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

VGluT2 neuron subtypes in the paraventricular thalamic nucleus regulate depression in paraquat-induced Parkinson's disease

Parkinson's disease (PD) is a prevalent neurodegenerative disease and approximately one third of patients with PD are estimated to experience depression. Paraquat (PQ) is the most widely used herbicide worldwide and PQ exposure is reported to induce PD with depression. However, the specific brain region and neural networks underlying the etiology of depression in PD, especially in the PQ-induced model, have not yet been elucidated. Here, we report that the VGluT2-positive glutamatergic neurons in the paraventricular thalamic nucleus (PVT) promote depression in the PQ-induced PD mouse model. Our results show that PVTVGluT2 neurons are activated by PQ and their activation increases the susceptibility to depression in PD mice. Conversely, inhibition of PVTVGluT2 neurons reversed the depressive-behavioral changes induced by PQ. Similar to the effects of intervention the soma of PVTVGluT2 neurons, stimulation of their projections into the central amygdaloid nucleus (CeA) also strongly influenced depression in PD mice. PQ induced malfunctioning of the glutamate system and changes in the dendritic and synaptic morphology in the CeA through its role on PVTVGluT2 neuronal activation. In summary, our results demonstrate that PVTVGluT2 neurons are key neuronal subtypes for depression in PQ-induced PD and promote depression processes through the PVTVGluT2-CeA pathway.

The basal forebrain to lateral habenula circuitry mediates social behavioral maladaptation

Elucidating the neural basis of fear allows for more effective treatments for maladaptive fear often observed in psychiatric disorders. Although the basal forebrain (BF) has an essential role in fear learning, its function in fear expression and the underlying neuronal and circuit substrates are much less understood. Here we report that BF glutamatergic neurons are robustly activated by social stimulus following social fear conditioning in male mice. And cell-type-specific inhibition of those excitatory neurons largely reduces social fear expression. At the circuit level, BF glutamatergic neurons make functional contacts with the lateral habenula (LHb) neurons and these connections are potentiated in conditioned mice. Moreover, optogenetic inhibition of BF-LHb glutamatergic pathway significantly reduces social fear responses. These data unravel an important function of the BF in fear expression via its glutamatergic projection onto the LHb, and suggest that selective targeting BF-LHb excitatory circuitry could alleviate maladaptive fear in relevant disorders.

Comparative brain-wide mapping of ketamine- and isoflurane-activated nuclei and functional networks in the mouse brain

Ketamine (KET) and isoflurane (ISO) are two widely used general anesthetics, yet their distinct and shared neurophysiological mechanisms remain elusive. In this study, we conducted a comparative analysis of the effects of KET and ISO on c-Fos expression across the mouse brain, utilizing hierarchical clustering and c-Fos-based functional network analysis to evaluate the responses of individual brain regions to each anesthetic. Our findings reveal that KET activates a wide range of brain regions, notably in the cortical and subcortical nuclei involved in sensory, motor, emotional, and reward processing, with the temporal association areas (TEa) as a strong hub, suggesting a top-down mechanism affecting consciousness by primarily targeting higher order cortical networks. In contrast, ISO predominantly influences brain regions in the hypothalamus, impacting neuroendocrine control, autonomic function, and homeostasis, with the locus coeruleus (LC) as a connector hub, indicating a bottom-up mechanism in anesthetic-induced unconsciousness. KET and ISO both activate brain areas involved in sensory processing, memory and cognition, reward and motivation, as well as autonomic and homeostatic control, highlighting their shared effects on various neural pathways. In conclusion, our results highlight the distinct but overlapping effects of KET and ISO, enriching our understanding of the mechanisms underlying general anesthesia.

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.

Stress relief as a natural resilience mechanism against depression-like behaviors

Relief, the appetitive state after the termination of aversive stimuli, is evolutionarily conserved. Understanding the behavioral role of this well-conserved phenomenon and its underlying neurobiological mechanisms are open and important questions. Here, we discover that the magnitude of relief from physical stress strongly correlates with individual resilience to depression-like behaviors in chronic stressed mice. Notably, blocking stress relief causes vulnerability to depression-like behaviors, whereas natural rewards supplied shortly after stress promotes resilience. Stress relief is mediated by reward-related mesolimbic dopamine neurons, which show minute-long, persistent activation after stress termination. Circuitry-wise, activation or inhibition of circuits downstream of the ventral tegmental area during the transient relief period bi-directionally regulates depression resilience. These results reveal an evolutionary function of stress relief in depression resilience and identify the neural substrate mediating this effect. Importantly, our data suggest a behavioral strategy of augmenting positive valence of stress relief with natural rewards to prevent depression.

Whole-brain monosynaptic inputs to lateral periaqueductal gray glutamatergic neurons in mice

OBJECTIVE

The lateral periaqueductal gray (LPAG), which mainly contains glutamatergic neurons, plays an important role in social responses, pain, and offensive and defensive behaviors. Currently, the whole-brain monosynaptic inputs to LPAG glutamatergic neurons are unknown. This study aims to explore the structural framework of the underlying neural mechanisms of LPAG glutamatergic neurons.

METHODS

This study used retrograde tracing systems based on the rabies virus, Cre-LoxP technology, and immunofluorescence analysis.

RESULTS

We found that 59 nuclei projected monosynaptic inputs to the LPAG glutamatergic neurons. In addition, seven hypothalamic nuclei, namely the lateral hypothalamic area (LH), lateral preoptic area (LPO), substantia innominata (SI), medial preoptic area, ventral pallidum, posterior hypothalamic area, and lateral globus pallidus, projected most densely to the LPAG glutamatergic neurons. Notably, we discovered through further immunofluorescence analysis that the inputs to the LPAG glutamatergic neurons were colocalized with several markers related to important neurological functions associated with physiological behaviors.

CONCLUSION

The LPAG glutamatergic neurons received dense projections from the hypothalamus, especially nuclei such as LH, LPO, and SI. The input neurons were colocalized with several markers of physiological behaviors, which show the pivotal role of glutamatergic neurons in the physiological behaviors regulation by LPAG.

The thalamic reticular nucleus-lateral habenula circuit regulates depressive-like behaviors in chronic stress and chronic pain

Chronic stress and chronic pain are two major predisposing factors to trigger depression. Enhanced excitatory input to the lateral habenula (LHb) has been implicated in the pathophysiology of depression. However, the contribution of inhibitory transmission remains unclear. Here, we dissect an inhibitory projection from the sensory thalamic reticular nucleus (sTRN) to the LHb, which is activated by acute aversive stimuli. However, chronic restraint stress (CRS) weakens sTRN-LHb synaptic strength, and this synaptic attenuation is indispensable for CRS-induced LHb neural hyperactivity and depression onset. Moreover, artificially inhibiting the sTRN-LHb circuit induces depressive-like behaviors in healthy mice, while enhancing this circuit relieves depression induced by both chronic stress and chronic pain. Intriguingly, neither neuropathic pain nor comorbid mechanical hypersensitivity in chronic stress is affected by this pathway. Altogether, our study demonstrates an sTRN-LHb circuit in establishing and modulating depression, thus shedding light on potential therapeutic targets for preventing or managing depression.

Ventral pallidal glutamatergic neurons regulate wakefulness and emotion through separated projections

Insomnia is often comorbid with depression, but the underlying neuronal circuit mechanism remains elusive. Recently, we reported that GABAergic ventral pallidum (VP) neurons control wakefulness associated with motivation. However, whether and how other subtypes of VP neurons regulate arousal and emotion are largely unknown. Here, we report glutamatergic VP (VPVglut2) neurons control wakefulness and depressive-like behaviors. Physiologically, the calcium activity of VPVglut2 neurons was increased during both NREM sleep-to-wake transitions and depressive/anxiety-like behaviors in mice. Functionally, activation of VPVglut2 neurons was sufficient to increase wakefulness and induce anxiety/depressive-like behaviors, whereas inhibition attenuated both. Dissection of the circuit revealed that separated projections of VPVglut2 neurons to the lateral hypothalamus and lateral habenula promote arousal and depressive-like behaviors, respectively. Our results demonstrate a subtype of VP neurons is responsible for wakefulness and emotion through separated projections, and may provide new lines for the intervention of insomnia and depression in patients.

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

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

NMDA receptors as therapeutic targets for depression treatment: Evidence from clinical to basic research

Ketamine, functioning as a channel blocker of the excitatory glutamate-gated N-methyl-d-aspartate (NMDA) receptors, displays compelling fast-acting and sustained antidepressant effects for treatment-resistant depression. Over the past decades, clinical and preclinical studies have implied that the pathology of depression is associated with dysfunction of glutamatergic transmission. In particular, the discovery of antidepressant agents modulating NMDA receptor function has prompted breakthroughs for depression treatment compared with conventional antidepressants targeting the monoaminergic system. In this review, we first summarized the signalling pathway of the ketamine-mediated antidepressant effects, based on the glutamate hypothesis of depression. Second, we reviewed the hypotheses of the synaptic mechanism and network of ketamine antidepressant effects within different brain areas and distinct subcellular localizations, including NMDA receptor antagonism on GABAergic interneurons, extrasynaptic and synaptic NMDA receptor-mediated antagonism, and ketamine blocking bursting activities in the lateral habenula. Third, we reviewed the different roles of NMDA receptor subunits in ketamine-mediated cognitive and psychiatric behaviours in genetically-manipulated rodent models. Finally, we summarized the structural basis of NMDA receptor channel blockers and discussed NMDA receptor modulators that have been reported to exert potential antidepressant effects in animal models or in clinical trials. Integrating the cutting-edge technologies of cryo-EM and artificial intelligence-based drug design (AIDD), we expect that the next generation of first-in-class rapid antidepressants targeting NMDA receptors would be an emerging direction for depression therapeutics. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Experimental Verification for Numerical Simulation of Thalamic Stimulation-Evoked Calcium-Sensitive Fluorescence and Electrophysiology with Self-Assembled Multifunctional Optrode

Owing to its capacity to eliminate a long-standing methodological limitation, fiber photometry can assist research gaining novel insight into neural systems. Fiber photometry can reveal artifact-free neural activity under deep brain stimulation (DBS). Although evoking neural potential with DBS is an effective method for mediating neural activity and neural function, the relationship between DBS-evoked neural Ca²⁺ change and DBS-evoked neural electrophysiology remains unknown. Therefore, in this study, a self-assembled optrode was demonstrated as a DBS stimulator and an optical biosensor capable of concurrently recording Ca²⁺ fluorescence and electrophysiological signals. Before the in vivo experiment, the volume of tissue activated (VTA) was estimated, and the simulated Ca²⁺ signals were presented using Monte Carlo (MC) simulation to approach the realistic in vivo environment. When VTA and the simulated Ca²⁺ signals were combined, the distribution of simulated Ca²⁺ fluorescence signals matched the VTA region. In addition, the in vivo experiment revealed a correlation between the local field potential (LFP) and the Ca²⁺ fluorescence signal in the evoked region, revealing the relationship between electrophysiology and the performance of neural Ca²⁺ concentration behavior. Concurrent with the VTA volume, simulated Ca²⁺ intensity, and the in vivo experiment, these data suggested that the behavior of neural electrophysiology was consistent with the phenomenon of Ca²⁺ influx to neurons.

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

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