New viral-genetic mapping uncovers an enrichment of corticotropin-releasing hormone-expressing neuronal inputs to the nucleus accumbens from stress-related brain regions

Increased CRF-R1 transmission in the nucleus accumbens shell facilitates maternal neglect in lactating rats and mediates anxiety-like behaviour in a sex-specific manner

During the transition to motherhood, complex brain adaptations occur to ensure adequate maternal responses to offspring' needs accompanied by reduced anxiety. Among others, the corticotropin-releasing factor (CRF) and oxytocin (OXT) systems have emerged as crucial regulators of these essential postpartum adaptations. Here, we investigated their roles within the nucleus accumbens shell (NAcSh), a central region of the reward and maternal circuits, in maternal neglect of lactating rats. Furthermore, we assessed the contribution of the local CRF system to anxiety-like behaviour, comparing lactating female, virgin female and male rats to evaluate potential sex-differences. Increasing CRF receptor (CRF-R) 1 transmission via local CRF infusion in the NAcSh led to maternal neglect, reducing nursing and increasing self-directed behaviours. In turn, local CRF-R1 inhibition impaired maternal motivation. Intra-NAcSh Urocortin3 infusion did not promote maternal neglect but increased anxiety-like behaviour in lactating and virgin female rats, whereas CRF infusion had anxiogenic effects only in male rats. Crh-r1 mRNA expression was higher in male and lactating rats compared to virgin females; furthermore, male rats had increased Crh-bp mRNA expression compared to virgin female rats, only. Lastly, pharmacological manipulations of the OXT system did not affect maternal responses. In conclusion, finely balanced CRF-R1 signalling in the NAcSh is required for the proper expression of maternal behaviours. Dampened CRF-R2 signalling prevents the onset of anxiety-like behaviour in female rats, whereas CRF-R1 plays a more prominent role in males, highlighting complex sex-differences of the CRF system's regulation of anxiety within the NAcSh.

Targeting corticotropin-releasing hormone receptor type 1 (Crhr1) neurons: validating the specificity of a novel transgenic Crhr1-FlpO mouse

Corticotropin-releasing hormone (CRH) signaling through its cognate receptors, CRHR1 and CRHR2, contributes to diverse stress-related functions in the mammalian brain. Whereas CRHR2 is predominantly expressed in choroid plexus and blood vessels, CRHR1 is abundantly expressed in neurons in discrete brain regions, including the neocortex, hippocampus and nucleus accumbens. Activation of CRHR1 influences motivated behaviors, emotional states, and learning and memory. However, it is unknown whether alterations in CRHR1 signaling contribute to aberrant motivated behaviors observed, for example, in stressful contexts. These questions require tools to manipulate CRHR1 selectively. Here we describe and validate a novel Crhr1-FlpO mouse. Using bacterial artificial chromosome (BAC) transgenesis, we engineered a transgenic mouse that expresses FlpO recombinase in CRHR1-expressing cells. We used two independent methods to assess the specificity of FlpO to CRHR1-expressing cells. First, we injected Crhr1-FlpO mice with Flp-dependent viruses expressing fluorescent reporter molecules. Additionally, we crossed the Crhr1-FlpO mouse with a transgenic Flp-dependent reporter mouse. CRHR1 and reporter molecules were identified using immunocytochemistry and visualized via confocal microscopy in several brain regions in which CRHR1 expression and function is established. Expression of Flp-dependent viral constructs was highly specific to CRHR1-expressing cells in all regions examined (over 90% co-localization). In accord, robust and specific expression of the Flp-dependent transgenic reporter was observed in a reporter mouse, recapitulating endogenous CRHR1 expression. The Crhr1-FlpO mouse enables selective genetic access to CRHR1-expressing cells within the mouse brain. When combined with Cre-lox or site-specific recombinases, the mouse facilitates intersectional manipulations of CRHR1-expressing neurons.

Extended amygdala corticotropin-releasing hormone neurons regulate sexually dimorphic changes in pair bond formation following social defeat in prairie voles (Microtus ochrogaster)

The neurobiological mechanisms underlying the connection between anxiety brought on by social stressors and the negative impact on relationship formation have remained elusive. In order to address this question, we used the social defeat model in the socially monogamous prairie vole to investigate the impact of this stress on pair bond formation. Social defeat experience inhibited partner preference formation in males but promoted preference in females. Furthermore, pair bonding increased corticotropin-releasing hormone (CRH) expression in the bed nucleus of the stria terminalis (BNST) in male prairie voles, while defeat experience increased BNST CRH expression in females. Chemogenetic excitation of BNST CRH neurons during a short cohabitation with a new partner promoted a partner preference in stress-naïve prairie voles. Interestingly, chemogenetic inhibition of BNST CRH neurons during cohabitation with a new partner blocked partner preference in stress-naïve males but promoted preference in defeated males. Inhibition of BNST CRH neurons also blocked partner preference in stress-naïve females but did not alter preference behavior in defeated females. This study revealed sexual dimorphism in not only the impact of social defeat on pair bond formation, but also in the role BNST CRHergic neurons play in regulating changes in pair bonding following social conflict.

Nucleus Accumbens Corticotropin-Releasing Hormone Neurons Projecting to the Bed Nucleus of the Stria Terminalis Promote Wakefulness and Positive Affective State

The nucleus accumbens (NAc) plays an important role in various emotional and motivational behaviors that rely on heightened wakefulness. However, the neural mechanisms underlying the relationship between arousal and emotion regulation in NAc remain unclear. Here, we investigated the roles of a specific subset of inhibitory corticotropin-releasing hormone neurons in the NAc (NAcCRH) in regulating arousal and emotional behaviors in mice. We found an increased activity of NAcCRH neurons during wakefulness and rewarding stimulation. Activation of NAcCRH neurons converts NREM or REM sleep to wakefulness, while inhibition of these neurons attenuates wakefulness. Remarkably, activation of NAcCRH neurons induces a place preference response (PPR) and decreased basal anxiety level, whereas their inactivation induces a place aversion response and anxious state. NAcCRH neurons are identified as the major NAc projection neurons to the bed nucleus of the stria terminalis (BNST). Furthermore, activation of the NAcCRH-BNST pathway similarly induced wakefulness and positive emotional behaviors. Taken together, we identified a basal forebrain CRH pathway that promotes the arousal associated with positive affective states.

Corticotropin-Releasing Factor Release From a Unique Subpopulation of Accumbal Neurons Constrains Action-Outcome Acquisition in Reward Learning

BACKGROUND

The nucleus accumbens (NAc) mediates reward learning and motivation. Despite an abundance of neuropeptides, peptidergic neurotransmission from the NAc has not been integrated into current models of reward learning. The existence of a sparse population of neurons containing corticotropin-releasing factor (CRF) has been previously documented. Here, we provide a comprehensive analysis of their identity and functional role in shaping reward learning.

METHODS

Our multidisciplinary approach included fluorescent in situ hybridization (n = ≥3 mice), tract tracing (n = 5 mice), ex vivo electrophysiology (n = ≥30 cells), in vivo calcium imaging with fiber photometry (n = ≥4 mice), and use of viral strategies in transgenic lines to selectively delete CRF peptide from NAc neurons (n = ≥4 mice). Behaviors used were instrumental learning, sucrose preference, and spontaneous exploration in an open field.

RESULTS

We showed that the vast majority of NAc CRF-containing neurons are spiny projection neurons (SPNs) comprising dopamine D1-, D2-, or D1/D2-containing SPNs that primarily project and connect to the ventral pallidum and to a lesser extent the ventral midbrain. As a population, they display mature and immature SPN firing properties. We demonstrated that NAc CRF-containing neurons track reward outcomes during operant reward learning and that CRF release from these neurons acts to constrain initial acquisition of action-outcome learning and at the same time facilitates flexibility in the face of changing contingencies.

CONCLUSIONS

CRF release from this sparse population of SPNs is critical for reward learning under normal conditions.

Corticotropin releasing factor alters the functional diversity of accumbal cholinergic interneurons

Cholinergic interneurons (ChIs) provide the main source of acetylcholine in the striatum and have emerged as a critical modulator of behavioral flexibility, motivation, and associative learning. In the dorsal striatum (DS), ChIs display heterogeneous firing patterns. Here, we investigated the spontaneous firing patterns of ChIs in the nucleus accumbens (NAc) shell, a region of the ventral striatum. We identified four distinct ChI firing signatures: regular single-spiking, irregular single-spiking, rhythmic bursting, and a mixed-mode pattern composed of bursting activity and regular single spiking. ChIs from females had lower firing rates compared with males and had both a higher proportion of mixed-mode firing patterns and a lower proportion of regular single-spiking neurons compared with males. We further observed that across the estrous cycle, the diestrus phase was characterized by higher proportions of irregular ChI firing patterns compared with other phases. Using pooled data from males and females, we examined how the stress-associated neuropeptide corticotropin releasing factor (CRF) impacts these firing patterns. ChI firing patterns showed differential sensitivity to CRF. This translated into differential ChI sensitivity to CRF across the estrous cycle. Furthermore, CRF shifted the proportion of ChI firing patterns toward more regular spiking activity over bursting patterns. Finally, we found that repeated stressor exposure altered ChI firing patterns and sensitivity to CRF in the NAc core, but not the NAc shell. These findings highlight the heterogeneous nature of ChI firing patterns, which may have implications for accumbal-dependent motivated behaviors.NEW & NOTEWORTHY Cholinergic interneurons (ChIs) within the dorsal and ventral striatum can exert a major influence on network output and motivated behaviors. However, the firing patterns and neuromodulation of ChIs within the ventral striatum, specifically the nucleus accumbens (NAc) shell, are understudied. Here, we report that NAc shell ChIs have heterogeneous ChI firing patterns that are labile and can be modulated by the stress-linked neuropeptide corticotropin releasing factor (CRF) and by the estrous cycle.

CRF release from a unique subpopulation of accumbal neurons constrains action-outcome acquisition in reward learning

Background

The nucleus accumbens (NAc) mediates reward learning and motivation. Despite an abundance of neuropeptides, peptidergic neurotransmission from the NAc has not been integrated into current models of reward learning. The existence of a sparse population of neurons containing corticotropin releasing factor (CRF) has been previously documented. Here we provide a comprehensive analysis of their identity and functional role in shaping reward learning.

Methods

To do this, we took a multidisciplinary approach that included florescent in situ hybridization (N mice ≥ 3), tract tracing (N mice = 5), ex vivo electrophysiology (N cells ≥ 30), in vivo calcium imaging with fiber photometry (N mice ≥ 4) and use of viral strategies in transgenic lines to selectively delete CRF peptide from NAc neurons (N mice ≥ 4). Behaviors used were instrumental learning, sucrose preference and spontaneous exploration in an open field.

Results

Here we show that the vast majority of NAc CRF-containing (NAc CRF ) neurons are spiny projection neurons (SPNs) comprised of dopamine D1-, D2- or D1/D2-containing SPNs that primarily project and connect to the ventral pallidum and to a lesser extent the ventral midbrain. As a population, they display mature and immature SPN firing properties. We demonstrate that NAc CRF neurons track reward outcomes during operant reward learning and that CRF release from these neurons acts to constrain initial acquisition of action-outcome learning, and at the same time facilitates flexibility in the face of changing contingencies.

Conclusion

We conclude that CRF release from this sparse population of SPNs is critical for reward learning under normal conditions.

CRF regulates pain sensation by enhancement of corticoaccumbal excitatory synaptic transmission

Both peripheral and central corticotropin-releasing factor (CRF) systems have been implicated in regulating pain sensation. However, compared with the peripheral, the mechanisms underlying central CRF system in pain modulation have not yet been elucidated, especially at the neural circuit level. The corticoaccumbal circuit, a structure rich in CRF receptors and CRF-positive neurons, plays an important role in behavioral responses to stressors including nociceptive stimuli. The present study was designed to investigate whether and how CRF signaling in this circuit regulated pain sensation under physiological and pathological pain conditions. Our studies employed the viral tracing and circuit-, and cell-specific electrophysiological methods to label the CRF-containing circuit from the medial prefrontal cortex to the nucleus accumbens shell (mPFCCRF-NAcS) and record its neuronal propriety. Combining optogenetic and chemogenetic manipulation, neuropharmacological methods, and behavioral tests, we were able to precisely manipulate this circuit and depict its role in regulation of pain sensation. The current study found that the CRF signaling in the NAc shell (NAcS), but not NAc core, was necessary and sufficient for the regulation of pain sensation under physiological and pathological pain conditions. This process was involved in the CRF-mediated enhancement of excitatory synaptic transmission in the NAcS. Furthermore, we demonstrated that the mPFCCRF neurons monosynaptically connected with the NAcS neurons. Chronic pain increased the protein level of CRF in NAcS, and then maintained the persistent NAcS neuronal hyperactivity through enhancement of this monosynaptic excitatory connection, and thus sustained chronic pain behavior. These findings reveal a novel cell- and circuit-based mechanistic link between chronic pain and the mPFCCRF → NAcS circuit and provide a potential new therapeutic target for chronic pain.

Annual Research Review: Puberty and the development of anhedonia - considering childhood adversity and inflammation

Anhedonia, or diminished pleasure and motivation, is a symptom of severe mental illness (e.g., depressive disorder, bipolar disorder, schizophrenia) that emerges during adolescence. Anhedonia is a pernicious symptom that is related to social impairments, treatment resistance, and suicide. As the mechanisms of anhedonia are postulated to include the frontostriatal circuitry and the dopamine neuromodulatory system, the development and plasticity of these systems during the vulnerable period of adolescence, as well as their sensitivity to pubertal hormones, suggest that pubertal maturation could play a role in the development of anhedonia. This review takes a developmental perspective, considering the possibility that anhedonia emerges in the context of pubertal maturation and adolescent development, with childhood adversity and chronic inflammation influencing neural reward systems to accelerate anhedonia's progression. Here, we review the relevant extant literature on the components of this model and suggest directions for future research.

Chronic Nicotine Consumption and Withdrawal Regulate Melanocortin Receptor, CRF, and CRF Receptor mRNA Levels in the Rat Brain

Alterations in the various neuropeptide systems in the mesocorticolimbic circuitry have been implicated in negative effects associated with drug withdrawal. The corticotropin-releasing factor (CRF) and α-melanocyte-stimulating hormone are two peptides that may be involved. This study investigated the regulatory effects of chronic nicotine exposure and withdrawal on the mRNA levels of melanocortin receptors (MC3R, MC4R), CRF, and CRF receptors (CRFR1 and CRFR2) expressed in the mesocorticolimbic system. Rats were given drinking water with nicotine or without nicotine (control group) for 12 weeks, after which they continued receiving nicotine (chronic exposure) or were withdrawn from nicotine for 24 or 48 h. The animals were decapitated following behavioral testing for withdrawal signs. Quantitative real-time PCR analysis demonstrated that nicotine exposure (with or without withdrawal) increased levels of CRF and CRFR1 mRNA in the amygdala, CRF mRNA in the medial prefrontal cortex, and CRFR1 mRNA in the septum. Nicotine withdrawal also enhanced MC3R and MC4R mRNA levels in different brain regions, while chronic nicotine exposure was associated with increased MC4R mRNA levels in the nucleus accumbens. These results suggest that chronic nicotine exposure and withdrawal regulate CRF and melanocortin signaling in the mesocorticolimbic system, possibly contributing to negative affective state and nicotine addiction.

Testing anxiety and reward processing in anorexia nervosa as predictors of longitudinal clinical outcomes

Anorexia nervosa (AN) is a psychiatric disorder with a tenuous longitudinal course marked by a high risk of relapse. Previous studies suggest that aberrant threat perception and reward processing operate in many with AN, and may produce obstacles to treatment engagement; therefore, these could potentially represent predictors for longitudinal clinical outcomes. In this study, anxiety and reward symptoms, behaviors, and neural circuit connectivity were measured in intensively treated AN-restrictive subtype patients (n = 33) and healthy controls (n = 31). Participants underwent an fMRI experiment using a monetary reward task in combination with either overlapping individually tailored anxiety-provoking words or neutral words. Behavioral/psychometric measures consisted of reaction times on the monetary reward task and self-ratings on anxiety symptoms at study entry. We tested multimodal, multivariate models based on neural, behavioral, and psychometric measures of reward and anxiety to predict physiological (Body Mass Index; BMI) and psychological (eating disorder symptom severity) longitudinal outcomes in AN over six months. Our results indicated that higher anxiety symptom psychometric scores significantly predicted BMI reductions at follow-up. Untreated anxiety after intensive treatment could put individuals with AN at heightened risk for weight loss. This represents a potentially modifiable risk factor that could be targeted more aggressively to help reduce the chance of future clinical worsening.

Genetic Tagging Uncovers a Robust, Selective Activation of the Thalamic Paraventricular Nucleus by Adverse Experiences Early in Life

Background

Early-life adversity (ELA) is associated with increased risk for mood disorders, including depression and substance use disorders. These disorders are characterized by impaired reward-related behaviors, suggesting compromised operations of reward-related brain circuits. However, the brain regions engaged by ELA that mediate these enduring consequences of ELA remain largely unknown. In an animal model of ELA, we identified aberrant reward-seeking behaviors, a discovery that provides a framework for assessing the underlying circuits.

Methods

Employing TRAP2 (targeted recombination in active populations) male and female mice, in which neurons activated within a defined time frame are permanently tagged, we compared ELA- and control-reared mice, assessing the quantity and distribution of ELA-related neuronal activation. After validating the TRAP2 results using native c-Fos labeling, we defined the molecular identity of this population of activated neurons.

Results

We uniquely demonstrated that the TRAP2 system is feasible and efficacious in neonatal mice. Surprisingly, the paraventricular nucleus of the thalamus was robustly and almost exclusively activated by ELA and was the only region distinguishing ELA from typical rearing. Remarkably, a large proportion of ELA-activated paraventricular nucleus of the thalamus neurons expressed CRF1, the receptor for the stress-related peptide, corticotropin-releasing hormone, but these neurons did not express corticotropin-releasing hormone itself.

Conclusions

The paraventricular nucleus of the thalamus, an important component of reward circuits that is known to encode remote, emotionally salient experiences to influence future motivated behaviors, encodes adverse experiences as remote as those occurring during the early postnatal period and is thus poised to contribute to the enduring deficits in reward-related behaviors consequent to ELA.

Opto-juxtacellular interrogation of neural circuits in freely moving mice

Neural circuits are assembled from an enormous variety of neuronal cell types. Although significant advances have been made in classifying neurons on the basis of morphological, molecular and electrophysiological properties, understanding how this diversity contributes to brain function during behavior has remained a major experimental challenge. Here, we present an extension to our previous protocol, in which we describe the technical procedures for performing juxtacellular opto-tagging of single neurons in freely moving mice by using Channelrhodopsin-2-expressing viral vectors. This method allows one to selectively target molecularly defined cell classes for in vivo single-cell recordings. The targeted cells can be labeled via juxtacellular procedures and further characterized via post-hoc morphological and molecular analysis. In its current form, the protocol allows multiple recording and labeling attempts to be performed within individual animals, by means of a mechanical pipette micropositioning system. We provide proof-of-principle validation of this technique by recording from Calbindin-positive pyramidal neurons in the mouse hippocampus during spatial exploration; however, this approach can easily be extended to other behaviors and cortical or subcortical areas. The procedures described here, from the viral injection to the histological processing of brain sections, can be completed in ~4-5 weeks.This protocol is an extension to: Nat. Protoc. 9, 2369-2381 (2014): https://doi.org/10.1038/nprot.2014.161.

Cocaine Regulates NLRP3 Inflammasome Activity and CRF Signaling in a Region- and Sex-Dependent Manner in Rat Brain

Cocaine, one of the most abused drugs worldwide, is capable of activating microglia in vitro and in vivo. Several neuroimmune pathways have been suggested to play roles in cocaine-mediated microglial activation. Previous work showed that cocaine activates microglia in a region-specific manner in the brains of self-administered mice. To further characterize the effects of cocaine on microglia and neuroimmune signaling in vivo, we utilized the brains from both sexes of outbred rats with cocaine self-administration to explore the activation status of microglia, NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome activity, corticotropin-releasing factor (CRF) signaling, and NF-κB levels in the striatum and hippocampus (HP). Age-matched rats of the same sex (drug naïve) served as controls. Our results showed that cocaine increased neuroinflammation in the striatum and HP of both sexes with a relatively higher increases in male brains. In the striatum, cocaine upregulated NLRP3 inflammasome activity and CRF levels in males but not in females. In contrast, cocaine increased NLRP3 inflammasome activity in the HP of females but not in males, and no effects on CRF signaling were observed in this region of either sex. Interestingly, cocaine increased NF-κB levels in the striatum and HP with no sex difference. Taken together, our results provide evidence that cocaine can exert region- and sex-specific differences in neuroimmune signaling in the brain. Targeting neuroimmune signaling has been suggested as possible treatment for cocaine use disorders (CUDs). Our current results indicate that sex should be taken into consideration when determining the efficacy of these new therapeutic approaches.

CB1R chronic intermittent pharmacological activation facilitates amphetamine seeking and self-administration and changes in CB1R/CRFR1 expression in the amygdala and nucleus accumbens in rats

Patterns of drug ingestion may have a dissimilar impact on the brain, and therefore also the development of drug addiction. One pattern is binge intoxication that refers to the ingestion of a high amount of drug on a single occasion followed by an abstinence period of variable duration. In this study, our goal was to contrast the effect of continuous low amounts with intermittent higher amounts of Arachidonyl-chloro-ethylamide (ACEA), a CB1R agonist, on amphetamine seeking and ingestion, and describe the effects on the expression of CB1R and CRFR1 in the central nucleus of the amygdala (CeA) and in the nucleus accumbens shell (NAcS). Adult male Wistar rats were treated with a daily administration of vehicle or 20 μg of ACEA, or four days of vehicle followed by 100 μg of ACEA on the fifth day, for a total of 30 days. Upon completion of this treatment, the CB1R and CRFR1 expression in the CeA and NAcS was evaluated by immunofluorescence. Additional groups of rats were evaluated for their anxiety levels (elevated plus maze, EPM), amphetamine (AMPH) self-administration (ASA) and breakpoint (A-BP), as well as AMPH-induced conditioned place preference (A-CPP). Results indicated that ACEA induced changes in the CB1R and CRFR1 expression in both the NAcS and CeA. An increase in anxiety-like behavior, ASA, A-BP and A-CPP was also observed. Since the intermittent administration of 100 μg of ACEA induced the most evident changes in most of the parameters studied, we concluded that binge-like ingestion of drugs induces changes in the brain that may make the subject more vulnerable to developing drug addiction.

Sex-related differences in endogenous pituitary adenylate cyclase-activating polypeptide (PACAP) in the thalamic paraventricular nucleus: Implications for addiction neuroscience

Males and females exhibit differences in motivated and affective behavior; however, the neural substrates underlying these differences remain poorly understood. In the paraventricular nucleus of the thalamus (PVT), sex-related differences in neuronal activity have been identified in response to motivated behavior tasks and affective challenges. Within the PVT, the neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), is highly expressed and is also involved in motivated and affective behavior. The purpose of this study was to compare the expression of PACAP mRNA and peptide in the PVT of males and females. Analysis with quantitative real-time PCR in mice revealed that females had significantly higher levels of PACAP mRNA than males in the whole PVT, but no differences in the neuropeptides enkephalin or corticotropin releasing factor (CRF) in this brain region. While in rats, females demonstrated a trend for greater gene expression than males in the anterior/middle and middle/posterior PVT, they again showed no differences in enkephalin or CRF. Analysis with immunofluorescent histochemistry revealed that female mice had significantly more PACAP-containing cells than males as a function of area throughout the PVT, and that female rats had significantly more PACAP-27 and PACAP-38-containing cells than males, both as a percentage of total cells and as a function of PVT area. For PACAP-27, this specifically occurred in the anterior PVT, and for PACAP-38, it occurred throughout the anterior, middle, and posterior PVT. These results suggest that sex-related differences in PVT PACAP may underly some of the established sex-related differences in motivated and affective behavior.

Stress-induced plasticity of a CRH/GABA projection disrupts reward behaviors in mice

Disrupted operations of the reward circuit underlie major emotional disorders, including depression, which commonly arise following early life stress / adversity (ELA). However, how ELA enduringly impacts reward circuit functions remains unclear. We characterize a stress-sensitive projection connecting basolateral amygdala (BLA) and nucleus accumbens (NAc) that co-expresses GABA and the stress-reactive neuropeptide corticotropin-releasing hormone (CRH). We identify a crucial role for this projection in executing disrupted reward behaviors provoked by ELA: chemogenetic and optogenetic stimulation of the projection in control male mice suppresses several reward behaviors, recapitulating deficits resulting from ELA and demonstrating the pathway's contributions to normal reward behaviors. In adult ELA mice, inhibiting-but not stimulating-the projection, restores typical reward behaviors yet has little effect in controls, indicating ELA-induced maladaptive plasticity of this reward-circuit component. Thus, we discover a stress-sensitive, reward inhibiting BLA → NAc projection with unique molecular features, which may provide intervention targets for disabling mental illnesses.

The Nucleus Accumbens CRH-CRHR1 System Mediates Early-Life Stress-Induced Sleep Disturbance and Dendritic Atrophy in the Adult Mouse

Adverse experiences in early life have long-lasting negative impacts on behavior and the brain in adulthood, one of which is sleep disturbance. As the corticotropin-releasing hormone (CRH)-corticotropin-releasing hormone receptor 1 (CRHR1) system and nucleus accumbens (NAc) play important roles in both stress responses and sleep-wake regulation, in this study we investigated whether the NAc CRH-CRHR1 system mediates early-life stress-induced abnormalities in sleep-wake behavior in adult mice. Using the limited nesting and bedding material paradigm from postnatal days 2 to 9, we found that early-life stress disrupted sleep-wake behaviors during adulthood, including increased wakefulness and decreased non-rapid eye movement (NREM) sleep time during the dark period and increased rapid eye movement (REM) sleep time during the light period. The stress-induced sleep disturbances were accompanied by dendritic atrophy in the NAc and both were largely reversed by daily systemic administration of the CRHR1 antagonist antalarmin during stress exposure. Importantly, Crh overexpression in the NAc reproduced the effects of early-life stress on sleep-wake behavior and NAc morphology, whereas NAc Crhr1 knockdown reversed these effects (including increased wakefulness and reduced NREM sleep in the dark period and NAc dendritic atrophy). Together, our findings demonstrate the negative influence of early-life stress on sleep architecture and the structural plasticity of the NAc, and highlight the critical role of the NAc CRH-CRHR1 system in modulating these negative outcomes evoked by early-life stress.

Sleep-Disturbance-Induced Microglial Activation Involves CRH-Mediated Galectin 3 and Autophagy Dysregulation

Chronic sleep disturbances (CSDs) including insomnia, insufficient sleep time, and poor sleep quality are major public health concerns around the world, especially in developed countries. CSDs are major health risk factors linked to multiple neurodegenerative and neuropsychological diseases. It has been suggested that CSDs could activate microglia (Mg) leading to increased neuroinflammation levels, which ultimately lead to neuronal dysfunction. However, the detailed mechanisms underlying CSD-mediated microglial activation remain mostly unexplored. In this study, we used mice with three-weeks of sleep fragmentation (SF) to explore the underlying pathways responsible for Mg activation. Our results revealed that SF activates Mg in the hippocampus (HP) but not in the striatum and prefrontal cortex (PFc). SF increased the levels of corticotropin-releasing hormone (CRH) in the HP. In vitro mechanism studies revealed that CRH activation of Mg involves galectin 3 (Gal3) upregulation and autophagy dysregulation. CRH could disrupt lysosome membrane integrity resulting in lysosomal cathepsins leakage. CRHR2 blockage mitigated CRH-mediated effects on microglia in vitro. SF mice also show increased Gal3 levels and autophagy dysregulation in the HP compared to controls. Taken together, our results show that SF-mediated hippocampal Mg activation involves CRH mediated galectin 3 and autophagy dysregulation. These findings suggest that targeting the hippocampal CRH system might be a novel therapeutic approach to ameliorate CSD-mediated neuroinflammation and neurodegenerative diseases.

Tripartite extended amygdala-basal ganglia CRH circuit drives locomotor activation and avoidance behavior

An adaptive stress response involves various mediators and circuits orchestrating a complex interplay of physiological, emotional, and behavioral adjustments. We identified a population of corticotropin-releasing hormone (CRH) neurons in the lateral part of the interstitial nucleus of the anterior commissure (IPACL), a subdivision of the extended amygdala, which exclusively innervate the substantia nigra (SN). Specific stimulation of this circuit elicits hyperactivation of the hypothalamic-pituitary-adrenal axis, locomotor activation, and avoidance behavior contingent on CRH receptor type 1 (CRHR1) located at axon terminals in the SN, which originate from external globus pallidus (GPe) neurons. The neuronal activity prompting the observed behavior is shaped by IPACL^CRH and GPe^CRHR1 neurons coalescing in the SN. These results delineate a previously unidentified tripartite CRH circuit functionally connecting extended amygdala and basal ganglia nuclei to drive locomotor activation and avoidance behavior.

Hyperexcitability: From Normal Fear to Pathological Anxiety and Trauma

Hyperexcitability in fear circuits is suggested to be important for development of pathological anxiety and trauma from adaptive mechanisms of fear. Hyperexcitability is proposed to be due to acquired sensitization in fear circuits that progressively becomes more severe over time causing changing symptoms in early and late pathology. We use the metaphor and mechanisms of kindling to examine gains and losses in function of one excitatory and one inhibitory neuropeptide, corticotrophin releasing factor and somatostatin, respectively, to explore this sensitization hypothesis. We suggest amygdala kindling induced hyperexcitability, hyper-inhibition and loss of inhibition provide clues to mechanisms for hyperexcitability and progressive changes in function initiated by stress and trauma.

Developmental Trajectories of Anhedonia in Preclinical Models

This chapter discusses how the complex concept of anhedonia can be operationalized and studied in preclinical models. It provides information about the development of anhedonia in the context of early-life adversity, and the power of preclinical models to tease out the diverse molecular, epigenetic, and network mechanisms that are responsible for anhedonia-like behaviors.Specifically, we first discuss the term anhedonia, reviewing the conceptual components underlying reward-related behaviors and distinguish anhedonia pertaining to deficits in motivational versus consummatory behaviors. We then describe the repertoire of experimental approaches employed to study anhedonia-like behaviors in preclinical models, and the progressive refinement over the past decade of both experimental instruments (e.g., chemogenetics, optogenetics) and conceptual constructs (salience, valence, conflict). We follow with an overview of the state of current knowledge of brain circuits, nodes, and projections that execute distinct aspects of hedonic-like behaviors, as well as neurotransmitters, modulators, and receptors involved in the generation of anhedonia-like behaviors. Finally, we discuss the special case of anhedonia that arises following early-life adversity as an eloquent example enabling the study of causality, mechanisms, and sex dependence of anhedonia.Together, this chapter highlights the power, potential, and limitations of using preclinical models to advance our understanding of the origin and mechanisms of anhedonia and to discover potential targets for its prevention and mitigation.

Mesolimbic Neurobehavioral Mechanisms of Reward Motivation in Anorexia Nervosa: A Multimodal Imaging Study

Diminished motivation to pursue and obtain primary and secondary rewards has been demonstrated in anorexia nervosa (AN). However, the neurobehavioral mechanisms underlying the behavioral activation component of aberrant reward motivation remains incompletely understood. This work aims to explore this underexplored facet of reward motivation in AN. We recruited female adolescents with AN, restricting type (n = 32) and a healthy control group (n = 28). All participants underwent functional magnetic resonance imaging (fMRI) while performing a monetary reward task. Diffusion MRI data was also collected to examine the reward motivation circuit's structural connectivity. Behavioral results demonstrated slower speed of reward-seeking behavior in those with AN compared with controls. Accompanying this was lower functional connectivity and reduced white matter structural integrity of the connection between the ventral tegmental area/substantia nigra pars compacta and the nucleus accumbens within the mesolimbic circuit. Further, there was evidence of neurobehavioral decoupling in AN between reward-seeking behavior and mesolimbic regional activation and functional connectivity. Aberrant activity of the bed nucleus of the stria terminalis (BNST) and its connectivity with the mesolimbic system was also evident in AN during the reward motivation period. Our findings suggest functional and structural dysconnectivity within a mesolimbic reward circuit, neurofunctional decoupling from reward-seeking behavior, and abnormal BNST function and circuit interaction with the mesolimbic system. These results show behavioral indicators of aberrant reward motivation in AN, particularly in its activational component. This is mediated neuronally by mesolimbic reward circuit functional and structural dysconnectivity as well as neurobehavioral decoupling. Based on these findings, we suggest a novel circuit-based mechanism of impaired reward processing in AN, with the potential for translation to developing more targeted and effective treatments in this difficult-to-treat psychiatric condition.

Noncanonical projections to the hippocampal CA3 regulate spatial learning and memory by modulating the feedforward hippocampal trisynaptic pathway

The hippocampal formation (HF) is well documented as having a feedforward, unidirectional circuit organization termed the trisynaptic pathway. This circuit organization exists along the septotemporal axis of the HF, but the circuit connectivity across septal to temporal regions is less well described. The emergence of viral genetic mapping techniques enhances our ability to determine the detailed complexity of HF circuitry. In earlier work, we mapped a subiculum (SUB) back projection to CA1 prompted by the discovery of theta wave back propagation from the SUB to CA1 and CA3. We reason that this circuitry may represent multiple extended noncanonical pathways involving the subicular complex and hippocampal subregions CA1 and CA3. In the present study, multiple retrograde viral tracing approaches produced robust mapping results, which supports this prediction. We find significant noncanonical synaptic inputs to dorsal hippocampal CA3 from ventral CA1 (vCA1), perirhinal cortex (Prh), and the subicular complex. Thus, CA1 inputs to CA3 run opposite the trisynaptic pathway and in a temporal to septal direction. Our retrograde viral tracing results are confirmed by anterograde-directed viral mapping of projections from input mapped regions to hippocampal dorsal CA3 (dCA3). We find that genetic inactivation of the projection of vCA1 to dCA3 impairs object-related spatial learning and memory but does not modulate anxiety-related behaviors. Our data provide a circuit foundation to explore novel functional roles contributed by these noncanonical hippocampal circuit connections to hippocampal circuit dynamics and learning and memory behaviors.

Short-Term Sleep Fragmentation Dysregulates Autophagy in a Brain Region-Specific Manner

In this study, we investigated autophagy, glial activation status, and corticotropin releasing factor (CRF) signaling in the brains of mice after 5 days of sleep fragmentation (SF). Three different brain regions including the striatum, hippocampus, and frontal cortex were selected for examination based on roles in sleep regulation and sensitivity to sleep disruption. For autophagy, we monitored the levels of various autophagic induction markers including beclin1, LC3II, and p62 as well as the levels of lysosomal associated membrane protein 1 and 2 (LAMP1/2) and the transcription factor EB (TFEB) which are critical for lysosome function and autophagy maturation stage. For the status of microglia and astrocytes, we determined the levels of Iba1 and GFAP in these brain regions. We also measured the levels of CRF and its cognate receptors 1 and 2 (CRFR1/2). Our results showed that 5 days of SF dysregulated autophagy in the striatum and hippocampus but not in the frontal cortex. Additionally, 5 days of SF activated microglia in the striatum but not in the hippocampus or frontal cortex. In the striatum, CRFR2 but not CRFR1 was significantly increased in SF-experienced mice. CRF did not alter its mRNA levels in any of the three brain regions assessed. Our findings revealed that autophagy processes are sensitive to short-term SF in a region-specific manner and suggest that autophagy dysregulation may be a primary initiator for brain changes and functional impairments in the context of sleep disturbances and disorders.

Hypoactive Thalamic Crh+ Cells in a Female Mouse Model of Alcohol Drinking After Social Trauma

BACKGROUND

Comorbid stress-induced mood and alcohol use disorders are increasingly prevalent among female patients. Stress exposure can disrupt salience processing and goal-directed decision making, contributing to persistent maladaptive behavioral patterns; these and other stress-sensitive cognitive and behavioral processes rely on dynamic and coordinated signaling by midline and intralaminar thalamic nuclei. Considering the role of social trauma in the trajectory of these debilitating psychopathologies, identifying vulnerable thalamic cells may provide guidance for targeting persistent stress-induced symptoms.

METHODS

A novel behavioral protocol traced the progression from social trauma to the development of social defensiveness and chronically escalated alcohol consumption in female mice. Recent cell activation-measured as cFos-was quantified in thalamic cells after safe social interactions, revealing stress-sensitive corticotropin-releasing hormone-expressing (Crh+) anterior central medial thalamic (aCMT) cells. These cells were optogenetically stimulated during stress-induced social defensiveness and abstinence-escalated binge drinking.

RESULTS

Crh+ aCMT neurons exhibited substantial activation after social interactions in stress-naïve but not in stressed female mice. Photoactivating Crh+ aCMT cells dampened stress-induced social deficits, whereas inhibiting these cells increased social defensiveness in stress-naïve mice. Optogenetically activating Crh+ aCMT cells diminished abstinence-escalated binge alcohol drinking in female mice, regardless of stress history.

CONCLUSIONS

This work uncovers a role for Crh+ aCMT neurons in maladaptive stress-induced social interactions and in binge drinking after forced abstinence in female mice. This molecularly defined thalamic cell population may serve as a critical stress-sensitive hub for social deficits caused by exposure to social trauma and for patterns of excessive alcohol drinking in female populations.

Efferent and Afferent Connections of Neuropeptide Y Neurons in the Nucleus Accumbens of Mice

Neuropeptide Y (NPY) is a neural peptide distributed widely in the brain and has various functions in each region. We previously reported that NPY neurons in the nucleus accumbens (NAc) are involved in the regulation of anxiety behavior. Anterograde and retrograde tracing studies suggest that neurons in the NAc project to several areas, such as the lateral hypothalamus (LH) and ventral pallidum (VP), and receive afferent projections from the cortex, thalamus, and amygdala. However, the neural connections between accumbal NPY neurons and other brain areas in mice remain unclear. In this study, we sought to clarify these anatomical connections of NPY neurons in the NAc by investigating their neural outputs and inputs. To selectively map NPY neuronal efferents from the NAc, we injected Cre-dependent adeno-associated viruses (AAVs) into the NAc of NPY-Cre mice. This revealed that NAc NPY neurons exclusively projected to the LH. We confirmed this by injecting cholera toxin b subunit (CTb), a retrograde tracer, into the LH and found that approximately 7–10% of NPY neurons in the NAc were double-labeled for mCherry and CTb. Moreover, retrograde tracing using recombinant rabies virus (rRABV) also identified NAc NPY projections to the LH. Finally, we investigated monosynaptic input to the NPY neurons in the NAc using rRABV. We found that NPY neurons in the NAc received direct synaptic connections from the midline thalamic nuclei and posterior basomedial amygdala. These findings provide new insight into the neural networks of accumbal NPY neurons and should assist in elucidating their functional roles.

Applications of adeno-associated virus vector-mediated gene delivery for neurodegenerative diseases and psychiatric diseases: Progress, advances, and challenges

Neurodegeneration is the most common disease in the elderly population due to its slowly progressive nature of neuronal deterioration, eventually leading to executive dysfunction. The pathological markers of neurological disorders are relatively well-established, however, detailed molecular mechanisms of progression and therapeutic targets are needed to develop novel treatments in human patients. Treating known therapeutic targets of neurological diseases has been aided by recent advancements in adeno-associated virus (AAV) technology. AAVs are known for their low-immunogenicity, blood-brain barrier (BBB) penetrating ability, selective neuronal tropism, stable transgene expression, and pleiotropy. In addition, the usage of AAVs has enormous potential to be optimized. Therefore, AAV can be a powerful tool used to uncover the underlying pathophysiology of neurological disorders and to increase the success in human gene therapy. This review summarizes different optimization approaches of AAV vectors with their current applications in disease modeling, neural tracing and gene therapy, hence exploring progressive mechanisms of neurodegenerative diseases as well as effective therapy. Lastly, this review discusses the limitations and future perspectives of the AAV-mediated transgene delivery system.

Longitudinal neural connection detection using a ferritin-encoding adeno-associated virus vector and in vivo MRI method

The investigation of neural circuits is important for interpreting both healthy brain function and psychiatric disorders. Currently, the architecture of neural circuits is always investigated with fluorescent protein encoding neurotropic virus and ex vivo fluorescent imaging technology. However, it is difficult to obtain a whole‐brain neural circuit connection in living animals, due to the limited fluorescent imaging depth. Herein, the noninvasive, whole‐brain imaging technique of MRI and the hypotoxicity virus vector AAV (adeno‐associated virus) were combined to investigate the whole‐brain neural circuits in vivo. AAV2‐retro are an artificially‐evolved virus vector that permits access to the terminal of neurons and retrograde transport to their cell bodies. By expressing the ferritin protein which could accumulate iron ions and influence the MRI contrast, the neurotropic virus can cause MRI signal changes in the infected regions. For mice injected with the ferritin‐encoding virus vector (rAAV2‐retro‐CAG‐Ferritin) in the caudate putamen (CPu), several regions showed significant changes in MRI contrasts, such as PFC (prefrontal cortex), HIP (hippocampus), Ins (insular cortex) and BLA (basolateral amygdala). The expression of ferritin in those regions was also verified with ex vivo fluorescence imaging. In addition, we demonstrated that changes in T2 relaxation time could be used to identify the spread area of the virus in the brain over time. Thus, the neural connections could be longitudinally detected with the in vivo MRI method. This novel technique could be utilized to observe the viral infection process and detect the neural circuits in a living animal.

Social isolation of adolescent male rats increases anxiety and K+ -induced dopamine release in the nucleus accumbens: Role of CRF-R1

Early life adversity can disrupt development leading to emotional and cognitive disorders. This study investigated the effects of social isolation after weaning on anxiety, body weight and locomotion, and on extracellular dopamine (DA) and glutamate (GLU) in the nucleus accumbens (NAc) and their modulation by corticotropin releasing factor receptor 1. On the day of weaning, male rats were housed singly or in groups for 10 consecutive days. Anxiety-like behaviors were assessed by an elevated plus maze (EPM) and an open field test (OF). Neurotransmitter levels were measured by in vivo microdialysis. Single-housed rats spent less time, and entered more, into the closed arms of an EPM than group-housed rats. They also spent less time in the center of an OF, weighed more and showed greater locomotion. In the NAc, no differences in CRF, or in basal extracellular DA or GLU between groups, were observed. A depolarizing stimulus increased DA release in both groups but to higher levels in isolated rats, whereas GLU increased only in single-housed rats. Blocking CRF-R1 receptors with CP-154,526 decreased DA release in single-housed but not in group-housed rats. The corticotropin releasing factor receptor type 1 receptor antagonist also decreased GLU in group-housed animals. These results show that isolating adolescent rats increases anxiety, body weight and ambulation, as well as the sensitivity of dopaminergic neurons to a depolarizing stimulus. This study provides further evidence of the detrimental effects of social isolation during early development and indicates that dysregulation of the CRF system in the NAc may contribute to the pathologies observed.

Activating Corticotropin-Releasing Factor Systems in the Nucleus Accumbens, Amygdala, and Bed Nucleus of Stria Terminalis: Incentive Motivation or Aversive Motivation?

BACKGROUND

Corticotropin-releasing factor (CRF) neural systems are important stress mechanisms in the central amygdala (CeA), bed nucleus of stria terminalis (BNST), nucleus accumbens (NAc), and related structures. CRF-containing neural systems are traditionally posited to generate aversive distress states that motivate overconsumption of rewards and relapse in addiction. However, CRF-containing systems may alternatively promote incentive motivation to increase reward pursuit and consumption without requiring aversive states.

METHODS

We optogenetically stimulated CRF-expressing neurons in the CeA, BNST, or NAc using Crh-Cre+ rats (n = 37 female, n = 34 male) to investigate roles in incentive motivation versus aversive motivation. We paired CRF-expressing neuronal stimulations with earning sucrose rewards in two-choice and progressive ratio tasks and investigated recruitment of distributed limbic circuitry. We further assessed valence with CRF-containing neuron laser self-stimulation tasks.

RESULTS

Channelrhodopsin excitation of CRF-containing neurons in the CeA and NAc amplified and focused incentive motivation and recruited activation of mesocorticolimbic reward circuitry. CRF systems in both the CeA and NAc supported laser self-stimulation, amplified incentive motivation for sucrose in a breakpoint test, and focused "wanting" on laser-paired sucrose over a sucrose alternative in a two-choice test. Conversely, stimulation of CRF-containing neurons in the BNST produced negative valence or aversive effects and recruited distress-related circuitry, as stimulation was avoided and suppressed motivation for sucrose.

CONCLUSIONS

CRF-containing systems in the NAc and CeA can promote reward consumption by increasing incentive motivation without involving aversion. In contrast, stimulation of CRF-containing systems in the BNST is aversive but suppresses sucrose reward pursuit and consumption rather than increase, as predicted by traditional hedonic self-medication hypotheses.

The Paraventricular Thalamus: A Potential Sensor and Integrator of Emotionally Salient Early-Life Experiences

Early-life experiences influence a broad spectrum of behaviors throughout the lifespan that contribute to resilience or vulnerability to mental health disorders. Yet, how emotionally salient experiences early in life are encoded, stored, and processed and the mechanisms by which they influence future behaviors remain poorly understood. The paraventricular nucleus of the thalamus (PVT) is a key structure in modulating positive and negative experiences and behaviors in adults. However, little is known of the PVT's role in encoding and integrating emotionally salient experiences that occur during neonatal, infancy, and childhood periods. In this review, we (1) describe the functions and connections of the PVT and its regulation of behavior, (2) introduce novel technical approaches to elucidating the role of the PVT in mediating enduring changes in adult behaviors resulting from early-life experiences, and (3) conclude that PVT neurons of neonatal rodents are engaged by both positive and negative emotionally salient experiences, and their activation may enduringly govern future behavior-modulating PVT activity during emotionally salient contexts.

Prefrontal corticotropin-releasing factor neurons impair sustained attention via distal transmitter release

The prefrontal cortex (PFC) supports cognitive processes critical for goal-directed behavior. Although the PFC contains a high density of corticotropin-releasing factor (CRF) neurons, their role in cognition has been largely unexplored. We recently demonstrated that CRF neurons in the caudal dorsomedial PFC (dmPFC) of rats act to impair working memory via activation of local CRF receptors. However, there is heterogeneity in the neural mechanisms that support the diversity of PFC-dependent cognitive processes. Currently, the degree to which PFC CRF neurons impact other forms of PFC-dependent cognition is unknown. To address this issue, the current studies examined the effects of chemogenetic manipulations of PFC CRF neurons on sustained attention in male rats. Similar to working memory, activation of caudal dmPFC CRF neurons impaired, while inhibition of these neurons or global CRF receptor antagonism improved, sustained attention. However, unlike working memory, the sustained attention-impairing effect of PFC CRF neurons was not dependent on local CRF receptors. Moreover, CRF infusion into the caudal dmPFC or other medial PFC subregions had no effect on task performance. Together, these observations demonstrate that while caudal dmPFC CRF neurons impair both working memory and sustained attention, these actions involve distinct neural circuits (local CRF release for working memory and extra-PFC release for sustained attention). Nonetheless, the procognitive actions of systemically administered CRF antagonists across both tasks are similar to those seen with attention deficit hyperactivity disorder-related treatments. Thus, CRF antagonists may have potential for use in the treatment of PFC cognitive dysfunction.

A hypothalamic-thalamostriatal circuit that controls approach-avoidance conflict in rats

Survival depends on a balance between seeking rewards and avoiding potential threats, but the neural circuits that regulate this motivational conflict remain largely unknown. Using an approach-food vs. avoid-predator threat conflict test in rats, we identified a subpopulation of neurons in the anterior portion of the paraventricular thalamic nucleus (aPVT) which express corticotrophin-releasing factor (CRF) and are preferentially recruited during conflict. Inactivation of aPVT^CRF neurons during conflict biases animal's response toward food, whereas activation of these cells recapitulates the food-seeking suppression observed during conflict. aPVT^CRF neurons project densely to the nucleus accumbens (NAc), and activity in this pathway reduces food seeking and increases avoidance. In addition, we identified the ventromedial hypothalamus (VMH) as a critical input to aPVT^CRF neurons, and demonstrated that VMH-aPVT neurons mediate defensive behaviors exclusively during conflict. Together, our findings describe a hypothalamic-thalamostriatal circuit that suppresses reward-seeking behavior under the competing demands of avoiding threats.

Functional Connectivity of the Human Paraventricular Thalamic Nucleus: Insights From High Field Functional MRI

The paraventricular thalamic nucleus (PVT) is a small but highly connected nucleus of the dorsal midline thalamus. The PVT has garnered recent attention as a context-sensitive node within the thalamocortical arousal system that modulates state-dependent motivated behaviors. Once considered related to generalized arousal responses with non-specific impacts on behavior, accumulating evidence bolsters the contemporary view that discrete midline thalamic subnuclei belong to specialized corticolimbic and corticostriatal circuits related to attention, emotions, and cognition. However, the functional connectivity patterns of the human PVT have yet to be mapped. Here, we combined high-quality, high-resolution 7T and 3T resting state MRI data from 121 young adult participants from the Human Connectome Project (HCP) and thalamic subnuclei atlas masks to investigate resting state functional connectivity of the human PVT. The 7T results demonstrated extensive positive functional connectivity with the brainstem, midbrain, ventral and dorsal medial prefrontal cortex (mPFC), anterior and posterior cingulate, ventral striatum, hippocampus, and amygdala. These connections persist upon controlling for functional connectivity of the rest of the thalamus. Whole-brain contrasts provided further evidence that, compared to three nearby midline thalamic subnuclei, functional connectivity of the PVT is strong with the hippocampus, amygdala, ventral and dorsal mPFC, and middle temporal gyrus. These findings suggest that, even during rest, the human PVT is functionally coupled with many regions known to be structurally connected to rodent and non-human primate PVT. Further, cosine similarity analysis results suggested the PVT is integrated into the default mode network (DMN), an intrinsic connectivity network associated with episodic memory and self-referential thought. The current work provides a much-needed foundation for ongoing and future work examining the functional roles of the PVT in humans.

Retrograde Axonal Transport Property of Adeno-Associated Virus and Its Possible Application in Future

Gene therapy has become a treatment method for many diseases. Adeno-associated virus (AAV) is one of the most common virus vectors, is also widely used in the gene therapy field. During the past 2 decades, the retrograde axonal transportability of AAV has been discovered and utilized. Many studies have worked on the retrograde axonal transportability of AAV, and more and more people are interested in this field. This review described the current application, influence factors, and mechanism of retrograde axonal transportability of AAV and predicted its potential use in disease treatment in near future.

Expression and Distribution of Neuropeptide-Expressing Cells Throughout the Rodent Paraventricular Nucleus of the Thalamus

The paraventricular nucleus of the thalamus (PVT) has been shown to make significant contributions to affective and motivated behavior, but a comprehensive description of the neurochemicals expressed in the cells of this brain region has never been presented. While the PVT is believed to be composed of projection neurons that primarily use as their neurotransmitter the excitatory amino acid, glutamate, several neuropeptides have also been described in this brain region. In this review article, we combine published literature with our observations from the Allen Brain Atlas to describe in detail the expression and distribution of neuropeptides in cells throughout the mouse and rat PVT, with a special focus on neuropeptides known to be involved in behavior. Several themes emerge from this investigation. First, while the majority of neuropeptides are expressed across the antero-posterior axis of the PVT, they generally exist in a gradient, in which expression is most dense but not exclusive in either the anterior or posterior PVT, although other neuropeptides display somewhat more equal expression in the anterior and posterior PVT but have reduced expression in the middle PVT. Second, we find overall that neuropeptides involved in arousal are more highly expressed in the anterior PVT, those involved in depression-like behavior are more highly expressed in the posterior PVT, and those involved in reward are more highly expressed in the medial PVT, while those involved in the intake of food and drugs of abuse are distributed throughout the PVT. Third, the pattern and content of neuropeptide expression in mice and rats appear not to be identical, and many neuropeptides found in the mouse PVT have not yet been demonstrated in the rat. Thus, while significantly more work is required to uncover the expression patterns and specific roles of individual neuropeptides in the PVT, the evidence thus far supports the existence of a diverse yet highly organized system of neuropeptides in this nucleus. Determined in part by their location within the PVT and their network of projections, the function of the neuropeptides in this system likely involves intricate coordination to influence both affective and motivated behavior.

Neural meaning making, prediction, and prefrontal-subcortical development following early adverse caregiving

Early adversities that are caregiving-related (crEAs) are associated with a significantly increased risk for mental health problems. Recent neuroscientific advances have revealed alterations in medial prefrontal cortex (mPFC)-subcortical circuitry following crEAs. While this work has identified alterations in affective operations (e.g., perceiving, reacting, controlling, learning) associated with mPFC-subcortical circuitry, this circuitry has a much broader function extending beyond operations. It plays a primary role in affective meaning making, involving conceptual-level, schematized knowledge to generate predictions about the current environment. This function of mPFC-subcortical circuitry motivates asking whether mPFC-subcortical phenotypes following crEAs support semanticized knowledge content (or the concept-level knowledge) and generate predictive models. I present a hypothesis motivated by research findings across four different lines of work that converge on mPFC-subcortical neuroanatomy, including (a) the neurobiology supporting emotion regulation processes in adulthood, (b) the neurobiology that is activated by caregiving cues during development, (c) the neurobiology that is altered by crEAs, and (d) the neurobiology of semantic-based meaning making. I hypothesize that the affective behaviors following crEAs result in part from affective semantic memory processes supported by mPFC-subcortical circuitry that over the course of development, construct affective schemas that generate meaning making and guide predictions. I use this opportunity to review some of the literature on mPFC-subcortical circuit development following crEAs to illustrate the motivation behind this hypothesis. Long recognized by clinical science and cognitive neuroscience, studying schema-based processes may be particularly helpful for understanding how affective meaning making arises from developmental trajectories of mPFC-subcortical circuitry.

Periaqueductal gray inputs to the paraventricular nucleus of the thalamus: Columnar topography and glucocorticoid (in)sensitivity

The ability to cope with a novel acute stressor in the context of ongoing chronic stress is of critical adaptive value. The hypothalamic-pituitary-adrenal (HPA) axis contributes to the integrated physiological and behavioural responses to stressors. Under conditions of chronic stress, the posterior portion of the paraventricular thalamic nucleus (pPVT) mediates the 'habituation' of HPA-axis responses, and also facilitates HPA-axis reactivation to novel acute stressors amidst this habituation. Since pPVT neurons are sensitive to the inhibitory effects of circulating glucocorticoids, a glucocorticoid-insensitive neural pathway to the pPVT is likely essential for this reactivation process. The pPVT receives substantial inputs from neurons of the periaqueductal gray (PAG) region, which is organised into longitudinal columns critical for processing acute and/or chronic stressors. We investigated the columnar organisation of PAG → pPVT projections and for the first time determined their glucocorticoid sensitivity. Retrograde tracer injections were made into different rostro-caudal regions of the pPVT, and their PAG columnar inputs compared. Glucocorticoid receptor immunoreactivity (GR-ir) was quantified in these projection neurons. We found that the dorsolateral PAG projected most strongly to rostral pPVT and the ventrolateral PAG most strongly to the caudal pPVT. Despite abundant GR-ir in the PAG, we report a striking absence of GR-ir in PAG → pPVT neurons. Our data suggests that these pathways, which are insensitive to the direct actions of circulating glucocorticoids, likely play an important role in both the habituation of HPA-axis to chronic stressors and its facilitation to acute stressors in chronically stressed rats.

Turning the 'Tides on Neuropsychiatric Diseases: The Role of Peptides in the Prefrontal Cortex

Recent advancements in technology have enabled researchers to probe the brain with the greater region, cell, and receptor specificity. These developments have allowed for a more thorough understanding of how regulation of the neurophysiology within a region is essential for maintaining healthy brain function. Stress has been shown to alter the prefrontal cortex (PFC) functioning, and evidence links functional impairments in PFC brain activity with neuropsychiatric disorders. Moreover, a growing body of literature highlights the importance of neuropeptides in the PFC to modulate neural signaling and to influence behavior. The converging evidence outlined in this review indicates that neuropeptides in the PFC are specifically impacted by stress, and are found to be dysregulated in numerous stress-related neuropsychiatric disorders including substance use disorder, major depressive disorder (MDD), posttraumatic stress disorder, and schizophrenia. This review explores how neuropeptides in the PFC function to regulate the neural activity, and how genetic and environmental factors, such as stress, lead to dysregulation in neuropeptide systems, which may ultimately contribute to the pathology of neuropsychiatric diseases.

Viral Vectors for Neural Circuit Mapping and Recent Advances in Trans-synaptic Anterograde Tracers

Viral tracers are important tools for neuroanatomical mapping and genetic payload delivery. Genetically modified viruses allow for cell-type-specific targeting and overcome many limitations of non-viral tracers. Here, we summarize the viruses that have been developed for neural circuit mapping, and we provide a primer on currently applied anterograde and retrograde viral tracers with practical guidance on experimental uses. We also discuss and highlight key technical and conceptual considerations for developing new safer and more effective anterograde trans-synaptic viral vectors for neural circuit analysis in multiple species.

Plasticity of the Reward Circuitry After Early-Life Adversity: Mechanisms and Significance

Disrupted operation of the reward circuitry underlies many aspects of affective disorders. Such disruption may manifest as aberrant behavior including risk taking, depression, anhedonia, and addiction. Early-life adversity is a common antecedent of adolescent and adult affective disorders involving the reward circuitry. However, whether early-life adversity influences the maturation and operations of the reward circuitry, and the potential underlying mechanisms, remain unclear. Here, we present novel information using cutting-edge technologies in animal models to dissect out the mechanisms by which early-life adversity provokes dysregulation of the complex interactions of stress and reward circuitries. We propose that certain molecularly defined pathways within the reward circuitry are particularly susceptible to early-life adversity. We examine regions and pathways expressing the stress-sensitive peptide corticotropin-releasing factor (CRF), which has been identified in critical components of the reward circuitry and interacting stress circuits. Notably, CRF is strongly modulated by early-life adversity in several of these brain regions. Focusing on amygdala nuclei and their projections, we provide evidence suggesting that aberrant CRF expression and function may underlie augmented connectivity of the nucleus accumbens with fear/anxiety regions, disrupting the function of this critical locus of pleasure and reward.

Corticotropin Releasing Factor Type 1 and 2 Receptor Signaling in the Medial Prefrontal Cortex Modulates Binge-Like Ethanol Consumption in C57BL/6J Mice

Corticotropin releasing factor (CRF) signaling via limbic CRF1 and 2 receptors (CRF1R and CRF2R, respectively) is known to modulate binge-like ethanol consumption in rodents. Though CRF signaling in the medial prefrontal cortex (mPFC) has been shown to modulate anxiety-like behavior and ethanol seeking, its role in binge ethanol intake is unknown. Here, we used “drinking-in-the-dark” (DID) procedures in male and female C57BL/6J mice to address this gap in the literature. First, the role of CRF1R and CRF2R signaling in the mPFC on ethanol consumption was evaluated through site-directed pharmacology. Next, we evaluated if CRF1R antagonist reduction of binge-intake was modulated in part through CRF2R activation by co-administration of a CRF1R and CRF2R antagonist. Intra-mPFC inhibition of CRF1R and activation of CRF2R resulted in decreased binge-like ethanol intake. Further, the inhibitory effect of the CRF1R antagonist was attenuated by co-administration of a CRF2R antagonist. We provide novel evidence that (1) inhibition of CRF1R or activation of CRF2R in the mPFC reduces binge-like ethanol intake; and (2) the effect of CRF1R antagonism may be mediated via enhanced CRF2R activation. These observations provide the first direct behavioral pharmacological evidence that CRF receptor activity in the mPFC modulates binge-like ethanol consumption.

Corticotropin-Releasing Factor (CRF) circuit modulation of cognition and motivation

The neuropeptide, corticotropin-releasing factor (CRF), is a key modulator of physiological, endocrine, and behavioral responses during stress. Dysfunction of the CRF system has been observed in stress-related affective disorders including post-traumatic stress disorder, depression, and anxiety. Beyond affective symptoms, these disorders are also characterized by impaired cognition, for which current pharmacological treatments are lacking. Thus, there is a need for pro-cognitive treatments to improve quality of life for individuals suffering from mental illness. In this review, we highlight research demonstrating that CRF elicits potent modulatory effects on higher-order cognition via actions within the prefrontal cortex and subcortical monoaminergic and cholinergic systems. Additionally, we identify questions for future preclinical research on this topic, such as the need to investigate sex differences in the cognitive and microcircuit actions of CRF, and whether CRF may represent a pharmacological target to treat cognitive dysfunction. Addressing these questions will provide new insight into pathophysiology underlying cognitive dysfunction and may lead to improved treatments for neuropsychiatric disorders.

Striatal Cholinergic Interneurons Are a Novel Target of Corticotropin Releasing Factor

Cholinergic interneurons (CINs) are critical regulators of striatal network activity and output. Changes in CIN activity are thought to encode salient changes in the environment and stimulus-response-outcome associations. Here we report that the stress-associated neuropeptide corticotropin releasing factor (CRF) produces a profound and reliable increase in the spontaneous firing of CINs in both dorsal striatum and nucleus accumbens (NAc) through activation of CRF type 1 receptors, production of cAMP and reduction in spike accommodation in male mice. The increase of CIN firing by CRF results in the activation muscarinic acetylcholine receptors type 5, which mediate potentiation of dopamine transmission in the striatum. This study provides critical mechanistic insight into how CRF modulates striatal activity and dopamine transmission in the NAc to likely account for CRF facilitation of appetitive behaviors.SIGNIFICANCE STATEMENT Although the presence of CRF receptors in the dorsal and ventral striatum has been acknowledged, the cellular identity and the functional consequences of receptor activation is unknown. Here we report that striatal cholinergic interneurons express CRF-R1 receptors and are acutely activated by the neuropeptide CRF that is released in response to salient environmental stimuli. Cholinergic interneurons make <1% of the cells in the striatum but are critical regulators of the striatal circuitry and its output. CRF's fast and potent activation of cholinergic interneurons could have far reaching behavioral implications across motivated behaviors controlled by the striatum.