Conditioned taste aversion (CTA) is a survival mechanism that prevents consumption of harmful foods. Yet its neural circuits, especially those for solid food aversion, are poorly understood. Using a male mouse model where high-fat food (HFF) was paired with LiCl injections, we identified the median raphe region (MRR) as essential for CTA. Optogenetic activation of MRR glutamatergic neurons replaced LiCl injections, inducing robust HFF aversion. Calcium signaling in MRR neurons increased upon HFF approach post-CTA. We uncovered a necessary glutamatergic projection from the medial preoptic area (MPOA) to the MRR; stimulating this circuit mimicked LiCl, to elicit HFF aversion. Following CTA, synaptic changes in MRR neurons included an increased mEPSC frequency and an altered paired-pulse ratio in the MPOAVgluT2-MRR pathway. Finally, MRR projections to the medial septum and lateral habenula differentially encode and retrieve CTA memory. These findings define a circuit for aversion learning, offering insights into maladaptive eating behaviors.

The lateral habenula (LHb) is a critical hub for stress-related behaviors, yet the sources of its corticotropin-releasing factor (CRF) inputs remain poorly defined. Using high-resolution imaging, RNAscope, and viral tracing, we identified a novel, intrinsic population of CRF-expressing LHb neurons (LHb CRF ). These neurons are primarily VGLUT2+, though a rostral subpopulation co-expresses GAD2. While chemogenetic activation of LHb CRF neurons did not impact place preference or anxiety-like behaviors, it selectively biased defensive strategies toward passive action-locking during the Visual Looming Shadow Test (VLST). Notably, this activation prolonged escape latencies in males and post-escape shelter stays in females. Electrophysiological and optogenetic characterization revealed significant sexual dimorphism: male LHb CRF neurons are more numerous and intrinsically excitable, whereas female LHb CRF neurons exhibit stronger local excitatory connectivity. These findings establish LHb CRF neurons as a sexually dimorphic circuit component that could modulate sex-specific defensive strategies under threat via divergent cellular and synaptic mechanisms between the sexes.

Neurotransmitter co-transmission contributes to diverse physiological processes throughout the mammalian brain, including sensory integration, motivational control, and social behaviors. Projections from the globus pallidus internus (GPi; the entopeduncular nucleus, EPN, in rodents) to the lateral habenula (LHb) are well-characterized by the co-transmission of both GABA and glutamate. These dual-release inputs modulate behavioral states in chronically learned helpless (cLH) rats, influencing both the onset and recovery of pathological phenotypes. Here, we employed confocal 3D reconstructions that confirmed the presence of both vesicular transporters VGAT and VGLUT2 in EPN axon terminals within the LHb. Further investigation revealed that GABA and glutamate are packaged in distinct vesicle populations within individual presynaptic terminals. Notably, the calcium (Ca²⁺) sensors Synaptotagmin-2 (Syt2) and Synaptotagmin-3 (Syt3) are highly expressed in the EPN whereas expression of the canonical Ca²⁺ sensor, Synaptotagmin 1 (Syt1), is downregulated. Additionally, using confocal microscopy, we observed selective spatial correlations of Syt2 and VGLUT2 and between Syt3 and VGAT in LHb axon terminals. These observations strongly suggested that Syt2 serves as the predominant Ca²⁺ sensor for glutamatergic vesicle fusion, and Syt3 serves as the predominant Ca²⁺ sensor for GABAergic vesicle fusion in the LHb. To test this hypothesis, we employed targeted antisense oligonucleotide (ASO) knockdown of Syt2 and Syt3 in EPN neurons and measured LHb glutamatergic and GABAergic currents. Syt2 knockdown resulted in an increase in mEPSC frequency, amplitude, half-width and decay, suggesting increased glutamate vesicle release probability and increased glutamate vesicle packing. However, Syt2 knockdown had no influence on mIPSCs amplitude or frequency. On the other hand, Syt3 knockdown had no apparent effect on glutamate release but caused an increase in mIPSC frequency suggesting increased quantal release probability of GABA. Together, these findings identify a molecular mechanism by which synaptotagmin isoforms govern differential glutamate and GABA release at EPN dual-transmitter terminals in the LHb. These results provide evidence for presynaptic mechanisms regulating excitatory-inhibitory balance within this brain structure and importantly provide molecular targets for pharmacological intervention.

The lateral habenula (LHb) is a small brain structure specialized in encoding aversive signals. Elevated bursting in the LHb has been linked to depressive-like behaviours in animal models. Bursting is a complex dynamic process that has been extensively studied and modelled in neuronal contexts. However, in the LHb, bursting activity has typically been described only as transient periods of high-frequency firing. Here, to provide a deeper understanding of LHb bursting, we analysed it from the perspective of dynamical systems. Ex vivo, LHb neurons display a variety of bursting patterns, characterized at one extreme by square wave-like bursts and at the other by parabolic bursts, plus transitional forms referred to as triangular bursts. Notably, these bursting patterns, which reflect different LHb output modes, can occur within the same neuron, reflecting distinct dynamic states. In particular, membrane hyperpolarization selectively promotes square-wave-type bursts, rather than triangular or parabolic ones. To capture these complex behaviours, we propose an idealized multiple-timescale dynamical model. This model successfully reproduces the three main bursting patterns observed in experimental data. Furthermore, we identify a special point in the parameter space, termed the saddle-node homoclinic bifurcation, which acts as an organizing centre demarcating the boundary between the two primary bursting patterns and around which the third pattern appears. Our model suggests that LHb bursting activity is structured around distinct dynamic states with potentially diverse and unexplored impacts on mood regulation. By providing new insights into the principles underlying LHb bursting, this framework may advance our understanding of its biological significance. KEY POINTS: Bursting activity of the brain nucleus of the lateral habenula has been linked to depressive states. Using brain slice experiments, we identified three key burst types: square wave-like, parabolic and intermediate 'triangular' patterns. These patterns likely represent different functional modes of the same neuron rather than different neuron types. A mathematical model was developed that replicates these patterns and reveals a critical transition point that organizes their dynamics. This framework offers new insight into how LHb bursting activity is organized and could potentially guide future treatments for depression.

Persistent facial and oral discomfort, particularly trigeminal neuralgia (TN), is frequently accompanied by anxiety, which has been closely linked to increased excitability of neurons in the lateral habenula (LHb). However, the mechanisms underlying this hyperexcitability remain unclear. Here, we show that partial transection of the infraorbital nerve (pT-ION) significantly upregulated the expression of transient receptor potential canonical 6 (TRPC6), β isoform of calcium/calmodulin-dependent protein kinase II (βCaMKII), phosphorylated extracellular regulated kinase (p-ERK), and phosphorylated cyclic adenosine monophosphate response element-binding protein (p-CREB) in the LHb. Pharmacological blockade of either TRPC6 or βCaMKII effectively reversed pT-ION-induced mechanical hypersensitivity and anxiety-like behaviors. TRPC6 overexpression in the LHb reproduced the behavioral and electrophysiological phenotypes observed in pT-ION mice, including increased LHb neuronal excitability. In contrast, bilateral knockdown of TRPC6 attenuated both pain- and anxiety-like behaviors and normalized neuronal activity in the LHb. Our study identified TRPC6 as a key mediator of LHb neuronal hyperexcitability, contributing to trigeminal neuralgia-associated pain and anxiety via the βCaMKII/ERK/CREB pathway, and suggests its potential as a target for treatment.

Flexible strategy use relies on the concerted effort of multiple cognitive processes. Originally appreciated for its role in aversive conditioning (for review, see Mondoloni et al., Transl Psychiatry 12: 86 [2022]), the lateral habenula (LHb) has recently been linked to flexible behavior more broadly (Baker et al., Front Behav Neurosci 9: 1-22 [2015]; Baker et al., Front Mol Neurosci 12: 1-15 [2019]; Mizumori and Baker, Trends Neurosci 40: 481-493 [2017]; Hones and Mizumori, Front Behav Neurosci 16: 852235 [2022]; Ahmadlou et al., Nature 641: 151-161 [2025]), prompting the question as to whether its encoding of negative outcomes contributes specifically to adaptive strategy switching. To address this gap in knowledge, the present study investigated how LHb inactivation with muscimol affects distinct aspects of flexible decision-making that depend on an understanding of negative outcomes when using a spatial set-shifting task. LHb inactivation resulted in a decreased ability to efficiently acquire new strategies after changes in reward contingencies but did not affect the exploitation of adopted strategies. A measure of choice flexibility confirmed that, without an intact LHb, rats fail to appropriately adapt to new strategies following errors. This effect suggests that the LHb contributes to the appropriate use of negative choice outcomes to inform future decisions. Therefore, aversive signaling in the LHb may play a broad role beyond purely aversive contexts, such as in guiding behavioral adaptation.

Tongmai Yishen Formula alleviates post-stroke depression by restoring neuronal homeostasis in the lateral habenula via the ITPKA signaling pathway.

Autism spectrum disorder (ASD) is characterized by social impairments and stereotyped behavior, with some individuals exhibiting heightened aggression in response to stress. This stress induced aggression (SIA) can severely impact quality of life, yet its underlying neural mechanisms remain poorly understood. Here, we investigated the behavioral phenotypes and neural activity that result as a consequence of stress in Cntnap2-/-:TRAP2+/-:Ai14+/- mice. Deletion of the CNTNAP2 gene leads to a highly penetrant syndromic form of ASD, and the targeted recombination in active populations (TRAP) system allows for permanent access to neuronal populations activated during a specific experience, such as stress and aggression. We implemented a behavioral paradigm consisting of a baseline resident intruder assay, with either a single day or four consecutive days of restraint stress, followed by a posttest resident intruder assay in Cntnap2-/-:TRAP2+/-:Ai14+/- and control mice. While a single day of restraint stress failed to induce changes in aggressive behavior in either genotype, 4 days of restraint stress significantly escalated aggression and reduced latency to attack selectively in Cntnap2-/- mice. Using TRAP-based labeling, we observed increased neuronal activity in the lateral septum, lateral habenula, lateral hypothalamus, nucleus accumbens, and prelimbic cortex of Cntnap2-/- mice. Interestingly, time aggressive and aggressive events were positively correlated with activity in the lateral septum, lateral habenula, and infralimbic cortex. These findings suggest that repeated stress engages specific fronto-striatal and limbic regions in Cntnap2-/- mice and provide insight into the neural substrates of maladaptive SIA, offering a foundation for targeted therapeutic strategies.

Insular cortex-lateral habenula circuit mediates chronic itch-associated affective comorbidities.

Sex differences have been noted in the prevalence and severity of several neurological and mental health disorders. Midbrain dopaminergic activity is implicated in the etiology of many of these disorders and therefore may also contribute to some commonly seen sex differences in presentation and treatment. The ability of the lateral habenula to inhibit midbrain dopamine firing activity is reduced in female rats, and we test here the hypothesis that circulating gonadal hormones contribute to this sex difference. In vivo, single unit, extracellular recordings of dopamine neurons were conducted in female and male rats that were intact, gonadectomized, or had hormone replacement. Both spontaneous and habenula-evoked activities were recorded. In accordance with previous findings, we found that habenular stimulation produces profound inhibition in dopamine neurons that is of longer duration in male rats than female rats. There was no effect of gonadectomy on duration of inhibition in either males or females. Although there was a trend toward stronger rebound excitation in control male rats, there was no significant effect of gonadectomy in either the male or female rats. Here we show that circulating gonadal hormones have no apparent effect on habenular evoked dopamine inhibition. We discuss the limitations of the current study, including the possibility that the influence of circulating gonadal hormones may be limited to sub-populations of midbrain dopamine neurons.

Social learning is the process of acquiring social skills, new information, or associating negative or positive valence to a context through the observation of others and through direct social interaction with others. Neurodevelopmental disorders such as autism spectrum disorder show deficits in social salience and reciprocal affective responses. Social learning implicates the basolateral amygdala (BLA), anterior cingulate cortex (ACC), and anterior insula (AI). The lateral habenula (LHb), a brain area renowned for its role in negative reinforcement learning, has not been yet extensively studied in the domain of social learning. We developed a fear conditioning by proxy paradigm called ‘social transmission of negative valence’ (STNV) and tested prairie voles on the task. Observers experienced negative social conditioning through a proxy cage mate that served as the demonstrator during retrieval of a cued fear memory. Observers went through a social memory recall session 24 h after observation. We measured observers’ freezing time, self-grooming, rearing, and ultrasonic vocalizations emitted as signs of distress. We also quantified immediate early gene translation as a proxy for neural activity using c-Fos immunochemistry 80 min after observing demonstrators going through memory recall. Socially-conditioned observers that were exposed to the fear-conditioned demonstrators displayed increased freezing time, self-grooming, and rearing during social recall sessions compared to control observers. They also displayed higher ultrasonic vocalization frequency compared to controls. Socially-conditioned observers showed increased c-Fos expression in the LHb, BLA, ACC and AI compared to controls. The c-Fos findings are correlational and additional experiments involving chemo- or optogenetic inhibition or excitation of LHb neurons in observers are necessary for causality confirmation. We found that the LHb is co-activated with other key areas during social learning in prairie voles. These findings extend the traditional view of the LHb as an area involved in negative reinforcement learning and position it as a critical area for social affect. This offers a fresh perspective on the neural mechanisms of social affect and opens a new line of inquiry into brain dysfunction of social salience in neurodevelopmental disorders.

Subanesthetic doses of ketamine, a non-competitive N-methyl-D-aspartate receptor (NMDAR) antagonist, produce rapid and robust antidepressant effects in patients with treatment-resistant depression (TRD). However, after a single administration, the therapeutic benefit is short-lived, and strategies to maintain its efficacy remain unclear. This study focused on the glutamate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR), whose activation is known to be a key effector for the action of ketamine. Thus, we developed a novel positive allosteric modulator of AMPAR (K-4) with potential antidepressant-like effects. In Wistar Kyoto rats, a model of TRD, K-4 produced a more sustained antidepressant-like effect than ketamine. Bulk RNA sequencing analysis revealed that K-4-treated rats showed lower expression of NADPH-oxidase-1 (NOX-1) in the medial prefrontal cortex (mPFC) than in ketamine-treated rats. Furthermore, simultaneous administration of a NOX-1 inhibitor with ketamine prolonged the antidepressant-like effect and reduced burst firing in the lateral habenula (LHb). Similarly, short hairpin RNA knockdown of NOX-1 in the mPFC sustained the antidepressant-like effects of ketamine and suppressed LHb bursting activity. These results indicate that NOX-1 suppression prolongs the antidepressant-like effect of ketamine and represents a promising target for maintenance strategies in TRD.

Pain encompasses both sensory discrimination and affective evaluation, yet the precise behavioral and neurobiological mechanisms of this well-conserved phenomenon are still incompletely understood. Although the lateral hypothalamus area (LHA) has been implicated in nociceptive modulation, its underlying circuitry and causal mechanisms remain elusive. In this study, formalin-induced pain-like behaviors in mice were associated with attenuated activity in LHA GAD2-positive neurons, a pattern also observed during acute restraint stress in adult male transgenetic mice. Chemogenetic activation of LHA GAD2 neurons significantly alleviated formalin-evoked nociceptive responses and reduced aversive behavioral phenotypes. Additionally, functional analyses revealed a GABAergic projection from the LHA to the lateral habenula that selectively mitigated affective disturbances in a neuropathic pain model. In parallel, projections from LHA GAD2 neurons to specific neuronal subsets within the ventrolateral periaqueductal gray modulated nociceptive responses under neuropathic pain conditions. These findings delineate a dual-pathway mechanism by which LHA GAD2 neurons independently regulate sensory and affective dimensions of pain-like behavior, offering a basis for targeted pain relief. Collectively, the results reveal previously uncharacterized aspects of pain processing by discrete LHA GABAergic subpopulations and potentially inform the development of subregion- or cell type-specific therapies for pain management.

Depression affects over 300 million people worldwide and is a leading cause of disability. Current treatments have limited efficacy in achieving remission and require several weeks to months of therapy for lessening depressive symptoms. Reduced autophagy is commonly observed in the brain of individuals with major depressive disorder, impairing cellular homeostasis and synaptic plasticity, the processes vital for mood regulation. A recent study published in the journal Nature reported that a key driver for depression in a mouse model of acute and chronic stress is an impaired autophagy in the lateral habenula, a brain region known to regulate motivation, reward, and aversion. Notably, direct infusion of beclin-1 peptide into this region rapidly restored autophagy markers and reduced depressive symptoms, highlighting a fast-acting mechanism distinct from the way conventional antidepressants act. Such effects were attributed to reduced excitatory neurotransmitter receptors, which could ease neuronal hyperactivity without affecting inhibitory neurotransmission, demonstrating that the selective autophagic degradation of excitatory receptors in the lateral habenula can mediate antidepressant effects. However, several issues remain to be addressed, including the long-term efficacy and the feasibility of the approach for clinical translation. This review critically discusses the proficiency, limitations, and clinical translatability of the lateral habenula autophagy enhancement approach. The promise of other autophagy enhancers and the possibility of combinational therapy, where drugs or dietary supplements could enhance autophagy, diminish neuroinflammation, and regulate neurotransmitters, is also discussed.

Light is the primary zeitgeber for circadian rhythms, and also through these mechanisms, is closely related to mood regulation. Bright light therapy (BLT) is a therapeutic intervention that specifically exploits this physiological mechanism. This review summarizes the clinical procedures of BLT, the mechanisms through which light influences circadian rhythms and mood, and the evidence supporting BLT in psychiatric disorders. BLT is administered by considering device distance, treatment duration, and light intensity. Through pathways originating in the retina and projecting to the Suprachiasmatic Nucleus (SCN), light might generate signals within the central nervous system that influence not only circadian regulation but also mood, via connections involving the limbic system, the lateral habenula, and interactions with the hormonal system. At the clinical level, the strongest evidence for BLT concerns seasonal affective disorder, but data also indicate antidepressant efficacy in major depressive disorder and bipolar disorder, with an excellent tolerability profile. Emerging evidence further suggests benefits for insomnia, and sporadic and heterogeneous findings have explored its potential role in other conditions. Future studies are needed to better define the role of BLT in additional psychiatric disorders and in specific symptom domains that may not adequately respond to standard treatments, such as sexual dysfunction.

Chronic pain remains a leading cause of disability worldwide. While the shift from a biomedical to a biopsychosocial model has reframed pain as an integrated neuro-affective experience, clinical strategies often overlook the bidirectional interaction between nociception and emotion. This narrative review was conducted using PubMed (MEDLINE), Scopus, and Web of Science (January 2000–February 2026), with supplementary searches performed in Google Scholar. Systematic reviews, meta-analyses, randomized controlled trials, cohort studies, and relevant preclinical studies addressing pain–affect intersections were prioritized. Reciprocal influences between emotion, pain, and analgesia are synthesised across neurobiological, psychological, and pharmacological domains. Shared substrates (the “pain matrix”), neurotransmitter pathways (serotonergic, noradrenergic, and opioid), and psychological modulators (pain catastrophizing and the fear-avoidance model) are discussed, with specific attention to the lateral habenula and cortical potentiation in relation to anhedonia. Mechanisms of placebo analgesia (via endogenous opioids) and nocebo hyperalgesia (via cholecystokinin) are summarized, highlighting the impact of cognitive-emotional states on pharmacodynamics. Evidence for an “affective shift” during pain chronification is outlined, and the “hidden psychopharmacology” of non-opioid analgesics is considered, including reported emotional blunting and reduced empathy associated with paracetamol (acetaminophen). The synthesis supports a multimodal therapeutic approach combining pharmacotherapy with psychotherapy and indicates that analgesics should not be assumed to be emotionally neutral during long-term pain management.

Electroconvulsive therapy (ECT) remains a highly effective intervention for acute episodes of major depressive disorder, offering rapid and robust antidepressant effects. However, its underlying mechanisms remain unclear, as prior studies focusing on conventional brain regions (e.g., the hippocampus) have not fully accounted for ECT's distinct therapeutic profile compared to slow-acting antidepressants. Emerging evidence implicates the lateral habenula (LHb) in mediating rapid antidepressant responses. Nevertheless, its role in ECT's efficacy and the involvement of key molecular targets within the LHb remain unexplored. We investigated the impact of electroconvulsive stimulation (ECS, an animal model of ECT) on depressive-like behaviors and neurological alterations in the LHb, hippocampus, and prefrontal cortex (PFC). Using a chronic restraint stress (CRS) mouse model of depression, we administered ECS and assessed behavioral outcomes alongside molecular and synaptic changes in different brain regions. To assess mechanistic involvement, we modulated βCaMKII expression in the LHb. ECS ameliorated CRS-induced depressive-like behaviors and reversed synaptic abnormalities in the LHb and hippocampus. ECS induced region-specific bidirectional changes in protein expression profiles in the LHb versus hippocampus, corresponding to its opposing effects on CRS-induced depressive impairments in these brain regions. Notably, LHb βCaMKII overexpression abolished all therapeutic effects of ECS. These findings identify the LHb as a crucial target for ECS-induced antidepressant-like effects, mediated through region-specific mechanisms that require βCaMKII-dependent synaptic modulation within the LHb.

Chronic stress facilitates behavioral engagement and alters lateral habenula activity during flexible decision making in a sex-dependent manner.

Role of lactic acid-mediated ALKBH5 in depression induced by blue light exposure at night.

Depression is one of the most common non-motor disorders and neuropsychiatric comorbidities in Parkinson's disease (PD). The pathophysiology of depression in PD patients remains unclear and has been largely unexplored. In this study, we employed chemogenetics and pharmacology to modulate the lateral habenula (LHb) and its downstream brain regions, the rostromedial tegmental nucleus (RMTg) and the ventral tegmental area (VTA) in wild type (WT) and 6-hydroxydopamine (6-OHDA) mice, to investigate the potential mechanisms underlying the improvement of PD-related depression. Inhibition of LHb glutamatergic neurons, as well as disruption of the LHb-RMTg pathway, along with inhibition of RMTg GABAergic neurons ameliorates depressive-like behavior in 6-OHDA mice. Conversely, activation of LHb glutamatergic neurons, the LHb-RMTg pathway, and activation of RMTg GABAergic neurons exacerbated depressive-like behavior in WT and 6-OHDA mice. Notably, either inhibition or activation of the LHb-VTA pathway did not produce any significant changes in depressive-like behavior in WT and 6-OHDA mice. Additionally, activation of VTA DAergic neurons effectively ameliorating depressive-like behavior in 6-OHDA mice. Inhibition of the LHb glutamatergic pathway ameliorates depressive-like behaviors in 6-OHDA PD mice model. These findings offer new insights for advancing research and developing novel treatments for PD-related depression.