Stress transforms lateral habenula reward responses into punishment signals

Adolescent stress differentially modifies dopamine and norepinephrine release in the medial prefrontal cortex of adult rats

Adolescent stress (AS) has been associated with higher vulnerability to psychiatric disorders such as schizophrenia, depression, or drug dependence. Moreover, the alteration of brain catecholamine (CAT) transmission in the medial prefrontal cortex (mPFC) has been found to play a major role in the etiology of psychiatric disturbances. We investigated the effect of adolescent stress on CAT transmission in the mPFC of freely moving adult rats because of the importance of this area in the etiology of psychiatric disorders, and because CAT transmission is the target of a relevant group of drugs used in the therapy of depression and psychosis. We assessed basal dopamine (DA) and norepinephrine (NE) extracellular concentrations (output) by brain microdialysis in in the mPFC of adult rats that were exposed to chronic mild stress in adolescence. To ascertain the role of an altered release or reuptake, we stimulated DA and NE output by administering either different doses of amphetamine (0.5 and 1.0 mg / kg s.c.), which by a complex mechanism determines a dose dependent increase in the CAT output, or reboxetine (10 mg/kg i.p.), a selective NE reuptake inhibitor. The results showed the following: (i) basal DA output in AS rats was lower than in controls, while no difference in basal NE output was observed; (ii) amphetamine, dose dependently, stimulated DA and NE output to a greater extent in AS rats than in controls; (iii) reboxetine stimulated NE output to a greater extent in AS rats than in controls, while no difference in stimulated DA output was observed between the two groups. These results show that AS determines enduring effects on DA and NE transmission in the mPFC and might lead to the occurrence of psychiatric disorders or increase the vulnerability to drug addiction.

Mixed representations of choice and outcome by GABA/glutamate cotransmitting neurons in the entopeduncular nucleus

The basal ganglia (BG) are an evolutionarily conserved and phylogenetically old set of sub-cortical nuclei that guide action selection, evaluation, and reinforcement. The entopeduncular nucleus (EP) is a major BG output nucleus that contains a population of GABA/glutamate cotransmitting neurons (EP Sst+ ) that specifically target the lateral habenula (LHb) and whose function in behavior remains mysterious. Here we use a probabilistic switching task that requires an animal to maintain flexible relationships between action selection and evaluation to examine when and how GABA/glutamate cotransmitting neurons contribute to behavior. We find that EP Sst+ neurons are strongly engaged during this task and show bidirectional changes in activity during the choice and outcome periods of a trial. We then tested the effects of either permanently blocking cotransmission or modifying the GABA/glutamate ratio on behavior in well-trained animals. Neither manipulation produced detectable changes in behavior despite significant changes in synaptic transmission in the LHb, demonstrating that the outputs of these neurons are not required for on-going action-outcome updating in a probabilistic switching task.

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.

Input-output specific orchestration of aversive valence in lateral habenula during stress dynamics

Stress has been considered as a major risk factor for depressive disorders, triggering depression onset via inducing persistent dysfunctions in specialized brain regions and neural circuits. Among various regions across the brain, the lateral habenula (LHb) serves as a critical hub for processing aversive information during the dynamic process of stress accumulation, thus having been implicated in the pathogenesis of depression. LHb neurons integrate aversive valence conveyed by distinct upstream inputs, many of which selectively innervate the medial part (LHbM) or lateral part (LHbL) of LHb. LHb subregions also separately assign aversive valence via dissociable projections to the downstream targets in the midbrain which provides feedback loops. Despite these strides, the spatiotemporal dynamics of LHb-centric neural circuits remain elusive during the progression of depression-like state under stress. In this review, we attempt to describe a framework in which LHb orchestrates aversive valence via the input-output specific neuronal architecture. Notably, a physiological form of Hebbian plasticity in LHb under multiple stressors has been unveiled to incubate neuronal hyperactivity in an input-specific manner, which causally encodes chronic stress experience and drives depression onset. Collectively, the recent progress and future efforts in elucidating LHb circuits shed light on early interventions and circuit-specific antidepressant therapies.

Lateral Habenula Neurons Signal Cold Aversion and Participate in Cold Aversion

The aversion to cold is a fundamental motivated behavior that contributes to the body temperature homeostasis. However, the involvement of the lateral habenula (LHb) as a regulatory hub for negative emotions in this physiological process remains uninvestigated. In this study, we demonstrate an elevation in the population activity of LHb neurons following exposure to cold stimuli. Additionally, we establish the necessity of Vglut2-expressing neurons within the LHb for the encoding of cold aversion behaviors. Furthermore, we have elucidated a neural circuit from excitatory neurons of the dorsomedial hypothalamus (DMH) to LHb that plays a crucial role in this progress. Manipulation of the DMH-LHb circuit has a significant impact on cold aversion behavior in mice. It is worth noting that this circuit does not exhibit any noticeable effects on autonomic thermoregulation or depression-like behavior. The identification of these neural mechanisms involved in behavioral thermoregulation provides a promising avenue for future research.

Bidirectional mechanism of comorbidity of depression and insomnia based on synaptic plasticity

Insomnia is one of the most common accompanying symptoms of depression, with both sharing highly overlapping molecular pathways. The same pathological changes can trigger comorbidity of insomnia and depression, which further forms a vicious cycle with the involvement of more mechanisms and disease progression. Thus, understanding the potential interaction mechanisms between insomnia and depression is critical for clinical diagnosis and treatment. Comorbidity genetic factors, the hypothalamic-pituitary-adrenal axis, along with circadian rhythms of cortisol and the brain reward mechanism, are important ways in contributing to the comorbidity occurrence and development. However, owing to lack of pertinent investigational data, intricate molecular mechanisms necessitate further elaboration. Synaptic plasticity is a solid foundation for neural homeostasis. Pathological alterations of depression and insomnia may perturb the production and release of neurotransmitter, dendritic spine remodeling and elimination, which converges and reflects in aberrant synaptic dynamics. Hence, the introduction of synaptic plasticity research route and the construction of a comprehensive model of depression and insomnia comorbidity can provide new ideas for clinical depression insomnia comorbidity treatment plans.

Neural valuation of rewards and punishments in posttraumatic stress disorder: a computational approach

Posttraumatic stress disorder (PTSD) is associated with changes in fear learning and decision-making, suggesting involvement of the brain's valuation system. Here we investigate the neural mechanisms of subjective valuation of rewards and punishments in combat veterans. In a functional MRI study, male combat veterans with a wide range of posttrauma symptoms (N = 48, Clinician Administered PTSD Scale, CAPS-IV) made a series of choices between sure and uncertain monetary gains and losses. Activity in the ventromedial prefrontal cortex (vmPFC) during valuation of uncertain options was associated with PTSD symptoms, an effect which was consistent for gains and losses, and specifically driven by numbing symptoms. In an exploratory analysis, computational modeling of choice behavior was used to estimate the subjective value of each option. The neural encoding of subjective value varied as a function of symptoms. Most notably, veterans with PTSD exhibited enhanced representations of the saliency of gains and losses in the neural valuation system, especially in ventral striatum. These results suggest a link between the valuation system and the development and maintenance of PTSD, and demonstrate the significance of studying reward and punishment processing within subject.

Alteration of Lateral Habenula Function Prevents the Proper Exploration of a Novel Environment

The lateral habenula (LHb) is an epithalamic brain region viewed as a converging hub, integrating information from a large connectome and then projecting to few critical midbrain monoaminergic systems. Numerous studies have explored the roles of the LHb, notably in aversion and avoidance. An important recurring finding when manipulating the LHb is the induction of anxiety-related behaviours. However, its exact role in such behaviours remains poorly understood. In the present study, we used two pharmacological approaches altering LHb activity, intra-LHb infusion of either the GABA-A receptor agonist, Muscimol, or the glutamatergic AMPA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and exposed rats to three consecutive open field (OF) sessions. We found that both pharmacological treatments prevented rats to explore the centre of the OF, considered as the most anxiogenic part of the apparatus, across the three OF sessions. In addition, during the first, but not the two consecutive sessions, both treatments prevented a thorough exploration of the OF. Altogether, these results confirm the crucial role played by the LHb in anxiety-related behaviours and further suggest its implication in the exploration of new anxiogenic environments.

Corticotropin Releasing Factor (CRF) Coexpression in GABAergic, Glutamatergic, and GABA/Glutamatergic Subpopulations in the Central Extended Amygdala and Ventral Pallidum of Young Male Primates

The central extended amygdala (CEA) and ventral pallidum (VP) are involved in diverse motivated behaviors based on rodent models. These structures are conserved, but expanded, in higher primates, including human. Corticotropin releasing factor (CRF), a canonical "stress molecule" associated with the CEA and VP circuitry across species, is dynamically regulated by stress and drugs of abuse and misuse. CRF's effects on circuits critically depend on its colocation with primary "fast" transmitters, making this crucial for understanding circuit effects. We surveyed the distribution and colocalization of CRF-, VGluT2- (vesicular glutamate transporter 2), and VGAT- (vesicular GABA transporter) mRNA in specific subregions of the CEA and VP in young male monkeys. Although CRF-containing neurons were clustered in the lateral central bed nucleus (BSTLcn), the majority were broadly dispersed throughout other CEA subregions, and the VP. CRF/VGAT-only neurons were highest in the BSTLcn, lateral central amygdala nucleus (CeLcn), and medial central amygdala nucleus (CeM) (74%, 73%, and 85%, respectively). In contrast, lower percentages of CRF/VGAT only neurons populated the sublenticular extended amygdala (SLEAc), ventrolateral bed nucleus (BSTLP), and VP (53%, 54%, 17%, respectively), which had higher complements of CRF/VGAT/VGluT2-labeled neurons (33%, 29%, 67%, respectively). Thus, the majority of CRF-neurons at the "poles" (BSTLcn and CeLcn/CeM) of the CEA are inhibitory, while the "extended" BSTLP and SLEAc subregions, and neighboring VP, have a more complex profile with admixtures of "multiplexed" excitatory CRF neurons. CRF's colocalization with its various fast transmitters is likely circuit-specific, and relevant for understanding CRF actions on specific target sites.SIGNIFICANCE STATEMENT The central extended amygdala (CEA) and ventral pallidum (VP) regulate multiple motivated behaviors through differential downstream projections. The stress neuropeptide corticotropin releasing factor (CRF) is enriched in the CEA, and is thought to "set the gain" through modulatory effects on coexpressed primary transmitters. Using protein and transcript assays in monkey, we found that CRF neurons are broadly and diffusely distributed in CEA and VP. CRF mRNA+ neurons colocalize with VGAT (GABA) and VGluT2 (glutamate) mRNAs in different proportions depending on subregion. CRF mRNA was also coexpressed in a subpopulation of VGAT/VGluT2 mRNA ("multiplexed") cells, which were most prominent in the VP and "pallidal"-like parts of the CEA. Heterogeneous CRF and fast transmitter coexpression across CEA/VP subregions implies circuit-specific effects.

Activity in a prefrontal-periaqueductal gray circuit overcomes behavioral and endocrine features of the passive coping stress response

The question of how the brain links behavioral and biological features of defensive responses has remained elusive. The importance of this problem is underscored by the observation that behavioral passivity in stress coping is associated with elevations in glucocorticoid hormones, and each may carry risks for susceptibility to a host of stress-related diseases. Past work implicates the medial prefrontal cortex (mPFC) in the top-down regulation of stress-related behaviors; however, it is unknown whether such changes have the capacity to buffer against the longer-lasting biological consequences associated with aversive experiences. Using the shock probe defensive burying test in rats to naturalistically measure behavioral and endocrine features of coping, we observed that the active behavioral component of stress coping is associated with increases in activity along a circuit involving the caudal mPFC and midbrain dorsolateral periaqueductal gray (PAG). Optogenetic manipulations of the caudal mPFC-to-dorsolateral PAG pathway bidirectionally modulated active (escape and defensive burying) behaviors, distinct from a rostral mPFC-ventrolateral PAG circuit that instead limited passive (immobility) behavior. Strikingly, under conditions that biased rats toward a passive coping response set, including exaggerated stress hormonal output and increased immobility, excitation of the caudal mPFC-dorsolateral PAG projection significantly attenuated each of these features. These results lend insight into how the brain coordinates response features to overcome passive coping and may be of importance for understanding how activated neural systems promote stress resilience.

Alterations of functional connectivity of the lateral habenula in subclinical depression and major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is a common cause of disability and morbidity, affecting about 10% of the population worldwide. Subclinical depression (SD) can be understood as a precursor of MDD, and therefore provides an MDD risk indicator. The pathogenesis of MDD and SD in humans is still unclear, and the current diagnosis lacks accurate biomarkers and gold standards.

METHODS

A total of 40 MDD, 34 SD, and 40 healthy control (HC) participants matched by age, gender, and education were included in this study. Resting-state functional magnetic resonance images (rs-fMRI) were used to analyze the functional connectivity (FC) of the posterior parietal thalamus (PPtha), which includes the lateral habenula, as the region of interest. Analysis of variance with the post hoc t-test test was performed to find significant differences in FC and clarify the variations in FC among the HC, SD, and MDD groups.

RESULTS

Increased FC was observed between PPtha and the left inferior temporal gyrus (ITG) for MDD versus SD, and between PPtha and the right ITG for SD versus HC. Conversely, decreased FC was observed between PPtha and the right middle temporal gyrus (MTG) for MDD versus SD and MDD versus HC. The FC between PPtha and the middle frontal gyrus (MFG) in SD was higher than that in MDD and HC. Compared with the HC group, the FC of PPtha-ITG (left and right) increased in both the SD and MDD groups, PPtha-MTG (right) decreased in both the SD and MDD groups and PPtha-MFG (right) increased in the SD group and decreased in the MDD group.

CONCLUSION

Through analysis of FC measured by rs-fMRI, the altered FC between PPtha and several brain regions (right and left ITG, right MTG, and right MFG) has been identified in participants with SD and MDD. Different alterations in FC between PPtha and these regions were identified for patients with depression. These findings might provide insights into the potential pathophysiological mechanisms of SD and MDD, especially related to PPtha and the lateral habenula.

Disrupted development from head to tail: Pervasive effects of postnatal restricted resources on neurobiological, behavioral, and morphometric outcomes

When a maternal rat nurtures her pups, she relies on adequate resources to provide optimal care for her offspring. Accordingly, limited environmental resources may result in atypical maternal care, disrupting various developmental outcomes. In the current study, maternal Long-Evans rats were randomly assigned to either a standard resource (SR) group, provided with four cups of bedding and two paper towels for nesting material or a limited resource (LR) group, provided with a quarter of the bedding and nesting material provided for the SR group. Offspring were monitored at various developmental phases throughout the study. After weaning, pups were housed in same-sex dyads in environments with SRs for continued observations. Subsequent behavioral tests revealed a sex × resource interaction in play behavior on PND 28; specifically, LR reduced play attacks in males while LR increased play attacks in females. A sex × resource interaction was also observed in anxiety-related responses in the open field task with an increase in thigmotaxis in LR females and, in the social interaction task, females exhibited more external rears oriented away from the social target. Focusing on morphological variables, tail length measurements of LR males and females were shorter on PND 9, 16, and 21; however, differences in tail length were no longer present at PND 35. Following the behavioral assessments, animals were perfused at 56 days of age and subsequent immunohistochemical assays indicated increased glucocorticoid receptors in the lateral habenula of LR offspring and higher c-Fos immunoreactivity in the basolateral amygdala of SR offspring. Further, when tail vertebrae and tail tendons were assessed via micro-CT and hydroxyproline assays, results indicated increased trabecular separation, decreased bone volume fraction, and decreased connectivity density in bones, along with reduced collagen concentration in tendons in the LR animals. In sum, although the restricted resources only persisted for a brief duration, the effects appear to be far-reaching and pervasive in this early life stress animal model.

The influence of the subcortex and brain stem on overeating: How advances in functional neuroimaging can be applied to expand neurobiological models to beyond the cortex

Functional neuroimaging has become a widely used tool in obesity and eating disorder research to explore the alterations in neurobiology that underlie overeating and binge eating behaviors. Current and traditional neurobiological models underscore the importance of impairments in brain systems supporting reward, cognitive control, attention, and emotion regulation as primary drivers for overeating. Due to the technical limitations of standard field strength functional magnetic resonance imaging (fMRI) scanners, human neuroimaging research to date has focused largely on cortical and basal ganglia effects on appetitive behaviors. The present review draws on animal and human research to highlight how neural signaling encoding energy regulation, reward-learning, and habit formation converge on hypothalamic, brainstem, thalamic, and striatal regions to contribute to overeating in humans. We also consider the role of regions such as the mediodorsal thalamus, ventral striatum, lateral hypothalamus and locus coeruleus in supporting habit formation, inhibitory control of food craving, and attentional biases. Through these discussions, we present proposals on how the neurobiology underlying these processes could be examined using functional neuroimaging and highlight how ultra-high field 7-Tesla (7 T) fMRI may be leveraged to elucidate the potential functional alterations in subcortical networks. Focus is given to how interactions of these regions with peripheral endocannabinoids and neuropeptides, such as orexin, could be explored. Technical and methodological aspects regarding the use of ultra-high field 7 T fMRI to study eating behaviors are also reviewed.

Reward ameliorates depressive-like behaviors via inhibition of the substantia innominata to the lateral habenula projection

The lateral habenula (LHb) is implicated in emotional processing, especially depression. Recent studies indicate that the basal forebrain (BF) transmits reward or aversive signals to the LHb. However, the contribution of the BF-LHb circuit to the pathophysiology of depression still needs to be determined. Here, we find that the excitatory projection to the LHb from the substantia innominata (SI), a BF subregion, is activated by aversive stimuli and inhibited by reward stimuli. Furthermore, chronic activation of the SI-LHb circuit is sufficient to induce depressive-like behaviors, whereas inhibition of the circuit alleviates chronic stress-induced depressive-like phenotype. We also find that reward consumption buffers depressive-like behaviors induced by chronic activation of the SI-LHb circuit. In summary, we systematically define the function and mechanism of the SI-LHb circuit in modulating depressive-like behaviors, thus providing important insights to better decipher LHb processing in the pathophysiology of depression.

Impact of stress on inhibitory neuronal circuits, our tribute to Bruce McEwen

This manuscript is dedicated to the memory of Bruce S. McEwen, to commemorate the impact he had on how we understand stress and neuronal plasticity, and the profound influence he exerted on our scientific careers. The focus of this review is the impact of stressors on inhibitory circuits, particularly those of the limbic system, but we also consider other regions affected by these adverse experiences. We revise the effects of acute and chronic stress during different stages of development and lifespan, taking into account the influence of the sex of the animals. We review first the influence of stress on the physiology of inhibitory neurons and on the expression of molecules related directly to GABAergic neurotransmission, and then focus on specific interneuron subpopulations, particularly on parvalbumin and somatostatin expressing cells. Then we analyze the effects of stress on molecules and structures related to the plasticity of inhibitory neurons: the polysialylated form of the neural cell adhesion molecule and perineuronal nets. Finally, we review the potential of antidepressants or environmental manipulations to revert the effects of stress on inhibitory circuits.

Hypothalamus-habenula potentiation encodes chronic stress experience and drives depression onset

Chronic stress is a major risk factor for depression onset. However, it remains unclear how repeated stress sculpts neural circuits and finally elicits depression. Given the essential role of lateral habenula (LHb) in depression, here, we attempt to clarify how LHb-centric neural circuitry integrates stress-related information. We identify lateral hypothalamus (LH) as the most physiologically relevant input to LHb under stress. LH neurons fire with a unique pattern that efficiently drives postsynaptic potential summation and a closely followed LHb bursting (EPSP-burst pairing) in response to various stressors. We found that LH-LHb synaptic potentiation is determinant in stress-induced depression. Mimicking this repeated EPSP-burst pairings at LH-LHb synapses by photostimulation, we artificially induced an "emotional status" merely by potentiating this pathway in mice. Collectively, these results delineate the spatiotemporal dynamics of chronic stress processing from forebrain onto LHb in a pathway-, cell-type-, and pattern-specific manner, shedding light on early interventions before depression onset.

Circadian Influences on the Habenula and Their Potential Contribution to Neuropsychiatric Disorders

The neural circadian system consists of the master circadian clock in the hypothalamic suprachiasmatic nuclei (SCN) communicating time of day cues to the rest of the body including other brain areas that also rhythmically express circadian clock genes. Over the past 16 years, evidence has emerged to indicate that the habenula of the epithalamus is a candidate extra-SCN circadian oscillator. When isolated from the SCN, the habenula sustains rhythms in clock gene expression and neuronal activity, with the lateral habenula expressing more robust rhythms than the adjacent medial habenula. The lateral habenula is responsive to putative SCN output factors as well as light information conveyed to the perihabenula area. Neuronal activity in the lateral habenula is altered in depression and intriguingly disruptions in circadian rhythms can elevate risk of developing mental health disorders including depression. In this review, we will principally focus on how circadian and light signals affect the lateral habenula and evaluate the possibility that alteration in these influences contribute to mental health disorders.

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.

A translational perspective on the anti-anhedonic effect of ketamine and its neural underpinnings

Anhedonia, a pronounced reduction in interest or pleasure in any of life's daily activities, is a cardinal symptom of major depression. In this Perspective article, we synthesise the recent evidence from rodent, monkey and human neuroimaging literature to highlight how the habenula, a small evolutionarily conserved subcortical structure located in the midbrain, may orchestrate the behavioural expression of anhedonia across fronto-mesolimbic networks. We then review how this circuitry can be modulated by ketamine, an NMDA receptor antagonist with rapid antidepressant properties. We propose that experimental paradigms founded in reinforcement learning and value-based decision-making can usefully probe this network and thereby help elucidate the mechanisms underlying ketamine's rapid antidepressant action.

Networks of habenula-projecting cortical neurons regulate cocaine seeking

How neurons in the medial prefrontal cortex broadcast stress-relevant information to subcortical brain sites to regulate cocaine relapse remains unclear. The lateral habenula (LHb) serves as a “hub” to filter and propagate stress- and aversion-relevant information in the brain. Here, we show that chemogenetic inhibition of cortical inputs to LHb attenuates relapse-like reinstatement of extinguished cocaine seeking in mice. Using an RNA sequencing–based brain mapping procedure with single-cell resolution, we identify networks of cortical neurons that project to LHb and then preferentially innervate different downstream brain sites, including the ventral tegmental area, median raphe nucleus, and locus coeruleus (LC). By using an intersectional chemogenetics approach, we show that inhibition of cortico-habenular neurons that project to LC, but not to other sites, blocks reinstatement of cocaine seeking. These findings highlight the remarkable complexity of descending cortical inputs to the habenula and identify a cortico-habenulo-hindbrain circuit that regulates cocaine seeking.

Neural Responsivity to Reward versus Punishment Shortly after Trauma Predicts Long-term Development of Post-Traumatic Stress Symptoms

BACKGROUND

Processing negative and positive valenced stimuli involve multiple brain regions including the amygdala and ventral striatum (VS). Post-Traumatic Stress Disorder (PTSD) is often associated with hyper-responsivity to negatively valenced, yet recent evidence also points to deficient positive valence functioning. It is yet unclear what is the relative contribution of such opposing valence processing shortly after trauma to the development of chronic PTSD.

METHODS

Neurobehavioral indicators of motivational positive vs. negative valence sensitivities were longitudinally assessed in 171 adults (87 females, age=34.19±11.47 years) at 1-, 6-, and 14-months following trauma exposure (TP1, TP2, TP3). Using a gambling fMRI paradigm, amygdala and VS functionality (activity and functional connectivity with the prefrontal cortex) in response to rewards vs. punishments were assessed with relation to PTSD severity at different time-points. The effect of valence processing was depicted behaviorally by the amount of risk taken to maximize reward.

RESULTS

PTSD severity at TP1 was associated with greater neural functionality in the amygdala (but not the VS) towards punishments vs. rewards, and fewer risky choices. PTSD severity at TP3 was associated with decreased neural functionality in both the VS and amygdala towards rewards vs. punishments at TP1 (but not with risky behavior). Explainable machine learning revealed the primacy of VS biased processing, over the amygdala, in predicting PTSD severity at TP3.

CONCLUSIONS

These results highlight the importance of biased neural responsivity to positive relative to negative motivational outcomes in PTSD development. Novel therapeutic strategies early after trauma may thus target both valence fronts.

Anhedonia as a central factor in depression: Neural mechanisms revealed from preclinical to clinical evidence

Anhedonia is one of the core symptoms of major depressive disorder (MDD), which is often inadequately treated by traditional antidepressants. The modern framework of anhedonia extends the definition from impaired consummatory pleasure or interest in rewards to a broad spectrum of deficits that impact functions such as reward anticipation, approach motivation, effort expenditure, reward valuation, expectation, and reward-cue association learning. Substantial preclinical and clinical research has explored the neural basis of reward deficits in the context of depression, and has implicated mesocorticolimbic reward circuitry comprising the nucleus accumbens, ventral pallidum, ventral tegmental area, amygdala, hippocampus, anterior cingulate, insula, orbitofrontal cortex, and other prefrontal cortex regions. Dopamine modulates several reward facets including anticipation, motivation, effort, and learning. As well, serotonin, norepinephrine, opioids, glutamate, Gamma aminobutyric acid (GABA), and acetylcholine are also involved in anhedonia, and medications targeting these systems may also potentially normalize reward processing in depression. Unfortunately, whereas reward anticipation and reward outcome are extensively explored by both preclinical and clinical studies, translational gaps remain in reward motivation, effort, valuation, and learning, where clinical neuroimaging studies are in the early stages. This review aims to synthesize the neurobiological mechanisms underlying anhedonia in MDD uncovered by preclinical and clinical research. The translational difficulties in studying the neural basis of reward are also discussed.

Repurposing Ketamine in Depression and Related Disorders: Can This Enigmatic Drug Achieve Success?

Repurposing ketamine in the therapy of depression could well represent a breakthrough in understanding the etiology of depression. Ketamine was originally used as an anesthetic drug and later its use was extended to other therapeutic applications such as analgesia and the treatment of addiction. At the same time, the abuse of ketamine as a recreational drug has generated a concern for its psychotropic and potential long-term effects; nevertheless, its use as a fast acting antidepressant in treatment-resistant patients has boosted the interest in the mechanism of action both in psychiatry and in the wider area of neuroscience. This article provides a comprehensive overview of the actions of ketamine and intends to cover: (i) the evaluation of its clinical use in the treatment of depression and suicidal behavior; (ii) the potential use of ketamine in pediatrics; (iii) a description of its mechanism of action; (iv) the involvement of specific brain areas in producing antidepressant effects; (v) the potential interaction of ketamine with the hypothalamic-pituitary-adrenal axis; (vi) the effect of ketamine on neuronal transmission in the bed nucleus of stria terminalis and on its output; (vii) the evaluation of any gender-dependent effects of ketamine; (viii) the interaction of ketamine with the inflammatory processes involved in depression; (ix) the evaluation of the effects observed with single or repeated administration; (x) a description of any adverse or cognitive effects and its abuse potential. Finally, this review attempts to assess whether ketamine's use in depression can improve our knowledge of the etiopathology of depression and whether its therapeutic effect can be considered an actual cure for depression rather than a therapy merely aimed to control the symptoms of depression.

Lateral Habenula Mediates Defensive Responses Only When Threat and Safety Memories Are in Conflict

Survival depends on the ability to adaptively react or execute actions based on previous aversive salient experiences. Although lateral habenula (LHb) activity has been broadly implicated in the regulation of aversively motivated responses, it is not clear under which conditions this brain structure is necessary to regulate defensive responses to a threat. To address this issue, we combined pharmacological inactivations with behavioral tasks that involve aversive and appetitive events and evaluated defensive responses in rats. We found that LHb pharmacological inactivation did not affect cued threat conditioning (fear) and extinction (safety) learning and memory, anxiety-like or reward-seeking behaviors. Surprisingly, we found that LHb inactivation abolished reactive defensive responses (tone-elicited freezing) only when threat (conditioning) and safety memories (extinction and latent inhibition) compete during retrieval. Consistently, we found that LHb inactivation impaired active defensive responses [platform-mediated avoidance (PMA)], thereby biasing choice behavior (between avoiding a threat or approaching food) toward reward-seeking responses. Together, our findings suggest that LHb activity mediates defensive responses only when guided by competing threat and safety memories, consequently revealing a previously uncharacterized role for LHb in experience-dependent emotional conflict.

Stress undermines reward-guided cognitive performance through synaptic depression in the lateral habenula

Weighing alternatives during reward pursuit is a vital cognitive computation that, when disrupted by stress, yields aspects of neuropsychiatric disorders. To examine the neural mechanisms underlying these phenomena, we employed a behavioral task in which mice were confronted by a reward and its omission (i.e., error). The experience of error outcomes engaged neuronal dynamics within the lateral habenula (LHb), a subcortical structure that supports appetitive behaviors and is susceptible to stress. A high incidence of errors predicted low strength of habenular excitatory synapses. Accordingly, stressful experiences increased error choices while decreasing glutamatergic neurotransmission onto LHb neurons. This synaptic adaptation required a reduction in postsynaptic AMPA receptors (AMPARs), irrespective of the anatomical source of glutamate. Bidirectional control of habenular AMPAR transmission recapitulated and averted stress-driven cognitive deficits. Thus, a subcortical synaptic mechanism vulnerable to stress underlies behavioral efficiency during cognitive performance.

Neural Computations of Threat

A host of learning, memory, and decision-making processes form the individual's response to threat and may be disrupted in anxiety and post-trauma psychopathology. Here we review the neural computations of threat, from the first encounter with a dangerous situation, through learning, storing, and updating cues that predict it, to making decisions about the optimal course of action. The overview highlights the interconnected nature of these processes and their reliance on shared neural and computational mechanisms. We propose an integrative approach to the study of threat-related processes, in which specific computations are studied across the various stages of threat experience rather than in isolation. This approach can generate new insights about the evolution, diagnosis, and treatment of threat-related psychopathology.

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.

Protein kinase C mediates neuropeptide Y-induced reduction in inhibitory neurotransmission in the lateral habenula

Neuropeptide Y (NPY) is one of peptide neuromodulators, well known for orexigenic, anxiolytic and antidepressant effects. We previously reported that NPY decreases GABAergic transmission in the lateral habenula (LHb). In the current study, we aim to investigate the underlying signaling pathways that mediate inhibitory action of NPY in the LHb by employing whole-cell patch clamp recording with pharmacological interventions. Here, we revealed that Y1 receptors (Y1Rs) but not Y2Rs mediate NPY-induced decrease of GABAergic transmission in the LHb. Surprisingly, NPY-induced decrease of inhibitory transmission in the LHb was not dependent on adenylyl cyclase (AC)/protein kinase A (PKA)-dependent pathway as reported in other brain areas. Instead, pharmacological blockade of phospholipase C (PLC) or protein kinase C (PKC) activity abolished the decrease of GABAergic transmission by NPY in the LHb. Our findings suggest that Y1Rs in the LHb may trigger the activation of PLC/PKC-dependent pathway but not the classical AC/PKA-dependent pathway to decrease inhibitory transmission of the LHb.

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.

Event-related functional MRI of awake behaving pigeons at 7T

Animal-fMRI is a powerful method to understand neural mechanisms of cognition, but it remains a major challenge to scan actively participating small animals under low-stress conditions. Here, we present an event-related functional MRI platform in awake pigeons using single-shot RARE fMRI to investigate the neural fundaments for visually-guided decision making. We established a head-fixated Go/NoGo paradigm, which the animals quickly learned under low-stress conditions. The animals were motivated by water reward and behavior was assessed by logging mandibulations during the fMRI experiment with close to zero motion artifacts over hundreds of repeats. To achieve optimal results, we characterized the species-specific hemodynamic response function. As a proof-of-principle, we run a color discrimination task and discovered differential neural networks for Go-, NoGo-, and response execution-phases. Our findings open the door to visualize the neural fundaments of perceptual and cognitive functions in birds-a vertebrate class of which some clades are cognitively on par with primates.

Total Recall: Lateral Habenula and Psychedelics in the Study of Depression and Comorbid Brain Disorders

Depression impacts the lives and daily activities of millions globally. Research into the neurobiology of lateral habenula circuitry and the use of psychedelics for treating depressive states has emerged in the last decade as new directions to devise interventional strategies and therapies. Several clinical trials using deep brain stimulation of the habenula, or using ketamine, and psychedelics that target the serotonergic system such as psilocybin are also underway. The promising early results in these fields require cautious optimism as further evidence from experiments conducted in animal systems in ecologically relevant settings, and a larger number of human studies with improved spatiotemporal neuroimaging, accumulates. Designing optimal methods of intervention will also be aided by an improvement in our understanding of the common genetic and molecular factors underlying disorders comorbid with depression, as well as the characterization of psychedelic-induced changes at a molecular level. Advances in the use of cerebral organoids offers a new approach for rapid progress towards these goals. Here, we review developments in these fast-moving areas of research and discuss potential future directions.

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.

Transcriptional and Spatial Resolution of Cell Types in the Mammalian Habenula

The habenula complex is appreciated as a critical regulator of motivated and pathological behavioral states via its output to midbrain nuclei. Despite this, transcriptional definition of cell populations that comprise both the medial habenular (MHb) and lateral habenular (LHb) subregions in mammals remain undefined. To resolve this, we performed single-cell transcriptional profiling and highly multiplexed in situ hybridization experiments of the mouse habenula complex in naive mice and those exposed to an acute aversive stimulus. Transcriptionally distinct neuronal cell types identified within the MHb and LHb, were spatially defined, differentially engaged by aversive stimuli, and had distinct electrophysiological properties. Cell types identified in mice also displayed a high degree of transcriptional similarity to those previously described in zebrafish, highlighting the well-conserved nature of habenular cell types across the phylum. These data identify key molecular targets within habenular cell types and provide a critical resource for future studies.

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.

Opioid system is necessary but not sufficient for antidepressive actions of ketamine in rodents

Slow response to the standard treatment for depression increases suffering and risk of suicide. Ketamine, an N-methyl-d-aspartate (NMDA) receptor antagonist, can rapidly alleviate depressive symptoms and reduce suicidality, possibly by decreasing hyperactivity in the lateral habenula (LHb) brain nucleus. Here we find that in a rat model of human depression, opioid antagonists abolish the ability of ketamine to reduce the depression-like behavioral and LHb hyperactive cellular phenotypes. However, activation of opiate receptors alone is not sufficient to produce ketamine-like effects, nor does ketamine mimic the hedonic effects of an opiate, indicating that the opioid system does not mediate the actions of ketamine but rather is permissive. Thus, ketamine does not act as an opiate but its effects require both NMDA and opiate receptor signaling, suggesting that interactions between these two neurotransmitter systems are necessary to achieve an antidepressant effect.

SYNPLA, a method to identify synapses displaying plasticity after learning

Which neural circuits undergo synaptic changes when an animal learns? Although it is widely accepted that changes in synaptic strength underlie many forms of learning and memory, it remains challenging to connect changes in synaptic strength at specific neural pathways to specific behaviors and memories. Here we introduce SYNPLA (synaptic proximity ligation assay), a synapse-specific, high-throughput, and potentially brain-wide method capable of detecting circuit-specific learning-induced synaptic plasticity.

Habenular connections with the dopaminergic and serotonergic system and their role in stress-related psychiatric disorders

The habenula (Hb) is a phylogenetically old epithalamic structure differentiated into two nuclear complexes, the medial (MHb) and lateral habenula (LHb). After decades of search for a great unifying function, interest in the Hb resurged when it was demonstrated that LHb plays a major role in the encoding of aversive stimuli ranging from noxious stimuli to the loss of predicted rewards. Consistent with a role as an anti-reward center, aberrant LHb activity has now been identified as a key factor in the pathogenesis of major depressive disorder. Moreover, both MHb and LHb emerged as new players in the reward circuitry by primarily mediating the aversive properties of distinct drugs of abuse. Anatomically, the Hb serves as a bridge that links basal forebrain structures with monoaminergic nuclei in the mid- and hindbrain. So far, research on Hb has focused on the role of the LHb in regulating midbrain dopamine release. However, LHb/MHb are also interconnected with the dorsal (DR) and median (MnR) raphe nucleus. Hence, it is conceivable that some of the habenular functions are at least partly mediated by the complex network that links MHb/LHb with pontomesencephalic monoaminergic nuclei. Here, we summarize research about the topography and transmitter phenotype of the reciprocal connections between the LHb and ventral tegmental area-nigra complex, as well as those between the LHb and DR/MnR. Indirect MHb outputs via interpeduncular nucleus to state-setting neuromodulatory networks will also be commented. Finally, we discuss the role of specific LHb-VTA and LHb/MHb-raphe circuits in anxiety and depression.

Biobehavioral utility of mindfulness-based art therapy: Neurobiological underpinnings and mental health impacts

Mindfulness-based art therapy (MBAT) combines mindfulness practices with art therapy to promote health, wellness, and adaptive responses to stress. Mindfulness-based stress reduction programs have been demonstrated to reduce anxiety symptoms in people with generalized anxiety disorder and serious medical conditions such as cancer. However, the benefits of MBAT specifically—not just in clinical anxiety disorders, but also for routine day-to-day anxiousness—have received little attention until recently. In this mini-review, we summarize how several established mindfulness-based interventions affect mental health with a specific focus on MBAT. We also describe and evaluate data indicating involvement of specific neural circuits and neuroendocrine markers of stress and/or anxiety. Lastly, we suggest areas of focus for future rigorous research on MBAT interventions and propose multiple biobehavioral and physiological mechanisms through which therapeutic benefits may be achieved.

Impact statement

Recent studies demonstrate the therapeutic potential of intensive MBAT and other mindfulness-based interventions for severe health conditions including cancer, heart disease, and anxiety, with effectiveness that rivals and sometimes even exceeds cognitive behavior therapy. MBAT-based approaches appear to be poised to mature into large-scale, cost-effective therapies for mental health disorders and symptoms comorbid with other serious health issues. However, the field currently suffers from inconsistent deployment protocols and needs additional validation data—at the behavioral, neuroendocrine, and neural levels—in order to establish best practices.

Wnt/β-catenin signaling in brain development and mental disorders: keeping TCF7L2 in mind

Canonical Wnt signaling, which is transduced by β-catenin and lymphoid enhancer factor 1/T cell-specific transcription factors (LEF1/TCFs), regulates many aspects of metazoan development and tissue renewal. Although much evidence has associated canonical Wnt/β-catenin signaling with mood disorders, the mechanistic links are still unknown. Many components of the canonical Wnt pathway are involved in cellular processes that are unrelated to classical canonical Wnt signaling, thus further blurring the picture. The present review critically evaluates the involvement of classical Wnt/β-catenin signaling in developmental processes that putatively underlie the pathology of mental illnesses. Particular attention is given to the roles of LEF1/TCFs, which have been discussed surprisingly rarely in this context. Highlighting recent discoveries, we propose that alterations in the activity of LEF1/TCFs, and particularly of transcription factor 7-like 2 (TCF7L2), result in defects previously associated with neuropsychiatric disorders, including imbalances in neurogenesis and oligodendrogenesis, the functional disruption of thalamocortical circuitry and dysfunction of the habenula.

Wnt/β-catenin signaling in brain development and mental disorders: keeping TCF7L2 in mind

Canonical Wnt signaling, which is transduced by β-catenin and lymphoid enhancer factor 1/T cell-specific transcription factors (LEF1/TCFs), regulates many aspects of metazoan development and tissue renewal. Although much evidence has associated canonical Wnt/β-catenin signaling with mood disorders, the mechanistic links are still unknown. Many components of the canonical Wnt pathway are involved in cellular processes that are unrelated to classical canonical Wnt signaling, thus further blurring the picture. The present review critically evaluates the involvement of classical Wnt/β-catenin signaling in developmental processes that putatively underlie the pathology of mental illnesses. Particular attention is given to the roles of LEF1/TCFs, which have been discussed surprisingly rarely in this context. Highlighting recent discoveries, we propose that alterations in the activity of LEF1/TCFs, and particularly of transcription factor 7-like 2 (TCF7L2), result in defects previously associated with neuropsychiatric disorders, including imbalances in neurogenesis and oligodendrogenesis, the functional disruption of thalamocortical circuitry and dysfunction of the habenula.

Stress transforms lateral habenula reward responses into punishment signals

Neuronal activity in the lateral habenula (LHb), a brain region implicated in depression [C. D. Proulx, O. Hikosaka, R. Malinow, Nat. Neurosci. 17, 1146-1152 (2014)], decreases during reward and increases during punishment or reward omission [M. Matsumoto, O. Hikosaka, Nature 447, 1111-1115 (2007)]. While stress is a major risk factor for depression and strongly impacts the LHb, its effect on LHb reward signals is unknown. Here we image LHb neuronal activity in behaving mice and find that acute stress transforms LHb reward responses into punishment-like neural signals; punishment-like responses to reward omission also increase. These neural changes matched the onset of anhedonic behavior and were specific to LHb neurons that distinguished reward and its omission. Thus, stress distorts LHb responsivity to positive and negative feedback, which could bias individuals toward negative expectations, a key aspect of the proposed pathogenesis of depression [A. T. Beck, Depression: Clinical, Experimental, and Theoretical Aspects, sixth Ed (1967)].