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

Nicotinic regulation of microglia: potential contributions to addiction

Clinical and preclinical studies have identified immunosuppressive effects of nicotine, with potential implications for treating nicotine addiction. Here we review how nicotine can regulate microglia, the resident macrophages in the brain, and corresponding effects of nicotine on neuroimmune signaling. There is significant evidence that activation of α7 nicotinic acetylcholine receptors (nAChRs) on microglia can trigger an anti-inflammatory cascade that alters microglial polarization and activity, cytokine release, and intracellular calcium concentrations, leading to neuroprotection. These anti-inflammatory effects of nicotine-dependent α7 nAChR signaling are lost during withdrawal, suggesting that neuroimmune signaling is potentiated during abstinence, and thus, heightened microglial activity may drive circuit disruption that contributes to withdrawal symptoms and hyperkatifeia. In sum, the clinical literature has highlighted immunomodulatory effects of nicotine and the potential for anti-inflammatory compounds to treat addiction. The preclinical literature investigating the underlying mechanisms points to a role of microglial engagement in the circuit dysregulation and behavioral changes that occur during nicotine addiction and withdrawal, driven, at least in part, by activation of α7 nAChRs on microglia. Specifically targeting microglial signaling may help alleviate withdrawal symptoms in people with nicotine dependence and help to promote abstinence.

Subjective stress and any drinking during alcohol treatment: Disentangling within and between person autoregressive effects

Alcohol use has been shown to increase stress, and there is some evidence that stress predicts subsequent alcohol use during treatment for alcohol use disorder (AUD), particularly among females who are more likely to report coping-motivated drinking. Gaining a better understanding of the processes by which stress and alcohol use are linked during treatment could potentially inform AUD treatment planning. The current study aimed to characterize the association between stress and drinking during the course of AUD treatment and whether there were sex differences in these associations. Secondary data analyses of the COMBINE study (N = 1375; 69% male, 76.3% non-Hispanic and white, average age of 44.4 years) were conducted to examine self-reported perceived stress and alcohol consumption across 16 weeks of treatment for AUD using a Bayesian random-intercept cross-lagged panel model. There was stronger evidence for any alcohol use predicting greater than typical stress in subsequent weeks and less strong evidence for stress increasing the subsequent probability of alcohol use, particularly among males. For females, greater stress predicted subsequent drinking earlier in the treatment period, and a lower probability of subsequent drinking in the last week of treatment. Interventions might specifically focus on targeting reductions in stress following drinking occasions.

Association between weekly working hours and risky alcohol use: A 12-year longitudinal, nationwide study from South Korea

We aimed to investigate the association between long working hours and onset of risky alcohol use. We included a nationally representative sample comprising 11,226 workers in South Korea (57,887 observations). The Alcohol Use Disorders Identification Test was used to assess risky alcohol use. Fixed effect regressions were employed to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Adjusted ORs (95% CIs) of risky alcohol use were 1.08 (0.95-1.22) for 41-48 h/week, 1.12 (0.96-1.31) for 49-54 h/week, and 1.40 (1.21-1.63) for ≥55 h/week, compared with standard working hours (35-40 h/week). ORs (95% CIs) of the association between working ≥55 h/week and risky alcohol use was 1.39 (1.17-1.65) for men and 1.34 (0.98-1.82) for women. Yearly cumulative exposure to long working hours (>40 h/week) is positively associated with risky alcohol use in a dose-dependent manner. For instance, exposure to long working hours for ≥3 years was associated with an increased likelihood of risky alcohol use (OR [95% CI]: 2.20 [1.78-2.72]). Sex-stratified analyses showed that long work hours are associated with risky alcohol use in both male and female workers. Appropriate work-hour policy is needed to prevent workers from risky alcohol use.

Interaction of stress and alcohol on discriminating fear from safety and reward in male and female rats

RATIONALE

Stressful events can have lasting and impactful effects on behavior, especially in terms of appropriate fear regulation and reward seeking. Our prior work in rats has shown baseline sex differences in fear expression and sucrose seeking in a discriminative reward-fear-safety conditioning task.

OBJECTIVES

The objectives of the current study were to determine how prior stress may affect alcohol consumption across a reward-fear-safety learning task, and how prior alcohol history may interact with stress to impact learning in this task.

METHODS

Male and female Long Evans rats were given home cage intermittent 24 h access to both water and alcohol for 5 weeks. A subset of rats then received exposure to stress (15 unsignaled footshocks), while remaining unstressed rats received context exposure without shock. One week later, all rats were trained on the same reward-fear-safety cue task while having continuous home cage access to both water and alcohol.

RESULTS

All rats increased consumption (g/kg/24 h) across the 5 weeks of intermittent access, with females showing higher consumption levels. Stress exposure did not alter alcohol consumption in the week following stress, but did increase home cage alcohol consumption during later reward-fear-safety cue learning. Stress in both sexes also elevated freezing levels to the reward cue resulting in decreased sucrose seeking and was positively correlated with home cage alcohol consumption.

CONCLUSIONS

While stress increased drinking in both males and females, the effects of stress were particularly pronounced in females, indicating our results could be capturing a higher propensity for females to display stress-induced drinking.

Reinstatement of Pavlovian responses to alcohol cues by stress

RATIONALE

Stress may contribute to relapse to alcohol use in part by enhancing reactivity to cues previously paired with alcohol. Yet, standard models of stress-induced reinstatement generally use contingent presentations of alcohol-paired cues to reinforce instrumental behaviors, making it difficult to isolate the ability of cues to invigorate alcohol-seeking.

OBJECTIVE

Here we sought to test the impact of stress on behavioral responses to alcohol-paired cues, using a model of stress-induced reinstatement of Pavlovian conditioned approach, inspired by Nadia Chaudhri's work on context-induced reinstatement.

METHODS

Long Evans rats were trained to associate one auditory cue with delivery of alcohol or sucrose and an alternative auditory cue with no reward. Following extinction training, rats were exposed to a stressor prior to being re-exposed to the cues under extinction conditions. We assessed the effects of yohimbine, intermittent footshock and olfactory cues paired with social defeat on responses to alcohol-paired cues and the effects of yohimbine on responses to sucrose-paired cues.

RESULTS

The pharmacological stressor, yohimbine, enhanced alcohol seeking in a Pavlovian setting, but not in a cue-selective manner. Intermittent footshock and social defeat cues did not enhance alcohol seeking in this paradigm.

CONCLUSIONS

While yohimbine elicited reinstatement of reward-seeking in a Pavlovian setting, these effects may be unrelated to activation of stress systems or to interactions with specific cues.

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.

Chronic Ethanol Causes Persistent Increases in Alzheimer's Tau Pathology in Female 3xTg-AD Mice: A Potential Role for Lysosomal Impairment

Epidemiological studies have found that heavy alcohol use is associated with increased risk for Alzheimer's disease (AD), with frequent drinking earlier in adulthood increasing risk. The increases in neuroinflammation featured in both heavy alcohol use and AD may be partially responsible for this link. However, it is unknown if abstinence mitigates this risk. We hypothesized that binge ethanol during mid adult life would persistently increase AD pathology even after prolonged abstinence. Male and female 3xTg-AD mice (APPSwe, tauP301, Psen1^tm1Mpm) which feature progressive amyloid (Aβ) and tau pathology, received chronic binge ethanol (5g/kg/day, 5-days-on/2-days-off, i.g.) or water during adulthood (from 5.5 to 9 months of age), followed by abstinence and assessment at 14 months of age. The effects of ethanol on protective AD genes (e.g., APOE and TREM2) as well as proinflammatory genes were measured by PCR. Levels of pathologic tau and Aβ were measured by immunohistochemistry and western blot. Ethanol caused persistent reductions in protective AD genes: APOE (25% reduction, *p < 0.05), TREM2 (28%, *p < 0.05), LPL (40%, ^** p < 0.01), and CTSD (24%, *p < 0.05) and promoted a proinflammatory gene signature in female, but not male cortex. Concurrently, ethanol increased total and hyperphosphorylated tau (AT8) in piriform cortex and hippocampus of females, but not males. Levels of AT8 were negatively correlated with APOE (R = -0.67, *p < 0.05) and TREM2 (R = -0.78, ^**p < 0.005) suggesting protective roles in pathogenesis. No differences were found in levels of main regulators of tau phosphorylation state (GSK3β, PKA, PP2A), suggesting ethanol disrupted clearance of tau. Therefore, we measured the effect of ethanol on lysosomes, which degrade tau, and lysosomal localization of tau using co-immunofluorescence. In females, ethanol caused a persistent reduction in mature LAMP1 lysosomes in CA1 of hippocampus (35%, *p < 0.05), along with a 60% increase in total tau (*p < 0.05). Thus, chronic binge ethanol during mid adult life causes a persistent enhancement of tau pathology in cortical and hippocampal brain regions of females. Persistent AD pathology was associated with an increased proinflammatory signature and a reduction of mature lysosomes. This implicates binge ethanol exposure with increased risk of AD pathologic progression in females.