A novel mouse model for vulnerability to alcohol dependence induced by early-life adversity

Pueraria Extract Ameliorates Alcoholic Liver Disease via the Liver-Gut-Brain Axis: Focus on Restoring the Intestinal Barrier and Inhibiting Alcohol Metabolism

Alcoholic liver disease (ALD) is one of the causes of hepatocellular carcinoma, accompanied by intestinal leakage and microbial changes. Pueraria has protective effects on liver injury. The aim of this study was to investigate the mechanism of pueraria in the treatment of ALD. UPLC-Q/TOF-MS was used to analyze the composition of the pueraria extract (PUE). Acute and chronic ALD models were established to evaluate the antialcoholic and hepatoprotective effects of PUE. As a result, PUE treatment reduced the serum levels of ALT, AST, TC, and TG and inflammatory factors and alleviated liver inflammation and drunk state. PUE decreased the gene expression of ADH1 and the serum level of acetaldehyde (ACH) to inhibit the generation of ACH from ethanol metabolism, increased the gene level of ALDH2 to accelerate the decomposition of ACH, and thereby alleviated liver inflammation and intestinal barrier damage. Meanwhile, 16 S rDNA revealed that PUE altered the microbiota composition, reduced the amount of Proteobacteria and Desulfobacterota, and thus inhibited the generation of lipopolysaccharide and its downstream-like TLR4/MyD88/NF-κB pathway. PUE also increased the abundance of Bacteroides, Ruminococcus, and Prevotella and producted short-chain fatty acids to protect the intestinal wall. Treatment with fecal microbiota transplantation further confirmed that PUE gut microbiota dependently alleviated ALD. Therefore, PUE regulated gut microbiota and inhibited ethanol metabolism to alleviate ALD through the liver-gut-brain axis. It has good prospects in the future.

Sex differences in basal motivated behavior, chronic ethanol drinking, and amygdala activity in female and male mice

Alcohol use disorder (AUD) is a major public health concern that despite its prevalence, lacks a widely-effective treatment due to the complexity of AUD pathology. AUD is highly comorbid with other psychiatric conditions including anxiety and mood disorders, however it is unclear how these disorders influence each other. The underlying etiology of these comorbidities is difficult to decipher and factors including sex, stress, and the environment further complicate both diagnosis and treatment strategies. To understand more about this bidirectional relationship between AUD and comorbid psychiatric disorders, we ran male and female C57Bl/6j mice through baseline behavioral testing followed by intermittent access-two bottle choice (IA-2BC) drinking. We found no sex differences in basal anxiety-like or depressive-like behavior, however females displayed enhanced motivated feeding behavior. Females consumed more ethanol than males, at both 1hr and 24hr timepoints. Basal affective state did not predict subsequent ethanol intake in either sex, however exploratory behavior was positively correlated with drinking in males but not females. We then re-assessed negative affect behavior following chronic ethanol drinking to determine if drinking impacted subsequent affective behavior and found no relationship between ethanol intake and affective state in males or females. We also examined how chronic ethanol drinking affected central amygdala (CeA) and basolateral amygdala (BLA) neuronal activity in males and females. Ethanol-drinking females had a decrease in CeA neuronal activity, driven by reduced activity in the lateral (CeAl) sub-region, while in males there was no significant difference in CeA activity compared to water controls. Neither males or females had a significant change in BLA neuronal activity following chronic ethanol drinking. Collectively, these results demonstrate sex differences in basal motivated behavior, drinking behavior, and subregion-specific amygdala neuronal activity following chronic ethanol drinking which may inform the sex differences seen in patients diagnosed with AUD and comorbid conditions.

Operant ethanol self-administration behaviors do not predict sex differences in continuous access home cage drinking

Understanding sex differences in disease prevalence is critical to public health, particularly in the context of alcohol use disorder (AUD). The goal of this study was to understand sex differences in ethanol drinking behavior and define the precise conditions under which sex differences emerge. Consistent with prior work, C57BL/6J females drank more than males under continuous access two-bottle choice conditions. However, using ethanol self-administration - where an operant response results in access to an ethanol sipper for a fixed time period - we found no sex differences in operant response rates or ethanol consumption (volume per body weight consumed, as well as lick behavior). This remained true across a wide range of parameters including acquisition, when the ethanol sipper access period was manipulated, and when the concentration of the ethanol available was scaled. The only sex differences observed were in total ethanol consumption, which was explained by differences in body weight between males and females, rather than by sex differences in motivation to drink. Using dimensionality reduction approaches, we found that drinking behavior in the operant context did not cluster by sex, but rather clustered by high and low drinking phenotypes. Interestingly, these high and low drinking phenotypes in the operant context showed no correlation with those same categorizations in the home cage context within the same animals. These data underscore the complexity of sex differences in ethanol consumption, highlighting the important role that drinking conditions/context plays in the expression of these differences.

Early life psychosocial stress increases binge-like ethanol consumption and CSF1R inhibition prevents stress-induced alterations in microglia and brain macrophage population density

Early life stress (ELS) has lasting consequences on microglia and brain macrophage function. During ELS, microglia and brain macrophages alter their engagement with synapses leading to changes in neuronal excitability. Further, ELS can induce innate immune memory formation in microglia and brain macrophages resulting in altered responsivity to future environmental stimuli. These alterations can result in lasting adaptations in circuit function and may mediate the relationship between ELS and the risk to develop alcohol use disorder (AUD). Whether microglia and brain macrophages truly mediate this relationship remains elusive. Here, we report: 1) an ELS model, psychosocial stress (PSS), increases binge-like ethanol consumption in early adulthood. 2) Repeated binge-like ethanol consumption increases microglia and brain macrophage population densities across the brain. 3) PSS may elicit innate immune memory formation in microglia and brain macrophages leading to altered population densities following repeated binge-like ethanol consumption. 4) Microglia and brain macrophage inhibition trended towards preventing PSS-evoked changes in binge-like ethanol consumption and normalized microglia and brain macrophage population densities. Therefore, our study suggests that acutely inhibiting microglia and brain macrophage function during periods of early life PSS may prevent innate immune memory formation and assist in reducing the risk to develop AUD.

Highlights

An early life psychosocial stress (PSS) exposure increases ethanol consumptionMicroglial inhibition during PSS trends towards reducing ethanol consumptionBinge ethanol consumption increases microglial count and alters cell proximityEarly life PSS alters microglial responsivity to binge ethanol consumptionMicroglial inhibition may prevent microglial innate immune memory formation.

Model of a striatal circuit exploring biological mechanisms underlying decision-making during normal and disordered states

Decision-making requires continuous adaptation to internal and external contexts. Changes in decision-making are reliable transdiagnostic symptoms of neuropsychiatric disorders. We created a computational model demonstrating how the striosome compartment of the striatum constructs a mathematical space for decision-making computations depending on context, and how the matrix compartment defines action value depending on the space. The model explains multiple experimental results and unifies other theories like reward prediction error, roles of the direct versus indirect pathways, and roles of the striosome versus matrix, under one framework. We also found, through new analyses, that striosome and matrix neurons increase their synchrony during difficult tasks, caused by a necessary increase in dimensionality of the space. The model makes testable predictions about individual differences in disorder susceptibility, decision-making symptoms shared among neuropsychiatric disorders, and differences in neuropsychiatric disorder symptom presentation. The model reframes the role of the striosomal circuit in neuroeconomic and disorder-affected decision-making.

Highlights

Striosomes prioritize decision-related data used by matrix to set action values. Striosomes and matrix have different roles in the direct and indirect pathways. Abnormal information organization/valuation alters disorder presentation. Variance in data prioritization may explain individual differences in disorders.

eTOC

Beck et al. developed a computational model of how a striatal circuit functions during decision-making. The model unifies and extends theories about the direct versus indirect pathways. It further suggests how aberrant circuit function underlies decision-making phenomena observed in neuropsychiatric disorders.

Mouse parasubthalamic Crh neurons drive alcohol drinking escalation and behavioral disinhibition

Corticotropin-releasing factor (CRF, encoded by Crh) signaling is thought to play a critical role in the development of excessive alcohol drinking and the emotional and physical pain associated with alcohol withdrawal. Here, we investigated the parasubthalamic nucleus (PSTN) as a potential source of CRF relevant to the control of alcohol consumption, affect, and nociception in mice. We identified PSTN Crh neurons as a neuronal subpopulation that exerts a potent and unique influence on behavior by promoting not only alcohol but also saccharin drinking, while PSTN neurons are otherwise known to suppress consummatory behaviors. Furthermore, PSTN Crh neurons are causally implicated in the escalation of alcohol and saccharin intake produced by chronic intermittent ethanol (CIE) vapor inhalation, a mouse model of alcohol use disorder. In contrast to our predictions, the ability of PSTN Crh neurons to increase alcohol drinking is not mediated by CRF1 signaling. Moreover, the pattern of behavioral disinhibition and reduced nociception driven by their activation does not support a role of negative reinforcement as a motivational basis for the concomitant increase in alcohol drinking. Finally, silencing Crh expression in the PSTN slowed down the escalation of alcohol intake in mice exposed to CIE and accelerated their recovery from withdrawal-induced mechanical hyperalgesia. Altogether, our results suggest that PSTN Crh neurons may represent an important node in the brain circuitry linking alcohol use disorder with sweet liking and novelty seeking.

Limited bedding and nesting increases ethanol drinking in female rats

Prenatal opioid exposure (POE) and postnatal adverse experiences are early life adversities (ELA) that often co-occur and increase problematic alcohol (EtOH) drinking during adolescence. We investigated the relationship between POE, postnatal adversity, and adolescent EtOH drinking in rats. We also sought to determine whether ELAs affect alpha-adrenoceptor density in the brain because the noradrenergic system is involved in problematic alcohol drinking and its treatment. We hypothesized that the combination of POE and postnatal adversity will increase alcohol drinking in rats compared to rats with exposure to either adversity alone or to control. We also predicted that POE and postnatal adversity would increase α1-adrenoceptor density and decrease α2-adrenoceptor density in brain to confer a stress-responsive phenotype. Pregnant rats received morphine (15 mg/kg/day) or saline via subcutaneous minipumps from gestational day 9 until birth. Limited bedding and nesting (LBN) procedures were introduced from postnatal day (PD) 3-11 to mimic early life adversity-scarcity. Offspring rats (PD 31-33) were given opportunities to drink EtOH (20 %, v/v) using intermittent-access, two-bottle choice (with water) procedures. Rats given access to EtOH were assigned into sub-groups that were injected with either yohimbine (1 mg/kg, ip) or vehicle (2 % DMSO, ip) 30 min prior to each EtOH access session to determine the effects of α2-adrenoceptor inhibition on alcohol drinking. We harvested cortices, brainstems, and hypothalami from EtOH-naïve littermates on either PD 30 or PD 70 and conducted radioligand receptor binding assays to quantify α1- and α2-adrenoceptor densities. Contrary to our hypothesis, only LBN alone increased EtOH intake in female adolescent rats compared to female rats with POE. Neither POE nor LBN affected α1- or α2-adrenoceptor densities in the cortex, brainstem, or hypothalamus of early- or late-aged adolescent rats. These results suggest a complex interaction between ELA type and sex on alcohol drinking.

Early-life inflammation increases ethanol consumption in adolescent male mice

Recent studies have demonstrated that stress during the critical windows of development can evoke a cascade of neurological changes that can result in neuropsychiatric disorders later in life. In this study, we examined the effect of early-life inflammation on ethanol consumption in adolescent mice. C57BL/6J mice were assigned to either the control or Lipopolysaccharide (LPS) group on postnatal day 14 (P14). In the latter group, LPS at a dose of 50 μg/kg was injected intraperitoneally. The mice were weaned at P21, and behavior tests were performed at P45. Ethanol consumption was assessed using a two-bottle choice drinking paradigm. Anxiety-like behaviors were assessed by marble burying test (MBT), open field (OF), and elevated plus maze (EPM). Ethanol-induced loss of righting reflex (LORR), hypothermia and ethanol metabolism were assessed to evaluate ethanol intoxication. P14 LPS-injected adolescent male mice exhibited significantly increased ethanol preference and consumption, with a similar taste preference for saccharin and avoidance of quinine. The adolescent male mice showed increased anxiety-like behaviors in the OF and EPM tests, and an increased duration of LORR, without affecting the hypothermic effects of ethanol and ethanol metabolism. Interestingly, these behavioral changes were not obvious in female mice. In conclusion, our data indicate that early-life inflammation may be a risk factor for ethanol consumption in adolescents with greater changes observed in male mice. SIGNIFICANCE STATEMENT: Our study is the first preclinical model to report the enhancement effect of early-life inflammation on ethanol consumption in adolescent male mice and our findings provide a valuable mouse model to examine the neurobiological mechanisms mediating the long-lasting effects of early-life inflammation on alcohol use disorders vulnerability.

The role of brain serotonin signaling in excessive alcohol consumption and withdrawal: A call for more research in females

Alcohol Use Disorder (AUD) is a leading cause of death and disability worldwide, but current treatments are insufficient in fully addressing the symptoms that often lead to relapses in alcohol consumption. The brain's serotonin system has been implicated in AUD for decades and is a major regulator of stress-related behaviors associated with increased alcohol consumption. This review will discuss the current literature on the association between neurobiological adaptations in serotonin systems and AUD in humans as well as the effectiveness of serotonin receptor manipulations on alcohol-related behaviors like consumption and withdrawal. We will further discuss how these findings in humans relate to findings in animal models, including a comparison of systemic pharmacological manipulations modulating alcohol consumption. We next provide a detailed overview of brain region-specific roles for serotonin and serotonin receptor signaling in alcohol-related behaviors in preclinical animal models, highlighting the complexity of forming a cohesive model of serotonin function in AUD and providing possible avenues for more effective therapeutic intervention. Throughout the review, we discuss what is known about sex differences in the sequelae of AUD and the role of serotonin in these sequelae. We stress a critical need for additional studies in women and female animals so that we may build a clearer path to elucidating sex-specific serotonergic mechanisms and develop better treatments.

Histone deacetylase inhibitor decreases hyperalgesia in a mouse model of alcohol withdrawal-induced hyperalgesia

BACKGROUND

Alcohol withdrawal-induced hyperalgesia (AWH) is characterized as an increased pain sensitivity observed after cessation of chronic alcohol use. Alcohol withdrawal-induced hyperalgesia can contribute to the negative affective state associated with abstinence and can increase susceptibility to relapse. We aimed to characterize pain sensitivity in mice during withdrawal from two different models of alcohol exposure: chronic drinking in the dark (DID) and the Lieber-DeCarli liquid diet. We also investigated whether treatment with a histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA), could ameliorate AWH in mice treated with the Lieber-DeCarli diet.

METHODS

Male and female C57BL/6J mice were used for these studies. In the DID model, mice received bottles of 20% ethanol or water during the dark cycle for 4 h per day on four consecutive days per week for 6 weeks. Peripheral mechanical sensitivity was measured weekly the morning of Day 5 using von Frey filaments. In the Lieber-DeCarli model, mice received ethanol (5% v/v) or control liquid diet for 10 days, along with a single binge ethanol gavage (5 g/kg) or control gavage, respectively, on Day 10. Peripheral mechanical sensitivity was measured during the liquid diet administration and at 24 and 72 h into ethanol withdrawal. An independent group of mice that received the Lieber-DeCarli diet were administered SAHA (50 mg/kg, i.p.) during withdrawal.

RESULTS

Male mice exhibited mechanical hypersensitivity after consuming ethanol for 5 weeks in the DID procedure. In the Lieber-DeCarli model, ethanol withdrawal led to hyperalgesia in both sexes. Suberoylanilide hydroxamic acid treatment during withdrawal from the ethanol liquid diet alleviated AWH.

CONCLUSIONS

These results demonstrate AWH in mice after chronic binge drinking in males and after Lieber-DeCarli liquid diet administration in both sexes. Like previous findings in rats, HDAC inhibition reduced AWH in mice, suggesting that epigenetic mechanisms are involved in AWH.

Early-life stress and ovarian hormones alter transcriptional regulation in the nucleus accumbens resulting in sex-specific responses to cocaine

Early-life stress and ovarian hormones contribute to increased female vulnerability to cocaine addiction. Here, we reveal molecular substrates in the reward area, the nucleus accumbens, through which these female-specific factors affect immediate and conditioning responses to cocaine. We find shared involvement of X chromosome inactivation-related and estrogen signaling-related gene regulation in enhanced conditioning responses following early-life stress and during the low-estrogenic state in females. Low-estrogenic females respond to acute cocaine by opening neuronal chromatin enriched for the sites of ΔFosB, a transcription factor implicated in chronic cocaine response and addiction. Conversely, high-estrogenic females respond to cocaine by preferential chromatin closing, providing a mechanism for limiting cocaine-driven chromatin and synaptic plasticity. We find that physiological estrogen withdrawal, early-life stress, and absence of one X chromosome all nullify the protective effect of a high-estrogenic state on cocaine conditioning in females. Our findings offer a molecular framework to enable understanding of sex-specific neuronal mechanisms underlying cocaine use disorder.

Chronic Intermittent Ethanol Vapor Exposure Paired with Two-Bottle Choice to Model Alcohol Use Disorder

Alcohol use disorder (AUD) is a chronic alcohol-related disorder that typically presents as uncontrolled drinking and preoccupation with alcohol. A key component of AUD research is using translationally relevant preclinical models. Over the past several decades, a variety of animal models have been used to study AUD. One prominent model of AUD is the chronic intermittent ethanol vapor exposure (CIE) model, which is a well-established approach for inducing alcohol dependence in rodents through repeated cycles of ethanol exposure via inhalation. To model AUD in mice, the CIE exposure is paired with a voluntary two-bottle choice (2BC) of alcohol drinking and water to measure the escalation of alcohol drinking. The 2BC/CIE procedure involves alternating weeks of 2BC drinking and CIE, which repeat until the escalation of alcohol drinking is achieved. In the present study, we outline the procedures for performing 2BC/CIE, including the daily use of the CIE vapor chamber, and provide an example of escalated alcohol drinking in C57BL/6J mice using this approach.

Chronic ethanol alters adrenergic receptor gene expression and produces cognitive deficits in male mice

Hyperkateifia and stress-induced alcohol cravings drive relapse in individuals with alcohol use disorder (AUD). The brain stress signal norepinephrine (also known as noradrenaline) tightly controls cognitive and affective behavior and was thought to be broadly dysregulated with AUD. The locus coeruleus (LC) is a major source of forebrain norepinephrine, and it was recently discovered that the LC sends distinct projections to addiction-associated regions suggesting that alcohol-induced noradrenergic changes may be more brain region-specific than originally thought. Here we investigated whether ethanol dependence alters adrenergic receptor gene expression in the medial prefrontal cortex (mPFC) and central amgydala (CeA), as these regions mediate the cognitive impairment and negative affective state of ethanol withdrawal. We exposed male C57BL/6J mice to the chronic intermittent ethanol vapor-2 bottle choice paradigm (CIE-2BC) to induce ethanol dependence, and assessed reference memory, anxiety-like behavior and adrenergic receptor transcript levels during 3-6 days of withdrawal. Dependence bidirectionally altered mouse brain α1 and β receptor mRNA levels, potentially leading to reduced mPFC adrenergic signaling and enhanced noradrenergic influence over the CeA. These brain region-specific gene expression changes were accompanied by long-term retention deficits and a shift in search strategy in a modified Barnes maze task, as well as greater spontaneous digging behavior and hyponeophagia. Current clinical studies are evaluating adrenergic compounds as a treatment for AUD-associated hyperkatefia, and our findings can contribute to the refinement of these therapies by increasing understanding of the specific neural systems and symptoms that may be targeted.

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

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

Chronic intermittent ethanol exposure disrupts stress-related tripartite communication to impact affect-related behavioral selection in male rats

Alcohol use disorder (AUD) is characterized by loss of intake control, increased anxiety, and susceptibility to relapse inducing stressors. Both astrocytes and neurons contribute to behavioral and hormonal consequences of chronic intermittent ethanol (CIE) exposure in animal models. Details on how CIE disrupts hypothalamic neuro-glial communication, which mediates stress responses are lacking. We conducted a behavioral battery (grooming, open field, reactivity to a single, uncued foot-shock, intermittent-access two-bottle choice ethanol drinking) followed by Ca²⁺ imaging in ex-vivo slices of paraventricular nucleus of the hypothalamus (PVN) from male rats exposed to CIE vapor or air-exposed controls. Ca²⁺ signals were evaluated in response to norepinephrine (NE) with or without selective α-adrenergic receptor (αAR) or GluN2B-containing N-methyl-D-aspartate receptor (NMDAR) antagonists, followed by dexamethasone (DEX) to mock a pharmacological stress response. Expectedly, CIE rats had altered anxiety-like, rearing, grooming, and drinking behaviors. Importantly, NE-mediated reductions in Ca²⁺ event frequency were blunted in both CIE neurons and astrocytes. Administration of the selective α1AR antagonist, prazosin, reversed this CIE-induced dysfunction in both cell types. Additionally, the pharmacological stress protocol reversed the altered basal Ca²⁺ signaling profile of CIE astrocytes. Signaling changes in astrocytes in response to NE were correlated with anxiety-like behaviors, such as the grooming:rearing ratio, suggesting tripartite synaptic function plays a role in switching between exploratory and stress-coping behavior. These data show how CIE exposure causes persistent changes to PVN neuro-glial function and provides the groundwork for how these physiological changes manifest in behavioral selection.

Influence of early-life adversity on responses to acute and chronic ethanol in female mice

BACKGROUND

Stressful early-life experiences increase the risk of developing an alcohol use disorder. We previously found that male C57BL/6J mice reared under limited bedding and nesting (LBN) conditions, a model of early-life adversity, escalate their ethanol intake in limited-access two-bottle choice (2BC) sessions faster than control (CTL)-reared counterparts when exposed to chronic intermittent ethanol (CIE) vapor inhalation. However, the alcohol consumption of female littermates was not affected by LBN or CIE. In the present study, we sought to determine whether this phenotype reflected a general insensitivity of female mice to the influence of early-life stress on alcohol responses.

METHODS

In a first experiment, CTL and LBN females with a history of 2BC combined or not with CIE were tested in affective and nociceptive assays during withdrawal. In a second group of CTL and LBN females, we examined ethanol-induced antinociception, sedation, plasma clearance, and c-Fos induction.

RESULTS

In females withdrawn from chronic 2BC, CIE increased digging, reduced grooming, and increased immobility in the tail suspension test regardless of early-life history. In contrast, LBN rearing lowered mechanical nociceptive thresholds regardless of CIE exposure. In females acutely treated with ethanol, LBN rearing facilitated antinociception and delayed the onset of sedation without influencing ethanol clearance rate or c-Fos induction in the paraventricular nucleus of the hypothalamus, paraventricular nucleus of the thalamus, central nucleus of the amygdala, or auditory cortex.

CONCLUSION

CIE withdrawal produced multiple indices of negative affect in C57BL/6J females, suggesting that their motivation to consume alcohol may differ from air-exposed counterparts despite equivalent intake. Contrasted with our previous findings in males, LBN-induced mechanical hyperalgesia in chronic alcohol drinkers was specific to females. Lower nociceptive thresholds combined with increased sensitivity to the acute antinociceptive effect of ethanol may contribute to reinforcing ethanol consumption in LBN females but are not sufficient to increase their intake.

Chronic MAP4343 reverses escalated alcohol drinking in a mouse model of alcohol use disorder

Alcohol use disorders can be driven by negative reinforcement. Alterations of the microtubule cytoskeleton have been associated with mood regulation in the context of depression. Notably, MAP4343, a pregnenolone derivative known to promote tubulin assembly, has antidepressant properties. In the present study, we tested the hypothesis that MAP4343 may reduce excessive alcohol drinking in a mouse model of alcohol dependence by normalizing affect during withdrawal. Adult male C57BL/6J mice were given limited access to voluntary alcohol drinking and ethanol intake escalation was induced by chronic intermittent ethanol (CIE) vapor inhalation. Chronic, but not acute, administration of MAP4343 reduced ethanol intake and this effect was more pronounced in CIE-exposed mice. There was a complex interaction between the effects of MAP4343 and alcohol on affective behaviors. In the elevated plus maze, chronic MAP4343 tended to increase open-arm exploration in alcohol-naive mice but reduced it in alcohol-withdrawn mice. In the tail suspension test, chronic MAP4343 reduced immobility selectively in Air-exposed alcohol-drinking mice. Finally, chronic MAP4343 countered the plasma corticosterone reduction induced by CIE. Parallel analysis of tubulin post-translational modifications revealed lower α-tubulin acetylation in the medial prefrontal cortex of CIE-withdrawn mice. Altogether, these data support the relevance of microtubules as a therapeutic target for the treatment of AUD.

Effects of prenatal opioid exposure on synaptic adaptations and behaviors across development

In this review, we focus on prenatal opioid exposure (POE) given the significant concern for the mental health outcomes of children with parents affected by opioid use disorder (OUD) in the view of the current opioid crisis. We highlight some of the less explored interactions between developmental age and sex on synaptic plasticity and associated behavioral outcomes in preclinical POE research. We begin with an overview of the rich literature on hippocampal related behaviors and plasticity across POE exposure paradigms. We then discuss recent work on reward circuit dysregulation following POE. Additional risk factors such as early life stress (ELS) could further influence synaptic and behavioral outcomes of POE. Therefore, we include an overview on the use of preclinical ELS models where ELS exposure during key critical developmental periods confers considerable vulnerability to addiction and stress psychopathology. Here, we hope to highlight the similarity between POE and ELS on development and maintenance of opioid-induced plasticity and altered opioid-related behaviors where similar enduring plasticity in reward circuits may occur. We conclude the review with some of the limitations that should be considered in future investigations. This article is part of the Special Issue on 'Opioid-induced addiction'.

Sex differences in addiction-relevant behavioral outcomes in rodents following early life stress

In humans, exposure to early life stress (ELS) is an established risk factor for the development of substance use disorders (SUDs) during later life. Similarly, rodents exposed to ELS involving disrupted mother-infant interactions, such as maternal separation (MS) or adverse caregiving due to scarcity-adversity induced by limited bedding and nesting (LBN) conditions, also exhibit long-term alterations in alcohol and drug consumption. In both humans and rodents, there is a range of addiction-related behaviors that are associated with drug use and even predictive of subsequent SUDs. In rodents, these include increased anxiety-like behavior, impulsivity, and novelty-seeking, altered alcohol and drug intake patterns, as well as disrupted reward-related processes involving consummatory and social behaviors. Importantly, the expression of these behaviors often varies throughout the lifespan. Moreover, preclinical studies suggest that sex differences play a role in how exposure to ELS impacts reward and addiction-related phenotypes as well as underlying brain reward circuitry. Here, addiction-relevant behavioral outcomes and mesolimbic dopamine (DA) dysfunction resulting from ELS in the form of MS and LBN are discussed with a focus on age- and sex-dependent effects. Overall, these findings suggest that ELS may increase susceptibility for later life drug use and SUDs by interfering with the normal maturation of reward-related brain and behavioral function.

Sex-specific behavioral outcomes of early-life adversity and emerging microglia-dependent mechanisms

Early-life adversity (ELA) is known to alter brain circuit maturation as well as increase vulnerability to cognitive and emotional disorders. However, the importance of examining sex as a biological variable when researching the effects of ELA has not been considered until recently. This perspective discusses the sex-specific behavioral outcomes of ELA in both humans and animal models, then proposes microglia-mediated mechanisms as a potential underlying cause. Recent work in rodent models suggests that ELA provokes cognitive deficits, anhedonia, and alcohol abuse primarily in males, whereas females exhibit greater risk-taking and opioid addiction-related behaviors. In addition, emerging evidence identifies microglia as a key target of ELA. For example, we have recently shown that ELA inhibits microglial synapse engulfment and process dynamics in male mice, leading to an increase in excitatory synapse number onto corticotrophin-releasing hormone (CRH)-expressing neurons in the paraventricular nucleus of the hypothalamus (PVN) and aberrant stress responses later in life. However, ELA-induced synaptic rewiring of neural circuits differs in females during development, resulting in divergent behavioral outcomes. Thus, examining the role of microglia in the sex-specific mechanisms underlying ELA-induced neuropsychiatric disorders is an important topic for future research.

Enduring disruption of reward and stress circuit activities by early-life adversity in male rats

In humans, early-life adversity (ELA) such as trauma, poverty, and chaotic environment is linked to increased risk of later-life emotional disorders including depression and substance abuse. These disorders involve underlying disruption of reward circuits and likely vary by sex. Accordingly, we previously found that ELA leads to anhedonia for natural rewards and cocaine in male rodents, whereas in females ELA instead increases vulnerability to addiction-like use of opioid drugs and palatable food. While these findings suggest that ELA-induced disruption of reward circuitry may differ between the sexes, the specific circuit nodes that are influenced by ELA in either sex remain poorly understood. Here, in adult male Sprague-Dawley rats, we ask how ELA impacts opioid addiction-relevant behaviors that we previously tested after ELA in females. We probe potential circuit mechanisms in males by assessing opioid-associated neuronal activation in stress and reward circuit nodes including nucleus accumbens (NAc), amygdala, medial prefrontal cortex (mPFC), and paraventricular thalamus. We find that ELA diminishes opioid-seeking behaviors in males, and alters heroin-induced activation of NAc, PFC, and amygdala, suggesting a potential circuit-based mechanism. These studies demonstrate that ELA leads to behavioral and neurobiological disruptions consistent with anhedonia in male rodents, unlike the increased opioid seeking we previously saw in females. Our findings, taken together with our prior work, suggest that men and women could face qualitatively different mental health consequences of ELA, which may be essential for individually tailoring future intervention strategies.

Central amygdala corticotropin-releasing factor neurons promote hyponeophagia but do not control alcohol drinking in mice

Corticotropin-releasing factor (CRF) signaling in the central nucleus of the amygdala (CeA) plays a critical role in rodent models of excessive alcohol drinking. However, the source of CRF acting in the CeA during alcohol withdrawal remains to be identified. In the present study, we hypothesized that CeA CRF interneurons may represent a behaviorally relevant source of CRF to the CeA increasing motivation for alcohol via negative reinforcement. We first observed that Crh mRNA expression in the anterior part of the mouse CeA correlates positively with alcohol intake in C57BL/6J males with a history of chronic binge drinking followed by abstinence and increases upon exposure to chronic intermittent ethanol (CIE) vapor inhalation. We then found that chemogenetic activation of CeA CRF neurons in Crh-IRES-Cre mouse brain slices increases gamma-aminobutyric acid (GABA) release in the medial CeA, in part via CRF1 receptor activation. While chemogenetic stimulation exacerbated novelty-induced feeding suppression (NSF) in alcohol-naïve mice, thereby mimicking the effect of withdrawal from CIE, it had no effect on voluntary alcohol consumption, following either acute or chronic manipulation. Furthermore, chemogenetic inhibition of CeA CRF neurons did not affect alcohol consumption or NSF in chronic alcohol drinkers exposed to air or CIE. Altogether, these findings indicate that CeA CRF neurons produce local release of GABA and CRF and promote hyponeophagia in naïve mice, but do not drive alcohol intake escalation or negative affect in CIE-withdrawn mice. The latter result contrasts with previous findings in rats and demonstrates species specificity of CRF circuit engagement in alcohol dependence.

Neurodevelopmental origins of substance use disorders: Evidence from animal models of early-life adversity and addiction

Addiction is a chronic relapsing disorder with devastating personal, societal, and economic consequences. In humans, early-life adversity (ELA) such as trauma, neglect, and resource scarcity are linked with increased risk of later-life addiction, but the brain mechanisms underlying this link are still poorly understood. Here, we focus on data from rodent models of ELA and addiction, in which causal effects of ELA on later-life responses to drugs and the neurodevelopmental mechanisms by which ELA increases vulnerability to addiction can be determined. We first summarize evidence for a link between ELA and addiction in humans, then describe how ELA is commonly modeled in rodents. Since addiction is a heterogeneous disease with many individually varying behavioral aspects that may be impacted by ELA, we next discuss common rodent assays of addiction-like behaviors. We then summarize the specific addiction-relevant behavioral phenotypes caused by ELA in male and female rodents and discuss some of the underlying changes in brain reward and stress circuits that are likely responsible. By better understanding the behavioral and neural mechanisms by which ELA promotes addiction vulnerability, we hope to facilitate development of new approaches for preventing or treating addiction in those with a history of ELA.

Assessing negative affect in mice during abstinence from alcohol drinking: Limitations and future challenges

Alcohol use disorder (AUD) is frequently comorbid with mood disorders, and these co-occurring neuropsychiatric disorders contribute to the development and maintenance of alcohol dependence and relapse. In preclinical models, mice chronically exposed to alcohol display anxiety-like and depressive-like behaviors during acute withdrawal and protracted abstinence. However, in total, results from studies using voluntary alcohol-drinking paradigms show variable behavioral outcomes in assays measuring negative affective behaviors. Thus, the main objective of this review is to summarize the literature on the variability of negative affective behaviors in mice after chronic alcohol exposure. We compare the behavioral phenotypes that emerge during abstinence across different exposure models, including models of alcohol and stress interactions. The complicated outcomes from these studies highlight the difficulties of assessing negative affective behaviors in mouse models designed for the study of AUD. We discuss new behavioral assays, comprehensive platforms, and unbiased machine-learning algorithms as promising approaches to better understand the interaction between alcohol and negative affect in mice. New data-driven approaches in the understanding of mouse behavior hold promise for improving the identification of mechanisms, cell subtypes, and neurocircuits that mediate negative affect. In turn, improving our understanding of the neurobehavioral basis of alcohol-associated negative affect will provide a platform to test hypotheses in mouse models that aim to improve the development of more effective strategies for treating individuals with AUD and co-occurring mood disorders.

Lateral Habenula Beyond Avoidance: Roles in Stress, Memory, and Decision-Making With Implications for Psychiatric Disorders

In this Perspective review, we highlight some of the less explored aspects of lateral habenula (LHb) function in contextual memory, sleep, and behavioral flexibility. We provide evidence that LHb is well-situated to integrate different internal state and multimodal sensory information from memory-, stress-, motivational-, and reward-related circuits essential for both survival and decision making. We further discuss the impact of early life stress (ELS) on LHb function as an example of stress-induced hyperactivity and dysregulation of neuromodulatory systems within the LHb that promote anhedonia and motivational deficits following ELS. We acknowledge that recent technological advancements in manipulation and recording of neural circuits in simplified and well-controlled behavioral paradigms have been invaluable in our understanding of the critical role of LHb in motivation and emotional regulation as well as the involvement of LHb dysfunction in stress-induced psychopathology. However, we also argue that the use of ethologically-relevant behaviors with consideration of complex aspects of decision-making is warranted for future studies of LHb contributions in a wide range of psychiatric illnesses. We conclude this Perspective with some of the outstanding issues for the field to consider where a multi-systems approach is needed to investigate the complex nature of LHb circuitry interactions with environmental stimuli that predisposes psychiatric disorders.

N6-substituated adenosine analog J4 attenuates anxiety-like behaviors in mice

RATIONALE

Withdrawal from chronic alcohol exposure produces various physical and mental withdrawal symptoms. Activation of adenosine receptors is known to inhibit withdrawal-induced excitation. However, limited studies investigate how adenosine analogs may prove helpful tools to alleviate alcohol withdrawal-related affective behaviors.

OBJECTIVES

This study aimed to investigate the effects of J4 compared with saline using the mice vapor or voluntary ethanol drinking model on behavioral endpoints representing ethanol-withdrawal negative emotionality commonly observed during abstinence from chronic alcohol use.

METHODS

We subjected C57BL/6 J mice to chronic intermittent ethanol (CIE) exposure schedule to investigate how 72-h withdrawal from alcohol alters affective-like behavior. Next, we determined how treatment with J4, a second-generation adenosine analog, influenced affective behaviors produced by alcohol withdrawal. Finally, we determined how J4 treatment alters voluntary ethanol drinking using the two-bottle-choice drinking paradigm.

RESULTS

Our results show that 72-h withdrawal from chronic intermittent ethanol exposure produces limited affective-like disturbances in male C57BL/6 J mice exposed to 4 cycles ethanol vapor. Most importantly, J4 treatment irrespective of ethanol exposure decreases innate anxiety-like behavior in mice.

CONCLUSIONS

Withdrawal from chronic intermittent ethanol exposure and subsequent behavioral testing 72 h later produces minimal affective-like behavior. J4 treatment did however reduce marble-burying behavior and increased time spent in open arms of the elevated plus maze, suggesting J4 may be useful as a general anxiolytic.

Sex differences in affective states and association with voluntary ethanol intake in Sprague-Dawley rats

Alcohol use disorders (AUDs) are a major problem across the USA. While AUD remains a complex human condition, it is difficult to isolate the directionality of anxiety and ethanol (EtOH) drinking from outside influences. The present study sought to investigate the relationship between affective states and EtOH intake using male and female Sprague-Dawley rats. Using complementary tests of anxiety- and depressive-like behavior, we found sex- and test-specific differences in basal affective behavior such that females displayed enhanced anxiety-like behavior in the splash test and males displayed enhanced anxiety-like behavior in the novelty-suppressed feeding test. Although, there were no sex differences in EtOH intake and no correlation between baseline anxiety-like behavior and subsequent EtOH intake, we did find that depressive-like behavior predicted future EtOH intake in female rats only. In addition, we observed an increase in depressive-like behavior is male rats in both the water and EtOH drinking groups (compared to baseline levels). Furthermore, post-drinking anxiety-like behavior, but not depressive-like behavior predicted subsequent EtOH intake in female rats. Lastly, we found a history of EtOH intake decreased pain thresholds in male and female rats, but increased anxiety-like and depressive-like behavior was associated with decreased thermal sensitivity only in EtOH-drinking males. Together, these experiments provide important information on the complex interaction between negative affect and EtOH intake and how these two contexts reciprocally do, or do not, influence each other in a sex-specific manner.

Resilience to the effects of social stress on vulnerability to developing drug addiction

We review the still scarce but growing literature on resilience to the effects of social stress on the rewarding properties of drugs of abuse. We define the concept of resilience and how it is applied to the field of drug addiction research. We also describe the internal and external protective factors associated with resilience, such as individual behavioral traits and social support. We then explain the physiological response to stress and how it is modulated by resilience factors. In the subsequent section, we describe the animal models commonly used in the study of resilience to social stress, and we focus on the effects of chronic social defeat (SD), a kind of stress induced by repeated experience of defeat in an agonistic encounter, on different animal behaviors (depression- and anxiety-like behavior, cognitive impairment and addiction-like symptoms). We then summarize the current knowledge on the neurobiological substrates of resilience derived from studies of resilience to the effects of chronic SD stress on depression- and anxiety-related behaviors in rodents. Finally, we focus on the limited studies carried out to explore resilience to the effects of SD stress on the rewarding properties of drugs of abuse, describing the current state of knowledge and suggesting future research directions.

Impact of Early Life Stress on Reward Circuit Function and Regulation

Early life stress - including experience of child maltreatment, neglect, separation from or loss of a parent, and other forms of adversity - increases lifetime risk of mood, anxiety, and substance use disorders. A major component of this risk may be early life stress-induced alterations in motivation and reward processing, mediated by changes in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Here, we review evidence of the impact of early life stress on reward circuit structure and function from human and animal models, with a focus on the NAc. We then connect these results to emerging theoretical models about the indirect and direct impacts of early life stress on reward circuit development. Through this review and synthesis, we aim to highlight open research questions and suggest avenues of future study in service of basic science, as well as applied insights. Understanding how early life stress alters reward circuit development, function, and motivated behaviors is a critical first step toward developing the ability to predict, prevent, and treat stress-related psychopathology spanning mood, anxiety, and substance use disorders.

Neonatal resource scarcity alters maternal care and impacts offspring core temperature and growth in rats

Stressful experiences during childhood, including poverty and inconsistent parental care, can enhance vulnerability for worsened physical and mental health outcomes in adulthood. Using Sprague Dawley rats, the present study explored the impact of limited resource availability on maternal behavior and physiological and emotional behavior outcomes in the offspring. Early life adversity was induced by incorporating aspects of the limited bedding and nesting and scarcity models, wherein limited resource availability has previously been shown to provoke unpredictable or adverse maternal care respectively. In our hands, neonatal limited bedding (NLB) stress during postnatal days (P)2-9 altered maternal care, augmenting pup-directed behaviors and reducing self-directed behaviors, and modestly increased the frequency of transitions between discrete behaviors across consecutive timed observations. NLB-exposed pups had lower core body temperatures immediately following the stressful manipulation and exhibited decreased body weight gain across development. However, NLB exposure did not impact adult offspring's social or emotional behavior outcomes in the three-chamber social interaction, novelty-suppressed feeding, splash, or forced swim tests. These findings add to the literature demonstrating that early life adversity impacts maternal care in rodents and can disrupt certain metabolic and thermoregulatory outcomes in the offspring.

The Paraventricular Thalamus: A Potential Sensor and Integrator of Emotionally Salient Early-Life Experiences

Early-life experiences influence a broad spectrum of behaviors throughout the lifespan that contribute to resilience or vulnerability to mental health disorders. Yet, how emotionally salient experiences early in life are encoded, stored, and processed and the mechanisms by which they influence future behaviors remain poorly understood. The paraventricular nucleus of the thalamus (PVT) is a key structure in modulating positive and negative experiences and behaviors in adults. However, little is known of the PVT's role in encoding and integrating emotionally salient experiences that occur during neonatal, infancy, and childhood periods. In this review, we (1) describe the functions and connections of the PVT and its regulation of behavior, (2) introduce novel technical approaches to elucidating the role of the PVT in mediating enduring changes in adult behaviors resulting from early-life experiences, and (3) conclude that PVT neurons of neonatal rodents are engaged by both positive and negative emotionally salient experiences, and their activation may enduringly govern future behavior-modulating PVT activity during emotionally salient contexts.