Elevation of Transient Receptor Potential Vanilloid 1 Function in the Lateral Habenula Mediates Aversive Behaviors in Alcohol-withdrawn Rats

Effective suppression of Ih and INa caused by capsazepine, known to be a blocker of TRPV1 receptor

A synthetic inhibitor of capsaicin-induced TRPV1 channel activation is called capsazepine (CPZ). In this study, we aimed to explore the effects of CPZ on hyperpolarization-activated cationic current (Ih) and voltage-gated Na + current (INa) in pituitary tumor (GH3) cells. Through patch-clamp recordings, we found that CPZ concentration-dependently inhibited Ih amplitude and slowed its activation time course. The IC50 and KD values were 3.1 and 3.16 μM, respectively. CPZ also shifted the steady-state activation curve of Ih towards a more hyperpolarized potential. However, there was no change in the gating charge of the curve. A modified Markovian model predicted the CPZ-induced decrease in the voltage-dependent hysteresis of Ih. CPZ suppressed INa in GH3 cells, without altering its activation or inactivation time course. Additionally, exposure to CPZ reduced spontaneous firing. These findings suggest that CPZ's inhibitory effects on Ih and INa are direct and not dependent on vanilloid receptor binding. This could provide light on an unidentified ionic mechanism influencing the membrane excitability of neurons and endocrine or neuroendocrine cells in vivo.

Reducing the harms of alcohol: nutritional interventions and functional alcohol alternatives

The health risks and harm associated with regular alcohol consumption are well documented. In a recent WHO statement published in The Lancet Public Health alcohol consumption has been estimated to contribute worldwide to 3 million deaths in 2016 while also being responsible for 5·1% of the global burden of disease and injury. The total elimination of alcohol consumption, which has been long imbedded in human culture and society, is not practical and prohibition policies have proved historically ineffective. However, valuable strategies to reduce alcohol harms are already available and improved alternative approaches are currently being developed. Here, we will review and discuss recent advances on two main types of approaches, that is nutritional interventions and functional alcohol alternatives.

Cannabidiol tempers alcohol intake and neuroendocrine and behavioural correlates in alcohol binge drinking adolescent rats. Focus on calcitonin gene-related peptide's brain levels

Alcohol binge drinking is common among adolescents and may challenge the signalling systems that process affective stimuli, including calcitonin gene-related peptide (CGRP) signalling. Here, we employed a rat model of adolescent binge drinking to evaluate reward-, social- and aversion-related behaviour, glucocorticoid output and CGRP levels in affect-related brain regions. As a potential rescue, the effect of the phytocannabinoid cannabidiol was explored. Adolescent male rats underwent the intermittent 20% alcohol two-bottle choice paradigm; at the binge day (BD) and the 24 h withdrawal day (WD), we assessed CGRP expression in medial prefrontal cortex (mPFC), nucleus accumbens (NAc), amygdala, hypothalamus and brainstem; in addition, we evaluated sucrose preference, social motivation and drive, nociceptive response, and serum corticosterone levels. Cannabidiol (40 mg/kg, i.p.) was administered before each drinking session, and its effect was measured on the above-mentioned readouts. At BD and WD, rats displayed decreased CGRP expression in mPFC, NAc and amygdala; increased CGRP levels in the brainstem; increased response to rewarding- and nociceptive stimuli and decreased social drive; reduced serum corticosterone levels. Cannabidiol reduced alcohol consumption and preference; normalised the abnormal corticolimbic CGRP expression, and the reward and aversion-related hyper-responsivity, as well as glucocorticoid levels in alcohol binge-like drinking rats. Overall, CGRP can represent both a mediator and a target of alcohol binge-like drinking and provides a further piece in the intricate puzzle of alcohol-induced behavioural and neuroendocrine sequelae. CBD shows promising effects in limiting adolescent alcohol binge drinking and rebalancing the bio-behavioural abnormalities.

LPA1 receptors in the lateral habenula regulate negative affective states associated with alcohol withdrawal

The role of lysophosphatidic acid (LPA) signaling in psychiatric disorders and drug abuse is significant. LPA receptors are widely expressed in the central nervous system, including the lateral habenula (LHb). Recent studies suggest that LHb is involved in a negative emotional state during alcohol withdrawal, which can lead to relapse. The current study examines the role of LHb LPA signaling in the negative affective state associated with alcohol withdrawal. Adult male Long-Evans rats were trained to consume either alcohol or water for eight weeks. At 48 h of withdrawal, alcohol-drinking rats showed anxiety- and depression-like symptoms, along with a significant increase in LPA signaling and related neuronal activation molecules, including autotaxin (ATX, Enpp2), LPA receptor 1/3 (LPA1/3), βCaMKII, and c-Fos. However, there was a decrease in lipid phosphate phosphatase-related protein type 4 (LPPR4) in the LHb. Intra-LHb infusion of the LPA1/3 receptor antagonist ki-16425 or PKC-γ inhibitor Go-6983 reduced the abnormal behaviors and elevated relapse-like ethanol drinking. It also normalized high LPA1/3 receptors and enhanced AMPA GluA1 phosphorylation in Ser831 and GluA1/GluA2 ratio. Conversely, selective activation of LPA1/3 receptors by intra-LHb infusion of 18:1 LPA induced negative affective states and upregulated βCaMKII-AMPA receptor phosphorylation in Naive rats, which were reversed by pretreatment with intra-LHb Go-6983. Our findings suggest that disturbances in LPA signaling contribute to adverse affective disorders during alcohol withdrawal, likely through PKC-γ/βCaMKII-linked glutamate signaling. Targeting LPA may therefore be beneficial for individuals suffering from alcohol use disorders.

The Utility of Capsicum annuum L. in Internal Medicine and In Dentistry: A Comprehensive Review

Capsaicin is a chili peppers extract, genus Capsicum, commonly used as a food spice. Since ancient times, Capsaicin has been used as a "homeopathic remedy" for treating a wild range of pathological conditions but without any scientific knowledge about its action. Several studies have demonstrated its potentiality in cardiovascular, nephrological, nutritional, and other medical fields. Capsaicin exerts its actions thanks to the bond with transient receptor potential vanilloid subtype 1 (TRPV1). TRPV1 is a nociceptive receptor, and its activation starts with a neurosensitive impulse, responsible for a burning pain sensation. However, constant local application of Capsaicin desensitized neuronal cells and leads to relief from neuropathic pain. In this review, we analyze the potential adjuvant role of Capsaicin in the treatment of different pathological conditions either in internal medicine or dentistry. Moreover, we present our experience in five patients affected by oro-facial pain consequent to post-traumatic trigeminal neuropathy, not responsive to any remedy, and successfully treated with topical application of Capsaicin. The topical application of Capsaicin is safe, effective, and quite tolerated by patients. For these reasons, in addition to the already-proven beneficial actions in the internal field, it represents a promising method for the treatment of neuropathic oral diseases.

The intersection of astrocytes and the endocannabinoid system in the lateral habenula: on the fast-track to novel rapid-acting antidepressants

Despite attaining significant advances toward better management of depressive disorders, we are still facing several setbacks. Developing rapid-acting antidepressants with sustained effects is an aspiration that requires thinking anew to explore possible novel targets. Recently, the lateral habenula (LHb), the brain's "anti-reward system", has been shown to go awry in depression in terms of various molecular and electrophysiological signatures. Some of the presumed contributors to such observed aberrations are astrocytes. These star-shaped cells of the brain can alter the firing pattern of the LHb, which keeps the activity of the midbrain's aminergic centers under tight control. Astrocytes are also integral parts of the tripartite synapses, and can therefore modulate synaptic plasticity and leave long-lasting changes in the brain. On the other hand, it was discovered that astrocytes express cannabinoid type 1 receptors (CB₁R), which can also take part in long-term plasticity. Herein, we recount how the LHb of a depressed brain deviates from the "normal" one from a molecular perspective. We then try to touch upon the alterations of the endocannabinoid system in the LHb, and cast the idea that modulation of astroglial CB₁R may help regulate habenular neuronal activity and synaptogenesis, thereby acting as a new pharmacological tool for regulation of mood and amelioration of depressive symptoms.

Lateral Habenula and Its Potential Roles in Pain and Related Behaviors

The lateral habenula (LHb) is a tiny structure that acts as a hub, relaying signals from the limbic forebrain structures and basal ganglia to the brainstem modulatory area. Facilitated by updated knowledge and more precise manipulation of circuits, the progress in figuring out the neural circuits and functions of the LHb has increased dramatically over the past decade. Importantly, LHb is found to play an integrative role and has profound effects on a variety of behaviors associated with pain, including depression-like and anxiety-like behaviors, antireward or aversion, aggression, defensive behavior, and substance use disorder. Thus, LHb is a potential target for improving pain management and related disorders. In this review, we focused on the functions, related circuits, and neurotransmissions of the LHb in pain processing and related behaviors. A comprehensive understanding of the relationship between the LHb and pain will help to find new pain treatments.

Behavioral characterization of withdrawal following chronic voluntary ethanol consumption via intermittent two-bottle choice points to different susceptibility categories

BACKGROUND

Alcohol is among the most commonly abused drugs worldwide. Cessation of chronic alcohol consumption can result in the appearance of withdrawal symptoms that commonly promote relapse in individuals with alcohol use disorder (AUD). Thus, preclinical models of voluntary alcohol consumption, in which animals manifest spontaneous signs of withdrawal after alcohol cessation, can be useful for studying AUD and its treatment. The intermittent two-bottle choice paradigm (I2BC) has been used extensively to examine alcohol intake in rodents. However, previous studies have reported conflicting observations regarding its potential to result in the spontaneous manifestation of withdrawal upon alcohol cessation.

METHODS

We employed a battery of behavioral tests to examine the emergence of affective and physical signs of withdrawal in female and male mice exposed to alcohol in the I2BC for 10 weeks. Specifically, mice of both sexes undergoing 24-h withdrawal from the I2BC were tested for physical signs of withdrawal, anxiety-like behavior in the open field arena (OFA) and elevated plus maze (EPM), and anxiety/compulsive-like behavior in the marble burying test (MBT). The main outcomes from these tests were combined into a behavioral severity score to describe the overall behavioral phenotype.

RESULTS

Both female and male mice undergoing withdrawal from the I2BC displayed elevated physical signs of withdrawal and anxiety-associated behavior in the EPM and MBT. Analysis of the overall behavioral severity score revealed more severe phenotypes in female and male mice undergoing withdrawal from the I2BC than controls. Additionally, stratification of the mice based on severity scores demonstrated a differential distribution of severities between the exposure groups.

CONCLUSIONS

We confirmed that a significant fraction of mice chronically exposed to alcohol in the I2BC display spontaneous withdrawal. In addition, we showed that computing a severity score from a combination of behavioral metrics can be useful in preclinical research to model evaluation tools used in patients with AUD.

TRPV1 blockers as potential new treatments for psychiatric disorders

The transient receptor potential vanilloid-1 channel (TRPV1) is responsible for decoding physical and chemical stimuli. TRPV1 is activated by capsaicin (a compound from chili peppers), heat (above 43°C) and acid environment, playing a major role in pain, inflammation and body temperature. Molecular and histological studies have suggested TRPV1 expression in specific brain regions, where it can be activated primarily by the endocannabinoid anandamide, fostering studies on its potential role in psychiatric disorders. TRPV1 blockers are effective in various animal models predictive of anxiolytic and antipanic activities, in addition to reducing conditioned fear. In models of antidepressant activity, these compounds reduce behavioral despair and promote active stress-coping behavior. TRPV1 blockers also reduce the effects of certain drugs of abuse and revert behavioral changes in animal models of neurodevelopmental disorders. The main limiting factor in developing TRPV1 blockers as therapeutic agents concerns their effects on body temperature, particularly hyperthermia. New compounds, which block specific states of the channel, could represent an alternative. Moreover, compounds blocking both TRPV1 and the anandamide-hydrolyzing enzyme, fatty acid amide hydrolase (FAAH), termed dual TRPV1/FAAH blockers, have been investigated with promising results. Overall, preclinical studies yield favorable results with TRPV1 blockers in animal models of psychiatric disorders.

Roles of corticotropin-releasing factor signaling in the lateral habenula in anxiety-like and alcohol drinking behaviors in male rats

Corticotropin-releasing factor (CRF) signaling in the mesocorticolimbic system is known to modulate anxiety-like behavior and alcohol consumption, behaviors that also have been associated with the hyper-glutamatergic state of the lateral habenula (LHb) neurons in rats. However, the role of CRF signaling in the LHb on the glutamate transmission, anxiety-like behaviors and alcohol consumption is unknown. Here, we used male rats that had been consuming alcohol for three months to address this gap in the literature. First, using electrophysiological techniques, we evaluated CRF's effects on the glutamate transmission in LHb neurons in brain slices. CRF facilitated glutamate transmission. The facilitation was greater in neurons of alcohol-withdrawing rats than in those of naïve rats. The facilitation was mimicked by the activation of CRF receptor 1 (CRF1R) but attenuated by the activation of CRF receptor 2 (CRF2R). This facilitation was mediated by upregulating CRF1R-protein kinase A signaling. Conversely, protein kinase C blockade attenuated CRF's facilitation in neurons of naïve rats but promoted it in neurons of alcohol-withdrawing rats. Next, using site-direct pharmacology, we evaluated the role of CRF signaling in the LHb on anxiety-like behaviors and alcohol consumption. Intra-LHb inhibition of CRF1R or activation of CRF2R ameliorated the anxiety-like behaviors in alcohol-withdrawing rats and reduced their alcohol intake when drinking was resumed. These observations provide the first direct behavioral pharmacological and cellular evidence that CRF signaling in the LHb modulates glutamate transmission, anxiety-like behaviors and alcohol consumption, and that adaptation occurs in CRF signaling in the LHb after chronic alcohol consumption.

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CRF regulates glutamate transmission in the lateral habenula of male rats.

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CRF1R blockage or CRF2R activation in the LHb reduces anxiety in male rats.

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CRF1R blockage/CRF2R activation in the LHb reduces alcohol consumption in male rats.

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Acute ethanol facilitates LHb glutamate transmission involving CRF signaling.

Acetaldehyde Excitation of Lateral Habenular Neurons via Multiple Cellular Mechanisms

Acetaldehyde (ACD), the first metabolite of ethanol, is implicated in several of ethanol's actions, including the reinforcing and aversive effects. The neuronal mechanisms underlying ACD's aversive effect, however, are poorly understood. The lateral habenula (LHb), a regulator of midbrain monoaminergic centers, is activated by negative valence events. Although the LHb has been linked to the aversive responses of several abused drugs, including ethanol, little is known about ACD. We, therefore, assessed ACD's action on LHb neurons in rats. The results showed that intraperitoneal injection of ACD increased cFos protein expression within the LHb and that intra-LHb infusion of ACD induced conditioned place aversion in male rats. Furthermore, electrophysiological recording in brain slices of male and female rats showed that bath application of ACD facilitated spontaneous firing and glutamatergic transmission. This effect of ACD was potentiated by an aldehyde dehydrogenase (ALDH) inhibitor, disulfiram (DS), but attenuated by the antagonists of dopamine (DA) receptor (DAR) subtype 1 (SCH23390) and subtype 2 (raclopride), and partly abolished by the pretreatment of DA or DA reuptake blocker (GBR12935; GBR). Moreover, application of ACD initiated a depolarizing inward current (I _ACD) and enhanced the hyperpolarizing-activated currents in LHb neurons. Bath application of Rp-cAMPs, a selective cAMP-PKA inhibitor, attenuated ACD-induced potentiation of EPSCs and I _ACD Finally, bath application of ZD7288, a selective blocker of hyperpolarization-activated cyclic nucleotide-gated channels, attenuated ACD-induced potentiation of firing, EPSCs, and I _ACD These results show that ACD exerts its aversive property by exciting LHb neurons via multiple cellular mechanisms, and new treatments targeting the LHb may be beneficial for alcoholism.SIGNIFICANCE STATEMENT Acetaldehyde (ACD) has been considered aversive peripherally and rewarding centrally. However, whether ACD has a central aversive property is unclear. Here, we report that ACD excites the lateral habenula (LHb), a brain region associated with aversion and negative valence, through multiple cellular and molecular mechanisms. Intra-LHb ACD produces significant conditioned place aversion. These results suggest that ACD's actions on the LHb neurons might contribute to its central aversive property and new treatments targeting the LHb may be beneficial for alcoholism.

Endocannabinoid signaling in the lateral habenula regulates pain and alcohol consumption

Hyperalgesia, which often occurs in people suffering from alcohol use disorder, may drive excessive drinking and relapse. Emerging evidence suggests that the lateral habenula (LHb) may play a significant role in this condition. Previous research suggests that endocannabinoid signaling (eCBs) is involved in drug addiction and pain, and that the LHb contains core components of the eCBs machinery. We report here our findings in rats subjected to chronic ethanol vapor exposure. We detected a substantial increase in endocannabinoid-related genes, including Mgll and Daglb mRNA levels, as well as monoacylglycerol lipase (MAGL) protein levels, as well as a decrease in Cnr1 mRNA and type-1 cannabinoid receptor (CB1R) protein levels, in the LHb of ethanol-exposed rats. Also, rats withdrawing from ethanol exposure displayed hypersensitivity to mechanical and thermal nociceptive stimuli. Conversely, intra-LHb injection of the MAGL inhibitor JZL184, the fatty acid amide hydrolase inhibitor URB597, or the CB1R agonist WIN55,212-2 produced an analgesic effect, regardless of ethanol or air exposure history, implying that alcohol exposure does not change eCB pain responses. Intra-LHb infusion of the CB1R inverse agonist rimonabant eliminated the analgesic effect of these chemicals. Rimonabant alone elicited hyperalgesia in the air-, but not ethanol-exposed animals. Moreover, intra-LHb JZL184, URB597, or WIN55,212-2 reduced ethanol consumption in both homecages and operant chambers in rats exposed to ethanol vapor but not air. These findings suggest that LHb eCBs play a pivotal role in nociception and facilitating LHb eCBs may attenuate pain in drinkers.

Electroacupuncture Relieves Pain During Alcohol Withdrawal

Background: Alcohol use disorder (AUD) is one of the most prevalent chronic relapsing substance use disorders. The negative emotional state, including pain hypersensitivity that often occurs during abstinence, is believed to be a significant driving force for intensive seeking and relapse drinking. Studies have revealed that this may involve the inhibition of midbrain dopamine transmission and activation of the "antireward" system in the lateral habenula (LHb). Acupuncture has been proven effective in reducing pain and certain syndromes associated with AUD. There have been extensive studies conducted on acupuncture. However, the neuroanatomical basis behind acupuncture practice is still unclear. Objective: To briefly describe recent research about acupuncture on pain, particularly those related to AUD. Results: Preclinical studies found that electrostimulation of acupoints (electroacupuncture [EA]) effectively relieves hyperalgesia during withdrawal from chronic alcohol administration. This effect is mediated by the μ-opioid receptors in the LHb. Other studies revealed that the analgesic effect of EA could be mediated by mechanisms independent of the opioid system. Other evidence shows that acupuncture's strong anti-inflammatory effect also contributes to its analgesic effect. Conclusion: Acupuncture could alleviate pain, including the pain in alcoholics, through mechanisms either dependent or independent of the opioid system. Since alcohol abuse causes inflammation, which is also a significant cause of pain, the strong anti-inflammatory effect of acupuncture may also contribute to its analgesic effect. Thus, acupuncture is a nonaddictive therapeutic choice for pain related to substance use disorders, including alcohol.

The Emerging Role of LHb CaMKII in the Comorbidity of Depressive and Alcohol Use Disorders

Depressive disorders and alcohol use disorders are widespread among the general population and are significant public health and economic burdens. Alcohol use disorders often co-occur with other psychiatric conditions and this dual diagnosis is called comorbidity. Depressive disorders invariably contribute to the development and worsening of alcohol use disorders, and vice versa. The mechanisms underlying these disorders and their comorbidities remain unclear. Recently, interest in the lateral habenula, a small epithalamic brain structure, has increased because it becomes hyperactive in depression and alcohol use disorders, and can inhibit dopamine and serotonin neurons in the midbrain reward center, the hypofunction of which is believed to be a critical contributor to the etiology of depressive disorders and alcohol use disorders as well as their comorbidities. Additionally, calcium/calmodulin-dependent protein kinase II (CaMKII) in the lateral habenula has emerged as a critical player in the etiology of these comorbidities. This review analyzes the interplay of CaMKII signaling in the lateral habenula associated with depressive disorders and alcohol use disorders, in addition to the often-comorbid nature of these disorders. Although most of the CaMKII signaling pathway's core components have been discovered, much remains to be learned about the biochemical events that propagate and link between depression and alcohol abuse. As the field rapidly advances, it is expected that further understanding of the pathology involved will allow for targeted treatments.

Alcohol and Pain: A Translational Review of Preclinical and Clinical Findings to Inform Future Treatment Strategies

Alcohol use disorder (AUD) and chronic pain are enduring and devastating conditions that share an intersecting epidemiology and neurobiology. Chronic alcohol use itself can produce a characteristic painful neuropathy, while the regular analgesic use of alcohol in the context of nociceptive sensitization and heightened affective pain sensitivity may promote negative reinforcement mechanisms that underlie AUD maintenance and progression. The goal of this review was to provide a broad translational framework that communicates research findings spanning preclinical and clinical studies, including a review of genetic, molecular, behavioral, and social mechanisms that facilitate interactions between persistent pain and alcohol use. We also consider recent evidence that will shape future investigations into novel treatment mechanisms for pain in individuals suffering from AUD.

Anxiety during alcohol withdrawal involves 5-HT2C receptors and M-channels in the lateral habenula

Anxiety disorders often co-occur with alcohol use disorders, but the mechanisms underlying this comorbidity remain elusive. Previously, we reported that rats withdrawn from chronic alcohol consumption (Post-EtOH rats) exhibited robust anxiety-like behaviors (AB), which were accompanied by neuronal hyperexcitability, and the downregulation of M-type potassium channels (M-channels) in the lateral habenula (LHb); and that serotonin (5-HT) stimulated LHb neurons via type 2C receptors (5-HT_2CRs). Also, 5-HT_2CR activation is known to inhibit M-current in mouse hypothalamic neurons. The present study investigated whether LHb 5-HT_2CRs and M-channels contribute to AB in adult male Long-Evans rats. We used the intermittent-access to 20% ethanol two-bottle free-choice drinking paradigm to induce dependence. We measured AB with the elevated plus-maze, open-field, and marble-burying tests at 24 h withdrawal. We found that intra-LHb infusion of SB242084, a selective 5-HT_2CR antagonist alleviated AB and reduced the elevated c-Fos expression in the LHb of Post-EtOH rats. By contrast, intra-LHb infusion of the selective 5-HT_2CR agonist WAY161503 induced AB and increased c-Fos expression in the LHb in alcohol-naive but not Post-EtOH rats. Also, intra-LHb SB242084 significantly reduced self-administration of alcohol intake in the operant chambers. Furthermore, both 5-HT_2CR protein levels and 5-HIAA/5-HT ratio was increased in the LHb of Post-EtOH rats. Finally, intra-LHb SB242084 increased LHb KCNQ2/3 membrane protein expression in Post-EtOH rats. Collectively, these results suggest that enhanced LHb 5-HT_2CR signaling that interacted with M-channels triggers AB in Post-EtOH rats and that 5-HT_2CRs may be a promising target for treating comorbid anxiety disorders in alcoholics.

Activation of glycine receptors in the lateral habenula rescues anxiety- and depression-like behaviors associated with alcohol withdrawal and reduces alcohol intake in rats

The lateral habenula (LHb) is activated by a range of aversive states including those related to alcohol withdrawal and has glycine receptors (GlyRs), a sensitive target of alcohol. However, whether GlyRs in the LHb contribute to alcohol-related behaviors is unknown. Here, we report that rats experiencing withdrawal from chronic alcohol consumption showed higher anxiety and sensitivity to stress compared to their alcohol-naïve counterparts. Intra-LHb injection of glycine attenuated these aberrant behaviors and reduced alcohol intake upon alcohol re-access. Glycine's effect was blocked by strychnine, a GlyR antagonist, indicating that it was mediated by strychnine-sensitive GlyRs. Conversely, intra-LHb strychnine elicited anxiety- and depression-like behaviors in Naïve rats but not in withdrawal rats. Additionally, both the frequency and the amplitude of the spontaneous IPSCs were lower in LHb neurons in slices of withdrawal rats compared to naïve rats. Also, there were sporadic strychnine-sensitive synaptic events in some LHb neurons. Bath perfusion of strychnine induced a depolarizing inward current and increased action potential firings in LHb neurons. By contrast, bath perfusion of glycine or sarcosine, a glycine transporter subtype 1 inhibitor, inhibited LHb activity. Collectively, these data reveal that LHb neurons are under the tonic glycine inhibition both in physiological and pathological conditions. Activation of GlyRs reverses LHb hyperactivity, alleviates aberrant behaviors, and reduces alcohol intake, thus highlighting the GlyRs in the LHb as a potential therapeutic target for alcohol-use disorders.

Differences between male and female rats in alcohol drinking, negative affects and neuronal activity after acute and prolonged abstinence

Alcohol consumption afflicts men and women differently. However, the underlying neuronal mechanisms that contribute to the difference are mostly unexplored. Although more men suffer from alcohol use disorders (AUD), women more frequently accelerate to dependence and develop adverse consequences of alcoholism sooner than men. Women also exhibit more significant negative emotions that cues more reactivity and alcohol-craving than men. Despite ample evidence that women are vulnerable to AUD, results of preclinical studies on sex differences in alcohol consumption and withdrawal-related behaviors are inconclusive. In this study, we trained adult male and female Sprague-Dawley rats to drink alcohol in the intermittent access to 20% ethanol two-bottle free-choice paradigm for two months. Their behaviors and Fos expression in related brain regions were measured at acute (24 h) and after prolonged (28 days) abstinence. We found that female rats drank more alcohol than males. After acute abstinence, rats of both sexes showed higher sensitivity to depressive, thermal, and mechanical stimuli. Females also displayed higher anxiety levels. After prolonged abstinence, rats of both sexes displayed depressive-like behaviors; the males displayed allodynia; the females showed higher anxiety levels and drank more alcohol upon reaccess to alcohol. Furthermore, during acute withdrawal, Fos-positive nuclei were increased in the prefrontal cortex, anterior cingulate cortex (ACC), nucleus accumbens (NAc), amygdala and lateral habenula (LHb) in the females, versus only in the ACC, amygdala, and LHb in the males. Conversely, after prolonged abstinence, Fos-positive nuclei were decreased in the prefrontal cortex, ACC, and NAc in the females, but fell in the ACC, NAc, and LHb of the males. Thus, adaptations in diverse brain regions may contribute to the sex differences in behaviors in ethanol-withdrawn rats.

Adaptation in 5-HT2 receptors-CaMKII signaling in lateral habenula underlies increased nociceptive-sensitivity in ethanol-withdrawn rats

Alcoholics often experience hyperalgesia, especially during abstinence, yet the underlying cellular and molecular bases are unclear. Recent evidence suggests that 5-HT type 2 receptors (5-HT₂Rs) at glutamatergic synapses on lateral habenula (LHb) neurons may play a critical role. We, therefore, measured paw withdrawal responses to thermal and mechanical stimuli, and alcohol intake in a rat model of intermittent drinking paradigm, as well as spontaneous glutamatergic transmission (sEPSCs), and firing of LHb neurons in brain slices. Here, we report that nociceptive sensitivity was higher in rats at 24 h withdrawal from chronic alcohol consumption than that of alcohol-naive counterparts. The basal frequency of sEPSCs and firings was higher in slices of withdrawn rats than that of Naïve rats, and 5-HT2R antagonists attenuated the enhancement. Also, an acute ethanol-induced increase of sEPSCs and firings was smaller in withdrawal than in Naïve rats; it was attenuated by 5-HT₂R antagonists but mimicked by 5-HT₂R agonists. Importantly, intra-LHb infusion of 5-HT₂R agonists increased nociceptive sensitivity in Naïve rats, while antagonists or 5-HT reuptake blocker decreased nociceptive sensitivity and alcohol intake in withdrawn rats. Additionally, KN-62, a CaMKII inhibitor, attenuated the enhancement of EPSCs and firing induced by acute alcohol and by 5-HT₂R agonist. Furthermore, intra-LHb KN-62 reduced nociceptive sensitivity and alcohol intake. Quantitative real-time PCR assay detected mRNA of 5-HT2A and 2C in the LHb. Thus adaptation in 5-HT₂R-CaMKII signaling pathway contributes to the hyper-glutamatergic state, the hyperactivity of LHb neurons as well as the higher nociceptive sensitivity in rats withdrawn from chronic alcohol consumption.