The CRF1 receptor mediates the excitatory actions of corticotropin releasing factor (CRF) in the developing rat brain: in vivo evidence using a novel, selective, non-peptide CRF receptor antagonist

A role of noradrenergic receptors in anxiolytic-like effect of high CRF in the rat frontal cortex

Corticotropin releasing factor (CRF) is a neuropeptide widely distributed in the brain as a hormonal modulator and neurotransmitter. The best known behavioral function of CRF is activation of stress and anxiety via the hypothalamus and limbic structures but the role of CRF in the cortex is still poorly understood. Our previous studies have shown anxiolytic-like effects of high doses of CRF injected into the Fr2 frontal cortex and involvement of CRF1 receptors (R) in that effect. These results seemed to be controversial as most other studies suggested anxiogenic and not anxiolytic effects of CRF1R stimulation. Since stress is associated with adrenergic system, in the present study, we focused on participation of alpha1 and alpha2 or beta adrenergic receptors in the anxiolytic-like effect of CRF. Moreover, we verified whether these effects of CRF in the Fr2 were really connected with CRF1R. Male Wistar rats were bilaterally microinjected with CRF in a dose of 0.2 μg/1 μl/site or with the specific agonist of CRF1R, stressin 1 (0.2-0.0125 μg/1 μl/site) into the Fr2 area. The elevated plus maze (EPM) test was performed 30 min later to assess the anxiolysis. An involvement of noradrenergic receptors in the CRF induced anxiolytic-like effect in the Fr2 was studied by pretreatment with the alpha1 antagonist prazosin, alpha2 agonist clonidine, alpha2 antagonist RS 79948 or beta antagonist propranolol, 20-30 min before CRF. The influence on anxiety was assessed in the EPM test. The results show that anxiolytic behavior after CRF microinjection into the Fr2 area seems to be mainly connected with the CRF1R activation because a similar effect was observed after stressin 1 administration and it was blocked by CRF1R antagonist. The results observed after administration of noradrenergic ligands indicated that anxiolytic effects of CRF in the Fr2 engaged the alpha1 and alpha2 adrenergic receptors but not beta receptors.

Sex differences in the neurochemistry of frontal cortex: Impact of early life stress

Traumatic events during early life have been linked with later life psychopathology. To understand this risk factor, researchers have studied the effects of prenatal and postnatal early life stress on neurochemical changes. Here we review the rodent literature on sex differences and sex-specific impact of early life stress on frontal cortex neurochemistry. This region is implicated in regulating motivation and emotion, which are often disrupted in psychological disorders. The prefrontal cortex (PFC) in particular is one of the last brain regions to develop, and there are sex differences in the rate of this development. To draw direct comparisons between sexes, our review of the literature was restricted to studies where the effects of prenatal or postnatal stress had been described in male and female littermates. This literature included research describing glutamate, γ-amino butyric acid (GABA), corticosteroids, monoamines, and cannabinoids. We found that sex-dependent effects of stress are mediated by the age at which stress is experienced, age at test, and type of stress endured. More research is required, particularly into the effects of adolescent stress on male and female littermates. We hope that a greater understanding of sex-specific susceptibilities in response to stress across development will help to uncover risk factors for psychological disorders in vulnerable populations.

G-Protein coupled receptors: structure and function in drug discovery

The G-protein coupled receptors (GPCRs) superfamily comprise similar proteins arranged into families or classes thus making it one of the largest in the mammalian genome. GPCRs take part in many vital physiological functions making them targets for numerous novel drugs. GPCRs share some distinctive features, such as the seven transmembrane domains, they also differ in the number of conserved residues in their transmembrane domain. Here we provide an introductory and accessible review detailing the computational advances in GPCR pharmacology and drug discovery. An overview is provided on family A-C GPCRs; their structural differences, GPCR signalling, allosteric binding and cooperativity. The dielectric constant (relative permittivity) of proteins is also discussed in the context of site-specific environmental effects.

Tectal CRFR1 receptor involvement in avoidance and approach behaviors in the South African clawed frog, Xenopus laevis

Animals in the wild must balance food intake with vigilance for predators in order to survive. The optic tectum plays an important role in the integration of external (predators) and internal (energy status) cues related to predator defense and prey capture. However, the role of neuromodulators involved in tectal sensorimotor processing is poorly studied. Recently we showed that tectal CRFR1 receptor activation decreases food intake in the South African clawed frog, Xenopus laevis, suggesting that CRF may modulate food intake/predator avoidance tradeoffs. Here we use a behavioral assay modeling food intake and predator avoidance to test the role of CRFR1 receptors and energy status in this tradeoff. We tested the predictions that 1) administering the CRFR1 antagonist NBI-27914 via the optic tecta will increase food intake and feeding-related behaviors in the presence of a predator, and 2) that prior food deprivation, which lowers tectal CRF content, will increase food intake and feeding-related behaviors in the presence of a predator. Pre-treatment with NBI-27914 did not prevent predator-induced reductions in food intake. Predator exposure altered feeding-related behaviors in a predictable manner. Pretreatment with NBI-27914 reduced the response of certain behaviors to a predator but also altered behaviors irrelevant of predator presence. Although 1-wk of food deprivation altered some non-feeding behaviors related to energy conservation strategy, food intake in the presence of a predator was not altered by prior food deprivation. Collectively, our data support a role for tectal CRFR1 in modulating discrete behavioral responses during predator avoidance/foraging tradeoffs.

Tectal CRFR1 receptors modulate food intake and feeding behavior in the South African clawed frog Xenopus laevis

The optic tectum and superior colliculus rapidly inhibit food intake when a visual threat is present. Previous work indicates that CRF, acting on CRFR1 receptors, may play a role in tectal inhibition of feeding behavior and food intake. Here we test the hypothesis that tectal CRFR1 receptors modulate food intake and feeding behavior in juvenile Xenopus laevis. We performed five experiments to test the following questions: 1) Does tectal CRF injection decrease food intake/feeding behavior? 2) Does a selective CRFR1 antagonist block CRF effects on feeding/feeding behavior? 3) Does a reactive stressor decrease food intake/feeding behavior? 4) Does a selective CRFR1 antagonist block reactive stress-induced decrease in feeding/feeding behavior? 5) Does food deprivation increase food intake/feeding behavior? Tectal CRF injections reduced food intake and influenced exploratory behavior, hindlimb kicks, and time in contact with food. These effects were blocked by the selective R1 antagonist NBI-27914. Exposure to a reactive stressor decreased food intake and this effect was blocked by NBI-27914. Neither food intake or feeding behavior changed following 1 wk of food deprivation. Overall, we conclude that activation of tectal CRFR1 inhibits food intake in juvenile X. laevis. Furthermore, tectal CRFR1 receptors appear to be involved in the reduction of food intake that occurs in response to a reactive stressor.

Stress and Seizures: Space, Time and Hippocampal Circuits

Stress is a major trigger of seizures in people with epilepsy. Exposure to stress results in the release of several stress mediators throughout the brain, including the hippocampus, a region sensitive to stress and prone to seizures. Stress mediators interact with their respective receptors to produce distinct effects on the excitability of hippocampal neurons and networks. Crucially, these stress mediators and their actions exhibit unique spatiotemporal profiles, generating a complex combinatorial output with time- and space-dependent effects on hippocampal network excitability and seizure generation.

Upregulations of CRH and CRHR1 in the Epileptogenic Tissues of Patients with Intractable Infantile Spasms

AIM

Infantile spasms (IS) are an age-specific epileptic syndrome with specific clinical symptom and electroencephalogram (EEG) features, lacking treatment options, and a poor prognosis. Excessive endogenous corticotropin-releasing hormone (CRH) in infant brain might result in IS. However, the data from human IS are limited. In our study, we investigated the expressions of CRH and its receptor type 1 (CRHR1) in surgical tissues from patients with IS and autopsy controls.

METHODS

Specimens surgically removed from 17 patients with IS, and six autopsy controls were included in the study. Real-time PCR, Western blotting, and immunostaining were used to detect the expressions of mRNA, protein expression, and distribution. The correlation between variates was analyzed by Spearman rank correlation.

RESULTS

The expressions of CRH and CRHR1 were significantly upregulated in the epileptogenic tissues of IS patients compared with the control group. CRH was distributed mainly in neurons, while CRHR1 was distributed in neurons, astrocytes, and microglia. The expression levels of CRH and CRHR1 were positively correlated with the frequency of epileptic spasms. Moreover, the expression of protein kinase C (PKC), which was an important downstream factor of CRHR1, was significantly upregulated in the epileptogenic tissues of patients with IS and was positively correlated with the CRHR1 expression levels and the frequency of epileptic spasms.

CONCLUSION

These results suggest that the CRH signal transduction pathway might participate in the epileptogenesis of IS, supporting the hypothesis that CRH is related to the pathogenesis of IS.

Postnatal Steroids and Febrile Seizure Susceptibility in Preterm Children

OBJECTIVE

To investigate risk factors, seizure characteristics, and outcomes of febrile seizure (FS) in children born very preterm.

METHODS

This study used a prospective registry data set of 844 preterm infants (birth weight <1500 g and gestational age <32 weeks) admitted to NICUs from 2001 to 2009 in southern Taiwan. We investigated the prevalence, risks, seizure patterns, and outcomes of FS in children aged 5 years.

RESULTS

Among 575 children (follow-up rate, 85.8%) followed up for 5 years, 35 (6.1%) developed FS. The FS and non-FS groups were comparable regarding their mean gestational age, birth weight, 5-minute Apgar score <6, and prenatal and postnatal complications. No difference was observed in the use of prenatal corticosteroids between the 2 groups. The FS group had a significantly higher rate of postnatal corticosteroid treatment than the non-FS group, even after adjusting for confounding factors (odds ratio, 5.4 [95% confidence interval, 1.9-15.8]; P = .006). No differences were observed in IQs or subsequent epilepsy rates between the 2 groups. Although no difference was observed in the age of FS onset or neurodevelopmental outcomes between the 2 groups, children with FS who received postnatal corticosteroid treatment had a significantly lower mean body temperature during the first FS attack compared with those who did not receive postnatal corticosteroid treatment (38.6 ± 0.4°C vs 39.2 ± 0.6°C; P = .034).

CONCLUSIONS

Children born very preterm have a higher rate of FS, and postnatal corticosteroid treatment was associated with FS susceptibility in these children.

Neuropeptides as targets for the development of anticonvulsant drugs

Epilepsy is a common neurological disorder characterized by recurrent seizures. These seizures are due to abnormal excessive and synchronous neuronal activity in the brain caused by a disruption of the delicate balance between excitation and inhibition. Neuropeptides can contribute to such misbalance by modulating the effect of classical excitatory and inhibitory neurotransmitters. In this review, we discuss 21 different neuropeptides that have been linked to seizure disorders. These neuropeptides show an aberrant expression and/or release in animal seizure models and/or epilepsy patients. Many of these endogenous peptides, like adrenocorticotropic hormone, angiotensin, cholecystokinin, cortistatin, dynorphin, galanin, ghrelin, neuropeptide Y, neurotensin, somatostatin, and thyrotropin-releasing hormone, are able to suppress seizures in the brain. Other neuropeptides, such as arginine-vasopressine peptide, corticotropin-releasing hormone, enkephalin, β-endorphin, pituitary adenylate cyclase-activating polypeptide, and tachykinins have proconvulsive properties. For oxytocin and melanin-concentrating hormone both pro- and anticonvulsive effects have been reported, and this seems to be dose or time dependent. All these neuropeptides and their receptors are interesting targets for the development of new antiepileptic drugs. Other neuropeptides such as nesfatin-1 and vasoactive intestinal peptide have been less studied in this field; however, as nesfatin-1 levels change over the course of epilepsy, this can be considered as an interesting marker to diagnose patients who have suffered a recent epileptic seizure.

An intrinsic CRF signaling system within the optic tectum

Previous work indicates that CRF administration inhibits visually guided feeding in amphibians. We used the African clawed frog Xenopus laevis to examine the hypothesis that CRF acts as a neurotransmitter in the optic tectum, the major brain area integrating the visual and premotor pathways regulating visually guided feeding in anurans. Reverse transcriptase PCR revealed that cells in the optic tectum express mRNA for CRF and the CRF R1 receptor but not the CRF R2 receptor. Radioligand binding studies indicated that specific binding of [(125)I]-Tyr-oCRF to tectal cell membranes can be displaced by the CRF R1 antagonists antalarmin or NBI-27914. CRF increased the expression of mRNA encoding regulator of G-protein signaling 2 (rgs2) in tectal explants and this effect was blocked by antalarmin. CRF had no effect on basal glutamate or gamma-aminobutyric acid (GABA) secretion but inhibited secretion of norepinephrine from tectal explants, an effect that completely blocked by antalarmin. Using a homologous radioimmunoassay we determined that CRF release from tectal explants in vitro was potassium- and calcium-dependent. Basal and depolarization-induced CRF secretion was greater from optic tectum than hypothalamus/thalamus, telencephalon, or brainstem. We concluded that the optic tectum possesses a CRF signaling system that may be involved in modulating communication between sensory and motor pathways involved in food intake.

Neurobehavioral risk is associated with gestational exposure to stress hormones

The developmental origins of disease or fetal programming model predict that early exposures to threat or adverse conditions have lifelong consequences that result in harmful outcomes for health. The maternal endocrine 'fight or flight' system is a source of programming information for the human fetus to detect threats and adjust their developmental trajectory for survival. Fetal exposures to intrauterine conditions including elevated stress hormones increase the risk for a spectrum of health outcomes depending on the timing of exposure, the timetable of organogenesis and the developmental milestones assessed. Recent prospective studies, reviewed here, have documented the neurodevelopmental consequences of fetal exposures to the trajectory of stress hormones over the course of gestation. These studies have shown that fetal exposures to biological markers of adversity have significant and largely negative consequences for fetal, infant and child emotional and cognitive regulation and reduced volume in specific brain structures.

Corticotropin-releasing factor modulation of forebrain GABAergic transmission has a pivotal role in the expression of anabolic steroid-induced anxiety in the female mouse

Increased anxiety is commonly observed in individuals who illicitly administer anabolic androgenic steroids (AAS). Behavioral effects of steroid abuse have become an increasing concern in adults and adolescents of both sexes. The dorsolateral bed nucleus of the stria terminalis (dlBnST) has a critical role in the expression of diffuse anxiety and is a key site of action for the anxiogenic neuromodulator, corticotropin releasing factor (CRF). Here we demonstrate that chronic, but not acute, exposure of female mice during adolescence to AAS augments anxiety-like behaviors; effects that were blocked by central infusion of the CRF receptor type 1 antagonist, antalarmin. AAS treatment selectively increased action potential (AP) firing in neurons of the central amygdala (CeA) that project to the dlBnST, increased the frequency of GABA(A) receptor-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) in dlBnST target neurons, and decreased both c-FOS immunoreactivity (IR) and AP frequency in these postsynaptic cells. Acute application of antalarmin abrogated the enhancement of GABAergic inhibition induced by chronic AAS exposure whereas application of CRF to brain slices of naïve mice mimicked the actions of this treatment. These results, in concert with previous data demonstrating that chronic AAS treatment results in enhanced levels of CRF mRNA in the CeA and increased CRF-IR in the dlBnST neuropil, are consistent with a mechanism in which the enhanced anxiety elicited by chronic AAS exposure involves augmented inhibitory activity of CeA afferents to the dlBnST and CRF-dependent enhancement of GABAergic inhibition in this brain region.

Exposure to prenatal psychobiological stress exerts programming influences on the mother and her fetus

BACKGROUND/AIMS

Accumulating evidence from a relatively small number of prospective studies indicates that exposure to prenatal stress profoundly influences the developing human fetus with consequences that persist into childhood and very likely forever.

METHODS

Maternal/fetal dyads are assessed at ∼20, ∼25, ∼31 and ∼36 weeks of gestation. Infant assessments begin 24 h after delivery with the collection of cortisol and behavioral responses to the painful stress of the heel-stick procedure and measures of neonatal neuromuscular maturity. Infant cognitive, neuromotor development, stress and emotional regulation are evaluated at 3, 6 12 and 24 months of age. Maternal psychosocial stress and demographic information is collected in parallel with infant assessments. Child neurodevelopment is assessed with cognitive tests, measures of adjustment and brain imaging between 5 and 8 years of age.

RESULTS

Psychobiological markers of stress during pregnancy, especially early in gestation, result in delayed fetal maturation, disrupted emotional regulation and impaired cognitive performance during infancy and decreased brain volume in areas associated with learning and memory in 6- to 8-year-old children. We review findings from our projects that maternal endocrine alterations that accompany pregnancy and influence fetal/infant/child development are associated with decreased affective responses to stress, altered memory function and increased risk for postpartum depression.

CONCLUSIONS

Our findings indicate that the mother and her fetus both are influenced by exposure to psychosocial and biological stress. The findings that fetal and maternal programming occur in parallel may have important implications for long-term child development and mother/child interactions.

Discovery of N-(1-ethylpropyl)-[3-methoxy-5-(2-methoxy-4-trifluoromethoxyphenyl)-6-methyl-pyrazin-2-yl]amine 59 (NGD 98-2): an orally active corticotropin releasing factor-1 (CRF-1) receptor antagonist

The design, synthesis, and structure-activity relationships of a novel series of pyrazines, acting as corticotropin releasing factor-1 (CRF-1) receptor antagonists, are described. Synthetic methodologies were developed to prepare a number of substituted pyrazine cores utilizing regioselective halogenation and chemoselective derivatization. Noteworthy, an efficient 5-step synthesis was developed for the lead compound 59 (NGD 98-2), which required no chromatography. Compound 59 was characterized as an orally bioavailable, brain penetrant, and highly selective CRF-1 receptor antagonist. Occupancy of rat brain CRF-1 receptors was quantified using ex vivo receptor occupancy assays, using both brain tissue homogenates as well as brain slices receptor autoradiography. Behaviorally, oral administration of 59 significantly antagonized CRF-induced locomotor activity at doses as low as 10 mg/kg and dose-dependently reduced the restraint stress-induced ACTH increases.

NMDAR2B tyrosine phosphorylation regulates anxiety-like behavior and CRF expression in the amygdala

Background

Anxiety disorders are a highly prevalent and disabling class of psychiatric disorders. There is growing evidence implicating the glutamate system in the pathophysiology and treatment of anxiety disorders, though the molecular mechanism by which the glutamate system regulates anxiety-like behavior remains unclear.

Results

In this study, we provide evidence suggesting that tyrosine phosphorylation of the NMDA receptor, an ionotropic glutamate receptor, contributes to anxiety-like behavior. The GluN2B subunit of the NMDA receptor is tyrosine-phosphorylated: Tyr-1472 is the major phosphorylation site. Homozygous knock-in mice that express a Tyr-1472-Phe mutant of GluN2B, which prevents phosphorylation of this site, show enhanced anxiety-like behavior in the elevated plus-maze test. Expression of corticotropin-releasing factor (CRF), which is important for the regulation of anxiety-like behavior, is increased in the amygdala of the knock-in mice. Furthermore, injection of CRF receptor antagonist attenuated the enhanced anxiety-like behavior of the knock-in mice. We also show that elevated plus-maze exposure simultaneously induced de-phosphorylation of Tyr-1472 and increased CRF expression.

Conclusions

These data suggest that Tyr-1472 phosphorylation on GluN2B is important for anxiety-like behavior by negative regulation of CRF expression in the amygdala.

Microinjections of urocortin1 into the nucleus ambiguus of the rat elicit bradycardia

Urocortins are members of the hypothalamic corticotropin-releasing factor (CRF) peptide family. Urocortin1 (UCN1) mRNA has been reported to be expressed in the brainstem neurons. The present investigation was carried out to test the hypothesis that microinjections of UCN1 into the nucleus ambiguus (nAmb) may elicit cardiac effects. Urethane-anesthetized, artificially ventilated, adult male Wistar rats, weighing between 300-350 g, were used. nAmb was identified by microinjections of l-glutamate (5 mM, 30 nl). Microinjections (30 nl) of different concentrations (0.062, 0.125, 0.25, and 0.5 mM) of UCN1 into the nAmb elicited bradycardic responses (26.5 ± 1, 30.1 ± 1.7, 46.9 ± 1.7, and 40.3 ± 2.6 beats/min, respectively). These heart rate responses were not accompanied by significant changes in mean arterial pressure. The bradycardic responses to maximally effective concentration of UCN1 (0.25 mM) were significantly (P < 0.05) attenuated by prior microinjections of a selective antagonist (NBI 27914, 1.5 mM) for CRF type 1 receptor (CRF1R). Prior microinjections of ionotropic glutamate receptor (iGLUR) antagonists [d-(-)-2-amino-7-phosphono-heptanoic acid and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo-(f)quinoxaline-7-sulfonamide disodium] also attenuated the bradycardia elicited by UCN1 microinjections into the nAmb. Microinjections of NBI 27914 (1.5 mM) into the nAmb did not alter baroreflex responses. Bilateral vagotomy abolished the bradycardic responses to microinjections of UCN1 into the nAmb. These results indicated that 1) microinjections of UCN1 into the nAmb elicited bradycardia, 2) the bradycardia was vagally mediated, 3) activation of CRF1Rs in the nAmb was responsible for the actions of UCN1, and 4) activation of iGLURs in the nAmb also participated in the bradycardia elicited by UCN1.

High pregnancy anxiety during mid-gestation is associated with decreased gray matter density in 6-9-year-old children

Because the brain undergoes dramatic changes during fetal development it is vulnerable to environmental insults. There is evidence that maternal stress and anxiety during pregnancy influences birth outcome but there are no studies that have evaluated the influence of stress during human pregnancy on brain morphology. In the current prospective longitudinal study we included 35 women for whom serial data on pregnancy anxiety was available at 19 (+/-0.83), 25 (+/-0.9) and 31 (+/-0.9) weeks gestation. When the offspring from the target pregnancy were between 6 and 9 years of age, their neurodevelopmental stage was assessed by a structural MRI scan. With the application of voxel-based morphometry, we found regional reductions in gray matter density in association with pregnancy anxiety after controlling for total gray matter volume, age, gestational age at birth, handedness and postpartum perceived stress. Specifically, independent of postnatal stress, pregnancy anxiety at 19 weeks gestation was associated with gray matter volume reductions in the prefrontal cortex, the premotor cortex, the medial temporal lobe, the lateral temporal cortex, the postcentral gyrus as well as the cerebellum extending to the middle occipital gyrus and the fusiform gyrus. High pregnancy anxiety at 25 and 31 weeks gestation was not significantly associated with local reductions in gray matter volume.This is the first prospective study to show that a specific temporal pattern of pregnancy anxiety is related to specific changes in brain morphology. Altered gray matter volume in brain regions affected by prenatal maternal anxiety may render the developing individual more vulnerable to neurodevelopmental and psychiatric disorders as well as cognitive and intellectual impairment.

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

An increase in corticotropin-releasing factor (CRF) is a putative factor in the pathophysiology of stress-related disorders. As CRF expression in the central nucleus of the amygdala (CeA) is important in adaptation to chronic stress, we hypothesized that unrestrained synthesis of CRF in CeA would mimic the consequences of chronic stress exposure and cause dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, increase emotionality and disrupt reproduction. To test this hypothesis, we used a lentiviral vector to increase CRF-expression site specifically in CeA of female rats. Increased synthesis of CRF in CeA amplified CRF and arginine vasopressin peptide concentration in the paraventricular nucleus of the hypothalamus, and decreased glucocorticoid negative feedback, both markers associated with the pathophysiology of depression. In addition, continuous expression of CRF in CeA also increased the acoustic startle response and depressive-like behavior in the forced swim test. Protein levels of gonadotropin-releasing hormone in the medial preoptic area were significantly reduced by continuous expression of CRF in CeA and this was associated with a lengthening of estrous cycles. Finally, sexual motivation but not sexual receptivity was significantly attenuated by continuous CRF synthesis in ovariectomized estradiol-progesterone-primed females. These data indicate that unrestrained CRF synthesis in CeA produces a dysregulation of the HPA axis, as well as many of the behavioral, physiological and reproductive consequences associated with stress-related disorders.Molecular Psychiatry (2009) 14, 37-50; doi:10.1038/mp.2008.91; published online 12 August 2008.

The behavioural and electrophysiological effects of CRF in rat frontal cortex

Corticotropin releasing factor (CRF) is a neuropeptide widely distributed in the brain. The role of CRF in the behavioural activity and modulation of anxiety states in several brain structures has been well documented, but its function in the cerebral cortex still remains unknown. The aim of our study was to investigate the effect of CRF injected bilaterally into rat frontal cortex on the locomotor and exploratory activity and anxiety of rats. We also examined the effect of CRF on extracellularly recorded field potentials in rat frontal cortical slices in vitro. Behavioural experiments showed that CRF in doses of 0.05, 0.1, 0.2 microg/1 microl/site decreased locomotor and exploratory activity during a 40-min session in the open field test. In the elevated plus-maze test, CRF in a dose of 0.2 microg/1 microl/site produced a significant anxiolytic-like effect, which was prevented by CRF receptor antagonists (alpha-helicalCRF(9-41) and NBI 27914). Electrophysiological experiments showed that CRF-induced a transient depression of field potentials in slices partly disinhibited by GABA(A) and GABA(B) receptors antagonists. The blockade of NMDA receptors prevented the occurrence of that effect. The obtained results suggest that CRF may have anxiolytic-like effects in the frontal cortex. Moreover, the peptide inhibits locomotor and exploratory activity and depresses excitatory synaptic transmission in a NMDA receptor-dependent manner.

Corticotropin-releasing factor modulates maternal separation-induced ultrasonic vocalization in rat pups via activation of CRF1 receptor

An infant animal isolated from its mother emits vocalizations spanning from the audible to the ultrasonic. These vocalizations are believed to represent distress signals from the pup. However, the neurobiological basis for vocalizations elicited by isolation has not been well characterized under different environmental conditions. The present study was designed to clarify the role of the corticotropin-releasing factor (CRF) system in vocalizations elicited by isolating a rat pup at ambient temperatures of 37 degrees C (temperature of the nest in which the mother and littermates are present) and 24 degrees C (room temperature). Sprague-Dawley rat pups at 7 days old were isolated from their dam, then the number of vocalizations was measured for 5 min. The number of vocalizations increased when ambient temperature was changed from 37 degrees C to 24 degrees C. Systemic administration of CRF (3 or 10 mg/kg) increased the number of vocalizations at 37 degrees C in a dose-dependent manner. CRF-induced increases in the number of vocalizations at 3 mg/kg were completely blocked by a selective CRF1 receptor antagonist, NBI27914 (3 mg/kg), but not by a selective CRF2 receptor antagonist, K41498 (3 mg/kg). NBI27914 (30 mg/kg), but not K41498 (3 mg/kg), suppressed the increased number of vocalizations at 24 degrees C. These results demonstrate involvement of the CRF-CRF1 receptor regulatory system on the modulation of ultrasonic vocalizations by rat pups separated from their dam.

Peripheral and central administration of exogenous urocortin 1 disrupts the fasted motility pattern of the small intestine in rats via the corticotrophin releasing factor receptor 2 and a cholinergic mechanism

BACKGROUND AND AIM

The action of the corticotrophin releasing factor (CRF) receptor on the small intestinal motility has been rarely investigated. The present study aimed to determine the effects of urocortin 1 on small intestinal motility in rats and the CRF receptor subtypes and autonomic pathways mediating the effects.

METHODS

Fasted or fed rats were used to investigate the effect of intravenous or intracerebroventricular urocortin 1 on duodenum and jejunum motility. NBI-27914 and astressin(2)-B (CRF receptor 1 and 2 antagonists, respectively), atropine (an M-receptor antagonist), phentolamine (an alpha-receptor antagonist), propranolol (a beta-receptor antagonist) and N(omega)-Nitro-L-arginine (a nitric oxide synthase [NOS] inhibitor) were applied to determine the involved CRF receptor subtypes and autonomic pathways.

RESULTS

In fasted rats, intravenous or intracerebroventricular injection of urocortin 1 disrupted duodenal and jejunal migrating myoelectric complex pattern, leading to an irregular spiking activity similar to the fed motility pattern. When urocortin 1 was given in the fed state, the fed motility pattern remained unchanged. In addition, urocortin 1 also inhibited small intestinal transit function. Astressin(2)-B injected intraperitoneally or intracerebroventricularly blocked urocortin 1-induced change, while NBI-27914 had no effect. The disruption of migrating myoelectric complex induced by urocortin 1 was abolished by atropine, but not affected by phentolamine, propranolol and N(omega)-Nitro-L-arginine.

CONCLUSION

Intravenous or intracerebroventricular injection of urocortin 1 acts, respectively, on peripheral and central CRF receptor 2 to disrupt the intestinal migrating myoelectric complex through an M-receptor-dependent mechanism, and such change has an inhibitory effect as proved by measuring the small intestinal transit function.

Cellular localization of the full-length isoform of the type 2 corticotropin releasing factor receptor in the postnatal mouse cerebellar cortex

Corticotropin releasing factor (CRF) and its cognate receptors, defined as Type 1 and Type 2 have been localized within the cerebellum. The Type 2 CRF receptor (CRF-R2) is known to have both a full length (CRF-R2alpha) and a truncated (CRF-R2alpha-tr) isoform. A recent study documented CRF-R2alpha primarily in Bergann glia and astrocytes, as well as in populations of Purkinje cells in the adult cerebellum. The goal of the present study is to determine if CRF-R2alpha is present in the postnatal cerebellum, and if so to describe its cellular distribution. RT-PCR data showed that CRF-R2alpha is expressed in the mouse cerebellum from birth through postnatal day 21. Between birth and P14, CRF-R2alpha-immunoreactivity was localized within the somata of Purkinje cells, and migrating GABAergic interneurons. GFAP-immunoreactive astrocytes, including Bergmann glia, also expressed CRF-R2alpha-immunoreactivity from P3-P14. There is a change, however, in CRF-R2alpha immunolabeling within neurons as the cerebellum matures. Compared to its expression in the adult cerebellum, Purkinje cells, and GABAergic interneurons showed more extensive CRF-R2alpha immunolabeling during early postnatal development. We postulate that CRF-R2alpha could be involved in developmental events related to the survival and differentiation of Purkinje cells and GABAergic neurons, whereas in the adult, this isoform of the CRF receptor family is likely involved in modulating Bergmann glia that have been shown to play a role in regulating the synaptic environment around Purkinje neurons.

Potential uses of corticotropin-releasing hormone antagonists

Corticotropin-releasing hormone (CRH), its natural homologs urocortins (UCN) 1, 2, and 3, and several types of CRH receptors (R), coordinate the behavioral, endocrine, autonomic, and immune responses to stress. The potential use of CRH antagonists is currently under intense investigation. Selective antagonists have been used experimentally to clarify the role of CRH-related peptides in anxiety and depression, addictive behavior, inflammatory disorders, acute and chronic neurodegeneration, and sleep disorders, as well as preterm labor.

The corticotropin-releasing factor receptor: a novel target for the treatment of depression and anxiety-related disorders

The treatment of mood disorders has been the subject of intense study for more than half a century and has resulted in the discovery and availability of a number of compounds that have seen tremendous success in the management of major depression and anxiety-related disorders. In spite of this success, these drugs have not provided a complete therapeutic solution for all patients and this has revitalised the need for a greater understanding of the underlying molecular mechanisms and targets involved in these disorders. Elucidation of these novel targets will enable the development of a better class of compounds which could benefit a greater majority of the patient population and be devoid of the current side effect liabilities. Towards that end, this review examines, in detail, the prospect of one such target, the corticotropin-releasing factor system, as having an enhanced therapeutic profile with the potential of a broader range of efficacy with reduced side effect liabilities.

Evidence for the presence of the type 2 corticotropin releasing factor receptor in the rodent cerebellum

Corticotropin releasing factor (CRF), localized in afferent inputs to the cerebellum, binds to two receptors defined as the Type 1 (CRF-R1) and the Type 2 (CRF-R2alpha). CRF-R1 has been localized to the cerebellum, as has a truncated isoform of CRF-R2alpha. Evidence for the presence of the full length isoform of CRF-R2alpha in the cerebellum is conflicting. We used RT-PCR, immunohistochemical, and physiologic techniques to resolve this conflict. RT-PCR data show low levels of CRF-R2alpha in the vermis and hemisphere of the cerebellum. These observations were confirmed by the Gene Expression Nervous System Atlas (GENSAT) database. A CRF-R2alpha antibody was used to determine the cellular distribution of the receptor in the cerebellum. The vast majority of the receptors are localized to Bergmann glial cells located throughout the cerebellum, as well as astrocytes in the granule cell layer. Neuronal labeling is present in sub-populations of Purkinje cells, Golgi cells, basket cells, and cerebellar nuclear neurons. Physiologic data show that urocortin II, which binds selectively to CRF-R2alpha, increases the firing rate of both Purkinje cells and nuclear neurons; this response can be blocked by the CRF-R2alpha-specific antagonist, antisauvagine-30. The present results confirm that CRF-R2alpha is present in the cerebellum and functions in circuits that modulate the firing rate of Purkinje cells and cerebellar nuclear neurons. A comparative analysis showed that the patterns of distribution of CRF-R1, CRF-R2alpha and CRF-R2alpha-tr are distinct. These data indicate that the CRF family of peptides modulates cerebellar output by binding to multiple CRF receptors.

Differential disinhibition of the neonatal hypothalamic- pituitary-adrenal axis in brain-specific CRH receptor 1-knockout mice

In the adult, corticotropin-releasing hormone (CRH) is the key mediator for the behavioural and neuroendocrine response to stress. It has also been hypothesized that, during postnatal development of the stress system, CRH controls the activity of the HPA axis and mediates the effects of early disturbances, e.g. 24 h of maternal deprivation. In the current study we investigated the function of specific brain corticotropin-releasing hormone receptor type 1 (CRHR1) subpopulations in the control of the HPA axis during postnatal development under basal conditions as well as after 24 h of maternal deprivation. We used two conditional CRHR1-deficient mouse lines which lack this receptor, either specifically in forebrain and limbic structures (Cam-CRHR1) or in all neurons (Nes-CRHR1). Basal circulating corticosterone was increased in Nes-CRHR1 mice compared to controls. Corticosterone response to maternal deprivation was significantly increased in both CRHR1-deficient lines. In the paraventricular nucleus, Cam-CRHR1 animals displayed enhanced CRH and decreased vasopressin expression levels. In contrast, gene expression in Nes-CRHR1 pups was strikingly similar to that in maternally deprived control pups. Furthermore, maternal deprivation resulted in an enhanced response of Cam-CRHR1 pups in the brain, while expression levels in Nes-CRHR1 mouse pups were mostly unchanged. Our results demonstrate that brainstem and/or hypothalamic CRHR1 contribute to the suppression of basal corticosterone secretion in the neonate, while limbic and/or forebrain CRHR1 dampen the activation of the neonatal HPA axis induced by maternal deprivation.

Hippocampal neuroplasticity induced by early-life stress: functional and molecular aspects

Whereas genetic factors contribute crucially to brain function, early-life events, including stress, exert long-lasting influence on neuronal function. Here, we focus on the hippocampus as the target of these early-life events because of its crucial role in learning and memory. Using a novel immature-rodent model, we describe the deleterious consequences of chronic early-life 'psychological' stress on hippocampus-dependent cognitive tasks. We review the cellular mechanisms involved and discuss the roles of stress-mediating molecules, including corticotropin releasing hormone, in the process by which stress impacts the structure and function of hippocampal neurons.

Pediatric epilepsy models

Pediatric epilepsy models are needed to help with development of drugs for specific childhood and infantile epilepsy syndromes. The major forms of pediatric epilepsy can be divided into those that occur in the neonatal period, infancy, early childhood and late childhood. Seizures in the immature brain are different from those in adult brain, often resulting in neuronal death. Rodent models are useful in mimicking seizures in the immature brain (neonatal seizures, infantile spasms, and febrile seizures). No specific models exist for syndromes (e.g., Lennox-Gastaut, Landau-Kleffner). The interaction between brain development and epilepsy in humans can be assisted by use of high resolution MRI, diffusion tensor imaging, and functional MRI.

Vital functions of corticotropin-releasing factor (CRF) pathways in maintenance and regulation of energy homeostasis

Regulation of energy homeostasis is a vital function of the CNS requiring adaptive responses to maintain and support life after stress perturbations. The mechanisms whereby these processes occur are, however, only partially understood. A major determinate of these responses is corticotropin-releasing factor (CRF). Receptors for CRF, CRFR1 and CRFR2, have been hypothesized to play distinct roles in the alterations necessary for homeostatic maintenance. The function of CRFR2, in particular, has remained elusive despite its presence in both the CNS and periphery. In this work, we have used complimentary gene deletion and pharmacological approaches to elucidate the crucial role CRFR2 plays in the regulation of regional tissue thermogenesis and adaptive physiology. Analyses of interscapular brown adipose tissue (IBAT) thermogenesis by thermal signature analysis and the concordant biochemical changes in key sympathetic components in mice deficient for CRFR2 revealed significantly elevated basal IBAT thermogenesis and prolonged adrenergic responsivity of IBAT in older mice. Measurement of metabolic rates by indirect calorimetry after chronic high-fat diet challenge and treatment with the CRFR1 antagonist NBI-27914 revealed a decreased respiratory exchange ratio of these mice that was normalized with NBI-27914. Further, as a definitive measure for physiological pathology, mice examined in a behavioral model of differential temperature selection showed a predilection for warmer external temperatures, supporting a loss of body heat in these mice. These studies provide physiological, biochemical, and behavioral evidence for the critical participation of CRF pathways in the maintenance and adaptive responses necessary for regulation of energy homeostasis.

Regulation of Synaptic Transmission by CRF Receptors

Corticotropin-releasing factor (CRF or CRH) and its family of related peptides have long been recognized as hypothalamic-pituitary-adrenal (HPA) axis peptides that function to regulate the release of other hormones, e.g., ACTH. In addition, CRF acts outside the HPA axis not as a hormone, but as a regulator of synaptic transmission, pre- and post-synaptically, within specific CNS neuronal circuits. Synaptic transmission within the nervous system is today understood to be a more complex process compared to the concepts associated with the term 'synapse' introduced by Sherrington in 1897. Based on more than a century of progress with modern cellular and molecular experimental techniques, prior definitions and functions of synaptic molecules and their receptors need to be reconsidered (see Glossary and Fig. 1), especially in light of the important roles for CRF, its family of peptides and other potential endogenous regulators of neurotransmission, e.g., vasopressin, NPY, etc. (see Glossary). In addition, the property of 'constitutive activity' which is associated with G-protein coupled receptors (GPCRs) provides a persistent tonic mechanism to fine-tune synaptic transmission during both acute and chronic information transfer. We have applied the term 'regulator', adapted from the hormone literature, to CRF, as an example of a specific endogenous substance that functions to facilitate or depress the actions of neuromodulators on fast and slow synaptic responses. As such, synaptic neuroregulators provide a basic substrate to prime or initiate silently plastic processes underlying neurotransmitter-mediated information transfer at CNS synapses. Here we review the role of CRF to regulate CNS synaptic transmission and also suggest how under a variety of allostatic changes, e.g., associated with normal plasticity, or adaptations resulting from mental disorders, the synaptic regulatory role for CRF may be 'switched' in its polarity and/or magnitude in order to provide a coping mechanism to deal with daily and life-long stressors. Thus, a prominent role we assign to non-HPA axis CRF, its family of peptides, and their receptors, is to maintain both acute and chronic synaptic stability.

The therapeutic potential of CRF1 antagonists for anxiety

Preclinical studies suggest that the brain corticotropin-releasing factor (CRF) systems mediate anxiety-like behavioural and somatic responses through actions at the CRF1 receptor. CRF1 antagonists block the anxiogenic-like effects of CRF and stress in animal models. Cerebrospinal fluid levels of CRF are elevated in some anxiety disorders and normalise with effective treatment, further implicating CRF systems as a therapeutic target. Prototypical CRF1 antagonists are highly lipophilic, non-competitive antagonists of peptide ligands. Modification of the chemotype and the identification of novel pharmacophores are yielding more drug-like structures with increased hydrophilicity at physiological pHs. Newer compounds exhibit improved solubility, pharmacokinetic properties, potency and efficacy. Several clinical candidates have entered Phase I/II trials. However, unmet challenges await resolution during further discovery, clinical development and therapeutic application of CRF1 antagonists.

Differential adaptive responses to chronic stress of maternally stressed male mice offspring

It is well established that stress in early life can alter the activity of the hypothalamus-pituitary-adrenal (HPA) axis, but most studies to date have focused on HPA reactivity in response to a single acute stress. The present study addressed whether stress in pregnant mice could influence the adaptive responses of their offspring to chronic stress. Male offspring were exclusively used in this study. Elevated plus maze tests revealed that 14 d of repeated restraint stress (6 h per day; from postnatal d 50-63) significantly increased anxiety-like behavior in maternally stressed mice. NBI 27914, a CRH receptor antagonist, completely eliminated anxiety-related behaviors in a dose-dependent manner, indicating an involvement of a hyperactive CRH system. In accordance with increased anxiety, CRH contents in the hypothalamus and amygdala were significantly higher in these mice. Despite an increased basal activity of the CRH-ACTH system, the combination of chronic prenatal and postnatal stress resulted in a significant reduction of basal plasma corticosterone level, presumably because of a defect in adrenal function. Along with alterations in hypothalamic and hippocampal corticosteroid receptors, it was also demonstrated that a dysfunction in negative feedback inhibition of the HPA axis could be deteriorated by chronic stress in maternally stressed male mice. Taken together, these results indicate that exposure to maternal stress in the womb can affect an animal's coping capacity to chronic postnatal stress.

Modulation of dendritic differentiation by corticotropin-releasing factor in the developing hippocampus

The interplay of environmental and genetic factors in the developmental organization of the hippocampus has not been fully elucidated. The neuropeptide corticotropin-releasing factor (CRF) is released from hippocampal interneurons by environmental signals, including stress, to increase synaptic efficacy. In the early postnatal hippocampus, we have previously characterized a transient population of CRF-expressing Cajal-Retzius-like cells. Here we queried whether this stress-activated neuromodulator influences connectivity in the developing hippocampal network. Using mice deficient in the principal hippocampal CRF receptor [CRF(1)(-/-)] and organotypic cultures grown in the presence of synthetic CRF, or CRF receptor antagonists, we found robust effects of CRF on dendritic differentiation in hippocampal neurons. In CRF(1)(-/-) mice, the dendritic trees of hippocampal principal cells were exuberant, an effect that was induced in normal hippocampi in vitro by the presence of CRF(1) antagonists. In both cases, total dendritic length and dendritic branching were significantly increased. In contrast, exogenous synthetic CRF blunted the dendritic growth in hippocampal organotypic cultures. Taken together, these findings suggest that endogenous CRF, if released excessively by previous early postnatal stress, might influence neuronal connectivity and thus function of the immature hippocampus.

Hippocampal corticotropin releasing hormone: pre- and postsynaptic location and release by stress

Neuropeptides modulate neuronal function in hippocampus, but the organization of hippocampal sites of peptide release and actions is not fully understood. The stress-associated neuropeptide corticotropin releasing hormone (CRH) is expressed in inhibitory interneurons of rodent hippocampus, yet physiological and pharmacological data indicate that it excites pyramidal cells. Here we aimed to delineate the structural elements underlying the actions of CRH, and determine whether stress influenced hippocampal principal cells also via actions of this endogenous peptide. In hippocampal pyramidal cell layers, CRH was located exclusively in a subset of GABAergic somata, axons and boutons, whereas the principal receptor mediating the peptide's actions, CRH receptor 1 (CRF1), resided mainly on dendritic spines of pyramidal cells. Acute 'psychological' stress led to activation of principal neurons that expressed CRH receptors, as measured by rapid phosphorylation of the transcription factor cyclic AMP responsive element binding protein. This neuronal activation was abolished by selectively blocking the CRF1 receptor, suggesting that stress-evoked endogenous CRH release was involved in the activation of hippocampal principal cells.

CRF and CRF receptors: role in stress responsivity and other behaviors

Since corticotropin-releasing factor (CRF) was first characterized, a growing family of ligands and receptors has evolved. The mammalian family members include CRF, urocortinI (UcnI), UcnII, and UcnIII, along with two receptors, CRFR1 and CRFR2, and a CRF binding protein. These family members differ in their tissue distribution and pharmacology. Studies have provided evidence supporting an important role of this family in regulation of the endocrine and behavioral responses to stress. Although CRF appears to play a stimulatory role in stress responsivity through activation of CRFR1, specific actions of UcnII and UcnIII on CRFR2 may be important for dampening stress sensitivity. As the only ligand with high affinity for both receptors, UcnI's role may be promiscuous. Regulation of the relative contribution of the two CRF receptors to brain CRF pathways may be essential in coordinating physiological responses to stress. The development of disorders related to heightened stress sensitivity and dysregulation of stress-coping mechanisms appears to involve regulatory mechanisms of CRF family members.

Reduced cerebral injury in CRH-R1 deficient mice after focal ischemia: a potential link to microglia and atrocytes that express CRH-R1

Corticotropin releasing hormone (CRH) and its family of related peptides are involved in regulating physiologic responses to multiple stressors, including stroke. Although CRH has been implicated in the exacerbation of injury after stroke, the mechanism remains unclear. After ischemia, both excitotoxic damage and inflammation contribute to the pathology of stroke. CRH is known to potentiate excitotoxic damage in the brain and has been shown to modulate inflammatory responses in the periphery. Here the present authors examine the relative contribution of the two known CRH receptors, CRH-R1 and CRH-R2, to ischemic injury using CRH receptor knockout mice. These results implicate CRH-R1 as the primary mediator of ischemic injury in this mouse model of stroke. In addition, the authors examine a potential role for CRH in inflammatory injury after stroke by identifying functional CRH receptors on astrocytes and microglia, which are cells that are known to be involved in brain inflammation. By single cell PCR, the authors show that microglia and astrocytes express mRNA for both CRH-R1 and CRH-R2. However, CRH-R1 is the primary mediator of cAMP accumulation in response to CRH peptides in these cells. The authors suggest that astrocytes and microglia are cellular targets of CRH, which could serve as a link between CRH and inflammatory responses in ischemic injury via CRH-R1.

Altered corticotropin-releasing factor (CRF) receptor immunoreactivity in the gerbil hippocampal complex following spontaneous seizure

Considerable attention has been focused on the role of corticotropin-releasing factor (CRF) in neuropsychiatric disorders and neurodegenerative diseases including epilepsy. Therefore, in the present study, we investigated the temporal and spatial alteration of CRF receptor in the gerbil hippocampal complex in order to characterize the possible changes and associations with different sequelae of spontaneous seizure in these animals. Thirty minutes postictal, a decline in CRF receptor immunoreactivity was observed in the granule cells and hilar neurons. In the subiculum, CRF receptor immunoreactivity was also significantly decreased at this time point. Twenty-four hours after seizure onset, the immunoreactivity in these regions recovered to the pre-seizure level. Moreover, 30 min after seizure in the entorhinal cortex, the density of CRF receptor immunoreactivity began to decrease, particularly in the layers II and III, compared to pre-seizure group. Nevertheless, 24h after seizure onset, CRF receptor immunodensity had recovered to its seizure-sensitive (SS) level. These results suggest that altered CRF receptor expression in the hippocampal complex may affect tissue excitability and seizure activity in SS gerbils.

Chemical neuroimmunology: health in a nutshell bidirectional communication between immune and stress (limbic-hypothalamic-pituitary-adrenal) systems

Stress is a ubiquitous and pervasive part of modern life that is frequently blamed for causing a plethora of diseases and other discomforting medical conditions. All higher organisms, including humans, experience stress in the form of a wide variety of stressors that range from environmental pollutants and drugs to traumatic events or self-induced trauma. Stressors registered by the central nervous system (CNS) generate physiological stress responses in the body (periphery) by means of the limbic-hypothalamic-pituitary-adrenal (LHPA) axis. This LHPA axis operates through the use of chemical messengers such as the stress hormones corticotropin-releasing hormone (CRH) and glucocorticoids (GCs). Under conditions of frequent exposure to acute stress and/or chronic, long-term exposure to stress, the LHPA axis becomes dysfunctional and in the process frequently overproduces both CRH and GCs, which results in many mild to severely toxic side effects. Bidirectional communication between the LHPA axis and immune/inflammatory systems can dramatically potentiate these side effects and create environments in the CNS and periphery ripe for the triggering and/or promotion of tissue degeneration and disease. This review aims to present as far as possible a molecular view of the processes involved so as to provide a bridge from the diffuse range of studies on molecular structure and receptor interactions to the burgeoning biological and medical literature that describes the empirical interplay between stress and disease. We hope that our review of this fast-growing field, which we christen chemical neuroimmunology, will give a clear indication of the striking range and depth of current molecular, cellular and medical evidence linking stress hormones to degeneration and disease. In so doing, we hope to provide encouragement for others to become interested in this critical and far-reaching field of research, which is very much at the heart of many important disease processes and very much a critical part of the crucial interface between chemistry and biology.

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.

Corticotropin releasing hormone type 2 receptors in the dorsal raphe nucleus mediate the behavioral consequences of uncontrollable stress

Uncontrollable shock produces a constellation of behavioral changes that are not observed after equivalent escapable shock. These include interference with escape and potentiation of fear conditioning. The activation of corticotropin-releasing hormone (CRH) receptors within the caudal dorsal raphe nucleus (DRN) during inescapable tailshock (IS) has been shown to be critical for the development of these behavioral changes. CRH binds to two receptor subtypes, both of which are found in the DRN. The present set of studies examined which CRH receptor subtype mediates the effects of IS. Intra-DRN administration of the CRH(2) receptor antagonist anti-sauvagine-30 before IS dose-dependently blocked IS-induced behavioral changes; the CRH(1) receptor antagonist 2-methyl-4-(N-propyl-N-cycloproanemethylamino)-5-chloro-6-(2,4,6-trichloranilino)pyrimidine (NBI27914), administered in the same manner, did not. Moreover, the highly selective CRH(2) receptor agonist urocortin II (Ucn II) dose-dependently caused behavioral changes associated with IS in the absence of shock. Ucn II was effective at doses 100-fold lower than those previously required for CRH. The relationship between CRH(2) receptors and DRN 5-HT is discussed.

Corticotropin-releasing factor receptor type 1 is involved in the stress-induced exacerbation of chronic contact dermatitis in rats

Cutaneous diseases such as psoriasis and atopic dermatitis are worsened by psychic stress. We attempted to clarify the involvement of the corticotropin-releasing factor (CRF) receptor (CRFR) in stress-induced exacerbation of chronic contact dermatitis in rats. Male Wistar rats, in which chronic contact dermatitis had been induced by 2,4,6-trinitro-1-chlorobenzene (TNCB), were exposed to a 1-h period of electric foot-shock following intraperitoneal administration of CRA1000, a selective CRFR type 1 (CRFR1) antagonist, or vehicle everyday for 9 days. Histological examination of the skin showed that the epidermis significantly thickened and the number of mast cells in the dermis significantly increased by repeated exposure to stress, and that these changes were blocked by CRA1000. These results suggest that CRFR1 is involved in the stress-induced exacerbation of chronic contact dermatitis.

Corticotropin releasing hormone type 2 receptors in the dorsal raphe nucleus mediate the behavioral consequences of uncontrollable stress

Uncontrollable shock produces a constellation of behavioral changes that are not observed after equivalent escapable shock. These include interference with escape and potentiation of fear conditioning. The activation of corticotropin-releasing hormone (CRH) receptors within the caudal dorsal raphe nucleus (DRN) during inescapable tailshock (IS) has been shown to be critical for the development of these behavioral changes. CRH binds to two receptor subtypes, both of which are found in the DRN. The present set of studies examined which CRH receptor subtype mediates the effects of IS. Intra-DRN administration of the CRH(2) receptor antagonist anti-sauvagine-30 before IS dose-dependently blocked IS-induced behavioral changes; the CRH(1) receptor antagonist 2-methyl-4-(N-propyl-N-cycloproanemethylamino)-5-chloro-6-(2,4,6-trichloranilino)pyrimidine (NBI27914), administered in the same manner, did not. Moreover, the highly selective CRH(2) receptor agonist urocortin II (Ucn II) dose-dependently caused behavioral changes associated with IS in the absence of shock. Ucn II was effective at doses 100-fold lower than those previously required for CRH. The relationship between CRH(2) receptors and DRN 5-HT is discussed.

The alteration of corticotropin-releasing factor (CRF) receptor immunoreactivity in the gerbil hippocampus and neocortex following ischemic insults

Recently, we suggested that the ectopic expression of corticotropin-releasing factor (CRF) is associated with processes linked to neuronal injury and/or degeneration in response to an ischemic insult. However, little experimental data currently links the CRF receptor directly to neuronal death induced by ischemia. Therefore, in the present study, we investigated the temporal and spatial changes in CRF receptor immunoreactivity in the hippocampus and the neocortex after transient ischemia. CRF receptor immunoreactivity in the hippocampus was reduced up to 24h after ischemia insult, as compared to the sham. Interestingly, CRF receptor immunoreactivity disappeared in the CA1 region of the hippocampus at 4 days in the post-ischemic group. The other regions of hippocampus maintained their immunoreactivities at this time point. On the other hand, in the neocortex, 3h after transient ischemia, the CRF receptor immunoreactivity was elevated in regions vulnerable to ischemia. At 12h post-ischemia, its immunoreactivity had decreased versus the sham operated animals. These results suggest that the selectively ectopic expression of CRF following ischemia, which we reported previously, may regulate inflammatory responses. In addition, these findings also suggest that the mechanisms of neuronal death as mediated by CRF receptor differ in the hippocampus and the neocortex.

Relationship between encephalopathy and abnormal neuronal activity in the developing brain

Infantile spasms represent a unique age-specific epileptic syndrome that is often associated with a focal or diffuse encephalopathy and can result in severe neurodevelopmental delay and retardation. The behavioral and electroencephalogram (EEG) phenotype of infantile spasms is similar, despite its association with multiple neurological disease states. The stereotypy suggests that the spasms originate from a highly age-specific hyperexcitable network. Treatment strategies for infantile spasms remain largely empirical due to the lack of understanding of the underlying neurochemistry and circuitry. This chapter reviews experimental evidence for the presence of unique developmental factors that appear to promote hyperexcitability in the immature brain and that may play a role in the generation of infantile spasms. In addition, this chapter evaluates the potential interplay between an associated developmental encephalopathy and enhanced neuronal hyperexcitability in infantile spasms.

Effects of antalarmin, a CRF type 1 receptor antagonist, on anxiety-like behavior and motor activation in the rat

Molecular studies point to a role for the type 1 corticotropin-releasing factor receptor (CRF(1)) in anxiogenic-like and activating effects of CRF and stress. However, CP-154,526, a selective CRF(1) antagonist, has yielded mixed results in such tests. Few studies have examined the behavioral effects of other CRF(1) antagonists. Therefore, we examined the effects of antalarmin, a structurally related analog of CP-154,526, on anxiety-like behavior and motor activation. Antalarmin blocked the anxiogenic-like effect of CRF in the elevated plus maze, without affecting anxiety-like behavior in vehicle-treated animals. Antalarmin decreased spontaneous defensive withdrawal behavior in a novel, brightly illuminated open field. Finally, antalarmin blocked the activating effects of CRF, but not D-amphetamine, without producing motor sedation. These findings indicate that the CRF(1) receptor mediates anxiogenic-like effects of novelty stress and the anxiogenic-like and activating effects of CRF and support the hypothesis that CRF(1) antagonists may be useful for the pharmacotherapy of pathological anxiety.