Impact of maternal deprivation on brain corticotropin-releasing hormone circuits: prevention of CRH receptor-2 mRNA changes by desipramine treatment

Infant pain vs. pain with parental suppression: Immediate and enduring impact on brain, pain and affect

BACKGROUND

In the short term, parental presence while a human infant is in pain buffers the immediate pain responses, although emerging evidence suggests repeated social buffering of pain may have untoward long-term effects.

METHODS/FINDING

To explore the short- and long-term impacts of social buffering of pain, we first measured the infant rat pup's [postnatal day (PN) 8, or 12] response to mild tail shock with the mother present compared to shock alone or no shock. Shock with the mother reduced pain-related behavioral activation and USVs of pups at both ages and reduced Fos expression in the periaqueductal gray, hypothalamic paraventricular nucleus, and the amygdala at PN12 only. At PN12, shock with the mother compared to shock alone differentially regulated expression of several hundred genes related to G-protein-coupled receptors (GPCRs) and neural development, whereas PN8 pups showed a less robust and less coherent expression pattern. In a second set of experiments, pups were exposed to daily repeated Shock-mother pairings (or controls) at PN5-9 or PN10-14 (during and after pain sensitive period, respectively) and long-term outcome assessed in adults. Shock+mother pairing at PN5-9 reduced adult carrageenan-induced thermal hyperalgesia and reduced Fos expression, but PN10-14 pairings had minimal impact. The effect of infant treatment on adult affective behavior showed a complex treatment by age dependent effect. Adult social behavior was decreased following Shock+mother pairings at both PN5-9 and PN10-14, whereas shock alone had no effect. Adult fear responses to a predator odor were decreased only by PN10-14 treatment and the infant Shock alone and Shock+mother did not differ.

CONCLUSIONS/SIGNIFICANCE

Overall, integrating these results into our understanding of long-term programming by repeated infant pain experiences, the data suggest that pain experienced within a social context impacts infant neurobehavioral responses and initiates an altered developmental trajectory of pain and affect processing that diverges from experiencing pain alone.

Early life stress and susceptibility to addiction in adolescence

Early life stress (ELS) is a risk factor for developing a host of psychiatric disorders. Adolescence is a particularly vulnerable period for the onset of these disorders and substance use disorders (SUDs). Here we discuss ELS and its effects in adolescence, especially SUDs, and their correlates with molecular changes to signaling systems in reward and stress neurocircuits. Using a maternal separation (MS) model of neonatal ELS, we studied a range of behaviors that comprise a "drug-seeking" phenotype. We then investigated potential mechanisms underlying the development of this phenotype. Corticotropin releasing factor (CRF) and serotonin (5-HT) are widely believed to be involved in "stress-induced" disorders, including addiction. Here, we show that ELS leads to the development of a drug-seeking phenotype indicative of increased susceptibility to addiction and concomitant sex-dependent upregulation of CRF and 5-HT system components throughout extended brain reward/stress neurocircuits.

Mechanisms of Shared Vulnerability to Post-traumatic Stress Disorder and Substance Use Disorders

Psychoactive substance use is a nearly universal human behavior, but a significant minority of people who use addictive substances will go on to develop an addictive disorder. Similarly, though ~90% of people experience traumatic events in their lifetime, only ~10% ever develop post-traumatic stress disorder (PTSD). Substance use disorders (SUD) and PTSD are highly comorbid, occurring in the same individual far more often than would be predicted by chance given the respective prevalence of each disorder. Some possible reasons that have been proposed for the relationship between PTSD and SUD are self-medication of anxiety with drugs or alcohol, increased exposure to traumatic events due to activities involved in acquiring illegal substances, or addictive substances altering the brain's stress response systems to make users more vulnerable to PTSD. Yet another possibility is that some people have an intrinsic vulnerability that predisposes them to both PTSD and SUD. In this review, we integrate clinical and animal data to explore these possible etiological links between SUD and PTSD, with an emphasis on interactions between dopaminergic, adrenocorticotropic, GABAergic, and glutamatergic neurobehavioral mechanisms that underlie different emotional learning styles.

The immediate effects of weaning stress on the hypothalamus-pituitary-adrenal alteration of newly weaned piglets

This study was conducted to examine the effects of weaning stress on gene expression of specific markers in hypothalamus-pituitary-adrenal (HPA) axis and neuronal activity in the newly weaned piglets. Twelve 28-days-old, newly weaned crossbred (Landrace × Yorkshire × Duroc) male piglets from 6 l (2 piglets/l) were randomly categorized into two groups: (a) weaning stress: piglets were separated from their dams, relocated and mixed with the unacquainted domestic piglets for 2 hr (stress, n = 6); (b) no-stress: piglets stayed with their dams in the farrowing house (NS; n = 6). After weaning stress, all piglets were electrically euthanized and the blood samples/HPA tissues were collected for subsequent analysis, including plasma cortisol and mRNA expression of c-fos, c-jun, corticotropin-releasing hormone (CRH), CRH receptor 1 (CRHR-1) and adrenocorticotropin hormone receptor (MC2R). Results: Weaning stress significantly (p < 0.05) increased the plasma cortisol level and suppressed the expression of c-fos and CRH in hypothalamus. In addition, weaning stress enhanced the mRNA abundance of c-jun and CRHR-1 in the pituitary gland. No significant differences in the gene expression of MC2R and CRHR-1 were observed in the adrenal gland between treatment groups. Taken together, HPA involved in weaning stress and CRHR-1 and c-jun could be potential markers to evaluate the activation of HPA axis.

Modulation of the Hypothalamic-Pituitary-Adrenal Axis by Early Life Stress Exposure

Exposure to stress during critical periods in development can have severe long-term consequences, increasing overall risk on psychopathology. One of the key stress response systems mediating these long-term effects of stress is the hypothalamic-pituitary-adrenal (HPA) axis; a cascade of central and peripheral events resulting in the release of corticosteroids from the adrenal glands. Activation of the HPA-axis affects brain functioning to ensure a proper behavioral response to the stressor, but stress-induced (mal)adaptation of the HPA-axis' functional maturation may provide a mechanistic basis for the altered stress susceptibility later in life. Development of the HPA-axis and the brain regions involved in its regulation starts prenatally and continues after birth, and is protected by several mechanisms preventing corticosteroid over-exposure to the maturing brain. Nevertheless, early life stress (ELS) exposure has been reported to have numerous consequences on HPA-axis function in adulthood, affecting both its basal and stress-induced activity. According to the match/mismatch theory, encountering ELS prepares an organism for similar ("matching") adversities during adulthood, while a mismatching environment results in an increased susceptibility to psychopathology, indicating that ELS can exert either beneficial or disadvantageous effects depending on the environmental context. Here, we review studies investigating the mechanistic underpinnings of the ELS-induced alterations in the structural and functional development of the HPA-axis and its key external regulators (amygdala, hippocampus, and prefrontal cortex). The effects of ELS appear highly dependent on the developmental time window affected, the sex of the offspring, and the developmental stage at which effects are assessed. Albeit by distinct mechanisms, ELS induced by prenatal stressors, maternal separation, or the limited nesting model inducing fragmented maternal care, typically results in HPA-axis hyper-reactivity in adulthood, as also found in major depression. This hyper-activity is related to increased corticotrophin-releasing hormone signaling and impaired glucocorticoid receptor-mediated negative feedback. In contrast, initial evidence for HPA-axis hypo-reactivity is observed for early social deprivation, potentially reflecting the abnormal HPA-axis function as observed in post-traumatic stress disorder, and future studies should investigate its neural/neuroendocrine foundation in further detail. Interestingly, experiencing additional (chronic) stress in adulthood seems to normalize these alterations in HPA-axis function, supporting the match/mismatch theory.

Noise stress changes mRNA expressions of corticotropin-releasing hormone, its receptors in amygdala, and anxiety-related behaviors

Noise is a psychological, environmental stressor that activates limbic sites in the brain. Limbic sites such as the amygdala and the amygdaloid corticotropin-releasing hormone (CRH) system play an important role in integrating stress response. We investigated the association between noise exposures, CRH-related molecules in the amygdala, and behavioral alterations. In total 54 Sprague-Dawley rats were divided into the following three groups: Control (CON), acute noise exposure (ANE), and chronic noise exposure (CNE). The ANE group was exposed to 100 dB white noise only once in 4 h and the CNE group was exposed to the same for 4 h per day for 30 days. Expression profiles of CRH and its receptors CRH-R1 and CRH-R2 were analyzed by quantitative real-time polymerase chain reaction (qPCR). The same stress procedure was applied to the ANE and CNE groups for behavior testing. The anxiety responses of the animals after acute and chronic stress exposure were measured in the defensive withdrawal test. CNE upregulated CRH and CRH-R1 mRNA levels but downregulated CRH-R2 mRNA levels. ANE led to a decrease in both CRH-R1 and CRH-R2 expression. In the defensive withdrawal test, while the ANE increased, CNE reduced anxiety-like behaviors. The present study shows that the exposure of rats to white noise (100 dB) leads to behavioral alterations and molecule-specific changes in the CRH system. Behavioral alterations can be related to these molecular changes in the amygdala.

CRHR1 links peripuberty stress with deficits in social and stress-coping behaviors

Stressful life events during childhood and adolescence are important risk factors for the development of psychopathologies later in life. The corticotropin releasing hormone (CRH) and the CRH receptor 1 (CRHR1) have been implicated in the link between early life adversity and adult anxiety and depression, with rodent studies identifying the very early postnatal period as highly susceptible to this programming. Here, we investigated whether stress exposure during the peripubertal period - comprising juvenility and puberty - is effective in inducing long-lasting changes in the expression of CRHR1 and CRHR2 in the hippocampus and amygdala, and whether treating animals with a CRHR1 antagonist following stress exposure could reverse behavioral alterations induced by peripuberty stress. We show that peripuberty stress leads to enhanced expression of the Crhr1, but not Crhr2, gene in the hippocampal CA1 and the central nucleus of the amygdala, in association with social deficits in the social exploration test and increased stress-coping behaviors in the forced swim test. Treatment with the CRHR1 antagonist NBI30775 (10 mg/kg) daily for 1 week (from P43 to P49), immediately following peripuberty stress exposure, prevented the occurrence of those psychopathological behaviors at adulthood. These findings highlight peripuberty as a period of plasticity for the enduring modulation of the CRHR1 system and support a growing body of data implicating the CRHR1 system in the programming effects of early life stress on eventual psychopathology. They also support recent evidence indicating that temporarily tackling CRHR1 during development might represent a therapeutic opportunity to correct behavioral trajectories linking early stress to adult psychopathology.

Corticotropin releasing hormone receptor 2 (CRHR-2) gene is associated with decreased risk and severity of posttraumatic stress disorder in women

BACKGROUND

The corticotropin releasing hormone (CRH) system has been implicated in a variety of anxiety and mood-based symptoms and disorders. CRH receptor-2 (CRHR-2) plays a role in attenuating biological responses to stressful life events and trauma, making the CRHR-2 gene a strong candidate to study in relationship to PTSD.

METHODS

The sample was 491 trauma-exposed white non-Hispanic veterans and their cohabitating intimate partners assessed via structured interview for lifetime DSM-IV PTSD; just over 60% met criteria for the disorder. Thirty-one single nucleotide polymorphisms (SNPs) in and near CRHR-2, obtained from an array of 2.5 million markers, were tested for association with PTSD diagnosis and symptom severity in the whole sample and in men and women separately.

RESULTS

Ten SNPs showed nominally significant evidence of association with PTSD in the full sample and two SNPs (rs8192496 and rs2190242) were significant after permutation-based multiple testing correction (uncorrected ps = .0004 and .0005, odds ratios = .60 and .58, respectively). Analyses stratified by sex revealed that the effect was specific to women, who comprised 35% of the sample (uncorrected ps = .0003 and .0002, odds ratios = .41 and .35, respectively). Two additional SNPs (rs2267715 and rs2284218) also showed significant association with PTSD in women (both uncorrected ps = .001, both odds ratios = .48).

CONCLUSIONS

Results suggest that CRHR-2 variants may affect risk for PTSD in women by attenuating the stress response and reducing symptoms of the disorder.

Corticotropin-releasing factor receptor type-2 is involved in the cocaine-primed reinstatement of cocaine conditioned place preference in rats

Here we explored the in vivo role of brain corticotropin-releasing factor receptor type-2 (CRFR2) in cocaine-primed reinstatement of drug seeking. Conditioned place preference (CPP) procedure was used to assess the acquisition, extinction and reinstatement of cocaine-seeking behavior in rats. First, expressions of CRFR2 were shown to be affected in a brain region-specific manner within cocaine-induced CPP and cocaine-extinct CPP models. Bilateral blockade of CRFR2 in the dorsal portion of the medial prefrontal cortex (mPFC), or hippocampus (HP) was partially inhibited, but in the dorsal striatum (DS) did not affect, the cocaine-primed reinstatement of cocaine CPP.

Severe life stress and oxidative stress in the brain: from animal models to human pathology

SIGNIFICANCE

Severe life stress (SLS), as opposed to trivial everyday stress, is defined as a serious psychosocial event with the potential of causing an impacting psychological traumatism.

RECENT ADVANCES

Numerous studies have attempted to understand how the central nervous system (CNS) responds to SLS. This response includes a variety of morphological and neurochemical modifications; among them, oxidative stress is almost invariably observed. Oxidative stress is defined as disequilibrium between oxidant generation and the antioxidant response.

CRITICAL ISSUES

In this review, we discuss how SLS leads to oxidative stress in the CNS, and how the latter impacts pathophysiological outcomes. We also critically discuss experimental methods that measure oxidative stress in the CNS. The review covers animal models and human observations. Animal models of SLS include sleep deprivation, maternal separation, and social isolation in rodents, and the establishment of hierarchy in non-human primates. In humans, SLS, which is caused by traumatic events such as child abuse, war, and divorce, is also accompanied by oxidative stress in the CNS.

FUTURE DIRECTIONS

The outcome of SLS in humans ranges from resilience, over post-traumatic stress disorder, to development of chronic mental disorders. Defining the sources of oxidative stress in SLS might in the long run provide new therapeutic avenues.

Alterations in the central CRF system of two different rat models of comorbid depression and functional gastrointestinal disorders

Clinical evidence suggests comorbidity between depression and irritable bowel syndrome (IBS). Early-life stress and genetic predisposition are key factors in the pathophysiology of both IBS and depression. Thus, neonatal maternal separation (MS), and the Wistar-Kyoto (WKY) rat, a genetically stress-sensitive rat strain, are two animal models of depression that display increased visceral hypersensitivity and alterations in the hypothalamic-pituitary-adrenal axis. Corticotrophin-releasing factor (CRF) is the primary peptide regulating this axis, acting through two receptors: CRF1 and CRF2. The central CRF system is also a key regulator in the stress response. However, there is a paucity of studies investigating alterations in the central CRF system of adult MS or WKY animals. Using in-situ hybridization we demonstrate that CRF mRNA is increased in the paraventricular nucleus (PVN) of WKY rats and the dorsal raphé nucleus (DRN) of MS animals, compared to Sprague-Dawley and non-separated controls, respectively. Additionally, CRF1 mRNA was higher in the PVN, amygdala and DRN of both animal models, along with high levels of CRF1 mRNA in the hippocampus of WKY animals compared to control animals. Finally, CRF2 mRNA was lower in the DRN of MS and WKY rats compared to control animals, and in the hippocampus and amygdala of MS rats. These results show that the central CRF system is altered in both animal models. Such alterations may affect HPA axis regulation, contribute to behavioural changes associated with stress-related disorders, and alter the affective component of visceral pain modulation, which is enhanced in IBS patients.

Experiential and genetic contributions to depressive- and anxiety-like disorders: clinical and experimental studies

Stressful events have been implicated in the precipitation of depression and anxiety. These disorders may evolve owing to one or more of an array of neuronal changes that occur in several brain regions. It seems likely that these stressor-provoked neurochemical alterations are moderated by genetic determinants, as well as by a constellation of experiential and environmental factors. Indeed, animal studies have shown that vulnerability to depressive-like behaviors involve mechanisms similar to those associated with human depression (e.g., altered serotonin, corticotropin releasing hormone and their receptors, growth factors), and that the effects of stressors are influenced by previous stressor experiences, particularly those encountered early in life. These stressor effects might reflect sensitization of neuronal functioning, phenotypic changes of processes that lead to neurochemical release or receptor sensitivity, or epigenetic processes that modify expression of specific genes associated with stressor reactivity. It is suggested that depression is a life-long disorder, which even after effective treatment, has a high rate of re-occurrence owing to sensitized processes or epigenetic factors that promote persistent alterations of gene expression.

Sexually dimorphic effects of maternal separation stress on corticotrophin-releasing factor and vasopressin systems in the adult rat brain

Neonatal maternal separation has been widely used to model the well-established causal relationship between stress in early life and the later development of depression. As corticotrophin-releasing factor (CRF) and vasopressin (AVP) have been implicated in depression, we aimed to determine the long-term effects of maternal separation stress on these neuropeptide systems, and also to explore whether these effects are gender-dependent. Immunohistochemical staining of CRF, AVP and c-Fos was used to assess whether these neuropeptide systems were affected following an acute swim stress in male and female maternally separated rats. There was an increase in CRF-immunoreactivity (IR) (p<0.05), and an increased co-localisation of c-Fos and CRF (p<0.05) following stress, in the paraventricular nucleus of the hypothalamus (PVN) of maternally separated female rats only. We found no differences in CRF in the hypothalamus of maternally separated and control male rats. However, male maternally separated rats exhibited decreases in AVP-IR in both the non-stressed and stressed groups relative to controls (p<0.001). These data provide further evidence of the involvement of the neuropeptides CRF and AVP in the long-term maladaptive effects of maternal separation stress in early life. The enhanced CRF response to stress in MS females relative to males suggests that maternal separation stress results in a more reactive neuroendocrinological stress system in females, than in males. Furthermore, the sexually dimorphic effects of maternal separation on these neuropeptides indicate that gender is an important factor influencing the trajectory of early life stress effects on CRF and AVP systems in the brain.

Neurobiology of addiction. An integrative review

Evidence that psychoactive substance use disorders, bulimia nervosa, pathological gambling, and sexual addiction share an underlying biopsychological process is summarized. Definitions are offered for addiction and addictive process, the latter being the proposed designation for the underlying biopsychological process that addictive disorders are hypothesized to share. The addictive process is introduced as an interaction of impairments in three functional systems: motivation-reward, affect regulation, and behavioral inhibition. An integrative review of the literature that addresses the neurobiology of addiction is then presented, organized according to the three functional systems that constitute the addictive process. The review is directed toward identifying candidate neurochemical substrates for the impairments in motivation-reward, affect regulation, and behavioral inhibition that could contribute to an addictive process.

Pathways involved in gut mucosal barrier dysfunction induced in adult rats by maternal deprivation: corticotrophin-releasing factor and nerve growth factor interplay

Neonatal maternal deprivation (NMD) increases gut paracellular permeability (GPP) through mast cells and nerve growth factor (NGF), and modifies corticotrophin-releasing factor (CRF) and corticosterone levels. CRF, corticosterone and mast cells are involved in stress-induced mucosal barrier impairment. Consequently, this study aimed to specify whether corticosteronaemia and colonic expression of both preproCRF and CRF are modified by NMD, and to determine if altered expression may participate in the elevated GPP in connection with NGF and mast cells. Male Wistar rat pups were either separated from postnatal days 2-14, or left undisturbed with their dam. At 12 weeks of age, adult rats were treated with mifepristone (an antagonist of corticoid receptors), alpha-helical CRF((9-41)) (a non-specific CRF receptor antagonist), or SSR-125543 (CRF-R(1) receptor antagonist). We also determined corticosteronaemia and both colonic preproCRF and CRF expression. Then, control rats were treated by CRF, doxantrazole (mast cell stabilizer), BRX-537A (a mast cell activator) and anti-NGF antibody. NMD did not modify colonic CRF level but increased colonic preproCRF expression and corticosteronaemia. Peripheral CRF, via CRF-R(1) receptor, but not corticosterone, was involved in the elevated GPP observed in these rats, through a mast-cell-mediated mechanism, since the increase of GPP induced by exogenous CRF was abolished by doxantrazole. Anti-NGF antibody treatment also reduced the elevated GPP induced by CRF or BRX-537A. CRF acts through CRF-R(1) receptors to stimulate NGF release from mast cells, which participates in the elevated GPP observed in NMD adult rats. This suggests that early traumatic experience induced neuro-endocrine dysfunction, involved in alterations of gut mucosal barrier.

Brain corticotropin-releasing hormone (CRH) circuits in the developing rat: effect of maternal deprivation

Early in life, there is a delicate and critical balance aimed to maintain low hormone responses derived from the stress responsive hypothalamic-pituitary-adrenal axis (HPA). However, in the infant rat hypothalamic corticotrophin-releasing hormone (CRH) stress responses to environmental events are clearly seen even though other elements of the HPA axis may have limited responses. In view of the role of CRH in mediating behavior associated with stress and anxiety, we considered the ontogeny and the effects of prolonged maternal deprivation (DEP) in brain areas that express CRH-related molecules outside the hypothalamus. We hypothesized that DEP would alter the ontogeny of CRH, CRH binding protein and CRH receptor 1 in prefrontal cortex, amygdala, septum and hippocampus, areas that are part of the CRH extra hypothalamic system, and that a differential modulation would be observed in response to restraint. We compared non-deprived animals to animals subjected to 24 h of DEP at 6, 12 and 18 days of life. We found (1) developmental patterns, which were idiosyncratic to the anatomical area examined, and (2) a temporal response of mRNA levels which was also site specific. The genomic changes are not always related to maternal deprivation status, in fact DEP enhanced, suppressed or had no consequence on the underlying ontogenic progression and restraint response of these CRH-related molecules. We conclude that the extra hypothalamic CRH system is a dynamic system responding to developmental and environmental demands challenging the basic assumption of stress hypo responsiveness in the infant rat. This modulation may have important repercussions on morphological organization and events leading to neuroprotection.

Maternal factors and monoamine changes in stress-resilient and susceptible mice: cross-fostering effects

Genetic factors influence stressor-provoked monoamine changes associated with anxiety and depression, but such effects might be moderated by early life experiences. To assess the contribution of maternal influences in determining adult brain monoamine responses to a stressor, strains of mice that were either stressor-reactive or -resilient (BALB/cByJ and C57BL/6ByJ, respectively) were assessed as a function of whether they were raising their biological offspring or those of the other strain. As adults, offspring were assessed with respect to stressor-provoked plasma corticosterone elevations and monoamine variations within discrete stressor-sensitive brain regions. BALB/cByJ mice demonstrated poorer maternal behaviors than C57BL/6ByJ dams, irrespective of the pups being raised. In response to a noise stressor, BALB/cByJ mice exhibited higher plasma corticosterone levels and elevated monoamine turnover in several limbic and hypothalamic sites. The stressor-provoked corticosterone increase in BALB/cByJ mice was diminished among males (but not females) raised by a C57BL/6ByJ dam. Moreover, increased prefrontal cortical dopamine utilization was attenuated among BALB/cByJ mice raised by a C57BL/6ByJ dam. These effects were asymmetrical as a C57BL/6ByJ mice raised by a BALB/cByJ dam did not exhibit increased stressor reactivity. It appears that stressors influence multiple neurochemical systems that have been implicated in anxiety and affective disorders. Although monoamine variations were largely determined by genetic factors, maternal influences contributed to stressor-elicited neurochemical changes in some regions, particularly dopamine activation within the prefrontal cortex.

Activation of the hypothalamic-pituitary-adrenal axis and autonomic nervous system during inflammation and altered programming of the neuroendocrine-immune axis during fetal and neonatal development: lessons learned from the model inflammagen, lipopolysaccharide

The hypothalamic-pituitary-adrenal axis (HPAA) and autonomic nervous system (ANS) are both activated during inflammation as an elaborate multi-directional communication pathway designed to restore homeostasis, in part, by regulating the inflammatory and subsequent immune response. During fetal and neonatal development programming of the HPAA, ANS and possibly the immune system is influenced by signals from the surrounding environment, as part of an adaptive mechanism to enhance the survival of the offspring. It is currently hypothesized that if this programming is either misguided, or the individual's environment is drastically altered such that neuroendocrine programming becomes maladaptive, it may contribute to the pathogenesis of certain diseases. Current research, suggests that exposure to inflammatory signals during critical windows of early life development may influence the programming of various genes within the neuroendocrine-immune axis. This review will provide, (1) an overview of the HPAA and ANS pathways that are activated during inflammation, highlighting studies that have used lipopolysaccharide as a model inflammagen and, (2) evidence to support the hypothesis that inflammatory stress during fetal and neonatal development can alter programming of the neuroendocrine-immune axis, influencing stress and immune responsiveness, and possibly disease resistance later in life.

The effects of acute stress on the regulation of central and basolateral amygdala CRF-binding protein gene expression

Corticotropin-releasing factor (CRF) is a key mediator of the behavioral, autonomic, and endocrine responses to stress. CRF binds two receptors and a CRF-binding protein (CRF-BP), which may inactivate or modulate the actions of CRF at its receptors. The amygdala is an important anatomical substrate for CRF and contains CRF, its receptors, and CRF-BP. Few studies have examined the effects of acute stress on the regulation of amygdala CRF-BP with other CRF system genes. Therefore, we examined the time course of the effects of acute restraint stress on central (CeA) and basolateral (BLA) amygdala CRF system genes. Consistent with our previous study, acute stress increased BLA CRF-BP mRNA shortly after stress offset. Surprisingly, BLA CRF-BP mRNA remained elevated up to 21 h after the stressor. This effect was selective in the BLA as stress did not alter CeA CRF-BP mRNA, and there were no changes in CRF or CRF receptor mRNAs in either amygdala nucleus. These results suggest that alterations in BLA CRF-BP gene expression are a primary response of the BLA/CeA CRF system to acute stress. Because CRF-BP can modulate CRF action, changes in amygdala CRF-BP levels after stress exposure may affect the ability of an organism to adapt to future stressors.

Early life genetic, epigenetic and environmental factors shaping emotionality in rodents

Childhood trauma is known to increase risk for emotional disorders and addiction. However, little is currently understood about the neurodevelopmental basis of these effects, or how genetic and epigenetic factors interact with the environment to shape the systems subserving emotionality. In this review, we discuss the use of rodent models of early life emotional experience to study these issues in the laboratory and present some of our pertinent findings. In rats, postnatal maternal separation can produce lasting increases in emotional behavior and stressor-reactivity, together with alterations in various brain neurotransmitter systems implicated in emotionality, including corticotropin-releasing factor, serotonin, norepinephrine, and glutamate. Genetic differences between inbred mouse strains have been exploited to further study how maternal behavior affects emotional development using techniques such as cross-fostering and generation of inter-strain hybrids. Together with our own recent data, the findings of these studies demonstrate the pervasive influence of maternal and social environments during sensitive developmental periods and reveal how genetic factors determine how these early life experiences can shape brain and behavior throughout life.

The dynamics of the hypothalamic-pituitary-adrenal axis during maternal deprivation

A close contact between the dam and the litter is essential for the normal development of the hypothalamic-pituitary-adrenal (HPA) axis in rats and mice. Maternal signals, as licking and feeding, have been shown to sustain the HPA axis of the pups in a hypo-responsive state. Disruption of this mother-pup interaction by 24 h of maternal deprivation activates the otherwise quiescent stress system of the neonates, resulting in an enhanced adrenal sensitivity to adrenocorticotropic hormone (ACTH) and a decreased expression of central HPA markers, such as corticotropin-releasing hormone (CRH). However, the dynamics of these central and peripheral changes over the 24h period are largely unknown. In this study, we examined the time course of some of the central and peripheral indices of HPA activity during 24 h of maternal deprivation. We measured corticosterone and ACTH in the blood as well as CRH, mineralocorticoid and glucocorticoid receptor expression in the brain. Our results demonstrate that each of the components of the HPA axis responds to maternal deprivation at different time points following removal of the mother and with a very specific time course. The main activation of the HPA axis occurred between 4 h and 8 h of maternal absence. By contrast, during the second half of the deprivation period, negativefeedback mechanisms restrained the further increase in ACTH and corticosterone release. We conclude that maternal deprivation triggers a cascade of sequential changes at the various levels of the stress system, and that measuring only one aspect of the system at one time point does not accurately reflect the dynamic alterations of the HPA axis.