Chronic alcohol disrupts hypothalamic responses to stress by modifying CRF and NMDA receptor function

Impact and Role of Hypothalamic Corticotropin Releasing Hormone Neurons in Withdrawal from Chronic Alcohol Consumption in Female and Male Mice

Worldwide, alcohol use and abuse are a leading risk of mortality, causing 5.3% of all deaths (World Health Organization, 2022). The endocrine stress system, initiated by the peripheral release of corticotropin releasing hormone (CRH) from primarily glutamatergic neurons in the paraventricular nucleus of the hypothalamus (PVN), is profoundly linked with alcohol use, abuse, and relapse (Blaine and Sinha, 2017). These PVN CRH-releasing (PVNCRH) neurons are essential for peripheral and central stress responses (Rasiah et al., 2023), but little is known about how alcohol affects these neurons. Here, we show that two-bottle choice alcohol consumption blunts the endocrine-mediated corticosterone response to stress during acute withdrawal in female mice. Conversely, using slice electrophysiology, we demonstrate that acute withdrawal engenders a hyperexcitable phenotype of PVNCRH neurons in females that is accompanied by increased glutamatergic transmission in both male and female mice. GABAergic synaptic transmission was unaffected by alcohol history. We then tested whether chemogenetic inhibition of PVNCRH neurons would restore stress response in female mice with a history of alcohol drinking in the looming disk test, which mimics an approaching predator threat. Accordingly, inhibition of PVNCRH neurons reduced active escape in hM4Di alcohol history mice only. This study indicates that stress-responsive PVNCRH neurons in females are particularly affected by a history of alcohol consumption. Interestingly, women have indicated an increase in heavy alcohol use to cope with stress (Rodriguez et al., 2020), perhaps pointing to a potential underlying mechanism in alcohol-mediated changes to PVNCRH neurons that alter stress response.SIGNIFICANCE STATEMENT Paraventricular nucleus of the hypothalamus neurons that release corticotropin releasing hormone (PVNCRH) are vital for stress response. These neurons have been understudied in relation to alcohol and withdrawal despite profound relations between stress, alcohol use disorders (AUD), and relapse. In this study, we use a variety of techniques to show that acute withdrawal from a history of alcohol impacts peripheral stress response, PVNCRH neurons, and behavior. Specifically, PVNCRH are in a hyperactive state during withdrawal, which drives an increase in active stress coping behaviors in female mice only. Understanding how alcohol use and withdrawal affects stress responding PVNCRH neurons may contribute to finding new potential targets for the treatment of alcohol use disorder.

The effect of MK-801 on stress-ethanol cross-sensitization is dissociable from its effects on nNOS activity

Locomotor behavioral sensitization represents an animal model for understanding neuroadaptive processes related to repeated drug exposure. Repeated stress can elicit a cross-sensitization to the stimulant response of ethanol, which involves neuronal nitric oxide synthase (nNOS). Activation of N-methyl d-aspartate (NMDA) glutamate receptors triggers nNOS and the synthesis of nitric oxide (NO). In this study, we investigated the effects of blocking NMDA receptors using the NMDA receptor antagonist MK-801 on the cross-sensitization between restraint stress and ethanol. We also evaluated the nNOS activity in the prefrontal cortex (PFC) and hippocampus. Mice were pretreated with saline or MK-801 30 min before an injection of saline or stress exposure for 14 days. On the following day, they were challenged with either saline or 1.8 g/kg ethanol. Swiss male mice pretreated with 0.25 mg/kg MK-801 exhibited a sensitized response to ethanol. Moreover, MK-801 potentiated the cross-sensitization between stress and ethanol. However, MK-801 prevented the enhanced nNOS activity in stress-exposed groups (challenged with saline or ethanol) in the PFC; the antagonist also prevented the ethanol-induced increase in nNOS activity and reduced this enzyme activity in mice exposed to stress in the hippocampus. These data indicate that systemic treatment with the NMDA antagonist potentiated, rather than blocked, ethanol-induced behavioral sensitization and that this effect is dissociable from the capacity of NMDA antagonists to reduce ethanol/stress-induced NOS stimulation in the PFC and hippocampus.

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

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

Circadian rhythm shifts and alcohol access in adolescence synergistically increase alcohol preference and intake in adulthood in male C57BL/6 mice

BACKGROUND

Adolescents have a natural tendency to be night owls, maintaining delayed circadian rhythms, and this rhythm is in direct conflict with the early wake times required during the school year. This leads to 'social jetlag', chronic circadian stress or desynchrony (CD) in which the rhythm of the intrinsic body clock is out of sync with behavior. CD increases alcohol intake in adolescents and adults, yet it is unknown whether adolescent CD also increases long-term addiction risk. The goal of this study was to determine whether adolescent alcohol intake in CD would increase adult alcohol preference and intake in male C57BL/6 J mice.

METHODS

We measured free access alcohol intake, water intake, and wheel-running activity during a normal 12 h (h) baseline photoperiod and then during shifting lighting schedules (Experiment 1) or a shortened circadian day (Experiment 2).

RESULTS

In Experiment 1, altered lighting produced a persistent increase in adolescent alcohol intake and in binge-like drinking (drinking at least 5 licks per minute, with no more than a 1 min break in drinking) in adulthood, but only a transient increase in total alcohol intake for the first week after alcohol was reintroduced in adulthood. In Experiment 2, the circadian shift produced a significant increase in alcohol intake in both adolescence and adulthood. Molecular analysis demonstrated changes in plasma corticosterone and neuronal markers of stress and addiction at the conclusion of these experiments in the CD and alcohol-exposed groups.

CONCLUSIONS

Thus, we conclude that circadian stress during adolescence is sufficient to produce a long-lasting susceptibility to alcohol use.

Transcriptional Regulation, Signaling Pathways, and Subcellular Localization of Corticotropin-Releasing Factor Receptors in the Central Nervous System

Corticotropin-releasing factor (CRF) receptors CRF-R1 and CRF-R2 are differentially distributed in body tissues, and although they respond differentially to stimuli due to their association with different signaling pathways, both receptors have a fundamental role in the response and adaptation to stressful stimuli. Here, we summarize the reported data on different forms of CRF-R1 and CRF-R2 regulation as well as on their subcellular localization. Although the presence of R1 has been described at pre- and postsynaptic sites, R2 is mainly associated with postsynaptic densities. Different studies have provided valuable information on how these receptors regulate responses at a central level, elucidating different and sometimes synergistic roles in response to stress, but despite their high sequence identity, both receptors have been described to be differentially regulated both by their ligands and by transcriptional factors. To date, and from the point of view of their promoter sequences, it has not yet been reported how the different consensus sites identified in silico could be modulating the transcriptional regulation and expression of the receptors under different conditions, which strongly limits the full understanding of their differential functions, providing a wide field to increase and expand the study of the regulation and role of CRF receptors in the CRF system. SIGNIFICANCE STATEMENT: A large number of physiological functions related to the organization of the stress response in different body tissues are associated with the corticotropin-releasing factor system. This system also plays a relevant role in depression and anxiety disorders, as well as being a direct connection between stress and addiction. A better understanding of how the receptors of this system are regulated would help to expand the understanding of how these receptors respond differently to both drugs and stressful stimuli.

Sex differences in α-adrenergic receptor function contribute to impaired hypothalamic metaplasticity following chronic intermittent ethanol exposure

BACKGROUND

Individuals with alcohol use disorder (AUD) exhibit maladaptive responses of the hypothalamic-pituitary-adrenal (HPA) axis to stress, which has been linked to high rates of relapse to drinking among abstinent individuals. Corticotropin-releasing factor (CRF) parvocellular neuroendocrine cells (PNCs) within the paraventricular nucleus of the hypothalamus (PVN) are critical to stress-induced HPA axis activation. Here, we investigate sex differences in synaptic transmission and plasticity in PNCs following the application of the stress-associated neurotransmitter norepinephrine (NE) in a rat model of AUD.

METHODS

Adult Sprague-Dawley rats were exposed to 40 days of chronic intermittent ethanol (CIE) vapor and 30 to 108 days of protracted withdrawal. We measured changes in holding current, evoked synaptic currents, and short-term glutamatergic plasticity (STP) in putative PNCs following the application of NE (10 μM) with and without the selective α1 adrenergic receptor (AR) antagonist prazosin (10 μM) or the α2AR antagonist atipamezole (10 μM). The experiments were performed using whole-cell patch clamp recordings in slices from CIE rats and air-exposed controls.

RESULTS

NE application caused two distinct effects: a depolarizing, inward, postsynaptic current and a reduction in amplitude of an evoked glutamatergic excitatory postsynaptic current (eEPSC). Both effects were sex- and CIE-specific. Prazosin blocked the postsynaptic inward current, while atipamezole blocked the NE-mediated suppression of eEPSCs. Additionally, STP formation was facilitated following NE application only in stress-naïve males and this response was lost in stressed animals exposed to a 30-min restraint stress following CIE exposure. Furthermore, NE + prazosin restored STP formation in stressed CIE males.

CONCLUSIONS

NE exerts excitatory and inhibitory effects on CRF PVN PNCs, and both effects are influenced by sex and CIE. Behavioral and hormonal responses to stress are influenced by STP formation within the PVN, which is lost following CIE and restored with the preapplication of prazosin. The selective blockade of α1AR may, therefore, ameliorate CIE-induced deficits in HPA responses to stress in a sex-specific manner.

Chronic alcohol consumption alters home-cage behaviors and responses to ethologically relevant predator tasks in mice

BACKGROUND

Alcohol withdrawal is a key component of severe alcohol use disorder. Animal models of alcohol withdrawal tend to focus on traditional anxiety/stress tests. While these have been essential to advancing our understanding of the biology of alcohol withdrawal, abrupt cessation of drinking following heavy alcohol consumption can also trigger withdrawal-related affective states that impact responses to a variety of life events and stressors. To this end, we show that behaviors in a variety of tasks that differ in task demand and intensity are altered during withdrawal in male and female mice after voluntary alcohol access.

METHODS

Male and female miceunderwent six weeks of intermittent two-bottle choice alcohol exposure followed by behavioral tests. The tests included-Home cage: low-stress baseline environment to measure spontaneous natural behaviors; Open field: anxiety-inducing bright novel environment; Looming disc: arena with a protective hut where mice are exposed to a series of discs that mimic an overhead advancing predator, and Robogator-simulated predator task: forced foraging behavioral choice in the presence of an advancing robot predator that "attacks" when mice are near a food pellet in a large open arena.

RESULTS

A history of alcohol exposure impacted behaviors in these tasks in a sex-dependent manner. In the home cage, alcohol induced reductions in digging and heightened stress coping through an increase in grooming time. In males, increased rearing yielded greater vigilance/exploration in a familiar environment. The open-field test revealed an anxiety phenotype in both male and female mice exposed to alcohol. Male mice showed no behavioral alterations to the looming disc task, while females exposed to alcohol showed greater escape responses than water controls, indicative of active stress-response behaviors. In males, the Robogator task revealed a hesitant/avoidant phenotype in alcohol-exposed mice under greater task demands.

CONCLUSIONS

Few drugs show robust evidence of efficacy in clinical trials for alcohol withdrawal. Understanding how withdrawal alters a variety of behaviors in both males and females that are linked to stress coping can increase our understanding of alcohol misuse and aid in developing better medications for treating individuals with AUD.

Long-Acting Glucagon-Like Peptide-1 Receptor Agonists Suppress Voluntary Alcohol Intake in Male Wistar Rats

Alcohol use disorder (AUD) is a chronic relapsing condition characterized by compulsive alcohol-seeking behaviors, with serious detrimental health consequences. Despite high prevalence and societal burden, available approved medications to treat AUD are limited in number and efficacy, highlighting a critical need for more and novel pharmacotherapies. Glucagon-like peptide-1 (GLP-1) is a gut hormone and neuropeptide involved in the regulation of food intake and glucose metabolism via GLP-1 receptors (GLP-1Rs). GLP-1 analogs are approved for clinical use for diabetes and obesity. Recently, the GLP-1 system has been shown to play a role in the neurobiology of addictive behaviors, including alcohol seeking and consumption. Here we investigated the effects of different pharmacological manipulations of the GLP-1 system on escalated alcohol intake and preference in male Wistar rats exposed to intermittent access 2-bottle choice of 10% ethanol or water. Administration of AR231453 and APD668, two different agonists of G-protein receptor 119, whose activation increases GLP-1 release from intestinal L-cells, did not affect voluntary ethanol intake. By contrast, injections of either liraglutide or semaglutide, two long-acting GLP-1 analogs, potently decreased ethanol intake. These effects, however, were transient, lasting no longer than 48 h. Semaglutide, but not liraglutide, also reduced ethanol preference on the day of injection. As expected, both analogs induced a reduction in body weight. Co-administration of exendin 9-39, a GLP-1R antagonist, did not prevent liraglutide- or semaglutide-induced effects in this study. Injection of exendin 9-39 alone, or blockade of dipeptidyl peptidase-4, an enzyme responsible for GLP-1 degradation, via injection of sitagliptin, did not affect ethanol intake or preference. Our findings suggest that among medications targeting the GLP-1 system, GLP-1 analogs may represent novel and promising pharmacological tools for AUD treatment.