Sex-dependent effects of maternal separation on plasma corticosterone and brain monoamines in response to chronic ethanol administration

Quercetin-loaded nanophytosome ameliorates early life stress-induced hippocampal oxido-inflammatory damages

Phytosome-based nanocarriers have emerged as innovative drug delivery systems in recent years, demonstrating significant potential in the treatment of neurodegenerative disorders. This study aimed to evaluate the therapeutic efficacy of quercetin-loaded nanophytosome (QNP) in modulating the oxido-inflammatory response in a rat model of early life stress (ELS) induced by maternal isolation (MI). To establish the ELS model, male rat pups were isolated from their dam for 3 hours daily from postnatal days 1-9. Following the lactation period (postpartum days 1-21), treatments with quercetin (10 and 40 mg/kg) and QNP (10 and 40 mg/kg) were administered continuously for 21 days. Cognitive behaviors, oxidative stress markers, hippocampal dopamine levels, and mRNA expression of TNF-α and IL-6 were assessed after ELS induction. Treatment with QNP (40 mg/kg) significantly improved cognitive function (P < 0.01), increased hippocampal dopamine levels (P < 0.001), and reduced oxidative stress (P < 0.01) as well as the expression of TNF-α (P < 0.001) and IL-6 (P < 0.001). In conclusion, QNP demonstrates potent hippocampal anti-oxidoinflammatory effects, making it a promising therapeutic candidate for mitigating the adverse effects of maternal isolation-induced early life stress.

Preclinical and clinical sex differences in the effects of alcohol on measures of brain dopamine: a systematic review

INTRODUCTION

Dopamine is involved in reward processing and plays a critical role in the development and progression of alcohol use disorder (AUD). However, little is known about the effect of sex on the relationship between dopamine and alcohol use/AUD. There is a critical need to identify the neurobiological mechanisms that contribute to sex differences in AUD to inform treatment approaches. This study aimed to review existing literature on sex differences in the effects of alcohol on brain dopamine measures in animals and individuals with heavy drinking/AUD.

METHODS

A systematic review was conducted using Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. PubMed was searched from inception to July 23rd, 2024.

RESULTS

Of the 1,412 articles identified, 10 met study criteria (1 human, 9 animal), including in vivo (two positron emission tomography, four microdialysis) and ex vivo (two liquid chromatography, two fast-scan cyclic voltammetry) studies. Six studies included an alcohol challenge; three showed that females had greater alcohol-induced dopamine release than males in the ventral striatum and frontal cortex, while three showed no sex-related differences. Notably, the latter three studies examined sex in a combined AUD/control group or measured dopamine levels days after alcohol exposure. Two studies that examined the effects of prenatal alcohol exposure showed that prenatal-alcohol-exposed male offspring versus sex-matched air-exposed controls had greater prefrontal cortical dopamine D1 receptor availability, and prenatal-alcohol-exposed female offspring versus sex-matched air-exposed controls had greater striatal dopamine concentration. Two studies investigating the mu-opioid receptor (MOR) regulation of alcohol-induced dopamine release showed a faster decline in females relative to males while the other study found females may be less dependent on MOR activity at lower doses of alcohol relative to higher doses.

CONCLUSIONS

This systematic review showed mixed results regarding sex differences in brain dopamine measures in alcohol-exposed animals and individuals with AUD, which may arise from differences in the timing, quantity, and duration of alcohol exposure, species, conditions, models, and techniques. More research examining the effect of sex on the relationship between alcohol use and brain dopamine measures is needed to enhance our understanding of AUD development, progression, and treatment in both females and males.

Androgen effects on mesoprefrontal dopamine systems in the adult male brain

Epidemiological data show that males are more often and/or more severely affected by symptoms of prefrontal cortical dysfunction in schizophrenia, Parkinson's disease and other disorders in which dopamine circuits associated with the prefrontal cortex are dysregulated. This review focuses on research showing that these dopamine circuits are powerfully regulated by androgens. It begins with a brief overview of the sex differences that distinguish prefrontal function in health and prefrontal dysfunction or decline in aging and/or neuropsychiatric disease. This review article then spotlights data from human subjects and animal models that specifically identify androgens as potent modulators of prefrontal cortical operations and of closely related, functionally critical measures of prefrontal dopamine level or tone. Candidate mechanisms by which androgens dynamically control mesoprefrontal dopamine systems and impact prefrontal states of hypo- and hyper-dopaminergia in aging and disease are then considered. This is followed by discussion of a working model that identifies a key locus for androgen modulation of mesoprefrontal dopamine systems as residing within the prefrontal cortex itself. The last sections of this review critically consider the ways in which the organization and regulation of mesoprefrontal dopamine circuits differ in the adult male and female brain, and highlights gaps where more research is needed.

The gold standard control groups in physiological and pharmacological research are not that shiny: Intraperitoneal saline injection and needle pricking affect prepubescent mice's behavior in a sex-specific manner

Study design and experimental tools are crucial for good quality science, and an essential part of it is the choice of control groups to best test the hypothesis. Two of the standard control groups in physiological and pharmacological research are needle pricking without substance injection (Sham) and/or vehicle injection (Saline). However, both needle pricking and saline injection can act as stressors, potentially influencing the analyzed outcome. This raises the question of whether the dependent variable remains unaffected by the stress induced by these procedures. Despite the significance of this issue, very few studies have investigated the behavioral effects of a single intraperitoneal (I.P.) Sham and/or single I.P. Saline injection in mice, and those that have used mostly adult males. In this study, we investigated if a single I.P. Sham and/or I.P. Saline injection affects female and male prepubertal (4-weeks-old) mice behavior. After Sham or Saline injection, we examined exploratory/motor behavior (open field test - OFT), anxiety-like behavior (elevated plus-maze - EPM), and behavioral despair/depressive-like behavior (forced swimming test - FST). We observed that both Sham prepubertal females and males showed behavioral alterations in OFT and EPM, and Saline males showed behavioral alterations in OFT and FST. On the other hand, prepubertal Saline females showed an increase in exploratory behavior, risk assessment/anxiety-like behavior, and behavioral despair/depressive-like behavior. Thus, our findings indicate that control procedures commonly used in physiological and pharmacological experimental designs affect the behavior of prepubescent mice, with more pronounced effects in females than in males. This study suggests considering Naïve animals together with Sham and/or Vehicle for a better and more honest interpretation of the data.

A review of the effects of different types of social behaviors on the recruitment of neuropeptides and neurotransmitters in the nucleus accumbens

There is a lack of understanding of the neural mechanisms regulating the rewarding effects of social interactions. A significant contributor to this lack of clarity is the diversity of social behaviors and animal models utilized to investigate mechanisms. Other sources of the lack of clarity are the diversity of brain regions that can regulate social reward and the diversity of signaling pathways that regulate reward. To provide some clarity into the mechanisms of social reward, this review focused on the brain region most implicated in reward for multiple stimuli, the nucleus accumbens, and surveyed (systematically reviewed) studies that investigated the relationship between social interaction and five signaling systems implicated in the regulation of reward and social behavior: oxytocin, vasopressin, serotonin, opioids and endocannabinoids. Moreover, all of these studies were organized by the type of social behavior studied: affiliative interactions, play behavior, aggression, social defeat, sex behavior, pair-bonding, parental behavior and social isolation. From this survey and organization, this review concludes that oxytocin, endocannabinoids and mu-opioid receptors in the nucleus accumbens positively regulate the rewarding social behaviors, and kappa-opioid receptors negatively regulate the rewarding social behaviors. The opposite profile is observed for these signaling systems for the aversive social behaviors. More studies are needed to investigate the directional role of the serotonin system in the nucleus accumbens in the regulation of many types of social behaviors, and vasopressin likely does not act in the nucleus accumbens in the regulation of the valence of social behaviors. Many of these different signaling systems are also interdependent of one another in the regulation of different types of social behaviors. Finally, the interaction of these signaling systems with dopamine in the nucleus accumbens is briefly discussed.

Effects of L-Dopa, SKF-38393, and quinpirole on exploratory, anxiety- and depressive-like behaviors in pubertal female and male mice

Adolescence is a phase of substantial changes in the brain, characterized by maturational remodeling of many systems. This remodeling allows functional plasticity to adapt to a changing environment. The dopaminergic system is under morphological and physiological changes during this phase. In the present study, we investigated if changes in the dopaminergic tone alter mice behavior in a receptor and sex-specific manner, specifically at the beginning of the puberty period. We administered L-Dopa, SKF-38393 (D1 dopamine receptor agonist), and Quinpirole (D2 dopamine receptor agonist) and tested male and female mice's motor, anxiety- and depressive-like behavior. While females displayed an impaired exploratory drive, males presented an intense depressive-like response. Our results provide insights into the function of dopaminergic development in adolescent behavior and highlight the importance of studies in this time window with male and female subjects.

FACTORS CONTRIBUTING TO THE ESCALATION OF ALCOHOL CONSUMPTION

Understanding factors that contribute to the escalation of alcohol consumption is key to understanding how an individual transitions from non/social drinking to AUD and to providing better treatment. In this review, we discuss how the way ethanol is consumed as well as individual and environmental factors contribute to the escalation of ethanol consumption from intermittent low levels to consistently high levels. Moreover, we discuss how these factors are modelled in animals. It is clear a vast array of complex, interacting factors influence changes in alcohol consumption. Some of these factors act early in the acquisition of ethanol consumption and initial escalation, while others contribute to escalation of ethanol consumption at a later stage and are involved in the development of alcohol dependence. There is considerable need for more studies examining escalation associated with the formation of dependence and other hallmark features of AUD, especially studies examining mechanisms, as it is of considerable relevance to understanding and treating AUD.

Corticotropin-releasing factor infusion in the bed nucleus of the stria terminalis of lactating mice alters maternal care and induces behavioural phenotypes in offspring

The peripartum period is accompanied by numerous physiological and behavioural adaptations organised by the maternal brain. These changes are essential for adequate expression of maternal behaviour, thereby ensuring proper development of the offspring. The corticotropin-releasing factor (CRF) plays a key role in a variety of behaviours accompanying stress, anxiety, and depression. There is also evidence that CRF contributes to maladaptations during the peripartum period. We investigated the effects of CRF in the bed nucleus of the stria terminalis (BNST) of lactating mice during maternal care and analysed locomotor activity and anxiety-like behaviour in the offspring. The BNST has been implicated in anxiety behaviour and regulation of the stress response. The effects of intra-BNST CRF administration were compared with those induced by the limited bedding (LB) procedure, a model that produces altered maternal behaviour. BALB/cJ dams were exposed to five infusions of CRF or saline into the BNST in the first weeks after birth while the LB dams were exposed to limited nesting material from postnatal days (P) 2–9. Maternal behaviour was recorded in intercalated days, from P1-9. Offspring anxiety-like behaviour was assessed during adulthood using the open-field, elevated plus-maze, and light/dark tests. Both intra-BNST CRF and LB exposure produced altered maternal care, represented by decreased arched-back nursing and increased frequency of exits from the nest. These changes in maternal care resulted in robust sex-based differences in the offspring’s behavioural responses during adulthood. Females raised by CRF-infused dams exhibited increased anxiety-like behaviour, whereas males presented a significant decrease in anxiety. On the other hand, both males and females raised by dams exposed to LB showed higher locomotor activity. Our study demonstrates that maternal care is impaired by intra-BNST CRF administrations, and these maladaptations are similar to exposure to adverse early environments. These procedures, however, produce distinct phenotypes in mice during young adulthood and suggest sex-based differences in the susceptibility to poor maternal care.

Sex differences in the neurochemistry of frontal cortex: Impact of early life stress

Traumatic events during early life have been linked with later life psychopathology. To understand this risk factor, researchers have studied the effects of prenatal and postnatal early life stress on neurochemical changes. Here we review the rodent literature on sex differences and sex-specific impact of early life stress on frontal cortex neurochemistry. This region is implicated in regulating motivation and emotion, which are often disrupted in psychological disorders. The prefrontal cortex (PFC) in particular is one of the last brain regions to develop, and there are sex differences in the rate of this development. To draw direct comparisons between sexes, our review of the literature was restricted to studies where the effects of prenatal or postnatal stress had been described in male and female littermates. This literature included research describing glutamate, γ-amino butyric acid (GABA), corticosteroids, monoamines, and cannabinoids. We found that sex-dependent effects of stress are mediated by the age at which stress is experienced, age at test, and type of stress endured. More research is required, particularly into the effects of adolescent stress on male and female littermates. We hope that a greater understanding of sex-specific susceptibilities in response to stress across development will help to uncover risk factors for psychological disorders in vulnerable populations.

Sex-Specific Effects of Early Life Stress on Brain Mitochondrial Function, Monoamine Levels and Neuroinflammation

Sex differences have been reported in the susceptibility to early life stress and its neurobiological correlates in humans and experimental animals. However, most of the current research with animal models of early stress has been performed mainly in males. In the present study, prolonged maternal separation (MS) paradigm was applied as an animal model to resemble the effects of adverse early experiences in male and female rats. Regional brain mitochondrial function, monoaminergic activity, and neuroinflammation were evaluated as adults. Mitochondrial energy metabolism was greatly decreased in MS females as compared with MS males in the prefrontal cortex, dorsal hippocampus, and the nucleus accumbens shell. In addition, MS males had lower serotonin levels and increased serotonin turnover in the prefrontal cortex and the hippocampus. However, MS females showed increased dopamine turnover in the prefrontal cortex and increased norepinephrine turnover in the striatum, but decreased dopamine turnover in the hippocampus. Sex differences were also found for pro-inflammatory cytokine levels, with increased levels of TNF-α and IL-6 in the prefrontal cortex and hippocampus of MS males, and increased IL-6 levels in the striatum of MS females. These results evidence the complex sex- and brain region-specific long-term consequences of early life stress.

Chronic social defeat stress: Impacts on ethanol-induced stimulation, corticosterone response, and brain monoamine levels

BACKGROUND

Chronic exposure to stress may dysregulate the hypothalamic-pituitary-adrenal axis and brain monoamine levels, contributing to the development of ethanol dependence. Exposure to chronic social defeat stress may impact ethanol-related effects, neural, and endocrine functions.

AIM

This study assessed ethanol-induced locomotor activity, corticosterone responses, and brain monoamine levels in Swiss albino mice 10 days post-exposure to chronic social defeat stress.

METHODS

During a period of 10 days, male Swiss mice were exposed to daily defeat episodes, followed by housing with an aggressive mouse for 24 h. Control mice were housed in pairs and rotated every 24 h. Ten days post-stress, locomotor behavior was recorded after a challenge with ethanol (2.2 g/kg; intraperitoneal) or saline. After the test, blood and brain samples were collected for determination of plasma corticosterone and brain monoamines across different brain areas through high-performance liquid chromatography.

RESULTS

Defeated mice failed to show a stimulant locomotor response to ethanol, while controls displayed the expected ethanol-induced stimulation. Ethanol increased plasma corticosterone levels, with lower corticosterone secretion in defeated mice. Brain monoamines were affected by social defeat and ethanol, varying in different brain regions. Social stress reduced levels of dopamine, noradrenaline, and serotonin in the hypothalamus. Defeated mice presented reduced serotonin and dopamine levels in the frontal cortex. In the striatum, ethanol treatment increased dopamine levels in controls, but failed to do so in defeated mice.

CONCLUSIONS

Our results suggest that chronic exposure to social defeat blunted ethanol-induced locomotor stimulation, and reduced ethanol-induced corticosterone secretion. Social stress promoted differential reductions in brain monoamine levels in the hypothalamus and frontal cortex and blunted ethanol-induced dopamine increases in the striatum.

Chronic repeated predatory stress induces resistance to quinine adulteration of ethanol in male mice

BACKGROUND

Trauma related psychiatric disorders, such as posttraumatic stress disorder (PTSD), and alcohol use disorder (AUD) are highly comorbid illnesses that separately present an opposing, sex-specific pattern, with increased prevalence of PTSD in females and increased prevalence of AUD diagnoses in males. Likewise, PTSD is a risk factor in the development of AUD, with conflicting data on the impact of sex in the comorbid development of both disorders. Because the likelihood of experiencing more than one traumatic event is high, we aim to utilize chronic repeated predatory stress (CRPS) to query the extent to which sex interacts with CRPS to influence alcohol consumption, or cessation of consumption.

METHODS

Male (n = 16) and female (n = 15) C57BL/6 J mice underwent CRPS or daily handling for two weeks during adolescence (P35-P49) and two weeks during adulthood (P65-P79). Following the conclusion of two rounds of repeated stress, behavior was assessed in the open field. Mice subsequently underwent a two-bottle choice intermittent ethanol access (IEA) assessment (P90-131) with the options of 20 % ethanol or water. After establishing drinking behavior, increasing concentrations of quinine were added to the ethanol to assess the drinking response to adulteration of the alcohol.

RESULTS

CRPS increased fecal corticosterone concentrations and anxiety-like behaviors in the open field in both male and female mice as compared to control mice that had not been exposed to CRPS. Consistent with previous reports, we observed a sex difference in alcohol consumption such that females consumed more ethanol per gram of body mass than males. In addition, CRPS reduced alcohol aversion in male mice such that higher concentrations of quinine were necessary to reduce alcohol intake as compared to control mice. CRPS did not alter alcohol-related behaviors in female mice.

CONCLUSION

Collectively, we demonstrate that repeated CRPS can induce anxiety-like behavior in both sexes but selectively influences the response to ethanol adulteration in males.

Impact of Maternal Separation on Dopamine System and its Association with Parkinson's Disease

As a type of stress, maternal separation (MS) has been one of the most widely used models in neuropsychiatric research. An increasing number of studies has found that MS not only affects the function of the hypothalamic-pituitary-adrenal axis and hippocampal 5-hydroxytryptamine system, but also causes dysfunction of the central dopamine (DA) system and increases the susceptibility of dopaminergic neurons to pathogenic factors of Parkinson's disease (PD), for instance, 6-hydroxydopamine, thus impairing motor function. We reviewed the impact of MS on the DA system and its correlation with PD and found the following: (1) discrepant effects of MS on the DA system have been reported; (2) MS is a good model to study the impact of stress on the occurrence and development of PD, however, unified modeling criteria of MS are required; (3) correlation between MS and PD may involve the impact of MS on the DA system, which however is not the only connection; (4) intervening measures can block pathways between MS and PD, which provides reference for the prevention of PD in specific populations such as left-behind children.

Maternal separation in rodents: a journey from gut to brain and nutritional perspectives

The developmental period constitutes a critical window of sensitivity to stress. Indeed, early-life adversity increases the risk to develop psychiatric diseases, but also gastrointestinal disorders such as the irritable bowel syndrome at adulthood. In the past decade, there has been huge interest in the gut-brain axis, especially as regards stress-related emotional behaviours. Animal models of early-life adversity, in particular, maternal separation (MS) in rodents, demonstrate lasting deleterious effects on both the gut and the brain. Here, we review the effects of MS on both systems with a focus on stress-related behaviours. In addition, we discuss more recent findings showing the impact of gut-directed interventions, including nutrition with pre- and probiotics, illustrating the role played by gut microbiota in mediating the long-term effects of MS. Overall, preclinical studies suggest that nutritional approaches with pro- and prebiotics may constitute safe and efficient strategies to attenuate the effects of early-life stress on the gut-brain axis. Further research is required to understand the complex mechanisms underlying gut-brain interaction dysfunctions after early-life stress as well as to determine the beneficial impact of gut-directed strategies in a context of early-life adversity in human subjects.

Effects of early life stress on biochemical indicators of the dopaminergic system: A 3 level meta-analysis of rodent studies

Adverse early life events are a well-established risk factor for the precipitation of behavioral disorders characterized by anomalies in the dopaminergic system, such as schizophrenia and addiction. The correlation between early life conditions and the dopaminergic system has been causally investigated in more than 90 rodent publications. Here, we tested the validity of the hypothesis that early life stress (ELS) alters dopamine signaling by performing an extensive 3-level mixed effect meta-analysis. We included several ELS models and biochemical indicators of the dopaminergic system in a variety of brain areas, for a total of 1009 comparisons. Contrary to our expectations, only a few comparisons displayed a significant effect. Specifically, the striatal area was the most vulnerable, displaying decreased dopamine precursor and increased metabolites after ELS. To make all data openly accessible, we created MaDEapp (https://osf.io/w25m4/), a tool to explore data of the meta-analysis with the intent to guide future (pre)clinical research and allow power calculations. All in all, ELS induces a few yet robust changes on biochemical indicators of the dopaminergic system.

Distinctive stress sensitivity and anxiety-like behavior in female mice: Strain differences matter

Epidemiologic studies have shown that the prevalence of stress-related mood disorders is higher in women, which suggests a different response of neuroendocrine circuits involved in the response to stressful events, as well as a genetic background influence. The aim of this study was to investigate the baseline differences in anxiety-like behaviors of females of two commonly used mice strains. Secondly, we have also aimed to study their behavioral and biochemical alterations following stress. Naïve 3-4 months-old Swiss and C57BL/6 female mice were evaluated in the elevated plus maze (EPM) and in the acoustic startle response (ASR) for anxiety-like behaviors. Besides, an independent group of animals from each strain was exposed to cold-restraint stress (30 min/4 °C, daily) for 21 consecutive days and then evaluated in EPM and in the sucrose consumption tests. Twenty-four hours following behavioral experimentation mice were decapitated and their hippocampi (HP) and cortex (CT) dissected for further Western blotting analysis of glucocorticoid receptor (GR) and glial fibrillary acid protein (GFAP). Subsequent to each behavioral protocol, animal blood samples were collected for further plasma corticosterone analysis. C57BL/6 presented a lower anxiety profile than Swiss female mice in both behavioral tests, EPM and ASR. These phenomena could be correlated with the fact that both strains have distinct corticosterone levels and GR expression in the HP at the baseline level. Moreover, C57BL/6 female mice were more vulnerable to the stress protocol, which was able to induce an anhedonic state characterized by lower preference for a sucrose solution. Behavioral anhedonic-like alterations in these animals coincide with reduced plasma corticosterone accompanied with increased GR and GFAP levels, both in the HP. Our data suggest that in C57BL/6 female mice a dysregulation of the hypothalamus-pituitary-adrenal axis (HPA-axis) occurs, in which corticosterone acting on GRs would possibly exert its pro-inflammatory role, ultimately leading to astrocyte activation in response to stress.

The impact of early life stress on the central oxytocin system and susceptibility for drug addiction: Applicability of oxytocin as a pharmacotherapy

Early life trauma is strongly associated with an increased vulnerability to abuse illicit drugs and the impairment of neural development. This includes alterations to the development of the oxytocin system, which plays a pivotal role in the regulation of social behaviours and emotion. Dysregulation of this important system also contributes to increased susceptibility to develop drug addiction. In this review, we provide an overview of the animal models of early life stress that are widely used, and discuss the impact that early life stress has on drug-taking behaviour in adolescence and adulthood in both sexes. We link this to the changes that early life stress has on the endogenous oxytocin system, and how exogenously administered oxytocin may help to re-establish functioning of the system, and in turn, reduce drug-taking behaviour.

Novel approaches to alcohol rehabilitation: Modification of stress-responsive brain regions through environmental enrichment

Relapse remains the most prominent hurdle to successful rehabilitation from alcoholism. The neural mechanisms underlying relapse are complex, but our understanding of the brain regions involved, the anatomical circuitry and the modulation of specific nuclei in the context of stress and cue-induced relapse have improved significantly in recent years. In particular, stress is now recognised as a significant trigger for relapse, adding to the well-established impact of chronic stress to escalate alcohol consumption. It is therefore unsurprising that the stress-responsive regions of the brain have also been implicated in alcohol relapse, such as the nucleus accumbens, amygdala and the hypothalamus. Environmental enrichment is a robust experimental paradigm which provides a non-pharmacological tool to alter stress response and, separately, alcohol-seeking behaviour and symptoms of withdrawal. In this review, we examine and consolidate the preclinical evidence that alcohol seeking behaviour and stress-induced relapse are modulated by environmental enrichment, and these are primarily mediated by modification of neural activity within the key nodes of the addiction circuitry. Finally, we discuss the limited clinical evidence that stress-reducing approaches such as mindfulness could potentially serve as adjunctive therapy in the treatment of alcoholism. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".

Social Origins of Developmental Risk for Mental and Physical Illness

Adversity in early childhood exerts an enduring impact on mental and physical health, academic achievement, lifetime productivity, and the probability of interfacing with the criminal justice system. More science is needed to understand how the brain is affected by early life stress (ELS), which produces excessive activation of stress response systems broadly throughout the child's body (toxic stress). Our research examines the importance of sex, timing and type of stress exposure, and critical periods for intervention in various brain systems across species. Neglect (the absence of sensitive and responsive caregiving) or disrupted interaction with offspring induces robust, lasting consequences in mice, monkeys, and humans. Complementary assessment of internalizing disorders and brain imaging in children suggests that early adversity can interfere with white matter development in key brain regions, which may increase risk for emotional difficulties in the long term. Neural circuits that are most plastic during ELS exposure in monkeys sustain the greatest change in gene expression, offering a mechanism whereby stress timing might lead to markedly different long-term behaviors. Rodent models reveal that disrupted maternal-infant interactions yield metabolic and behavioral outcomes often differing by sex. Moreover, ELS may further accelerate or delay critical periods of development, which reflect GABA circuit maturation, BDNF, and circadian Clock genes. Such factors are associated with several mental disorders and may contribute to a premature closure of plastic windows for intervention following ELS. Together, complementary cross-species studies are elucidating principles of adaptation to adversity in early childhood with molecular, cellular, and whole organism resolution.

An Update on CRF Mechanisms Underlying Alcohol Use Disorders and Dependence

Alcohol is the most commonly used and abused substance worldwide. The emergence of alcohol use disorders, and alcohol dependence in particular, is accompanied by functional changes in brain reward and stress systems, which contribute to escalated alcohol drinking and seeking. Corticotropin-releasing factor (CRF) systems have been critically implied in the transition toward problematic alcohol drinking and alcohol dependence. This review will discuss how dysregulation of CRF function contributes to the vulnerability for escalated alcohol drinking and other consequences of alcohol consumption, based on preclinical evidence. CRF signaling, mostly via CRF1 receptors, seems to be particularly important in conditions of excessive alcohol taking and seeking, including during early and protracted withdrawal, relapse, as well as during withdrawal-induced anxiety and escalated aggression promoted by alcohol. Modulation of CRF1 function seems to exert a less prominent role over low to moderate alcohol intake, or to species-typical behaviors. While CRF mechanisms in the hypothalamic-pituitary-adrenal axis have some contribution to the neurobiology of alcohol abuse and dependence, a pivotal role for extra-hypothalamic CRF pathways, particularly in the extended amygdala, is well characterized. More recent studies further suggest a direct modulation of brain reward function by CRF signaling in the ventral tegmental area, nucleus accumbens, and the prefrontal cortex, among other structures. This review will further discuss a putative role for other components of the CRF system that contribute for the overall balance of CRF function in reward and stress pathways, including CRF2 receptors, CRF-binding protein, and urocortins, a family of CRF-related peptides.

An overview of maternal separation effects on behavioural outcomes in mice: Evidence from a four-stage methodological systematic review

Early life stress (ELS) developmental effects have been widely studied by preclinical researchers. Despite the growing body of evidence from ELS models, such as the maternal separation paradigm, the reported results have marked inconsistencies. The maternal separation model has several methodological pitfalls that could influence the reliability of its results. Here, we critically review 94 mice studies that addressed the effects of maternal separation on behavioural outcomes. We also discuss methodological issues related to the heterogeneity of separation protocols and the quality of reporting methods. Our findings indicate a lack of consistency in maternal separation effects: major studies of behavioural and biological phenotypes failed to find significant deleterious effects. Furthermore, we identified several specific variations in separation methodological procedures. These methodological variations could contribute to the inconsistency of maternal separation effects by producing different degrees of stress exposure in maternal separation-reared pups. These methodological problems, together with insufficient reporting, might lead to inaccurate and unreliable effect estimates in maternal separation studies.

Naltrexone Prevents in Males and Attenuates in Females the Expression of Behavioral Sensitization to Ethanol Regardless of Maternal Separation

Maternal separation alters the activity of the opioid system, which modulates ethanol-induced stimulation and behavioral sensitization. This study examined the effects of an opioid antagonist, naltrexone (NTX), on the expression of behavioral sensitization to ethanol in adult male and female mice submitted to maternal separation from postnatal days (PNDs) 2 to 14. Whole litters of Swiss mice were either not separated [animal facility rearing (AFR)] or separated from their mothers for 3 h [long maternal separation (LMS)]. Starting on PND 90, male and female AFR and LMS mice received daily i.p. injections of saline (SAL) or ethanol (EtOH, 2.2 g/kg) for 21 days. Locomotor activity was assessed in cages containing photoelectric beams, once a week, to examine the development of behavioral sensitization. Five days after the end of the chronic treatment, animals were submitted to four locomotor activity tests spaced by 48 h, to assess the expression of behavioral sensitization. In all tests, animals received two i.p. injections with a 30-min interval and were then assessed for locomotor response to different treatment challenges, which were: SAL/SAL, SAL/EtOH (2.2 g/kg), NTX 2.0 mg/kg (NTX2)/EtOH, and NTX 4.0 mg/kg (NTX4)/EtOH. Regardless of maternal separation, EtOH-treated male and female mice displayed increased locomotor responses to EtOH during the 21-day treatment, indicating the development of behavioral sensitization. In the SAL/EtOH challenge, EtOH-treated LMS and AFR male and female mice exhibited higher locomotor activity than their SAL-treated counterparts, indicating the expression of sensitization. The coadministration of either dose of NTX blocked the expression of locomotor sensitization in both AFR and LMS male mice with a history of EtOH sensitization. In females, a significant attenuation of EtOH sensitization was promoted by both NTX doses, while still maintaining an augmented stimulant response to EtOH. Importantly, maternal separation did not interfere in this phenomenon. These results indicate that expression of behavioral sensitization was importantly modulated by opioidergic mechanisms both in male and female mice and that maternal separation did not play a major role in either development or expression of this EtOH sensitization.

Early Life Stress, Nicotinic Acetylcholine Receptors and Alcohol Use Disorders

Stress is a major driving force in alcohol use disorders (AUDs). It influences how much one consumes, craving intensity and whether an abstinent individual will return to harmful alcohol consumption. We are most vulnerable to the effects of stress during early development, and exposure to multiple traumatic early life events dramatically increases the risk for AUDs. However, not everyone exposed to early life stress will develop an AUD. The mechanisms determining whether an individual’s brain adapts and becomes resilient to the effects of stress or succumbs and is unable to cope with stress remain elusive. Emerging evidence suggests that neuroplastic changes in the nucleus accumbens (NAc) following early life stress underlie the development of AUDs. This review discusses the impact of early life stress on NAc structure and function, how these changes affect cholinergic signaling within the mesolimbic reward pathway and the role nicotinic acetylcholine receptors (nAChRs) play in this process. Understanding the neural pathways and mechanism determining stress resilience or susceptibility will improve our ability to identify individuals susceptible to developing AUDs, formulate cognitive interventions to prevent AUDs in susceptible individuals and to elucidate and enhance potential therapeutic targets, such as the nAChRs, for those struggling to overcome an AUD.

Long-term impact of early life events on physiology and behaviour

This review discusses the effects of stress and nutrition throughout development and summarises studies investigating how exposure to stress or alterations in nutrition during the pre-conception, prenatal and early postnatal periods can affect the long-term health of an individual. In general, the data presented here suggest that that anything signalling potential adverse conditions later in life, such as high levels of stress or low levels of food availability, will lead to alterations in the offspring, possibly of an epigenetic nature, preparing the offspring for these conditions later in life. However, when similar environmental conditions are not met in adulthood, these alterations may have maladaptive consequences, resulting in obesity and heightened stress sensitivity. The data also suggest that the mechanism underlying these adult phenotypes might be dependent on the type and the timing of exposure.