Distinctiveness and continuity in transcriptome and connectivity in the anterior-posterior axis of the paraventricular nucleus of the thalamus

Genotype-dependent functional role of the anterior and posterior paraventricular thalamus in pavlovian conditioned approach

RATIONALE

The specific location of deviations from normative models of brain function varies considerably across individuals with the same diagnoses. However, as pathological processes are distributed across interconnected systems, this heterogeneity of individual brain deviations may also reveal similarities and differences between disorders. The paraventricular nucleus of the thalamus (PVT) is a potential switcher to various behavioral responses where functionally distinct cell types exist across its antero-posterior axis.

OBJECTIVES

This study aimed to test the hypothesis that genotype-dependent differences in the anterior and posterior PVT subregions (aPVT and pPVT) are involved in the Sign-tracking (ST) behavior expressed by C57BL/6J (C57) and DBA/2J (DBA) inbred mice.

METHODS

Based on previous findings, male mice of the two strains were tested at ten weeks of age. The density of c-Fos immunoreactivity along the antero-posterior axis of PVT was assessed following the expression of ST behavior. Selective excitotoxic lesions of the aPVT or the pPVT by the NMDA infusion were performed prior to development of ST behavior. Finally, the distribution of neuronal populations expressing the Drd2 and Gal genes (D2R + and Gal +) was measured by in situ hybridization (ISH).

RESULTS

The involvement of PVT subregions in ST behavior is strain-specific, as aPVT is crucial for ST acquisition in DBA mice while pPVT is crucial for C57 mice. Despite similar antero-posterior distribution of D2R + and Gal + neurons, density of D2R + neurons differentiate aPVT in C57 and DBA mice.

CONCLUSIONS

These genotype-dependent results offer valuable insights into the nuanced organization of brain networks and individual variability in behavioral responses.

Possible role of mosaic mutations of neurodevelopmental disorder-related genes in bipolar disorder: lessons from Kmt2c chimeric knockout mice

We recently found a loss of function mosaic mutation of KMT2C, a causative gene for autism spectrum disorder and Kleefstra syndrome, in a patient with bipolar disorder and reported that somatic mutations in neurodevelopmental disorder-related genes are increased in bipolar disorder by deep exome sequencing analysis. However, causal roles of neurodevelopmental disorder-related mutations in bipolar disorder, a qualitatively different mental disorder, are not known. In this study, we focused on a loss of function mutation of Kmt2c, that causes autism-like phenotypes in mice. To simulate a mosaic mutation found in the patient, we generated mosaic Kmt2c knockout mice using conventional chimera mice technology. We showed that the mosaic Kmt2c knockout mice did not show autism-like behavior but presented anxiety disorder-like symptom, which is avoidance to a corner where the mice previously experienced air-puff. The rate of depression-like episodes measured by wheel running recording did not differ from control mosaic mice. These results suggest that mosaic mutations of neurodevelopmental disorder-related genes can cause qualitatively different anxiety disorder-like phenotypes. Because anxiety is one of symptomatic spectrum of bipolar disorder, these findings support the role of mosaic mutations of neurodevelopmental disorder-related genes as a component of the genetic architecture of bipolar disorder.

The encoding of interoceptive-based predictions by the paraventricular nucleus of the thalamus D2+ neurons

Understanding how the brain integrates internal physiological states with external sensory cues to guide behavior is a fundamental question in neuroscience. This process relies on interoceptive predictions-internal models that anticipate changes in the body's physiological state based on sensory inputs and prior experiences. Despite recent advances in identifying the neural substrates of interoceptive predictions, the precise neuronal circuits involved remain elusive. In our study, we demonstrate that Dopamine 2 Receptor (D2+) expressing neurons in the paraventricular nucleus of the thalamus (PVT) play key roles in interoception and interoceptive predictions. Specifically, these neurons are engaged in behaviors leading to physiologically relevant outcomes, with their activity highly dependent on the interoceptive state of the mice and the expected outcome. Furthermore, we show that chronic inhibition of PVT D2+ neurons impairs the long-term performance of interoceptive-guided motivated behavior. Collectively, our findings provide insights into the role of PVT D2+ neurons in learning and updating state-dependent predictions, by integrating past experiences with current physiological conditions to optimize goal-directed behavior.

Utility of a commercial antibody against NTRK1 for western blotting and potential application to immunohistochemistry in adult mouse brain

Ntrk1 (also known as TrkA) is a nerve growth factor receptor with essential roles in the development and function of the cholinergic nervous system. Ntrk1 is expressed in a few specific and defined brain areas. Specific antibodies are necessary to identify the expression and localization of Ntrk1 in the brain, and validating signal authenticity is critical. These issues have not been investigated sufficiently. We evaluated the utility of commercial antibodies for Ntrk1 using western blotting in brain lysates from Ntrk1 knockout mice and tested the utility of the antibody that showed specificity in western blotting for immunohistochemistry applications in the adult mouse brain. We confirmed specificity for one of the seven commercial antibodies in western blots, in which the specific bands were absent in the knockout samples. Using this antibody, we performed immunohistochemical staining of the brain tissues of adult mice to examine Ntrk1 localization. Distinct signals were observed in regions with known Ntrk1 expression, such as the striatum and basal forebrain. The characteristic expression pattern of Ntrk1 in the paraventricular thalamic nucleus (PVT) was verified at the protein level, with high and low expression levels in the anterior and posterior PVT, respectively.

Posterior Basolateral Amygdala is a Critical Amygdaloid Area for Temporal Lobe Epilepsy

The amygdaloid complex consists of multiple nuclei and is a key node in controlling temporal lobe epilepsy (TLE) in both human and animal model studies. However, the specific nucleus in the amygdaloid complex and the neural circuitry governing seizures remain unknown. Here, it is discovered that activation of glutamatergic neurons in the posterior basolateral amygdala (pBLA) induces severe seizures and even mortality. The pBLA glutamatergic neurons project collateral connections to multiple brain regions, including the insular cortex (IC), bed nucleus of the stria terminalis (BNST), and central amygdala (CeA). Stimulation of pBLA-targeted IC neurons triggers seizures, whereas ablation of IC neurons suppresses seizures induced by activating pBLA glutamatergic neurons. GABAergic neurons in the BNST and CeA establish feedback inhibition on pBLA glutamatergic neurons. Deleting GABAergic neurons in the BNST or CeA leads to sporadic seizures, highlighting their role in balancing pBLA activity. Furthermore, pBLA neurons receive glutamatergic inputs from the ventral hippocampal CA1 (vCA1). Ablation of pBLA glutamatergic neurons mitigates both acute and chronic seizures in the intrahippocampal kainic acid-induced mouse model of TLE. Together, these findings identify the pBLA as a pivotal nucleus in the amygdaloid complex for regulating epileptic seizures in TLE.

Differential modulation of pain and associated anxiety by GABAergic neuronal circuits in the lateral habenula

Persistent pain frequently precipitates the development of anxiety disorders, yet the underlying mechanisms are not fully understood. In this study, we employed a mouse model that simulates trigeminal neuralgia and observed a marked reduction in the activity of GABAergic neurons in the lateral habenula (LHb), a critical region for modulating pain and anxiety. We utilized precise optogenetic and chemogenetic techniques to modulate these neurons, which significantly alleviated behaviors associated with pain and anxiety. Our investigations revealed an inhibitory pathway from the LHb GABAergic neurons to the posterior paraventricular thalamus. Activation of this pathway primarily mitigated pain-related behaviors, with minimal effects on anxiety. Conversely, interactions between GABAergic and glutamatergic neurons within the LHb were essential in alleviating both pain and anxiety following trigeminal nerve damage. Additionally, we identified that β-sitosterol interacts directly with LHb GABAergic neurons via the estrogen receptor α, providing dual therapeutic effects for both pain and anxiety. These findings highlight the critical role of reduced GABAergic neuronal activity in the LHb in the intersection of pain and anxiety, pointing to promising therapeutic possibilities.

A conserved cell-type gradient across the human mediodorsal and paraventricular thalamus

The mediodorsal thalamus (MD) and adjacent midline nuclei are important for cognition and mental illness, but their cellular composition is not well defined. Using single-nucleus and spatial transcriptomics, we identified a conserved excitatory neuron gradient, with distinct spatial mapping of individual clusters. One end of the gradient was expanded in human MD compared to mice, which may be related to the expansion of granular prefrontal cortex in hominids. Moreover, neurons preferentially mapping onto the parvocellular division MD were associated with genetic risk for schizophrenia and bipolar disorder. Midbrain-derived inhibitory interneurons were enriched in human MD and implicated in genetic risk for major depressive disorder.

Melatonin targets the paraventricular thalamus to promote non-rapid eye movement sleep in C3H/HeJ mice

Melatonin (MLT) is an important circadian signal for sleep regulation, but the neural circuitries underlying the sleep-promoting effects of MLT are poorly understood. The paraventricular thalamus (PVT) is a critical thalamic area for wakefulness control and expresses MLT receptors, raising a possibility that PVT neurons may mediate the sleep-promoting effects of MLT. Here, we found that MLT receptors were densely expressed on PVT neurons and exhibited circadian-dependent variations in C3H/HeJ mice. Application of exogenous MLT decreased the excitability of PVT neurons, resulting in hyperpolarization of membrane potential and reduction of action potential firing. MLT also inhibited the spontaneous activity of PVT neurons at both population and single-neuron levels in freely behaving mice. Furthermore, pharmacological manipulations revealed that local infusion of exogeneous MLT into the PVT promoted non-rapid eye movement (NREM) sleep and increased NREM sleep duration, whereas MLT receptor antagonists decreased NREM sleep. Moreover, we found that selectively knocking down endogenous MLT receptors in the PVT decreased NREM sleep and correspondingly increased wakefulness, with particular changes shortly after the onset of the dark or light phase. Taken together, these results demonstrate that PVT is an important target of MLT for promoting NREM sleep.

Paraventricular Thalamus Neuronal Ensembles Encode Early-life Adversity and Mediate the Consequent Sex-dependent Disruptions of Adult Reward Behaviors

Early-life adversity increases risk for mental illnesses including depression and substance use disorders, disorders characterized by dysregulated reward behaviors. However, the mechanisms by which transient ELA enduringly impacts reward circuitries are not well understood. In mice, ELA leads to anhedonia-like behaviors in males and augmented motivation for palatable food and sex-reward cues in females. Here, the use of genetic tagging demonstrated robust, preferential, and sex-specific activation of the paraventricular nucleus of the thalamus (PVT) during ELA and a potentiated reactivation of these PVT neurons during a reward task in adult ELA mice. Chemogenetic manipulation of specific ensembles of PVT neurons engaged during ELA identified a role for the posterior PVT in ELA-induced aberrantly augmented reward behaviors in females. In contrast, anterior PVT neurons activated during ELA were required for the anhedonia-like behaviors in males. Thus, the PVT encodes adverse experiences early-in life, prior to the emergence of the hippocampal memory system, and contributes critically to the lasting, sex-modulated impacts of ELA on reward behaviors.

Sustained antidepressant effects of ketamine metabolite involve GABAergic inhibition-mediated molecular dynamics in aPVT glutamatergic neurons

Despite the rapid and sustained antidepressant effects of ketamine and its metabolites, their underlying cellular and molecular mechanisms are not fully understood. Here, we demonstrate that the sustained antidepressant-like behavioral effects of (2S,6S)-hydroxynorketamine (HNK) in repeatedly stressed animal models involve neurobiological changes in the anterior paraventricular nucleus of the thalamus (aPVT). Mechanistically, (2S,6S)-HNK induces mRNA expression of extrasynaptic GABAA receptors and subsequently enhances GABAA-receptor-mediated tonic currents, leading to the nuclear export of histone demethylase KDM6 and its replacement by histone methyltransferase EZH2. This process increases H3K27me3 levels, which in turn suppresses the transcription of genes associated with G-protein-coupled receptor signaling. Thus, our findings shed light on the comprehensive cellular and molecular mechanisms in aPVT underlying the sustained antidepressant behavioral effects of ketamine metabolites. This study may support the development of potentially effective next-generation pharmacotherapies to promote sustained remission of stress-related psychiatric disorders.

Dissociable encoding of motivated behavior by parallel thalamo-striatal projections

The successful pursuit of goals requires the coordinated execution and termination of actions that lead to positive outcomes. This process relies on motivational states that are guided by internal drivers, such as hunger or fear. However, the mechanisms by which the brain tracks motivational states to shape instrumental actions are not fully understood. The paraventricular nucleus of the thalamus (PVT) is a midline thalamic nucleus that shapes motivated behaviors via its projections to the nucleus accumbens (NAc)1,2,3,4,5,6,7,8 and monitors internal state via interoceptive inputs from the hypothalamus and brainstem.3,9,10,11,12,13,14 Recent studies indicate that the PVT can be subdivided into two major neuronal subpopulations, namely PVTD2(+) and PVTD2(-), which differ in genetic identity, functionality, and anatomical connectivity to other brain regions, including the NAc.4,15,16 In this study, we used fiber photometry to investigate the in vivo dynamics of these two distinct PVT neuronal types in mice performing a foraging-like behavioral task. We discovered that PVTD2(+) and PVTD2(-) neurons encode the execution and termination of goal-oriented actions, respectively. Furthermore, activity in the PVTD2(+) neuronal population mirrored motivation parameters such as vigor and satiety. Similarly, PVTD2(-) neurons also mirrored some of these parameters, but to a much lesser extent. Importantly, these features were largely preserved when activity in PVT projections to the NAc was selectively assessed. Collectively, our results highlight the existence of two parallel thalamo-striatal projections that participate in the dynamic regulation of goal pursuits and provide insight into the mechanisms by which the brain tracks motivational states to shape instrumental actions.

Discrete prefrontal neuronal circuits determine repeated stress-induced behavioral phenotypes in male mice

Chronic stress is a major risk factor for psychiatric disorders, including depression. Although depression is a highly heterogeneous syndrome, it remains unclear how chronic stress drives individual differences in behavioral responses. In this study, we developed a subtyping-based approach wherein stressed male mice were divided into four subtypes based on their behavioral patterns of social interaction deficits and anhedonia, the core symptoms of psychiatric disorders. We identified three prefrontal cortical neuronal projections that regulate repeated stress-induced behavioral phenotypes. Among them, the medial prefrontal cortex (mPFC)→anterior paraventricular thalamus (aPVT) pathway determines the specific behavioral subtype that exhibits both social deficits and anhedonia. Additionally, we identified the circuit-level molecular mechanism underlying this subtype: KDM5C-mediated epigenetic repression of Shisa2 transcription in aPVT projectors in the mPFC led to social deficits and anhedonia. Thus, we provide a set of biological aspects at the cellular, molecular, and epigenetic levels that determine distinctive stress-induced behavioral phenotypes.