A Key Role for Neurotensin in Chronic-Stress-Induced Anxiety-Like Behavior in Rats

Neurotensin agonist PD149163 modulates lipopolysaccharide induced inflammation and oxidative stress in the female reproductive system of mice

Inflammation-mediated reproductive health problems in females have become an emerging concern. The present investigation was aimed to elucidate the efficacy of the PD149163, agonist of the type I neurotensin receptor, in preventing/ameliorating the lipopolysaccharide (LPS) induced inflammation of the female reproductive system of the mice. Female Swiss Albino Mice (8 weeks old) were maintained in three groups (6/group): Group I as Control, Group II and Group III were exposed to intraperitoneal (i.p) LPS (1 mg/kg bw) for 5 days followed by treatment with PD149163 (100 μg/kg BW i.p.) to Group III (LPS + PD) for 28 days. After termination of the experiment on 29th day, plasma levels of inflammatory cytokines, LH, FSH, estradiol, corticosterone, oxidative stress effects in the ovary and histopathological study of the ovary and uterine horn were done. LPS-induced inflammation of the ovary and uterine horn was ameliorated/prevented by PD149163 as reflected in the reduced histopathological scores, significant elevation of the plasma anti-inflammatory cytokine IL-10 and decrease of the pro inflammatory cytokines TNF-α and IL-6. Significant decrease of lipid peroxide, increase of antioxidant defense enzymes, Superoxide dismutase and Catalase in the ovary indicated reduction of oxidative stress. The plasma levels of the reproduction related hormones and corticosterone were restored. PD149163 acts as an anti-inflammatory and anti-oxidative agent in modulation of inflammation in the female reproductive system (ovary & uterine horn). These findings suggest that the therapeutic potential of the analogs of neurotensin including PD149163 should be explored for the treatment of the female reproductive health issues.

Interplay between hippocampal TACR3 and systemic testosterone in regulating anxiety-associated synaptic plasticity

Tachykinin receptor 3 (TACR3) is a member of the tachykinin receptor family and falls within the rhodopsin subfamily. As a G protein-coupled receptor, it responds to neurokinin B (NKB), its high-affinity ligand. Dysfunctional TACR3 has been associated with pubertal failure and anxiety, yet the mechanisms underlying this remain unclear. Hence, we have investigated the relationship between TACR3 expression, anxiety, sex hormones, and synaptic plasticity in a rat model, which indicated that severe anxiety is linked to dampened TACR3 expression in the ventral hippocampus. TACR3 expression in female rats fluctuates during the estrous cycle, reflecting sensitivity to sex hormones. Indeed, in males, sexual development is associated with a substantial increase in hippocampal TACR3 expression, coinciding with elevated serum testosterone and a significant reduction in anxiety. TACR3 is predominantly expressed in the cell membrane, including the presynaptic compartment, and its modulation significantly influences synaptic activity. Inhibition of TACR3 activity provokes hyperactivation of CaMKII and enhanced AMPA receptor phosphorylation, associated with an increase in spine density. Using a multielectrode array, stronger cross-correlation of firing was evident among neurons following TACR3 inhibition, indicating enhanced connectivity. Deficient TACR3 activity in rats led to lower serum testosterone levels, as well as increased spine density and impaired long-term potentiation (LTP) in the dentate gyrus. Remarkably, aberrant expression of functional TACR3 in spines results in spine shrinkage and pruning, while expression of defective TACR3 increases spine density, size, and the magnitude of cross-correlation. The firing pattern in response to LTP induction was inadequate in neurons expressing defective TACR3, which could be rectified by treatment with testosterone. In conclusion, our study provides valuable insights into the intricate interplay between TACR3, sex hormones, anxiety, and synaptic plasticity. These findings highlight potential targets for therapeutic interventions to alleviate anxiety in individuals with TACR3 dysfunction and the implications of TACR3 in anxiety-related neural changes provide an avenue for future research in the field.

Neurotensin and Neurotensin Receptors in Stress-related Disorders: Pathophysiology & Novel Drug Targets

Neurotensin (NT) is a 13-amino acid neuropeptide widely distributed in the CNS that has been involved in the pathophysiology of many neural and psychiatric disorders. There are three known neurotensin receptors (NTSRs), which mediate multiple actions, and form the neurotensinergic system in conjunction with NT. NTSR1 is the main mediator of NT, displaying effects in both the CNS and the periphery, while NTSR2 is mainly expressed in the brain and NTSR3 has a broader expression pattern. In this review, we bring together up-to-date studies showing an involvement of the neurotensinergic system in different aspects of the stress response and the main stress-related disorders, such as depression and anxiety, post-traumatic stress disorder (PTSD) and its associated symptoms, such as fear memory and maternal separation, ethanol addiction, and substance abuse. Emphasis is put on gene, mRNA, and protein alterations of NT and NTSRs, as well as behavioral and pharmacological studies, leading to evidence-based suggestions on the implicated regulating mechanisms as well as their therapeutic exploitation. Stress responses and anxiety involve mainly NTSR1, but also NTSR2 and NTSR3. NTSR1 and NTSR3 are primarily implicated in depression, while NTSR2 and secondarily NTSR1 in PTSD. NTSR1 is interrelated with substance and drug abuse and NTSR2 with fear memory, while all NTSRs seem to be implicated in ethanol consumption. Some of the actions of NT and NTSRs in these pathological settings may be driven through interactions between NT and corticotrophin releasing factor (CRF) in their regulatory contribution, as well as by NT's pro-inflammatory mediating actions.

The neurophysiological basis of stress and anxiety - comparing neuronal diversity in the bed nucleus of the stria terminalis (BNST) across species

The bed nucleus of the stria terminalis (BNST), as part of the extended amygdala, has become a region of increasing interest regarding its role in numerous human stress-related psychiatric diseases, including post-traumatic stress disorder and generalized anxiety disorder amongst others. The BNST is a sexually dimorphic and highly complex structure as already evident by its anatomy consisting of 11 to 18 distinct sub-nuclei in rodents. Located in the ventral forebrain, the BNST is anatomically and functionally connected to many other limbic structures, including the amygdala, hypothalamic nuclei, basal ganglia, and hippocampus. Given this extensive connectivity, the BNST is thought to play a central and critical role in the integration of information on hedonic-valence, mood, arousal states, processing emotional information, and in general shape motivated and stress/anxiety-related behavior. Regarding its role in regulating stress and anxiety behavior the anterolateral group of the BNST (BNSTALG) has been extensively studied and contains a wide variety of neurons that differ in their electrophysiological properties, morphology, spatial organization, neuropeptidergic content and input and output synaptic organization which shape their activity and function. In addition to this great diversity, further species-specific differences are evident on multiple levels. For example, classic studies performed in adult rat brain identified three distinct neuron types (Type I-III) based on their electrophysiological properties and ion channel expression. Whilst similar neurons have been identified in other animal species, such as mice and non-human primates such as macaques, cross-species comparisons have revealed intriguing differences such as their comparative prevalence in the BNSTALG as well as their electrophysiological and morphological properties, amongst other differences. Given this tremendous complexity on multiple levels, the comprehensive elucidation of the BNSTALG circuitry and its role in regulating stress/anxiety-related behavior is a major challenge. In the present Review we bring together and highlight the key differences in BNSTALG structure, functional connectivity, the electrophysiological and morphological properties, and neuropeptidergic profiles of BNSTALG neurons between species with the aim to facilitate future studies of this important nucleus in relation to human disease.

Neurotensin and Alcohol Use Disorders: Towards a Pharmacological Treatment

Harmful alcohol use is responsible for a group of disorders collectively named alcohol use disorders (AUDs), according to the DSM-5 classification. The damage induced by alcohol depends on the amount, time, and consumption patterns (continuous and heavy episodic drinking). It affects individual global well-being and social and familial environments with variable impact. Alcohol addiction manifests with different degrees of organ and mental health detriment for the individual, exhibiting two main traits: compulsive drinking and negative emotional states occurring at withdrawal, frequently causing relapse episodes. Numerous individual and living conditions, including the concomitant use of other psychoactive substances, lie in the complexity of AUD. Ethanol and its metabolites directly impact the tissues and may cause local damage or alter the homeostasis of brain neurotransmission, immunity scaffolding, or cell repair biochemical pathways. Brain modulator and neurotransmitter-assembled neurocircuitries govern reward, reinforcement, social interaction, and consumption of alcohol behaviors in an intertwined manner. Experimental evidence supports the participation of neurotensin (NT) in preclinical models of alcohol addiction. For example, NT neurons in the central nucleus of the amygdala projecting to the parabrachial nucleus strengthen alcohol consumption and preference. In addition, the levels of NT in the frontal cortex were found to be lower in rats bred to prefer alcohol to water in a free alcohol-water choice compared to wild-type animals. NT receptors 1 and 2 seem to be involved in alcohol consumption and alcohol effects in several models of knockout mice. This review aims to present an updated picture of the role of NT systems in alcohol addiction and the possible use of nonpeptide ligands modulating the activity of the NT system, applied to experimental animal models of harmful drinking behavior mimicking alcohol addiction leading to health ruin in humans.

Control of Emotion and Wakefulness by Neurotensinergic Neurons in the Parabrachial Nucleus

The parabrachial nucleus (PBN) integrates interoceptive and exteroceptive information to control various behavioral and physiological processes including breathing, emotion, and sleep/wake regulation through the neural circuits that connect to the forebrain and the brainstem. However, the precise identity and function of distinct PBN subpopulations are still largely unknown. Here, we leveraged molecular characterization, retrograde tracing, optogenetics, chemogenetics, and electrocortical recording approaches to identify a small subpopulation of neurotensin-expressing neurons in the PBN that largely project to the emotional control regions in the forebrain, rather than the medulla. Their activation induces freezing and anxiety-like behaviors, which in turn result in tachypnea. In addition, optogenetic and chemogenetic manipulations of these neurons revealed their function in promoting wakefulness and maintaining sleep architecture. We propose that these neurons comprise a PBN subpopulation with specific gene expression, connectivity, and function, which play essential roles in behavioral and physiological regulation.

Text4Hope Effectiveness in Reducing Psychological Symptoms among Young Adults in Canada: Longitudinal and Naturalistic Controlled Program Evaluation

BACKGROUND

Chronic stress, anxiety, and depression are psychological problems that can hurt young adults, interfering with their everyday function, academic achievement, and interpersonal relationships. This study aimed to assess the impact of Text4Hope, an online mental health service, on the psychological well-being of young adults.

METHODS

This study adopted both longitudinal and naturalistic controlled trial designs. It examined clinical outcomes in young adult (≤26 years old) subscribers of Text4Hope who completed surveys at baseline and six weeks and compared clinical parameters in two groups of subscribers. The first group comprised the intervention group (IG) (young adult subscribers who received once-daily supportive text messages for six weeks and completed sixth-week evaluation measures between 26 April and 12 July 2020), and the second group was the control group (CG) (young adult subscribers who joined Text4Hope in the same time frame and completed a baseline survey and were yet to receive any text messages). The prevalence of moderate to high stress, anxiety, and depression was measured at baseline and six weeks in the longitudinal study and between the two groups for the naturalistic controlled study using the Perceived Stress Scale (PSS-10), Generalized Anxiety Disorder 7-item (GAD-7), and Patient Health Questionnaire-9 (PHQ-9). Inferential statistics, including the t-test, McNemar test, chi-square, and binary logistic regression analyses, were used to evaluate the differences in the prevalence and severity of the psychological symptoms.

RESULTS

In the longitudinal study, of the 9214 subscribers to Text4Hope who completed the baseline survey, 1047 (11.4%) were identified as youth. For the young adult subscribers who completed both the baseline and sixth-week surveys (n = 114), a significant reduction in the prevalence of moderate to high stress (8%) and likely GAD (20%) from baseline to six weeks was reported. Similarly, there was a significant reduction in the mean scores on the PSS-10, GAD-7, and Composite Mental Health score but not the PHQ-9 from baseline to six weeks. The largest reduction in mean scores was for the GAD-7 scale (18.4%), with a small effect size overall. For the naturalistic study, the IG included 173 young adult subscribers of Text4Hope who completed the sixth-week survey compared to 92 subscribers in the CG who completed the baseline survey during the designated period. There was a significantly lower prevalence for likely Moderate Depressive Disorder (MDD) (25.2%) and suicidal thoughts/thoughts of self-harm (48.4%), with a small effect size in the IG compared to the CG. Similarly, lower mean scores were reported for all outcome variables in the IG compared to the CG, with a small to medium effect size. The receipt of daily supportive text messages for six weeks resulted in significantly lower odds of both likely GAD and experiencing thoughts of self-harm or death wish while controlling for sociodemographic characteristics.

CONCLUSIONS

The Text4Hope service is an effective tool for mental health support for young adult subscribers. Young adults receiving the service exhibited a reduction in psychological symptoms, including thoughts of self-harm or death wish. This population-level intervention program can be used to effectively support young adult mental health and in suicide prevention programs.

Glutamatergic neurotransmission: A potential pharmacotherapeutic target for the treatment of cognitive disorders

In the mammalian brain, glutamate is regarded to be the primary excitatory neurotransmitter due to its widespread distribution and wide range of metabolic functions. Glutamate plays key roles in regulating neurogenesis, synaptogenesis, neurite outgrowth, and neuron survival in the brain. Ionotropic and metabotropic glutamate receptors, neurotransmitters, neurotensin, neurosteroids, and others co-ordinately formulate a complex glutamatergic network in the brain that maintains optimal excitatory neurotransmission. Cognitive activities are potentially synchronized by the glutamatergic activities in the brain via restoring synaptic plasticity. Dysfunctional glutamate receptors and other glutamatergic components are responsible for the aberrant glutamatergic activity in the brain that cause cognitive impairments, loss of synaptic plasticity, and neuronal damage. Thus, controlling the brain's glutamatergic transmission and modifying glutamate receptor function could be a potential therapeutic strategy for cognitive disorders. Certain drugs that regulate glutamate receptor activities have shown therapeutic promise in improving cognitive functions in preclinical and clinical studies. However, several issues regarding precise functional information of glutamatergic activity are yet to be comprehensively understood. The present article discusses the scope of developing glutamatergic systems as prospective pharmacotherapeutic targets to treat cognitive disorders. Special attention has been given to recent developments, challenges, and future prospects.

Effect of D1- and D2-like Dopamine Receptor Antagonists on the Rewarding and Anxiolytic Effects of Neurotensin in the Ventral Pallidum

Background: Neurotensin (NT) acts as a neurotransmitter and neuromodulator in the central nervous system. It was shown previously that NT in the ventral pallidum (VP) has rewarding and anxiolytic effects. NT exerts its effect in interaction with dopamine (DA) receptors in numerous brain areas; however, this has not yet been investigated in the VP. The aim of this study was to examine whether the inhibition of D1-like and D2-like DA receptors of the VP can modify the above mentioned effects of NT. Methods: Microinjection cannulas were implanted by means of stereotaxic operations into the VP of male Wistar rats. The rewarding effect of NT was examined by means of a conditioned place preference test. Anxiety was investigated with an elevated plus maze test. To investigate the possible interaction, D1-like DA receptor antagonist SCH23390 or D2-like DA receptor antagonist sulpiride were microinjected prior to NT. All of the drugs were also injected independently to analyze their effects alone. Results: In the present experiments, both the rewarding and anxiolytic effects of NT in the VP were prevented by both D1-like and D2-like DA receptor antagonists. Administered on their own, the antagonists did not influence reward and anxiety. Conclusion: Our present results show that the activity of the D1-like and D2-like DA receptors of the VP is a necessary requirement for both the rewarding and anxiolytic effects of NT.

Neurotensin Release from Dopamine Neurons Drives Long-Term Depression of Substantia Nigra Dopamine Signaling

Midbrain dopamine neurons play central physiological roles in voluntary movement, reward learning, and motivated behavior. Inhibitory signaling at somatodendritic dopamine D2 receptor (D2R) synapses modulates excitability of dopamine neurons. The neuropeptide neurotensin is expressed by many inputs to the midbrain and induces LTD of D2R synaptic currents (LTD_DA); however, the source of neurotensin that is responsible for LTD_DA is not known. Here we show, in brain slices from male and female mice, that LTD_DA is driven by neurotensin released by dopamine neurons themselves. Optogenetic stimulation of dopamine neurons was sufficient to induce LTD_DA in the substantia nigra, but not the VTA, and was dependent on neurotensin receptor signaling, postsynaptic calcium, and vacuolar-type H⁺-ATPase activity in the postsynaptic cell. These findings reveal a novel form of signaling between dopamine neurons involving release of the peptide neurotensin, which may act as a feedforward mechanism to increase dopamine neuron excitability.SIGNIFICANCE STATEMENT Dopamine neurons in the midbrain play a critical role in reward learning and the initiation of movement. Aberrant dopamine neuron function is implicated in a range of diseases and disorders, including Parkinson's disease, schizophrenia, obesity, and substance use disorders. D2 receptor-mediated PSCs are produced by a rare form of dendrodendritic synaptic transmission between dopamine neurons. These D2 receptor-mediated PSCs undergo LTD following application of the neuropeptide neurotensin. Here we show that release of neurotensin by dopamine neurons themselves is sufficient to induce LTD of dopamine transmission in the substantia nigra. Neurotensin signaling therefore mediates a second form of interdopamine neuron communication and may provide a mechanism by which dopamine neurons maintain excitability when nigral dopamine is elevated.

Anxiety and Depression: What Do We Know of Neuropeptides?

In modern society, there has been a rising trend of depression and anxiety. This trend heavily impacts the population’s mental health and thus contributes significantly to morbidity and, in the worst case, to suicides. Modern medicine, with many antidepressants and anxiolytics at hand, is still unable to achieve remission in many patients. The pathophysiology of depression and anxiety is still only marginally understood, which encouraged researchers to focus on neuropeptides, as they are a vast group of signaling molecules in the nervous system. Neuropeptides are involved in the regulation of many physiological functions. Some act as neuromodulators and are often co-released with neurotransmitters that allow for reciprocal communication between the brain and the body. Most studied in the past were the antidepressant and anxiolytic effects of oxytocin, vasopressin or neuropeptide Y and S, or Substance P. However, in recent years, more and more novel neuropeptides have been added to the list, with implications for the research and development of new targets, diagnostic elements, and even therapies to treat anxiety and depressive disorders. In this review, we take a close look at all currently studied neuropeptides, their related pathways, their roles in stress adaptation, and the etiology of anxiety and depression in humans and animal models. We will focus on the latest research and information regarding these associated neuropeptides and thus picture their potential uses in the future.

Neuropeptide Y, calcitonin gene-related peptide, and neurokinin A in brain regions of HAB rats correlate with anxiety-like behaviours

Anxiety disorders are pervasive psychiatric disorders causing great suffering. The high (HAB) and low (LAB) anxiety-related behaviour rats were selectively bred to investigate neurobiological correlates of anxiety. We compared the level of neuropeptides relevant for anxiety- and depression-related behaviours in selected brain regions of HAB and LAB rats. Increased anxiety and depression-like behaviours of male and female HAB rats in the elevated plus-maze and forced swim tests were accompanied by elevated levels of neuropeptide Y (NPY) in the prefrontal (PFC), frontal (FC) and cingulate cortex (CCx), the striatum, and periaqueductal grey (PAG). Moreover, HAB rats displayed sex-dependent, elevated levels of calcitonin gene-related peptide (CGRP) in PFC, FC, CCx, hippocampus, and PAG. Higher neurokinin A (NKA) levels were detected in CCx, striatum, and PAG in HAB males and in CCx and hypothalamus in HAB females. Increased neurotensin was detected in CCx and PAG in HAB males and in hypothalamus in HAB females. Elevated corticotropin-releasing hormone (CRH) levels appeared in female HAB hypothalamus. Significant correlations were found between anxiety-like behaviour and NPY, CGRP, NKA, and neurotensin, particularly with NPY in CCx and striatum, CGRP in FC and hippocampus, and NKA in entorhinal cortex. This is the first report of NPY, CGRP, NKA, Neurotensin, and CRH measurements in brain regions of HAB and LAB rats, which showed widespread NPY and CGRP alterations in cortical regions, with NKA and neurotensin changes localised in sub-cortical areas. The results may contribute to elucidate pathophysiological mechanisms underlying anxiety and depression and should facilitate identifying novel therapeutic targets.

Diverse intracellular signaling pathways mediate the effects of neurotensin on the excitability of type II neurons in the rat dorsolateral bed nucleus of the stria terminalis

We examined the effects of neurotensin (NTS) on the excitability of type II neurons in the rat dorsolateral bed nucleus of the stria terminalis (dlBNST) using whole-cell patch-clamp electrophysiology. Bath-application of NTS depolarized type II dlBNST neurons. Analyses of the steady-state I-V relationships implied that the depolarizing effect of NTS is due to potassium conductance blocking. The depolarizing effect of NTS was abolished in the presence of a PLC inhibitor, but not affected by a protein kinase C inhibitor. In the presence of a CaMKII inhibitor, NTS showed depolarizing effects via the increase in non-selective cation conductance in addition to the decrease in potassium conductance. Unexpectedly, in the presence of a PKA inhibitor, NTS hyperpolarized type II dlBNST neurons. These results reveal that diverse signaling pathways mediate the effects of NTS on the excitability of type II dlBNST neurons. The elevation of intracellular Ca2+ levels via the inositol phosphate-mediated signaling activates both Ca2+-dependent adenylate cyclase (AC) and CaMKII. Activation of the AC-cAMP-PKA pathway exerts depolarizing effects on type II dlBNST neurons by decreasing potassium conductance and increasing non-selective cation conductance, whereas activation of the CaMKII pathway exerts hyperpolarizing effects on dlBNST neurons by decreasing non-selective cation conductance.

Modulation of behavioral and neurochemical responses of adult zebrafish by fluoxetine, eicosapentaenoic acid and lipopolysaccharide in the prolonged chronic unpredictable stress model

Long-term recurrent stress is a common cause of neuropsychiatric disorders. Animal models are widely used to study the pathogenesis of stress-related psychiatric disorders. The zebrafish (Danio rerio) is emerging as a powerful tool to study chronic stress and its mechanisms. Here, we developed a prolonged 11-week chronic unpredictable stress (PCUS) model in zebrafish to more fully mimic chronic stress in human populations. We also examined behavioral and neurochemical alterations in zebrafish, and attempted to modulate these states by 3-week treatment with an antidepressant fluoxetine, a neuroprotective omega-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA), a pro-inflammatory endotoxin lipopolysaccharide (LPS), and their combinations. Overall, PCUS induced severe anxiety and elevated norepinephrine levels, whereas fluoxetine (alone or combined with other agents) corrected most of these behavioral deficits. While EPA and LPS alone had little effects on the zebrafish PCUS-induced anxiety behavior, both fluoxetine (alone or in combination) and EPA restored norepinephrine levels, whereas LPS + EPA increased dopamine levels. As these data support the validity of PCUS as an effective tool to study stress-related pathologies in zebrafish, further research is needed into the ability of various conventional and novel treatments to modulate behavioral and neurochemical biomarkers of chronic stress in this model organism.

Cell-type diversity in the bed nucleus of the stria terminalis to regulate motivated behaviors

Over the past few decades, the bed nucleus of the stria terminalis (BNST) gained popularity as a unique brain region involved in regulating motivated behaviors related to neuropsychiatric disorders. The BNST, a component of the extended amygdala, consists of a variety of subnuclei and neuronal ensembles. Multiple studies have highlighted the BNST as playing a fundamental role in integrating information by interfacing with other brain regions to regulate distinct aspects of motivated behaviors associated with stress, anxiety, depression, and decision-making. However, due to the high molecular heterogeneity found within BNST neurons, the precise mechanisms by which this region regulates distinct motivational states remains largely unclear. Single-cell RNA sequencing data have revealed that the BNST consists of multiple genetically identifiable cell-type clusters. Contemporary tools can therefore be leveraged to target and study such cell-types and elucidate their precise functional role. In this review, we discuss the different subsets of neurons found in the BNST, their anatomical distribution, and what is currently known about BNST cell-types in regulating motivated behaviors.

The Paraventricular Nucleus of the Thalamus as an Integrating and Relay Node in the Brain Anxiety Network

The brain anxiety network is composed of a number of interconnected cortical regions that detect threats and execute appropriate defensive responses via projections to the shell of the nucleus accumbens (NAcSh), dorsolateral region of the bed nucleus of the stria terminalis (BSTDL) and lateral region of the central nucleus of the amygdala (CeL). The paraventricular nucleus of the thalamus (PVT) is anatomically positioned to integrate threat- and arousal-related signals from cortex and hypothalamus and then relay these signals to neural circuits in the NAcSh, BSTDL, and CeL that mediate defensive responses. This review describes the anatomical connections of the PVT that support the view that the PVT may be a critical node in the brain anxiety network. Experimental findings are reviewed showing that the arousal peptides orexins (hypocretins) act at the PVT to promote avoidance of potential threats especially following exposure of rats to a single episode of footshocks. Recent anatomical and experimental findings are discussed which show that neurons in the PVT provide divergent projections to subcortical regions that mediate defensive behaviors and that the projection to the NAcSh is critical for the enhanced social avoidance displayed in rats exposed to footshocks. A theoretical model is proposed for how the PVT integrates cortical and hypothalamic signals to modulate the behavioral responses associated with anxiety and other challenging situations.

Neurotensin and Xenin Show Positive Correlations With Perceived Stress, Anxiety, Depressiveness and Eating Disorder Symptoms in Female Obese Patients

Objective

Neurotensin and xenin are two closely related anorexigenic neuropeptides synthesized in the small intestine that exert diverse peripheral and central functions. Both act via the neurotensin-1-receptor. In animal models of obesity reduced central concentrations of these peptides have been found. Dysregulations of the acute and chronic stress response are associated with development and maintenance of obesity. Until now, associations of both peptides with stress, anxiety, depressiveness, and eating disorder symptoms have not been investigated. The aim of the present study was to examine associations of neurotensin and xenin with these psychological characteristics under conditions of obesity.

Materials and Methods

From 2010 to 2016 we consecutively enrolled 160 inpatients (63 men and 97 women), admitted due to obesity and its mental and somatic comorbidities. Blood withdrawal und psychometric tests (PSQ-20, GAD-7, PHQ-9, and EDI-2) occurred within one week after admission. We measured levels of neurotensin and xenin in plasma by ELISA.

Results

Mean body mass index was 47.2 ± 9.5 kg/m². Concentrations of neurotensin and xenin positively correlated with each other (women: r = 0.788, p < 0.001; men: r = 0.731, p < 0.001) and did not significantly differ between sexes (p > 0.05). Women generally displayed higher psychometric values than men (PSQ-20: 58.2 ± 21.7 vs. 47.0 ± 20.8, p = 0.002; GAD-7: 9.7 ± 5.8 vs. 7.1 ± 5.3, p = 0.004; PHQ-9: 11.6 ± 6.6 vs. 8.8 ± 5.9, p = 0.008; EDI-2: 50.5 ± 12.8 vs. 39.7 ± 11.9, p < 0.001). Only women showed positive correlations of both neuropeptides with stress (neurotensin: r = 0.231, p = 0.023; xenin: r = 0.254, p = 0.013), anxiety (neurotensin: r = 0.265, p = 0.009; xenin: r = 0.257, p = 0.012), depressiveness (neurotensin: r = 0.281, p = 0.006; xenin: r = 0.241, p = 0.019) and eating disorder symptoms (neurotensin: r = 0.276, p = 0.007; xenin: r = 0.26, p = 0.011), whereas, men did not (p > 0.05).

Conclusion

Neurotensin and xenin plasma levels of female obese patients are positively correlated with perceived stress, anxiety, depressiveness, and eating disorder symptoms. These associations could be influenced by higher prevalence of mental disorders in women and by sex hormones. In men, no correlations were observed, which points toward a sex-dependent regulation.

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.

Cytokines in the colon, central nervous system and serum of irritable bowel syndrome rats

Objective

The aim of this study was to detect the expression of interleukin (IL)-1β and transforming growth factor (TGF)-β1 in the colonic tissue and serum of irritable bowel syndrome (IBS) rats, as well as the distribution and expression of corticotropin-releasing factor (CRF) in the spinal cord and brain of the visceral hypersensitivity rats, thus to ascertain the mechanism of visceral hypersensitivity signal conduction pathway.

Methods

The expression of IL-1β and TGF-β1 in the colonic tissue and serum of IBS rats was screened by the liquid chip technology and verified by RT-PCR technology. Then the quantitative analysis of CRF in the spinal cord and brain was achieved by the immunohistochemical method and computerized image system.

Result

The rat model with visceral hypersensitivity was successfully established. Among the screened indicators of IL-1β and TGF-β1 in colon tissue and serum, only the expression of IL-1β in the model group was up-regulated (P < 0.05). The immunohistochemical method showed that CRF was expressed in the spinal cord, hypothalamus, and the third ventricle. The positive index number of the model groups was higher than that of the control group (P < 0.01).

Conclusion

From the research, it can be inferred that IL-1β may participate in the pathogenesis mechanism of IBS via regulating the colon function. The increasing expression of CRF linked to stress in the spinal cord, hypothalamus and the third ventricle indicated that it might play an important role in the mechanisms of visceral hypersensitivity signal conduction pathway.

Neurotensin 1 receptor in the prelimbic cortex regulates anxiety-like behavior in rats

The central neurotensin system has been implicated in reward, memory processes, also in the regulation of anxiety. However, the neural substrates where neurotensin acts to regulate anxiety have not been fully identified. The prelimbic region of medial prefrontal cortex (PrL) holds a key position in the modulation of anxiety-related behaviors and expresses neurotensin 1 receptor (NTS1). This study investigated the effects of activation or blockade of NTS1 in the PrL on anxiety-like behaviors of rats. Our results demonstrated that infusion of a selective NTS1 agonist or neurotensin into the PrL produced anxiogenic-like effects. Administration of a NTS1 antagonist into the PrL did not affect anxiety-like behaviors of normal rats, but attenuated anxiogenic effects induced by restraint stress. Moreover, we employed molecular approaches to downregulate the expression of NTS1 in the PrL, and found that downregulation of NTS1 in the PrL induced anxiolytic effects in restraint stress rats, also confirming the pharmacological results. Together, these findings suggest that NTS1 in the PrL is actively involved in the regulation of anxiety.

Effect of Monoclonal Antibody Blockade of Long Fragment Neurotensin on Weight Loss, Behavior, and Metabolic Traits After High-Fat Diet Induced Obesity

BACKGROUND

Obesity is a major public health problem of our time as a risk factor for cardiometabolic disease and the available pharmacological tools needed to tackle the obesity pandemic are insufficient. Neurotensin (NTS) is a 13 amino acid peptide, which is derived from a larger precursor hormone called proneurotensin or Long Form NTS (LF NTS). NTS modulates neuro-transmitter release in the central system nervous, and facilitates intestinal fat absorption in the gastrointestinal tract. Mice lacking LF NTS are protected from high fat diet (HFD) induced obesity, hepatic steatosis and glucose intolerance. In humans, increased levels of LF NTS strongly and independently predict the development of obesity, diabetes mellitus, cardiovascular disease and mortality. With the perspective to develop therapeutic tools to neutralize LF NTS, we developed a monoclonal antibody, specifically inhibiting the function of the LF NTS (LF NTS mAb). This antibody was tested for the effects on body weight, metabolic parameters and behavior in mice made obese by high-fat diet.

METHODS

C57bl/6j mice were subjected to high-fat diet (HFD) until they reached an obesity state, then food was switched to chow. Mice were treated with either PBS (control therapy) or LF NTS mAb at the dose of 5 mg/kg once a week (i.v.). Mice weight, plasma biochemical analysis, fat and muscle size and distribution and behavioral tests were performed during the losing weight period and the stabilization period.

RESULTS

Obese mice treated with the LF NTS mAb lost weight significantly faster than the control treated group. LF NTS mAb treatment also resulted in smaller fat depots, increased fecal cholesterol excretion, reduced liver fat and larger muscle fiber size. Moreover, mice on active therapy were also less stressed, more curious and more active, providing a possible explanation to their weight loss.

CONCLUSION

Our results demonstrate that in mice subjected to HFD-induced obesity, a blockade of LF NTS with a monoclonal antibody results in reduced body weight, adipocyte volume and increased muscle fiber size, possibly explained by beneficial effects on behavior. The underlying mechanisms as well as any future role of LF NTS mAb as an anti-obesity agent warrants further studies.

Chemoarchitecture of the bed nucleus of the stria terminalis: Neurophenotypic diversity and function

The bed nucleus of the stria terminalis (BNST) is a compact but neurophenotypically complex structure in the ventral forebrain that is structurally and functionally linked to other limbic structures, including the amygdala nuclear complex, hypothalamic nuclei, hippocampus, and related midbrain structures, to participate in a wide range of functions, especially emotion, emotional learning, stress-related responses, and sexual behaviors. From a variety of sensory inputs, the BNST acts as a node for signal integration and coordination for information relay to downstream central neuroendocrine and autonomic centers for appropriate homeostatic physiological and behavioral responses. In contrast to the role of the amygdala in fear, the BNST has gained wide interest from work suggesting that it has main roles in mediating sustained responses to diffuse, unpredictable and/or long-duration threats that are typically associated with anxiety-related responses. Further, some BNST subregions are highly sexually dimorphic which appear contributory to the differential stress and social interactive behaviors, including reproductive responses, between males and females. Notably, maladaptive BNST neuroplasticity and function have been implicated in chronic pain, depression, anxiety-related abnormalities, and other psychopathologies including posttraumatic stress disorders. The BNST circuits are predominantly GABAergic-the glutaminergic neurons represent a minor population-but the complexity of the system results from an overlay of diverse neuropeptide coexpression in these neurons. More than a dozen neuropeptides may be differentially coexpressed in BNST neurons, and from variable G protein-coupled receptor signaling, may inhibit or activate downstream circuit activities. The mechanisms and roles of these peptides in modulating intrinsic BNST neurocircuit signaling and BNST long-distance target cell projections are still not well understood. Nevertheless, an understanding of some of the principal players may allow assembly of the circuit interactions.

A projection from the paraventricular nucleus of the thalamus to the shell of the nucleus accumbens contributes to footshock stress-induced social avoidance

The paraventricular nucleus of the thalamus (PVT) is an area of the dorsal midline thalamus that contributes to footshock induced anxiety. The PVT sends a dense projection to the shell of the nucleus accumbens (NAcSh) and the present study explored if this projection is involved in the behavioral changes produced by a single exposure of rats to inescapable footshocks. The inhibitory Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) hM4Di was transduced in PVT neurons that project to the NAcSh. Rats were exposed to an episode of moderately intense footshock (1.5 mA × 2 s × 5) and assigned to either high-responder (HR) or low-responder groups (LR) according to their level of fear generalization 24 h later. The effect of chemogenetic inhibition of the PVT-NAcSh projection on anxiety- and fear-like behaviors was assessed at approximately 2 weeks post-footshock. HR showed a higher level of social avoidance compared to non-shocked animals and LR. The elevated level of social avoidance was attenuated in the HR treated with the hM4Di agonist clozapine (0.01 mg/kg, i.p.) or clozapine N-oxide (CNO) administrations in the NAcSh while avoidance of open spaces and contextual fear expression were not affected. Analysis of protein product of the early to immediate gene cfos indicated that these effects were mediated by dynorphin neurons in the NAcSh. This study provides evidence for a role of a projection from the PVT to the NAcSh in stress-induced social avoidance independent of anxiety to non-social stimuli and contextual fear mechanisms.

Inhibitory synaptic transmissions to the bed nucleus of the stria terminalis neurons projecting to the ventral tegmental area are enhanced in rats exposed to chronic mild stress

The comorbidities of depression and chronic pain have long been recognized in the clinic, and several preclinical studies have demonstrated depression-like behaviors in animal models of chronic pain. These findings suggest a common neuronal basis for depression and chronic pain. Recently, we reported that the mesolimbic dopaminergic system was tonically suppressed during chronic pain by enhanced inhibitory synaptic inputs to neurons projecting from the dorsolateral bed nucleus of the stria terminalis (dlBNST) to the ventral tegmental area (VTA), suggesting that tonic suppression of the mesolimbic dopaminergic system by this neuroplastic change may be involved in chronic pain-induced depression-like behaviors. In this study, we hypothesized that inhibitory synaptic inputs to VTA-projecting dlBNST neurons are also enhanced in animal models of depression, thereby suppressing the mesolimbic dopaminergic system. To test this hypothesis, we performed whole-cell patch-clamp electrophysiology using brain slices prepared from rats exposed to chronic mild stress (CMS), a widely used animal model of depression. The results showed a significant enhancement in the frequency of spontaneous inhibitory postsynaptic currents in VTA-projecting dlBNST neurons in the CMS group compared with the no stress group. The findings revealed enhanced inhibitory synaptic inputs to VTA-projecting dlBNST neurons in this rat model of depression, suggesting that this neuroplastic change is a neuronal mechanism common to depression and chronic pain that causes dysfunction of the mesolimbic dopaminergic system, thereby inducing depression-like behaviors.

Dissecting the Roles of GABA and Neuropeptides from Rat Central Amygdala CRF Neurons in Anxiety and Fear Learning

Central amygdala (CeA) neurons that produce corticotropin-releasing factor (CRF) regulate anxiety and fear learning. These CeA^CRF neurons release GABA and several neuropeptides predicted to play important yet opposing roles in these behaviors. We dissected the relative roles of GABA, CRF, dynorphin, and neurotensin in CeA^CRF neurons in anxiety and fear learning by disrupting their expression using RNAi in male rats. GABA, but not CRF, dynorphin, or neurotensin, regulates baseline anxiety-like behavior. In contrast, chemogenetic stimulation of CeA^CRF neurons evokes anxiety-like behavior dependent on CRF and dynorphin, but not neurotensin. Finally, knockdown of CRF and dynorphin impairs fear learning, whereas knockdown of neurotensin enhances it. Our results demonstrate distinct behavioral roles for GABA, CRF, dynorphin, and neurotensin in a subpopulation of CeA neurons. These results highlight the importance of considering the repertoire of signaling molecules released from a given neuronal population when studying the circuit basis of behavior.

Pomrenze et al. demonstrate that CRF neurons of the central amygdala differentially regulate fear and anxiety through the release of GABA and different neuropeptides.

Neurotensin in reward processes

Neurotensin (NTS) is a neuropeptide neurotransmitter expressed in the central and peripheral nervous systems. Many studies over the years have revealed a number of roles for this neuropeptide in body temperature regulation, feeding, analgesia, ethanol sensitivity, psychosis, substance use, and pain. This review provides a general survey of the role of neurotensin with a focus on modalities that we believe to be particularly relevant to the study of reward. We focus on NTS signaling in the ventral tegmental area, nucleus accumbens, lateral hypothalamus, bed nucleus of the stria terminalis, and central amygdala. Studies on the role of NTS outside of the ventral tegmental area are still in their relative infancy, yet they reveal a complex role for neurotensinergic signaling in reward-related behaviors that merits further study. This article is part of the special issue on 'Neuropeptides'.

Mirogabalin prevents repeated restraint stress-induced dysfunction in mice

Gabapentinoids, which are the common analgesics, are also thought to be an effective treatment for anxiety disorder, which is one of several psychiatric disorders triggered and exacerbated by stress. The aim of the present study was to investigate whether mirogabalin, a recently launched gabapentinoid, protects multiple brain functions against repeated restraint stress. Adult male ddY mice were restrained for 7 days (repeated restraint stress: 2 h/day) or for 30 min (single restraint stress). Mirogabalin (intraperitoneal, intracerebroventricular or intrahippocampal injection) was administered prior to the restraint stress. Y-maze, elevated-plus maze and c-Fos immunohistochemistry were performed to evaluate learning function, anxiety levels and hippocampal neuronal activities, respectively, after the 7th day of the repeated restraint stress. Intestinal function was evaluated in terms of defecation, which was scored after the 5th day of repeated restraint stress and by the number of fecal pellets excreted after a single session of restraint stress. Repeated restraint stress induced memory dysfunction, anxiety-like behavior, an abnormal defecation score and increased hippocampal c-Fos expression. These changes were prevented by systemic administration of mirogabalin. Abnormal defecation was also induced by single restraint stress, and was inhibited by both systemic and central administration of mirogabalin, suggesting that the effect on the intestinal function was also mediated via the central nervous system. Enhancement of c-Fos expression by repeated stress was decreased by intrahippocampal injection of mirogabalin. Together, these observations suggest that mirogabalin protects multiple brain functions from repeated stress, which may be mediated by inhibition of hippocampal neuron hyperactivation.

Anxiogenesis induced by social defeat in male mice: Role of nitric oxide, NMDA, and CRF1 receptors in the medial prefrontal cortex and BNST

Nitric oxide (NO) release in the right medial prefrontal cortex (RmPFC) produces anxiogenesis. In the bed nucleus of the stria terminalis (BNST), a region that receives neuronal projections from the mPFC, NO provokes anxiety, an effect that is blocked by local injections of corticotrophin-releasing factor type 1 receptor (CRF₁) or n-methyl-d-aspartate receptor (NMDAr) antagonist. Anxiety is also enhanced by social defeat stress, and chronic stress impairs and facilitates, respectively, PFC and BNST roles in modulating behavioral responses to aversive situations. This study investigated whether the (i) chronic social defeat stress (CSDS) increases NO signaling in the mPFC; and/or (ii) anxiogenic effects provoked by the intra-RmPFC injection of NOC-9 (an NO donor) or by CSDS are prevented by intra-BNST injections of AP-7 (0.05 nmol) or CP 376395 (3.0 nmol), respectively, NMDAr and CRF₁ antagonists, in male Swiss-Webster mice exposed to the elevated plus-maze (EPM). Results showed that (a) CSDS increased anxiety (i.e., reduced open-arm exploration) and repeatedly activated nNOS-containing neurons, as measured by ΔFosB (a stable nonspecific marker of neural activity) + nNOS double-labeling, in the right (but not left) mPFC, (b) NOC-9 in the RmPFC also increased anxiety, and (c) both CSDS and NOC-9 effects were reversed by injections of AP-7 or CP 376395 into the BNST. These results suggest that NMDA and CRF₁ receptors located in BNST play an important role in the modulation of anxiety provoked by NO in the RmPFC, as well as by chronic social defeat in mice.

Zataria multiflora extract reverses lipopolysaccharide-induced anxiety and depression behaviors in rats

OBJECTIVE

Stressors have an important role in sickness behaviors. We checked the effect of Zataria multiflora (ZM) extract against lipopolysaccharide (LPS)-induced anxiety and depression behaviors in rats.

MATERIALS AND METHODS

Rats were distributed in the following groups (n=10): Control, LPS (1 mg/kg), LPS-ZM50, LPS-ZM100 and LPS-ZM200. LPS was syringed intraperitoneally (ip) 2 hr before performing behavioral tests. LPS-ZM groups were treated with 50, 100 and 200 mg/kg (ip) of ZM extract 30 min before LPS administration. Open field (OF), elevated plus maze (EPM) and forced swimming (FS) tests were done. White blood cell (WBC) was counted in all groups.

RESULTS

In OF, pretreatment with ZM extract augmented the number of lines crossed and traveled distance in central and peripheral areas. The rats treated with ZM extract spent more time in the central zone and less time in the peripheral area compared to the LPS group. In EPM, the number of entries into the open and closed arms and stop time in the open arms in LPS-ZM groups were higher than the LPS group. The stop time in the closed arms of ZM-LPS groups was less than the LPS group. In FS test, swimming and climbing time in groups treated with ZM extract was more than the LPS group while their immobility time was less. WBC count in the LPS-ZM100 and LPS-ZM200 was lower than that of the LPS group.

CONCLUSION

Based on the results, pretreatment with ZM extract restituted anxiety and depression caused by LPS in rats. This effect of ZM was associated with amelioration of LPS-promoted inflammation.

Gender Related Changes in Gene Expression Induced by Valproic Acid in A Mouse Model of Autism and the Correction by S-adenosyl Methionine. Does It Explain the Gender Differences in Autistic Like Behavior?

In previous studies we produced autism like behavioral changes in mice by Valproic acid (VPA) with significant differences between genders. S-adenosine methionine (SAM) prevented the autism like behavior in both genders. The expression of 770 genes of pathways involved in neurophysiology and neuropathology was studied in the prefrontal cortex of 60 days old male and female mice using the NanoString nCounter. In females, VPA induced statistically significant changes in the expression of 146 genes; 71 genes were upregulated and 75 downregulated. In males, VPA changed the expression of only 19 genes, 16 were upregulated and 3 downregulated. Eight genes were similarly changed in both genders. When considering only the genes that were changed by at least 50%, VPA changed the expression of 15 genes in females and 3 in males. Only Nts was similarly downregulated in both genders. SAM normalized the expression of most changed genes in both genders. We presume that genes that are involved in autism like behavior in our model were similarly changed in both genders and corrected by SAM. The behavioral and other differences between genders may be related to genes that were differently affected by VPA in males and females and/or differently affected by SAM.

A novel GPR55-mediated satiety signal in the oval Bed Nucleus of the Stria Terminalis

Nestled within feeding circuits, the oval (ov) region of the Bed Nucleus of the Stria Terminalis (BNST) may be critical for monitoring energy balance through changes in synaptic strength. Here we report that bidirectional plasticity at ovBNST GABA synapses was tightly linked to the caloric state of male rats, seesawing between long-term potentiation (iLTP, fed) and depression (iLTD, food restricted). L-α-lysophosphatidylinositol (LPI) acting on GPR55 receptors and 2-arachidonoylglycerol (2-AG) through CB1R were respectively responsible for fed (iLTP) and food restricted (iLTD) states. Thus, we have characterized a potential gating mechanism within the ovBNST that may signal metabolic state within the rat brain feeding circuitry.

Chronic stress induces cell type-selective transcriptomic and electrophysiological changes in the bed nucleus of the stria terminalis

Distinct regions and cell types in the anterolateral group of the bed nucleus of the stria terminalis (BNST_ALG) act to modulate anxiety in opposing ways. A history of chronic stress increases anxiety-like behavior with lasting electrophysiological effects on the BNST_ALG. However, the opposing circuits within the BNST_ALG suggest that stress may have differential effects on the individual cell types that comprise these circuits to shift the balance to favor anxiogenesis. Yet, the effects of stress are generally examined by treating all neurons within a particular region of the BNST as a homogenoeus population. We used patch-clamp electrophysiology and single-cell quantitative reverse transcriptase PCR (scRT-PCR) to determine how chronic shock stress (CSS) affects electrophysiological and neurochemical properties of Type I, Type II, and Type III neurons in the BNST_ALG. We report that CSS resulted in changes in the input resistance, time constant, action potential waveform, and firing rate of Type III but not Type I or II neurons. Additionally, only the Type III neurons exhibited an increase in Crf mRNA and a decrease in striatal-enriched protein tyrosine phosphatase (Ptpn5) mRNA after CSS. In contrast, only non-Type III cells showed a reduction in calcium-permeable AMPA receptor (CP-AMPAR) current and changes in mRNA expression of genes encoding AMPA receptor subunits after CSS. Importantly, none of the effects of CSS observed were seen in all cell types. Our results suggest that Type III neurons play a unique role in the BNST_ALG circuit and represent a population of CRF neurons particularly sensitive to chronic stress.

A Corticotropin Releasing Factor Network in the Extended Amygdala for Anxiety

The central amygdala (CeA) is important for fear responses to discrete cues. Recent findings indicate that the CeA also contributes to states of sustained apprehension that characterize anxiety, although little is known about the neural circuitry involved. The stress neuropeptide corticotropin releasing factor (CRF) is anxiogenic and is produced by subpopulations of neurons in the lateral CeA and the dorsolateral bed nucleus of the stria terminalis (dlBST). Here we investigated the function of these CRF neurons in stress-induced anxiety using chemogenetics in male rats that express Cre recombinase from a Crh promoter. Anxiety-like behavior was mediated by CRF projections from the CeA to the dlBST and depended on activation of CRF1 receptors and CRF neurons within the dlBST. Our findings identify a CRF^CeA→CRF^dlBST circuit for generating anxiety-like behavior and provide mechanistic support for recent human and primate data suggesting that the CeA and BST act together to generate states of anxiety.SIGNIFICANCE STATEMENT Anxiety is a negative emotional state critical to survival, but persistent, exaggerated apprehension causes substantial morbidity. Identifying brain regions and neurotransmitter systems that drive anxiety can help in developing effective treatment. Much evidence in rodents indicates that neurons in the bed nucleus of the stria terminalis (BST) generate anxiety-like behaviors, but more recent findings also implicate neurons of the CeA. The neuronal subpopulations and circuitry that generate anxiety are currently subjects of intense investigation. Here we show that CeA neurons that release the stress neuropeptide corticotropin-releasing factor (CRF) drive anxiety-like behaviors in rats via a pathway to dorsal BST that activates local BST CRF neurons. Thus, our findings identify a CeA→BST CRF neuropeptide circuit that generates anxiety-like behavior.

Neurotensin and dynorphin Bi-Directionally modulate CeA inhibition of oval BNST neurons in male mice

Neuropeptides are often co-expressed in neurons, and may therefore be working together to coordinate proper neural circuit function. However, neurophysiological effects of neuropeptides are commonly studied individually possibly underestimating their modulatory roles. Here, we triggered the release of endogenous neuropeptides in brain slices from male mice to better understand their modulation of central amygdala (CeA) inhibitory inputs onto oval (ov) BNST neurons. We found that locally-released neurotensin (NT) and dynorphin (Dyn) antagonistically regulated CeA inhibitory inputs onto ovBNST neurons. NT and Dyn respectively increased and decreased CeA-toovBNST inhibitory inputs through NT receptor 1 (NTR1) and kappa opioid receptor (KOR). Additionally, NT and Dyn mRNAs were highly co-localized in ovBNST neurons suggesting that they may be released from the same cells. Together, we showed that NT and Dyn are key modulators of CeA inputs to ovBNST, paving the way to determine whether different conditions or states can alter the neuropeptidergic regulation of this particular brain circuit.

Comprehensive Identification and Spatial Mapping of Habenular Neuronal Types Using Single-Cell RNA-Seq

The identification of cell types and marker genes is critical for dissecting neural development and function, but the size and complexity of the brain has hindered the comprehensive discovery of cell types. We combined single-cell RNA-seq (scRNA-seq) with anatomical brain registration to create a comprehensive map of the zebrafish habenula, a conserved forebrain hub involved in pain processing and learning. Single-cell transcriptomes of ∼13,000 habenular cells with 4× cellular coverage identified 18 neuronal types and dozens of marker genes. Registration of marker genes onto a reference atlas created a resource for anatomical and functional studies and enabled the mapping of active neurons onto neuronal types following aversive stimuli. Strikingly, despite brain growth and functional maturation, cell types were retained between the larval and adult habenula. This study provides a gene expression atlas to dissect habenular development and function and offers a general framework for the comprehensive characterization of other brain regions.

Diverse actions of the modulatory peptide neurotensin on central synaptic transmission

Neurotensin (NT) is a 13 amino acid neuropeptide that is expressed throughout the central nervous system and is implicated in the etiology of multiple diseases and disorders. Many primary investigations of NT-induced modulation of neuronal excitability at the level of the synapse have been conducted, but they have not been summarized in review form in nearly 30 years. Therefore, the goal of this review is to discuss the many actions of NT on neuronal excitability across brain regions as well as NT circuit architecture. In the basal ganglia as well as other brain nuclei, NT can act through diverse intracellular signaling cascades to enhance or depress neuronal activity by modulating activity of ion channels, ionotropic and metabotropic neurotransmitter receptors, and presynaptic release of neurotransmitters. Further, NT can produce indirect effects by evoking endocannabinoid release, and recently has itself been identified as a putative retrograde messenger. In the basal ganglia, the diverse actions and circuit architecture of NT signaling allow for input-specific control of reward-related behaviors.