Persistent escalation of alcohol consumption by mice exposed to brief episodes of social defeat stress: suppression by CRF-R1 antagonism

Neurokinin-1 receptors in the nucleus accumbens shell influence sensitivity to social defeat stress and stress-induced alcohol consumption in male mice

Chronic social defeat stress (SDS) is a widely employed preclinical model of depression involving repeated exposure to physical defeats using a resident-intruder model in male mice. Exposure to SDS induces depressive-like phenotypes including anhedonia, social withdrawal, and increased drug and alcohol consumption. Previously, we found that expression of the neurokinin-1 receptor (NK1R) is increased in the nucleus accumbens (NAC) of mice that are sensitive to this stressor and increase their alcohol intake. The NK1R is the endogenous receptor for the neuropeptide substance P (SP) and plays a prominent role in stress, anxiety, and addiction. In the present study, we assessed changes in NK1R protein levels in the NAC shell and implemented viral vector strategies to demonstrate a functional role of the NK1R in sensitivity to SDS. Specifically, we found that NK1R protein levels were increased in the NAC shell following SDS exposure. Next, we found that NK1R overexpression in the NAC shell increased the sensitivity to SDS and stress-induced alcohol consumption. Together, these experiments provide evidence for a role of the NK1R in the NAC shell in the sensitivity to SDS and the subsequent escalation in alcohol intake.

BLA KOR inputs to the BNST regulate social stress-escalated alcohol consumption

Background

Aversive social experiences can lead to escalated drug consumption and increase the risk of relapse to drug seeking. Individuals who consume alcohol to alleviate the effects of social stress are more likely to develop an alcohol use disorder (AUD). Repeated social defeat stress (SDS) enhances the rewarding and reinforcing effects of alcohol. However, the neural mechanisms that underlie social stress-escalated alcohol drinking are not well understood. Here we explored the role of the dynorphin/kappa opioid receptor (Dyn/KOR) system in regulating social stress-escalated alcohol consumption.

Methods

Male and female mice were subjected to repeated SDS for 10 days following which they were left undisturbed in their home cages. They were then subject to intermittent access (IA) two-bottle choice alcohol consumption procedure. The effects of systemic and BNST-specific KOR antagonism using the selective KOR antagonist NorBNI on stress-escalated drinking were evaluated. Using chemogenetic approaches in Oprk1-Cre mice, we examined the role of KOR expressing cells in the basolateral amygdala (BLA KORs ) and BLA KOR -BNST pathway in social stress-escalated alcohol consumption.

Results

Repeated SDS increased alcohol consumption and preference in both males and females. Systemic KOR antagonism attenuated SDS-escalated alcohol consumption in both males and females. BNST -specific KOR antagonism also attenuated stress-escalated drinking in males. Finally, selective chemogenetic activation of BLA KORs and BKA KOR -BNST pathway attenuated social stress-escalated alcohol consumption in both sexes.

Conclusion

Our results suggest a significant role for BLA KOR projections to the BNST in regulating social stress-escalated alcohol consumption. Our results provide further evidence that the Dyn/KOR system maybe a viable target for medications development to tareat comorbid stress and AUD.

Animal models for studying therapeutic targets and treatments for alcohol use disorder

Over the decades, preclinical models have been developed and refined to investigate the rewarding effects of addictive substances and the neurobiological underpinnings of alcohol and other drug use disorders. This chapter delves into the methodological foundations, advantages, and limitations of leading animal models used to study alcohol use disorders (AUDs). Some models focus on the early stages of alcohol use and abuse. For instance, conditioned place preference assesses associative learning between a specific context and the effects of the drug, while locomotor sensitization measures increased locomotor activity following repeated drug exposure. In contrast, contingent models such as operant and non-operant alcohol self-administration protocols gauge voluntary intake, preference, motivation, and seeking behavior for alcohol solutions among experimental subjects. Additionally, we discuss the chronic intermittent alcohol vapor model, extensively utilized to induce a phenotype resembling dependence through non-contingent inhalation of alcohol vapor, resulting in elevated blood alcohol concentrations. Given the focus on pharmacological treatments for AUDs, we explore how different animal models can be employed to evaluate potential therapies and extrapolate findings to alcohol-related behaviors in humans. This chapter aims to provide readers with a comprehensive understanding of various animal models for AUDs, aiding in the interpretation of preclinical studies and the selection of suitable models for future research endeavors.

The CRF/Urocortin systems as therapeutic targets for alcohol use disorders

Development and maintenance of alcohol use disorders have been proposed to recruit critical mechanisms involving Corticotropin Releasing Factor and Urocortins (CRF/Ucns). The CRF/Ucns system is comprised of a family of peptides (CRF, Ucn 1, Ucn 2, Ucn 3) which act upon two receptor subtypes, CRFR1 and CRFR2, each with different affinity profiles to the endogenous peptides and differential brain distribution. Activity of CRF/Ucn system is further modulated by CRF binding protein (CRF-BP), which regulates availability of CRF and Ucns to exert their actions. Extensive evidence in preclinical models support the involvement of CRF/Ucn targets in escalated alcohol drinking, as well as point to changes in CRF/Ucn brain function as a result of chronic alcohol exposure and/or withdrawal. It highlights the role of CRF and CRFR1-mediated signaling in conditions of excessive alcohol taking and seeking, including during various stages of withdrawal and relapse to alcohol. Besides its role in the hypothalamic-pituitary-adrenal (HPA) axis, the importance of extra-hypothalamic CRF pathways, especially in the extended amygdala, in the neurobiology of alcohol abuse and dependence is emphasized. Emerging roles for other targets of the CRF/Ucn system, such as CRF2 receptors, CRF-BP and Ucns in escalated alcohol drinking is also discussed. Finally, the limited translational value of CRF/Ucn interventions in stress-related and alcohol use disorders is discussed. So far, CRFR1 antagonists have shown little or no efficacy in human clinical trials, although a range of unexplored conditions and possibilities remain to be explored.

Alcohol exacerbates psychosocial stress-induced neuropsychiatric symptoms: Attenuation by geraniol

Adaptation to psychosocial stress is psychologically distressing, initiating/promoting comorbidity with alcohol use disorders. Emerging evidence moreover showed that ethanol (EtOH) exacerbates social-defeat stress (SDS)-induced behavioral impairments, neurobiological sequelae, and poor therapeutic outcomes. Hence, this study investigated the effects of geraniol, an isoprenoid monoterpenoid alcohol with neuroprotective functions on EtOH escalated SDS-induced behavioral impairments, and neurobiological sequelae in mice. Male mice chronically exposed to SDS for 14 days were repeatedly fed with EtOH (2 g/kg, p. o.) from days 8-14. From days 1-14, SDS-EtOH co-exposed mice were concurrently treated with geraniol (25 and 50 mg/kg) or fluoxetine (10 mg/kg) orally. After SDS-EtOH translational interactions, arrays of behavioral tasks were examined, followed by investigations of oxido-inflammatory, neurochemicals levels, monoamine oxidase-B and acetylcholinesterase activities in the striatum, prefrontal-cortex, and hippocampus. The glial fibrillary acid protein (GFAP) expression was also quantified in the prefrontal-cortex immunohistochemically. Adrenal weights, serum glucose and corticosterone concentrations were measured. EtOH exacerbated SDS-induced low-stress resilience, social impairment characterized by anxiety, depression, and memory deficits were attenuated by geraniol (50 and 100 mg/kg) and fluoxetine. In line with this, geraniol increased the levels of dopamine, serotonin, and glutamic-acid decarboxylase enzyme, accompanied by reduced monoamine oxidase-B and acetylcholinesterase activities in the prefrontal-cortex, hippocampus, and striatum. Geraniol inhibited SDS-EtOH-induced adrenal hypertrophy, corticosterone, TNF-α, IL-6 release, malondialdehyde and nitrite levels, with increased antioxidant activities. Immunohistochemical analyses revealed that geraniol enhanced GFAP immunoreactivity in the prefrontal-cortex relative to SDS-EtOH group. We concluded that geraniol ameliorates SDS-EtOH interaction-induced behavioral changes via normalization of neuroimmune-endocrine and neurochemical dysregulations in mice brains.

Diosgenin alleviates alcohol-mediated escalation of social defeat stress and the neurobiological sequalae

RATIONALE

Emerging evidence indicates that persistent alcohol consumption escalates psychosocial trauma achieved by social defeat stress (SDS)-induced neurobiological changes and behavioral outcomes. Treatment with compounds with neuroprotective functions is believed to reverse ethanol (EtOH)-aggravated SDS-induced behavioral impairments.

OBJECTIVES

We investigated the outcomes of diosgenin treatment, a phytosteroidal sapogenin in mice co-exposed to repeated SDS and EtOH administration.

METHODS

During a period of 14 days, SDS male mice were repeatedly administered EtOH (20%, 10 mL/kg) orally from days 8-14 (n = 9). Within days 1-14, SDS mice fed with EtOH were simultaneously treated with diosgenin (25 and 50 mg/kg) or fluoxetine (10 mg/kg) by oral gavage. Locomotor, cognitive-, depressive-, and anxiety-like behaviors were assessed. Adrenal weight, serum glucose, and corticosterone levels were assayed. Brain markers of oxido-inflammatory, neurochemical levels, monoamine oxidase-B, and acetylcholinesterase activities were measured in the striatum, prefrontal cortex, and hippocampus.

RESULTS

The anxiety-like behavior, depression, low stress resilience, social, and spatial/non-spatial memory decline exhibited by SDS mice exposed to repeated EtOH administration were alleviated by diosgenin (25 and 50 mg/kg) and fluoxetine, illustrated by increased dopamine and serotonin concentrations and reduced monoamine oxidase-B and acetylcholinesterase activities in the prefrontal cortex, hippocampus, and striatum. Diosgenin attenuated SDS + EtOH interaction induced corticosterone release and adrenal hypertrophy, accompanied by reduced TNF-α, IL-6, malondialdehyde, and nitrite levels in the striatum, prefrontal cortex, and hippocampus. Diosgenin increased glutathione, superoxide dismutase, and catalase levels in SDS + EtOH-exposed mice.

CONCLUSIONS

Our data suggest that diosgenin reverses SDS + EtOH interaction-induced behavioral changes via normalization of hypothalamic-pituitary-adrenal axis, neurochemical neurotransmissions, and inhibition of oxidative and inflammatory mediators in mice brains.

Gestational environmental enrichment prevents chronic social stress induced anxiety- and ethanol-related behaviors in offspring

Epidemiological surveys have shown a strong relationship between maternal stress and offspring's mood disorders. Growing evidence suggested that environmental enrichment (EE) improves cognitive function in models of psychiatric and neurological disorders. However, the potential protective effects of gestational EE on social stress-elicited mood disorders in offspring have not been studied. Knowing that the undeveloped brain is more sensitive to gestational environmental stimuli, we hypothesized that initiating cognitive stimulation, during gestation, would protect against social stress-induced behavioral alterations in adulthood. Therefore, the present study aimed to investigate the effects of gestational EE on social stress-elicited anxiety- and ethanol-related behaviors in adult offspring. EE consisted of free access, of dams, to tubular devices of different shapes, colors, and sizes that were changed regularly. After birth and weaning, young adult offspring were exposed to 19 days of social stress and anxiety-like behavior was evaluated by elevated plus maze, open field, and marbles burying tests. The two-bottle choice (TBC) drinking paradigm was used to assess stress-induced ethanol intake. Results showed that gestational EE prevented social stress-elicited anxiogenic-like effects with no differences in spontaneous locomotor activity. Moreover, in the TBC paradigm, mice pre-exposed to EE consistently showed a significantly decreased consumption and preference for ethanol with no effects on tastants' intakes. Interestingly, gestational EE increased serum BDNF levels, which showed a correlation with measures of anxiety- and ethanol-related behaviors. These findings indicate that some neurodevelopmental changes associated with prenatal EE may counteract adult social stress-induced behavioral alterations through a BDNF mechanism. Therefore, we propose that gestational EE has significant protective and beneficial effects on social stress-induced cognitive impairment. It can also alleviate anxiety-like behavior and subsequent excessive alcohol consumption.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) of the Bed Nucleus of the Stria Terminalis Mediates Heavy Alcohol Drinking in Mice

Alcohol use disorder (AUD) is a complex psychiatric disease characterized by periods of heavy drinking and periods of withdrawal. Chronic exposure to ethanol causes profound neuroadaptations in the extended amygdala, which cause allostatic changes promoting excessive drinking. The bed nucleus of the stria terminalis (BNST), a brain region involved in both excessive drinking and anxiety-like behavior, shows particularly high levels of pituitary adenylate cyclase-activating polypeptide (PACAP), a key mediator of the stress response. Recently, a role for PACAP in withdrawal-induced alcohol drinking and anxiety-like behavior in alcohol-dependent rats has been proposed; whether the PACAP system of the BNST is also recruited in other models of alcohol addiction and whether it is of local or nonlocal origin is currently unknown. Here, we show that PACAP immunoreactivity is increased selectively in the BNST of C57BL/6J mice exposed to a chronic, intermittent access to ethanol. While pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor-expressing cells were unchanged by chronic alcohol, the levels of a peptide closely related to PACAP, the calcitonin gene-related neuropeptide, were found to also be increased in the BNST. Finally, using a retrograde chemogenetic approach in PACAP-ires-Cre mice, we found that the inhibition of PACAP neuronal afferents to the BNST reduced heavy ethanol drinking. Our data suggest that the PACAP system of the BNST is recruited by chronic, voluntary alcohol drinking in mice and that nonlocally originating PACAP projections to the BNST regulate heavy alcohol intake, indicating that this system may represent a promising target for novel AUD therapies.

The Role of Corticotropin-Releasing Factor (CRF) and CRF-Related Peptides in the Social Behavior of Rodents

Since the corticotropin-releasing factor (CRF) was isolated from an ovine brain, a growing family of CRF-related peptides has been discovered. Today, the mammalian CRF system consists of four ligands (CRF, urocortin 1 (Ucn1), urocortin 2 (Ucn2), and urocortin 3 (Ucn3)); two receptors (CRF receptor type 1 (CRF1) and CRF receptor type 2 (CRF2)); and a CRF-binding protein (CRF-BP). Besides the regulation of the neuroendocrine, autonomic, and behavioral responses to stress, CRF and CRF-related peptides are also involved in different aspects of social behavior. In the present study, we review the experiments that investigated the role of CRF and the urocortins involved in the social behavior of rats, mice, and voles, with a special focus on sociability and preference for social novelty, as well as the ability for social recognition, discrimination, and memory. In general, these experiments demonstrate that CRF, Ucn1, Ucn2, and Ucn3 play important, but distinct roles in the social behavior of rodents, and that they are mediated by CRF1 and/or CRF2. In addition, we suggest the possible brain regions and pathways that express CRF and CRF-related peptides and that might be involved in social interactions. Furthermore, we also emphasize the differences between the species, strains, and sexes that make translation of these roles from rodents to humans difficult.

Glucocorticoid receptors regulate central amygdala GABAergic synapses in Marchigian-Sardinian alcohol-preferring rats

Impairments in the function of the hypothalamic-pituitary-adrenal (HPA) axis and enhanced glucocorticoid receptor (GR) activity in the central amygdala (CeA) are critical mechanisms in the pathogenesis of alcohol use disorder (AUD). The GR antagonist mifepristone attenuates craving in AUD patients, alcohol consumption in AUD models, and decreases CeA γ-aminobutyric acid (GABA) transmission in alcohol-dependent rats. Previous studies suggest elevated GR activity in the CeA of male alcohol-preferring Marchigian-Sardinian (msP) rats, but its contribution to heightened CeA GABA transmission driving their characteristic post-dependent phenotype is largely unknown. We determined Nr3c1 (the gene encoding GR) gene transcription in the CeA in male and female msP and Wistar rats using in situ hybridization and studied acute effects of mifepristone (10 μM) and its interaction with ethanol (44 mM) on pharmacologically isolated spontaneous inhibitory postsynaptic currents (sIPSCs) and electrically evoked inhibitory postsynaptic potentials (eIPSPs) in the CeA using ex vivo slice electrophysiology. Female rats of both genotypes expressed more CeA GRs than males, suggesting a sexually dimorphic GR regulation of CeA activity. Mifepristone reduced sIPSC frequencies (GABA release) and eIPSP amplitudes in msP rats of both sexes, but not in their Wistar counterparts; however, it did not prevent acute ethanol-induced increase in CeA GABA transmission in male rats. In msP rats, GR regulates CeA GABAergic signaling under basal conditions, indicative of intrinsically active GR. Thus, enhanced GR function in the CeA represents a key mechanism contributing to maladaptive behaviors associated with AUD.

Vicarious Social Defeat Increases Conditioned Rewarding Effects of Cocaine and Ethanol Intake in Female Mice

Stress is a critical factor in the development of mood and drug use disorders. The social defeat model is not appropriate for female rodents due to their low level of aggression. Therefore, a robust female model of social stress needs to be developed and validated. The aim of the present study was to unravel the long-lasting effects of vicarious social defeat (VSD) on the conditioned rewarding effects of cocaine and ethanol intake in female mice. Although VSD seems to be a good model for inducing behavioral and physiologic endophenotypes induced by stress, there are no studies to date that characterize the effect of VSD on cocaine or alcohol use. The results confirm that VSD females showed an increase in corticosterone levels after a vicarious experience while also displaying an increase in anxiety- and anhedonic-like behaviors. Three weeks after the last VSD, vicariously defeated female mice showed an increased developed preference for a non-effective dose of cocaine in the conditioned place preference (CPP) paradigm and showed an increase in ethanol intake. Our results suggest that female mice vicariously experience a state of distress through the social observation of others suffering from adverse events, confirming the use of VSD as a valid model to study the response to social stress in females. The fact that VSD in females induced a comparable behavioral phenotype to that observed in physically defeated males could indicate a relationship with the higher rate of psychopathologies observed in women. Notwithstanding, more studies are needed to dissect the neurobiological and behavioral peculiarities of the female response to social stress.

Corticotropin releasing factor and drug seeking in substance use disorders: Preclinical evidence and translational limitations

The neuropeptide, corticotropin releasing factor (CRF), has been an enigmatic target for the development of medications aimed at treating stress-related disorders. Despite a large body of evidence from preclinical studies in rodents demonstrating that CRF receptor antagonists prevent stressor-induced drug seeking, medications targeting the CRF-R1 have failed in clinical trials. Here, we provide an overview of the abundant findings from preclinical rodent studies suggesting that CRF signaling is involved in stressor-induced relapse. The scientific literature that has defined the receptors, mechanisms and neurocircuits through which CRF contributes to stressor-induced reinstatement of drug seeking following self-administration and conditioned place preference in rodents is reviewed. Evidence that CRF signaling is recruited with repeated drug use in a manner that heightens susceptibility to stressor-induced drug seeking in rodents is presented. Factors that may determine the influence of CRF signaling in substance use disorders, including developmental windows, biological sex, and genetics are examined. Finally, we discuss the translational failure of medications targeting CRF signaling as interventions for substance use disorders and other stress-related conditions. We conclude that new perspectives and research directions are needed to unravel the mysterious role of CRF in substance use disorders.

Excessive alcohol consumption after exposure to two types of chronic social stress: intermittent episodes vs. continuous exposure in C57BL/6J mice with a history of drinking

RATIONALE

The attraction to alcohol can be greatly increased when it is consumed in a social context. While pro-social interactions can potentiate voluntary alcohol drinking under some conditions, aversive social experience (i.e., social stress) can similarly intensify alcohol consumption.

OBJECTIVE

We sought to determine how exposure to different types of chronic social stress (i.e., intermittent episodes of social defeat or continuous social stress) influences alcohol consumption and the reinforcing effects of alcohol in mice with a history of drinking.

METHODS

Separate cohorts of male C57BL/6J mice were exposed to either 10 days of continuous or intermittent social defeat stress. In experiment 1, mice were assigned to 20% w/v alcohol consumption in a two-bottle choice protocol both prior to and after exposure to social defeat stress. In a second experiment, mice engaged in an operant response sequence to gain access to alcohol wherein completion of a fixed interval (FI; 5 min) schedule was reinforced with continuous access to alcohol (fixed ratio; FR1) for up to 1.8 g/kg. Alcohol-reinforced responding and subsequent alcohol consumption were assessed daily for 4 weeks prior to the 10-day social stress exposure and for 6-week post-stress. Machine learning was implemented to standardize the analysis of defeat behaviors exhibited by the intruder mouse during confrontation with an attacking resident.

RESULTS

In mice with a prior history of alcohol drinking, intermittent episodes of social defeat stress produced a significant increase in 20% EtOH consumption in preference over concurrently available water. This increased intake persisted for at least 6 weeks after the final social stress experience. Intermittently stressed mice also accelerated their anticipatory responding during the fixed interval component of the operant response chain that was reinforced by alcohol. Neither unstressed controls nor mice exposed to continuous social stress exhibited significant increases in alcohol consumption and alcohol reinforcement.

DISCUSSION

Episodic social defeat stress promotes the seeking and consumption of alcohol, extending earlier work to alcohol-experienced mice. We hypothesize that intermittent access to alcohol and intermittent episodes of social stress are additive and share common sensitizing neural mechanisms that engender excessive alcohol consumption.

Chronic, but not sub-chronic, stress increases binge-like alcohol consumption in male and female c57BL6 mice

Stress is known to contribute to mental illness and alcohol use disorders, which are highly prevalent and lead to considerable disability. These stress-related disorders are characterized by significant sex differences, which remain poorly understood. Preclinical research comparing the effects of stress in males and females has the potential to provide new insights into the neurobiology of these conditions. The current study compared the effects of chronic and sub-chronic exposure to variable environmental stressors on binge-like alcohol consumption using the drinking-in-the-dark model in male and female c57BL6 mice. The results reveal that chronic, but not sub-chronic, exposure to variable stress increases alcohol intake in both sexes. Stress-induced alterations in gene expression were also compared in the nucleus accumbens, a brain region widely known to play a key role in stress susceptibility and reward processing. Real-time PCR data indicate that chronic, but not sub-chronic, environmental stress leads to downregulation of adenosine 2A (A2A) receptor mRNA. By contrast, sub-chronic stress increased CREB expression, while chronic stress did not. Several sex differences in the effects of stress on gene expression were also noted. Our results demonstrate that reductions in A2A receptor mRNA in the nucleus accumbens are associated with the increased binge drinking of chronically stressed animals, but future work will be required to determine the functional importance of this gene expression change. Continuing to define the molecular alterations associated with stress-induced increases in alcohol intake has the potential to provide insights into the development and progression of stress-related disorders.

Challenges in the use of animal models and perspectives for a translational view of stress and psychopathologies

The neurobiology and development of treatments for stress-related neuropsychiatric disorders rely heavily on animal models. However, the complexity of these disorders makes it difficult to model them entirely, so only specific features of human psychopathology are emulated and these models should be used with great caution. Importantly, the effects of stress depend on multiple factors, like duration, context of exposure, and individual variability. Here we present a review on pre-clinical studies of stress-related disorders, especially those developed to model posttraumatic stress disorder, major depression, and anxiety. Animal models provide relevant evidence of the underpinnings of these disorders, as long as face, construct, and predictive validities are fulfilled. The translational challenges faced by scholars include reductionism and anthropomorphic/anthropocentric interpretation of the results instead of a more naturalistic and evolutionary understanding of animal behavior that must be overcome to offer a meaningful model. Other limitations are low statistical power of analysis, poor evaluation of individual variability, sex differences, and possible conflicting effects of stressors depending on specific windows in the lifespan.

Sex differences in stress-induced alcohol intake: a review of preclinical studies focused on amygdala and inflammatory pathways

Clinical studies suggest that women are more likely than men to relapse to alcohol drinking in response to stress; however, the mechanisms underlying this sex difference are not well understood. A number of preclinical behavioral models have been used to study stress-induced alcohol intake. Here, we review paradigms used to study effects of stress on alcohol intake in rodents, focusing on findings relevant to sex differences. To date, studies of sex differences in stress-induced alcohol drinking have been somewhat limited; however, there is evidence that amygdala-centered circuits contribute to effects of stress on alcohol seeking. In addition, we present an overview of inflammatory pathways leading to microglial activation that may contribute to alcohol-dependent behaviors. We propose that sex differences in neuronal function and inflammatory signaling in circuits centered on the amygdala are involved in sex-dependent effects on stress-induced alcohol seeking and suggest that this is an important area for future studies.

Friend of the Devil: Negative Social Influences Driving Substance Use Disorders

Substance use disorders in humans have significant social influences, both positive and negative. While prosocial behaviors promote group cooperation and are naturally rewarding, distressing social encounters, such as aggression exhibited by a conspecific, are aversive and can enhance the sensitivity to rewarding substances, promote the acquisition of drug-taking, and reinstate drug-seeking. On the other hand, withdrawal and prolonged abstinence from drugs of abuse can promote social avoidance and suppress social motivation, accentuating drug cravings and facilitating relapse. Understanding how complex social states and experiences modulate drug-seeking behaviors as well as the underlying circuit dynamics, such as those interacting with mesolimbic reward systems, will greatly facilitate progress on understanding triggers of drug use, drug relapse and the chronicity of substance use disorders. Here we discuss some of the common circuit mechanisms underlying social and addictive behaviors that may underlie their antagonistic functions. We also highlight key neurochemicals involved in social influences over addiction that are frequently identified in comorbid psychiatric conditions. Finally, we integrate these data with recent findings on (±)3,4-methylenedioxymethamphetamine (MDMA) that suggest functional segregation and convergence of social and reward circuits that may be relevant to substance use disorder treatment through the competitive nature of these two types of reward. More studies focused on the relationship between social behavior and addictive behavior we hope will spur the development of treatment strategies aimed at breaking vicious addiction cycles.

Alcohol dependence and withdrawal increase sensitivity of central amygdalar GABAergic synapses to the glucocorticoid receptor antagonist mifepristone in male rats

Aberrant glucocorticoid signaling via glucocorticoid receptors (GR) plays a critical role in alcohol use disorder (AUD). Acute alcohol withdrawal and protracted abstinence in dependent rats are associated with increased GR signaling and changes in GR-mediated transcriptional activity in the rat central nucleus of the amygdala (CeA). The GR antagonist mifepristone decreases alcohol consumption in dependent rats during acute withdrawal and protracted abstinence. Regulation of CeA synaptic activity by GR is currently unknown. Here, we utilized mifepristone and the selective GR antagonist CORT118335 (both at 10 μM) as pharmacological tools to dissect the role of GR on GABA transmission in male, adult Sprague-Dawley rats using slice electrophysiology. We subjected rats to chronic intermittent alcohol vapor exposure for 5–7 weeks to induce alcohol dependence. A subset of dependent rats subsequently underwent protracted alcohol withdrawal for 2 weeks, and air-exposed rats served as controls. Mifepristone reduced the frequency of pharmacologically-isolated spontaneous inhibitory postsynaptic currents (sIPSC) in the CeA (medial subdivision) without affecting postsynaptic measures in all groups, suggesting decreased GABA release with the largest effect in dependent rats. CORT118335 did not significantly alter GABA transmission in naive, but decreased sIPSC frequency in dependent rats. Similarly, mifepristone decreased amplitudes of evoked inhibitory postsynaptic potentials only in dependent rats and during protracted withdrawal. Collectively, our study provides insight into regulation of CeA GABAergic synapses by GR. Chronic ethanol enhances the efficiency of mifepristone and CORT118335, thus highlighting the potential of drugs targeting GR as a promising pharmacological avenue for the treatment of AUD.

Neurobiological Bases of Alcohol Consumption After Social Stress

The urge to seek and consume excessive alcohol is intensified by prior experiences with social stress, and this cascade can be modeled under systematically controlled laboratory conditions in rodents and non-human primates. Adaptive coping with intermittent episodes of social defeat stress often transitions to maladaptive responses to traumatic continuous stress, and alcohol consumption may become part of coping responses. At the circuit level, the neural pathways subserving stress coping intersect with those for alcohol consumption. Increasingly discrete regions and connections within the prefrontal cortex, the ventral and dorsal striatum, thalamic and hypothalamic nuclei, tegmental areas as well as brain stem structures begin to be identified as critical for reacting to and coping with social stress while seeking and consuming alcohol. Several candidate molecules that modulate signals within these neural connections have been targeted in order to reduce excessive drinking and relapse. In spite of some early clinical failures, neuropeptides such as CRF, opioids, or oxytocin continue to be examined for their role in attenuating stress-escalated drinking. Recent work has focused on neural sites of action for peptides and steroids, most likely in neuroinflammatory processes as a result of interactive effects of episodic social stress and excessive alcohol seeking and drinking.

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.

Maternal Separation Stress Affects Voluntary Ethanol Intake in a Sex Dependent Manner

Maternal separation (MS) stress is a predictive animal model for evaluating the effects of early stress exposure on alcohol use disorders (AUD). The extended amygdala (AMY) is a complex circuit involved in both stress- and ethanol-related responses. We hypothesized that MS stress may increase ethanol consumption in adulthood, as well as augment neuronal activity in extended AMY, in a sex-dependent manner. We aimed to investigate the influence of MS stress on the ethanol consumption of male and female mice, and the involvement of extended amygdala sub-nuclei in this process. The C57BL/6J pups were subjected to 180min of MS, from postnatal day (PND) 1 to 14. The control group was left undisturbed. On PND 45, mice (n=28) in cages were exposed to a bottle containing 20% ethanol (w/v) for 4h during the dark period of the light-dark cycle, for 3weeks. Afterward, mice underwent ethanol self-administration training in operant chambers under fixed ratio (FR) schedule. Then, subjects were tested under 2h sessions of a progressive-ratio (PR) schedule of reinforcement (the last ratio achieved was considered the breaking point), and at the end, a 4h session of FR schedule (binge-intake). An immunohistochemistry assay for Fos protein was performed in Nucleus Accumbens (NAcc), Bed Nucleus of Stria Terminalis (BNST), and AMY. Our results showed that in the third week of training, the female MS group consumed more ethanol than the respective control group. The MS group presented increased breakpoint parameters. Female control group and male MS group were more resistant to bitter quinine taste. Increased Fos-immunoreactive neurons (Fos-IR) were observed in the central nucleus of AMY, but not in NAcc nor BNST in male maternal-separated mice. Maternal separation stress may influence ethanol intake in adulthood, and it is dependent on the sex and reinforcement protocol.

Ethanol intake in male mice exposed to social defeat: Environmental enrichment potentiates resilience

Large preclinical evidence shows that exposure to social defeat (SD) increases vulnerability to drug abuse, increasing the consumption of ethanol. However, not all subjects are equally affected by the changes induced by stress. Previous reports have evidenced that the resilient phenotype to depressive-like behaviors after SD is associated with the resistant phenotype to cocaine-increased rewarding effects and the smaller neuroinflammatory response. The aim of the present study was to further clarify whether the resilient profile to depressive-like behavior also predicts a protection against the increase in ethanol intake induced by SD. The neuroinflammatory profile was studied after the end of the oral ethanol self-administration (SA) procedure, measuring levels of the pro-inflammatory cytokine IL-6 and the chemokine CX3CL1 or fractalkine in the striatum and prefrontal cortex. Previous studies have shown that environmental enrichment (EE) is an effective mechanism to dimish the detrimental effects of social stress. In a second study, we aimed to evaluate if EE housing before exposure to SD could potentiate resilience. Our results showed that mice with a phenotype susceptible to SD-induced depressive-like behaviors showed increased ethanol consumption and increased neuroinflammatory signaling. In contrast, despite the lack of effect on depressive-like behaviors, defeated mice previously housed under EE conditions did not show an increase in ethanol SA or an increase in immune response. To sum up, the resilient phenotype to SD develops at different levels, such as depressive-like behaviors, ethanol consumption and the neuroinflammatory response. Our results also point to the protective role of EE in potentiating resilience to SD effects.

Hypoactive Thalamic Crh+ Cells in a Female Mouse Model of Alcohol Drinking After Social Trauma

BACKGROUND

Comorbid stress-induced mood and alcohol use disorders are increasingly prevalent among female patients. Stress exposure can disrupt salience processing and goal-directed decision making, contributing to persistent maladaptive behavioral patterns; these and other stress-sensitive cognitive and behavioral processes rely on dynamic and coordinated signaling by midline and intralaminar thalamic nuclei. Considering the role of social trauma in the trajectory of these debilitating psychopathologies, identifying vulnerable thalamic cells may provide guidance for targeting persistent stress-induced symptoms.

METHODS

A novel behavioral protocol traced the progression from social trauma to the development of social defensiveness and chronically escalated alcohol consumption in female mice. Recent cell activation-measured as cFos-was quantified in thalamic cells after safe social interactions, revealing stress-sensitive corticotropin-releasing hormone-expressing (Crh+) anterior central medial thalamic (aCMT) cells. These cells were optogenetically stimulated during stress-induced social defensiveness and abstinence-escalated binge drinking.

RESULTS

Crh+ aCMT neurons exhibited substantial activation after social interactions in stress-naïve but not in stressed female mice. Photoactivating Crh+ aCMT cells dampened stress-induced social deficits, whereas inhibiting these cells increased social defensiveness in stress-naïve mice. Optogenetically activating Crh+ aCMT cells diminished abstinence-escalated binge alcohol drinking in female mice, regardless of stress history.

CONCLUSIONS

This work uncovers a role for Crh+ aCMT neurons in maladaptive stress-induced social interactions and in binge drinking after forced abstinence in female mice. This molecularly defined thalamic cell population may serve as a critical stress-sensitive hub for social deficits caused by exposure to social trauma and for patterns of excessive alcohol drinking in female populations.

Glutamate transporter-1 link astrocytes with heightened aggressive behavior induced by steroid abuse in male CF1 mice

The astrocytic glutamate transporter GLT-1 performs glutamate uptake thereby mediating NMDAr responses in neurons. Ceftriaxone (CEF) upregulates astrocytic GLT-1 expression/activity, which could counteract excessive glutamate levels and aggressive behavior induced by anabolic synthetic steroids such as nandrolone decanoate (ND). Here, adult male CF-1 mice were allocated to oil (VEH), ND, CEF, and ND/CEF groups. Mice were subcutaneously (s.c.) injected with ND (15 mg/kg) or VEH for 19 days, and received intraperitoneal (i.p.) injections of CEF (200 mg/kg) or saline for 5 days. The ND/CEF group received ND for 19 days plus coadministration of CEF in the last 5 days. On the 19th day, the aggressive phenotypes were evaluated through the resident-intruder test. After 24 h, cerebrospinal fluid was collected to measure glutamate levels, and the pre-frontal cortex was used to assess GLT-1, pGluN2B^Tyr1472, and pGluN2A^Tyr1246 by Western blot. Synaptosomes from the left brain hemisphere was used to evaluate mitochondrial function including complex II-succinate dehydrogenase (SDH), Ca²⁺ handling, membrane potential (ΔѰ_m), and H₂O₂ production. ND decreased the latency for the first attack and increased the number of attacks by the resident mice against the intruder, mechanistically associated with an increase in glutamate levels and pGluN2B^Tyr1472 but not pGluN2A^Tyr1244, and GLT-1 downregulation. The abnormalities in mitochondrial Ca²⁺ influx, SDH, ΔѰ_m, and H₂O₂ implies in deficient energy support to the synaptic machinery. The ND/CEF group displayed a decreased aggressive behavior, normalization of glutamate and pGluN2B^Tyr1472levels, and mitochondrial function at synaptic terminals. In conclusion, the pharmacological modulation of GLT-1 highlights its relevance as an astrocytic target against highly impulsive and aggressive phenotypes.

Oxytocin reverses ethanol consumption and neuroinflammation induced by social defeat in male mice

Oxytocin (OXT) modulates social interactions, attenuates stressful responses and can decrease drug-seeking and taking behaviors. In previous studies, we observed that social defeat (SD) induced a long-lasting increase in ethanol intake and neuroinflammation in male mice. We also know that OXT blocks the increase in cocaine reward induced by SD. Therefore, in the present study we aimed to evaluate the effect of 1 mg/kg of OXT administered 30 min before each episode of SD on ethanol consumption and the neuroinflammatory response in adult male mice. Three weeks after the last SD, mice underwent oral ethanol self-administration (SA) procedure, and striatal levels of the two chemokines CX3CL1 and CXCL12 were measured after the last SD and at the end of the ethanol SA. OXT administration blocked the increase in voluntary ethanol consumption observed in defeated mice, although it did not affect motivation for ethanol. An increase in the striatal levels of CX3CL1 and CXCL12 was observed in defeated animals immediately after the last defeat and after the ethanol SA. However, defeated mice treated with OXT did not show this increase in the neuroinflammatory response. In conclusion, OXT treatment can be a powerful therapeutic target to reduce the negative effects of social stress on ethanol consumption and the neuroinflammatory process.

Beclin1 haploinsufficiency rescues low ambient temperature-induced cardiac remodeling and contractile dysfunction through inhibition of ferroptosis and mitochondrial injury

OBJECTIVE

Cold exposure provokes cardiac remodeling and cardiac dysfunction. Autophagy participates in cold stress-induced cardiovascular dysfunction. This study was designed to examine the impact of Beclin1 haploinsufficiency (BECN^+/-) in cold stress-induced cardiac geometric and contractile responses.

METHODS AND MATERIALS

Wild-type (WT) and BECN^+/- mice were assigned to normal or cold exposure (4 °C) environment for 4 weeks prior to evaluation of cardiac geometry, contractile and mitochondrial properties. Autophagy, apoptosis and ferroptosis were evaluated.

RESULTS

Our data revealed that cold stress triggered cardiac remodeling, compromised myocardial contractile capacity including ejection fraction, fractional shortening, peak shortening and maximal velocity of shortening/relengthening, duration of shortening and relengthening, intracellular Ca²⁺ release, intracellular Ca²⁺ decay, mitochondrial ultrastructural disarray, superoxide production, unchecked autophagy, apoptosis and ferroptosis, the effects of which were negated by Beclin1 haploinsufficiency. Circulating levels of corticosterone were elevated in both WT and BECN^+/- mice. Treatment of corticosterone synthesis inhibitor metyrapone or ferroptosis inhibitor liproxstatins-1 rescued cold stress-induced cardiac dysfunction and mitochondrial injury. In vitro study noted that corticosterone challenge compromised cardiomyocyte function, provoked lipid peroxidation and mitochondrial injury, the effects of which were nullified by Beclin1 haploinsufficiency, inhibitors of lipoxygenase, ferroptosis and autophagy. In addition, ferroptosis inducer erastin abrogated Beclin1 deficiency-offered cardioprotection.

CONCLUSION

These data suggest that Beclin1 haploinsufficiency protects against cold exposure-induced cardiac dysfunction possibly through corticosterone- and ferroptosis-mediated mechanisms.

The Sigma-2 receptor / transmembrane protein 97 (σ2R/TMEM97) modulator JVW-1034 reduces heavy alcohol drinking and associated pain states in male mice

Alcohol Use Disorder (AUD) is a chronic relapsing disorder characterized by compulsive alcohol intake, loss of control over alcohol intake, and a negative emotional state when access to alcohol is prevented. AUD is also closely tied to pain, as repeated alcohol drinking leads to increased pain sensitivity during withdrawal. The sigma-2 receptor, recently identified as transmembrane protein 97 (σ2R/TMEM97), is an integral membrane protein involved in cholesterol homeostasis and lipid metabolism. Selective σ2R/Tmem97 modulators have been recently shown to relieve mechanical hypersensitivity in animal models of neuropathic pain as well as to attenuate alcohol withdrawal signs in C. elegans and to reduce alcohol drinking in rats, suggesting a potential key role for this protein in alcohol-related behaviors. In this study, we tested the effects of a potent and selective σ2R/TMEM97 ligand, JVW-1034, on heavy alcohol drinking and alcohol-induced heightened pain states in mice using an intermittent access model. Administration of JVW-1034 decreased both ethanol intake and preference for ethanol, without affecting water intake, total fluid intake, or food intake. Notably, this effect was specific for alcohol, as JVW-1034 had no effect on sucrose intake. Furthermore, JVW-1034 reduced both thermal hyperalgesia and mechanical hypersensitivity in ethanol withdrawn mice. Our data provide important evidence that modulation of σ2R/TMEM97 with small molecules can mediate heavy alcohol drinking as well as chronic alcohol-induced heightened pain sensitivity, thereby identifying a promising novel pharmacological target for AUD and associated pain states.

Depression and substance use disorders: Clinical comorbidity and shared neurobiology

Mood disorders, including major depressive disorder (MDD), are the most prevalent psychiatric illnesses, and pose an incredible burden to society, both in terms of disability and in terms of costs associated with medical care and lost work time. MDD has extremely high rates of comorbidity with substance use disorders (SUD) as many of the same neurobiological circuits and molecular mechanisms regulate the reward pathways disrupted in both conditions. MDD may induce SUDs, SUD may contribute to MDD development, or underlying vulnerabilities and common life experience may confer risk to developing both conditions. In this chapter we explore theories of MDD and SUD comorbidity, the neurobiological underpinnings of depression, overlapping cellular and molecular pathways for both conditions, and current treatment approaches for these comorbid conditions.

The neural, behavioral, and epidemiological underpinnings of comorbid alcohol use disorder and post-traumatic stress disorder

Alcohol use disorder (AUD) and (PTSD) frequently co-occur and individuals suffering from this dual diagnosis often exhibit increased symptom severity and poorer treatment outcomes than those with only one of these diseases. Although there have been significant advances in our understanding of the neurobiological mechanisms underlying each of these disorders, the neural underpinnings of the comorbid condition remain poorly understood. This chapter summarizes recent epidemiological findings on comorbid AUD and PTSD, with a focus on vulnerable populations, the temporal relationship between these disorders, and the clinical consequences associated with the dual diagnosis. We then review animal models of the comorbid condition and emerging human and non-human animal research that is beginning to identify maladaptive neural changes common to both disorders, primarily involving functional changes in brain reward and stress networks. We end by proposing a neural framework, based on the emerging field of affective valence encoding, that may better explain the epidemiological and neural findings on AUD and PTSD.

Critical role of TLR4 in uncovering the increased rewarding effects of cocaine and ethanol induced by social defeat in male mice

BACKGROUND

Substance use disorders and social stress are currently associated with changes in the immune system response by which they induce a proinflammatory state in neurons and glial cells that eventually modulates the reward system.

AIMS

The aim of the present work was to assess the role of the immune TLR4 (Toll-like receptors 4) and its signaling response in the increased contextual reinforcing effects of cocaine and reinforcing effects of ethanol (EtOH) induced by social defeat (SD) stress.

METHODS

Adult male C57BL/6 J wild-type (WT) mice and mice deficient in TLR4 (TLR4-KO) were assigned to experimental groups according to stress condition (exploration or SD). Three weeks after the last SD, conditioned place preference (CPP) was induced by a subthreshold cocaine dose (1 mg/kg), while another set underwent EtOH 6% operant self-administration (SA). Several inflammatory molecules were analyzed in the hippocampus and the striatum.

RESULTS

SD induced higher vulnerability to the conditioned rewarding effects of cocaine only in defeated WT mice. Similarly, defeated WT mice exhibited higher 6% EtOH consumption, an effect that was not observed in the defeated TLR4-KO group. However, the motivation to obtain the drug was observed in both genotypes of defeated animals. Notably, a significant upregulation of the protein proinflammatory markers NFkBp-p65, IL-1β, IL-17 A and COX-2 were observed only in the defeated WT mice, but not in their defeated TLR4-KO counterparts.

CONCLUSIONS

These results suggest that TLR4 receptors mediate the neuroinflammatory response underlying the increase in the rewarding effects of cocaine and EtOH induced by social stress.

Bidirectional Control of Alcohol-drinking Behaviors Through Locus Coeruleus Optoactivation

The relationship between stress and alcohol-drinking behaviors has been intensively explored; however, neuronal substrates and neurotransmitter dynamics responsible for a causal link between these conditions are still unclear. Here, we optogenetically manipulated locus coeruleus (LC) norepinephrine (NE) activity by applying distinct stimulation protocols in order to explore how phasic and tonic NE release dynamics control alcohol-drinking behaviors. Our results clearly demonstrate contrasting behavioral consequences of LC-NE circuitry activation during low and high frequency stimulation. Specifically, applying tonic stimulation during a standard operant drinking session resulted in increased intake, while phasic stimulation decreased this measure. Furthermore, stimulation during extinction probe trials, when the lever press response was not reinforced, did not significantly alter alcohol-seeking behavior if a tonic pattern was applied. However, phasic stimulation substantially suppressed the number of lever presses, indicating decreased alcohol seeking under the same experimental condition. Given the well-established correlative link between stress and increased alcohol consumption, here we provide the first evidence that tonic LC-NE activity plays a causal role in stress-associated increases in drinking.

Voluntary wheel running protects against the increase in ethanol consumption induced by social stress in mice

Previous studies have shown that exposure to social defeat (SD), a model of social stress, produces a long-term increase in the consumption of ethanol, most likely through an increase in the neuroinflammation response. The aim of the present study was to evaluate whether exposure to physical activity in the form of voluntary wheel running (VWR) could block the increase in ethanol consumption and the neuroinflammatory response induced by social stress. Mice were exposed to either 4 sessions of repeated social defeat (RSD) or a non-stressful experience. During the whole procedure, half of the mice were exposed to controlled physical activity, being allowed 1 h access to a low-profile running wheel three times a week. Three weeks after the last RSD, animals started the oral self-administration (SA) of ethanol (6% EtOH) procedure. Biological samples were taken 4 h after the first and the fourth RSD, 3 weeks after the last RSD, and after the SA procedure. Brain tissue (striatum) was used to determine protein levels of the chemokines fractalkine (CX3CL1) and SDF-1 (CXCL12). RSD induced an increase in ethanol consumption and caused greater motivation to obtain ethanol. The striatal levels of CX3CL1 and CXCL12 were also increased after the last RSD. VWR was able to reverse the increase in ethanol intake induced by social stress and the neuroinflammatory response. In conclusion, our results suggest that VWR could be a promising tool to prevent and reduce the detrimental effects induced by social stress.

Non-pharmacological factors that determine drug use and addiction

Based on their pharmacological properties, psychoactive drugs are supposed to take control of the natural reward system to finally drive compulsory drug seeking and consumption. However, psychoactive drugs are not used in an arbitrary way as pure pharmacological reinforcement would suggest, but rather in a highly specific manner depending on non-pharmacological factors. While pharmacological effects of psychoactive drugs are well studied, neurobiological mechanisms of non-pharmacological factors are less well understood. Here we review the emerging neurobiological mechanisms beyond pharmacological reinforcement which determine drug effects and use frequency. Important progress was made on the understanding of how the character of an environment and social stress determine drug self-administration. This is expanded by new evidence on how behavioral alternatives and opportunities for drug instrumentalization generate different patterns of drug choice. Emerging evidence suggests that the neurobiology of non-pharmacological factors strongly determines pharmacological and behavioral drug action and may, thus, give rise for an expanded system's approach of psychoactive drug use and addiction.

Environmental enrichment decreases chronic psychosocial stress-impaired extinction and reinstatement of ethanol conditioned place preference in C57BL/6 male mice

RATIONALE

During the last few decades, alcohol use disorders (AUD) have reached an epidemic prevalence, yet social influences on alcoholism have not been fully addressed. Several factors can modulate alcohol intake. On one hand, stress can reinforce ethanol-induced behaviors and be an important component in AUD and alcoholism. On the other hand, environmental enrichment (EE) has a neuroprotective role and prevents the development of excessive ethanol intake in rodents. However, studies showing the role of EE in chronic psychosocial stress-impaired ethanol-conditioned rewards are nonexistent.

AIM

The purpose of the current study is to explore the potential protective role of EE on extinction and reinstatement of ethanol-conditioned place preference (EtOH-CPP) following chronic psychosocial stress.

METHODS

In the first experiment and after the EtOH-CPP test, the mice were subjected to 15 days of chronic stress, then housed in a standard (SE) or enriched environment (EE) while EtOH-CPP extinction was achieved by repeated exposure to the CPP chambers without ethanol injection. In the second experiment and after the EtOH-CPP test, extinction was achieved as described above. Mice were then exposed to chronic stress for 2 weeks before being housed in a SE or EE. EtOH-CPP reinstatement was induced by a single exposure to the conditioning chambers.

RESULTS

As expected, stress exposure increased anxiety-like behavior and reduced weight gain. More importantly, we found that EE significantly shortened chronic stress-delayed extinction and decreased the reinstatement of EtOH-CPP.

CONCLUSION

These results support the hypothesis that EE reduces the impact of alcohol-associated environmental stimuli, and hence it may be a general intervention for reducing cue-elicited craving and relapse in humans.

Intermittent Ethanol Access Increases Sensitivity to Social Defeat Stress

BACKGROUND

Comorbidity between alcoholism and depression is extremely common. Recent evidence supports a relationship between alcohol exposure and stress sensitivity, an underlying factor in the development of depression. Our laboratory has recently shown that chronic alcohol gavage increases sensitivity to social defeat stress (SDS). However, the effects of voluntary alcohol consumption, resulting from protocols such as intermittent ethanol access (IEA), on defeat stress sensitivity have yet to be elucidated.

METHODS

We first assessed the effects of 4 weeks of IEA to 20% alcohol on sensitivity to subthreshold SDS exposure. Next, to examine neuroinflammatory mechanisms, we analyzed gene expression of inhibitor of NFkB (IkB) following IEA or chronic alcohol exposure (10 days of 3.0 g/kg alcohol via intragastric gavage). Then, we quantified NFkB activation via β-galactosidase immunohistochemistry following IEA or chronic alcohol gavage in NFkB-LacZ mice.

RESULTS

IEA-exposed mice displayed an increase in sensitivity to subthreshold SDS compared to water-drinking controls. We also found that IkB gene expression was decreased in the nucleus accumbens (NAC) and amygdala (AMY) following IEA but was not altered following chronic alcohol gavage. Finally, we observed increased NFkB activity in the central amygdala (CEA), basolateral amygdala (BLA), and medial amygdala (MEA) after IEA, and increased NFkB activity solely in the CEA following chronic alcohol gavage.

CONCLUSIONS

These findings further corroborate that prior alcohol exposure, in this case intermittent voluntary consumption, can impact development of depressive-like behavior by altering stress sensitivity. Furthermore, our results suggest the CEA as a potential mediator of alcohol's effects on stress sensitivity, as NFkB was activated in this region following both IEA and chronic alcohol gavage. Thus, this study provides novel insight on alterations in the NFkB pathway and identifies specific regions to target in future experiments assessing the functional role of NFkB in these processes.

The role of central amygdala corticotropin-releasing factor in predator odor stress-induced avoidance behavior and escalated alcohol drinking in rats

Post-traumatic stress disorder (PTSD) is characterized by avoidance of trauma-associated stimuli and amygdala hyperreactivity, and is highly co-morbid with alcohol use disorder (AUD). Our lab uses a predator odor (bobcat urine) stress model that produces conditioned avoidance of an odor-paired context in a subset of rats, mirroring avoidance symptoms that manifest in some but not all humans exposed to trauma. We previously showed that after predator odor stress, Avoiders exhibit escalated operant alcohol self-administration (SA), higher aversion-resistant operant alcohol responding, hyperalgesia, and greater anxiety-like behavior compared to unstressed Controls. We also showed previously that systemic antagonism of corticotropin-releasing factor-1 receptors (CRFR1) reduced escalation of operant alcohol SA in rats not indexed for avoidance, that corticotropin-releasing factor (CRF) infusions into the central amygdala (CeA) produced conditioned place avoidance in stress-naïve rats, and that intra-CeA infusion of a CRFR1 antagonist reduced hyperalgesia in Avoiders. Here, we show that avoidance behavior is persistent after repeated predator odor exposure. In addition, Avoiders showed lower weight gain than Controls after predator odor re-exposure. In the brain, higher avoidance was correlated with higher number of c-Fos + cells and CRF immunoreactivity in the CeA. Finally, we show that intra-CeA CRFR1 antagonism reversed post-stress escalation of alcohol SA and reduced avoidance behavior in Avoiders. Collectively, these findings suggest that elucidation of the mechanisms by which CRFR1-gated CeA circuits regulate avoidance behavior and alcohol SA may lead to better understanding of the neural mechanisms underlying co-morbid PTSD and AUD.

Biobehavioral Interactions Between Stress and Alcohol

In this review, the effects of stress on alcohol drinking are discussed. The interactions between biological stress systems and alcohol drinking are examined, with a focus on the hypothalamic pituitary adrenal axis, corticotropin releasing factor, dynorphin, neuropeptide Y, and norepinephrine systems. Findings from animal models suggest that these biological stress systems may be useful targets for medications development for alcohol use disorder and co-occurring stress-related disorders in humans.

Predator odor stress blunts alcohol conditioned aversion

Alcohol use disorder is highly co-morbid with traumatic stress disorders in humans, and dually diagnosed individuals cite negative affective symptoms as a primary reason for drinking alcohol. Therefore, it is reasonable to hypothesize that traumatic stress history increases the rewarding properties and/or blunts the aversive properties of alcohol. We used a place conditioning procedure to test the rewarding/aversive properties of alcohol in adult male Wistar rats with or without a traumatic stress (i.e., predator odor exposure) history, and with or without an alcohol drinking history. Because extended amygdala regions have documented roles in stress, reward, and stress-induced changes in reward, we also tested the effect of acute alcohol on CREB phosphorylation (pCREB) and striatal-enriched protein tyrosine phosphatase (STEP) expression in central amygdala (CeA) and bed nucleus of stria terminalis (BNST). Our results show that a moderate alcohol dose (1.0 g/kg) produces conditioned place aversion (CPA) that is blunted by stress history but is not affected by alcohol drinking history, and this effect differed in pair-housed versus single-housed rats. Stress history reduced pCREB expression in BNST of rats with and without an alcohol drinking history. Finally, acute alcohol effects on pCREB and STEP expression in CeA were positively associated with preference for the alcohol-paired chamber. These data suggest that stress history reduces the aversive properties of moderate alcohol doses, and that alcohol aversion is associated with acute alcohol effects on pCREB and STEP expression in the extended amygdala.

Social defeat stress and escalation of cocaine and alcohol consumption: Focus on CRF

Both the ostensibly aversive effects of unpredictable episodes of social stress and the intensely rewarding effects of drugs of abuse activate the mesocorticolimbic dopamine systems. Significant neuroadaptations in interacting stress and reward neurocircuitry may underlie the striking connection between stress and substance use disorders. In rodent models, recurring intermittent exposure to social defeat stress appears to produce a distinct profile of neuroadaptations that translates most readily to the repercussions of social stress in humans. In the present review, preclinical rodent models of social defeat stress and subsequent alcohol, cocaine or opioid consumption are discussed with regard to: (1) the temporal pattern of social defeat stress, (2) male and female protocols of social stress-escalated drug consumption, and (3) the neuroplastic effects of social stress, which may contribute to escalated drug-taking. Neuroadaptations in corticotropin-releasing factor (CRF) and CRF modulation of monoamines in the ventral tegmental area and the bed nucleus of the stria terminalis are highlighted as potential mechanisms underlying stress-escalated drug consumption. However, the specific mechanisms that drive CRF-mediated increases in dopamine require additional investigation as do the stress-induced neuroadaptations that may contribute to the development of compulsive patterns of drug-taking.