR and p-4E-BP1/4E-BP1 in hippocampus was significantly decreased, while the expression of p-JNK/JNK, Beclin1, and LC3 was significantly increased in the medium- and high-dose puerarin groups.

CONCLUSIONS

Puerarin could improve the cognitive impairment induced by 50% alcohol. The mTOR and JNK pathways related to autophagy might be involved in this process.

Altered Cortico-Subcortical Network After Adolescent Alcohol Exposure Mediates Behavioral Deficits in Flexible Decision-Making

Behavioral flexibility, the ability to modify behavior according to changing conditions, is essential to optimize decision-making. Deficits in behavioral flexibility that persist into adulthood are one consequence of adolescent alcohol exposure, and another is decreased functional connectivity in brain structures involved in decision-making; however, a link between these two outcomes has not been established. We assessed effects of adolescent alcohol and sex on both Pavlovian and instrumental behaviors and resting-state functional connectivity MRI in adult animals to determine associations between behavioral flexibility and resting-state functional connectivity. Alcohol exposure impaired attentional set reversals and decreased functional connectivity among cortical and subcortical regions-of-interest that underlie flexible behavior. Moreover, mediation analyses indicated that adolescent alcohol-induced reductions in functional connectivity within a subnetwork of affected brain regions statistically mediated errors committed during reversal learning. These results provide a novel link between persistent reductions in brain functional connectivity and deficits in behavioral flexibility resulting from adolescent alcohol exposure.

The persistent impact of adolescent binge alcohol on adult brain structural, cellular, and behavioral pathology: A role for the neuroimmune system and epigenetics

Adolescence is a critical neurodevelopmental window for maturation of brain structure, neurocircuitry, and glia. This development is sculpted by an individual's unique experiences and genetic background to establish adult level cognitive function and behavioral makeup. Alcohol abuse during adolescence is associated with an increased lifetime risk for developing an alcohol use disorder (AUD). Adolescents participate in heavy, episodic binge drinking that causes persistent changes in neurocircuitry and behavior. These changes may underlie the increased risk for AUD and might also promote cognitive deficits later in life. In this chapter, we have examined research on the persistent effects of adolescent binge-drinking both in humans and in rodent models. These studies implicate roles for neuroimmune signaling as well as epigenetic reprogramming of neurons and glia, which create a vulnerable neuroenvironment. Some of these changes are reversible, giving hope for future treatments to prevent many of the long-term consequences of adolescent alcohol abuse.

Alcohol drinking during early adolescence activates microglial cells and increases frontolimbic Interleukin-1 beta and Toll-like receptor 4 gene expression, with heightened sensitivity in male rats compared to females

Adolescent drinking is risky because neural circuits in the frontal lobes are undergoing maturational processes important for cognitive function and behavioral control in adulthood. Previous studies have shown that myelinated axons in the medial prefrontal cortex (mPFC) are particularly sensitive to alcohol drinking, especially in males. Pro-inflammatory mediators like toll-like receptor 4 (TLR4) and interleukin-1 beta (IL1b) have been implicated in alcohol induced-inflammation and demyelination; thus, herein we test the hypothesis that voluntary alcohol drinking early in adolescence elicits a pro-inflammatory state that is more pronounced in the brain of males compared to females. Adolescent male and female Wistar rats self-administered sweetened alcohol or sweetened water from postnatal days 28-42 and separate sets of brains were processed for 1) immunolabeling for ionized calcium-binding adapter molecule 1 to analyze microglial cell morphology, or 2) qPCR analysis of gene expression of pro-inflammatory mediators. Binge drinking alcohol activated microglia in the mPFC and hippocampus of both males and females, suggesting that voluntary alcohol exposure initiates an inflammatory response. Il1b mRNA was upregulated in the mPFC of both sexes. Conversely, Tlr4 mRNA levels were elevated after drinking only in males, which could explain more robust effects of alcohol on myelin in this region in developing males compared to females. Il1b mRNA changes were not observed in the hippocampus, but alcohol elevated Tlr4 mRNA in both sexes, highlighting regional specificity in inflammatory responses to alcohol. Overall, these findings give insight into potential mechanisms by which low-to-moderate voluntary alcohol intake impacts the developing brain. This article is part of the special Issue on 'Vulnerabilities to Substance Abuse'.

Galantamine prevents and reverses neuroimmune induction and loss of adult hippocampal neurogenesis following adolescent alcohol exposure

BACKGROUND

Binge ethanol exposure during adolescence reduces hippocampal neurogenesis, a reduction which persists throughout adulthood despite abstinence. This loss of neurogenesis, indicated by reduced doublecortin+ immunoreactivity (DCX+IR), is paralleled by an increase in hippocampal proinflammatory signaling cascades. As galantamine, a cholinesterase inhibitor, has anti-inflammatory actions, we tested the hypothesis that galantamine would prevent (study 1) or restore (study 2) AIE induction of proinflammatory signals within the hippocampus as well as AIE-induced loss of hippocampal neurogenesis.

METHODS

Galantamine (4 mg/kg) or vehicle (saline) was administered to Wistar rats during adolescent intermittent ethanol (AIE; 5.0 g/kg ethanol, 2 days on/2 days off, postnatal day [P] 25-54) (study 1, prevention) or after AIE during abstinent maturation to adulthood (study 2, restoration).

RESULTS

Results indicate AIE reduced DCX+IR and induced cleaved caspase3 (Casp3) in DCX-expressing immature neurons. Excitingly, AIE induction of activated Casp3 in DCX-expressing neurons is both prevented and reversed by galantamine treatment, which also resulted in prevention and restoration of neurogenesis (DCX+IR). Similarly, galantamine prevented and/or reversed AIE induction of proinflammatory markers, including the chemokine (C-C motif) ligand 2 (CCL2), cyclooxygenase-2 (COX-2), and high mobility group box 1 (HMGB1) protein, suggesting that AIE induction of proinflammatory signaling mediates both cell death cascades and hippocampal neurogenesis. Interestingly, galantamine treatment increased Ki67+IR generally as well as increased pan-Trk expression specifically in AIE-treated rats but failed to reverse AIE induction of NADPH-oxidase (gp91phox).

CONCLUSIONS

Collectively, our studies suggest that (1) loss of neurogenesis after AIE is mediated by persistent induction of proinflammatory cascades which drive activation of cell death machinery in immature neurons, and (2) galantamine can prevent and restore AIE disruptions in the hippocampal environmental milieu to then prevent and restore AIE-mediated loss of neurogenesis.

The role of sex in the persistent effects of adolescent alcohol exposure on behavior and neurobiology in rodents

Alcohol drinking is often initiated during adolescence, and this frequently escalates to binge drinking. As adolescence is also a period of dynamic neurodevelopment, preclinical evidence has highlighted that some of the consequences of binge drinking can be long lasting with deficits persisting into adulthood in a variety of cognitive-behavioral tasks. However, while the majority of preclinical work to date has been performed in male rodents, the rapid increase in binge drinking in adolescent female humans has re-emphasized the importance of addressing alcohol effects in the context of sex as a biological variable. Here we review several of the consequences of adolescent ethanol exposure in light of sex as a critical biological variable. While some alcohol-induced outcomes, such as non-social approach/avoidance behavior and sleep disruption, are generally consistent across sex, others are variable across sex, such as alcohol drinking, sensitivity to ethanol, social anxiety-like behavior, and induction of proinflammatory markers.

Chronic alcohol exposure during critical developmental periods differentially impacts persistence of deficits in cognitive flexibility and related circuitry

Cognitive flexibility in decision making depends on prefrontal cortical function and is used by individuals to adapt to environmental changes in circumstances. Cognitive flexibility can be measured in the laboratory using a variety of discrete, translational tasks, including those that involve reversal learning and/or set-shifting ability. Distinct components of flexible behavior rely upon overlapping brain circuits, including different prefrontal substructures that have separable impacts on decision making. Cognitive flexibility is impaired after chronic alcohol exposure, particularly during development when the brain undergoes rapid maturation. This review examines how cognitive flexibility, as indexed by reversal and set-shifting tasks, is impacted by chronic alcohol exposure in adulthood, adolescent, and prenatal periods in humans and animal models. We also discuss areas for future study, including mechanisms that may contribute to the persistence of cognitive deficits after developmental alcohol exposure and the compacting consequences from exposure across multiple critical periods.