A neuroendocrine mechanism for sustaining fear

Does the stress axis mediate behavioural flexibility in a social cichlid, Neolamprologus pulcher?

Behavioural flexibility plays a major role in the way animals cope with novel situations, and physiological stress responses are adaptive and highly efficient mechanisms to cope with unpredictable events. Previous studies investigating the role of stress responses in mediating behavioural flexibility were mostly done in laboratory rodents using stressors and cognitive challenges unrelated to the ecology of the species. To better understand how stress mediates behavioural flexibility in a natural context, direct manipulations of the stress response and cognitive tests in ecologically relevant contexts are needed. To this aim, we pharmacologically blocked glucocorticoid receptors (GR) in adult Neolamprologus pulcher using a minimally invasive application of a GR antagonist. GR blockade prevents the recovery after a stressful event, which we predicted to impair behavioural flexibility. After the application of the GR antagonist, we repeatedly exposed fish to a predator and tested their behavioural flexibility using a detour task, i.e. fish had to find a new, longer route to the shelter when the shortest route was blocked. While the latencies to find the shelter were not different between treatments, GR blocked fish showed more failed attempts during the detour tasks than control fish. Furthermore, weak performance during the detour tasks was accompanied by an increase of fear related behaviours. This suggests that blocking GR changed the perception of fear and resulted in an impaired behavioural flexibility. Therefore, our results support a potential link between the capacity to recover from stressors and behavioural flexibility in N. pulcher with potential consequences for an effective and adaptive coping with changing environments.

Response of CRH system in brain and gill of marine medaka to seawater acidification

Corticotropin-releasing hormone (CRH) is mainly secreted by the hypothalamus to regulate stress when environmental factors change. Gills contact with water directly and may also secrete CRH to maintain local homeostasis. Ocean acidification changes water chemical parameters and is becoming an important environmental stressor for marine fish. The response of brain and gill CRH systems to ocean acidification remains unclear. In this study, marine medaka were exposed to CO2-acidified seawater (440 ppm, 1000 ppm, and 1800 ppm CO2) for 2 h, 4 h, 24 h, and 7 d, respectively. At 2 h and 4 h, the expression of crh mRNA in gills increased with increasing CO2 concentration. Crh protein is expressed mainly in the lamellae cells. crhbp and crhr1 expression also increased significantly. However, at 2 h and 4 h, acidification caused little changes in these genes and Crh protein expression in the brain. At 7 d, Crh-positive cells were detected in the hypothalamus; moreover, Crh protein expression in the whole brain increased. It is suggested that CRH autocrine secretion in gills is responsible for local acid-base regulation rather than systemic mobilization after short-term acidification stress, which may help the rapid regulation of body damage caused by environmental stress.

The Role of Serotonin in Fear Learning and Memory: A Systematic Review of Human Studies

Fear is characterized by distinct behavioral and physiological responses that are essential for the survival of the human species. Fear conditioning (FC) serves as a valuable model for studying the acquisition, extinction, and expression of fear. The serotonin (5-hydroxytryptamine, 5-HT) system is known to play a significant role in emotional and motivational aspects of human behavior, including fear learning and expression. Accumulating evidence from both animal and human studies suggests that brain regions involved in FC, such as the amygdala, hippocampus, and prefrontal cortex, possess a high density of 5-HT receptors, implicating the crucial involvement of serotonin in aversive learning. Additionally, studies exploring serotonin gene polymorphisms have indicated their potential influence on FC. Therefore, the objective of this work was to review the existing evidence linking 5-HT with fear learning and memory in humans. Through a comprehensive screening of the PubMed and Web of Science databases, 29 relevant studies were included in the final review. These studies investigated the relationship between serotonin and fear learning using drug manipulations or by studying 5-HT-related gene polymorphisms. The results suggest that elevated levels of 5-HT enhance aversive learning, indicating that the modulation of serotonin 5-HT2A receptors regulates the expression of fear responses in humans. Understanding the role of this neurochemical messenger in associative aversive learning can provide insights into psychiatric disorders such as anxiety and post-traumatic stress disorder (PTSD), among others.

Association between adverse experiences during Hurricane María and mental and emotional distress among adults in Puerto Rico

OBJECTIVES

To evaluate the association between adverse experiences during Hurricane María and mental and emotional distress in Puerto Rico.

METHODS

This cross-sectional study used baseline data from adult (30-75 years) participants of the Puerto Rico Observational Study of Psychosocial, Environmental, and Chronic Disease Trends (PROSPECT). Enrolled individuals prior to COVID-19 who completed a 33-item questionnaire on Hurricane María-related experiences (sub-categorized as personal, service, or property losses), depression symptomatology, post-traumatic stress disorder (PTSD), and anxiety were included for analysis (n = 456).

RESULTS

Most participants experienced fear for their family's safety, damage to their home and personal items, communication outages, and water shortages. Each additional stressor was significantly associated with higher odds of depression symptoms, PTSD, and anxiety. Personal losses were significantly associated with higher likelihood of all outcomes, while services losses were associated with depression symptoms and anxiety; property loss was not significantly associated with any outcome.

CONCLUSIONS

Adverse experiences during a major natural disaster are associated with mental and emotional distress. Strategies to minimize hardships during natural disasters, especially personal and service losses, are essential to preserve mental health. Post-disaster psychological support to individuals is crucial.

Hyperexcitability: From Normal Fear to Pathological Anxiety and Trauma

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

Coordinated Action of Corticotropin-Releasing Hormone and Cortisol Shapes the Acute Stress-Induced Behavioural Response in Zebrafish

INTRODUCTION

The stress response mediated by the hypothalamus-pituitary-adrenal (HPA) axis activation is highly conserved in vertebrates. Hyperactivity is one such established acute stress response, and corticotropin-releasing hormone (CRH), the primary step in HPA activation, signalling has been implicated in this stressor-mediated behaviour. However, whether CRH mediates the acute behavioural effects either alone or in conjunction with glucocorticoids (GCs) are far from clear. We hypothesized that the CRH receptor 1 (CRHR1)-mediated rise in GCs post-stress is necessary for the initiation and maintenance of the acute stress-related behaviour.

METHODS

We first generated zebrafish (Danio rerio) with a mutation in the CRHR1 gene (CRHR1-KO) to assess the function of CRH. The behavioural readout utilized for this study was the locomotor activity of larval zebrafish in response to an acute light exposure, a protocol that freezes the larvae in response to the light stimulus. To test whether cortisol signalling is involved in the stress-mediated hyperactivity, we treated wildtype fish with metyrapone (MET), an inhibitor of 11β-hydroxylase, to suppress cortisol production. The temporal role for cortisol signalling in the stress-related hyperactivity was tested using the glucocorticoid receptor knockout (GRKO) and mineralocorticoid receptor knockout (MRKO) zebrafish mutants.

RESULTS

CRHR1-KO larvae did not increase cortisol, the principal GC in teleosts, post-stress, confirming a functional knockout. An acute stress resulted in the hyperactivity of the larvae in light at 15, 60, and 240 min post-stress, and this was absent in CRHR1-KO larvae. Addition of MET effectively blocked the attendant rise in cortisol post-stress; however, the stress-mediated hyperactivity was inhibited only at 60 and 240 min but not at 15 min post-stress. Addition of human CRH peptide caused hyperactivity at 15 min, and this response was also abolished in the CRHR1-KO mutants. The stress-induced hyperactivity was absent in the MRKO fish, while GRKO mutants showed transient effects.

CONCLUSIONS

The results suggest that the stress-induced hyperactivity is induced by the CRH/CRHR1 system, while the temporal activation of cortisol production and the associated GR/MR signalling is essential for prolonging the stressor-induced hyperactivity. This study underscores the importance of systems-level analysis to assess stress responsivity.

Distinguishing selective mutism and social anxiety in children: a multi-method study

Selective mutism (SM) is an anxiety disorder in which a child fails to speak in some situations (e.g., school) despite the ability to speak in other situations (e.g., home). Some work has conceptualized SM as a variant of social anxiety disorder (SAD) characterized by higher levels of social anxiety. Here, we empirically tested this hypothesis to see whether there were differences in social anxiety (SA) between SM and SAD across behavioral, psychophysiological, self-, parent-, and teacher-report measures. Participants included 158 children (M_age = 8.76 years, SD = 3.23) who were classified into three groups: children with SM and who were also highly socially anxious (SM + HSA; n = 48), highly socially anxious children without SM (HSA; n = 48), and control children (n = 62). Children participated in a videotaped self-presentation task, following which observed SA behaviors were coded, and salivary cortisol reactivity was measured. We also collected child, parent, and teacher reports of children's trait SA symptoms. The SM + HSA and HSA groups had similar observed non-verbal SA behavior, cortisol reactivity, and trait SA symptom levels according to parent and child reports, but SM + HSA children had significantly higher SA according to teacher report and observer-rated verbal SA behavior relative to the HSA group. As expected, control children had lower cortisol reactivity and SA across all measures relative to the other groups. Although SM and SAD in children share many similarities, SM may be characterized by greater SA in certain social contexts (e.g., school) and is distinguishable from SAD on behavioral measures of verbal SA.

Trajectories of behavioral avoidance in real time: Associations with temperament and physiological dysregulation in preschoolers

Although excessive avoidance has been implicated in mental health problems and socioemotional difficulties, relatively little is known about dynamic changes of avoidance behaviors. We used a latent class growth analysis to examine the temporal course of avoidance behaviors in real time and determined whether the derived classes were distinguishable on temperament and physiological markers of regulation and reactivity (N = 153; M_age = 4.20 years). A three-class solution was found and identified a low, medium, and high increasing avoidance group. The high and increasing avoidance group had the highest physiological reactivity (cortisol reactivity) and shyness, and the lowest physiological regulation (i.e., respiratory sinus arrythmia suppression). High and increasing avoidance may therefore be associated with temperamental and physiological indices of risk implicated in maladjustment and highlight the value of data-driven, group-based approaches for examining dynamic patterns of behavior.

Stress hormones mediate developmental plasticity in vertebrates with complex life cycles

The environment experienced by developing organisms can shape the timing and character of developmental processes, generating different phenotypes from the same genotype, each with different probabilities of survival and performance as adults. Chordates have two basic modes of development, indirect and direct. Species with indirect development, which includes most fishes and amphibians, have a complex life cycle with a free-swimming larva that is typically a growth stage, followed by a metamorphosis into the adult form. Species with direct development, which is an evolutionarily derived developmental mode, develop directly from embryo to the juvenile without an intervening larval stage. Among the best studied species with complex life cycles are the amphibians, especially the anurans (frogs and toads). Amphibian tadpoles are exposed to diverse biotic and abiotic factors in their developmental habitat. They have extensive capacity for developmental plasticity, which can lead to the expression of different, adaptive morphologies as tadpoles (polyphenism), variation in the timing of and size at metamorphosis, and carry-over effects on the phenotype of the juvenile/adult. The neuroendocrine stress axis plays a pivotal role in mediating environmental effects on amphibian development. Before initiating metamorphosis, if tadpoles are exposed to predators they upregulate production of the stress hormone corticosterone (CORT), which acts directly on the tail to cause it to grow, thereby increasing escape performance. When tadpoles reach a minimum body size to initiate metamorphosis they can vary the timing of transformation in relation to growth opportunity or mortality risk in the larval habitat. They do this by modulating the production of thyroid hormone (TH), the primary inducer of metamorphosis, and CORT, which synergizes with TH to promote tissue transformation. Hypophysiotropic neurons that release the stress neurohormone corticotropin-releasing factor (CRF) are activated in response to environmental stress (e.g., pond drying, food restriction, etc.), and CRF accelerates metamorphosis by directly inducing secretion of pituitary thyrotropin and corticotropin, thereby increasing secretion of TH and CORT. Although activation of the neuroendocrine stress axis promotes immediate survival in a deteriorating larval habitat, costs may be incurred such as reduced tadpole growth and size at metamorphosis. Small size at transformation can impair performance of the adult, reducing probability of survival in the terrestrial habitat, or fecundity. Furthermore, elevations in CORT in the tadpole caused by environmental stressors cause long term, stable changes in neuroendocrine function, behavior and physiology of the adult, which can affect fitness. Comparative studies show that the roles of stress hormones in developmental plasticity are conserved across vertebrate taxa including humans.

An exploratory analysis of testosterone, cortisol, and aggressive behavior type in men and women

Increasing evidence indicates that the interaction between testosterone and cortisol is associated with variation in aggressive behavior. However, results are mixed. The current study further explored the association between testosterone, cortisol, and both reactive and proactive aggression in a large sample of university students. Models considered direct and interactive effects between baseline measures of testosterone and cortisol as well as change in hormones in response to a social stressor. In women, baseline cortisol had a negative direct association with reactive aggression and was further associated with reactive aggression in interaction with baseline testosterone (positive interaction). Hormones were unrelated to reactive aggression in men. Baseline cortisol had a negative direct association with proactive aggression in women. In contrast, the association between change in cortisol and proactive aggression was positive. Cortisol was not associated with proactive aggression in men. In addition, testosterone was not related to proactive aggression either directly or in interaction with cortisol in either men or women. Collectively, these results show that the association between hormones and aggression varies across aggressive behavior type and across sex.

Corticotropin-releasing factor infusion in the bed nucleus of the stria terminalis of lactating mice alters maternal care and induces behavioural phenotypes in offspring

The peripartum period is accompanied by numerous physiological and behavioural adaptations organised by the maternal brain. These changes are essential for adequate expression of maternal behaviour, thereby ensuring proper development of the offspring. The corticotropin-releasing factor (CRF) plays a key role in a variety of behaviours accompanying stress, anxiety, and depression. There is also evidence that CRF contributes to maladaptations during the peripartum period. We investigated the effects of CRF in the bed nucleus of the stria terminalis (BNST) of lactating mice during maternal care and analysed locomotor activity and anxiety-like behaviour in the offspring. The BNST has been implicated in anxiety behaviour and regulation of the stress response. The effects of intra-BNST CRF administration were compared with those induced by the limited bedding (LB) procedure, a model that produces altered maternal behaviour. BALB/cJ dams were exposed to five infusions of CRF or saline into the BNST in the first weeks after birth while the LB dams were exposed to limited nesting material from postnatal days (P) 2–9. Maternal behaviour was recorded in intercalated days, from P1-9. Offspring anxiety-like behaviour was assessed during adulthood using the open-field, elevated plus-maze, and light/dark tests. Both intra-BNST CRF and LB exposure produced altered maternal care, represented by decreased arched-back nursing and increased frequency of exits from the nest. These changes in maternal care resulted in robust sex-based differences in the offspring’s behavioural responses during adulthood. Females raised by CRF-infused dams exhibited increased anxiety-like behaviour, whereas males presented a significant decrease in anxiety. On the other hand, both males and females raised by dams exposed to LB showed higher locomotor activity. Our study demonstrates that maternal care is impaired by intra-BNST CRF administrations, and these maladaptations are similar to exposure to adverse early environments. These procedures, however, produce distinct phenotypes in mice during young adulthood and suggest sex-based differences in the susceptibility to poor maternal care.

Agonistic behaviors and neuronal activation in sexually naïve female Mongolian gerbils

Agonistic interaction is important for establishing social hierarchy and determining access to limited resources. Although there are substantial studies investigating the neural mechanisms of aggressive or defensive behavior in male rodents, little attention has been paid to the mechanisms underlying agonistic behaviors in females. In the present study, we depicted patterns of agonistic behaviors in sexually naïve female Mongolian gerbils (Meriones unguiculatus) and examined the neuronal activation in the brain by Fos-immunoreactive (Fos-ir) staining. We found that the winner-loser relationship was established rapidly. Winners displayed higher levels of aggression, environmental exploration, scent marking, and self-grooming, but less defensive behavior, in comparison to losers. Several patterns of Fos-ir expression emerged following agonistic interactions. Winners had the number of Fos-ir cells in the ventrolateral subnucleus of the ventromedial hypothalamus (VMHvl) and dorsal periaqueductal grey (PAGd) more than the controls but less than the losers. Losers also had more Fos-ir cells in the paraventricular nucleus of the hypothalamus (PVN), anterior medial (BSTam) and anteriolateral (BSTal) subnuclei of the bed nucleus of the stria terminalis (BST), and the ventral subnucleus of the lateral septum (LSv), as well as less Fos-ir cells in the dentate gyrus of the hippocampus (DG), compared to the controls. In addition, the number of Fos-ir cells showed similar increases in the principal nucleus (BSTpr) and interfascicular nucleus (BSTif) of the BST and amygdala (AMYG) in both the winners and losers, compared to the controls. Together, these data illustrate the patterns of altered neuronal activation in a behavior-, social status-, and brain region-specific manner, implicating potential roles of the brain neural circuit in mediating agonistic interactions in female Mongolian gerbils.

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.

Behavioral inhibition and EEG delta-beta correlation in early childhood: Comparing a between-subjects and within-subjects approach

Heightened delta-beta correlation has been conceptualized as reflecting exaggerated neural regulation and has been implicated in anxiety. Behavioral inhibition (BI) is a temperament characterized by wariness to novelty and is a robust predictor of anxiety, but delta-beta correlation has not been investigated in relation to childhood BI. We examined the relation between BI and between-subjects (i.e., across participants) and within-subjects (i.e., across data epochs) measures of baseline EEG delta-beta correlation in 118 children. Using a between-subjects measure, children scoring high on BI had higher delta-beta correlation relative to low BI children at frontal and central, and marginally higher in parietal, brain regions. Using a within-subjects measure, continuous BI scores were positively correlated with central and parietal delta-beta correlation. Delta-beta correlation may be a neural correlate of BI in childhood that displays differences in region specificity, correlation strength, and variability of correlation values when comparing between- and within-subjects measures.

Stress Across Generations: DNA Methylation as a Potential Mechanism Underlying Intergenerational Effects of Stress in Both Post-traumatic Stress Disorder and Pre-clinical Predator Stress Rodent Models

Although most humans will experience some type of traumatic event in their lifetime only a small set of individuals will go on to develop post-traumatic stress disorder (PTSD). Differences in sex, age, trauma type, and comorbidity, along with many other elements, contribute to the heterogenous manifestation of this disorder. Nonetheless, aberrant hypothalamus-pituitary-adrenal (HPA) axis activity, especially in terms of cortisol and glucocorticoid receptor (GR) alterations, has been postulated as a tenable factor in the etiology and pathophysiology of PTSD. Moreover, emerging data suggests that the harmful effects of traumatic stress to the HPA axis in PTSD can also propagate into future generations, making offspring more prone to psychopathologies. Predator stress models provide an ethical and ethologically relevant way to investigate tentative mechanisms that are thought to underlie this phenomenon. In this review article, we discuss findings from human and laboratory predator stress studies that suggest changes to DNA methylation germane to GRs may underlie the generational effects of trauma transmission. Understanding mechanisms that promote stress-induced psychopathology will represent a major advance in the field and may lead to novel treatments for such devastating, and often treatment-resistant trauma and stress-disorders.

A Tilted Axis: Maladaptive Inflammation and HPA Axis Dysfunction Contribute to Consequences of TBI

Each year approximately 1.7 million people sustain a traumatic brain injury (TBI) in the US alone. Associated with these head injuries is a high prevalence of neuropsychiatric symptoms including irritability, depression, and anxiety. Neuroinflammation, due in part to microglia, can worsen or even cause neuropsychiatric disorders after TBI. For example, mounting evidence demonstrates that microglia become “primed” or hyper-reactive with an exaggerated pro-inflammatory phenotype following multiple immune challenges. Microglial priming occurs after experimental TBI and correlates with the emergence of depressive-like behavior as well as cognitive dysfunction. Critically, immune challenges are various and include illness, aging, and stress. The collective influence of any combination of these immune challenges shapes the neuroimmune environment and the response to TBI. For example, stress reliably induces inflammation and could therefore be a gateway to altered neuropathology and behavioral decline following TBI. Given the increasing incidence of stress-related psychiatric disorders after TBI, the degree in which stress affects outcome is of particular interest. This review aims to highlight the role of the hypothalamic-pituitary-adrenal (HPA) axis as a key mediator of stress-immune pathway communication following TBI. We will first describe maladaptive neuroinflammation after TBI and how stress contributes to inflammation through both anti- and pro-inflammatory mechanisms. Clinical and experimental data describing HPA-axis dysfunction and consequences of altered stress responses after TBI will be discussed. Lastly, we will review common stress models used after TBI that could better elucidate the relationship between HPA axis dysfunction and maladaptive inflammation following TBI. Together, the studies described in this review suggest that HPA axis dysfunction after brain injury is prevalent and contributes to the dynamic nature of the neuroinflammatory response to brain injury. Experimental stressors that directly engage the HPA axis represent important areas for future research to better define the role of stress-immune pathways in mediating outcome following TBI.

FAAH genotype, CRFR1 genotype, and cortisol interact to predict anxiety in an aging, rural Hispanic population: A Project FRONTIER study

The neurophysiological underpinnings involved in susceptibility to and maintenance of anxiety are not entirely known. However, two stress-responsive systems, the hypothalamic-pituitary-adrenal axis and the endocannabinoid system, may interact in anxiety. Here, we examine the relationship between FAAH genotype, CRFR1 genotype, baseline cortisol, and state anxiety in a rural adult population using data from Project FRONTIER. We predicted that FAAH A (AA and AC vs CC; rs324420) and three CRFR1 SNP minor alleles (rs7209436 C→ T [minor allele]; rs110402, G → A [minor]; and rs242924 G→ T [minor]), would interact to predict low baseline cortisol and low state anxiety scores. We found partial support for our prediction. In CRFR1 minor carriers, the FAAH AA or AC (vs. CC) genotype was associated with higher cortisol and with lower anxiety. In CRFR1 non-minors, those with FAAH AA or AC (vs. CC) showed decreased cortisol and higher anxiety. These results suggest that FAAH CC genotype only conveys risk for anxiety in individuals who are also carriers of the CRFR1 minor combination. FAAH genotype was significantly associated with baseline cortisol but was not independently associated with anxiety. Contrary to our predictions, baseline cortisol was negatively associated with anxiety. Lastly, we did not find any independent relationships between any of our SNPs and baseline cortisol or anxiety. These data suggest FAAH and cortisol interact to predict state anxiety, but that the relationship depends on CRFR1 genotype. The Project FRONTIER dataset is supported by Texas Tech University Health Sciences Center Garrison Institute on Aging.

Peripubertal stress-induced heightened aggression: modulation of the glucocorticoid receptor in the central amygdala and normalization by mifepristone treatment

Despite the enormous negative impact of excessive aggression for individuals and societies, there is a paucity of treatments. Here, using a peripubertal stress model of heightened aggression in rats, we investigated the involvement of the glucocorticoid system and tested the effectiveness of antiglucocorticoid treatment to normalize behavior. We assessed peripubertal stress-induced changes in glucocorticoid (GR) and mineralocorticoid (MR) gene expression in different amygdala nuclei and hippocampus, and report a specific increase in GR mRNA expression in the central amygdala (CeA). Administration of mifepristone (10 mg/kg), a GR antagonist, before stressor exposure at peripuberty prevented the habituation of plasma corticosterone responses observed throughout the stress protocol. This treatment also prevented the increase in aggression and GR expression in the CeA observed in peripubertally stressed rats at adulthood. Viral downregulation of CeA GR expression at adulthood led to reduced aggression. Subsequently, we showed that a brief, 3-day, treatment with mifepristone at adulthood was effective to normalize the abnormal aggression phenotype in peripubertally stressed rats. Our results support a key role for GR actions during peripubertal stress for the long-term programming of heightened aggression. Strikingly, they also support the translational interest of testing the effectiveness of mifepristone treatment to diminish reactive aggression in early adversity-related human psychopathologies.

Cocaine- and amphetamine-regulated transcript (CART): A multifaceted neuropeptide

Over the last 35 years, the continuous discovery of novel neuropeptides has been the key to the better understanding of how the central nervous system has integrated with neuronal signals and behavioral responses. Cocaine and amphetamine-regulated transcript (CART) was discovered in 1995 in the rat striatum but later was found to be highly expressed in the hypothalamus. The widespread distribution of CART peptide in the brain complicated the understanding of the role played by this neurotransmitter. The main objective of the current compact review is to piece together the fragments of available information about origin, expression, distribution, projection, and function of CART peptides. Accumulative evidence suggests CART as a neurotransmitter and neuroprotective agent that is mainly involved in regulation of feeding, addiction, stress, anxiety, innate fear, neurological disease, neuropathic pain, depression, osteoporosis, insulin secretion, learning, memory, reproduction, vision, sleep, thirst and body temperature. In spite of the vast number of studies about the CART, the overall pictures about the CART functions are sketchy. First, there is a lack of information about cloned receptor, specific agonist and antagonist. Second, CART peptides are detected in discrete sets of neurons that can modulate countless activities and third; CART peptides exist in several fragments due to post-translational processing. For these reasons the overall picture about the CART peptides are sketchy and confounding.

Associations between glucocorticoids and sociality across a continuum of vertebrate social behavior

The causes and consequences of individual differences in animal behavior and stress physiology are increasingly studied in wild animals, yet the possibility that stress physiology underlies individual variation in social behavior has received less attention. In this review, we bring together these study areas and focus on understanding how the activity of the vertebrate neuroendocrine stress axis (HPA-axis) may underlie individual differences in social behavior in wild animals. We first describe a continuum of vertebrate social behaviors spanning from initial social tendencies (proactive behavior) to social behavior occurring in reproductive contexts (parental care, sexual pair-bonding) and lastly to social behavior occurring in nonreproductive contexts (nonsexual bonding, group-level cooperation). We then perform a qualitative review of existing literature to address the correlative and causal association between measures of HPA-axis activity (glucocorticoid levels or GCs) and each of these types of social behavior. As expected, elevated HPA-axis activity can inhibit social behavior associated with initial social tendencies (approaching conspecifics) and reproduction. However, elevated HPA-axis activity may also enhance more elaborate social behavior outside of reproductive contexts, such as alloparental care behavior. In addition, the effect of GCs on social behavior can depend upon the sociality of the stressor (cause of increase in GCs) and the severity of stress (extent of increase in GCs). Our review shows that the while the associations between stress responses and sociality are diverse, the role of HPA-axis activity behind social behavior may shift toward more facilitating and less inhibiting in more social species, providing insight into how stress physiology and social systems may co-evolve.

The influence of stress hormones and aggression on cooperative behaviour in subordinate meerkats

In cooperative breeders, aggression from dominant breeders directed at subordinates may raise subordinate stress hormone (glucocorticoid) concentrations. This may benefit dominants by suppressing subordinate reproduction but it is uncertain whether aggression from dominants can elevate subordinate cooperative behaviour, or how resulting changes in subordinate glucocorticoid concentrations affect their cooperative behaviour. We show here that the effects of manipulating glucocorticoid concentrations in wild meerkats (Suricata suricatta) on cooperative behaviour varied between cooperative activities as well as between the sexes. Subordinates of both sexes treated with a glucocorticoid receptor antagonist (mifepristone) exhibited significantly more pup protection behaviour (babysitting) compared to those treated with glucocorticoids (cortisol) or controls. Females treated with mifepristone had a higher probability of exhibiting pup food provisioning (pup-feeding) compared to those treated with cortisol. In males, there were no treatment effects on the probability of pup-feeding, but those treated with cortisol gave a higher proportion of the food they found to pups than those treated with mifepristone. Using 19 years of behavioural data, we also show that dominant females did not increase the frequency with which they directed aggression at subordinates at times when the need for assistance was highest. Our results suggest that it is unlikely that dominant females manipulate the cooperative behaviour of subordinates through the effects of aggression on their glucocorticoid levels and that the function of aggression directed at subordinates is probably to reduce the probability they will breed.

Probing for Neuroadaptations to Unpredictable Stressors in Addiction: Translational Methods and Emerging Evidence

Stressors clearly contribute to addiction etiology and relapse in humans, but our understanding of specific mechanisms remains limited. Rodent models of addiction offer the power, flexibility, and precision necessary to delineate the causal role and specific mechanisms through which stressors influence alcohol and other drug use. This review describes a program of research using startle potentiation to unpredictable stressors that is well positioned to translate between animal models and clinical research with humans on stress neuroadaptations in addiction. This research rests on a solid foundation provided by three separate pillars of evidence from (a) rodent behavioral neuroscience on stress neuroadaptations in addiction, (b) rodent affective neuroscience on startle potentiation, and (c) human addiction and affective science with startle potentiation. Rodent stress neuroadaptation models implicate adaptations in corticotropin-releasing factor and norepinephrine circuits within the central extended amygdala following chronic alcohol and other drug use that mediate anxious behaviors and stress-induced reinstatement among drug-dependent rodents. Basic affective neuroscience indicates that these same neural mechanisms are involved in startle potentiation to unpredictable stressors in particular (vs. predictable stressors). We believe that synthesis of these evidence bases should focus us on the role of unpredictable stressors in addiction etiology and relapse. Startle potentiation in unpredictable stressor tasks is proposed to provide an attractive and flexible test bed to encourage tight translation and reverse translation between animal models and human clinical research on stress neuroadaptations. Experimental therapeutics approaches focused on unpredictable stressors hold high promise to identify, repurpose, or refine pharmacological and psychosocial interventions for addiction.

CART neuropeptide modulates the extended amygdalar CeA-vBNST circuit to gate expression of innate fear

Innate fear is critical for the survival of animals and is under tight homeostatic control. Deregulation of innate fear processing is thought to underlie pathological phenotypes including, phobias and panic disorders. Although central processing of conditioned fear has been extensively studied, the circuitry and regulatory mechanisms subserving innate fear remain relatively poorly defined. In this study, we identify cocaine- and amphetamine-regulated transcript (CART) neuropeptide signaling in the central amygdala (CeA) - ventral bed nucleus of stria terminalis (vBNST) axis as a key modulator of innate fear expression. 2,4,5-trimethyl-3-thiazoline (TMT), a component of fox faeces, induces a freezing response whose intensity is regulated by the extent of CART-signaling in the CeA neurons. Abrogation of CART activity in the CeA attenuates the freezing response and reduces activation of vBNST neurons. Conversely, ectopically elevated CART signaling in the CeA potentiates the fear response concomitant with enhanced vBNST activation. We show that local levels of CART signaling modulate the activation of CeA neurons by NMDA receptor-mediated glutamatergic inputs, in turn, regulating activity in the vBNST. This study identifies the extended amygdalar CeA-vBNST circuit as a CART modulated axis encoding innate fear. CART signaling regulates the glutamatergic excitatory drive in the CeA-vBNST circuit, in turn, gating the expression of the freezing response to TMT.

Corticotropin Releasing Factor in the Bed Nucleus of the Stria Terminalis in Socially Defeated and Non-stressed Mice with a History of Chronic Alcohol Intake

Stress exposure has been identified as one risk factor for alcohol abuse that may facilitate the transition from social or regulated use to the development of alcohol dependence. Preclinical studies have shown that dysregulation of the corticotropin releasing factor (CRF) neurotransmission has been implicated in stress-related psychopathologies such as depression and anxiety, and may affect alcohol consumption. The bed nucleus of the stria terminalis (BNST) contains CRF-producing neurons which seem to be sensitive to stress. In this study, adult male C57BL/6 mice previously defeated in resident-intruder confrontations were evaluated in the elevated plus-maze and tail suspension test. Mice were also tested for sweet solution intake before and after social stress. After having had continuous access to ethanol (20% weight/volume) for 4 weeks, control and stressed mice had CRF type 1 (CRFR1) or type 2 (CRFR2) receptor antagonists infused into the BNST and then had access to ethanol for 24 h. In separate cohorts of control and stressed mice, we assessed mRNA levels of BNST CRF, CRFR1 and CRFR2. Stressed mice increased their intake of sweet solution after ten sessions of social defeat and showed reduced activity in the open arms of the elevated plus-maze. When tested for ethanol consumption, stressed mice persistently drank significantly more than controls during the 4 weeks of access. Also, social stress induced higher BNST CRF mRNA levels. The selective blockade of BNST CRFR1 with CP376,395 effectively reduced alcohol drinking in non-stressed mice, whereas the selective CRFR2 antagonist astressin2B produced a dose-dependent increase in ethanol consumption in both non-stressed controls and stressed mice. The 10-day episodic defeat stress used here elicited anxiety- but not depressive-like behaviors, and promoted an increase in ethanol drinking. CRF-CRFR1 signaling in the BNST seems to underlie ethanol intake in non-stressed mice, whereas CRFR2 modulates alcohol consumption in both socially defeated and non-stressed mice with a history of chronic intake.

Context Processing and the Neurobiology of Post-Traumatic Stress Disorder

Progress in clinical and affective neuroscience is redefining psychiatric illness as symptomatic expression of cellular/molecular dysfunctions in specific brain circuits. Post-traumatic stress disorder (PTSD) has been an exemplar of this progress, with improved understanding of neurobiological systems subserving fear learning, salience detection, and emotion regulation explaining much of its phenomenology and neurobiology. However, many features remain unexplained and a parsimonious model that more fully accounts for symptoms and the core neurobiology remains elusive. Contextual processing is a key modulatory function of hippocampal-prefrontal-thalamic circuitry, allowing organisms to disambiguate cues and derive situation-specific meaning from the world. We propose that dysregulation within this context-processing circuit is at the core of PTSD pathophysiology, accounting for much of its phenomenology and most of its biological findings. Understanding core mechanisms like this, and their underlying neural circuits, will sharpen diagnostic precision and understanding of risk factors, enhancing our ability to develop preventive and "personalized" interventions.

The role of glucocorticoids and corticotropin-releasing hormone regulation on anxiety symptoms and response to treatment

The stress response has been linked to the expression of anxiety and depression, but the mechanisms for these connections are under continued consideration. The activation and expression of glucocorticoids and CRH are variable and may hold important clues to individual experiences of mood disorders. This paper explores the interactions of glucocorticoids and CRH in the presentation of anxiety and depressive disorders in an effort to better describe their differing roles in each of these clinical presentations. In addition, it focuses on ways in which extra-hypothalamic glucocorticoids and CRH, often overlooked, may play important roles in the presentation of clinical disorders.

The visible burrow system: A view from across the hall

The visible burrow system (VBS) is an ethologically relevant social stress model that creates a distinct dominance hierarchy in rats. Randall Sakai's laboratory performed an impressive series of studies documenting the very different impact of VBS exposure on the brain and behavior of dominants (DOM) and subordinates (SUBs). Hierarchy formation causes pronounced changes in metabolism in SUBs relative to both DOMs and unstressed controls, resulting in marked weight loss and metabolic imbalance. Stress testing revealed multiple phenotypes in the VBS, including DOMs, stress-responsive SUBs and stress-non-responsive SUBs. Stress-responsive SUBs have adrenal hypertrophy and elevated baseline corticosterone, consistent with prolonged HPA axis activation; however, peak acute stress responses are not sensitized. In contrast, stress non-responsive individuals do not mount a response to an acute stress, suggesting HPA axis hypofunction. In brain, SUBs exhibit a pattern of gene regulation consistent with impaired stress inhibition (e.g., hippocampal adrenocorticosteroid receptor down-regulation and dendritic retraction) and drive of stress pathways (e.g., increased locus coeruleus tyrosine hydroxylase expression). The non-responsive phenotype is distinguished by down-regulation of paraventricular nucleus corticotropin releasing hormone expression and enhanced neuropeptide Y expression in amygdala. The brain 'signature' created by VBS hierarchy formation differed substantially from that of another well-studied chronic stress model (chronic variable stress). Thus, the impact of VBS is mediated by neurocircuit mechanisms at least in part distinct that of other chronic stress modalities, and suggests that the nature of the stressor may be an essential consideration in development of treatment strategies for stress-related diseases.

Behavioral effects of chronically elevated corticosterone in subregions of the medial prefrontal cortex

The medial prefrontal cortex is a key mediator of behavioral aspects of the defense response. Since chronic exposure to elevated glucocorticoids alters the dendritic structure of neurons in the medial prefrontal cortex, such exposure may alter behavioral responses to danger as well. We examined the effects of chronically elevated corticosterone in discrete regions of the medial prefrontal cortex on exploration of the elevated plus-maze. Chronically elevated corticosterone in the prelimbic or infralimbic cortices reduced open arm exploration. This effect was specific to the ventral regions of the medial prefrontal cortex as corticosterone had no effect on plus-maze exploration when administered into the anterior cingulate cortex. Taken together, these findings demonstrate clear regional differences for the effects of corticosterone in the medial prefrontal cortex.

Association between gastrointestinal symptoms and affectivity in patients with bipolar disorder

AIM

To study if anxiety, depression and experience of stress are associated with gastrointestinal (GI) symptoms in patients with bipolar disorder.

METHODS

A total of 136 patients with bipolar disorder (mean age 49.9 years; 61% women) and 136 controls from the general population (mean age 51.0 years; 60% women) were included in the study. GI symptoms were assessed with The Gastrointestinal Symptom Rating Scale-irritable bowel syndrome (GSRS-IBS), level of anxiety and depression with The Hospital Anxiety and Depression Scale (HADS) and stress-proneness with Perceived Stress Questionnaire. Over a ten year period, all visits in primary care were retrospectively recorded in order to identify functional GI disorders.

RESULTS

In subjects with low total HADS-score, there were no significant differences in GI-symptoms between patients and controls (GSRS-IBS 7.0 vs 6.5, P = 0.513). In the patients with bipolar disorder there were significant correlations between all GSRS and HADS subscores for all symptom clusters except for “constipation” and “reflux”. Factors associated to GI symptoms in the patient group were female sex (adjusted OR = 2.37, 95%CI: 1.07-5.24) and high HADS-Depression score (adjusted OR = 3.64, 95%CI: 1.07-12.4). These patients had also significantly more visits for IBS than patients with low HADS-Depression scores (29% vs 8%, P = 0.008). However, there was no significant differences in consulting behaviour for functional GI disorders between patients and controls (25% vs 17%, P = 0.108).

CONCLUSION

Female patients and patients with high HADS depression score reported significantly more GI symptoms, whereas patients with low HADS scores did not differ from control subjects.

Anxiolytic activity of the neuroprotective peptide HLDF-6 and its effects on brain neurotransmitter systems in BALB/c and C57BL/6 mice

This study is focused on a new amide derivative of the peptide HLDF-6 (Thr-Gly-Glu-Asn-His-Arg). This hexapeptide is a fragment of Human Leukaemia Differentiation Factor (HLDF). It displays a broad range of nootropic and neuroprotective activities. We showed, for the first time, that the peptide HLDF-6-amide has high anxiolytic activity. We used 'open field' and 'elevated plus maze' tests to demonstrate anxiolytic effects of HLDF-6-amide (0.1 and 0.3 mg/kg intranasally), which were comparable to those of the reference drug diazepam (0.5 mg/kg). Five daily equipotent doses of HLDF-6-amide selectively mitigated anxiety and increased the density of NMDA receptors in the hippocampus of stress-susceptible BALB/c mice, and had no effect on stress-resilient C57BL/6 mice. The subchronic administration of HLDF-6-amide showed no effect on the density of GABAA and nicotine receptors but was accompanied by a nonselective decrease of the 5-HT2A serotonin receptor density in frontal cortex of both strains. The mechanism of the specific anxiolytic activity of HLDF-6-amide may include its action on the NMDA-glutamatergic receptor system of the hippocampus and on serotonin 5-HT2A-receptors in the prefrontal cortex. The psychotropic activity of HLDF-6-amide is promising for its introduction to medical practice as a highly effective anxiolytic medicine for mental and neurological diseases.

Corticotropin releasing factor type-1 receptor antagonism in the dorsolateral bed nucleus of the stria terminalis disrupts contextually conditioned fear, but not unconditioned fear to a predator odor

The bed nucleus of the stria terminalis (BNST) plays a critical role in fear and anxiety. The BNST is important for contextual fear learning, but the mechanisms regulating this function remain unclear. One candidate mechanism is corticotropin-releasing-factor (CRF) acting at CRF type 1 receptors (CRFr1s). Yet, there has been little progress in elucidating if CRFr1s in the BNST are involved in different types of fear (conditioned and/or unconditioned). Therefore, the present study investigated the effect of antalarmin, a potent CRFr1 receptor antagonist, injected intracerebroventricularly (ICV) and into the dorsolateral BNST (LBNST) during single trial contextual fear conditioning or exposure to the predator odor 2,5-dihydro-2,4,5-trimethylthiazoline (TMT). Neither ICV nor LBNST antalarmin disrupted unconditioned freezing to TMT. In contrast, ICV and LBNST antalarmin disrupted the retention of contextual fear when tested 24h later. Neither ICV nor LBNST antalarmin affected baseline or post-shock freezing-indicating antalarmin does not interfere with the early phases of contextual fear acquisition. Antalarmin did not (1) permanently affect the ability to learn and express contextual fear, (2) change responsivity to footshocks, or (3) affect the ability to freeze. Our findings highlight an important role for CRFr1s within the LBNST during contextually conditioned fear, but not unconditioned predator odor fear.

Estradiol's interesting life at the cell's plasma membrane

Clearly, we have presented here evidence of a very complex set of mechanisms and proteins involved with various and intricate actions of steroids at the plasma membrane. Steroids do MUCH more at the plasma membrane than simply passing passively through it. They may sit in the membrane; they are bound by numerous proteins in the membrane, including ERs, SHBG, steroid-binding globulin receptors, and perhaps elements of cellular architecture such as tubulin. It also seems likely that the membrane itself responds graphically to the presence of steroids by actually changing its shape as well, perhaps, as accumulating steroids. Clara Szego suggested in the 1980s that actions of E2 at one level would act synergistically with its actions at another level (e.g. membrane actions would complement nuclear actions). Given the sheer number of proteins involved in steroid actions, just at the membrane level, it seems unlikely that every action of a steroid on every potential protein effector will act to the same end. It seems more likely that these multiple effects and sites of effect of steroids contribute to the confusion that exists as to what actions steroids always have. For example, there is confusion with regard to synthetic agents (SERMs etc.) that have different and often opposite actions depending on which organ they act upon. A better understanding of the basic actions of steroids should aid in understanding the variability of their clinical effects.

Allelic variation in CRHR1 predisposes to panic disorder: evidence for biased fear processing

Corticotropin-releasing hormone (CRH) is a major regulator of the hypothalamic-pituitary-adrenal axis. Binding to its receptor CRHR1 triggers the downstream release of the stress response-regulating hormone cortisol. Biochemical, behavioral and genetic studies revealed CRHR1 as a possible candidate gene for mood and anxiety disorders. Here we aimed to evaluate CRHR1 as a risk factor for panic disorder (PD). Allelic variation of CRHR1 was captured by 9 single-nucleotide polymorphisms (SNPs), which were genotyped in 531 matched case/control pairs. Four SNPs were found to be associated with PD, in at least one sub-sample. The minor allele of rs17689918 was found to significantly increase risk for PD in females after Bonferroni correction and furthermore decreased CRHR1 mRNA expression in human forebrains and amygdalae. When investigating neural correlates underlying this association in patients with PD using functional magnetic resonance imaging, risk allele carriers of rs17689918 showed aberrant differential conditioning predominantly in the bilateral prefrontal cortex and safety signal processing in the amygdalae, arguing for predominant generalization of fear and hence anxious apprehension. Additionally, the risk allele of rs17689918 led to less flight behavior during fear-provoking situations but rather increased anxious apprehension and went along with increased anxiety sensitivity. Thus reduced gene expression driven by CRHR1 risk allele leads to a phenotype characterized by fear sensitization and hence sustained fear. These results strengthen the role of CRHR1 in PD and clarify the mechanisms by which genetic variation in CRHR1 is linked to this disorder.

Anxiety-like responses induced by nitric oxide within the BNST in mice: Role of CRF1 and NMDA receptors

It has been shown that the bed nucleus of the stria terminalis (BNST) of rats contains nitrergic neurons, which are activated during animal exposure to aversive stimuli. The BNST is also populated by glutamatergic and corticotrophin releasing factor (CRFergic) neurons, which in turn are activated under stressful situations. Here we investigated the anxiogenic-like effects of intra-BNST injections of a nitric oxide (NO) donor, NOC-9 in mice. The role of CRFergic and glutamatergic systems on defensive behavior induced by NOC-9 was investigated with previous intra-BNST infusion of different doses of CP376395, a CRF type 1 receptor antagonist (CRF1), or AP-7, an NMDA (N-methyl-D-aspartate) receptor antagonist. Anxiety-like behavior was assessed immediately and 5 min after intra-BNST drug injection, exposing mice to a novel arena and to the elevated plus-maze (EPM; an anxiogenic situation). Results showed that NOC-9 provoked a short period (≈ 150 s) of freezing behavior in the novel arena and increased anxiety in the EPM. Both CP and AP-7 attenuated the anxiogenic-like effects of NOC-9 in the EPM without changing freezing behavior in the novel arena. When given alone (i.e. without prior intra-BNST injection of NOC-9), AP-7 (0.20 nmol), but not CP (0.75, 1.50, or 3.00 nmol), attenuated anxiety in mice exposed to the EPM. These results suggest that CRF1 and NMDA receptors located within the BNST differentially modulate aversive effects induced by NO production in this limbic forebrain structure.

Epigenetic modulation of chronic anxiety and pain by histone deacetylation

Prolonged exposure of the central amygdala (CeA) to elevated corticosteroids (CORT) facilitates long-term anxiety and pain through activation of glucocorticoid receptors (GRs) and corticotropin-releasing factor (CRF). However, the mechanisms maintaining these responses are unknown. Since chronic phenotypes can be sustained by epigenetic mechanisms, including histone modifications such as deacetylation, we tested the hypothesis that histone deacetylation contributes to the maintenance of chronic anxiety and pain induced by prolonged exposure of the CeA to CORT. We found that bilateral infusions of a histone deacetylase inhibitor into the CeA attenuated anxiety-like behavior as well as somatic and visceral hypersensitivity resulting from elevated CORT exposure. Moreover, we delineated a novel pathway through which histone deacetylation could contribute to CORT regulation of GR and subsequent CRF expression in the CeA. Specifically, deacetylation of histone 3 at lysine 9 (H3K9), through the coordinated action of the NAD+-dependent protein deacetylase sirtuin-6 (SIRT6) and nuclear factor kappa B (NFκB), sequesters GR expression leading to disinhibition of CRF. Our results indicate that epigenetic programming in the amygdala, specifically histone modifications, is important in the maintenance of chronic anxiety and pain.

The smell of fear: innate threat of 2,5-dihydro-2,4,5-trimethylthiazoline, a single molecule component of a predator odor

In the last several years, the importance of understanding what innate threat and fear is, in addition to learning of threat and fear, has become evident. Odors from predators are ecologically relevant stimuli used by prey animals as warnings for the presence of danger. Of importance, these odors are not necessarily noxious or painful, but they have innate threat-like properties. This review summarizes the progress made on the behavioral and neuroanatomical fundamentals of innate fear of the predator odor, 2,5-dihydro-2,4,5-trimethylthiazoline (TMT), a component of fox feces. TMT is one of several single molecule components of predator odors that have been isolated in the last several years. Isolation of these single molecules has allowed for rapid advances in delineating the behavioral constraints and selective neuroanatomical pathways of predator odor induced fear. In naïve mice and rats, TMT induces a number of fear and defensive behaviors, including robust freezing, indicating it is an innate threat stimulus. However, there are a number of behavioral constraints that we do not yet understand. Similarly, while some of the early olfactory sensory pathways for TMT-induced fear are being delineated, the pathways from olfactory systems to emotional and motor output regions are less well understood. This review will focus on what we know and what we still need to learn about the behavior and neuroanatomy of TMT-induced fear.

Studying longitudinal trajectories in animal models of psychiatric illness and their translation to the human condition

Many forms of psychopathology and/or psychiatric illness can occur through the pathways of altered environmental sensitivity, impulsivity, social functioning, and anxious responding. While these traits are also heritable, environmental conditions are known to play a critical role. The genetic factors that contribute to these traits may be adaptive in certain contexts, but can - under the environmental conditions commonly faced among modern humans - also be key moderators of risk for psychopathological outcomes. This article will discuss how animal studies inform us of the various environmental mechanisms through which prenatal or early postnatal environmental challenge can produce long-term effects on behavior and will briefly address how pre-copulatory, pre-natal and early postnatal epigenetic effects can contribute to persistent alterations in offspring behavior. Its main focus will be how nonhuman primate studies have helped us to understand how genetic vulnerability factors can moderate responses to early environmental factors, suggesting pathways through which early stress might produce long-term effects, thus pointing to systems that might moderate risk for psychiatric illnesses in humans.

Peer pressures: social instability stress in adolescence and social deficits in adulthood in a rodent model

Studies in animal models generate and test hypotheses regarding developmental stage-specific vulnerability that might inform research questions about human development. In both rats and humans, peer relationships are qualitatively different in adolescence than at other stages of development, and social experiences in adolescence are considered important determinants of adult social function. This review describes our adolescent rat social instability stress model and the long-lasting effects social instability has on social behaviour in adulthood as well as the possible neural underpinnings. Effects of other adolescent social stress experiences in rats on social behaviours in adulthood also are reviewed. We discuss the role of hypothalamic-pituitary-adrenal (HPA) function and glucocorticoid release in conferring differential susceptibility to social experiences in adolescents compared to adults. We propose that although differential perception of social experiences rather than immature HPA function may underlie the heightened vulnerability of adolescents to social instability, the changes in the trajectory of brain development and resultant social deficits likely are mediated by the heightened glucocorticoid release in response to repeated social stressors in adolescence compared to in adulthood.

Adolescents' internalizing and externalizing problems predict their affect-specific HPA and HPG axes reactivity

We examined psychopathology-neuroendocrine associations in relation to the transition into adolescence within a developmental framework that acknowledged the interdependence of the HPA and HPG hormone systems in the regulation of responses to everyday affective contexts. Saliva samples were collected during anxiety and anger inductions from 51 young adolescents (M 13.47, SD = .60 years) to evaluate cortisol, DHEA, and testosterone responses. Internalizing and externalizing problems were assessed at pre-adolescence (M = 9.27, SD = .58 years) while youths were in elementary school and concurrently with hormones in early adolescence. Externalizing problems from elementary school predicted adolescents' reduced DHEA reactivity during anxiety induction. Follow up analyses simultaneously examining the contributions of elementary school and adolescent problems showed a trend suggesting that youths with higher levels of internalizing problems during elementary school eventuated in a profile of heightened DHEA reactivity as adolescents undergoing anxiety induction. For both the anxiety and the anger inductions, it was normative for DHEA and testosterone to be positively coupled. Adolescents with high externalizing problems but low internalizing problems marshaled dual axes co-activation during anger induction in the form of positive cortisol-testosterone coupling. This is some of the first evidence suggesting affective context determines whether dual axes coupling is reflective of normative or problematic functioning in adolescence.

Identification of the CART neuropeptide circuitry processing TMT-induced predator stress

Abundance of cocaine- and amphetamine-regulated transcript (CART) neuropeptide in the limbic areas like the olfactory system, central nucleus of amygdala (CeA), ventral bed nucleus of stria terminalis (vBNST) and the hypothalamus suggests involvement of the peptide in emotive processing. We examined the role of CART in mediating fear, a strong emotion with profound survival value. Rats, exposed to 2,4,5-trimethyl-3-thiazoline (TMT), a predator related cue extracted from fox feces, showed significant increase in freezing, escape and risk assessment behavior, whereas grooming was reduced. Neuronal activity was up-regulated in the CeA and vBNST in terms of increased immunoreactivity in CART elements and c-Fos expression. Increased expression of both the markers was also seen in some discrete magnocellular as well as parvicellular subdivisions of the paraventricular nucleus (PVN). However, CART containing mitral cells in the main or accessory olfactory bulb did not respond. CART antibody was stereotaxically injected bilaterally into the CeA to locally immunoneutralize endogenous CART. On exposure to TMT, these rats showed reduced freezing, risk assessment and escape behavior while grooming was restored to normal value. We suggest that the CART signaling in the CeA and vBNST, but not in the olfactory system, might be an important component of the innate fear processing, and expression of stereotypic behavior, while CART in the PVN subdivisions might mediate the neuroendocrine response to predator stress.

Efficacy of adjunctive celecoxib treatment for patients with major depressive disorder: a meta-analysis

BACKGROUND

Numerous studies have reported that inflammation is closely associated with depression, and adjunctive non-steroidal anti-inflammatory drug (NSAID) treatment has been suggested as a novel therapeutic approach for depression.

METHODS

We searched electronic databases including Medline, Embase, and the Cochrane Central Register of Controlled Trials. We only included randomized controlled trials comparing adjunctive NSAIDs with placebos for treating depressive episodes.

RESULTS

Of the 654 retrieved entries, we identified four relevant studies with a total of 150 patients (75 NSAID patients and 75 placebo patients) with depressive episodes. All four studies used celecoxib as the NSAID. The patients receiving adjunctive celecoxib had significantly higher mean changes in the Hamilton Rating Scale for Depression scores between baseline and endpoint measurements compared with those receiving placebo (weighted mean difference=3.26, 95% confidence interval; CI=1.81 to 4.71). The adjunctive celecoxib group also showed better remission (odds ratio; OR=6.58, 95% CI=2.55 to 17.00) and response rates (OR=6.49, 95% CI=2.89 to 14.55) than the placebo group. The all-cause drop-out rate was more favorable for the celecoxib group than for the placebo group (OR=0.45, 95% CI=0.18 to 1.13), although the statistical significance was not statistically significant (p=0.09).

CONCLUSION

Adjunctive treatment with NSAIDs, particularly celecoxib, can be a promising strategy for patients with depressive disorder. Future studies with a larger sample size and longer study duration are needed to confirm the efficacy and tolerability of NSAIDs for depression.

Medial prefrontal cortex Transient Receptor Potential Vanilloid Type 1 (TRPV1) in the expression of contextual fear conditioning in Wistar rats

RATIONALE

Contextual fear is evoked by re-exposing an animal to an environment that has been previously paired with an aversive or unpleasant stimulus. It can be assessed by freezing and cardiovascular changes such as increase in mean arterial pressure and heart rate. A marked increase in neuronal activity is associated with contextual fear conditioning, especially in limbic structures involved with defense reactions, such as the ventral portion of medial prefrontal cortex.

OBJECTIVE

Given the fact that transient receptor potential vanilloid type 1 (TRPV1) receptors could be involved in the expression of defensive behavior, the present work tested the hypothesis that TRPV1 manipulation in the ventromedial prefrontal cortex (vMPFC) modulates the expression of contextual conditioned fear.

METHODS

Male Wistar rats received bilateral microinjections into the vMPFC of the TRPV1 receptor antagonists capsazepine (1, 10, and 60 nmol/200 nL) or 6-iodonordihydrocapsaicin (3 nmol/200 nL), and the TRPV1 agonist capsaicin (1 nmol/200 nL) preceded by vehicle or 6-iodonordihydrocapsaicin before re-exposure to the experimental chamber for 10 min, 48 h after conditioning in two different protocols distinct by their aversiveness.

RESULTS

Both antagonists reduced the freezing and cardiovascular responses in the high aversive protocol. Capsaicin caused an increase in fear-associated responses that could be blocked by 6-iodonordihydrocapsaicin.

CONCLUSIONS

Our results indicate that TRPV1 receptors located in the vMPFC have a tonic involvement in the modulation of the expression of contextual fear conditioning.