Sensitivity and Resilience to Predator Stress-Enhanced Ethanol Drinking Is Associated With Sex-Dependent Differences in Stress-Regulating Systems

Role of microglia in stress-induced alcohol intake in female and male mice

Rates of alcohol use disorder (AUD) have escalated in recent years, with a particular increase among women. Women are more susceptible to stress-induced alcohol drinking, and preclinical data suggest that stress can increase alcohol intake in female rodents; however, a comprehensive understanding of sex-specific neurobiological substrates underlying this phenomenon is still emerging. Microglia, the resident macrophages of the brain, are essential for reshaping neuronal processes, and microglial activity contributes to overall neuronal plasticity. We investigated microglial dynamics and morphology in limbic brain structures of male and female mice following exposure to stress, alcohol or both challenges. In a modified paradigm of intermittent binge drinking (repeated "drinking in the dark"), we determined that female, but not male, mice increased their alcohol consumption after exposure to a physical stressor and re-exposure trials in the stress-paired context. Ethanol (EtOH) drinking and stress altered a number of microglial parameters, including overall number, in subregions of the amygdala and hippocampus, with effects that were somewhat more pronounced in female mice. We used the CSF1R antagonist PLX3397 to deplete microglia in female mice to determine whether microglia contribute to stress-induced escalation of EtOH intake. We observed that microglial depletion attenuated stress-induced alcohol intake with no effect in the unstressed group. These findings suggest that microglial activity can contribute to alcohol intake under stressful conditions, and highlight the importance of evaluating sex-specific mechanisms that could result in tailored interventions for AUD in women.

Predator odor stress reactivity, alcohol drinking and the endocannabinoid system

Post-traumatic stress disorder (PTSD) and alcohol use disorder (AUD) are highly comorbid and individual differences in response to stress suggest resilient and susceptible populations. Using animal models to target neurobiological mechanisms associated with individual variability in stress coping responses and the relationship with subsequent increases in alcohol consumption has important implications for the field of traumatic stress and alcohol disorders. The current review discusses the unique advantages of utilizing predator odor stressor exposure models, specifically using 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) on better understanding PTSD pathophysiology and neurobiological mechanisms associated with stress reactivity and subsequent increases in alcohol drinking. Furthermore, there has been increasing interest regarding the role of the endocannabinoid system in modulating behavioral responses to stress with an emphasis on stress coping and individual differences in stress-susceptibility. Therefore, the current review focuses on the topic of endocannabinoid modulation of stress reactive behaviors during and after exposure to a predator odor stressor, with implications on modulating distinctly different behavioral coping strategies.

Traumatic stress-enhanced alcohol drinking: Sex differences and animal model perspectives

Purpose of review

Stress is associated with alcohol drinking, and epidemiological studies document the comorbidity of alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD), with higher comorbid prevalence in females than in males. The aim of this paper is to highlight information related to sex differences in stress-enhanced alcohol drinking from clinical studies and from preclinical studies utilizing an animal model of traumatic stress.

Recent findings

Stress is associated with alcohol drinking and relapse in males and females, but there are sex differences in the alcohol-related adaptation of stress pathways and in the association of different prefrontal regions with stress-induced anxiety. The predator stress model of traumatic stress produced enhanced alcohol drinking in a subgroup of stress-sensitive male and female animals, which could be associated with sex and subgroup differences in stress axis responsivity, behavioral responses to predator odors, and epigenetic mechanisms engaged by traumatic experiences.

Summary

While additional studies in females are necessary, existing clinical and preclinical evidence suggests that biological mechanisms underlying stress-enhanced drinking likely differ between males and females. Thus, effective treatment strategies may differ between the sexes.

Chemogenetic inhibition of central amygdala CRF-expressing neurons decreases alcohol intake but not trauma-related behaviors in a rat model of post-traumatic stress and alcohol use disorder

Post-traumatic stress disorder (PTSD) and alcohol use disorder (AUD) are often comorbid. Few treatments exist to reduce comorbid PTSD/AUD. Elucidating the mechanisms underlying their comorbidity could reveal new avenues for therapy. Here, we employed a model of comorbid PTSD/AUD, in which rats were subjected to a stressful shock in a familiar context followed by alcohol drinking. We then examined fear overgeneralization and irritability in these rats. Familiar context stress elevated drinking, increased fear overgeneralization, increased alcohol-related aggressive signs, and elevated peripheral stress hormones. We then examined transcripts of stress- and fear-relevant genes in the central amygdala (CeA), a locus that regulates stress-mediated alcohol drinking. Compared with unstressed rats, stressed rats exhibited increases in CeA transcripts for Crh and Fkbp5 and decreases in transcripts for Bdnf and Il18. Levels of Nr3c1 mRNA, which encodes the glucocorticoid receptor, increased in stressed males but decreased in stressed females. Transcripts of Il18 binding protein (Il18bp), Glp-1r, and genes associated with calcitonin gene-related peptide signaling (Calca, Ramp1, Crlr-1, and Iapp) were unaltered. Crh, but not Crhr1, mRNA was increased by stress; thus, we tested whether inhibiting CeA neurons that express corticotropin-releasing factor (CRF) suppress PTSD/AUD-like behaviors. We used Crh-Cre rats that had received a Cre-dependent vector encoding hM4D(Gi), an inhibitory Designer Receptors Exclusively Activated by Designer Drugs. Chemogenetic inhibition of CeA CRF neurons reduced alcohol intake but not fear overgeneralization or irritability-like behaviors. Our findings suggest that CeA CRF modulates PTSD/AUD comorbidity, and inhibiting CRF neural activity is primarily associated with reducing alcohol drinking but not trauma-related behaviors that are associated with PTSD/AUD.

Stress-enhanced ethanol drinking does not increase sensitivity to the effects of a CRF-R1 antagonist on ethanol intake in male and female mice

Research confirms that stress is associated with alcohol drinking and relapse in males and females and that there are sex differences in the alcohol-related adaptations of stress pathways. The predator stress (PS) model of traumatic stress produces an increase in alcohol drinking or self-administration in a subpopulation of rodents, so it is utilized as an animal model of comorbid alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD). Previous work determined that sensitivity to PS-enhanced drinking produced sex differences in proteins related to stress-regulating systems in the medial prefrontal cortex and hippocampus. The present studies examined whether male and female C57BL/6J mice differ in sensitivity to the ability of the corticotropin releasing factor receptor 1 antagonist CP-376395 to decrease PS-enhanced drinking. In control studies, CP-376395 doses of 5, 10, and 20 mg/kg dose-dependently decreased 4-hour ethanol drinking. Next, CP-376395 doses of 5 and 10 mg/kg were tested for effects on ethanol drinking in mice with differential sensitivity to PS-enhanced drinking. Subgroups of "Sensitive" and "Resilient" male and female mice were identified based on changes in ethanol intake in an unrestricted access ethanol drinking procedure following four exposures to PS (dirty rat bedding). During the first 2 hours post-injection of CP-376395, both doses significantly decreased ethanol licks versus vehicle in the females, with no significant interaction between subgroups, whereas the 10 mg/kg dose significantly decreased ethanol licks versus vehicle in the "Resilient" males. Thus, sensitivity to the suppressive effect of CP-376395 on stress-induced ethanol intake was greater in females versus males, whereas sensitivity and resilience to PS-enhanced drinking produced differential sensitivity to the ability of CP-376395 to decrease ethanol drinking only in male mice. Our results argue against greater efficacy of CRF-R1's ability to decrease ethanol intake in subjects with traumatic stress-enhanced ethanol drinking.

Effects of fisetin on ethanol-induced rewarding properties in mice

Background: Alcohol use disorder (AUD) is a chronic relapsing disorder associated with compulsive drinking of alcohol. Natural flavonoid fisetin affects a variety of transmitter systems relevant to AUD, such as aminobutyric acid, N-methyl-D-aspartate, and dopamine, as well as peroxisome proliferator-activated receptors.Objectives: This study investigated fisetin's impact on the motivational properties of ethanol using conditioned place preference (CPP) in mice (n = 50).Methods: Mice were conditioned with ethanol (2 g/kg, i.p.) or saline on alternating days for 8 consecutive days and were given intragastric (i.g.) fisetin (10, 20, or 30 mg/kg, i.g.), 45 min before ethanol conditioning. During extinction, physiological saline was injected to the control and ethanol groups, and fisetin was administered to the fisetin groups. To evaluate the effect of fisetin on the reinstatement of ethanol-induced CPP, fisetin was given 45 min before a priming dose of ethanol (0.4 g/kg, i.p.; reinstatement test day).Results: Fisetin decreased the acquisition of ethanol-induced CPP (30 mg/kg, p < .05) and accelerated extinction (20 and 30 mg/kg, p < .05). Furthermore, fisetin attenuated reinstatement of ethanol-induced CPP (30 mg/kg, p < .05).Conclusions: Fisetin appears to diminish the rewarding properties of ethanol, as indicated by its inhibitory effect and facilitation of extinction in ethanol-induced CPP. These findings imply a potential therapeutic application of fisetin in preventing ethanol-seeking behavior, promoting extinction, and reducing the risk of relapse.

Predator Odor Stressor, 2,3,5-Trimethyl-3-Thiazoline (TMT): Assessment of Stress Reactive Behaviors During an Animal Model of Traumatic Stress in Rats

Animal models utilizing predator odor stress are important in understanding implications for post-traumatic stress disorder. 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) has been used to measure stress reactive behaviors during TMT exposure, indicative of stress coping behaviors. In addition, long-term consequences of stress including contextual-induced stress memory, anxiety-like and hyperarousal behaviors, and subsequent increases in alcohol self-administration can also be examined after TMT exposure. In this article, we describe the TMT exposure protocol used in our lab and how we measure different stress-reactive behaviors that rats engage in during the TMT exposure. Rats are placed in Plexiglass chambers that contain white bedding on the bottom of the chamber and a metal basket in the top right corner containing a filter paper that 10 µl of TMT is pipetted onto. During the 10 min exposure, rats can move around the chamber freely. Exposures are recorded by a video camera for later analysis. During TMT exposure, rats engage in a variety of stress-reactive behaviors, including digging and immobility behavior. These are two distinctly different types of stress-induced behavioral coping strategies to measure individual differences in stress responsivity. To examine individual differences, we group rats into TMT-subgroups based on time spent engaging in digging or immobility behavior. We calculate a digging/immobility ratio score in which we divide the total time spent digging by the total time spent immobile. A cut-off strategy is used such that rats with a criterion ratio score <1.0 are classified as TMT-1 (i.e., low digging/high immobility; greater passive coping) and rats with a ratio score >1.0 are classified as TMT-2 (i.e., high digging/low immobility; greater active coping). Here, we provide a detailed description of the TMT exposure protocol and step-by-step process in evaluation of stress-reactive behaviors. © 2024 Wiley Periodicals LLC. Basic Protocol 1: Predator odor stressor exposure using TMT Basic Protocol 2: Description of stress-reactive behaviors during TMT exposure and formation of TMT-subgroups.

Differential c-Fos Response in Neurocircuits Activated by Repeated Predator Stress in Male and Female C57BL/6J Mice with Stress Sensitive or Resilient Alcohol Intake Phenotypes

Comorbidity of post-traumatic stress disorder (PTSD) and alcohol use disorder (AUD) worsens the prognosis for each of these individual disorders. The current study aimed to identify neurocircuits potentially involved in regulation of PTSD-AUD comorbidity by mapping expression of c-Fos in male and female C57BL/6J mice following repeated predator stress (PS), modeled by exposure to dirty rat bedding. In experiment 1, the levels of c-Fos in the paraventricular nucleus of the hypothalamus (PVH) and the nucleus accumbens shell were higher after the second PS vs the first PS, indicating a sensitized response to this stressor. Additional brain regions showed varied sex-dependent and independent regulation by the two consecutive PS exposures. In experiment 2, mice that increased voluntary alcohol consumption following four exposures to PS (Sensitive subgroup) showed higher c-Fos induction in the PVH, piriform cortex and ventromedial hypothalamus than mice that decreased consumption following these exposures (Resilient subgroup). In contrast to these brain regions, c-Fos was higher in the anterior olfactory nucleus of Resilient vs Sensitive mice. Taken together, these data demonstrate that repeated PS exposure and voluntary alcohol consumption increase neuronal activity across neurocircuits in which specific components depend on the vulnerability of individual mice to these stressors. Increased PVH activity observed across both experiments suggests this brain area as a potential mediator of PS-induced increases in alcohol consumption. Future investigations of specific neuronal populations within the PVH activated by PS, and manipulation of these specific neuronal populations, could improve our understanding of the mechanisms leading to PTSD-AUD comorbidity.

Stress and gonadal steroid influences on alcohol drinking and withdrawal, with focus on animal models in females

Sexually dimorphic effects of alcohol, following binge drinking, chronic intoxication, and withdrawal, are documented at the level of the transcriptome and in behavioral and physiological responses. The purpose of the current review is to update and to expand upon contributions of the endocrine system to alcohol drinking and withdrawal in females, with a focus on animal models. Steroids important in the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-adrenal axes, the reciprocal interactions between these axes, the effects of chronic alcohol use on steroid levels, and the genomic and rapid membrane-associated effects of steroids and neurosteroids in models of alcohol drinking and withdrawal are described. Importantly, comparison between males and females highlight some divergent effects of sex- and stress-steroids on alcohol drinking- and withdrawal-related behaviors, and the distinct differences in response emphasize the importance of considering sex in the development of novel pharmacotherapies for the treatment of alcohol use disorder.