Exposure to neonatal separation stress alters exploratory behavior and corticotropin releasing factor expression in neurons in the amygdala and hippocampus

Evidence is accumulating that early emotional experience interferes with the development of the limbic system, which is involved in perception and regulation of emotional behaviors as well as in learning and memory formation. Limbic brain regions, as well as hypothalamic regions and other, nonlimbic areas contain specific neuron subpopulations, which express and release corticotropin releasing factor (CRF). Since these neurons serve to connect limbic function to endocrine, stress-related responses, we proposed that stressful experience during early postnatal brain development should interfere with the development of CRF-containing neurons, particularly in brain regions essential for emotional regulation. Applying neonatal separation stress (daily 1 h separation from the parents and litter mates) as stressor, the number of immunocytochemically identified CRF-expressing neurons/fibers was quantified in the amygdala, hippocampus, paraventricular nucleus of the hypothalamus, piriform cortex, and the somatosensory cortex of 3-week-old stressed and nonstressed Octodon degus, a semi-precocial rodent. Compared to controls neonatally stressed animals showed significantly lower levels of CRF-positive fibers (-60%) in the central amygdala, significantly less CRF-positive neurons in the dentate gyrus (-28%) and the CA1 region (-29%) and significantly lower CRF cell densities in the somatosensory cortex (-26%). On the other hand, we found significantly higher numbers of CRF-immunoreactive neurons in the basolateral amygdaloid complex (+192%) of stressed animals compared to nonstressed controls. No differences in CRF-immunoreactive cell densities were detected in the other regions. Additional behavioral analysis revealed significantly elevated exploratory behavior (+34%) in stressed animals compared to controls, which might indicate reduced anxiety in the stressed animals.     

Stress sensitivity and the development of affective disorders

Depressive disorders are the most common form of mental illness in America, affecting females twice as often as males. The great variability of symptoms and responses to therapeutic treatment emphasize the complex underlying neurobiology of disease onset and progression. Evidence from human and animal studies reveals a vital link between individual stress sensitivity and the predisposition toward mood disorders. While the stress response is essential for maintenance of homeostasis and survival, chronic stress and maladaptive responses to stress insults can lead to depression or other affective disorders. A key factor in the mediation of stress responsivity is the neuropeptide corticotropin-releasing factor (CRF). Studies in animal models of heightened stress sensitivity have illustrated the involvement of CRF downstream neurotransmitter targets, including serotonin and norepinephrine, in the profound neurocircuitry failure that may underlie maladaptive coping strategies. Stress sensitivity may also be a risk factor in affective disorder development susceptibility. As females show an increased stress response and recovery time compared to males, they may be at an increased vulnerability for disease. Therefore, examination of sex differences in CRF and downstream targets may aid in the elucidation of the underlying causes of the increased disease presentation in females. While we continue to make progress in our understanding of mood disorder etiology, we still have miles to go before we sleep. As an encouraging number of new animal models of altered stress sensitivity and negative stress coping strategies have been developed, the future looks extremely promising for the possibility of a new generation of drug targets to be developed.     

Corticotropin-releasing factor, vasopressin and receptor systems in depression and anxiety

Summary. Affective disorders tend to be chronic and life-threatening diseases: suicide is estimated to be the cause of death in 10–15% of individuals with major depressive disorders. Major depression is one of the most prevalent and costly brain diseases with up to 20% of the worldwide population suffering from moderate to severe forms of the disease. Only 50% of individuals with depression show full remission in response to currently available antidepressant drug therapies which are based on serendipitous discoveries made in the 1950s. Previously underestimated, other severe depression-associated deleterious health-related effects have increasingly been recognized. Epidemiological studies have provided substantial evidence that patients with depression have a 2–4-fold increased risk both of developing cardiovascular disease and of mortality after experiencing a myocardial infarction. The majority of patients suffering from affective disorders have measurable shifts in their stress hormone regulation as reflected by elevated secretion of central and peripheral stress hormones or by altered hormonal responses to neuroendocrine challenge tests. In recent years, these alterations have increasingly been translated into testable hypotheses addressing the pathogenesis of illness. Refined molecular technologies and the creation of genetically engineered mice have allowed to specifically target individual genes involved in regulation of corticotropin releasing factor (CRF) and vasopressin (AVP) system elements. The cumulative evidence makes a strong case implicating dysfunction of these systems in the etiology and pathogenesis of depression and pathological anxiety. Translation of these advances into novel therapeutic strategies has already been started.     

Comparison of the anorexigenic activity of CRF family peptides

Corticotropin releasing factor (CRF) family peptides have an important role in the control of food intake. We investigated the effects of CRF family peptides on food intake and body weight gain in mice. Of the CRF family peptides, including CRF, urocortin1 (Ucn1), urocortin2 (Ucn2) and urocortin3 (Ucn3), peripherally administered Ucn1 was shown to have the most potent inhibitory effect on the food intake and body weight gain of both lean and high fat fed obese mice. In addition, repeated administration of Ucn1 lowered blood glucose and acylated ghrelin, and decreased the visceral fat weight of high fat fed obese mice.     

Endogenous corticotropin releasing factor regulates adrenergic and opioid receptors

Previous work from this laboratory demonstrated that intracerebroventricular (i.c.v.) administration of IgG antibodies directed against selected neuropeptides changed the density of opioid receptors, suggesting that neuropeptides in the CNS can perform a regulatory role. To further test this hypothesis, we administered anticorticotropin (CRF) IgG to rats via the i.c.v. route and measured the density of opioid mu and delta receptors and also beta- and alpha₂-adrenergic receptors. The results demonstrated that anti-CRF IgG upregulates mu and beta-adrenergic receptors. We conclude that CRF in the cerebrospinal fluid may exert regulatory effects throughout the brain.     

蛇胸腺肌样细胞呈CRF和Mot免疫反应阳性

蛇胸腺肌样细胞呈ＣＲＦ和Ｍｏｔ免疫反应阳性陆宇燕李丕鹏（烟台师范学院生物系烟台２６４０２５）关键词蛇胸腺ＣＲＦＭｏｔ胸腺微环境在Ｔ细胞发育分化过程中起着重要的作用,因此研究胸腺基质细胞的生物学特性已成为免疫生物学的又一热点。胸腺微环境结构复杂,基质...     

Stress effects on AVT and CRF systems in two strains of rainbow trout (Oncorhynchus mykiss) divergent in stress responsiveness

The aim for this study was to examine whether the F4 generation of two strains of rainbow trout divergent in their plasma cortisol response to confinement stress (HR: high responder or LR: low responder) would also differ in stress-induced effects on forebrain concentrations of mRNA for corticotropin-releasing factor (CRF), arginine vasotocin (AVT), CRF receptor type 1 (CRF-R1), CRF receptor type 2 (CRF-R2) and AVT receptor (AVT-R). In addition, plasma cortisol concentrations, brainstem levels of monoamines and monoamine metabolites, and behaviour during confinement were monitored. The results confirm that HR and LR trout differ in their cortisol response to confinement and show that fish of these strains also differ in their behavioural response to confinement. The HR trout displayed significantly higher locomotor activity while in confinement than LR trout. Moreover, following 180 min of confinement HR fish showed significantly higher forebrain concentrations of CRF mRNA than LR fish. Also, when subjected to 30 min of confinement HR fish showed significantly lower CRF-R2 mRNA concentrations than LR fish, whereas there were no differences in CRF-R1, AVT or AVT-R mRNA expression between LR and HR fish either at 30 or 180 min of confinement. Differences in the expression of CRF and CRF-R2 mRNA may be related to the divergence in stress coping displayed by these rainbow trout strains.     

Intragranular colocalization of arginine vasopressin and methionine-enkephalin-octapeptide in CRF-axons in the rat median eminence

Summary Ultrastructural appearances of axonal terminals containing corticoliberin (CRF) were examined in the rat median eminence prepared by a freeze-drying procedure. Immunolabeling was performed by using 5-, 8-, or 15-nm gold-antibody complexes for CRF, arginine vasopressin (VP) and methionine-enkephalin-octapeptide (Enk-8), singly or in combination. In intact animals, the CRF-containing secretory granules were only slightly labeled with goldanti-VP or -Enk-8. In adrenalectomized rats, granules within single axons appeared to be labeled with all the immunogold complexes. This intragranular colocalization of the three antigens was confirmed by using three neighboring sections of the same axon terminals which were stained separately with each one of the antibodies and visualized with the avidin-biotin-peroxidase complex method. The granules labeled for CRF had decreased 9 days after adrenalectomy but had increased again by day 21, while those labeled for VP steadily increased after adrenalectomy. However, this did not correspond with the appearances of cell bodies in the paraventricular nucleus; the cell bodies labeled for both CRF and VP steadily increased in number and in stainability. By contrast, Enk-8 immunoreactivity in the axonal terminals and cell bodies was not affected by adrenalectomy. These findings suggest that although the three peptides could be released simultaneously from the axonal terminals, VP may play some special role in the expression of CRF activity.     

CRF type 1 receptors in the dorsal periaqueductal gray modulate anxiety-induced defensive behaviors

The dorsal periaqueductal gray (dPAG) is involved in defensive coping reactions to threatening stimuli. Corticotropin releasing factor (CRF) is substantially implicated as a direct modulator of physiological, endocrine and behavioral responses to a stressor. Previous findings demonstrate a direct role of the central CRF system in dPAG-mediated defensive reactions toward a threatening stimulus. These include anxiogenic behaviors in the elevated plus maze (EPM) in rats and defensive reactions in both the mouse defense test battery (MDTB) and rat exposure test (RET) paradigms in mice. Furthermore, CRF was shown to directly and dose-dependently excite PAG neurons in vitro. The aim of the present series of experiments was to directly evaluate the role of the CRF1 receptor (CRF1) in dPAG-induced defensive behaviors in the MDTB and the RET paradigms. For this purpose, cortagine, a novel CRF1-selective agonist, was directly infused into the dPAG. In the RET the high dose of cortagine (100 ng) significantly affected spatial avoidance measures and robustly increased burying behavior, an established avoidance activity, while having no effects on behaviors in the MDTB. Collectively, these results implicate CRF1 in the dPAG as a mediator of temporally and spatially dependent avoidance in response to controllable and constant stimuli.     

Opiocortin and catecholamine input to CRF-immunoreactive neurons in rat forebrain

Neural input to distinct and separate populations of CRF-immunoreactive (ir) neurons in rat forebrain was investigated. The relationship of opiocortin and/or catecholamine fibers to different groups of CRF-containing neurons was elucidated using single and dual labeling immunocytochemical procedures. Antibodies to CRF, ACTH(1–39) and the catecholamine synthesizing enzymes which are tyrosine hydroxylase (TH), dopamine β-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) were utilized. CRF-ir neuronal populations are localized predominantly in the following regions of rat forebrain: bed nucleus of stria terminalis, medial preoptic area, suprachiasmatic and paraventricular (PVN) nuclei of hypothalamus and central nucleus of amygdala. The present study demonstrates that CRF-ir neuronal groups in rat forebrain are not homogenous in that each population received a characteristic neural input. CRF-ir neurons in the PVN received a dense input of ACTH-, TH-, DBH-, and PNMT-ir fibers. In contrast, CRF-ir neurons in the central nucleus of amygdala are colocalized predominantly with TH-ir fiber/terminals. In the ventral portion of the bed nucleus of stria terminalis, TH-, ACTH- and DBH-ir fibers are demonstrated in close anatomical proximity to CRF-containing perikarya; in the dorsal portion of this nucleus, TH-ir fiber/terminals are colocalized with CRF-ir neurons. In the suprachiasmatic nucleus, neither opiocortin- nor catecholamine-immunostained fibers are observed in association with CRF-ir neurons. Our data suggest that there is a transmitter specificity of neural input to each CRF-ir neuronal population in rat forebrain.