Static and dynamic functional connectivity of the habenula in late-life depression patient with suicidal ideation

BACKGROUND

Suicide is one of the most lethal complications of late-life depression (LLD), and habenular dysfunction may be involved in depression-related suicidality and may serve as a potential target for alleviating suicidal ideation. This study aimed to investigate abnormal functional connectivity of the habenula in LLD patients with suicidal ideation.

METHODS

One hundred twenty-seven patients with LLD (51 with suicidal ideation (LLD-S) and 76 without suicidal ideation (LLD-NS)) and 75 healthy controls (HCs) were recruited. The static functional connectivity (sFC) and dynamic functional connectivity (dFC) between the habenula and the whole brain were compared among the three groups, and correlation and moderation analyses were applied to investigate whether suicidal ideation moderated the relationships of habenular FC with depressive symptoms and cognitive impairment.

RESULTS

The dFC between the right habenula and the left orbitofrontal cortex (OFC) increased in the following order: LLD-S > LLD-NS > control. No significant difference in the habenular sFC was found among the LLD-S, LLD-NS and control groups. The dFC between the right habenula and the left OFC was positively associated with global cognitive function and visuospatial skills, and the association between this dFC and visuospatial skills was moderated by suicidal ideation in patients with LLD.

CONCLUSION

The increased variability in dFC between the right habenula and left OFC was more pronounced in the LLD-S group than in the LLD-NS group, and the association between habenular-OFC dFC and visuospatial skills was moderated by suicidal ideation in patients with LLD.

Habenula Volume and Functional Connectivity Changes Following Laparoscopic Sleeve Gastrectomy for Obesity Treatment

BACKGROUND

Neuroimaging studies have revealed alterations in habenular (Hb) structure and functional connectivity (FC) in psychiatric conditions. The Hb plays a particularly critical role in regulating negative emotions, which trigger excessive food intake and obesity. However, obesity and weight loss intervention (i.e., laparoscopic sleeve gastrectomy [LSG])-associated changes in Hb structure and FC have not been studied.

METHODS

We used voxel-based morphometry analysis to measure changes in gray matter volume (GMV) in the Hb in 56 patients with obesity at pre-LSG and 12 months post-LSG and in 78 normal-weight (NW) control participants. Then, we conducted Hb seed-based resting-state FC (RSFC) to examine obesity-related and LSG-induced alterations in RSFC. Finally, we used mediation analysis to characterize the interrelationships among Hb GMV, RSFC, and behaviors.

RESULTS

Compared with NW participants, Hb GMV was smaller in patients at pre-LSG and increased at 12 months post-LSG to levels equivalent to that of NW; in addition, increases in Hb GMV were correlated with reduced body mass index (BMI). Compared with NW participants, pre-LSG patients showed greater RSFCs of the Hb-insula, Hb-precentral gyrus, and Hb-rolandic operculum and weaker RSFCs of the Hb-thalamus, Hb-hypothalamus, and Hb-caudate; LSG normalized these RSFCs. Decreased RSFC of the Hb-insula was correlated with reduced BMI, Yale Food Addiction Scale rating, and emotional eating; reduced hunger levels were correlated with increased RSFCs of the Hb-thalamus and Hb-hypothalamus; and reduced BMI and Yale Food Addiction Scale ratings were correlated with increased RSFCs of the Hb-thalamus and Hb-hypothalamus, respectively. The bidirectional relationships between Hb GMV and RSFC of the Hb-insula contributed to reduced BMI.

CONCLUSIONS

These findings indicate that LSG increased Hb GMV and that its related improvement in RSFC of the Hb-insula may mediate long-term benefits of LSG for eating behaviors and weight loss.

Nicotine modulation of the lateral habenula/ventral tegmental area circuit dynamics: An electrophysiological study in rats

Nicotine, the addictive component of tobacco, has bivalent rewarding and aversive properties. Recently, the lateral habenula (LHb), a structure that controls ventral tegmental area (VTA) dopamine (DA) function, has attracted attention as it is potentially involved in the aversive properties of drugs of abuse. Hitherto, the LHb-modulation of nicotine-induced VTA neuronal activity in vivo is unknown. Using standard single-extracellular recording in anesthetized rats, we observed that intravenous administration of nicotine hydrogen tartrate (25-800 μg/kg i.v.) caused a dose-dependent increase in the basal firing rate of the LHb neurons of nicotine-naïve rats. This effect underwent complete desensitization in chronic nicotine (6 mg/kg/day for 14 days)-treated animals. As previously reported, acute nicotine induced an increase in the VTA DA neuronal firing rate. Interestingly, only neurons located medially (mVTA) but not laterally (latVTA) within the VTA were responsive to acute nicotine. This pattern of activation was reversed by chronic nicotine exposure which produced the selective increase of latVTA neuronal activity. Acute lesion of the LHb, similarly to chronic nicotine treatment, reversed the pattern of DA cell activation induced by acute nicotine increasing latVTA but not mVTA neuronal activity. Our evidence indicates that LHb plays an important role in mediating the effects of acute and chronic nicotine within the VTA by activating distinct subregional responses of DA neurons. The LHb/VTA modulation might be part of the neural substrate of nicotine aversive properties. By silencing the LHb chronic nicotine could shift the balance of motivational states toward the reward.

Increased theta/alpha synchrony in the habenula-prefrontal network with negative emotional stimuli in human patients

Lateral habenula is believed to encode negative motivational stimuli and plays key roles in the pathophysiology of psychiatric disorders. However, how habenula activities are modulated during the processing of emotional information is still poorly understood. We recorded local field potentials from bilateral habenula areas with simultaneous cortical magnetoencephalography in nine patients with psychiatric disorders during an emotional picture-viewing task. Transient activity in the theta/alpha band (5-10 Hz) within the habenula and prefrontal cortical regions, as well as the coupling between these structures, is increased during the perception and processing of negative emotional stimuli compared to positive emotional stimuli. The increase in theta/alpha band synchronization in the frontal cortex-habenula network correlated with the emotional valence but not the arousal score of the stimuli. These results provide direct evidence for increased theta/alpha synchrony within the habenula area and prefrontal cortex-habenula network in the perception of negative emotion in human participants.

Alterations of amygdala-prefrontal cortical coupling and attention deficit/hyperactivity disorder-like behaviors induced by neonatal habenula lesion: normalization by Ecklonia stolonifera extract and its active compound fucosterol

Alterations of monoamine transmission in mesocorticolimbic regions have been suggested in the pathophysiology of attention deficit/hyperactivity disorder (ADHD). The habenula is an important brain area in regulation of monoamine transmission. In this study, we investigated behavioral and electrophysiological alterations induced by neonatal habenula lesion (NHL) in rats. In NHL rats, age-dependent behavioral alterations relevant to the ADHD symptoms, such as hyperlocomotion, impulsivity, and attention deficit, were observed. Local field potentials (LFPs) in mesocorticolimbic regions of anesthetized rats were examined with in vivo electrophysiological recordings. Abnormally enhanced synchronization of slow (delta) and fast (gamma) LFP oscillations between the amygdala (AMY) and prefrontal cortex (PFC) was found in juvenile, but not in adult, NHL rats. We further examined the effects of an extract and the active compound from the perennial large brown algae Ecklonia stolonifera (ES), which have previously been demonstrated to modulate monoamine transmission, on these NHL-induced alterations. One week of ES extract treatments normalized the NHL-induced behavioral alterations, whereas the active compound fucosterol improved attention deficit and impulsivity, but not hyperlocomotion, in NHL rats. Consistent with the behavioral effects, ES extract treatments also normalized augmented AMY-PFC coupling. These results suggest that altered limbic-cortical information processing may be involved in ADHD-like behavioral alterations induced by NHL, which could be ameliorated by the natural substance, such as ES that affects monoamine transmission.

Lateral habenula dysfunctions in Tm4sf2-/y mice model for neurodevelopmental disorder

Mutations in the TM4SF2 gene, which encodes TSPAN7, cause a severe form of intellectual disability (ID) often comorbid with autism spectrum disorder (ASD). Recently, we found that TM4SF2 loss in mice affects cognition. Here, we report that Tm4sf2-/y mice, beyond an ID-like phenotype, display altered sociability, increased repetitive behaviors, anhedonic- and depressive-like states. Cognition relies on the integration of information from several brain areas. In this context, the lateral habenula (LHb) is strategically positioned to coordinate the brain regions involved in higher cognitive functions. Furthermore, in Tm4sf2-/y mice we found that LHb neurons present hypoexcitability, aberrant neuronal firing pattern and altered sodium and potassium voltage-gated ion channels function. Interestingly, we also found a reduced expression of voltage-gated sodium channel and a hyperactivity of the PKC-ERK pathway, a well-known modulator of ion channels activity, which might explain the functional phenotype showed by Tm4sf2-/y mice LHb neurons. These findings support Tm4sf2-/y mice as useful in modeling some ASD-like symptoms. Additionally, we can speculate that LHb functional alteration in Tm4sf2-/y mice might play a role in the disease pathophysiology.

Habenula Connectivity and Intravenous Ketamine in Treatment-Resistant Depression

BACKGROUND

Ketamine's potent and rapid antidepressant properties have shown great promise to treat severe forms of major depressive disorder (MDD). A recently hypothesized antidepressant mechanism of action of ketamine is the inhibition of N-methyl-D-aspartate receptor-dependent bursting activity of the habenula (Hb), a small brain structure that modulates reward and affective states.

METHODS

Resting-state functional magnetic resonance imaging was conducted in 35 patients with MDD at baseline and 24 hours following treatment with i.v. ketamine. A seed-to-voxel functional connectivity (FC) analysis was performed with the Hb as a seed-of-interest. Pre-post changes in FC and the associations between changes in FC of the Hb and depressive symptom severity were examined.

RESULTS

A reduction in Montgomery-Åsberg Depression Rating Scale scores from baseline to 24 hours after ketamine infusion was associated with increased FC between the right Hb and a cluster in the right frontal pole (t = 4.65, P = .03, false discovery rate [FDR]-corrected). A reduction in Quick Inventory of Depressive Symptomatology-Self Report score following ketamine was associated with increased FC between the right Hb and clusters in the right occipital pole (t = 5.18, P < .0001, FDR-corrected), right temporal pole (t = 4.97, P < .0001, FDR-corrected), right parahippocampal gyrus (t = 5.80, P = .001, FDR-corrected), and left lateral occipital cortex (t = 4.73, P = .03, FDR-corrected). Given the small size of the Hb, it is possible that peri-habenular regions contributed to the results.

CONCLUSIONS

These preliminary results suggest that the Hb might be involved in ketamine's antidepressant action in patients with MDD, although these findings are limited by the lack of a control group.

From controlled to compulsive drug-taking: The role of the habenula in addiction

Addiction is now recognized as a neurobiological and cognitive brain disorder and is generally viewed as a switch from recreational or voluntary to compulsive substance use despite aversive consequences. The habenula, composed of medial (MHb) and lateral (LHb) domains, has been implicated in regulating behavioral flexibility and anxiety-related behaviors and is considered a core component of the brain "anti-reward" system. These functions position the habenula to influence voluntary behaviors. Consistent with this view, emerging evidence points to alterations in habenula activity as important factors to contributing the loss of control over the use of drugs of abuse and the emergence of compulsive drug seeking behaviors. In this review, we will discuss the general functions of the MHb and LHb and describe how these functional properties allow this brain region to promote or suppress volitional behaviors. Then, we highlight mechanisms by which drugs of abuse may alter habenular activity, precipitating the emergence of addiction-relevant behavioral abnormalities.

Chronic Stress Induces Activity, Synaptic, and Transcriptional Remodeling of the Lateral Habenula Associated with Deficits in Motivated Behaviors

Chronic stress (CS) is a major risk factor for the development of depression. Here, we demonstrate that CS-induced hyperactivity in ventral tegmental area (VTA)-projecting lateral habenula (LHb) neurons is associated with increased passive coping (PC), but not anxiety or anhedonia. LHb→VTA neurons in mice with increased PC show increased burst and tonic firing as well as synaptic adaptations in excitatory inputs from the entopeduncular nucleus (EP). In vivo manipulations of EP→LHb or LHb→VTA neurons selectively alter PC and effort-related motivation. Conversely, dorsal raphe (DR)-projecting LHb neurons do not show CS-induced hyperactivity and are targeted indirectly by the EP. Using single-cell transcriptomics, we reveal a set of genes that can collectively serve as biomarkers to identify mice with increased PC and differentiate LHb→VTA from LHb→DR neurons. Together, we provide a set of biological markers at the level of genes, synapses, cells, and circuits that define a distinctive CS-induced behavioral phenotype.

Advances in Molecular and Circuitry Mechanisms of Depressive Disorder-A Focus on Lateral Habenula

Depression is a devastating disorder with a combination of diverse symptoms such as low self-esteem, lack of motivation, anhedonia, loss of appetite, low energy, and discomfort without a clear cause. Depression has been suggested to be the result of maladaptive changes in specific brain circuits. Recently, the lateral habenula (LHb) has emerged as a key brain region in the pathophysiology of depression. Increasing evidence from rodent, nonhuman primate, and human studies indicates that the aberrant activity of the LHb is associated with depressive symptoms such as helplessness, anhedonia, and excessive negative focus. Revealing the molecular, cellular, and circuit properties of the LHb will help explain how abnormalities in LHb activity are linked to depressive disorders and shed light on developing novel strategies for depression treatment.

[The Role of the Habenula in Depression: A Review of the Human fMRI Studies]

Depression has various symptoms, such as depressed mood or loss of motivation, and the pathophysiological mechanisms remain unclear. Recent studies have increased the understanding of the role of the habenula, since the habenula is reported to control the metabolism of monoamine neurotransmitters in the brain through direct projections to the ventral tegmental area and raphe nucleus. Human neuroimaging studies have been performed to attempt to clarify the mechanisms of depression. This manuscript mainly introduces human neuroimaging studies of the role of the habenula in depression.

Corticosterone Signaling and a Lateral Habenula-Ventral Tegmental Area Circuit Modulate Compulsive Self-Injurious Behavior in a Rat Model

Self-injurious behavior (SIB) is commonly observed in patients with neuropsychiatric disorders, as well as in nonclinical populations with stress-related mental-health problems. However, the exact circuitry mechanisms underlying SIB have remained poorly understood. Here, with bilateral injection of muscimol into the entopeduncular nucleus (EP), we established a rat model of SIB. Following the muscimol injection, the male rats exhibited in a dose-dependent manner stereotypic self-biting behavior that lasted for hours and often resulted in wounds of various severities. The SIB was associated with an elevated level of serum corticosterone and could be exacerbated by enhancing the corticosterone signaling and, conversely, alleviated by inhibiting the corticosterone signaling. Activity mapping using c-fos immunostaining, combined with connectivity mapping using herpes simplex virus-based anterograde tracing from the EP and pseudorabies virus-based retrograde tracing from the masseter muscle, revealed the potential involvement of many brain areas in SIB. In particular, the lateral habenula (LHb) and the ventral tegmental area (VTA), the two connected brain areas involved in stress response and reward processing, showed a significant increase in neuronal activation during SIB. Furthermore, suppressing the LHb activity or modulating the GABAergic transmission in the VTA could significantly reduce the occurrence of SIB. These results demonstrate the importance of stress hormone signaling and the LHb-VTA circuit in modulating SIB resulting from EP malfunction, and suggest potential targets for therapeutic intervention of SIB and related disorders.SIGNIFICANCE STATEMENT Self-injurious behavior (SIB) occurs in ∼4% of the general population, with substantially higher occurrence among adolescents and patients of neuropsychiatric disorders. Stress has been linked to the occurrence of SIB, yet the underlying mechanisms have remained unclear. Using a rat model of SIB induced by disruption of activity in the entopeduncular nucleus (EP), we found that the behavior is regulated by stress and linked to corticosterone signaling. Viral tracing and c-fos immunostaining revealed the involvement of various subcortical areas, especially the EP-lateral habenula (LHb)-ventral tegmental area (VTA) circuit, in SIB. Furthermore, regulating activity in the LHb or the VTA alleviates SIB. These results may have implications in the development of new strategies for treating SIB.

Lesions of the lateral habenula improve working memory performance in hemiparkinsonian rats

The lateral habenula (LHb) is an important structure involved in various brain functions, because it controls the activity of dopaminergic and serotonergic systems in the midbrain. The impairment of working memory commonly occurs in Parkinson's disease; however, it is not clear whether the LHb involves in the regulation of working memory in rats with unilateral 6-hydroxydopamine lesions of the medial forebrain bundle (MFB). In this study, we found that the MFB lesions in rats decreased choice accuracy as measured by the T-maze rewarded alternation test compared to control rats, indicating the induction of working memory impairment, and decreased dopamine (DA) levels in the medial prefrontal cortex (mPFC), hippocampus and amygdala. Further, rats in the MFB and LHb lesion group showed increased choice accuracy compared to rats in the MFB lesion group, indicating the enhancement of working memory after lesioning the LHb. Neurochemical results found that lesions of the LHb increased DA levels in the mPFC, hippocampus and amygdala in the MFB and LHb lesion group, as well as serotonin (5-HT) level in the mPFC. These findings suggest that DA depletion plays a key role in working memory impairment, and lesions of the LHb improve working memory in the MFB-lesioned rats, which involves in increases in the levels of DA and 5-HT in the mPFC, hippocampus and amygdala. Additionally, the present results may have implications for improving our understanding of the neuropathology and/or treatment of PD.

Association between habenula dysfunction and motivational symptoms in unmedicated major depressive disorder

The lateral habenula plays a central role in reward and punishment processing and has been suggested to drive the cardinal symptom of anhedonia in depression. This hypothesis is largely based on observations of habenula hypermetabolism in animal models of depression, but the activity of habenula and its relationship with clinical symptoms in patients with depression remains unclear. High-resolution functional magnetic resonance imaging (fMRI) and computational modelling were used to investigate the activity of the habenula during a probabilistic reinforcement learning task with rewarding and punishing outcomes in 21 unmedicated patients with major depression and 17 healthy participants. High-resolution anatomical scans were also acquired to assess group differences in habenula volume. Healthy individuals displayed the expected activation in the left habenula during receipt of punishment and this pattern was confirmed in the computational analysis of prediction error processing. In depressed patients, there was a trend towards attenuated left habenula activation to punishment, while greater left habenula activation was associated with more severe depressive symptoms and anhedonia. We also identified greater habenula volume in patients with depression, which was associated with anhedonic symptoms. Habenula dysfunction may contribute to abnormal response to punishment in patients with depression, and symptoms such as anhedonia.

The lateral hypothalamus to lateral habenula projection, but not the ventral pallidum to lateral habenula projection, regulates voluntary ethanol consumption

The lateral habenula (LHb) is an epithalamic brain region implicated in aversive processing via negative modulation of midbrain dopamine (DA) and serotonin (5-HT) systems. Given the role of the LHb in inhibiting DA and 5-HT systems, it is thought to be involved in various psychiatric pathologies, including drug addiction. In support, it has been shown that LHb plays a critical role in cocaine- and ethanol-related behaviors, most likely by mediating drug-induced aversive conditioning. In our previous work, we showed that LHb lesions increased voluntary ethanol consumption and operant ethanol self-administration and blocked yohimbine-induced reinstatement of ethanol self-administration. LHb lesions also attenuated ethanol-induced conditioned taste aversion suggesting that a mechanism for the increased intake of ethanol may be reduced aversion learning. However, whether afferents to the LHb are required for mediating effects of the LHb on these behaviors remained to be investigated. Our present results show that lesioning the fiber bundle carrying afferent inputs to the LHb, the stria medullaris (SM), increases voluntary ethanol consumption, suggesting that afferent structures projecting to the LHb are important for mediating ethanol-directed behaviors. We then chose two afferent structures as the focus of our investigation. We specifically studied the role of the inputs from the lateral hypothalamus (LH) and ventral pallidum (VP) to the LHb in ethanol-directed behaviors. Our results show that the LH-LHb projection is necessary for regulating voluntary ethanol consumption. These results are an important first step towards understanding the functional role of afferents to LHb with regard to ethanol consumption.

Translating the Habenula-From Rodents to Humans

The habenula (Hb) is a central structure connecting forebrain to midbrain regions. This microstructure regulates monoaminergic systems, notably dopamine and serotonin, and integrates cognitive with emotional and sensory processing. Early preclinical data have described Hb as a brain nucleus activated in anticipation of aversive outcomes. Evidence has now accumulated to show that the Hb encodes both rewarding and aversive aspects of external stimuli, thus driving motivated behaviors and decision making. Human Hb research is still nascent but develops rapidly, alongside with the growth of neuroimaging and deep brain stimulation techniques. Not surprisingly, Hb dysfunction has been associated with psychiatric disorders, and studies in patients have established evidence for Hb involvement in major depression, addiction, and schizophrenia, as well as in pain and analgesia. Here, we summarize current knowledge from animal research and overview the existing human literature on anatomy and function of the Hb. We also discuss challenges and future directions in targeting this small brain structure in both rodents and humans. By combining animal data and human experimental studies, this review addresses the translational potential of preclinical Hb research.

Increased excitability of lateral habenula neurons in adolescent rats following cocaine self-administration

BACKGROUND

The lateral habenula is a brain region that has been critically implicated in modulating negative emotional states and responses to aversive stimuli. Exposure to addictive drugs such as cocaine negatively impacts affective states, an effect persisting longer than acute drug effects. However, the mechanisms of this effect are poorly understood. We hypothesized that drugs of abuse, such as cocaine, may contribute to drug-induced negative affective states by altering the firing properties of lateral habenula neurons, thus changing the signaling patterns from the lateral habenula to downstream circuits.

METHODS

Using whole-cell current-clamp recording of acutely prepared brain slices of rats after various periods of withdrawal from cocaine self-administration, we characterized an important heterogeneous subregion of the lateral habenula based on membrane properties.

RESULTS

We found two major relevant neuronal subtypes: burst firing neurons and regular spiking neurons. We also found that lateral habenula regular spiking neurons had higher membrane excitability for at least 7 days following cocaine self-administration, likely due to a greater membrane resistance. Both the increase in lateral habenula excitability and membrane resistance returned to baseline when tested after a more prolonged period of 45 days of withdrawal.

CONCLUSION

This is the first study to look at intrinsic lateral habenula neuron properties following cocaine exposure beyond acute drug effects. These results may help to explain how cocaine and other drugs negatively impact affect states.

Lesions of the lateral habenula increase voluntary ethanol consumption and operant self-administration, block yohimbine-induced reinstatement of ethanol seeking, and attenuate ethanol-induced conditioned taste aversion

The lateral habenula (LHb) plays an important role in learning driven by negative outcomes. Many drugs of abuse, including ethanol, have dose-dependent aversive effects that act to limit intake of the drug. However, the role of the LHb in regulating ethanol intake is unknown. In the present study, we compared voluntary ethanol consumption and self-administration, yohimbine-induced reinstatement of ethanol seeking, and ethanol-induced conditioned taste aversion in rats with sham or LHb lesions. In rats given home cage access to 20% ethanol in an intermittent access two bottle choice paradigm, lesioned animals escalated their voluntary ethanol consumption more rapidly than sham-lesioned control animals and maintained higher stable rates of voluntary ethanol intake. Similarly, lesioned animals exhibited higher rates of responding for ethanol in operant self-administration sessions. In addition, LHb lesion blocked yohimbine-induced reinstatement of ethanol seeking after extinction. Finally, LHb lesion significantly attenuated an ethanol-induced conditioned taste aversion. Our results demonstrate an important role for the LHb in multiple facets of ethanol-directed behavior, and further suggest that the LHb may contribute to ethanol-directed behaviors by mediating learning driven by the aversive effects of the drug.

Concurrent activation of the somatosensory forebrain and deactivation of periaqueductal gray associated with diabetes-induced neuropathic pain

We combined behavioral testing with brain imaging using (99m)Tc-HMPAO (Amersham Health) to identify CNS structures reflecting alterations in pain perception in the streptozotocin (STZ) model of type I diabetes. We induced diabetic hyperglycemia (blood glucose >300 mg/dl) by injecting male Sprague-Dawley rats with STZ (45 mg/kg i.p.). Four weeks after STZ-diabetic rats exhibited behaviors indicative of neuropathic pain (hypersensitivity thermal stimuli) and this hypersensitivity persisted for up to 6 weeks. Imaging data in STZ-diabetic rats revealed significant increases in the activation of brain regions involved in pain processing after 6 weeks duration of diabetes. These regions included secondary somatosensory cortex, ventrobasal thalamic nuclei and the basolateral amygdala. In contrast, the activation in habenular nuclei and the midbrain periaqueductal gray were markedly decreased in STZ rats. These data suggest that pain in diabetic neuropathy may be due in part to hyperactivity in somatosensory structures coupled with a concurrent deactivation of structures mediating antinociception.

Schizophrenia in translation: the presence of absence: habenular regulation of dopamine neurons and the encoding of negative outcomes

Many patients with schizophrenia have pronounced deficits in the use of negative feedback to guide problem solving and learning, as seen on tasks like the Wisconsin Card Sorting Test. There is now a compelling body of evidence from nonhuman primates that suggests transient decreases in dopamine cell activity may reflect the occurrence of unexpected negative outcomes, such as the absence of an expected reward, and, generalizing to the human, the occurrence of negative feedback or the absence of expected reward. We present preliminary evidence that habenula projections to the midbrain are capable of producing a transient, but nearly complete, inhibition of dopamine neurons at a population level similar to that observed in behaving primates following an unexpected negative outcome. Human functional imaging studies offer further evidence that the habenula is activated following receipt of unexpected negative feedback or the absence of expected positive feedback. We present initial evidence that patients with schizophrenia lack appropriate modulation of habenula activity in response to feedback. Collectively, these data suggest that the habenula may play a critical role in mediating the feedback-processing deficits of schizophrenia.

Lesions of the habenula produce stress- and dopamine-dependent alterations in prepulse inhibition and locomotion

The habenula complex modulates the activity of dopamine and serotonin systems in the brain. An important question remains whether there is a link between habenula dysfunction and monoamine-related disorders, such as schizophrenia. In this study, we describe an interaction between habenula lesions and stress that produces long-lasting effects on behavior. Mice received control lesions or bilateral electrolytic lesions of the habenula and were tested for fear-potentiated startle and freezing measures of conditioned fear. They were also tested for prepulse inhibition (PPI) and locomotor activity in the presence or absence of a dopaminergic agonist (apomorphine) or an atypical antipsychotic with mixed dopamine/serotonin antagonist properties (clozapine). There were no detectable effects of habenula lesions on fear conditioning and no effects on PPI in the absence of stress. However, following conditioned fear stress, habenula-lesioned animals showed decreased PPI which normalized with clozapine. Lesioned animals also showed diminished activity at baseline, with hyperlocomotion following apomorphine. These data support the hypothesis that the habenula may be normally involved in stress-dependent regulation of monoamine systems.

Bilateral lesions of the habenula induce attentional disturbances in rats

The habenular nuclear complex is a major influence on brainstem cell groups that influence attention, but its role in attentional performance has not previously been explored. The present study investigated how habenula lesions affect attentional function as assessed by the 5-choice serial reaction time task (5-CSRTT) in male Lister-Hooded rats. Rats were pretrained in the 5-CSRTT before receiving discrete bilateral lesions of the habenula or a sham procedure. In test sessions immediately following recovery from surgery, lesioned rats showed a marked increase in premature responding. Over the course of testing this increase of premature responding declined in magnitude. In contrast, choice accuracy showed no impairment during the earliest postsurgery test sessions but progressively deteriorated over the course of testing. These opposite time courses strongly imply that different mechanisms mediate these two effects of the habenula lesion. Differential effects of drug treatment on these effects further supported this view. Thus, D-amphetamine (0.2 mg/kg s.c.) increased premature responding without affecting choice accuracy. On the other hand, haloperidol (0.01-0.03 mg/kg i.p.) decreased premature responding without significantly affecting choice accuracy. The results are consistent with the view that elevated premature responding in habenula-lesioned animals is mediated by increased dopaminergic activity, whereas impaired choice accuracy is not. Implications of these findings for the hypothesis that habenula dysfunction is involved in cognitive symptoms of schizophrenia are discussed.

The role of the habenular complex in the elevation of dorsal raphe nucleus serotonin and the changes in the behavioral responses produced by uncontrollable stress

Previous research indicates that the serotonergic neurons of the caudal dorsal raphe nucleus (DRN) are activated to a greater degree by inescapable shock (IS) as compared to escapable shock (ES), causing a greater release of serotonin (5-HT) in the DRN and in target regions. This differential activation is necessary for the behavioral changes that occur after exposure to IS, but not to ES (i.e. learned helplessness/behavioral depression). Although the critical role of the DRN in learned helplessness is clear, the neural inputs to the caudal DRN which result in this selective activation are unknown. One structure that may be involved in the activation of the DRN and the induction of learned helplessness/behavioral depression is the habenular complex. In experiment 1, habenula lesions eliminated the differential rise in DRN extracellular 5-HT levels in response to IS and ES exposure by severely attenuating the rise in 5-HT for both groups. In experiment 2, sham operated and habenula lesioned rats were exposed to either ES, IS or no stress (home cage control; HCC). Twenty-four hours later, sham rats previously exposed to IS exhibited longer escape latencies as compared to both ES and HCC rats (i.e. learned helplessness). The habenular lesion eliminated the differences in escape latency between groups, thus eliminating the induction of learned helplessness/behavioral depression. These results suggest that the habenula is necessary for the differential activation of the DRN and the escape deficits produced by IS.

Nicotine produces selective degeneration in the medial habenula and fasciculus retroflexus

Nicotine's neurotoxic properties in rats were investigated by administering (-)-nicotine tartrate for 5 days either continuously in doses of 5.01, 5.72, 6.44, 7.13, 20.41 and 43.1 mg/kg/day via osmotic minipump or intermittently at 11.32 mg/kg/day via one daily subcutaneous injection. As assessed by silver staining, neurotoxicity was seen almost exclusively in the axons of the medial habenula and its output tract, the fasciculus retroflexus, in all treatment groups except the lowest dose. Within the habenula, the damage was noted in the ventral-medial-most portion of the nucleus which is thought to be dense with the alpha 4 beta 2 and/or alpha 3 beta 4 receptor subtypes. Past research has shown the medial habenula to be highly sensitive to the effects of nicotine, and these findings, in conjunction with related research using dopaminergic stimulants, indicate that the habenula may be a weak link in the neurotoxicity seen following stimulant drugs of abuse.

Covariation of activity in habenula and dorsal raphé nuclei following tryptophan depletion

Abnormal serotonergic function is implicated in the pathogenesis of affective disorders. We induced transient depressive relapses in volunteer patients by rapidly depleting plasma tryptophan, the precursor of serotonin (5-HT), and measured neural activity during different cognitive tasks using positron emission tomography (PET). Neural activity in several 5-HT-related brain areas, e.g., dorsal raphé, habenula, septal region, amygdala, and orbitofrontal cortex, covaried significantly with plasma levels of tryptophan and ratings of depressed mood. Task-specific responses in left amygdala and left anterior cingulate were attenuated by tryptophan depletion. We used these PET data to test the hypothesis that projections from the habenula modulate dorsal raphé activity and that this modulation is enhanced in patients experiencing a profound mood change following serotonergic challenge. A strong linear correlation (r(2) > 0.5) between habenula and raphé activity was observed in subjects with postdepletion ratings >/=10 on a modified Hamilton depression scale, whereas subjects experiencing milder changes in mood had weaker habenula-raphé coupling (r(2) < 0.5). These data support a model of the serotonergic system in which the habenula projection to the raphé represents a convergent feedback pathway that controls the release of 5-HT throughout the brain. In our experiment we were able to engage this system in patients who were sensitive to tryptophan depletion.

[Involvement of habenula nucleus in the pathogenesis of stress induced hypertension and the underlying mechanisms]

Stress-induced hypertension (SIH) was performed by electric shock on hind paw in rats. Habenula(Hb) lesion decreased the degree of SIH. After stress, the Ang II concentration in blood plasma and in Hb were increased. BP was elevated after icv or MHb administration of Ang II, and decreased after microinjection of saralasin into MHb. The BP changes induced by Ang II and saralasin were more prominent in SIH than in normotensive rats. Iontophoresis of AngII (or saralasin) into Hb increased (or decreased) the discharges of the excitatory neurons related to cardiovascular activity. Ang II could inhibit the activity of Ik channel. Using the same methods, the actions of L-NNA and SNP were investigated. From above, it is suggested that Hb is involved in the development of SIH. Stress stimulus strengthened the sensitivity of Hb, especially MHb to AngII, and also induced in increase of AngII. These changes would promote the response of sensitized Hb in the development of SIH.