The developmental profile of the corticotropin releasing factor receptor (CRF2) in rat brain predicts distinct age-specific functions

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

Background

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

Methods

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

Results

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

Conclusions

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

Type 1 Corticotropin-Releasing Factor Receptor Differentially Modulates Neurotransmitter Levels in the Nucleus Accumbens of Juvenile versus Adult Rats

Adversity is particularly pernicious in early life, increasing the likelihood of developing psychiatric disorders in adulthood. Juvenile and adult rats exposed to social isolation show differences in anxiety-like behaviors and significant changes in dopamine (DA) neurotransmission in the nucleus accumbens (NAc). Brain response to stress is partly mediated by the corticotropin-releasing factor (CRF) system, composed of CRF and its two main receptors, CRF-R1 and CRF-R2. In the NAc shell of adult rats, CRF induces anxiety-like behavior and changes local DA balance. However, the role of CRF receptors in the control of neurotransmission in the NAc is not fully understood, nor is it known whether there are differences between life stages. Our previous data showed that infusion of a CRF-R1 antagonist into the NAc of juvenile rats increased DA levels in response to a depolarizing stimulus and decreased basal glutamate levels. To extend this analysis, we now evaluated the effect of a CRF-R1 antagonist infusion in the NAc of adult rats. Here, we describe that the opposite occurred in the NAc of adult compared to juvenile rats. Infusion of a CRF-R1 antagonist decreased DA and increased glutamate levels in response to a depolarizing stimulus. Furthermore, basal levels of DA, glutamate, and γ-Aminobutyric acid (GABA) were similar in juvenile animals compared to adults. CRF-R1 protein levels and localization were not different in juvenile compared to adult rats. Interestingly, we observed differences in the signaling pathways of CRF-R1 in the NAc of juveniles compared to adult rats. We propose that the function of CRF-R1 receptors is differentially modulated in the NAc according to life stage.

Early life stress induces a transient increase in hippocampal corticotropin-releasing hormone in rat neonates that precedes the effects on hypothalamic neuropeptides

Early life stress (ELS) programs hypothalamus-pituitary-adrenal (HPA) axis activity and affects synaptic plasticity and cognitive performance in adults; however, the effects of ELS during the temporal window of vulnerability are poorly understood. This study aimed to thoroughly characterize the effects of ELS in the form of periodic maternal separation (MS180) during the time of exposure to stress. Hippocampal corticotropin-releasing hormone (CRH) gene expression and baseline HPA axis activity were analyzed at postnatal (P) days 6, 12, 15, and 21, and in adulthood (P75); these factors were correlated with plasticity markers and adult behavior. Our results indicate that MS180 induces an increase in hippocampal CRH expression at P9, P12, and P15, whereas an increase in hypothalamic CRH expression was observed from P12 to P21. Increased arginine-vasopressin expression and corticosterone levels were observed only at P21. Moreover, MS180 caused transient alterations in hypothalamic synaptophysin expression during early life. As adults, MS180 rats showed a passive coping strategy in the forced swimming test, cognitive impairments in the object location test, increased hypothalamic CRH expression, and decreased oxytocin (OXT) expression. Spearman's analysis indicated that cognitive impairments correlated with CRH and OXT expression. In conclusion, our data indicate that MS180 induces a transient increase in hippocampal CRH expression in neonates that precedes the effects on hypothalamic neuropeptides, confirming the role of increased CRH during the temporal window of vulnerability as a mediator of some of the detrimental effects of ELS on brain development and adult behavior.

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

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

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

Corticotropin-releasing hormone (CRH) is an essential, evolutionarily-conserved stress neuropeptide. In addition to hypothalamus, CRH is expressed in brain regions including amygdala and hippocampus where it plays crucial roles in modulating the function of circuits underlying emotion and cognition. CRH⁺ fibers are found in nucleus accumbens (NAc), where CRH modulates reward/motivation behaviors. CRH actions in NAc may vary by the individual's stress history, suggesting roles for CRH in neuroplasticity and adaptation of the reward circuitry. However, the origin and extent of CRH⁺ inputs to NAc are incompletely understood. We employed viral genetic approaches to map both global and CRH⁺ projection sources to NAc in mice. We injected into NAc variants of a new designer adeno-associated virus that permits robust retrograde access to NAc-afferent projection neurons. Cre-dependent viruses injected into CRH-Cre mice enabled selective mapping of CRH⁺ afferents. We employed anterograde AAV1-directed axonal tracing to verify NAc CRH⁺ fiber projections and established the identity of genetic reporter-labeled cells via validated antisera against native CRH. We quantified the relative contribution of CRH⁺ neurons to total NAc-directed projections. Combined retrograde and anterograde tracing identified the paraventricular nucleus of the thalamus, bed nucleus of stria terminalis, basolateral amygdala, and medial prefrontal cortex as principal sources of CRH⁺ projections to NAc. CRH⁺ NAc afferents were selectively enriched in NAc-projecting brain regions involved in diverse aspects of the sensing, processing and memory of emotionally salient events. These findings suggest multiple, complex potential roles for the molecularly-defined, CRH-dependent circuit in modulation of reward and motivation behaviors.

A role for corticotropin-releasing factor signaling in the lateral habenula and its modulation by early-life stress

Centrally released corticotropin-releasing factor or hormone (extrahypothalamic CRF or CRH) in the brain is involved in the behavioral and emotional responses to stress. The lateral habenula (LHb) is an epithalamic brain region involved in value-based decision-making and stress evasion. Through its inhibition of dopamine-mediated reward circuitry, the increased activity of the LHb is associated with addiction, depression, schizophrenia, and behavioral disorders. We found that extrahypothalamic CRF neurotransmission increased neuronal excitability in the LHb. Through its receptor CRFR1 and subsequently protein kinase A (PKA), CRF application increased the intrinsic excitability of LHb neurons by affecting changes in small-conductance SK-type and large-conductance BK-type K⁺ channels. CRF also reduced inhibitory γ-aminobutyric acid-containing (GABAergic) synaptic transmission onto LHb neurons through endocannabinoid-mediated retrograde signaling. Maternal deprivation is a severe early-life stress that alters CRF neural circuitry and is likewise associated with abnormal mental health later in life. LHb neurons from pups deprived of maternal care exhibited increased intrinsic excitability, reduced GABAergic transmission, decreased abundance of SK2 channel protein, and increased activity of PKA, without any substantial changes in Crh or Crhr1 expression. Furthermore, maternal deprivation blunted the response of LHb neurons to subsequent, acute CRF exposure. Activating SK channels or inhibiting postsynaptic PKA activity prevented the effects of both CRF and maternal deprivation on LHb intrinsic excitability, thus identifying potential pharmacological targets to reverse central CRF circuit dysregulation in patients with associated disorders.

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.

CRF type 1 receptor antagonism in ventral tegmental area of adolescent rats during social defeat: prevention of escalated cocaine self-administration in adulthood and behavioral adaptations during adolescence

BACKGROUND

Activation of corticotropin-releasing factor type 1 receptors (CRF-R1) in the ventral tegmental area (VTA) represents a critical mechanism for social defeat to escalate cocaine self-administration in adult rats.

OBJECTIVE

We determined the acute effect of a CRF-R1 antagonist (CP376395) microinfusion into the VTA prior to each episode of social defeat in adolescent rats and determined whether this drug treatment could prevent later escalation of cocaine taking in early adulthood.

METHODS

Rats were implanted with bilateral cannulae aimed at the VTA 5 days before the first social defeat. Bilateral microinfusion of CP376395 (500 ng/side) or vehicle occurred 20 min before each episode of social defeat on postnatal days (P) 35, 38, 41, and 44. Behavior was quantified on P35 and P44. On P57, rats were implanted with intra-jugular catheters, and subsequent cocaine self-administration was analyzed.

RESULTS

CP376395-treated adolescent rats walked less and were attacked more slowly but were socially investigated more than vehicle-treated adolescents. Vehicle-treated rats showed increased social and decreased non-social exploration from P35 to P44, while CP376395-treated rats did not. Socially defeated, vehicle-treated adolescents took more cocaine during a 24-h unlimited access binge during adulthood. The latency to supine posture on P44 was inversely correlated with later cocaine self-administration during fixed and progressive ratio schedules of reinforcement and during the binge.

CONCLUSIONS

CP376395 treatment in adolescence blocked escalation of cocaine taking in adulthood. Episodes of social defeat stress engender neuroadaptation in CRF-R1s in the VTA that alter coping with social stress and that persist into adulthood.

Fetal and Neonatal HPA Axis

Stress is an integral part of life. Activation of the hypothalamus-pituitary-adrenal (HPA) axis in the adult can be viewed as mostly adaptive to restore homeostasis in the short term. When stress occurs during development, and specifically during periods of vulnerability in maturing systems, it can significantly reprogram function, leading to pathologies in the adult. Thus, it is critical to understand how the HPA axis is regulated during developmental periods and what are the factors contributing to shape its activity and reactivity to environmental stressors. The HPA axis is not a passive system. It can actively participate in critical physiological regulation, inducing parturition in the sheep for instance or being a center stage actor in the preparation of the fetus to aerobic life (lung maturation). It is also a major player in orchestrating mental function, metabolic, and cardiovascular function often reprogrammed by stressors even prior to conception through epigenetic modifications of gametes. In this review, we review the ontogeny of the HPA axis with an emphasis on two species that have been widely studied-sheep and rodents-because they each share many similar regulatory mechanism applicable to our understanding of the human HPA axis. The studies discussed in this review should ultimately inform us about windows of susceptibility in the developing brain and the crucial importance of early preconception, prenatal, and postnatal interventions designed to improve parental competence and offspring outcome. Only through informed studies will our public health system be able to curb the expansion of many stress-related or stress-induced pathologies and forge a better future for upcoming generations.

Molecular evolution of GPCRs: CRH/CRH receptors

Corticotrophin-releasing hormone (CRH) is the pivotal neuroendocrine peptide hormone associated with the regulation of the stress response in vertebrates. However, CRH-like peptides are also found in a number of invertebrate species. The origin of this peptide can be traced to a common ancestor of lineages leading to chordates and to arthropods, postulated to occur some 500 million years ago. Evidence indicates the presence of a single CRH-like receptor and a soluble binding protein system that acted to transduce and regulate the actions of the early CRH peptide. In vertebrates, genome duplications led to the divergence of CRH receptors into CRH1 and CRH2 forms in tandem with the development of four paralogous ligand lineages that included CRH; urotensin I/urocortin (Ucn), Ucn2 and Ucn3. In addition, taxon-specific genome duplications led to further local divergences in CRH ligands and receptors. Functionally, the CRH ligand-receptor system evolved initially as a molecular system to integrate early diuresis and nutrient acquisition. As multicellular organisms evolved into more complex forms, this ligand-receptor system became integrated with the organismal stress response to coordinate homoeostatic challenges with internal energy usage. In vertebrates, CRH and the CRH1 receptor became associated with the hypothalamo-pituitary-adrenal/interrenal axis and the initial stress response, whereas the CRH2 receptor was selected to play a greater role in diuresis, nutrient acquisition and the latter aspects of the stress response.

Stress in adolescence and drugs of abuse in rodent models: role of dopamine, CRF, and HPA axis

RATIONALE

Research on adolescence and drug abuse increased substantially in the past decade. However, drug-addiction-related behaviors following stressful experiences during adolescence are less studied. We focus on rodent models of adolescent stress cross-sensitization to drugs of abuse.

OBJECTIVES

Review the ontogeny of behavior, dopamine, corticotropin-releasing factor (CRF), and the hypothalamic-pituitary-adrenal (HPA) axis in adolescent rodents. We evaluate evidence that stressful experiences during adolescence engender hypersensitivity to drugs of abuse and offer potential neural mechanisms.

RESULTS AND CONCLUSIONS

Much evidence suggests that final maturation of behavior, dopamine systems, and HPA axis occurs during adolescence. Stress during adolescence increases amphetamine- and ethanol-stimulated locomotion, preference, and self-administration under many conditions. The influence of adolescent stress on subsequent cocaine- and nicotine-stimulated locomotion and preference is less clear. The type of adolescent stress, temporal interval between stress and testing, species, sex, and the drug tested are key methodological determinants for successful cross-sensitization procedures. The sensitization of the mesolimbic dopamine system is proposed to underlie stress cross-sensitization to drugs of abuse in both adolescents and adults through modulation by CRF. Reduced levels of mesocortical dopamine appear to be a unique consequence of social stress during adolescence. Adolescent stress may reduce the final maturation of cortical dopamine through D2 dopamine receptor regulation of dopamine synthesis or glucocorticoid-facilitated pruning of cortical dopamine fibers. Certain rodent models of adolescent adversity are useful for determining neural mechanisms underlying the cross-sensitization to drugs of abuse.

Age differences in the impact of forced swimming test on serotonin transporter levels in lateral septum and dorsal raphe

BACKGROUND

Forced swimming test (FST) is an animal model which evaluates behavioral despair and the effect of antidepressants such as the selective serotonin reuptake inhibitors; the FST modifies the expression of some receptors related to antidepressant response, but it is not known whether serotonin transporter (SERT), their main target, is affected by this test in animals of different ages. Antidepressant response has shown age-dependent variations which could be associated with SERT expression. The aim of the present study was to analyze changes in the SERT immunoreactivity (SERT-IR) in dorsal raphe and lateral septum of male rats from different age groups with or without behavioral despair induced by their exposure to the FST, since these two structures are related to the expression of this behavior.

METHODS

Prepubertal (24 PN), pubertal (40 PN), young adult (3-5 months) and middle-aged (12 months) male rats were assigned to a control group (non-FST) or depressed group (FST, two sessions separated by 24 h). Changes in SERT-IR in dorsal raphe and lateral septum were determined with immunofluorescence.

RESULTS

Pubertal and middle-aged rats showed higher levels of immobility behavior compared to prepubertal rats on the FST. SERT-IR showed an age-dependent increase followed by a moderate decrease in middle-aged rats in both structures; a decreased in SERT-IR in lateral septum and dorsal raphe of pubertal rats was observed after the FST.

CONCLUSIONS

Age differences were observed in the SERT-IR of structures related to behavioral despair; SERT expression was modified by the FST in lateral septum and dorsal raphe of pubertal rats.

NMDA receptor activation and calpain contribute to disruption of dendritic spines by the stress neuropeptide CRH

The complex effects of stress on learning and memory are mediated, in part, by stress-induced changes in the composition and structure of excitatory synapses. In the hippocampus, the effects of stress involve several factors including glucocorticoids and the stress-released neuropeptide corticotropin-releasing hormone (CRH), which influence the integrity of dendritic spines and the structure and function of the excitatory synapses they carry. CRH, at nanomolar, presumed-stress levels, rapidly abolishes short-term synaptic plasticity and destroys dendritic spines, yet the mechanisms for these effects are not fully understood. Here we tested the hypothesis that glutamate receptor-mediated processes, which shape synaptic structure and function, are engaged by CRH and contribute to spine destabilization. In cultured rat hippocampal neurons, CRH application reduced dendritic spine density in a time- and dose-dependent manner, and this action depended on the CRH receptor type 1. CRH-mediated spine loss required network activity and the activation of NMDA, but not of AMPA receptors; indeed GluR1-containing dendritic spines were resistant to CRH. Downstream of NMDA receptors, the calcium-dependent enzyme, calpain, was recruited, resulting in the breakdown of spine actin-interacting proteins including spectrin. Pharmacological approaches demonstrated that calpain recruitment contributed critically to CRH-induced spine loss. In conclusion, the stress hormone CRH co-opts mechanisms that contribute to the plasticity and integrity of excitatory synapses, leading to selective loss of dendritic spines. This spine loss might function as an adaptive mechanism preventing the consequences of adverse memories associated with severe stress.

The three-hit concept of vulnerability and resilience: toward understanding adaptation to early-life adversity outcome

Stressful experiences during early-life can modulate the genetic programming of specific brain circuits underlying emotional and cognitive aspects of behavioral adaptation to stressful experiences later in life. Although this programming effect exerted by experience-related factors is an important determinant of mental health, its outcome depends on cognitive inputs and hence the valence an individual assigns to a given environmental context. From this perspective we will highlight, with studies in rodents, non-human primates and humans, the three-hit concept of vulnerability and resilience to stress-related mental disorders, which is based on gene-environment interactions during critical phases of perinatal and juvenile brain development. The three-hit (i.e., hit-1: genetic predisposition, hit-2: early-life environment, and hit-3: later-life environment) concept accommodates the cumulative stress hypothesis stating that in a given context vulnerability is enhanced when failure to cope with adversity accumulates. Alternatively, the concept also points to the individual's predictive adaptive capacity, which underlies the stress inoculation and match/mismatch hypotheses. The latter hypotheses propose that the experience of relatively mild early-life adversity prepares for the future and promotes resilience to similar challenges in later-life; when a mismatch occurs between early and later-life experience, coping is compromised and vulnerability is enhanced. The three-hit concept is fundamental for understanding how individuals can either be prepared for coping with life to come and remain resilient or are unable to do so and succumb to a stress-related mental disorder, under seemingly identical circumstances.

Repeated restraint stress increases basolateral amygdala neuronal activity in an age-dependent manner

Chronic stress is a precipitating factor for affective disorders such as depression and anxiety. This is associated with the effects of chronic stress on the amygdala. Adolescents may be more vulnerable to the effects of chronic stress, which may be related to its impact on amygdala function. However, the stress-induced changes in amygdala neuronal activity, and the age-dependent impact of chronic stress on amygdala neuronal activity have not been studied in depth. In this study, we investigated how repeated restraint impacts basolateral amygdala (BLA) projection neuron activity in both adolescent and adult rats. Using in vivo extracellular recordings from anesthetized rats, we found that repeated restraint increased the number of spontaneously firing neurons in the BLA of adolescent rats, but did not significantly increase the firing rate. In contrast, repeated restraint increased the firing rate of BLA neurons in adult rats, but did not change the number of spontaneously firing neurons. This is the first direct evidence of how stress differently impacts amygdala physiology in adolescent and adult rats. These findings may shed light on the mechanism by which chronic stress may age-dependently precipitate psychiatric disorders.

Postnatal developmental profile of urocortin 1 and cocaine- and amphetamine-regulated transcript in the perioculomotor region of C57BL/6J mice

Urocortin 1 (Ucn 1) is an endogenous corticotropin releasing factor (CRF)-related peptide. Ucn 1 is most highly expressed in the perioculomotor urocortin containing neurons (pIIIu), previously known as the non-preganglionic Edinger-Westphal nucleus (npEW). Various studies indicate that these cells are involved in stress adaptation and the regulation of ethanol (EtOH) intake. However, the developmental trajectory of these neurons remained unexamined. Expression of the cocaine- and amphetamine-regulated transcript (CART), which co-localizes with Ucn 1 in the perioculomotor area (pIII) has been examined prenatally, but not postnatally. The goal of the current study was to characterize the ontogenetic profile of Ucn 1 and CART during postnatal development in C57BL/6J (B6) mice. B6 mice were bred, and brains were collected at postnatal days (PND) 1, 4, 8, 12, 16, 24 and 45. Brightfield immunohistochemical staining for Ucn 1 and CART showed that Ucn 1-immunoreactivity (ir) was absent at PND 1, while CART-ir was already apparent in pIIIu at birth, a finding indicating that although the pIIIu neurons have already migrated to their adult position, Ucn 1 expression is triggered in them at later postnatal stages. Ucn 1-ir gradually increased with age, approaching adult levels at PND 16. This developmental profile was confirmed by double-immunofluorescence, which showed that Ucn 1 was absent in CART-positive cells of pIII at PND 4 and that Ucn 1 and CART are strongly but not completely co-localized in pIII at PND 24. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis confirmed that Ucn 1 mRNA levels are significantly lower at PND 4 and PND 12 than in adult animals. The lack of brain Ucn 1 immunoreactivity at birth and the gradual postnatal increase in Ucn 1 in pIIIu suggests that this peptide plays a greater behavioral role in adulthood than during the early postnatal development of an organism.

The central corticotropin releasing factor system during development and adulthood

Corticotropin releasing factor (CRH) has been shown to contribute critically to molecular and neuroendocrine responses to stress during both adulthood and development. This peptide and its receptors are expressed in the hypothalamus, as well as in limbic brain areas including amygdala and hippocampus. This is consistent with roles for CRH in mediating the influence of stress on emotional behavior and cognitive function. The expression of CRH and of its receptors in hypothalamus, amygdala and hippocampus is age-dependent, and is modulated by stress throughout life (including the first postnatal weeks). Uniquely during development, the cardinal influence of maternal care on the central stress response governs the levels of central CRH expression, and may alter the 'set-point' of CRH-gene sensitivity to stress in a lasting manner.

Corticotropin releasing hormone receptor alterations elicited by acute and chronic unpredictable stressor challenges in stressor-susceptible and resilient strains of mice

Stressors increase corticotropin releasing hormone (CRH) functioning in hypothalamic and frontal cortical brain regions, and thus may contribute to the provocation of anxiety and depressive disorder. As the effects of stressors on these behavioral changes are more pronounced in some strains of mice (e.g., BALB/cByJ) than in others (e.g., C57BL/6ByJ), the present investigation assessed whether acute and chronic stressors would differentially influence CRH receptor immunoreactivity (ir-CRHr) and CRH receptor mRNA expression (CRH(1) and CRH(2)) in the orbital frontal cortex (OFC) of these strains. An acute noise stressor, and to a greater extent a chronic, variable stressor regimen reduced ir-CRHr in BALB/cByJ mice. In contrast, in the hardier C57BL/6ByJ mice the acute stressor increased ir-CRHr in portions of the OFC, whereas a chronic stressor tended to reduce ir-CRHr. However, whereas the acute stressor did not influence CRH(1) mRNA expression, the chronic stressor increased CRH(1) mRNA expression in both mouse strains. The CRH(2) expression appeared in low abundance in both strains and was unaltered by the stressor. In addition to the OFC variations, quantitative immunohistochemistry indicated that the chronic stressor treatment increased CRH immunoreactivity in the median eminence of C57BL/6ByJ mice, but co-expression of CRH and arginine vasopressin (AVP) immunoreactivity was not provoked by the stressors. The data support the view that stressors provoke marked variations of ir-CRHr in the OFC that might contribute to the differential anxiety/depression-like profiles ordinarily apparent in the stressor-vulnerable and -resilient mouse strains.

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.

Corticotropin-releasing hormone during pregnancy is associated with infant temperament

During pregnancy corticotropin-releasing hormone (CRH) is released into maternal and fetal circulation from the placenta. Elevated concentrations of placental CRH are associated with spontaneous preterm birth, but the consequences for infant development, independent of birth outcome, are unknown. In this study, the effects of placental CRH on infant temperament were examined in a sample of 248 full-term infants. Maternal blood samples were collected at 19, 25 and 31 weeks of gestation for CRH analysis. Infant temperament was assessed with measures of fear and distress at 2 months of age. Infants of mothers with low CRH at 25 weeks of gestation scored lower in fear and distress at 2 months. CRH at 19 and 31 weeks' gestation was not significantly associated with measures of infant temperament, suggesting the possibility that there is a sensitive period for its effects. These data suggest that prenatal exposure to CRH may exert influences that persist into the postnatal period.

Differential neuroendocrine responses to chronic variable stress in adult Long Evans rats exposed to handling-maternal separation as neonates

Burgeoning evidence supports a preeminent role for early- and late-life stressors in the development of physio- and psychopathology. Handling-maternal separation (HMS) in neonatal Long Evans hooded rats leads to stable phenotypes ranging from resilient to vulnerable to later stressor exposure. Handling with 180 min of maternal separation yields a phenotype of stress hyper-responsiveness associated with facilitation of regional CRF neurocircuits and glucocorticoid resistance. This study assessed whether or not prolonged HMS (180 min/day, HMS180) on post-natal days 2-14 sensitizes the adult limbic hypothalamo-pituitary-adrenal (LHPA) axis to chronic variable stress (CS) compared to brief HMS (15 min/day, HMS15). We examined regional mRNA densities of corticotropin-releasing factor (CRF), its receptor CRF1, glucocorticoid receptor (GR), and mineralocorticoid receptor (MR); regional CRF1 and CRF2alpha binding, and pituitary-adrenal responses to an acute air-puff startle (APS) stressor in four groups: HMS15, nonstressed; HMS15, stressed; HMS180, nonstressed; HMS180, stressed. As expected we observed exaggerated pituitary-adrenal responses to APS, increased regional CRF mRNA density, decreased regional CRF1 binding, and decreased cortical GR mRNA density in nonstressed HMS180 vs. HMS15 animals. However, in contrast to our hypothesis, CS decreased pituitary-adrenal reactivity and central amygdala CRF mRNA density in HMS180 rats, while increasing cortical GR mRNA density and CRF1 binding. CS had no effect on the pituitary-adrenal response to APS in HMS15 rats, despite tripling hypothalamic paraventricular CRF mRNA density. The data suggest that many effects of prolonged HMS are reversible in adulthood by CS, while the neuroendocrine adaptations imbued by brief HMS are sufficiently stable to restrain pituitary-adrenal stress responses even following CS.

Brain region-specific neuroprotective action and signaling of corticotropin-releasing hormone in primary neurons

CRH regulates the body's response to stressful stimuli by modulating the activity of the hypothalamic pituitary axis. In primary cultures and cell lines, CRH also acts as a potent neuroprotective factor in response to a number of toxins. Using primary neuronal cultures from the cerebellum, cerebral cortex, and hippocampus, we demonstrate that CRH exerts a brain region-specific neuroprotective effect on amyloid beta 25-35 toxicity. At low CRH concentrations (10(-8) M), neuroprotective effects can be observed only in cerebellar and hippocampal cultures, but a higher CRH concentration (10(-7) M) additionally led to the protection of cortical neurons. These neuroprotective effects were inhibited by H89, a specific protein kinase A inhibitor. Western blot analysis, carried out using phospho-specific antibodies directed against MAPK, cAMP response element-binding protein (CREB), and glycogen synthase kinase (GSK)3 beta also resulted in brain legion-specific differences regarding intracellular signaling. Correlating with cell survival, low CRH concentrations resulted in activation of the CREB pathway and inactivation of GSK3 beta in cerebellar and hippocampal cultures, but higher concentrations additionally resulted in activated CREB and inactivated GSK3 beta in cortical cultures. In contrast, MAPK activation occurred only in cortical neurons. Differences in signaling were found to be independent of receptor expression levels because RT-PCR analysis indicated no region-specific differences in CRHR1 mRNA expression.

Mild prenatal stress in rats is associated with enhanced conditioned fear

We tested the hypothesis that prenatal stress would enhance conditioned fear in adult rats. Pregnant Sprague-Dawley rats were stressed by exposure to a novel environment and subcutaneous injection of saline (0.1 ml 0.9% NaCl) at random times daily from Days 14 to 21 of pregnancy. When compared to adult control (CON) male rats from unmanipulated pregnancies, adult prenatally stressed (PS) male rats showed increased freezing behavior in response to acute footshock as well as increased freezing behavior the next day in the same context, without shock delivery. In another experiment, the gestational stressor was examined for elevations in corticosterone and ACTH. At gestational days (G)15, G17, G19 and G21, maternal and fetal plasma was collected. Analysis showed elevations in corticosterone and ACTH in the PS dams when compared to the CON dams. Additionally, increased corticosterone was found in the PS fetuses when compared to the CON fetuses. Finally, some CON and PS litters were examined for alterations in length of gestation, number of pups born, bodyweight on postnatal day (P)1 and anogenital distance on P1 and differences were not found. In conclusion, our data demonstrate that a mild stressor during gestation, sufficient to raise plasma corticosterone and ACTH, is associated with enhanced conditioned fear during adulthood.

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

Corticotropin-releasing hormone (CRH) acts within the brain and pituitary to coordinate the overall endocrinological and behavioral stress response. From postnatal day (PND) 4 to 14, the infant rat displays minimal adrenal response to mild stress. However, maternal deprivation alters the pituitary-adrenal system such that the infants become responsive to specific stimuli. We hypothesized that maternal deprivation would also affect CRH brain circuits. Since tricyclic antidepressants have been shown to decrease the adrenal response to stress in adult rats, we hypothesized that CRH-related changes induced by maternal deprivation would be prevented by this treatment. Thus, we investigated CRH-related molecules on animals that were maternally deprived on PND 13 compared with nondeprived animals. We found that maternal deprivation caused alterations in the gene expression of both CRH receptors (CRHr) 1 and 2 in specific brain regions, and that some of these effects were augmented by chronic isotonic saline injections. There was a significant increase in CRH, CRHr1, and r2 mRNA in the cortex. In amygdala, CRHr1 and r2 mRNAs were decreased. CRHr2 mRNA was also decreased in the ventromedial nucleus of the hypothalamus, whereas an increase was detected in the hippocampal pyramidal cells. One week of desipramine (DES) administration preceding the maternal deprivation event prevented all the deprivation-induced changes in CRHr2 mRNA, regardless of the direction of the original change. We also found that chronic injection treatments enhanced the adrenocortical response and improved the efficiency of negative feedback in maternal deprivation animals. These results demonstrate that maternal deprivation elicits modifications of CRH brain circuits in a site-specific manner, and that the regulation of CRHr2 gene expression is mediated by mechanisms different from those involved with the modulation of CRHr1 in the infant rat.

Stress and the developing hippocampus: a double-edged sword?

The mechanisms that regulate neuronal function are a sum of genetically determined programs and experience. The effect of experience on neuronal function is particularly important during development, because early-life positive and adverse experience (stress) may influence the still "plastic" nervous system long-term. Specifically, for hippocampal-mediated learning and memory processes, acute stress may enhance synaptic efficacy and overall learning ability, and conversely, chronic or severe stress has been shown to be detrimental. The mechanisms that enable stress to act as this "double-edged sword" are unclear. Here, we discuss the molecular mediators of the stress response in the hippocampus with an emphasis on novel findings regarding the role of the neuropeptide known as corticotropin-releasing hormone (CRH). We highlight the physiological and pathological roles of this peptide in the developing hippocampus, and their relevance to the long-term effects of early-life experience on cognitive function during adulthood.

Leptin regulates appetite-related neuropeptides in the hypothalamus of developing rats without affecting food intake

Leptin regulates food intake in adult mammals by stimulating hypothalamic anorexigenic pathways and inhibiting orexigenic ones. In developing rodents, fat stores are low, yet circulating leptin levels are high and do not appear to regulate food intake. We determined whether two appetite-related neuropeptides [neuropeptide Y (NPY) and proopiomelanocortin (POMC)] and food intake behavior are sensitive to leptin [3 mg/kg body weight (BW), ip] in neonates. We measured the effects of 1) acute leptin administration (3 mg/kg BW, ip, 3 h before testing) on food intake on postnatal day (PND) 5, 8, and 10; and 2) chronic leptin treatment (3 mg/kg BW, ip, daily PND3-PND10) on BW gain and fat pads weight on PND10. In addition to hypothalamic POMC and NPY expression, we determined the expression of suppressor of cytokine signaling-3, all subtypes of leptin receptors, and corticotropin-releasing factor receptor-2 mRNA in PND10 pups receiving either an acute (PND10) or a chronic (PND 3-10) leptin (3 mg/kg BW, ip) or vehicle treatment. Brains were removed 30 or 120 min after the last injection. Acute leptin administration did not affect food intake at any age tested. Chronic leptin treatment did not change BW but decreased fat pad weight significantly. In the arcuate nucleus (ARC), acute leptin increased SOCS-3 and POMC mRNA levels, but decreased NPY mRNA levels in the rostral part of ARC. Chronic leptin down-regulated all subtypes of leptin receptors mRNA and decreased NPY mRNA levels in the caudal ARC but had no further effect on POMC expression. Chronic leptin increased corticotropin-releasing factor receptor-2 mRNA levels in the ventromedial hypothalamus. We conclude that despite adult-like effects of leptin on POMC, NPY, and CRFR-2 expression in neonates, leptin does not regulate food intake during early development.

Corticotropin-releasing hormone (CRH) downregulates the function of its receptor (CRF1) and induces CRF1 expression in hippocampal and cortical regions of the immature rat brain

In addition to regulating the neuroendocrine stress response, corticotropin-releasing hormone (CRH) has been implicated in both normal and pathological behavioral and cognitive responses to stress. CRH-expressing cells and their target neurons possessing CRH receptors (CRF1 and CRF2) are distributed throughout the limbic system, but little is known about the regulation of limbic CRH receptor function and expression, including regulation by the peptide itself. Because CRH is released from limbic neuronal terminals during stress, this regulation might play a crucial role in the mechanisms by which stress contributes to human neuropsychiatric conditions such as depression or posttraumatic stress disorder. Therefore, these studies tested the hypothesis that CRH binding to CRF1 influenced the levels and mRNA expression of this receptor in stress-associated limbic regions of immature rat. Binding capacities and mRNA levels of both CRF1 and CRF2 were determined at several time points after central CRH administration. CRH downregulated CRF1 binding in frontal cortex significantly by 4 h. This transient reduction (no longer evident at 8 h) was associated with rapid increase of CRF1 mRNA expression, persisting for >8 h. Enhanced CRF1 expression-with a different time course-occurred also in hippocampal CA3, but not in CA1 or amygdala, CRF2 binding and mRNA levels were not altered by CRH administration. To address the mechanisms by which CRH regulated CRF1, the specific contributions of ligand-receptor interactions and of the CRH-induced neuronal stimulation were examined. Neuronal excitation without occupation of CRF1 induced by kainic acid, resulted in no change of CRF1 binding capacity, and in modest induction of CRF1 mRNA expression. Furthermore, blocking the neuroexcitant effects of CRH (using pentobarbital) abolished the alterations in CRF1 binding and expression. These results indicate that CRF1 regulation involves both occupancy of this receptor by its ligand, as well as "downstream" cellular activation and suggest that stress-induced perturbation of CRH-CRF1 signaling may contribute to abnormal neuronal communication after some stressful situations.

Centrally administered corticotropin-releasing hormone and peripheral injections of strychnine hydrochloride potentiate the acoustic startle response in preweanling rats

Attempts to condition fear potentiation of startle (FPS) in rats younger than 23 days of age have not been successful, regardless of the type of aversively conditioned stimulus used (P. S. Hunt, R. Richardson, & B. A. Campbell, 1994; R. Richardson, G. Paxinos, & J. Lee, 2000; R. Richardson & A. Vishney, 2000). In the present study, the authors report that peripheral injections of strychnine hydrochloride, a glycine receptor antagonist, and intracerebroventricular infusions of corticotropin releasing hormone (CRH) both potentiated the acoustic startle response (ASR) in 16-18-day-old rats. Because strychnine and CRH have distinct sites of activation in the primary startle pathway, it can be concluded that this pathway is functional and modifiable in rats younger than 23 days of age. This finding suggests that the failure to observe conditioned FPS in preweanling rats is due to an immaturity of the secondary fear circuit responsible for enhancing the ASR during a fear state.

Neurobiology of the stress response early in life: evolution of a concept and the role of corticotropin releasing hormone

Over the last few decades, concepts regarding the presence of hormonal and molecular responses to stress during the first postnatal weeks in the rat and the role of the neuropeptide corticotropin releasing hormone (CRH) in these processes, have been evolving. CRH has been shown to contribute critically to molecular and neuroendocrine responses to stress during development. In turn the expression of this neuropeptide in both hypothalamus and amygdala is differentially modulated by single and recurrent stress, and is determined also by the type of stress (eg, psychological or physiological). A likely transcriptional regulatory factor for modulating CRH gene expression, the cAMP responsive element binding protein CREB, is phosphorylated (activated) in the developing hypothalamus within seconds of stress onset, preceding the transcription of the CRH gene and initiating the activation of stress-induced cellular and neuroendocrine cascades. Finally, early life stress may permanently modify the hypothalamic pituitary adrenal axis and the response to further stressful stimuli, and recent data suggest that CRH may play an integral role in the mechanisms of these long-term changes.

Elevated corticotropin releasing hormone/corticotropin releasing hormone-R1 expression in postmortem brain obtained from children with generalized epilepsy

The corticotropin releasing hormone (CRH) system has been suggested to initiate seizure activity in the developing brain. However, human data to support this theory is lacking. In this study, we have demonstrated that the expression of CRH, CRH-binding protein, and CRH-R1 (a CRH membrane receptor) were significantly elevated in cortical tissue obtained from 6 children with generalized epilepsy (mean age 8.2+/-1.5 years) relative to age-matched controls (mean age 7.8+/-1.4 years). In contrast, no significant difference in the expression of CRH-R2 was observed. The advent of CRH-R1 receptor antagonists may prove useful as novel anticonvulsants.

Distribution of mRNAs encoding CRF receptors in brain and pituitary of rat and mouse

Two G protein-coupled receptors have been identified that bind corticotropin-releasing factor (CRF) and urocortin (UCN) with high affinity. Hybridization histochemical methods were used to shed light on controversies concerning their localization in rat brain, and to provide normative distributional data in mouse, the standard model for genetic manipulation in mammals. The distribution of CRF-R1 mRNA in mouse was found to be fundamentally similar to that in rat, with expression predominating in the cerebral cortex, sensory relay nuclei, and in the cerebellum and its major afferents. Pronounced species differences in distribution were few, although more subtle variations in the relative strength of R1 expression were seen in several forebrain regions. CRF-R2 mRNA displayed comparable expression in rat and mouse brain, distinct from, and more restricted than that of CRF-R1. Major neuronal sites of CRF-R2 expression included aspects of the olfactory bulb, lateral septal nucleus, bed nucleus of the stria terminalis, ventromedial hypothalamic nucleus, medial and posterior cortical nuclei of the amygdala, ventral hippocampus, mesencephalic raphe nuclei, and novel localizations in the nucleus of the solitary tract and area postrema. Several sites of expression in the limbic forebrain were found to overlap partially with ones of androgen receptor expression. In pituitary, rat and mouse displayed CRF-R1 mRNA signal continuously over the intermediate lobe and over a subset of cells in the anterior lobe, whereas CRF-R2 transcripts were expressed mainly in the posterior lobe. The distinctive expression pattern of CRF-R2 mRNA identifies additional putative central sites of action for CRF and/or UCN. Constitutive expression of CRF-R2 mRNA in the nucleus of the solitary tract, and stress-inducible expression of CRF-R1 transcripts in the paraventricular nucleus may provide a basis for understanding documented effects of CRF-related peptides at a loci shown previously to lack a capacity for CRF-R expression or CRF binding. Other such "mismatches" remain to be reconciled.

Activation of specific neuronal circuits by corticotropin releasing hormone as indicated by c-fos expression and glucose metabolism

The neuropeptide corticotropin releasing hormone (CRH) is the central nervous system (CNS) transducer of stressful stimuli. Endogenous CRH is released from neuronal terminals in several central nervous system regions-for example, amygdala and hypothalamus-during stress, and exogenous CRH administration mimics stress-related behaviors and hormonal patterns. However, whereas the role of endogenous CRH as a stress neuromodulator has been established, recent findings suggest that the peptide also functions to influence cognitive, emotional, and neuroimmune functions by modulating neuronal communication in a number of circuits. Although anatomic and pharmacologic approaches have provided evidence for this wider spectrum of CRH actions, the discrete regions and specific circuits activated by CRH have not been fully elucidated. In this article, the authors report on the use of two complementary methods to discern specific regions and cell groups activated by the administration of CRH. Glucose metabolism analysis provided quantitative measures of CRH-induced activation, but at a regional resolution; expression of the immediate early gene c-fos permitted a single cell resolution, but underestimated the neuroanatomic extent of CRH-induced activation. Overlapping regions activated using both methods delineated discrete cortical, limbic. and motor pathways. Importantly, cell groups activated by CRH included those possessing either or both members of the CRH receptor family, suggesting that both receptors may mediate the effects of the endogenous ligand. In summary, CRH activates a broad but selective array of neuronal structures belonging to cortical, limbic, and motor circuits. These findings indicate that stress-related release of this peptide may contribute to a spectrum of important modulations of CNS function.

The role of CRF receptor subtypes in stress-induced behavioural responses

The actions of corticotropin-releasing factor (CRF) and CRF-related peptides in the brain and periphery are mediated through multiple receptors. Two CRF receptor subtypes that differ markedly in their pharmacological profiles and anatomical distribution have been identified and characterized. Important advances have been made in understanding CRF and its actions through the development of specific CRF receptor antagonists, application of antisense oligonucleotides, and the production of transgenic mice lacking functional CRF(1) receptors. This chapter describes recent findings with respect to CRF-related peptides and CRF receptors and their role in stress-induced behaviours.

Immunocytochemical distribution of corticotropin-releasing hormone receptor type-1 (CRF(1))-like immunoreactivity in the mouse brain: light microscopy analysis using an antibody directed against the C-terminus

Corticotropin-releasing hormone (CRH) receptor type 1 (CRF(1)) is a member of the receptor family mediating the effects of CRH, a critical neuromediator of stress-related endocrine, autonomic, and behavioral responses. The detailed organization and fine localization of CRF(1)-like immunoreactivity (CRF(1)-LI) containing neurons in the rodent have not been described, and is important to better define the functions of this receptor. Here we characterize in detail the neuroanatomical distribution of CRF(1)-immunoreactive (CRF(1)-ir) neurons in the mouse brain, using an antiserum directed against the C-terminus of the receptor. We show that CRF(1)-LI is abundantly yet selectively expressed, and its localization generally overlaps the target regions of CRH-expressing projections and the established distribution of CRF(1) mRNA, with several intriguing exceptions. The most intensely CRF(1)-LI-labeled neurons are found in discrete neuronal systems, i.e., hypothalamic nuclei (paraventricular, supraoptic, and arcuate), major cholinergic and monoaminergic cell groups, and specific sensory relay and association thalamic nuclei. Pyramidal neurons in neocortex and magnocellular cells in basal amygdaloid nucleus are also intensely CRF(1)-ir. Finally, intense CRF(1)-LI is evident in brainstem auditory associated nuclei and several cranial nerves nuclei, as well as in cerebellar Purkinje cells. In addition to their regional specificity, CRF(1)-LI-labeled neurons are characterized by discrete patterns of the intracellular distribution of the immunoreaction product. While generally membrane associated, CRF(1)-LI may be classified as granular, punctate, or homogenous deposits, consistent with differential membrane localization. The selective distribution and morphological diversity of CRF(1)-ir neurons suggest that CRF(1) may mediate distinct functions in different regions of the mouse brain.

Corticotrophin-releasing hormone and fetal responses in human pregnancy

During human pregnancy, maternal and fetal compartments of the human placenta produce and release corticotrophic-releasing hormone (CRH). Elevations of placental CRH are associated with decreased gestational length (including preterm delivery). The effects of elevated placental CRH on human fetal neurological development are not known. Pregnant women in the 31st and 32nd week of gestation consented to procedures for collection of blood and measurement of fetal heart rate (FHR) in response to a series of 40 vibro-acoustic stimuli (VAS). Measures of habituation and dishabituation were calculated from the FHR. All subjects were followed to delivery. Fetuses (N = 33) of women with highly elevated CRH were least responsive (p < .03) to stimulation after presentation of a novel (dishabituating) stimulus with control for parity, fetal gender, medical (antepartum) risk, and gestational length at term. In a larger sample (N = 156) a polynomial model predicted the pattern of FHR reactivity for the first 15 trials. Placental CRH concentration significantly predicted FHR reactivity after controlling for the effects of trial number, baseline FHR, inter-trial interval, and presence of uterine contractions. Increased maternal CRH levels were significantly related to the length of gestation after controlling for the effects of fetal gender, parity, and medical risk (p = .05). The relationship between length of gestation and FHR was not significant suggesting separate actions of CRH on these events. Elevated placental CRH appears to accelerate certain developmental events (gestational length) and may influence the fetal nervous system. The impaired fetal responses to novelty and increased arousal observed in this study suggest that neurological systems may be targets for placental CRH during sensitive developmental periods.

Infantile spasms: hypothesis-driven therapy and pilot human infant experiments using corticotropin-releasing hormone receptor antagonists

BACKGROUND AND RATIONALE

Infantile spasms (IS) are an age-specific seizure disorder occurring in 1:2,000 infants and associated with mental retardation in approximately 90% of affected individuals. The costs of IS in terms of loss of lifetime productivity and emotional and financial burdens on families are enormous. It is generally agreed that the seizures associated with IS respond poorly to most conventional anticonvulsants. In addition, in the majority of patients, a treatment course with high-dose corticotropin (ACTH) arrests the seizures completely within days, often without recurrence on discontinuation of the hormone. However, the severe side effects of ACTH require development of better treatments for IS. Based on the rapid, all-or-none and irreversible effects of ACTH and on the established physiological actions of this hormone, it was hypothesized that ACTH eliminated IS via an established neuroendocrine feedback mechanism involving suppression of the age-specific endogenous convulsant neuropeptide corticotropin-releasing hormone (CRH). Indeed, IS typically occur in the setting of injury or insult that activate the CNS stress system, of which CRH is a major component. CRH levels may be elevated in the IS brain, and the neuropeptide is known to cause seizures in infant rats, as well as neuronal death in brain regions involved in learning and memory. If 'excess' CRH is involved in the pathogenesis of IS, then blocking CRH receptors should eliminate both seizures and the excitotoxicity of CRH-receptor-rich neurons subserving learning and memory.

PATIENTS AND METHODS

With FDA approval, alpha-helical CRH, a competitive antagonist of the peptide, was given as a phase I trial to 6 infants with IS who have either failed conventional treatment or who have suffered a recurrence. The study was performed at the Clinical Research Center of the Childrens Hospital, Los Angeles. The effects of alpha-helical CRH on autonomic parameters (blood pressure, pulse, temperature, respiration) were determined. In addition, immediate and short-term effects on ACTH and cortisol and on electrolytes and glucose were examined. The potential efficacy of alpha-helical CRH for IS was studied, using clinical diaries and video EEG.

RESULTS

alpha-Helical CRH, a peptide, did not alter autonomic or biochemical parameters. Blocking peripheral CRH receptors was evident from a transient reduction in plasma ACTH and cortisol. No evidence for the compound's penetration of the blood-brain barrier was found, since no central effects on arousal, activity or seizures and EEG patterns were observed. In addition, a striking resistance of the patients' plasma ACTH to the second infusion of alpha-helical CRH was noted.

CONCLUSIONS

Peptide analogs of CRH do not cross the blood-brain barrier, and their effects on peripheral stress hormones are transient and benign. Nonpeptide compouds that reach CNS receptors are required to test the hypothesis that blocking CRH receptors may ameliorate IS and its cognitive consequences.

Differential regulation of the expression of corticotropin-releasing factor receptor type 2 (CRF2) in hypothalamus and amygdala of the immature rat by sensory input and food intake

The physiological consequences of activating corticotropin-releasing factor receptor type 2 (CRF2) are not fully understood. The neuroanatomic distribution of this CRF receptor family member is consistent with roles in mediating the actions of CRF and similar ligands on food intake control and integrative aspects of stress-related behaviors. However, CRF2 expression in the adult rat is not influenced by stress, corticosterone (CORT), or food intake. In immature rat we have demonstrated striking downregulation of CRF2mRNA in hypothalamic ventromedial nucleus (VMH) after 24 hr of maternal deprivation, a paradigm consisting of both physiological/psychological stress and food deprivation. The current study aimed to distinguish which element or elements of maternal deprivation govern CRF2mRNA expression by isolating the effects of food intake and discrete maternal sensory cues on CRF2mRNA levels in VMH and in reciprocally communicating amygdala nuclei. In maternally deprived pups, CRF2mRNA levels in VMH and basomedial (BMA) and medial (MEA) amygdala nuclei were 62, 72, and 102% of control levels, respectively. Sensory inputs of grooming and handling as well as of the pups' own suckling activity-but not food intake-fully restored CRF2mRNA expression in VMH. In contrast, all manipulations tended to increase CRF2mRNA levels in BMA of maternally deprived rats, and surrogate grooming increased CRF2mRNA expression significantly above that of nondeprived controls. CRF2mRNA expression was not influenced significantly by plasma adrenocorticotropic hormone (ACTH) and CORT levels. Thus, in the immature rat, (1) CRF2 expression is regulated differentially in hypothalamic and amygdala regions, and (2) CRF2mRNA levels in VMH are governed primarily by maternal or suckling-derived sensory input rather than food intake or peripheral stress hormones. These findings indicate a region-specific regulation of CRF2mRNA, supporting the participation of the receptor in neurochemically defined circuits integrating sensory cues to influence specific behavioral and visceral functions.

Differential regulation of the expression of corticotropin-releasing factor receptor type 2 (CRF2) in hypothalamus and amygdala of the immature rat by sensory input and food intake

The physiological consequences of activating corticotropin-releasing factor receptor type 2 (CRF2) are not fully understood. The neuroanatomic distribution of this CRF receptor family member is consistent with roles in mediating the actions of CRF and similar ligands on food intake control and integrative aspects of stress-related behaviors. However, CRF2 expression in the adult rat is not influenced by stress, corticosterone (CORT), or food intake. In immature rat we have demonstrated striking downregulation of CRF2mRNA in hypothalamic ventromedial nucleus (VMH) after 24 hr of maternal deprivation, a paradigm consisting of both physiological/psychological stress and food deprivation. The current study aimed to distinguish which element or elements of maternal deprivation govern CRF2mRNA expression by isolating the effects of food intake and discrete maternal sensory cues on CRF2mRNA levels in VMH and in reciprocally communicating amygdala nuclei. In maternally deprived pups, CRF2mRNA levels in VMH and basomedial (BMA) and medial (MEA) amygdala nuclei were 62, 72, and 102% of control levels, respectively. Sensory inputs of grooming and handling as well as of the pups' own suckling activity-but not food intake-fully restored CRF2mRNA expression in VMH. In contrast, all manipulations tended to increase CRF2mRNA levels in BMA of maternally deprived rats, and surrogate grooming increased CRF2mRNA expression significantly above that of nondeprived controls. CRF2mRNA expression was not influenced significantly by plasma adrenocorticotropic hormone (ACTH) and CORT levels. Thus, in the immature rat, (1) CRF2 expression is regulated differentially in hypothalamic and amygdala regions, and (2) CRF2mRNA levels in VMH are governed primarily by maternal or suckling-derived sensory input rather than food intake or peripheral stress hormones. These findings indicate a region-specific regulation of CRF2mRNA, supporting the participation of the receptor in neurochemically defined circuits integrating sensory cues to influence specific behavioral and visceral functions.

Maternal corticotropin-releasing hormone and habituation in the human fetus

Elevated concentrations of maternal corticotrophin-releasing hormone (CRH) during the 2nd and early 3rd trimester of human pregnancy are associated with spontaneous preterm birth, but the effects of maternal CRH on the fetus are unknown. Maternal plasma was collected for analysis of CRH concentration, m = 156.24 +/- 130.91 pg/ml, from 33 pregnant women during Weeks 31-33 of gestation. Immediately after collection of plasma, fetal heart rate (FHR) measures were obtained in response to a challenge with a series of vibroacoustic stimuli. Fetuses of mothers with highly elevated CRH did not respond significantly to the presence of a novel stimulus in a repeated series, p = 0.016. These effects on the FHR response were not related to parity, fetal gender, medical (antepartum) risk, or eventual birth outcomes. Impaired dishabituation in these fetuses of mothers with high concentrations of CRH suggests that neurological systems rich with CRH receptors that support learning and memory, such as parahippocampal regions, may be targets for maternal/placental CRH, with implications for fetal neurological development.