High intracerebral levels of CRH result in CRH receptor downregulation in the amygdala and neuroimmune desensitization

Biochemical mechanisms in pathogenesis of infantile epileptic spasm syndrome

The molecular mechanisms leading to infantile epileptic spasm syndrome (IESS) remain obscure. The only common factor seems to be that the spasms are restricted to a limited period of infancy, during a certain maturational state. Here the current literature regarding the biochemical mechanisms of brain maturation in IESS is reviewed, and various hypotheses of the pathophysiology are put together. They include: (1) imbalance of inhibitory (NGF, IGF-1, ACTH, GABA) and excitatory factors (glutamate, nitrites) which distinguishes the different etiological subgroups, (2) abnormality of the hypothalamic pituitary adrenal (HPA) axis linking insults and early life stress, (3) inflammation (4) yet poorly known genetic and epigenetic factors, and (5) glucocorticoid and vigabatrin action on brain development, pinpointing at molecular targets of the pathophysiology from another angle. An altered maturational process may explain why so many, seemingly independent etiological factors lead to the same clinical syndrome and frequently to developmental delay. Understanding these factors can provide ideas for novel therapies.

The Effects of Acute Neonatal Pain on Expression of Corticotropin-Releasing Hormone and Juvenile Anxiety in a Rodent Model

Premature infants in the neonatal intensive care unit (NICU) may be subjected to numerous painful procedures without analgesics. One necessary, though acutely painful, procedure is the use of heel lances to monitor blood composition. The current study examined the acute effects of neonatal pain on maternal behavior as well as amygdalar and hypothalamic activation, and the long-term effects of neonatal pain on later-life anxiety-like behavior, using a rodent model. Neonatal manipulations consisted of either painful needle pricks or non-painful tactile stimulation in subjects’ left plantar paw surface which occurred four times daily during the first week of life [postnatal day (PND)1–PND7]. Additionally, maternal behaviors in manipulated litters were compared against undisturbed litters via scoring of videotaped interactions to examine the long-term effects of pain on dam-pup interactions. Select subjects underwent neonatal brain collection (PND6) and fluorescent in situ hybridization (FISH) for corticotropin-releasing hormone (CRH) and the immediate early gene c-fos. Other subjects were raised to juvenile age (PND24 and PND25) and underwent innate anxiety testing utilizing an elevated plus maze (EPM) protocol. FISH indicated that neonatal pain influenced amygdalar CRH and c-fos expression, predominately in males. No significant increase in c-fos or CRH expression was observed in the hypothalamus. Additionally, neonatal pain altered anxiety behaviors independent of sex, with neonatal pain subjects showing the highest frequency of exploratory behavior. Neonatal manipulations did not alter maternal behaviors. Overall, neonatal pain drives CRH expression and produces behavioral changes in anxiety that persist until the juvenile stage.

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.

Reversible Adrenal Insufficiency in Three Patients With Post-Roux-en-Y Gastric Bypass Noninsulinoma Pancreatogenous Hypoglycemia Syndrome

Objective. Noninsulinoma pancreatogenous hypoglycemia syndrome (NIPHS) is a disorder of endogenous hyperinsulinemia that is clinically distinguishable from insulinoma, with a greater preponderance after Roux-en-Y gastric bypass (RYBG). Hyperinsulinemic hypoglycemia can predispose to attenuation of counterregulatory hormone responses to hypoglycemia, and consequent suppression of the hypothalamic-pituitary-adrenal (HPA) axis. This case series describes 3 individuals who were diagnosed with adrenal insufficiency (AI) after undergoing RYGB, complicated by NIPHS. Methods. A retrospective chart review was performed for each individual. Chart review applied particular attention to the onset of hyperinsulinemic hypoglycemia following bariatric surgery and the dynamic testing leading to the diagnoses of NIPHS and AI. Results. In each case, reactive hypoglycemia ensued within months to years after RYGB. Cosyntropin stimulation testing confirmed the diagnosis of AI. Hydrocortisone therapy reduced the frequency and severity of hypoglycemia and was continued until successful medical and/or surgical management of hyperinsulinism occurred. Follow-up testing of the HPA axis demonstrated resolution of AI. In all cases, hydrocortisone therapy was finally discontinued without incident. Conclusion. We speculate that transient AI is a potential complication in patients who experience recurrent hyperinsulinemic hypoglycemia after RYGB. The putative mechanism for this observation may be attenuation of the HPA axis after prolonged exposure to severe, recurrent hypoglycemia. We conclude that biochemical screening for AI should be considered in individuals who develop post-RYGB hyperinsulinemic hypoglycemia. If AI is diagnosed, supportive treatment should be maintained until hyperinsulinemic hypoglycemia has been managed effectively.

Human psychoneuroimmunology: 20 years of discovery

An important component of psychoneuroimmunology research is to reveal the myriad ways that behaviors and health are inter-related, with a focus on the immunological mechanisms that underlie these interactions. Research in human psychoneuroimmunology has shown that immunoregulatory processes are an integral part of a complex network of adaptive responses. As such, this review provides a perspective from our laboratory over the last 20 years to define the inter-relationships between behavior and immunity; to identify the hypothalamic pituitary adrenal (HPA) and autonomic mechanisms that link the central nervous system and immune responses; to examine the clinical implications of immune alterations during depression or life stress on inflammatory and infectious disease risk; and to explore the reciprocal role of immune mediators on behavior in humans.

Corticotropin releasing factor (CRF) receptor signaling in the central nervous system: new molecular targets

Corticotropin-releasing factor (CRF) and the related urocortin peptides mediate behavioral, cognitive, autonomic, neuroendocrine and immunologic responses to aversive stimuli by activating CRF(1) or CRF(2) receptors in the central nervous system and anterior pituitary. Markers of hyperactive central CRF systems, including CRF hypersecretion and abnormal hypothalamic-pituitary-adrenal axis functioning, have been identified in subpopulations of patients with anxiety, stress and depressive disorders. Because CRF receptors are rapidly desensitized in the presence of high agonist concentrations, CRF hypersecretion alone may be insufficient to account for the enhanced CRF neurotransmission observed in these patients. Concomitant dysregulation of mechanisms stringently controlling magnitude and duration of CRF receptor signaling also may contribute to this phenomenon. While it is well established that the CRF(1) receptor mediates many anxiety- and depression-like behaviors as well as HPA axis stress responses, CRF(2) receptor functions are not well understood at present. One hypothesis holds that CRF(1) receptor activation initiates fear and anxiety-like responses, while CRF(2) receptor activation re-establishes homeostasis by counteracting the aversive effects of CRF(1) receptor signaling. An alternative hypothesis posits that CRF(1) and CRF(2) receptors contribute to opposite defensive modes, with CRF(1) receptors mediating active defensive responses triggered by escapable stressors, and CRF(2) receptors mediating anxiety- and depression-like responses induced by inescapable, uncontrollable stressors. CRF(1) receptor antagonists are being developed as novel treatments for affective and stress disorders. If it is confirmed that the CRF(2) receptor contributes importantly to anxiety and depression, the development of small molecule CRF(2) receptor antagonists would be therapeutically useful.

Immunohistochemical visualization of corticotropin-releasing factor type 1 (CRF1) receptors in monkey brain

Corticotropin-releasing factor receptor type 1, CRF1, plays a prominent role in the hypothalamic-pituitary-adrenal (HPA) axis and is implicated in the autonomic and behavioral responses to stress. Dysregulation of the CRF system may underlie the pathophysiology of several disorders, including depression and anxiety. The distribution of CRF1 mRNA and CRF1 specific ligand binding has been reported by multiple groups in rodents using in situ hybridization and receptor autoradiography, respectively. More recently, somewhat conflicting rodent anti-CRF1 immunohistochemical studies were reported. In this study we report the generation of an antihuman CRF1 antiserum and provide the first immunohistochemical description of CRF1 distribution in a primate brain, that of the rhesus monkey. The specificity of anti-CRF-R1 antiserum R221 was demonstrated using transfected hCRF1-expressing HEK 293 cells and rhesus monkey pituitary. CRF1-immunoreactive neurons were widespread in the rhesus brain. CRF1 staining was associated with neuronal cell bodies and dendrites and was primarily intracellular, suggesting a high rate of receptor turnover or receptor sequestration. Anti-CRF1 immunoreactivity was most abundant in pituitary, cerebellum, and in portions of brain stem associated with sensorimotor function. CRF1 staining was also observed in cerebral cortex, basal forebrain, portions of the basal ganglia, and thalamus. Staining was relatively low in prefrontal cortex and in limbic areas, which may reflect masking of the N-terminal epitope. The distribution of CRF1 immunoreactivity is suggestive of roles in attentional processing as well as the processing of motor and sensory information.

5-HT1A receptor knockout mice and mice overexpressing corticotropin-releasing hormone in models of anxiety

Pharmacological experiments have implicated a role for serotonin (5-HT)(1A) receptors in the modulation of anxiety. More recent is the interest in corticotropin-releasing hormone (CRH) system as a potential target for the treatment of anxiety disorders. However, selective pharmacological tools for the CRH system are limited, hampering research in this field. Gene targeting is a relatively new approach to study mechanisms underlying anxiety disorders. 5-HT(1A) receptor knockout (1AKO) mice have been created on three different background strains, and two different lines of mice, overexpressing CRH (CRH-OE), have been generated. In the present review, behavioural and physiological findings reported for 1AKO mice and CRH-OE mice will be reviewed. As behavioural phenotyping is often limited to one or two approach avoidance paradigms, we extended these observations and also tested 1AKO and CRH-OE mice in a conditioned fear paradigm. This paradigm reflects essentially different aspect of anxiety than approach avoidance paradigms. 1AKO mice on a 129/Sv background strain showed similar freezing as wild-type (WT) mice. In CRH-OE mice, less freezing was observed than in the corresponding wild-type mice. The fact that the anxious phenotype of these genetically altered mice seems less clear than initially reported will be discussed. Rather than studying the direct consequences of alterations in the targeted gene, 1AKO and CRH-OE mice seem very valuable to study compensatory processes that seem to have taken place in reaction to life-long changes in gene expression.

ACTH treatment of infantile spasms: mechanisms of its effects in modulation of neuronal excitability

The efficacy of ACTH, particularly in high doses, for rapid and complete elimination of infantile spasms (IS) has been demonstrated in prospective controlled studies. However, the mechanisms for this efficacy remain unknown. ACTH promotes the release of adrenal steroids (glucocorticoids), and most ACTH effects on the central nervous system have been attributed to activation of glucocorticoid receptors. The manner in which activation of these receptors improves IS and the basis for the enhanced therapeutic effects of ACTH--compared with steroids--for this disorder are the focus of this chapter. First, a possible "common excitatory pathway," which is consistent with the many etiologies of IS and explains the confinement of this disorder to infancy, is proposed. This notion is based on the fact that all of the entities provoking IS activate the native "stress system" of the brain. This involves increased synthesis and release of the stress-activated neuropeptide, corticotropin-releasing hormone (CRH), in limbic, seizure-prone brain regions. CRH causes severe seizures in developing experimental animals, as well as limbic neuronal injury. Steroids, given as therapy or secreted from the adrenal gland upon treatment with ACTH, decrease the production and release of CRH in certain brain regions. Second, the hypothesis that ACTH directly influences limbic neurons via the recently characterized melanocortin receptors is considered, focusing on the effects of ACTH on the expression of CRH. Experimental data showing that ACTH potently reduces CRH expression in amygdala neurons is presented. This downregulation was not abolished by experimental elimination of steroids or by blocking their receptors and was reproduced by a centrally administered ACTH fragment that does not promote steroid release. Importantly, selective blocking of melanocortin receptors prevented ACTH-induced downregulation of CRH expression, providing direct evidence for the involvement of these receptors in the mechanisms by which ACTH exerts this effect. Thus, ACTH may reduce neuronal excitability in IS by two mechanisms of action: (1) by inducing steroid release and (2) by a direct, steroid-independent action on melanocortin receptors. These combined effects may explain the robust established clinical effects of ACTH in the therapy of IS.

How do the many etiologies of West syndrome lead to excitability and seizures? The corticotropin releasing hormone excess hypothesis

West syndrome (WS) is associated with diverse etiological factors. This fact has suggested that there must be a 'final common pathway' for these etiologies, which operates on the immature brain to result in WS only at the maturational state present during infancy. Any theory for the pathogenesis of WS has to account for the unique features of this disorder. For example, how can a single entity have so many etiologies? Why does WS arise only in infancy, even when a known insult had occurred prenatally, and why does it disappear? Why is WS associated with lasting cognitive dysfunction? And, importantly, why do these seizures--unlike most others--respond to treatment by a hormone, ACTH? The established hormonal role of ACTH in human physiology is to function in the neuroendocrine cascade of the responses to all stressful stimuli, including insults to the brain. As part of this function, ACTH is known to suppress the production of corticotropin releasing hormone (CRH), a peptide that is produced in response to diverse insults and stressors.The many etiologies of WS all lead to activation of the stress response, including increased production and secretion of the stress-neurohormone CRH. CRH has been shown, in infant animal models, to cause severe seizures and death of neurons in areas involved with learning and memory. These effects of CRH are restricted to the infancy period because the receptors for CRH, which mediate its action on neurons, are most abundant during this developmental period. ACTH administration is known to inhibit production and release of CRH via a negative feedback mechanism. Therefore, the efficacy of ACTH for WS may depend on its ability to decrease the levels of the seizure-promoting stress-neurohormone CRH.This CRH-excess theory for the pathophysiology of WS is consistent not only with the profile of ACTH effects, but also with the many different 'causes' of WS, with the abnormal ACTH levels in the cerebrospinal fluid of affected infants and with the spontaneous disappearance of the seizures. Furthermore, if CRH is responsible for the seizures, and CRH-mediated neuronal injury contributes to the worsened cognitive outcome of individuals with WS, then drugs which block the actions of CRH on its receptors may provide a better therapy for this disorder.

Persistent corticotropin-releasing factor(1) receptor desensitization and downregulation in the human neuroblastoma cell line IMR-32

Brain corticotropin-releasing factor (CRF) systems integrate various responses to stress. Pathological responses to stress may result from errors in CRF receptor regulation in response to changes in synaptic CRF levels. To establish an in vitro model to study brain CRF receptors, we characterized the CRF-induced modulation of CRF(1) receptors in the human neuroblastoma cell line, IMR-32. Treatment with CRF decreased CRF(1) receptor binding and desensitized CRF-induced increases in cAMP. The decrease in binding had an EC(50) of approximately 10 nM, was maximal by 30 min, and was blocked by the CRF receptor antagonist [D-Phe(12), Nle(21,38), C(alpha)-MeLeu(37)]CRF(12-41). The desensitization was homologous as vasoactive intestinal polypeptide-induced increases in cAMP were unchanged, and elevation of cAMP did not alter CRF(1) receptor binding. Treatment with CRF for up to 24 h did not alter CRF(1) receptor mRNA levels, suggesting that a posttranscriptional mechanism maintains the decrease in receptor binding. Interestingly, recovery of CRF receptor binding and CRF-stimulated cAMP production was only partial following exposure to 100 nM CRF. In contrast, receptor binding recovered to control levels following exposure to 10 nM CRF. These data suggest that exposure to high doses of CRF result in permanent changes characterized by only partial recovery. Identifying the mechanisms underlying this partial recovery may provide insights into mechanisms underlying the acute and chronic effects of stress on CRF receptor regulation.

Stress-induced changes in peripheral natural killer cell cytotoxicity in pigs may not depend on plasma cortisol

The study examined cortisol (COR) involvement in stress-related changes in natural killer cell cytotoxicity (NKCC). The relationship between blood COR level, phasic changes in NKCC, and the number of large granular lymphocytes (LGL) was examined in pigs during the course of 4-h immobilization stress (IMB) and for 6 days after its termination. NKCC was determined using 18-h 51Cr-release assay, LGL number was assessed with a standard hematological method, and plasma COR level was measured by radioimmunoassay. The blood level of COR was increasing during IMB (max 446Delta% at the second hour) and decreased after its termination (max -59Delta% on day 2). Changes in NKCC level and LGL number were biphasic; i.e., an initial increase in both measures (NKCC max 24Delta%, LGL max 18Delta%) in an early phase of stress (0-1h) was followed by their subsequent decrease (NKCC max -35Delta%, LGL max -41Delta%) in the late phase (3-4 h) of stress, which persisted for several days after termination of IMB. Thus, in the early phase of stress, there was a positive correlation between NKCC, LGL number, and COR levels (all elevated); a positive correlation between the measures also occurred after termination of IMB (all decreased). A negative correlation between COR and NKCC, which might be indicative of COR-related immunosuppression, was found only in the late (3-4 h) phase of stress. It is concluded that COR may be only one of multiple factors (possibly antagonistic) determining an actual immune response during stress.

Chronic treatment with the antidepressant amitriptyline decreases CRF-R1 receptor mRNA levels in the rat amygdala

Using semi-quantitative in situ hybridization, corticotropin-releasing factor (CRF) and CRF receptor 1 (CRF-R1) mRNA levels were determined in the rat hypothalamus and amygdala after short-term (10 days) and chronic (4 weeks) treatment with the antidepressant amitriptyline. We found that chronic treatment with amitriptyline produced a significant decrease in CRF mRNA (to 33% of control) in the hypothalamic paraventricular nucleus (PVN). Short-term or chronic amitriptyline treatment had no effect on CRF-R1 mRNA levels in the PVN. However, after chronic treatment, there was a significant decrease of CRF-R1 mRNA levels in the lateral + basolateral (to 60% of control), and in the medial (to 70% of control) amygdala nuclei. These results suggest that the tricyclic antidepressant amitriptyline may exert part of its effects through modulation of hypothalamic CRF and of CRF-R1 gene expression in the amygdala.

The rationale for corticotropin-releasing hormone receptor (CRH-R) antagonists to treat depression and anxiety

Neuroendocrine studies strongly suggest that dysregulation of the hypothalamic pituitary-adrenocortical (HPA) system plays a causal role in the development and course of depression. Whereas the initial mechanism resulting in HPA hyperdrive remains to be elucidated, evidence has emerged that corticosteroid receptor function is impaired in many patients with depression and in many healthy individuals at increased genetic risk for an depressive disorder. Assuming such impaired receptor function, then central secretion of CRH would be enhanced in many brain areas, which would account for a variety of depressive symptoms. As shown in rats and also in transgenic mice with impaired glucocorticoid receptor function, antidepressants enhance the signaling through corticosteroid receptors. This mechanism of action can be amplified through blocking central mechanisms that drive the HPA system. Animal experiments using antisense oligodeoxynucleotides directed against the mRNA of both CRH receptor subtypes identified the CRH1 receptor as the mediator of the anxiogenic effects of CRH. Studies in mouse mutants in which this receptor subtype had been deleted extended these findings as the animals were less anxious than wild-type mice when experimentally stressed. Thus, patients with clinical conditions that are causally related to HPA hyperactivity may profit from treatment with a CRH1 receptor antagonist.

Changes in hippocampal theta following intrahippocampal corticotropin-releasing hormone (CRH) infusions in the rat

Hippocampal theta activity is a large amplitude, sinusoidal wave that occurs during attentive immobility and exploratory behaviour in the rat, and it is thought to be involved in memory formation. Recent reports suggest that corticotropin-releasing hormone (CRH) has pro-mnemonic effects in rodents. Because memory-enhancing substances/manipulations generally alter either theta frequencies or amplitudes, these variables were monitored in urethane-anaesthetised rats following intrahippocampal infusions of CRH. Adult male, Lister hooded rats were implanted with a hippocampal recording electrode and a guide cannula, both aimed at the dentate gyrus. When CRH was infused into the hippocampus, the main change in the hippocampal EEG was a slow onset increase in the amplitude of spontaneous theta and, paradoxically, a significant decrease in the amount of time spent displaying theta. These data suggest that CRH has the ability to modulate ongoing hippocampal theta, but, considering the slow effect, the involvement of hippocampal CRH receptors is suspect. Regardless of locus, the described electrophysiological changes suggest that hippocampal cholinergic systems may play a role in the memory-enhancing effects of CRH.

Changes in brain corticotropin-releasing factor messenger RNA expression in aged Fischer 344 rats

Adaptation in aging may become impaired from abnormal expression of corticotropin-releasing factor (CRF) and altered CRF receptor function. In this study, we measured CRF mRNA levels in Fischer 344 rats at various ages. The brains of these rats were processed for in situ hybridization. Relative to 3-month-old rats, levels of CRF mRNA were significantly decreased in the following brain areas at the following ages: at 24 months in the paraventricular hypothalamus, at 11, 17, and 24 months in the amygdala and at 17 and 24 months in the bed nucleus of the stria terminalis. These changes may contribute to impaired adaptations to stress, cognitive decline and other pathophysiological processes during aging.

Effect of a chronic stress on CRF neuronal activity and expression of its type 1 receptor in the rat brain

The purpose of this study was to compare the effect of an acute versus a chronic immobilization stress on the genetic expression of c-fos and corticotropin-releasing factor type 1 receptor (CRF1 receptor) in the paraventricular nucleus (PVN) of the rat hypothalamus. Male Sprague-Dawley rats were exposed to either a single 90-min immobilization stress or the same session for 11 consecutive days. Animals were deeply anesthetized before (control); immediately, 1.5, 3, 6, or 12 h after the acute stress; or after the last session of the repeated exposures to immobilization. Coronal frozen sections (30 micrometers) of the brains were cut and mRNAs encoding the rat c-fos and CRF1 receptor were assayed by in situ hybridization histochemistry using 35S-labeled riboprobes. Localization of these transcripts within PVN CRF-immunoreactive (ir) neurons was also determined. The expression of the mRNA encoding either c-fos or CRF1 receptor was barely detectable to low in the PVN of control animals, but the acute stress session induced a robust signal for both transcripts in this endocrine nucleus. Numerous CRF-ir neurons were positive for the gene encoding either c-fos or CRF1 receptor in the PVN of acutely stressed animals. In contrast, the PVN of chronically stressed animals displayed a significantly lower CRF1 receptor mRNA signal after the last stress session. In these animals, stress-induced transcription of c-fos mRNA occurred in the magnocellular PVN 90 min after the end of the last stress session but only a low signal was detected in the parvocellular division. Moreover, very few CRF-ir neurons of the PVN expressed either the CRF1 receptor or c-fos transcript in chronically stressed rats. These data provide evidence for an adaptive cellular mechanism involving an attenuated action of CRF within the PVN in response to repeated homotypic stress exposures.

Physiological and neurochemical aspects of corticotropin-releasing factor actions in the brain: the role of the locus coeruleus

Corticotropin-releasing factor (CRF) is both a major regulator of the hypothalamo-pituitary-adrenal (HPA) axis and the activity of the autonomic nervous system. Besides, it exerts numerous effects on other physiological functions such as appetite control, motor and cognitive behavior and immune function. The basis for these effects is constituted by its distribution in hypothalamic and extra-hypothalamic brain areas, the latter being represented by limbic structures such as the central nucleus of the amygdala or by brain stem neurons such as the locus coeruleus (LC) or nucleus of the solitary tract (NTS). The effects of CRF are mediated through recently described CRF-receptor subtypes, whose molecular biology, biochemistry and pharmacological regulation are discussed in detail. In the second part of this review, we will focus on the physiology of CRF-systems in the brain, with a particular emphasis on cardiovascular regulation, respiration, appetite control and stress-related behavior. Finally, the role of the locus coeruleus in the control of CRF-mediated behavioral activities is discussed. The interaction of noradrenergic and CRF-neurons clearly implies that CRF appears to directly activate LC neurons in a stressful situation, thus ultimately coordinating the bodily response to a stressful stimulus.

Alterations in corticotropin-releasing hormone gene expression of central amygdaloid neurons following long-term paraventricular lesions and adrenalectomy

Corticotropin-releasing hormone messenger RNA expression in the amygdala of rats after adrenalectomy and bilateral lesions of the hypothalamic paraventricular nucleus was examined by in situ hybridization histochemistry. Corticotropin-releasing hormone messenger RNA-containing cells are abundant in the intermediate subdivision of the central amygdaloid nucleus. Some corticotropin-releasing hormone-labeled cells are scattered in other subdivisions of the central nucleus and throughout the anterior amygdaloid area. Five days after bilateral adrenalectomy, the number of corticotropin-releasing hormone messenger RNA-containing cells was reduced both in the central nucleus and the anterior area of the amygdala. This reduction was prevented by corticosterone replacement and contrasts sharply with the known rise of corticotropin-releasing hormone messenger RNA in the paraventricular nucleus after adrenalectomy. Corticotropin-releasing hormone messenger RNA expression in the amygdala was up-regulated in rats with six-week bilateral lesions of the paraventricular nucleus. This elevation in corticotropin-releasing hormone messenger RNA was not influenced by adrenalectomy or corticosterone, and it did not correlate with plasma levels of adrenocorticotrophic hormone or corticosterone. The possible direct innervation of the amygdala by the paraventricular nucleus is supported by the demonstration of labeled axons from the paraventricular nucleus to the amygdala after injection of an anterograde tracer, Phaseolus vulgaris leucoagglutinin, into the paraventricular nucleus. Labeled fibers take two courses: through the lateral hypothalamus ventral amygdalofugal path and through the stria terminalis. Data presented here suggest that the paraventricular nucleus-amygdala connection is likely to be inhibitory to corticotropin-releasing hormone neurons in the central amygdala. These neurons may participate in behavioral responses to stress effected through brainstem autonomic centers rather than directly through the hypothalamo-pituitary adrenal axis.

Reduced activity of hypothalamic corticotropin-releasing hormone neurons in transgenic mice with impaired glucocorticoid receptor function

Loss of central glucocorticoid receptor (GR) function is thought to be involved in the development of neuroendocrine and psychiatric disorders associated with corticotropin-releasing hormone (CRH) hyperactivity. The possible causal relationship between defective GR function and altered activity of CRH neurons was studied in transgenic mice (TG) expressing antisense RNA against GR. Immunocytochemical studies showed significant reductions in CRH immunoreactive neurons in the paraventricular nucleus (PVN) and in CRH and vasopressin (AVP) stores in the external zone of the median eminence. Concomitantly, stimulus-evoked CRH secretion from mediobasal hypothalami of TG mice in vitro was reduced significantly. However, CRH mRNA levels in the PVN of TG mice were marginally lower than those in wild-type (WT) mice. 125I-CRH binding autoradiography revealed no differences between WT and TG animals in any of the brain regions that were studied. Basal plasma corticosterone (cort) levels and 125I-CRH binding, CRH-R1 mRNA, POMC mRNA, and POMC hnRNA levels in the anterior pituitary gland were similar in WT and TG mice. Intraperitoneal injection of interleukin-1beta (IL-1beta) increased plasma cort levels, CRH mRNA in the PVN, and anterior pituitary POMC hnRNA similarly in WT and TG mice. The injection of saline significantly reduced anterior pituitary CRH-R1 mRNA levels in WT mice, but not in TG mice, whereas IL-1beta produced a decrease in these mRNA levels in both strains. The data show that long-term GR dysfunction can be associated with reduced activity of CRH neurons in the PVN and decreased sensitivity of pituitary CRH-R1 mRNA to stimulus-induced downregulation. Moreover, the hypothalamic changes observed in this model suggest that impaired GR function, at least if present since early embryonic life, does not necessarily result in CRH hyperexpression characteristics of disorders such as major depression.

Differential effects of NMDA-induced lesions into the insular cortex and amygdala on the acquisition and evocation of conditioned immunosuppression

It has been established that the insular cortex (IC) mediates conditioned taste aversion, and recently we have demonstrated that lesions of this structure disrupt the acquisition of conditioned immunosuppression (CIS). The IC is functionally and reciprocally interconnected with the amygdala (AM) which has been suggested to be involved in neural-immune interactions. The aim of this work was to test the effects of NMDA-induced lesions in either the IC or AM in the acquisition (lesions made before conditioning) and evocation (lesions made after conditioning) of a conditioned immunosuppression task, obtained by one single pairing of saccharin taste and the immunosuppressive drug, cyclophosphamide. AM and IC lesioned rats were separated into four groups: the first two received lesions before and the other two were lesioned after the acquisition of conditioned immunosuppression. Twenty days after conditioning, animals were reexposed to saccharin and immunized with ovalbumin. After immunization, blood samples were taken, and analyzed by ELISA. The results showed that IC lesions disrupted the acquisition and evocation of CTA and CIS. Conversely, AM lesions disrupted only the acquisition of CIS. These data suggest that the IC is involved in the neural mechanisms underlying the acquisition and evocation of conditioned immunosuppression, and the amygdala could be important in mediating the input of the immune information necessary for the acquisition of conditioned immunosuppression.

Corticotropin-releasing factor and defensive withdrawal: inhibition of monoamine oxidase prevents habituation to chronic stress

There is growing evidence for a role of extrahypothalamic corticotropin-releasing factor (CRF) in the pathogenesis of anxiety. A modified form of the defensive withdrawal test was used to test the anxiogenic effects of acute administration of intracerebroventricular (1 microg, i.c.v.) CRF in adult male rats. Habituation to the mild stress of daily handling and subcutaneous (s.c.) saline injection over 2-6 weeks abolished the anxiogenic effects of exogenous CRF. At 6 weeks this habituation also resulted in attenuation of baseline withdrawal behavior. CRF receptor binding was significantly decreased in the amygdala of chronically handled animals and may have been responsible for this habituation phenomenon. Comparison of rats treated with the monoamine oxidase (MAO) inhibitor, phenelzine [3 mg/kg, s.c., daily for 2-6 weeks] to the saline-treated groups revealed a failure to habituate to the chronic handling, as the baseline withdrawal (after injection of artificial CSF) by the phenelzine-treated animals was not different from the baseline withdrawal by unhandled rats. In comparison to rats treated chronically with saline, phenelzine treatment enhanced the anxiogenic effect of CRF. In summary, habituation to a mild chronic stress decreased baseline defensive withdrawal. Intraventricular administration of CRF produced an anxiogenic response as measured in the defensive withdrawal test, which was lost through exposure to mild chronic stress. Two or 6 weeks of daily handling and SC saline injection caused a downregulation of CRF receptors in the amygdala, which could account for the behavioral habituation and the loss of CRF-induced defensive withdrawal. Phenelzine treatment concurrent with mild chronic stress prevented habituation and maintained the anxiogenic effect of CRF in spite of the downregulation of CRF receptors in the amygdala.

Altered neuroimmunoendocrine communication during a condition of chronically increased brain corticotropin-releasing hormone drive

Presently, it is clear that the brain, immune system, and endocrine system build a complex network of interactions at various levels. Inflammation, which may be regarded as a stressful challenge, initiates apart from immunological, autonomic, and neuroendocrine responses also profound behavioral (e.g., immobility, social disinterest) changes. Key mediators herein are corticotropin-releasing hormone (CRH) and cytokines, such as interleukin-1 beta (IL-1 beta). Currently, the behavioral changes, collectively termed sickness behavior, are thought to be adaptive responses to support the body's efforts to fight the infection. Using in vivo microdialysis and biotelemetry in freely moving animals, we have studied the monoaminergic circuits in the brain implicated in the regulation of physiological and behavioral responses to a peripheral inflammatory challenge (see also chapter of Linthorst and Reul in this volume). To expand our insight into the relationship between hypersecretion of CRH and physiological and behavioral abnormalities associated with stress-related disorders, a series of experiments was conducted with long-term centrally CRH-infused rats. These rats showed reduced body weight gain, decreased food intake, elevated plasma ACTH and corticosterone levels, thymus involution and immunosuppression, but, paradoxically, enhanced IL-1 beta mRNA expression in spleen macrophages. After a peripheral endotoxic challenge on the seventh day of treatment, the CRH-infused rats produced aberrant (i.e., blunted and/or delayed) HPA axis, fever, behavioral, and hippocampal serotonergic responses. However, endotoxin-induced plasma IL-1 and IL-6 bioactivities were significantly enhanced in these animals. The data show that chronically elevated central CRH levels as occurring during chronic stress result in defective central nervous system and immune system responses to an acute (inflammatory) challenge. These observations provide evidence that chronic CRH hypersecretion is an important factor in the etiology of stress-related disorders.

The impact of a new emotional self-management program on stress, emotions, heart rate variability, DHEA and cortisol

This study examined the effects on healthy adults of a new emotional self-management program, consisting of two key techniques, "Cut-Thru" and the "Heart Lock-In." These techniques are designed to eliminate negative thought loops and promote sustained positive emotional states. The hypotheses were that training and practice in these techniques would yield lowered levels of stress and negative emotion and cortisol, while resulting in increased positive emotion and DHEA levels over a one-month period. In addition, we hypothesized that increased coherence in heart rate variability patterns would be observed during the practice of the techniques. Forty-five healthy adults participated in the study, fifteen of whom acted as a comparison group for the psychological measures. Salivary DHEA/DHEAS and cortisol levels were measured, autonomic nervous system function was assessed by heart rate variability analysis, and emotions were measured using a psychological questionnaire. Individuals in the experimental group were assessed before and four weeks after receiving training in the self-management techniques. The experimental group experienced significant increases in the positive affect scales of Caring and Vigor and significant decreases in the negative affect scales of Guilt, Hostility, Burnout, Anxiety and Stress Effects, while no significant changes were seen in the comparison group. There was a mean 23 percent reduction in cortisol and a 100 percent increase in DHEA/DHEAS in the experimental group. DHEA was significantly and positively related to the affective state Warmheartedness, whereas cortisol was significantly and positively related to Stress Effects. Increased coherence in heart rate variability patterns was measured in 80 percent of the experimental group during the use of the techniques. The results suggest that techniques designed to eliminate negative thought loops can have important positive effects on stress, emotions and key physiological systems. The implications are that relatively inexpensive interventions may dramatically and positively impact individuals' health and well-being. Thus, individuals may have greater control over their minds, bodies and health than previously suspected.

Behavioral and physiological consequences of repeated daily intracerebroventricular injection of corticotropin-releasing factor in the rat

The present study was conducted to investigate the long-term consequences of repeated daily bolus injections of corticotropin-releasing factor (CRF) intracerebroventricularly (ICV) on ongoing locomotor activity and physiology in the home cage of individually housed rats. For this purpose ovine CRF (1 microgram/3 microliters) was injected once daily during the early resting phase into the lateral ventricle for a period of 10 days. Changes in daily rhythms in heart rate, body temperature and motor activity were recorded telemetrically before and during the treatment period. Daily central CRF injection delayed the body weight gain, increased adrenal weight, and decreased the weight of the thymus at the end of the experiment. The acute behavioral and physiological responses to CRF did not habituate with repetition of treatment. CRF treatment also failed to affect the long-term regulation of baseline heart rate, body temperature and motor activity during the light phase, as measured during the hour preceding the daily CRF injection. Mean heart rate during the dark phase was, however, significantly decreased in CRF-treated rats during the whole experimental 10-day period, without any sign of habituation. The failure of episodic CRF to affect long-term regulation of baseline body temperature during the light as well as the dark phase was noteworthy because an increased daytime body temperature lasting for several days is a characteristic marker of various behavioral stressors. Since a previous study showed that the temperature response during chronic CRF infusion was similar to the long-term effects of behavioral stress it is hypothesized that chronic but not episodic increases in central CRF levels are related to the induction and persistence of part of the stress-related behavioral and physiological disorders.

Physiological and behavioral effects of chronic intracerebroventricular infusion of corticotropin-releasing factor in the rat

The present study was conducted to investigate the long-term effects of chronic elevation of centrally circulating levels of corticotropin-releasing factor (CRF) on behavior and physiology. For this purpose ovine CRF was infused continuously for a period of 10 days into the lateral ventricle of rats with the aid of osmotic pumps (calculated CRF delivery was 4.9 micrograms/day). Changes in daily rhythms in body temperature and home cage motor activity were recorded telemetrically during the infusion period. The most prominent physiological findings were a delayed body weight gain and a long-lasting hyperthermia following CRF infusion. The peptide treatment furthermore increased adrenal weight and suppressed the weight of the thymus at the end of the experiment. Behaviorally, CRF administration elicited a short-lasting increase in activity during the light phase and an increased anxiety in an elevated plus-maze 1 week after the start of infusion. The similarities between the present results and the long-term changes previously described in behaviorally stressed rats indicate that chronically elevated levels of CRF in the brain might play an important role in the induction and persistence of stress-related behavioral and physiological disorders.

Neuroimmunomodulation via limbic structures--the neuroanatomy of psychoimmunology

During the last 20 years, mutual communications between the immune, the endocrine and the nervous systems have been defined on the basis of physiological, cellular, and molecular data. Nevertheless, a major problem in the new discipline "Psychoneuroimmunology" is that controversial data and differences in the interpretation of the results make it difficult to obtain a comprehensive overview of the implications of immunoneuroendocrine interactions in the maintenance of physiological homeostasis, as well as in the initiation and the course of pathological conditions within these systems. In this article, we will first discuss the afferent pathways by which immune cells may affect CNS functions and, conversely, how neural tissues can influence the peripheral immune response. We will then review recent data, which emphasize the (patho)physiological roles of hippocampal-amygdala structures and the nucleus accumbens in neuroimmunomodulation. Neuronal activity within the hippocampal formation, the amygdaloid body, and the ventral parts of the basal ganglia has been examined most thoroughly in studies on neuroendocrine, autonomic and cognitive functions, or at the level of emotional and psychomotor behaviors. The interplay of these limbic structures with components of the immune system and vice versa, however, is still less defined. We will attempt to review and discuss this area of research taking into account recent evidences for neuroendocrine immunoregulation via limbic neuronal systems, as well as the influence of cytokines on synaptic transmission, neuronal growth and survival in these brain regions. Finally, the role of limbic structures in stress responses and conditioning of immune reactivity will be commented. Based on these data, we propose new directions of future research.

Functional corticotropin-releasing factor receptors in human neuroblastoma cells

The present study examined the presence of functional corticotropin-releasing factor (CRF) receptors in IMR-32 neuroblastoma cells. [125I]Tyro-ovine CRF binding was linear with increasing protein concentrations, saturable, reversible and of high affinity. Scatchard analysis indicated a Kd of approximately 0.8 nM and a Bmax of approximately 32 fmol/mg protein. Competition studies with CRF and related peptides revealed a pharmacological profile characteristic of the CRF1 receptor subtype. CRF stimulated cAMP production in a dose-dependent manner with an apparent EC50 of approximately 4 nM. In addition, the putative CRF receptor antagonist alpha-helical CRF9-41 dose-dependently inhibited CRF stimulated (10 nM) cAMP production with an IC50 of approximately 60 nM. CRF treatment down regulated its own receptor while treatment with the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), increased CRF binding in neuroblastoma cells. Taken together, these data demonstrate the utility of the human neuroblastoma cell line for functional studies on CRF receptors and suggest that CRF may play a regulatory role in the pathophysiology of human neuroblastoma.

Reciprocal cross-desensitization of locus coeruleus electrophysiological responsivity to corticotropin-releasing factor and stress

While acutely administered corticotropin-releasing factor (CRF) and acute stress each activate neurons of the locus coeruleus (LC), desensitization to both develops with repeated treatment. The present experiments were designed to investigate whether cross-desensitization develops between CRF and stress. Because acute hemodynamic stress caused by intravenous infusion of sodium nitroprusside increases LC electrophysiological discharge rate via a CRF-dependent mechanism, it was hypothesized that repeated CRF administration would cause desensitization to the effect of this stressor on LC. For a complementary experiment, it was hypothesized that repeated stress, which presumably results in the repeated release of endogenous CRF, would result in desensitization to subsequent exogenous CRF. The results of the first experiment showed that repeated intracerebroventricular (i.c.v.) administration of CRF caused a significant attenuation of the sodium nitroprusside-induced increase in LC discharge rate seen in naive rats, although this pretreatment actually potentiated the decrease in blood pressure produced by sodium nitroprusside. In the second experiment, either one or eight sessions of white-noise stress attenuated the effect of CRF on LC activity 24 h after the last stress exposure, and this attenuation was more pronounced following eight sessions of stress than following one session. In a test of the specificity of this effect, stress-induced desensitization did not generalize to the LC electrophysiological response to clonidine (i.c.v.). One week following the last of eight sessions of stress, LC responsivity to CRF had recovered to control levels. These experiments demonstrate reciprocal cross-desensitization between CRF and stress using LC electrophysiological responsivity as an assay. This modifiability of the interaction between CRF and the LC may represent the operation of mechanisms mediating adaptive responding to stress.

Developmental profile of messenger RNA for the corticotropin-releasing hormone receptor in the rat limbic system

The ontogeny of corticotropin-releasing hormone (CRH) receptor messenger ribonucleic acid (mRNA) in rat brain, using in situ hybridization, is the focus of this study. The developmental profile of CRH receptor using binding assays and receptor autoradiography has been reported, but may be confounded by the presence of a binding protein. The recent cloning of the rat CRH receptor gene has permitted the use of in situ hybridization histochemistry to map the distribution of cells expressing CRH receptor mRNA in the developing brain. We used antisense 35S-labeled oligodeoxynucleotide probes for the two reported splice-variants of the CRH receptor mRNA, which yielded essentially identical localization patterns. CRH receptor mRNA was clearly detectable in infant brain starting on the second postnatal day. Signal in hippocampal CA1, CA2 and CA3a increased to 300-600% of adult levels by postnatal day 6 with a subsequent gradual decline. In the amygdala, in contrast, CRH receptor mRNA abundance increased steadily between the second and the ninth postnatal days, to levels twice higher than those in the adult. In the cortex, CRH receptor mRNA levels were high on postnatal day 2 and decreased to adult levels by day 12. Transient signal over the hypothalamic paraventricular nucleus, observed on the second postnatal day, was not evident at older ages. These results demonstrate robust synthesis of CRH receptor as early as on the second postnatal day and unique region-specific developmental profiles for CRH receptor gene expression.

Homologous desensitization of human corticotropin-releasing factor1 receptor in stable transfected mouse fibroblast cells

Previous radioligand binding and second messenger studies have shown that corticotropin-releasing factor (CRF) modulates its receptor following both in vivo and in vitro treatment. In the present study, we determined the sequence of events leading to CRF-induced downregulation and desensitization of cloned CRF receptors in murine fibroblast cells (Ltk-) stably transfected with CRF1 DNA (from human pituitary). Treatment of cells with rat/human CRF produced a dose- and time-dependent decrease in [125I]Tyr degrees-ovine CRF ([125I]oCRF) binding and a concomitant decrease in CRF-stimulated adenylate cyclase activity. Significant decreases in [125I]oCRF binding and agonist-stimulated cAMP production were evident minutes after CRF treatment with maximal (60-80%) reductions seen following 1 h of CRF treatment. Scatchard analysis revealed that the decrease in [125I]oCRF binding was due to the downregulation of the receptor with no significant alteration seen in the affinity of the ligand. Since the transfected cell line is engineered using an artificial promoter, we did not detect any significant changes in CRF1 receptor mRNA levels following CRF treatment for up to 24 h.

Behavioral, neurochemical, and immunological responses to CRF administration. Is CRF a mediator of stress?

The effect of subacute intracerebroventricular (icv 0.1, 0.5, and 1.0 microgram) administration of corticotropin-releasing factor (CRF) for 5 days on behavior, neurotransmitter concentrations, and immune functions was studied in rats. The results showed that CRF administration produced a dose-dependent increase in locomotor activity in the "open field" test compared with controls; rearing scores were also significantly increased. In the elevated plus maze apparatus, rats given 1.0 microgram CRF spent considerably less time on the open arms when compared with controls. Following 0.5 and 1.0 microgram of CRF infusion, the concentrations of noradrenaline (NA), dopamine (DA) and 5-hydroxy indole acetic acid (5-HIAA) were significantly increased in the hypothalamus. There was no significant change in the concentrations of neurotransmitters in the other brain regions. CRF administration also produced a dose-dependent increase in the levels of corticosterone in the serum. The immunological results clearly showed that subacute icv CRF administration caused a reduction of lymphocyte proliferation, a decrease in the percentage of lymphocytes, and an increase in neutrophil percentage in the differential white blood cell (WBC) count, a decrease in neutrophil phagocytosis, and elevated leucocyte adhesiveness/aggregation (LAA) compared with control animals. These results suggest that icv subacute administration of CRF has anxiogenic effects, increases biogenic amine concentrations in the hypothalamus, and changes in some aspects of immune functions that may reflect the stress-inducing properties of the peptide. These effects are time and dose dependent.

A role for CRH and the sympathetic nervous system in stress-induced immunosuppression

Central CRH coordination of the behavioral and physiologic sequelae of stress has been well established, and so it is parsimonious to suggest that CRH might also coordinate the immunologic sequelae. The studies presented here lend support to this suggestion. CRH administration into the brain was shown to modulate aspects of both cellular and humoral immune function, and the inhibition of CRH release in the brain following stress inhibited stress-associated immunosuppression. The effects of CRH appear to be mediated by the sympathetic branch of the autonomic nervous system, as chemical sympathectomy and pharmacological blockade of beta-adrenergic receptors both reversed the effects of CRH on immune function. In contrast, removal of the adrenal glands did not alter the immunologic effects of CRH. These links among CRH in the brain, sympathetic activation, and immune function suggest the possibility that immune function may be altered in other conditions characterized by elevated sympathetic tone, such as depression and aging, and that these alterations may be attributed to CRH dysregulation in the brain. These studies shed light on the intricate relationship between the brain and the immune system, and also illuminate its complexity. The differential regulation of CRH in the brain and the periphery is one example of the latter. These findings also set the stage for potential clinical intervention with CRH antagonists, for example, to treat compromised immune function associated with chronic stress, depression, or aging.

Effects of pretreatment with corticotropin-releasing factor on the electrophysiological responsivity of the locus coeruleus to subsequent corticotropin-releasing factor challenge

Both acute central administration of exogenous, and stress-induced release of endogenous corticotropin-releasing factor result in electrophysiological activation of the noradrenergic neurons constituting the locus coeruleus. The present experiments were designed to examine whether single (1) or repeated (8) intracerebroventricular pretreatment with exogenous corticotropin-releasing factor would alter locus coeruleus electrophysiological responsivity to subsequent corticotropin-releasing factor challenge in rats. A single corticotropin-releasing factor (3 microg) pretreatment significantly attenuated challenge-induced locus coeruleus activation 24 and 72, but no 96 h later, while a single vehicle pretreatment had no significant effect on the response to subsequent challenge at any pretreatment-to-test interval. Repeated pretreatment with either corticotropin-releasing factor or vehicle completely attenuated locus coeruleus response to challenge 24 h after the final pretreatment. Seventy-two hours after the last vehicle pretreatment, challenge resulted in a significant increase in locus coeruleus activity, though the response was less than in naive controls. Challenge continued to produce no effect on locus coeruleus activity in repeated corticotropin-releasing factor-pretreated rats at this (72 h) time point. One week (168 h) after the cessation of repeated pretreatment, challenge resulted in a significant increase in locus coeruleus activity which was equal to that of naive controls in vehicle-pretreated rats, but reduced by comparison to controls in corticotropin-releasing factor-pretreated rats. Basal discharge rates of locus coeruleus neurons 24 h after the last repeated corticotropin-releasing factor pretreatment were significantly less than in naive controls. Thus, the failure of challenge to increase neuronal activity in these rats was not due to a "ceiling" effect caused by elevated tonic discharge rate. Repeated vehicle pretreatment produced a functional change similar to that produced by exogenous corticotropin-releasing factor administration. One hypothesis is that repeated vehicle pretreatment was stressful and caused the repeated release of endogenous corticotropin-releasing factor. This hypothesis was tested by determining whether locus coeruleus neurons remained responsive to challenge following repeated administration of a corticotropin-releasing factor antagonist. Thus, the effect if repeated pretreatment with the antagonist, [D-Phe, Nle, Calpha MeLeu]CRF was also examined. Challenge resulted ina significant increase in discharge rate 24 h after the final antagonist pretreatment, providing support for the hypothesis. Additionally, in rats repeatedly pretreated with vehicle, carbachol challenge induced an increase in locus coeruleus activity equal to that induced in naive controls. These results indicate that prior exposure to corticotropin-releasing factor, or the repeated mild stress of vehicle infusions, reduces locus coeruleus responsiveness to corticotropin-releasing factor, and reveal that the relationship between these two neurotransmitter systems is modifiable. This altered relationship may contribute to stress-related affective disorders in which both systems have been implicated.

Cerebrospinal fluid corticotropin and cortisol are reduced in infantile spasms

Infantile spasms respond to ACTH, and levels of the hormone in cerebrospinal fluid of untreated infants with this disorder were found to be lower than in age-matched controls. In this study we analyzed cerebrospinal fluid cortisol and ACTH using improved immunoassays in a larger cohort of infants with infantile spasms. Analysis of 20 patients and 15 age-matched controls revealed significantly lower levels of both ACTH and cortisol in the cerebrospinal fluid. These data, combined with the efficacy of ACTH and glucocorticoids for infantile spasms, support an involvement of the brain-adrenal-axis in this disorder.

Modulation of binding sites for corticotropin-releasing hormone by chronic psychosocial stress

This study was conducted to determine whether long lasting psychosocial stress would affect corticotropin-releasing hormone (CRH) binding sites in the brain, the pituitary, and the adrenal gland. As a model for sustained emotional stress we used chronic psychosocial conflict in male tree shrews. In subordinate tree shrews, repeated confrontation with a dominant conspecific results in constant hyperactivity of the HPA-axis and an elevated neurosympathetic tone. After 24 days of psychosocial conflict, CRH binding sites were quantified by in vitro-autoradiography with 125I-ovine CRH in 23 discrete brain regions, the pituitaries, and the adrenal glands of subordinate and control animals. Chronic stress significantly reduced the number of binding sites (Bmax) in the anterior lobe of the pituitary, the dentate gyrus, the CA1-CA3 areas of the hippocampus, and in both the stratum griseum superficiale and the stratum opticum of the superior colliculus. In cortical area 17, the reduction of Bmax was counterbalanced by an increase in the affinity (Kd) of the radioligand for the binding sites. A significant stress-induced enhancement of Bmax was observed in the frontal cortex, cingulate cortex, claustrocortex, the central and lateral nucleus of the amygdala, and in the choroid plexus. This increase was accompanied by a significant decrease of Kd-values in the frontal and cingulate cortex, the lateral nucleus of the amygdala, and the choroid plexus. These findings represent the first in vivo demonstration of a modulation of extrahypothalamic CRH receptors by a naturally occurring form of stress. The different response patterns of the central CRH binding sites reflect distinct neuroendocrine processes which are presumed to coordinate behavioral, autonomic, endocrine, and immune responses to long-lasting psychosocial conflict.