Opposite responses to aversive stimuli in lateral habenula neurons

The behavioral relevance of a modular organization in the lateral habenula

Behavioral strategies for survival rely on the updates the brain continuously makes based on the surrounding environment. External stimuli-neutral, positive, and negative-relay core information to the brain, where a complex anatomical network rapidly organizes actions, including approach or escape, and regulates emotions. Human neuroimaging and physiology in nonhuman primates, rodents, and teleosts suggest a pivotal role of the lateral habenula in translating external information into survival behaviors. Here, we review the literature describing how discrete habenular modules-reflecting the molecular signatures, anatomical connectivity, and functional components-are recruited by environmental stimuli and cooperate to prompt specific behavioral outcomes. We argue that integration of these findings in the context of valence processing for reinforcing or discouraging behaviors is necessary, offering a compelling model to guide future work.

The lateral habenula: A hub for value-guided behavior

The habenula is an evolutionarily highly conserved diencephalic brain region divided into two major parts, medial and lateral. Over the past two decades, studies of the lateral habenula (LHb), in particular, have identified key functions in value-guided behavior in health and disease. In this review, we focus on recent insights into LHb connectivity and its functional relevance for different types of aversive and appetitive value-guided behavior. First, we give an overview of the anatomical organization of the LHb and its main cellular composition. Next, we elaborate on how distinct LHb neuronal subpopulations encode aversive and appetitive stimuli and on their involvement in more complex decision-making processes. Finally, we scrutinize the afferent and efferent connections of the LHb and discuss their functional implications for LHb-dependent behavior. A deepened understanding of distinct LHb circuit components will substantially contribute to our knowledge of value-guided behavior.

Brain state-dependent responses of midbrain dopaminergic neurons to footshock under urethane anaesthesia

For a long time, it has been assumed that dopaminergic (DA) neurons in both the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNc) uniformly respond to rewarding and aversive stimuli by either increasing or decreasing their activity, respectively. This response was believed to signal information about the perceived stimuli's values. The identification of VTA&SNc DA neurons that are excited by both rewarding and aversive stimuli has led to the categorisation of VTA&SNc DA neurons into two subpopulations: one signalling the value and the other signalling the salience of the stimuli. It has been shown that the general state of the brain can modulate the electrical activity of VTA&SNc DA neurons, but it remains unknown whether this factor may also influence responses to aversive stimuli, such as a footshock (FS). To address this question, we have recorded the responses of VTA&SNc DA neurons to FSs across cortical activation and slow wave activity brain states in urethane-anaesthetised rats. Adding to the knowledge of aversion signalling by midbrain DA neurons, we report that significant proportion of VTA&SNc DA neurons can change their responses to an aversive stimulus in a brain state-dependent manner. The majority of these neurons decreased their activity in response to FS during cortical activation but switched to increasing it during slow wave activity. It can be hypothesised that this subpopulation of DA neurons may be involved in the 'dual signalling' of both the value and the salience of the stimuli, depending on the general state of the brain.

Plasticity of neuronal dynamics in the lateral habenula for cue-punishment associative learning

The brain's ability to associate threats with external stimuli is vital to execute essential behaviours including avoidance. Disruption of this process contributes instead to the emergence of pathological traits which are common in addiction and depression. However, the mechanisms and neural dynamics at the single-cell resolution underlying the encoding of associative learning remain elusive. Here, employing a Pavlovian discrimination task in mice we investigate how neuronal populations in the lateral habenula (LHb), a subcortical nucleus whose excitation underlies negative affect, encode the association between conditioned stimuli and a punishment (unconditioned stimulus). Large population single-unit recordings in the LHb reveal both excitatory and inhibitory responses to aversive stimuli. Additionally, local optical inhibition prevents the formation of cue discrimination during associative learning, demonstrating a critical role of LHb activity in this process. Accordingly, longitudinal in vivo two-photon imaging tracking LHb calcium neuronal dynamics during conditioning reveals an upward or downward shift of individual neurons' CS-evoked responses. While recordings in acute slices indicate strengthening of synaptic excitation after conditioning, support vector machine algorithms suggest that postsynaptic dynamics to punishment-predictive cues represent behavioral cue discrimination. To examine the presynaptic signaling in LHb participating in learning we monitored neurotransmitter dynamics with genetically-encoded indicators in behaving mice. While glutamate, GABA, and serotonin release in LHb remain stable across associative learning, we observe enhanced acetylcholine signaling developing throughout conditioning. In summary, converging presynaptic and postsynaptic mechanisms in the LHb underlie the transformation of neutral cues in valued signals supporting cue discrimination during learning.

The circuit basis for chronic pain and its comorbidities

PURPOSE OF REVIEW

Chronic pain is poorly treated with many developing disabling comorbidities such as anxiety, depression and insomnia. Considerable evidence supports the idea that pain and anxiodepressive disorders share a common neurobiology and can mutually reinforce, which has significant long-term implications as the development of comorbidities leads to poorer treatment outcomes for both pain and mood disorders. This article will review recent advances in the understanding of the circuit basis for comorbidities in chronic pain.

RECENT FINDINGS

A growing number of studies have aimed to determine the mechanisms underlying chronic pain and comorbid mood disorders by using modern viral tracing tools for precise circuit manipulation with optogenetics and chemogenetics. These have revealed critical ascending and descending circuits, which advance the understanding of the interconnected pathways that modulate the sensory dimension of pain and the long-term emotional consequences of chronic pain.

SUMMARY

Comorbid pain and mood disorders can produce circuit-specific maladaptive plasticity; however, several translational issues require addressing to maximise future therapeutic potential. These include the validity of preclinical models, the translatability of endpoints and expanding analysis to the molecular and system levels.

The role of lateral habenula NMDA receptors in tramadol-induced conditioning

The role of the lateral habenula (LHb) as a hub for receiving and relaying signals from the limbic system to serotonergic, dopaminergic, and norepinephrinergic regions in the brainstem makes this area a critical region in the control of reward and addiction. Behavioral evidence reveals the vital role of the LHb in negative symptoms during withdrawal. In this investigation, we study the role of the LHb N-Methyl D-Aspartate receptor (NMDAR) in the modulation of tramadol reward. Male adult Wistar rats were used in this study. The effect of intra-LHb micro-injection of NMDAR agonist (NMDA, 0.1, 0.5, 2 µg/rat) and antagonist (D-AP5, 0.1, 0.5, 1 µg/rat) was evaluated in conditioned place preference (CPP) paradigm. The obtained results showed that intra-LHb administration of NMDA induced place aversion dose-dependently, while blockade of NMDAR in the LHb using D-AP5 micro-injection led to an increased preference score in the CPP task. Co-administration of NMDA (0.5 µg/rat) with tramadol (4 mg/kg) reduced preference score, while co-administration of D-AP5 (0.5 µg/rat) with a non-effective dose of tramadol (1 mg/kg) potentiate the rewarding effect of tramadol. LHb receives inputs from the limbic system and projects to the monoaminergic nuclei in the brainstem. It has been declared that NMDAR is expressed in LHb, and as obtained data revealed, these receptors could modulate the rewarding effect of tramadol. Therefore, NMDA receptors in the LHb might be a new target for modulating tramadol abuse.

Deep brain stimulation in the lateral habenula reverses local neuronal hyperactivity and ameliorates depression-like behaviors in rats

Deep brain stimulation (DBS) is a promising therapy for treatment-resistant depression, while mechanisms underlying its therapeutic effects remain poorly defined. Increasing evidence has revealed an intimate association between the lateral habenula (LHb) and major depression, and suggests that the LHb might be an effective target of DBS therapy for depression. Here, we found that DBS in the LHb effectively decreased depression-like behaviors in rats experienced with chronic unpredictable mild stress (CUMS), a well-accepted paradigm for modeling depression in rodents. In vivo electrophysiological recording unveiled that CUMS increased neuronal burst firing, as well as the proportion of neurons showing hyperactivity to aversive stimuli in the LHb. Nevertheless, DBS downregulated local field potential power, reversed the CUMS-induced increase of LHb burst firing and neuronal hyperactivity to aversive stimuli, and decreased the coherence between LHb and ventral tegmental area (VTA). Our results demonstrate that DBS in the LHb exerts antidepressant-like effects and reverses local neural hyperactivity, supporting the LHb as a target of DBS therapy for depression.

A neural substrate for negative affect dictates female parental behavior

Parental behaviors secure the well-being of newborns and concomitantly limit negative affective states in adults, which emerge when coping with neonatal distress becomes challenging. Whether negative-affect-related neuronal circuits orchestrate parental actions is unknown. Here, we identify parental signatures in lateral habenula neurons receiving bed nucleus of stria terminalis innervation (^BNSTLHb). We find that LHb neurons of virgin female mice increase their activity following pup distress vocalization and are necessary for pup-call-driven aversive behaviors. LHb activity rises during pup retrieval, a behavior worsened by LHb inactivation. Intersectional cell identification and transcriptional profiling associate ^BNSTLHb cells to parenting and outline a gene expression in female virgins similar to that in mothers but different from that in non-parental virgin male mice. Finally, tracking and manipulating ^BNSTLHb cell activity demonstrates their specificity for encoding negative affect and pup retrieval. Thus, a negative affect neural circuit processes newborn distress signals and may limit them by guiding female parenting.

Effects of maternal deprivation and environmental enrichment on anxiety-like and depression-like behaviors correlate with oxytocin system and CRH level in the medial-lateral habenula

The medial-lateral habenula (LHbM)'s role in anxiety and depression behaviors in female mice remains unclear. Here, we used neonatal maternal deprivation (MD) and post-weaning environmental enrichment (EE) to treat female BALB/c offspring and checked anxiety-like and depression-like behaviors as well as the corticotropin-releasing hormone (CRH), oxytocin receptor (OTR), estrogen receptor-beta (ERβ) levels in their LHbM at adulthood. We found that MD enhanced state anxiety-like behaviors in the elevated plus-maze test, and EE caused trait anxiety-like behaviors in the open field test and depression-like behaviors in the tail suspension test. The immunochemistry showed that MD reduced OT immunoreactive neuron numbers in the hypothalamic paraventricular nucleus but increased OTR levels in the LHbM; EE increased CRH levels in the LHbM but decreased OTR levels in the LHbM. The additive effects of EE and MD maintained the behavioral parameters, OT-ir neuronal numbers, CRH levels, and OTR levels similar to the additive of non-MD and non-EE. The correlation analysis showed that CRH levels correlated with synaptic connection levels, OTR levels correlated with nucleus densities, and ERβ levels correlated with Nissl body levels and body weights in female mice. Neither MD nor EE affected ERβ levels in the LHbM. Together, the study revealed the relationships between behaviors and neuroendocrine and neuronal alterations in female LHbM and the effects of experiences including MD and EE on them.

Astrocytes mediate long-lasting synaptic regulation of ventral tegmental area dopamine neurons

The plasticity of glutamatergic transmission in the ventral tegmental area (VTA) represents a fundamental mechanism in the modulation of dopamine neuron burst firing and phasic dopamine release at target regions. These processes encode basic behavioral responses, including locomotor activity, learning and motivated behaviors. Here we describe a hitherto unidentified mechanism of long-term synaptic plasticity in mouse VTA. We found that the burst firing in individual dopamine neurons induces a long-lasting potentiation of excitatory synapses on adjacent dopamine neurons that crucially depends on Ca²⁺ elevations in astrocytes, mediated by endocannabinoid CB1 and dopamine D2 receptors co-localized at the same astrocytic process, and activation of pre-synaptic metabotropic glutamate receptors. Consistent with these findings, selective in vivo activation of astrocytes increases the burst firing of dopamine neurons in the VTA and induces locomotor hyperactivity. Astrocytes play, therefore, a key role in the modulation of VTA dopamine neuron functional activity.

Response Flexibility: The Role of the Lateral Habenula

The ability to make appropriate decisions that result in an optimal outcome is critical for survival. This process involves assessing the environment as well as integrating prior knowledge about the environment with information about one’s current internal state. There are many neural structures that play critical roles in mediating these processes, but it is not yet known how such information coalesces to influence behavioral output. The lateral habenula (LHb) has often been cited as a structure critical for adaptive and flexible responding when environmental contexts and internal state changes. A challenge, however, has been understanding how LHb promotes response flexibility. In this review, we hypothesize that the LHb enables flexible responding following the integration of context memory and internal state information by signaling downstream brainstem structures known to drive hippocampal theta. In this way, animals respond more flexibly in a task situation not because the LHb selects a particular action, but rather because LHb enhances a hippocampal neural state that is often associated with greater attention, arousal, and exploration. In freely navigating animals, these are essential conditions that are needed to discover and implement appropriate alternative choices and behaviors. As a corollary to our hypothesis, we describe short- and intermediate-term functions of the LHb. Finally, we discuss the effects on the behavior of LHb dysfunction in short- and intermediate-timescales, and then suggest that new therapies may act on the LHb to alleviate the behavioral impairments following long-term LHb disruption.

PACAP-expressing neurons in the lateral habenula diminish negative emotional valence

The lateral habenula (LHb) is a small, bilateral, epithalamic nucleus which processes aversive information. While primarily glutamatergic, LHb neurons express genes coding for many neuropeptides, such as Adcyap1 the gene encoding pituitary adenylate cyclase-activating polypeptide (PACAP), which itself has been associated with anxiety and stress disorders. Using Cre-dependent viral vectors, we targeted and characterized these neurons based on their anatomical projections and found that they projected to both the raphe and rostromedial tegmentum but only weakly to ventral tegmental area. Using RiboTag to capture ribosomal-associated mRNA from these neurons and reanalysis of existing single cell RNA sequencing data, we did not identify a unique molecular phenotype that characterized these PACAP-expressing neurons in LHb. In order to understand the function of these neurons, we conditionally expressed hM₃ Dq DREADD selectively in LHb PACAP-expressing neurons and chemogenetically excited these neurons during behavioral testing in the open field test, contextual fear conditioning, sucrose preference, novelty suppressed feeding, and conditioned place preference. We found that Gq activation of these neurons produce behaviors opposite to what is expected from the LHb as a whole-they decreased anxiety-like and fear behavior and produced a conditioned place preference. In conclusion, PACAP-expressing neurons in LHb represents a molecularly diverse population of cells that oppose the actions of the remainder of LHb neurons by being rewarding or diminishing the negative consequences of aversive events.

Reward and aversion encoding in the lateral habenula for innate and learned behaviours

Throughout life, individuals experience a vast array of positive and aversive events that trigger adaptive behavioural responses. These events are often unpredicted and engage actions that are likely anchored on innate behavioural programs expressed by each individual member of virtually all animal species. In a second step, environmental cues, that are initially neutral, acquire value through the association with external sensory stimuli, and become instrumental to predict upcoming positive or negative events. This process ultimately prompts learned goal-directed actions allowing the pursuit of rewarding experience or the avoidance of a danger. Both innate and learned behavioural programs are evolutionarily conserved and fundamental for survival. Among the brain structures participating in the encoding of positive/negative stimuli and contributing to innate and learned behaviours is the epithalamic lateral habenula (LHb). The LHb provides top-down control of monoaminergic systems, responds to unexpected appetitive/aversive stimuli as well as external cues that predict the upcoming rewards or punishments. Accordingly, the LHb controls a number of behaviours that are innate (originating from unpredicted stimuli), and learned (stemming from predictive cues). In this review, we will discuss the progresses that rodent's experimental work made in identifying how LHb activity governs these vital processes, and we will provide a view on how these findings integrate within a complex circuit connectivity.

Multi-level variations of lateral habenula in depression: A comprehensive review of current evidence

Despite extensive research in recent decades, knowledge of the pathophysiology of depression in neural circuits remains limited. Recently, the lateral habenula (LHb) has been extensively reported to undergo a series of adaptive changes at multiple levels during the depression state. As a crucial relay in brain networks associated with emotion regulation, LHb receives excitatory or inhibitory projections from upstream brain regions related to stress and cognition and interacts with brain regions involved in emotion regulation. A series of pathological alterations induced by aberrant inputs cause abnormal function of the LHb, resulting in dysregulation of mood and motivation, which present with depressive-like phenotypes in rodents. Herein, we systematically combed advances from rodents, summarized changes in the LHb and related neural circuits in depression, and attempted to analyze the intrinsic logical relationship among these pathological alterations. We expect that this summary will greatly enhance our understanding of the pathological processes of depression. This is advantageous for fostering the understanding and screening of potential antidepressant targets against LHb.

Habenula as a Neural Substrate for Aggressive Behavior

Over the past decades, an ever growing body of literature has explored the anatomy, connections, and functions of the habenula (Hb). It has been postulated that the Hb plays a central role in the control of the monoaminergic system, thus influencing a wide range of behavioral responses, and participating in the pathophysiology of a number of psychiatric disorders and neuropsychiatric symptoms, such as aggressive behaviors. Aggressive behaviors are frequently accompanied by restlessness and agitation, and are commonly observed in patients with psychiatric disorders, intellectual disabilities, and neurodegenerative diseases of aging. Recently, the Hb has been explored as a new target for neuromodulation therapies, such as deep brain stimulation, with promising results. Here we review the anatomical organization of the habenula and discuss several distinct mechanisms by which the Hb is involved in the modulation of aggressive behaviors, and propose new investigations for the development of novel treatments targeting the habenula to reduce aggressive behaviors.

Discovery of TAK-041: a Potent and Selective GPR139 Agonist Explored for the Treatment of Negative Symptoms Associated with Schizophrenia

The orphan G-protein-coupled receptor GPR139 is highly expressed in the habenula, a small brain nucleus that has been linked to depression, schizophrenia (SCZ), and substance-use disorder. High-throughput screening and a medicinal chemistry structure-activity relationship strategy identified a novel series of potent and selective benzotriazinone-based GPR139 agonists. Herein, we describe the chemistry optimization that led to the discovery and validation of multiple potent and selective in vivo GPR139 agonist tool compounds, including our clinical candidate TAK-041, also known as NBI-1065846 (compound 56). The pharmacological characterization of these GPR139 agonists in vivo demonstrated GPR139-agonist-dependent modulation of habenula cell activity and revealed consistent in vivo efficacy to rescue social interaction deficits in the BALB/c mouse strain. The clinical GPR139 agonist TAK-041 is being explored as a novel drug to treat negative symptoms in SCZ.

Stress induces divergent gene expression among lateral habenula efferent pathways

The lateral habenula (LHb) integrates critical information regarding aversive stimuli that shapes decision making and behavioral responses. The three major LHb outputs innervate dorsal raphe nucleus (DRN), ventral tegmental area (VTA), and the rostromedial tegmental nucleus (RMTg). LHb neurons that project to these targets are segregated and nonoverlapping, and this led us to consider whether they have distinct molecular phenotypes and adaptations to stress exposure. In order to capture a time-locked profile of gene expression after repeated forced swim stress, we used intersectional expression of RiboTag in rat LHb neurons and next-gen RNA sequencing to interrogate the RNAs actively undergoing translation from each of these pathways. The “translatome” in the neurons comprising these pathways was similar at baseline, but diverged after stress, especially in the neurons projecting to the RMTg. Using weighted gene co-expression network analysis, we found one module, which had an overrepresentation of genes associated with phosphoinositide 3 kinase (PI3K) signaling, comprising genes downregulated after stress in the RMTg-projecting LHb neurons. Reduced PI3K signaling in RMTg-projecting LHb neurons may be a compensatory adaptation that alters the functional balance of LHb outputs to GABAergic vs. monoaminergic neurons following repeated stress exposure.

Heterogeneous Habenular Neuronal Ensembles during Selection of Defensive Behaviors

Optimal selection of threat-driven defensive behaviors is paramount to an animal's survival. The lateral habenula (LHb) is a key neuronal hub coordinating behavioral responses to aversive stimuli. Yet, how individual LHb neurons represent defensive behaviors in response to threats remains unknown. Here, we show that in mice, a visual threat promotes distinct defensive behaviors, namely runaway (escape) and action-locking (immobile-like). Fiber photometry of bulk LHb neuronal activity in behaving animals reveals an increase and a decrease in calcium signal time-locked with runaway and action-locking, respectively. Imaging single-cell calcium dynamics across distinct threat-driven behaviors identify independently active LHb neuronal clusters. These clusters participate during specific time epochs of defensive behaviors. Decoding analysis of this neuronal activity reveals that some LHb clusters either predict the upcoming selection of the defensive action or represent the selected action. Thus, heterogeneous neuronal clusters in LHb predict or reflect the selection of distinct threat-driven defensive behaviors.

Sex differences in vasopressin 1a receptor regulation of social communication within the lateral habenula and dorsal raphe of mice

The neuropeptide arginine-vasopressin (AVP) has long been implicated in the regulation of social behavior and communication in diverse taxa, often through its actions on the V1a receptor (V1aR) and in a sex-different and steroid-dependent way. One source of sex-different brain AVP is the steroid-sensitive and sexually-dimorphic AVP neurons in the bed nucleus of the stria terminalis (BNST), a cell population that regulates social behavior in a sex-dependent manner. Potential targets of these BNST-AVP cells include the lateral habenula (LHb) and dorsal raphe (DR), areas known to be important for social behavior, yet few studies have investigated AVP action within these regions. Consequently, to test if V1aR action in the LHb or DR controls social behavior in a sexually dimorphic manner, we administered a highly-specific V1aR antagonist (or saline vehicle) in the LHb or DR of C57BL/6 male and female mice and tested its effects on social investigation, social communication (urine marking, ultrasonic vocalizations), and territorial aggression. V1aR antagonism of the LHb or DR decreased male urine marking toward unfamiliar males, but not toward unfamiliar females. Additionally, V1aR blockade of the LHb decreased ultrasonic vocalizations generated in the presence of females. Social investigation, locomotion and aggressive behavior were not altered by V1aR antagonism in either area. Blocking V1aR in the LHb or DR of females had no effect, indicating V1aR action in the DR and LHb drives sex differences in social communication.

Circuits and functions of the lateral habenula in health and in disease

The past decade has witnessed exponentially growing interest in the lateral habenula (LHb) owing to new discoveries relating to its critical role in regulating negatively motivated behaviour and its implication in major depression. The LHb, sometimes referred to as the brain's 'antireward centre', receives inputs from diverse limbic forebrain and basal ganglia structures, and targets essentially all midbrain neuromodulatory systems, including the noradrenergic, serotonergic and dopaminergic systems. Its unique anatomical position enables the LHb to act as a hub that integrates value-based, sensory and experience-dependent information to regulate various motivational, cognitive and motor processes. Dysfunction of the LHb may contribute to the pathophysiology of several psychiatric disorders, especially major depression. Recently, exciting progress has been made in identifying the molecular and cellular mechanisms in the LHb that underlie negative emotional state in animal models of drug withdrawal and major depression. A future challenge is to translate these advances into effective clinical treatments.

Three Rostromedial Tegmental Afferents Drive Triply Dissociable Aspects of Punishment Learning and Aversive Valence Encoding

Persistence of reward seeking despite punishment or other negative consequences is a defining feature of mania and addiction, and numerous brain regions have been implicated in such punishment learning, but in disparate ways that are difficult to reconcile. We now show that the ability of an aversive punisher to inhibit reward seeking depends on coordinated activity of three distinct afferents to the rostromedial tegmental nucleus (RMTg) arising from cortex, brainstem, and habenula that drive triply dissociable RMTg responses to aversive cues, outcomes, and prediction errors, respectively. These three pathways drive correspondingly dissociable aspects of punishment learning. The RMTg in turn drives negative, but not positive, valence encoding patterns in the ventral tegmental area (VTA). Hence, punishment learning involves pathways and functions that are highly distinct, yet tightly coordinated.

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.