Continuous expression of corticotropin-releasing factor in the central nucleus of the amygdala emulates the dysregulation of the stress and reproductive axes

Activation of CRF/CRFR1 Signaling in the Central Nucleus of the Amygdala Contributes to Chronic Stress-Induced Exacerbation of Neuropathic Pain by Enhancing GluN2B-NMDA Receptor-Mediated Synaptic Plasticity in Adult Male Rats

Exacerbation of pain by chronic stress and comorbidity of pain with stress-related disorders such as depression and post-traumatic stress disorder, represent significant clinical challenges. Previously we have documented that chronic forced swim (FS) stress exacerbates neuropathic pain in spared nerve injury (SNI) rats, associated with an up-regulation of GluN2B-containing N-methyl-D-aspartate receptors (GluN2B-NMDARs) in the central nucleus of the amygdala (CeA). However, the molecular mechanisms underlying chronic FS stress (CFSS)-mediated exacerbation of pain sensitivity in SNI rats still remain unclear. In this study, we demonstrated that exposure of CFSS to rats activated the corticotropin-releasing factor (CRF)/CRF receptor type 1 (CRFR1) signaling in the CeA, which was shown to be necessary for CFSS-induced depressive-like symptoms in stressed rats, and as well, for CFSS-induced exacerbation of pain hypersensitivity in SNI rats exposed to chronic FS stress. Furthermore, we discovered that activation of CRF/CRFR1 signaling in the CeA upregulated the phosphorylation of GluN2B-NMDARs at tyrosine 1472 (pGluN2BY1472) in the synaptosomal fraction of CeA, which is highly correlated to the enhancement of synaptic GluN2B-NMDARs expression that has been observed in the CeA in CFSS-treated SNI rats. In addition, we revealed that activation of CRF/CRFR1 signaling in the CeA facilitated the CFSS-induced reinforcement of long-term potentiation as well as the enhancement of NMDAR-mediated excitatory postsynaptic currents in the basolateral amygdala (BLA)-CeA pathway in SNI rats. These findings suggest that activation of CRF/CRFR1 signaling in the CeA contributes to chronic stress-induced exacerbation of neuropathic pain by enhancing GluN2B-NMDAR-mediated synaptic plasticity in rats subjected to nerve injury. PERSPECTIVE: Our present study provides a novel mechanism for elucidating stress-induced hyperalgesia and highlights that the CRF/CRFR1 signaling and the GluN2B-NMDAR-mediated synaptic plasticity in the CeA may be important as potential therapeutic targets for chronic stress-induced pain exacerbation in human neuropathic pain. DATA AVAILABILITY: The data that support the findings of this study are available from the corresponding author upon reasonable request.

Chronic kidney disease may evoke anxiety by altering CRH expression in the amygdala and tryptophan metabolism in rats

Chronic kidney disease (CKD) is associated with anxiety; however, its exact mechanism is not well understood. Therefore, the aim of the present study was to assess the effect of moderate CKD on anxiety in rats. 5/6 nephrectomy was performed in male Wistar rats. 7 weeks after, anxiety-like behavior was assessed by elevated plus maze (EPM), open field (OF), and marble burying (MB) tests. At weeks 8 and 9, urinalysis was performed, and blood and amygdala samples were collected, respectively. In the amygdala, the gene expression of Avp and the gene and protein expression of Crh, Crhr1, and Crhr2 were analyzed. Furthermore, the plasma concentration of corticosterone, uremic toxins, and tryptophan metabolites was measured by UHPLC-MS/MS. Laboratory tests confirmed the development of CKD. In the CKD group, the closed arm time increased; the central time and the total number of entries decreased in the EPM. There was a reduction in rearing, central distance and time in the OF, and fewer interactions with marbles were detected during MB. CKD evoked an upregulation of gene expression of Crh, Crhr1, and Crhr2, but not Avp, in the amygdala. However, there was no alteration in protein expression. In the CKD group, plasma concentrations of p-cresyl-sulfate, indoxyl-sulfate, kynurenine, kynurenic acid, 3-hydroxykynurenine, anthranilic acid, xanthurenic acid, 5-hydroxyindoleacetic acid, picolinic acid, and quinolinic acid increased. However, the levels of tryptophan, tryptamine, 5-hydroxytryptophan, serotonin, and tyrosine decreased. In conclusion, moderate CKD evoked anxiety-like behavior that might be mediated by the accumulation of uremic toxins and metabolites of the kynurenine pathway, but the contribution of the amygdalar CRH system to the development of anxiety seems to be negligible at this stage.

The role of the circadian system in the etiology of depression

Circadian rhythms have evolved in almost all organisms enabling them to anticipate alternating changes in the environment. As a consequence, the circadian clock controls a broad range of bodily functions including appetite, sleep, activity and cortisol levels. The circadian clock synchronizes itself to the external world mainly by environmental light cues and can be disturbed by a variety of factors, including shift-work, jet-lag, stress, ageing and artificial light at night. Interestingly, mood has also been shown to follow a diurnal rhythm. Moreover, circadian disruption has been associated with various mood disorders and patients suffering from depression have irregular biological rhythms in sleep, appetite, activity and cortisol levels suggesting that circadian rhythmicity is crucially involved in the etiology and pathophysiology of depression. The aim of the present review is to give an overview and discuss recent findings in both humans and rodents linking a disturbed circadian rhythm to depression. Understanding the relation between a disturbed circadian rhythm and the etiology of depression may lead to novel therapeutic and preventative strategies.

Effect of Papaver rhoeas hydroalcoholic extract on blood corticosterone and psychosocial behaviors in the mice model of predator exposure-induced post-traumatic stress disorder

The function of hypothalamic-pituitary-adrenal (HPA) axis and psychosocial behaviors are affected in post-traumatic stress disorder (PTSD). Based on presence of several beneficial alkaloids in Papaver rhoeas (PR) plant, we assessed the effects of PR hydroalcoholic extract on blood corticosterone and psychosocial behaviors in the mice model of predator exposure-induced PTSD. Male NMARI mice were assigned into two main groups (control or PTSD) according to stress exposure (presence or absent of the predator). Each main group was divided into four subgroups according to treatment with the different doses of PR extract. Mice were treated intraperitoneally by PR extract at three different doses (1,5&10 mg/kg) 30 min before the beginning of test on days 1, 2&3. Corticosterone concentration determined in the blood samples on days 1, 3&21, and mice examined for the psychosocial behaviors on the third day. PTSD induction in mice by exposing to hungry predator increased blood corticosterone and changed the psychosocial and physiological behaviors. PR extract decreased blood corticosterone in PTSD mice on the third day as well as 21st day. Also, PR extract improved the psychosocial and physiological behaviors in PTSD mice. Moreover, PR extract increased blood corticosterone in control mice at a dose-response manner. PR extract is able to decrease blood corticosterone in PTSD condition and probably prevent the HPA hyperactivity in PTSD mice when exposed to the stress stimuli. Accordingly, decreased blood corticosterone by PR extract might be involved in improvement of the physiological and psychosocial behaviors in PTSD mice.

Deficiency in the cell-adhesion molecule dscaml1 impairs hypothalamic CRH neuron development and perturbs normal neuroendocrine stress axis function

The corticotropin-releasing hormone (CRH)-expressing neurons in the hypothalamus are critical regulators of the neuroendocrine stress response pathway, known as the hypothalamic-pituitary-adrenal (HPA) axis. As developmental vulnerabilities of CRH neurons contribute to stress-associated neurological and behavioral dysfunctions, it is critical to identify the mechanisms underlying normal and abnormal CRH neuron development. Using zebrafish, we identified Down syndrome cell adhesion molecule like-1 (dscaml1) as an integral mediator of CRH neuron development and necessary for establishing normal stress axis function. In dscaml1 mutant animals, hypothalamic CRH neurons had higher crhb (the CRH homolog in zebrafish) expression, increased cell number, and reduced cell death compared to wild-type controls. Physiologically, dscaml1 mutant animals had higher baseline stress hormone (cortisol) levels and attenuated responses to acute stressors. Together, these findings identify dscaml1 as an essential factor for stress axis development and suggest that HPA axis dysregulation may contribute to the etiology of human DSCAML1-linked neuropsychiatric disorders.

Anxiety in children and youth with autism spectrum disorder and the association with amygdala subnuclei structure

Autism spectrum disorder (ASD) is clinically characterized by social and communication difficulties as well as repetitive behaviors. Many children with ASD also suffer from anxiety, which has been associated with alterations in amygdala structure. In this work, the association between amygdala subnuclei volumes and anxiety was assessed in a cohort of 234 participants (mean age = 11.0 years, SD = 3.9, 95 children with ASD, 139 children were non-autistic). Children underwent magnetic resonance imaging. Amygdala subnuclei volumes were extracted automatically. Anxiety was assessed using the Screen for Child Anxiety Related Disorders, the Child Behavior Checklist, and the Strength and Difficulties Questionnaire. Children with ASD had higher anxiety scores relative to non-autistic children on all anxiety measures (all, p < 0.05). Anxiety levels were significantly predicted in children with ASD by right basal (right: B = 0.235, p = 0.002) and paralaminar (PL) (B = −0.99, p = 0.009) volumes. Basal nuclei receive multisensory information from cortical and subcortical areas and have extensive projections within the limbic system while the PL nuclei are involved in emotional processing. Alterations in basal and PL nuclei in children with ASD and the association with anxiety may reflect morphological changes related to in the neurocircuitry of anxiety in ASD.

Lay abstract

Autism spectrum disorder (ASD) is clinically characterized by social communication difficulties as well as restricted and repetitive patterns of behavior. In addition, children with ASD are more likely to experience anxiety compared with their peers who do not have ASD. Recent studies suggest that atypical amygdala structure, a brain region involved in emotions, may be related to anxiety in children with ASD. However, the amygdala is a complex structure composed of heterogeneous subnuclei, and few studies to date have focused on how amygdala subnuclei relate to in anxiety in this population. The current sample consisted of 95 children with ASD and 139 non-autistic children, who underwent magnetic resonance imaging (MRI) and assessments for anxiety. The amygdala volumes were automatically segmented. Results indicated that children with ASD had elevated anxiety scores relative to peers without ASD. Larger basal volumes predicted greater anxiety in children with ASD, and this association was not seen in non-autistic children. Findings converge with previous literature suggesting ASD children suffer from higher levels of anxiety than non-autistic children, which may have important implications in treatment and interventions. Our results suggest that volumetric estimation of amygdala’s subregions in MRI may reveal specific anxiety-related associations in children with ASD.

Effects of neonatal rearing by different types of foster mother on the distribution of corticotropin-releasing factor neurons in the central amygdaloid nucleus in rats

The mother-child relationship of newborns plays an essential role in the development of the central nervous system, and an inadequate relationship, such as mother-child separation, can cause deficits of mental function in adulthood. However, insufficient research has examined the effects of foster mothers. We assigned some neonatal rats to one of two foster mothers: one that was lactating and feeding her first litter (FL group) and one that had one previous experience of childbirth and feeding but no current litter (FE group). Other pups were raised by their own mother (OM group) or subjected to maternal separation (MS group). Pups were placed with the foster mother (FL and FE groups) or separated from their mother (MS group) for 3 h/day on postnatal days 1-20. At age 6 weeks, each group was divided into two subgroups, one with 30 min of acute restraint stress loading (FL-R, FE-R, OM-R, and MS-R) and one without it (FL, FE, OM, and MS). Then, we compared the density of corticotropin-releasing factor-immunoreactive (CRF-ir) neurons in the central amygdaloid nucleus (CeA). The density of CRF-ir neurons in the CeA was significantly lower in the FL-R and MS-R subgroups than in the FL and MS subgroups, respectively. The results suggest that differences in care received during the neonatal period affect maturation of CRF neurons in the CeA and may have negative effects on the synthesis and release of CRF.

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.

Amygdala subnuclei volumes and anxiety behaviors in children and adolescents with autism spectrum disorder, attention deficit hyperactivity disorder, and obsessive-compulsive disorder

Alterations in the structural maturation of the amygdala subnuclei volumes are associated with anxiety behaviors in adults and children with neurodevelopmental and associated disorders. This study investigated the relationship between amygdala subnuclei volumes and anxiety in 233 children and adolescents (mean age = 11.02 years; standard deviation = 3.17) with autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), and children with obsessive compulsive disorder (OCD), as well as typically developing (TD) children. Parents completed the Child Behavior Checklist (CBCL), and the children underwent structural MRI at 3 T. FreeSurfer software was used to automatically segment the amygdala subnuclei. A general linear model revealed that children and adolescents with ASD, ADHD, and OCD had higher anxiety scores compared to TD children (p < .001). A subsequent interaction analysis revealed that children with ASD (B = 0.09, p < .0001) and children with OCD (B = 0.1, p < .0001) who had high anxiety had larger right central nuclei volumes compared with TD children. Similar results were obtained for the right anterior amygdaloid area. Amygdala subnuclei volumes may be key to identifying children with neurodevelopmental disorders or those with OCD who are at high risk for anxiety. Findings may inform the development of targeted behavioral interventions to address anxiety behaviors and to assess the downstream effects of such interventions.

Exploring the role of neuropeptides in depression and anxiety

Depression is one of the most prevalent forms of mental disorders and is the most common cause of disability in the Western world. Besides, the harmful effects of stress-related mood disorders on the patients themselves, they challenge the health care system with enormous social and economic impacts. Due to the high proportion of patients not responding to existing drugs, finding new treatment strategies has become an important topic in neurobiology, and there is much evidence that neuropeptides are not only involved in the physiology of stress but may also be clinically important. Based on preclinical trial data, new neuropharmaceutical candidates may target neuropeptides and their receptors and are expected to be essential and valuable tools in the treatment of psychiatric disorders. In the current article, we have summarized data obtained from animal models of depressive disorder and transgenic mouse models. We also focus on previously published research data of clinical studies on corticotropin-releasing hormone (CRH), galanin (GAL), neuropeptide Y (NPY), neuropeptide S (NPS), Oxytocin (OXT), vasopressin (VP), cholecystokinin (CCK), and melanin-concentrating hormone (MCH) stress research fields.

Therapeutic potential of nociceptin/orphanin FQ peptide (NOP) receptor modulators for treatment of traumatic brain injury, traumatic stress, and their co-morbidities

The nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor is a member of the opioid receptor superfamily with N/OFQ as its endogenous agonist. Wide expression of the NOP receptor and N/OFQ, both centrally and peripherally, and their ability to modulate several biological functions has led to development of NOP receptor modulators by pharmaceutical companies as therapeutics, based upon their efficacy in preclinical models of pain, anxiety, depression, Parkinson's disease, and substance abuse. Both posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) are debilitating conditions that significantly affect the quality of life of millions of people around the world. PTSD is often a consequence of TBI, and, especially for those deployed to, working and/or living in a war zone or are first responders, they are comorbid. PTSD and TBI share common symptoms, and negatively influence outcomes as comorbidities of the other. Unfortunately, a lack of effective therapies or therapeutic agents limits the long term quality of life for either TBI or PTSD patients. Ours, and other groups, demonstrated that PTSD and TBI preclinical models elicit changes in the N/OFQ-NOP receptor system, and that administration of NOP receptor ligands alleviated some of the neurobiological and behavioral changes induced by brain injury and/or traumatic stress exposure. Here we review the past and most recent progress on understanding the role of the N/OFQ-NOP receptor system in PTSD and TBI neurological and behavioral sequelae. There is still more to understand about this neuropeptide system in both PTSD and TBI, but current findings warrant further examination of the potential utility of NOP modulators as therapeutics for these disorders and their co-morbidities. We advocate the development of standards for common data elements (CDE) reporting for preclinical PTSD studies, similar to current preclinical TBI CDEs. That would provide for more standardized data collection and reporting to improve reproducibility, interpretation and data sharing across studies.

Exposure of male mice to perfluorooctanoic acid induces anxiety-like behaviors by increasing corticotropin-releasing factor in the basolateral amygdala complex

Perfluorooctanoic acid (PFOA), a hazardous environmental pollutant, has been found to enhance hepatic synthesis of fibroblast growth factor 21 (FGF21). FGF21 can enter the brain and increase the expression of corticotropin-releasing factor (CRF) in the paraventricular nucleus (PVN). In this study, adult male mice were orally administered PFOA to evaluate how it regulates emotion. Exposure of mice to PFOA (1 mg kg-1 bw) for 10 consecutive days (PFOA-mice) caused anxiety-like behaviors and a peroxisome proliferator-activated receptor α (PPARα)-dependent increase in hepatic FGF21 synthesis. The levels of CRF expression in not only PVN but also basolateral amygdala complex (BLA) neurons of PFOA-mice were increased via FGF receptor 1 (FGF-R1) activation. However, the microinjection of FGF-R1 or CRF 1 receptor (CRF-R1) antagonist in the BLA rather than the PVN of PFOA-mice could relieve their anxiety-like behaviors. In addition, external capsule-BLA synaptic transmission in PFOA-mice was enhanced by increasing CRF-R1-mediated presynaptic glutamate release, which was corrected by the blockade of PPARα, FGF-R1 and CRF-R1 or the inhibition of PKA. Furthermore, the threshold of frequency-dependent long-term potentiation (LTP) induction was decreased in the BLA of PFOA-mice, which depended on the activation of PPARα, FGF-R1, CRF-R1, PKA and NMDA receptor (NMDAR), whereas long-term depression (LTD) induction was unchanged. Thus, the results indicate that the exposure of male mice to PFOA (1 mg kg-1 bw) enhances CRF expression in BLA neurons by increasing hepatic FGF21 synthesis, which then enhances CRF-R1-mediated presynaptic glutamate release to facilitate NMDAR-dependent BLA-LTP induction, leading to the production of anxiety-like behaviors.

Population Numbers and Reproductive Health

A recent study published in The Lancet predicts a remarkable drop in population numbers following a peak that will be reached by 2064. A unique feature of the upcoming population drop is that it will be almost exclusively caused by decreased reproduction, rather than factors that increase rates of mortality. The reasons for decreased reproduction are also unique, as, unlike previous centuries, limited reproduction today is hardly due to a shortage in resources. In other words, the predicted population drop is almost exclusively due to changes in reproductive behavior and reproductive physiology. Today, global changes in reproductive behavior are mostly explained by social sciences in a framework of demographic transition hypotheses, while changes in reproductive physiology are usually attributed to effects of endocrine-disrupting pollutants. This review outlines a complementary/alternative hypothesis, which connects reproductive trends with population densities. Numerous wildlife and experimental studies of a broad range of animal species have demonstrated that reproductive behavior and reproductive physiology are negatively controlled via endocrine and neural signaling in response to increasing population densities. The causal chain of this control system, although not fully understood, includes suppression of every level of hypothalamic-pituitary-gonadal cascade by hypothalamic-pituitary-adrenal axis, activated in response to increasing stress of social interactions. This paper discusses evidence in support of a hypothesis that current trends in reproductive physiology and behavior may be partly explained by increasing population densities. Better understanding of the causal chain involved in reproduction suppression by population density-related factors may help in developing interventions to treat infertility and other reproductive conditions.

Developmental variation in testosterone:cortisol ratio alters cortical- and amygdala-based cognitive processes

Testosterone (T) and cortisol (C) are the end products of neuroendocrine axes that interact with the process of shaping brain structure and function. Relative levels of T:C (TC ratio) may alter prefrontal-amygdala functional connectivity in adulthood. What remains unclear is whether TC-related effects are rooted to childhood and adolescence. We used a healthy cohort of 4-22-year-olds to test for associations between TC ratios, brain structure (amygdala volume, cortical thickness (CTh), and their coordinated growth), as well as cognitive and behavioral development. We found greater TC ratios to be associated with the growth of specific brain structures: 1) parietal CTh; 2) covariance of the amygdala with CTh in visual and somatosensory areas. These brain parameters were in turn associated with lower verbal/executive function and higher spatial working memory. In sum, individual TC profiles may confer a particular brain phenotype and set of cognitive strengths and vulnerabilities, prior to adulthood.

Translating Across Circuits and Genetics Toward Progress in Fear- and Anxiety-Related Disorders

(Reprinted with permission from Am J Psychiatry 2020; 177:214-222).

Effect of early life social adversity on drug abuse vulnerability: Focus on corticotropin-releasing factor and oxytocin

Early life adversity can set the trajectory for later psychiatric disorders, including substance use disorders. There are a host of neurobiological factors that may play a role in the negative trajectory. The current review examines preclinical evidence suggesting that early life adversity specifically involving social factors (maternal separation, adolescent social isolation and adolescent social defeat) may influence drug abuse vulnerability by strengthening corticotropin-releasing factor (CRF) systems and weakening oxytocin (OT) systems. In adulthood, pharmacological and genetic evidence indicates that both CRF and OT systems are directly involved in drug reward processes. With early life adversity, numerous studies show an increase in drug abuse vulnerability measured in adulthood, along a concomitant strengthening of CRF systems and a weakening of OT systems. Mechanistic studies, while relatively few in number, are generally consistent with the theme that strengthened CRF systems and weakened OT systems mediate, at least in part, the link between early life adversity and drug abuse vulnerability. Establishing a direct role of CRF and OT in mediating the relation between early life social stressors and drug abuse vulnerability will inform clinical researchers and practitioners toward the development of intervention strategies to reduce risk among those suffering from early life adversities. This article is part of the special issue on 'Vulnerabilities to Substance Abuse'.

Genome-wide translational profiling of amygdala Crh-expressing neurons reveals role for CREB in fear extinction learning

Fear and extinction learning are adaptive processes caused by molecular changes in specific neural circuits. Neurons expressing the corticotropin-releasing hormone gene (Crh) in central amygdala (CeA) are implicated in threat regulation, yet little is known of cell type-specific gene pathways mediating adaptive learning. We translationally profiled the transcriptome of CeA Crh-expressing cells (Crh neurons) after fear conditioning or extinction in mice using translating ribosome affinity purification (TRAP) and RNAseq. Differential gene expression and co-expression network analyses identified diverse networks activated or inhibited by fear vs extinction. Upstream regulator analysis demonstrated that extinction associates with reduced CREB expression, and viral vector-induced increased CREB expression in Crh neurons increased fear expression and inhibited extinction. These findings suggest that CREB, within CeA Crh neurons, may function as a molecular switch that regulates expression of fear and its extinction. Cell-type specific translational analyses may suggest targets useful for understanding and treating stress-related psychiatric illness.

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.

Role of corticotropin-releasing factor in alcohol and nicotine addiction

The two most prevalent substance use disorders involve alcohol and nicotine, which are often co-abused. Robust preclinical and translational evidence indicates that individuals initiate drug use for the acute rewarding effects of the substance. The development of negative emotional states is key for the transition from recreational use to substance use disorders as subjects seek the substance to obtain relief from the negative emotional states of acute withdrawal and protracted abstinence. The neuropeptide corticotropin-releasing factor (CRF) is a major regulator of the brain stress system and key in the development of negative affective states. The present review examines the role of CRF in preclinical models of alcohol and nicotine abuse and explores links between CRF and anxiety-like, dysphoria-like, and other negative affective states. Finally, the present review discusses preclinical models of nicotine and alcohol use with regard to the CRF system, advances in molecular and genetic manipulations of CRF, and the importance of examining both males and females in this field of research.

Translating Across Circuits and Genetics Toward Progress in Fear- and Anxiety-Related Disorders

Anxiety and fear-related disorders are common and disabling, and they significantly increase risk for suicide and other causes of morbidity and mortality. However, there is tremendous potential for translational neuroscience to advance our understanding of these disorders, leading to novel and powerful interventions and even to preventing their initial development. This overview examines the general circuits and processes thought to underlie fear and anxiety, along with the promise of translational research. It then examines some of the data-driven "next-generation" approaches that are needed for discovery and understanding but that do not always fit neatly into established models. From one perspective, these disorders offer among the most tractable problems in psychiatry, with a great deal of accumulated understanding, across species, of neurocircuit, behavioral, and, increasingly, genetic mechanisms, of how dysregulation of fear and threat processes contributes to anxiety-related disorders. One example is the progressively sophisticated understanding of how extinction underlies the exposure therapy component of cognitive-behavioral therapy approaches, which are ubiquitously used across anxiety and fear-related disorders. However, it is also critical to examine gaps in our understanding between reasonably well-replicated examples of successful translation, areas of significant deficits in knowledge, and the role of large-scale data-driven approaches in future progress and discovery. Although a tremendous amount of progress is still needed, translational approaches to understanding, treating, and even preventing anxiety and fear-related disorders offer great opportunities for successfully bridging neuroscience discovery to clinical practice.

Amygdalar corticotropin-releasing factor mediates stress-induced anxiety

The extended amygdala, including the Central nucleus of the Amygdala (CeA) and the Bed Nucleus of the Stria Terminalis (BNST), is a complex structure that plays a pivotal role in emotional behavior. The CeA and the BNST are highly interconnected, being the amygdala traditionally more associated with fear and the BNST with anxiety. Yet, studies using excitotoxic lesions also show the involvement of the CeA in the development of stress-induced anxiety. Likewise, others have also highlighted the role of corticotropin-releasing factor (CRF), a neuropeptide highly expressed in CeA, as an anxiogenic factor and, consequently, important for in anxiety disorders. Here, we used an inducible RNAi lentiviral system to assess the effects of reducing CRF expression in CeA in the development of anxiety-like behavior in a model of Chronic Unpredictable Stress. In addition, we evaluated CRF RNAi-mediated alterations in the stress-triggered molecular signature in the BNST. Knockdown of CRF in the CeA decreased stress-induced anxiety levels. No differences were found in a fear-potentiated startle paradigm. Additionally, we observed that stress-induced alterations in the expression of CRF receptors within the BNST are attenuated by CRF knockdown in the CeA. These results emphasize the importance of the role that amygdalar CRF plays in the modulation of anxiety-like behavior and in the molecular signature of stress in the BNST.

Hypothalamic-pituitary-adrenal axis responsivity to an acute novel stress in female rats subjected to the chronic mild stress paradigm

The chronic mild stress (CMS) paradigm is the most frequently investigated animal model for major depression. The hypothalamic-pituitary-adrenal (HPA) axis participates in the generation of depressive symptomatology. We examined whether the depression-like state induced by CMS is associated with immediate changes in HPA axis activation in response to a novel acute stress and whether this response could be modified by hormonal status. Adult female Wistar rats were ovariectomized and received estrogen or vehicle pellets. After 2 weeks, rats were subjected to CMS (or control) conditions for 2.5 or 4.5 weeks. Rats were subsequently subjected to restraint stress for 1 h, and plasma corticosterone (CT) levels were determined before (2:00 p.m.) and after acute stress induction (3:00 and 4:00 p.m.). CT levels and FOS expression were measured in the medial parvocellular subdivision of the PVN (PaMP), central (CeA) and medial amygdala (MeA) and ventral subiculum of the hippocampus (vSub). Plasma CT levels in animals treated with 6.5 weeks of estrogen were elevated before and 1 h after restraint stress induction. Results indicate that the estrogen chronicity and CMS exposure impacted CT secretion. Neuronal PaMP, CeA, MeA and vSub activity decreased after 4.5 weeks of CMS in all groups. No differences were detected between CMS and non-CMS groups. These data suggest that the HPA central hyporesponsiveness observed in the experimental groups subjected to a longer protocol period was independent to CMS paradigm and estrogen treatment restored partially its activity. These data suggest that additional stressors could be responsible for the observed alterations of the HPA axis.

Role of the posterodorsal medial amygdala in predator odour stress-induced puberty delay in female rats

Puberty onset is influenced by various factors, including psychosocial stress. The present study investigated cat-odour stress on puberty onset and oestrous cyclicity in rats. Female weanling rats were exposed to either soiled cat litter or fresh unused litter for 10 consecutive days. Following vaginal opening (VO), rats were smeared for 14 days to determine oestrous cyclicity. Anxiety-like behaviour was assessed using standard anxiety tests. Brains were collected to determine corticotrophin-releasing factor (CRF), CRF receptor 1 (CRF-R1) and CRF receptor 2 (CRF-R2) mRNA in the paraventricular nucleus (PVN), as well as the central nucleus of the amygdala (CEA) and the medial nucleus of the amygdala (MEA). Cat odour delayed VO and first oestrus, disrupted oestrous cycles and caused anxiogenic responses. Cat odour elicited increased CRF mRNA expression in the PVN but not in the CeA. CRF-R1 and CRF-R2 mRNA levels in the PVN and CeA were unaffected by cat odour; however, CRF-R1 mRNA levels were decreased in the MeA. The role of CRF signalling in the MeA, particularly its posterodorsal subnucleus (MePD), with respect to pubertal timing was directly examined by unilateral intra-MePD administration of CRF (0.2 nmol day^-1 for 14 days) via an osmotic mini-pump from postnatal day 24 and was shown to delay VO and first oestrus. These data suggest that CRF signalling in the MePD may be associated with predator odour-induced puberty delay.

Infant Temperament: Repercussions of Superstorm Sandy-Related Maternal Stress

This study recruited a prospective cohort of 380 pregnant women before, during, or after Superstorm Sandy in 2012 to examine the association between disaster-related pre- and post-natal maternal stress and offspring temperament at 6 months-old. Mothers prospectively reported stressful experiences during the storm and rated their child's temperament 6 months postpartum. Results indicated that length of time without phone or electricity and financial loss was associated with offspring negative affect, whereas financial loss and threat of death or injury was associated with emotion dysregulation. Furthermore, offspring born before the storm had greater negative affect and lower emotion regulation than those born after the storm. Given the probable increase in the occurrence of natural disasters due to climate change in recent years (McCarthy, Intergovernmental Panel on Climate Change, Climate change 2001: impacts, adaptation, and vulnerability: contribution of Working Group II to the third assessment report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, 2001), our results highlight the necessity of education and planning to help ameliorate any potential consequences on the developing infant.

Adult mammalian neurogenesis and motivated behaviors

Adult neurogenesis continues to captivate the curiosity of the scientific community; and researchers seem to have a particular interest in identifying the functional implications of such plasticity. While the majority of research focuses on the association between adult neurogenesis and learning and memory (including spatial learning associated with hippocampal neurogenesis and olfactory discrimination associated with neurogenesis in the olfactory system), the following review will explore the link to motivated behaviors. In particular, goal-directed behaviors such as sociosexual, parental, aggressive, as well as depression- and anxiety-like behaviors and their reciprocal association to adult neurogenesis will be evaluated. The review will detail research in humans and other mammalian species. Furthermore, the potential mechanisms underlying these neurogenic alterations will be highlighted. Lastly, the review will conclude with a discussion on the functional significance of these newly generated cells in mediating goal-directed behaviors.

The CRF Family of Neuropeptides and their Receptors - Mediators of the Central Stress Response

Background:

Dysregulated stress neurocircuits, caused by genetic and/or environmental changes, underlie the development of many neuropsychiatric disorders. Corticotropin-releasing factor (CRF) is the major physiological activator of the hypothalamic-pituitary-adrenal (HPA) axis and conse-quently a primary regulator of the mammalian stress response. Together with its three family members, urocortins (UCNs) 1, 2, and 3, CRF integrates the neuroendocrine, autonomic, metabolic and behavioral responses to stress by activating its cognate receptors CRFR1 and CRFR2.

Objective:

Here we review the past and current state of the CRF/CRFR field, ranging from pharmacologi-cal studies to genetic mouse models and virus-mediated manipulations.

Results:

Although it is well established that CRF/CRFR1 signaling mediates aversive responses, includ-ing anxiety and depression-like behaviors, a number of recent studies have challenged this viewpoint by revealing anxiolytic and appetitive properties of specific CRF/CRFR1 circuits. In contrast, the UCN/CRFR2 system is less well understood and may possibly also exert divergent functions on physiol-ogy and behavior depending on the brain region, underlying circuit, and/or experienced stress conditions.

Conclusion:

A plethora of available genetic tools, including conventional and conditional mouse mutants targeting CRF system components, has greatly advanced our understanding about the endogenous mecha-nisms underlying HPA system regulation and CRF/UCN-related neuronal circuits involved in stress-related behaviors. Yet, the detailed pathways and molecular mechanisms by which the CRF/UCN-system translates negative or positive stimuli into the final, integrated biological response are not completely un-derstood. The utilization of future complementary methodologies, such as cell-type specific Cre-driver lines, viral and optogenetic tools will help to further dissect the function of genetically defined CRF/UCN neurocircuits in the context of adaptive and maladaptive stress responses.

Stress and immune biomarkers interact with parenting behavior to shape anxiety symptoms in trauma-exposed youth

The relations between stress, HPA-axis, and the immune system have been extensively studied; however, no study to date addressed the joint contribution of immune and HPA biomarkers to the development of anxiety in youth exposed to chronic trauma as mediated by mother-child interaction patterns. A unique cohort of war-exposed children and their mothers, compared to matched controls, were followed from infancy and the current study reports findings from early adolescence (mean age = 11.66, SD = 1.23; N = 111; exposed = 58 control = 53). Youth and mothers' salivary cortisol (CT) and secretory immunoglobulin (s-IgA) levels were measured three times during a 4-hour lab visit, mother-child interaction patterns were quantified from a joint task, and children's anxiety symptoms diagnosed. Trauma-exposed children had higher levels of CT and s-IgA, exhibited more anxiety symptoms, and showed lower social collaboration with mother during the joint task. Trauma-exposed mothers had higher CT and s-IgA levels and showed less supportive parenting during mother-child interaction. Structural equation modeling defined three bio-behavioral paths by which trauma increases anxiety in youth. While the first path charted a behavioral link from exposure to child anxiety via diminished maternal support, the other two paths described mediated biological paths, one through HPA-axis functioning, the other via the immune system. Paths via the child's HPA and immune system were mediated by the parallel maternal variable. Findings are the first to describe the complex bio-behavioral interplay of stress and immune biomarkers and parenting behavior in shaping to the development of risk and resilience trajectories in youth growing up amidst chronic trauma.

Conservatism and the neural circuitry of threat: economic conservatism predicts greater amygdala-BNST connectivity during periods of threat vs safety

Political conservatism is associated with an increased negativity bias, including increased attention and reactivity toward negative and threatening stimuli. Although the human amygdala has been implicated in the response to threatening stimuli, no studies to date have investigated whether conservatism is associated with altered amygdala function toward threat. Furthermore, although an influential theory posits that connectivity between the amygdala and bed nucleus of the stria terminalis (BNST) is important in initiating the response to sustained or uncertain threat, whether individual differences in conservatism modulate this connectivity is unknown. To test whether conservatism is associated with increased reactivity in neural threat circuitry, we measured participants’ self-reported social and economic conservatism and asked them to complete high-resolution fMRI scans while under threat of an unpredictable shock and while safe. We found that economic conservatism predicted greater connectivity between the BNST and a cluster of voxels in the left amygdala during threat vs safety. These results suggest that increased amygdala–BNST connectivity during threat may be a key neural correlate of the enhanced negativity bias found in conservatism.

Glucocorticoid receptor gene expression in a CLP-induced ARDS-like rat model treated with dexamethasone and metyrapone

Glucocorticoids (GCs) are used for acute respiratory distress syndrome (ARDS) to improve or prevent lung injury. The mechanisms underlying the effects of GCs involve inadequate GC-receptor (GR)-mediated downregulation of pro-inflammatory factors despite elevated levels of cortisol. Within this context, knowledge of the transcriptional pattern of the GR gene in response to variations in physiological parameters may shed light on this issue. We addressed this problem by measuring plasmatic corticosterone (CCT) levels and assessing GR expression at transcript and protein levels in rats with caecal ligation and puncture (CLP)-induced ARDS-like syndrome treated with dexamethasone and metyrapone. Seventy male rats were randomized into three main groups: Naïve (any treatment), Sham (caecum-exposed) and CLP. CLP animals were divided into three groups according to pretreatments performed before surgery: CLP sal (0.9% NaCl ip), CLP metyrapone (50 mg.kg-1 ip) and CLP dexamethasone (0.5 mg.kg-1 ip). Our results showed that CLP sal promotes elevation in CCT levels, which are significantly reduced with metyrapone to levels comparable to untreated animals when dexamethasone is used. In this hormonal milieu, the GR gene transcript levels of both variants, GRα and GRβ, are produced in comparable levels and in response to caecum-exposing surgery. Nonetheless, the expression of the GRα variant demonstrated positive sensitivity to variations in CCT levels and was downregulated in animals treated with dexamethasone. Moreover, nuclear translocation of GR protein decreased with high levels of plasma CCT and higher GR translocation was found in animals with moderate CCT levels; in either case, the process seemed to be positively associated with the CLP procedure.

The Corticotropin-Releasing Factor Family: Physiology of the Stress Response

The physiological stress response is responsible for the maintenance of homeostasis in the presence of real or perceived challenges. In this function, the brain activates adaptive responses that involve numerous neural circuits and effector molecules to adapt to the current and future demands. A maladaptive stress response has been linked to the etiology of a variety of disorders, such as anxiety and mood disorders, eating disorders, and the metabolic syndrome. The neuropeptide corticotropin-releasing factor (CRF) and its relatives, the urocortins 1–3, in concert with their receptors (CRFR1, CRFR2), have emerged as central components of the physiological stress response. This central peptidergic system impinges on a broad spectrum of physiological processes that are the basis for successful adaptation and concomitantly integrate autonomic, neuroendocrine, and behavioral stress responses. This review focuses on the physiology of CRF-related peptides and their cognate receptors with the aim of providing a comprehensive up-to-date overview of the field. We describe the major molecular features covering aspects of gene expression and regulation, structural properties, and molecular interactions, as well as mechanisms of signal transduction and their surveillance. In addition, we discuss the large body of published experimental studies focusing on state-of-the-art genetic approaches with high temporal and spatial precision, which collectively aimed to dissect the contribution of CRF-related ligands and receptors to different levels of the stress response. We discuss the controversies in the field and unravel knowledge gaps that might pave the way for future research directions and open up novel opportunities for therapeutic intervention.

Essential Role of Ovarian Hormones in Susceptibility to the Consequences of Witnessing Social Defeat in Female Rats

BACKGROUND

Women are at greater risk than men of developing depression and comorbid disorders such as cardiovascular disease. This enhanced risk begins at puberty and ends following menopause, suggesting a role for ovarian hormones in this sensitivity. Here we used a model of psychosocial witness stress in female rats to determine the stress-induced neurobiological adaptations that underlie stress susceptibility in an ovarian hormone-dependent manner.

METHODS

Intact or ovariectomized (OVX) female rats were exposed to five daily 15-minute witness-stress exposures. Witness-stress-evoked burying, behavioral despair, and anhedonia were measured. Cardiovascular telemetry was combined with plasma measurements of inflammation, epinephrine, and corticosterone as indices of cardiovascular dysfunction. Finally, levels of interleukin-1β and corticotropin-releasing factor were assessed in the central amygdala.

RESULTS

Witness stress produced anxiety-like burying, depressive-like anhedonia, and behavioral despair selectively in intact female rats, which was associated with enhanced sympathetic responses during stress, including increased blood pressure, heart rate, and arrhythmias. Moreover, intact female rats exhibited increases in 12-hour resting systolic pressure and heart rate and reductions in heart rate variability. Notably, OVX female rats remained resilient. Moreover, intact, but not OVX, female rats exposed to witness stress exhibited a sensitized cytokine and epinephrine response to stress and distinct increases in levels of corticotropin-releasing factor and interleukin-1β in the central amygdala.

CONCLUSIONS

Together these data suggest that ovarian hormones play a critical role in the behavioral, inflammatory, and cardiovascular susceptibility to social stress in female rats and reveal putative systems that are sensitized to stress in an ovarian hormone-dependent manner.

Thalamostriatal and cerebellothalamic pathways in a songbird, the Bengalese finch

The thalamostriatal system is a major network in the mammalian brain, originating principally from the intralaminar nuclei of thalamus. Its functions remain unclear, but a subset of these projections provides a pathway through which the cerebellum communicates with the basal ganglia. Both the cerebellum and basal ganglia play crucial roles in motor control. Although songbirds have yielded key insights into the neural basis of vocal learning, it is unknown whether a thalamostriatal system exists in the songbird brain. Thalamic nucleus DLM is an important part of the song system, the network of nuclei required for learning and producing song. DLM receives output from song system basal ganglia nucleus Area X and sits within dorsal thalamus, the proposed avian homolog of the mammalian intralaminar nuclei that also receives projections from the cerebellar nuclei. Using a viral vector that specifically labels presynaptic axon segments, we show in Bengalese finches that dorsal thalamus projects to Area X, the basal ganglia nucleus of the song system, and to surrounding medial striatum. To identify the sources of thalamic input to Area X, we map DLM and cerebellar-recipient dorsal thalamus (DTCbN ). Surprisingly, we find both DLM and dorsal anterior DTCbN adjacent to DLM project to Area X. In contrast, the ventral medial subregion of DTCbN projects to medial striatum outside Area X. Our results suggest the basal ganglia in the song system, like the mammalian basal ganglia, integrate feedback from the thalamic region to which they project as well as thalamic regions that receive cerebellar output.

Anhedonia Following Early-Life Adversity Involves Aberrant Interaction of Reward and Anxiety Circuits and Is Reversed by Partial Silencing of Amygdala Corticotropin-Releasing Hormone Gene

BACKGROUND

Anhedonia, the diminished ability to experience pleasure, is an important dimensional entity linked to depression, schizophrenia, and other emotional disorders, but its origins and mechanisms are poorly understood. We have previously identified anhedonia, manifest as decreased sucrose preference and social play, in adolescent male rats that experienced chronic early-life adversity/stress (CES). Here we probed the molecular, cellular, and circuit processes underlying CES-induced anhedonia and tested them mechanistically.

METHODS

We examined functional brain circuits and neuronal populations activated by social play in adolescent CES and control rats. Structural connectivity between stress- and reward-related networks was probed using high-resolution diffusion tensor imaging, and cellular/regional activation was probed using c-Fos. We employed viral-genetic approaches to reduce corticotropin-releasing hormone (Crh) expression in the central nucleus of the amygdala in anhedonic rats, and tested for anhedonia reversal in the same animals.

RESULTS

Sucrose preference was reduced in adolescent CES rats. Social play, generally considered an independent measure of pleasure, activated brain regions involved in reward circuitry in both control and CES groups. In CES rats, social play activated Crh-expressing neurons in the central nucleus of the amygdala, typically involved in anxiety/fear, indicating aberrant functional connectivity of pleasure/reward and fear circuits. Diffusion tensor imaging tractography revealed increased structural connectivity of the amygdala to the medial prefrontal cortex in CES rats. Crh-short hairpin RNA, but not control short hairpin RNA, given into the central nucleus of the amygdala reversed CES-induced anhedonia without influencing other emotional measures.

CONCLUSIONS

These findings robustly demonstrate aberrant interactions of stress and reward networks after early-life adversity and suggest mechanistic roles for Crh-expressing amygdala neurons in emotional deficits portending major neuropsychiatric disorders.

Linking Stress and Infertility: A Novel Role for Ghrelin

Infertility affects a remarkable one in four couples in developing countries. Psychological stress is a ubiquitous facet of life, and although stress affects us all at some point, prolonged or unmanageable stress may become harmful for some individuals, negatively impacting on their health, including fertility. For instance, women who struggle to conceive are twice as likely to suffer from emotional distress than fertile women. Assisted reproductive technology treatments place an additional physical, emotional, and financial burden of stress, particularly on women, who are often exposed to invasive techniques associated with treatment. Stress-reduction interventions can reduce negative affect and in some cases to improve in vitro fertilization outcomes. Although it has been well-established that stress negatively affects fertility in animal models, human research remains inconsistent due to individual differences and methodological flaws. Attempts to isolate single causal links between stress and infertility have not yet been successful due to their multifaceted etiologies. In this review, we will discuss the current literature in the field of stress-induced reproductive dysfunction based on animal and human models, and introduce a recently unexplored link between stress and infertility, the gut-derived hormone, ghrelin. We also present evidence from recent seminal studies demonstrating that ghrelin has a principal role in the stress response and reward processing, as well as in regulating reproductive function, and that these roles are tightly interlinked. Collectively, these data support the hypothesis that stress may negatively impact upon fertility at least in part by stimulating a dysregulation in ghrelin signaling.

Molecular and Cellular Effects of Traumatic Stress: Implications for PTSD

PURPOSE OF REVIEW

Posttraumatic stress disorder (PTSD) is characterized by hyperarousal and recurrent stressful memories after an emotionally traumatic event. Extensive research has been conducted to identify the neurobiological determinants that underlie the pathophysiology of PTSD. In this review, we examine evidence regarding the molecular and cellular pathophysiology of PTSD focusing on two primary brain regions: the vmPFC and the amygdala.

RECENT FINDINGS

This discussion includes a review of the molecular alterations related to PTSD, focusing mainly on changes to glucocorticoid receptor signaling. We also examine postmortem gene expression studies that have been conducted to date and the molecular changes that have been observed in peripheral blood studies of PTSD patients. Causal, mechanistic evidence is difficult to obtain in human studies, so we also review preclinical models of PTSD. Integration of peripheral blood and postmortem studies with preclinical models of PTSD has begun to reveal the molecular changes occurring in patients with PTSD. These findings indicate that the pathophysiology of PTSD includes disruption of glucocorticoid signaling and inflammatory systems and occurs at the level of altered gene expression. We will assess the impact of these findings on the future of PTSD molecular research.

Dexamethasone facilitates fear extinction and safety discrimination in PTSD: A placebo-controlled, double-blind study

Psychophysiological hallmarks of posttraumatic stress disorder (PTSD) include exaggerated fear responses, impaired inhibition and extinction of conditioned fear, and decreased discrimination between safety and fear cues. This increased fear load associated with PTSD can be a barrier to effective therapy thus indicating the need for new treatments to reduce fear expression in people with PTSD. One potential biological target for reducing fear expression in PTSD is the hypothalamic-pituitary-adrenal (HPA) axis, which is dysregulated in PTSD. Recent translational rodent studies and cross-sectional clinical studies have shown that dexamethasone administration and the resulting suppression of cortisol in individuals with PTSD leads to a decrease in the fear responses characteristic of PTSD. These data, taken together, suggest that dexamethasone may serve as a novel pharmacologic intervention for heightened fear responses in PTSD. We conducted a double-blind, placebo-controlled trial to test our hypothesis that dexamethasone administration and the concomitant suppression of HPA axis hyperactivity would attenuate fear expression and enhance fear extinction in individuals with PTSD. Study participants (n=62) were recruited from Grady Memorial Hospital in Atlanta, GA. Participants were randomized to receive dexamethasone or placebo prior to fear conditioning and extinction, in a counterbalanced design (treatments separated by a week). Both PTSD- (n=37) and PTSD+ (n=25) participants showed significant startle increases in the presence of the danger signal during placebo and dexamethasone treatments (all p<0.05). However, only PTSD- control participants showed decreases in fear-potentiated startle across extinction blocks during both conditions (p's≤0.001), with PTSD+ participants showing deficits in fear extinction and safety discrimination in the placebo condition. Notably, extinction and discrimination deficits in PTSD+ subjects were markedly reversed with dexamethasone (p<0.001). These data suggest that dexamethasone may serve as a pharmacological agent with which to facilitate fear extinction and discrimination in individuals with PTSD.

Isoform switching of steroid receptor co-activator-1 attenuates glucocorticoid-induced anxiogenic amygdala CRH expression

Maladaptive glucocorticoid effects contribute to stress-related psychopathology. The glucocorticoid receptor (GR) that mediates many of these effects uses multiple signaling pathways. We have tested the hypothesis that manipulation of downstream factors ('coregulators') can abrogate potentially maladaptive GR-mediated effects on fear-motivated behavior that are linked to corticotropin releasing hormone (CRH). For this purpose the expression ratio of two splice variants of steroid receptor coactivator-1 (SRC-1) was altered via antisense-mediated 'exon-skipping' in the central amygdala of the mouse brain. We observed that a change in splicing towards the repressive isoform SRC-1a strongly reduced glucocorticoid-induced responsiveness of Crh mRNA expression and increased methylation of the Crh promoter. The transcriptional GR target gene Fkbp5 remained responsive to glucocorticoids, indicating gene specificity of the effect. The shift of the SRC-1 splice variants altered glucocorticoid-dependent exploratory behavior and attenuated consolidation of contextual fear memory. In conclusion, our findings demonstrate that manipulation of GR signaling pathways related to the Crh gene can selectively diminish potentially maladaptive effects of glucocorticoids.

Neuroendocrine Underpinnings of Increased Risk for Posttraumatic Stress Disorder in Women

Women are particularly vulnerable to the effects of psychological trauma and the development of trauma-, stressor-, and anxiety-related mental illnesses such as posttraumatic stress disorder (PTSD). In the current chapter, we examine the female hormonal systems that interact with psychobiological stress response systems to elicit maladaptive behavior and mental disease states in traumatized female populations. In addition, we provide a contemporary translational example of a stress vulnerability genomic profile (coding for pituitary adenylate cyclase-activating polypeptide) that may underlie the specific susceptibilities observed in women. Translational scientific investigations such as those described herein may lead to the identification of risk and resilience factors for PTSD as well as enhanced clinical interventions for treating excessive fear and anxiety.

The Physiology of Fear: Reconceptualizing the Role of the Central Amygdala in Fear Learning

The historically understood role of the central amygdala (CeA) in fear learning is to serve as a passive output station for processing and plasticity that occurs elsewhere in the brain. However, recent research has suggested that the CeA may play a more dynamic role in fear learning. In particular, there is growing evidence that the CeA is a site of plasticity and memory formation, and that its activity is subject to tight regulation. The following review examines the evidence for these three main roles of the CeA as they relate to fear learning. The classical role of the CeA as a routing station to fear effector brain structures like the periaqueductal gray, the lateral hypothalamus, and paraventricular nucleus of the hypothalamus will be briefly reviewed, but specific emphasis is placed on recent literature suggesting that the CeA 1) has an important role in the plasticity underlying fear learning, 2) is involved in regulation of other amygdala subnuclei, and 3) is itself regulated by intra- and extra-amygdalar input. Finally, we discuss the parallels of human and mouse CeA involvement in fear disorders and fear conditioning, respectively.

Region-specific roles of the corticotropin-releasing factor-urocortin system in stress

Dysregulation of the corticotropin-releasing factor (CRF)-urocortin (UCN) system has been implicated in stress-related psychopathologies such as depression and anxiety. It has been proposed that CRF-CRF receptor type 1 (CRFR1) signalling promotes the stress response and anxiety-like behaviour, whereas UCNs and CRFR2 activation mediate stress recovery and the restoration of homeostasis. Recent findings, however, provide clear evidence that this view is overly simplistic. Instead, a more complex picture has emerged that suggests that there are brain region- and cell type-specific effects of CRFR signalling that are influenced by the individual's prior experience and that shape molecular, cellular and ultimately behavioural responses to stressful challenges.

Overexpressing Corticotropin-Releasing Factor in the Primate Amygdala Increases Anxious Temperament and Alters Its Neural Circuit

BACKGROUND

Nonhuman primate models are critical for understanding mechanisms underlying human psychopathology. We established a nonhuman primate model of anxious temperament (AT) for studying the early-life risk to develop anxiety and depression. Studies have identified the central nucleus of the amygdala (Ce) as an essential component of AT's neural substrates. Corticotropin-releasing factor (CRF) is expressed in the Ce, has a role in stress, and is linked to psychopathology. Here, in young rhesus monkeys, we combined viral vector technology with assessments of anxiety and multimodal neuroimaging to understand the consequences of chronically increased CRF in the Ce region.

METHODS

Using real-time intraoperative magnetic resonance imaging-guided convection-enhanced delivery, five monkeys received bilateral dorsal amygdala Ce-region infusions of adeno-associated virus serotype 2 containing the CRF construct. Their cagemates served as unoperated control subjects. AT, regional brain metabolism, resting functional magnetic resonance imaging, and diffusion tensor imaging were assessed before and 2 months after viral infusions.

RESULTS

Dorsal amygdala CRF overexpression significantly increased AT and metabolism within the dorsal amygdala. Additionally, we observed changes in metabolism in other AT-related regions, as well as in measures of functional and structural connectivity.

CONCLUSIONS

This study provides a translational roadmap that is important for understanding human psychopathology by combining molecular manipulations used in rodents with behavioral phenotyping and multimodal neuroimaging measures used in humans. The results indicate that chronic CRF overexpression in primates not only increases AT but also affects metabolism and connectivity within components of AT's neural circuitry.

Early life adversity and serotonin transporter gene variation interact to affect DNA methylation of the corticotropin-releasing factor gene promoter region in the adult rat brain

The interaction between childhood maltreatment and the serotonin transporter (5-HTT) gene linked polymorphic region has been associated with increased risk to develop major depression. This Gene × Environment interaction has furthermore been linked with increased levels of anxiety and glucocorticoid release upon exposure to stress. Both endophenotypes are regulated by the neuropeptide corticotropin-releasing factor (CRF) or hormone, which is expressed by the paraventricular nucleus of the hypothalamus, the bed nucleus of the stria terminalis, and the central amygdala (CeA). Therefore, we hypothesized that altered regulation of the expression of CRF in these areas represents a major neurobiological mechanism underlying the interaction of early life stress and 5-HTT gene variation. The programming of gene transcription by Gene × Environment interactions has been proposed to involve epigenetic mechanisms such as DNA methylation. In this study, we report that early life stress and 5-HTT genotype interact to affect DNA methylation of the Crf gene promoter in the CeA of adult male rats. Furthermore, we found that DNA methylation of a specific site in the Crf promoter significantly correlated with CRF mRNA levels in the CeA. Moreover, CeA CRF mRNA levels correlated with stress coping behavior in a learned helplessness paradigm. Together, our findings warrant further investigation of the link of Crf promoter methylation and CRF expression in the CeA with behavioral changes that are relevant for psychopathology.

Genetic Approaches to Hypothalamic-Pituitary-Adrenal Axis Regulation

The normal function of the hypothalamic-pituitary-adrenal (HPA) axis, and resultant glucocorticoid (GC) secretion, is essential for human health. Disruption of GC regulation is associated with pathologic, psychological, and physiological disease states such as depression, post-traumatic stress disorder, hypertension, diabetes, and osteopenia, among others. As such, understanding the mechanisms by which HPA output is tightly regulated in its responses to environmental stressors and circadian cues has been an active area of investigation for decades. Over the last 20 years, however, advances in gene targeting and genome modification in rodent models have allowed the detailed dissection of roles for key molecular mediators and brain regions responsible for this control in vivo to emerge. Here, we summarize work done to elucidate the function of critical neuropeptide systems, GC-signaling targets, and inflammation-associated pathways in HPA axis regulation and behavior, and highlight areas for future investigation.

Interaction of CRF and kappa opioid systems on GABAergic neurotransmission in the mouse central amygdala

The corticotropin-releasing factor (CRF) and kappa-opioid receptor (KOR) systems are both implicated in stress-related behaviors and drug dependence. Although previous studies suggest that antagonism of each system blocks aspects of experimental models of drug dependence, the possible interaction between these systems at the neuronal level has not been completely examined. We used an in vitro brain slice preparation to investigate the interaction of these two peptide systems on inhibitory neurotransmission in the central nucleus of the amygdala (CeA). Application of exogenous CRF increased the mean frequency of GABAergic miniature inhibitory postsynaptic currents (mIPSC) by 20.2%, suggesting an increase in presynaptic GABA release. Although the pharmacological blockade of KORs by norBNI alone did not significantly affect mIPSC frequency, it significantly enhanced the effect of CRF (by 43.9%, P = 0.02). Similarly, the CRF effects in slices from KOR knockout (KO) mice (84.0% increase) were significantly greater than in wild-type (WT) mice (24.6%, P = 0.01), although there was no significant difference in baseline mIPSC frequency between slices from KOR KO and WT mice. The increase in CRF action in the presence of norBNI was abolished by a CRF-1 receptor antagonist but was unaffected by a CRF-2 receptor antagonist. We hypothesize that CRF facilitates the release of an endogenous ligand for KORs and that subsequent activation of KOR receptors modulates presynaptic effects of CRF in CeA. These results suggest that potential pharmacotherapies aimed at neurobehavioral and addictive disorders may need to involve both the KOR/dynorphin and the CRF systems in CeA.

Psychophysiology and posttraumatic stress disorder symptom profile in pregnant African-American women with trauma exposure

While female sex is a robust risk factor for posttraumatic stress disorder (PTSD), pregnant women are an understudied population in regards to PTSD symptom expression profiles. Because circulating hormones during pregnancy affect emotionality, we assessed whether pregnant women would have increased expression of the intermediate phenotypes of hyperarousal and fear-potentiated startle (FPS) compared to non-pregnant women. We examined PTSD symptom profiles in pregnant (n = 207) and non-pregnant women (n = 370). In a second study, FPS responses were assessed in 15 pregnant and 24 non-pregnant women. All participants were recruited from the obstetrics and gynecology clinic at a public hospital serving a primarily African-American, low socioeconomic status, inner-city population. Our results indicate that overall PTSD symptoms were not different between the groups of women. However, pregnant women reported being more hypervigilant (p = 0.036) than non-pregnant women. In addition, pregnant women showed increased FPS to a safety signal compared to non-pregnant women (p = 0.024). FPS to a safety signal in pregnant women was significantly correlated with PTSD hyperarousal symptoms (r = 0.731, p < 0.001). Furthermore, discrimination between danger and safety signals was present in non-pregnant women (p = 0.008), but not in pregnant women (p = 0.895). Together, these data suggest that pregnant women show clinical and psychophysiological hyperarousal compared to non-pregnant women, and support screening for PTSD and assessment of PTSD risk in pregnant women.

Translational approach to studying panic disorder in rats: hits and misses

Panic disorder (PD) patients are specifically sensitive to 5–7% carbon dioxide. Another startling feature of clinical panic is the counterintuitive lack of increments in ‘stress hormones’. PD is also more frequent in women and highly comorbid with childhood separation anxiety (CSA). On the other hand, increasing evidence suggests that panic is mediated at dorsal periaqueductal grey matter (DPAG). In line with prior studies showing that DPAG-evoked panic-like behaviours are attenuated by clinically-effective treatments with panicolytics, we show here that (i) the DPAG harbors a hypoxia-sensitive alarm system, which is activated by hypoxia and potentiated by hypercapnia, (ii) the DPAG suffocation alarm system is inhibited by clinically-effective treatments with panicolytics, (iii) DPAG stimulations do not increase stress hormones in the absence of physical exertion, (iv) DPAG-evoked panic-like behaviours are facilitated in neonatally-isolated adult rats, a model of CSA, and (v) DPAG-evoked responses are enhanced in the late diestrus of female rats. Data are consistent with the DPAG mediation of both respiratory and non-respiratory types of panic attacks.