Fos induction in selective hypothalamic neuroendocrine and medullary nuclei by intravenous injection of urocortin and corticotropin-releasing factor in rats

The Role of Corticotropin-Releasing Factor (CRF) and CRF-Related Peptides in the Social Behavior of Rodents

Since the corticotropin-releasing factor (CRF) was isolated from an ovine brain, a growing family of CRF-related peptides has been discovered. Today, the mammalian CRF system consists of four ligands (CRF, urocortin 1 (Ucn1), urocortin 2 (Ucn2), and urocortin 3 (Ucn3)); two receptors (CRF receptor type 1 (CRF1) and CRF receptor type 2 (CRF2)); and a CRF-binding protein (CRF-BP). Besides the regulation of the neuroendocrine, autonomic, and behavioral responses to stress, CRF and CRF-related peptides are also involved in different aspects of social behavior. In the present study, we review the experiments that investigated the role of CRF and the urocortins involved in the social behavior of rats, mice, and voles, with a special focus on sociability and preference for social novelty, as well as the ability for social recognition, discrimination, and memory. In general, these experiments demonstrate that CRF, Ucn1, Ucn2, and Ucn3 play important, but distinct roles in the social behavior of rodents, and that they are mediated by CRF1 and/or CRF2. In addition, we suggest the possible brain regions and pathways that express CRF and CRF-related peptides and that might be involved in social interactions. Furthermore, we also emphasize the differences between the species, strains, and sexes that make translation of these roles from rodents to humans difficult.

Superior colliculus projections to target populations in the supraoculomotor area of the macaque monkey

A projection by the superior colliculus to the supraoculomotor area (SOA) located dorsal to the oculomotor complex was first described in 1978. This projection’s targets have yet to be identified, although the initial study suggested that vertical gaze motoneuron dendrites might receive this input. Defining the tectal targets is complicated by the fact the SOA contains a number of different cell populations. In the present study, we used anterograde tracers to characterize collicular axonal arbors and retrograde tracers to label prospective SOA target populations in macaque monkeys. Close associations were not found with either superior or medial rectus motoneurons whose axons supply singly innervated muscle fibers. S-group motoneurons, which supply superior rectus multiply innervated muscle fibers, appeared to receive a very minor input, but C-group motoneurons, which supply medial rectus multiply innervated muscle fibers, received no input. A number of labeled boutons were observed in close association with SOA neurons projecting to the spinal cord, or the reticular formation in the pons and medulla. These descending output neurons are presumed to be peptidergic cells within the centrally projecting Edinger–Westphal population. It is possible the collicular input provides a signaling function for neurons in this population that serve roles in either stress responses, or in eating and drinking behavior. Finally, a number of close associations were observed between tectal terminals and levator palpebrae superioris motoneurons, suggesting the possibility that the superior colliculus provides a modest direct input for raising the eyelids during upward saccades.

Activation of CRF2 receptor increases gastric vagal afferent mechanosensitivity

Gastric vagal afferent (GVA) sensing of food-related mechanical stimuli is a crucial mechanism in the control of feeding behavior and gastric function. Stress is an important factor contributing to eating disorders and gastric diseases. Chronic stress has been shown to increase the mechanosensitivity of GVAs in mice and to reduce food intake and body weight. Whether the mechanosensitivity of GVAs is modulated by stress hormones is not known. This study aimed to determine the effect of stress hormones on GVA mechanosensitivity. The expression of stress hormone receptors in GVA cell bodies was determined in 8-wk-old male C57BL/6 mice using quantitative RT-PCR combined with laser capture microdissection. The mechanosensitivity of GVAs was determined in the absence and presence of stress hormones using an in vitro single-fiber recording preparation. NR3C1 and CRHR2 (mRNA isoforms of glucocorticoid receptor and CRF2 receptor, respectively) were expressed in GVA neurons. The glucocorticoid receptor agonist corticosterone had no effect on the mechanosensitivity of either tension or mucosal GVAs. Activation of CRF2 receptor by its specific analog, urocortin 3, significantly increased the mechanosensitivity of both tension and mucosal GVAs, an effect prevented by the CRF2 receptor antagonist astressin 2B. In conclusion, activation of CRF2 receptor increases the mechanosensitivity of GVAs. This may contribute to the stress- and CRF2 receptor-associated changes in feeding behavior and gastric function, possibly contributing to the hypersensitivity of GVAs in chronic stress conditions.

NEW & NOTEWORTHY Gastric vagal afferents (GVAs) relay food-related signals to the central nervous system, where they are processed, eventually leading to modulation of food intake and gastric function. GVA signaling can be modulated by an array of hormones. Stress has been shown to induce GVA hypersensitivity. This study demonstrates that GVA neurons express subtypes of stress hormone receptors, specifically CRF2. Furthermore, activation of CRF2 receptor increases GVA mechanosensitivity, which could have implications for food intake and gastric function.

Gut-Brain Neuroendocrine Signaling Under Conditions of Stress-Focus on Food Intake-Regulatory Mediators

The gut-brain axis represents a bidirectional communication route between the gut and the central nervous system comprised of neuronal as well as humoral signaling. This system plays an important role in the regulation of gastrointestinal as well as homeostatic functions such as hunger and satiety. Recent years also witnessed an increased knowledge on the modulation of this axis under conditions of exogenous or endogenous stressors. The present review will discuss the alterations of neuroendocrine gut-brain signaling under conditions of stress and the respective implications for the regulation of food intake.

Corticotropin-releasing factor receptor type 1 and type 2 interaction in irritable bowel syndrome

Irritable bowel syndrome (IBS) displays chronic abdominal pain or discomfort with altered defecation, and stress-induced altered gut motility and visceral sensation play an important role in the pathophysiology. Corticotropin-releasing factor (CRF) is a main mediator of stress responses and mediates these gastrointestinal functional changes. CRF in brain and periphery acts through two subtype receptors such as CRF receptor type 1 (CRF1) and type 2 (CRF2), and activating CRF1 exclusively stimulates colonic motor function and induces visceral hypersensitivity. Meanwhile, several recent studies have demonstrated that CRF2 has a counter regulatory action against CRF1, which may imply that CRF2 inhibits stress response induced by CRF1 in order to prevent it from going into an overdrive state. Colonic contractility and sensation may be explained by the state of the intensity of CRF1 signaling. CRF2 signaling may play a role in CRF1-triggered enhanced colonic functions through modulation of CRF1 activity. Blocking CRF2 further enhances CRF-induced stimulation of colonic contractility and activating CRF2 inhibits stress-induced visceral sensitization. Therefore, we proposed the hypothesis, i.e., balance theory of CRF1 and CRF2 signaling as follows. Both CRF receptors may be activated simultaneously and the signaling balance of CRF1 and CRF2 may determine the functional changes of gastrointestinal tract induced by stress. CRF signaling balance might be abnormally shifted toward CRF1, leading to enhanced colonic motility and visceral sensitization in IBS. This theory may lead to understanding the pathophysiology and provide the novel therapeutic options targeting altered signaling balance of CRF1 and CRF2 in IBS.

CRF and urocortin peptides as modulators of energy balance and feeding behavior during stress

Early on, corticotropin-releasing factor (CRF), a hallmark brain peptide mediating many components of the stress response, was shown to affect food intake inducing a robust anorexigenic response when injected into the rodent brain. Subsequently, other members of the CRF signaling family have been identified, namely urocortin (Ucn) 1, Ucn 2, and Ucn 3 which were also shown to decrease food intake upon central or peripheral injection. However, the kinetics of feeding suppression was different with an early decrease following intracerebroventricular injection of CRF and a delayed action of Ucns contrasting with the early onset after systemic injection. CRF and Ucns bind to two distinct G-protein coupled membrane receptors, the CRF1 and CRF2. New pharmacological tools such as highly selective peptide CRF1 or CRF2 agonists or antagonists along with genetic knock-in or knock-out models have allowed delineating the primary role of CRF2 involved in the anorexic response to exogenous administration of CRF and Ucns. Several stressors trigger behavioral changes including suppression of feeding behavior which are mediated by brain CRF receptor activation. The present review will highlight the state-of-knowledge on the effects and mechanisms of action of CRF/Ucns-CRF1/2 signaling under basal conditions and the role in the alterations of food intake in response to stress.

Intravenous injection of urocortin 1 induces a CRF2 mediated increase in circulating ghrelin and glucose levels through distinct mechanisms in rats

Urocortins (Ucns) injected peripherally decrease food intake and gastric emptying through peripheral CRF(2) receptors in rodents. However, whether Ucns influence circulating levels of the orexigenic and prokinetic hormone, ghrelin has been little investigated. We examined plasma levels of ghrelin and blood glucose after intravenous (iv) injection of Ucn 1, the CRF receptor subtype involved and underlying mechanisms in ad libitum fed rats equipped with a chronic iv cannula. Ucn 1 (10 μg/kg, iv) induced a rapid onset and long lasting increase in ghrelin levels reaching 68% and 219% at 0.5 and 3h post injection respectively and a 5-h hyperglycemic response. The selective CRF(2) agonist, Ucn 2 (3 μg/kg, iv) increased fasting acyl (3h: 49%) and des-acyl ghrelin levels (3h: 30%) compared to vehicle while the preferential CRF(1) agonist, CRF (3 μg/kg, iv) had no effect. Ucn 1's stimulatory actions were blocked by the selective CRF(2) antagonist, astressin(2)-B (100 μg/kg, iv). Hexamethonium (10 mg/kg, sc) prevented Ucn 1-induced rise in total ghrelin levels while not altering the hyperglycemic response. These data indicate that systemic injection of Ucns induces a CRF(2)-mediated increase in circulating ghrelin levels likely via indirect actions on gastric ghrelin cells that involves a nicotinic pathway independently from the hyperglycemic response.

Pattern of Fos expression in the brain induced by selective activation of somatostatin receptor 2 in rats

Central activation of somatostatin (sst) receptors by oligosomatostatin analogs inhibits growth hormone and stress-related rise in catecholamine plasma levels while stimulating grooming, feeding behaviors, gastric transit and acid secretion, which can be mimicked by selective sst(2) receptor agonist. To evaluate the pattern of neuronal activation induced by peptide sst receptor agonists, we assessed Fos-expression in rat brain after intracerebroventricular (i.c.v.) injection of a newly developed selective sst(2) agonist compared to the oligosomatostatin ODT8-SST, a pan-sst(1-5) agonist. Ninety min after injection of vehicle (10 microl) or previously established maximal orexigenic dose of peptides (1 microg=1 nmol/rat), brains were assessed for Fos-immunohistochemistry and doublelabeling. Food and water were removed after injection. The sst(2) agonist and ODT8-SST induced a similar Fos distribution pattern except in the arcuate nucleus where only the sst(2) agonist increased Fos. Compared to ODT8-SST, the sst(2) agonist induced higher Fos-expression by 3.7-times in the basolateral amygdaloid nucleus, 1.2-times in the supraoptic nucleus (SON), 1.6-times in the magnocellular paraventricular hypothalamic nucleus (mPVN), 4.1-times in the external lateral parabrachial nucleus, and 2.6-times in both the inferior olivary nucleus and superficial layer of the caudal spinal trigeminal nucleus. Doublelabeling in the hypothalamus showed that ODT8-SST activates 36% of oxytocin, 63% of vasopressin and 79% of sst(2) immunoreactive neurons in the mPVN and 28%, 55% and 25% in the SON, respectively. Selective activation of sst(2) receptor results in a more robust neuronal activation than the pan-sst(1-5) agonist in various brain regions that may have relevance in sst(2) mediated alterations of behavioral, autonomic and endocrine functions.

Abdominal surgery activates nesfatin-1 immunoreactive brain nuclei in rats

Abdominal surgery-induced postoperative gastric ileus is well established to induce Fos expression in specific brain nuclei in rats within 2-h after surgery. However, the phenotype of activated neurons has not been thoroughly characterized. Nesfatin-1 was recently discovered in the rat hypothalamus as a new anorexigenic peptide that also inhibits gastric emptying and is widely distributed in rat brain autonomic nuclei suggesting an involvement in stress responses. Therefore, we investigated whether abdominal surgery activates nesfatin-1-immunoreactive (ir) neurons in the rat brain. Two hours after abdominal surgery with cecal palpation under short isoflurane anesthesia or anesthesia alone, rats were transcardially perfused and brains processed for double immunohistochemical labeling of Fos and nesfatin-1. Abdominal surgery, compared to anesthesia alone, induced Fos expression in neurons of the supraoptic nucleus (SON), paraventricular nucleus (PVN), locus coeruleus (LC), Edinger-Westphal nucleus (EW), rostral raphe pallidus (rRPa), nucleus of the solitary tract (NTS) and ventrolateral medulla (VLM). Double Fos/nesfatin-1 labeling showed that of the activated cells, 99% were nesfatin-1-immunoreactive in the SON, 91% in the LC, 82% in the rRPa, 74% in the EW and VLM, 71% in the anterior parvicellular PVN, 47% in the lateral magnocellular PVN, 41% in the medial magnocellular PVN, 14% in the NTS and 9% in the medial parvicellular PVN. These data established nesfatin-1 immunoreactive neurons in specific nuclei of the hypothalamus and brainstem as part of the neuronal response to abdominal surgery and suggest a possible implication of nesfatin-1 in the alterations of food intake and gastric transit associated with such a stressor.

Central nesfatin-1 reduces dark-phase food intake and gastric emptying in rats: differential role of corticotropin-releasing factor2 receptor

Nesfatin-1, derived from nucleobindin2, is expressed in the hypothalamus and reported in one study to reduce food intake (FI) in rats. To characterize the central anorexigenic action of nesfatin-1 and whether gastric emptying (GE) is altered, we injected nesfatin-1 into the lateral brain ventricle (intracerebroventricular, icv) or fourth ventricle (4v) in chronically cannulated rats or into the cisterna magna (intracisternal, ic) under short anesthesia and compared with ip injection. Nesfatin-1 (0.05 microg/rat, icv) decreased 2-3 h and 3-6 h dark-phase FI by 87 and 45%, respectively, whereas ip administration (2 microg/rat) had no effect. The corticotropin-releasing factor (CRF)(1)/CRF(2) antagonist astressin-B or the CRF(2) antagonist astressin(2)-B abolished icv nesfatin-1's anorexigenic action, whereas an astressin(2)-B analog, devoid of CRF-receptor binding affinity, did not. Nesfatin-1 icv induced a dose-dependent reduction of GE by 26 and 43% that was not modified by icv astressin(2)-B. Nesfatin-1 into the 4v (0.05 microg/rat) or ic (0.5 microg/rat) decreased cumulative dark-phase FI by 29 and 60% at 1 h and by 41 and 37% between 3 and 5 h, respectively. This effect was neither altered by ic astressin(2)-B nor associated with changes in GE. Cholecystokinin (ip) induced Fos expression in 43% of nesfatin-1 neurons in the paraventricular hypothalamic nucleus and 24% of those in the nucleus tractus solitarius. These data indicate that nesfatin-1 acts centrally to reduce dark phase FI through CRF(2)-receptor-dependent pathways after forebrain injection and CRF(2)-receptor-independent pathways after hindbrain injection. Activation of nesfatin-1 neurons by cholecystokinin at sites regulating food intake may suggest a role in gut peptide satiation effect.

Restraint stress activates nesfatin-1-immunoreactive brain nuclei in rats

Nesfatin-1 is a newly discovered peptide that was reported to reduce food intake when injected centrally. We recently described its wide distribution in rat brain autonomic nuclei which implies potential recruitment of nesfatin-1 by stress. We investigated whether restraint, a mixed psychological and physical stressor, activates nesfatin-1-immunoreactive (ir) neurons in the rat brain. Male Sprague-Dawley rats were either subjected to 30 min restraint or left undisturbed and 90 min later brains were processed for double immunohistochemical labeling of Fos and nesfatin-1. Restraint induced significant Fos expression in neurons of the supraoptic nucleus (SON), paraventricular nucleus (PVN), locus coeruleus (LC), rostral raphe pallidus (rRPa), nucleus of the solitary tract (NTS), and ventrolateral medulla (VLM). Double Fos/nesfatin-1 labeling revealed that Fos-ir neurons comprised 95% of nesfatin-1-ir cells in the SON, 90% in the VLM, 80% in the LC, 48% in the caudal NTS, 57% in the rRPa, 48% in the anterior parvicellular PVN, 27% in the medial magnocellular PVN, 18% in the lateral magnocellular PVN and 10% in the medial parvicellular PVN. These data demonstrate that nesfatin-1 neurons are part of the hypothalamic and hindbrain neuronal cell groups activated by restraint suggesting a possible role of nesfatin-1 in the response to stress.

Physiology, pharmacology, and therapeutic relevance of urocortins in mammals: ancient CRF paralogs

Urocortins, three paralogs of the stress-related peptide corticotropin-releasing factor (CRF) found in bony fish, amphibians, birds, and mammals, have unique phylogenies, pharmacologies, and tissue distributions. As a result and despite a structural family resemblance, the natural functions of urocortins and CRF in mammalian homeostatic responses differ substantially. Endogenous urocortins are neither simply counterpoints nor mimics of endogenous CRF action. In their own right, urocortins may be clinically relevant molecules in the pathogenesis or management of many conditions, including congestive heart failure, hypertension, gastrointestinal and inflammatory disorders (irritable bowel syndrome, active gastritis, gastroparesis, and rheumatoid arthritis), atopic/allergic disorders (dermatitis, urticaria, and asthma), pregnancy and parturition (preeclampsia, spontaneous abortion, onset, and maintenance of effective labor), major depression and obesity. Safety trials for intravenous urocortin treatment have already begun for the treatment of congestive heart failure. Further understanding the unique functions of urocortin 1, urocortin 2, and urocortin 3 action may uncover other therapeutic opportunities.

Corticotropin releasing factor 2 receptor agonists reduce the denervation-induced loss of rat skeletal muscle mass and force and increase non-atrophying skeletal muscle mass and force

Of the two corticotropin releasing factor receptors known, corticotrophin releasing factor 2 receptor (CRF2R) is expressed in skeletal muscle. The function of this receptor in skeletal muscle is at present unknown. In order to better understand the role of the CRF2R in skeletal muscle, we treated rats with CRF2R agonists and evaluated the effect of these agents on normal and denervated muscle mass. Rats treated with the non-selective CRFR agonist, sauvagine, did not demonstrate any significant and consistent change in non-denervated and denervated fast twitch [tibialis anterior (TA) or extensor digitorum longus (EDL)] or slow/mixed twitch [medial gastrocnemius (MG) or soleus] fiber muscle mass. In adrenalectomized rats, sauvagine treatment resulted in no significant and consistent change in non-denervated fast or slow/mixed twitch fiber muscles but did cause a significant and consistent increase in denervated fast twitch (TA and EDL) but not slow/mixed twitch muscle mass. Interestingly adrenalectomy had no effect on the degree of muscle atrophy. Rats treated with the CRF2R selective agonist urocortin 2 demonstrated an increase in non-denervated and denervated fast and slow/mix twitch fiber muscle mass. The urocortin 2 induced increase in muscle mass was accompanied by an increase in muscle fiber cross-sectional area and muscle absolute force. These studies demonstrated that activation of the CRF2R decreased the level of skeletal muscle mass, force, and myocyte cross-sectional area loss resulting from sciatic nerve damage and increased the mass, force and myocyte cross-sectional area of normal (non-atrophying) skeletal muscle. In addition, we also observed that removal of the adrenals increased the effectiveness of the non-selective CRFR agonists sauvagine, presumably via the removal of the pro-atrophy influence of adrenal produced corticosteroids. These results demonstrate that pharmacological modulation of the CRF2R may be a viable method to treat skeletal muscle atrophy.

Peripheral secretin-induced Fos expression in the rat brain is largely vagal dependent

I.v. injection of secretin activates neurons in brain areas controlling autonomic function and emotion. Peripheral administration of secretin inhibits gastric functions through a central mechanism that is mediated by vagal dependent pathways. We investigated whether the vagus nerve is involved in i.p. injection of secretin-induced brain neuronal activation in conscious rats as monitored by Fos immunohistochemistry. Secretin (40 or 100 microg/kg, i.p., 90 min) induced a dose-related increase in the number of Fos positive neurons in the central nucleus of the amygdala (CeA), and a plateau Fos response in the area postrema (AP), nucleus tractus solitarii (NTS), locus coeruleus (LC), Barrington's nucleus (Bar), external lateral subnucleus of parabrachial nucleus (PBel) and arcuate nucleus, and at 100 microg/kg, in the dorsal motor nucleus of the vagus (DMV) compared with i.p. injection of vehicle. Double immunohistochemistry showed that secretin (40 microg/kg, i.p.) activates tyrosine hydroxylase neurons in the NTS. Subdiaphragmatic vagotomy (7 days) abolished Fos expression-induced by i.p. secretin (40 microg/kg) in the NTS, DMV, LC, Bar, PBel and CeA, while a significant rise in the AP was maintained. In contrast, s.c. capsaicin (10 days) did not influence the Fos induction in the above nuclei. Reverse transcription polymerase chain reaction (RT-PCR) and quantitative real-time PCR showed that secretin receptor mRNA is expressed in the nodose ganglia and levels were higher in the right compared with the left ganglion. These results indicate that peripheral secretin activates catecholaminergic NTS neurons as well as neurons in medullary, pontine and limbic nuclei regulating autonomic functions and emotion through vagal-dependent capsaicin-resistant pathways. Secretin injected i.p. may signal to the brain by interacting with secretin receptors on vagal afferent as well as on AP neurons outside the blood-brain barrier.

Urocortins and the regulation of gastrointestinal motor function and visceral pain

Urocortin (Ucn) 1, 2 and 3 are corticotropin-releasing factor (CRF)-related peptides recently characterized in mammals. Urocortin 1 binds with high affinity to CRF type 1 (CRF1) and type 2 (CRF2) receptors while Ucn 2 and Ucn 3 are selective CRF2 ligands. They also have a distinct pattern of distribution, both in the brain and the gastrointestinal tract, compatible with a role mediating, with CRF, the response to stress. In rats and mice, Ucn 1 injected centrally or peripherally inhibited gastric emptying and stimulated colonic propulsive motor function, mimicking the effects of stress or exogenous CRF. Centrally administered Ucn 2 inhibited gastric emptying with similar potency as CRF, while Ucn 1 and Ucn 3 were less potent. However, after peripheral administration, Ucn 1 and Ucn 2 were more potent than CRF. In mice, centrally administered Ucn 1 and 2 stimulated colonic motility with lower potency than CRF, and Ucn 3 was inactive. Studies with selective CRF1 and CRF2 antagonists demonstrated that the gastric-inhibitory and colonic-stimulatory effects of exogenously administered Ucns are mediated through CRF2 and CRF1 receptors, respectively. In addition, Ucn 2 showed visceral anti-nociceptive activity associated with the selective activation of CRF2 receptors. These observations suggest that, acting centrally and peripherally, Ucns might play a significant role in the modulation of gastrointestinal motor and pain responses during stress and stress-related pathophysiological conditions.

Corticotropin-releasing factor 2 receptor localization in skeletal muscle

Our objective in this study was to localize the corticotropin-releasing factor 2 receptor (CRF2R) in rodent and human skeletal muscle. We found CRF2R protein to be abundant in neural tissues in skeletal muscle, including large nerve fibers and bundles, neural tissue associated with mechanoreceptors, muscle spindles, and the Golgi tendon organ. CRF2R protein was also abundant in blood vessels in skeletal muscle. CRF2R protein was also observed, although with less abundance, in the endo/perimysial regions in skeletal muscle. The localization of the CRF2R to blood vessels is consistent with the CRF2R-mediated vascular phenomena observed previously, but the observation of CRF2R in neural tissue in skeletal muscle is a novel finding with an unknown function.

Stress-induced sensitization of the hypothalamic-pituitary adrenal axis is associated with alterations of hypothalamic and pituitary gene expression

We have previously reported that inescapable tail shock (IS) produces persistent changes in hypothalamic-pituitary-adrenal (HPA) axis function. These changes are manifest as an elevation in basal corticosterone (CORT) levels, a sensitization of adrenocorticotropin hormone (ACTH) and CORT responses to subsequent challenge, and a failure of dexamethasone to suppress both the ACTH and CORT responses to a subsequent challenge. The experiments presented here examine IS-induced alterations in the responsiveness of the HPA axis, particularly at the level of the anterior pituitary. The data presented show that adrenalectomy does not abolish the IS-induced sensitization of the HPA axis, suggesting that the sensitization is not solely caused by a defect in glucocorticoid negative feedback. Analysis of gene expression in the anterior pituitary revealed that IS exposure persistently elevated basal levels of proopiomelanocortin (POMC; the precursor to ACTH) mRNA and sensitized the POMC hnRNA and c-fos mRNA response to a subsequent challenge. Analysis of gene expression in the parvocellular division of the paraventricular nucleus of the hypothalamus (pPVN) after IS exposure revealed that basal levels of corticotropin-releasing hormone (CRH) mature mRNA are elevated and the c-fos mRNA response to a subsequent challenge is enhanced. Finally, a blunted in vitro ACTH response to CRH challenge is observed after IS exposure. These data suggest that the ultimate source of the IS-induced sensitization is not the anterior pituitary and implicate an increased drive on the anterior pituitary from the pPVN.

Nibbling at CRF receptor control of feeding and gastrocolonic motility

Inadequate pharmacological tools, until recently, hindered the understanding of the roles of corticotropin-releasing factor (CRF) receptor subtypes in appetite regulation and gastrocolonic motor function. Now, novel ligands that are selective for CRF(1) or CRF(2) receptors are helping to uncover the specific functions of CRF receptor subtypes. Central or peripheral CRF(2) receptor activation suppresses feeding independently of CRF(1) receptors. In the rat, central administration of CRF(2) receptor agonists promotes satiation without eliciting the malaise, behavioral arousal or anxiogenesis associated with CRF(1) receptor agonists. Conversely, central administration of CRF(1) receptor agonists elicits short-onset anorexia independently of CRF(2) receptor activation. With respect to gastrointestinal motor function, stress inhibits gastric motility through CRF(2) receptor-dependent central autonomic and peripheral myenteric systems. By contrast, stress stimulates colonic motility via CRF(1) receptor-dependent sacral parasympathetic and colonic myenteric mechanisms. These findings have important physiological implications and suggest targeted approaches for the pharmacotherapy of obesity and stress-related functional gastrointestinal and eating disorders.

The effect of urocortin on ingestive behaviours and brain Fos immunoreactivity in mice

The influence of urocortin (UCN) on ingestive behaviours and brain neural activity, as measured immunohistochemically by the presence of Fos protein, was determined in mice. Rat UCN was administered by continuous intracerebroventricular (ICV) or subcutaneous (SC) infusion. ICV infusion of UCN (100 ng/h, 14 days) transiently reduced daily food and water intakes (days 1-4) but body weight was reduced from day 2 into the post-infusion period. Sodium intake was reduced from day 3 to the end of infusion. SC infusion of UCN caused similar but smaller reductions in food and water intakes and body weight, without change in sodium intake. In separate experiments, Fos immunoreactivity was increased in several brain nuclei known to be involved in the control of body fluid and energy homeostasis, e.g. central nucleus of the amygdala, median preoptic nucleus, bed nucleus of the stria terminalis and arcuate nucleus. Increased Fos expression was similar for ICV and SC infusions when measured on days 2-3 or 6-7 of infusion. In conclusion, increases of brain activity by UCN may be associated with stimulation of adrenocorticotrophic hormone release and sympathetic nervous activity, but increases may also indicate suppression of ingestive behaviours by stimulating central inhibitory mechanisms located in areas known to control body fluid and energy homeostasis.

Intraperitoneal corticotropin-releasing factor and urocortin induce Fos expression in brain and spinal autonomic nuclei and long lasting stimulation of colonic motility in rats

CRF injected intraperitoneally (i.p.) stimulates colonic motor function and induces Fos expression in colonic myenteric neurons. We investigated central and spinal Fos expression and changes in colonic motility in response to i.p. injection of CRF and urocortin. Ovine CRF(9-33) that is devoid of intrinsic activity at the CRF receptors, was used as control peptide. Myoelectrical activity was monitored for 1 h before and after peptide injection (10 microg/kg, i.p.) in conscious non fasted rats with chronically implanted intraparietal electrodes in the cecum and proximal colon. Brain and lumbosacral spinal cord were processed for Fos immunohistochemistry at 1 h postinjection. CRF and urocortin elicited defecation and a new pattern of ceco-colonic clustered spike bursts that peaked within 15 min and lasted for the 1 h experimental period while CRF(9-33) did not modify baseline myoelectrical activity and defecation. CRF increased significantly Fos expression in the central nucleus of the amygdala (lateral part), parabrachial nucleus (external lateral subnucleus), area postrema, nucleus tractus solitarius, locus coeruleus, paraventricular nucleus of the hypothalamus, the intermediolateral column and area I-VII, X at the L6-S1 level of the spinal cord by 11-, 6.5-, 5.3-, 5.0-, 4.7-, 2.7- and 1.4-fold, respectively compared with i.p. CRF(9-33) injected rats that had little Fos expression. Urocortin induced a similar pattern of Fos response in the brain and the spinal cord. These results indicate that i.p. CRF and urocortin induce a peptide specific activation of brain nuclei receiving viscerosensory inputs and involved in autonomic circuitries whose effector limbs may impact on visceral function.

Role of corticotrophin-releasing hormone in the impairment of counterregulatory responses to hypoglycemia

We have explored the role of individual elements of the hypothalamic pituitary adrenal axis on the pathogenesis of hypoglycemia-associated autonomic failure. Five groups of male Sprague-Dawley rats were used. Control animals had 3 days of sham treatment followed by a hyperinsulinemic/hypoglycemic glucose clamp on day 4. A second group underwent 3 days of antecedent insulin-induced hypoglycemia then a subsequent clamp. Three more groups underwent pretreatment with corticosterone, adrenocorticotrophic hormone (ACTH), or corticotrophin-releasing hormone (CRH) mirroring the glucocorticoid response of the hypoglycemic group. Subsequent counterregulatory responses showed marked differences. CRH- (and insulin-treated) animals showed markedly reduced epinephrine responses (CRH 1,276 +/- 404 pg/ml, controls 3,559 +/- 563 pg/ml; P < 0.05). In contrast, ACTH pretreatment augmented epinephrine responses (6,681 +/- 814 pg/ml; P = 0.007 versus controls); corticosterone pretreatment caused a similar but nonsignificant enhancement. The same pattern was seen for norepinephrine. CRH pretreatment also suppressed glucagon responses to hypoglycemia (control 157 +/- 21, CRH 68 +/- 10 pg/ml; P = 0.004). The addition of a CRH receptor 1 (CRHr1) antagonist to the antecedent CRH reversed the subsequent suppression of epinephrine. These findings suggest that CRH acting via CRHr1 plays an important role in the sympathoadrenal downregulation seen in this rodent model of antecedent hypoglycemia; this action is not mediated via activation of the hypothalamic-pituitary-adrenal axis.

The highly selective CRF(2) receptor antagonist K41498 binds to presynaptic CRF(2) receptors in rat brain

1. Novel analogues of antisauvagine-30 (aSvg-30), a selective antagonist for CRF(2) receptors, have been synthesized and characterized in vitro and in vivo. 2. The analogues were tested for their ability to compete for [(125)I-Tyr(0)]Svg binding and to inhibit Svg-stimulated adenylate cyclase activity in human embryonic kidney (HEK) 293 cells, permanently transfected with cDNA coding for the human CRF(1) (hCRF(1)), hCRF(2alpha) and hCRF(2beta) receptor. One analogue [D-Phe(11), His(12), Nle(17)]Svg(11-40), named K41498, showed high affinity binding to hCRF(2alpha) (K(i)=0.66+/-0.03 nM) and hCRF(2beta) (K(i)=0.62+/-0.01 nM) but not the hCRF(1) receptor (k(i)=425+50 nM) and decreased Svg-stimulated cAMP accumulation in hCRF(2) expressing cells. In conscious Wistar-Kyoto rats, K41498 (1.84 microg, i.v.) antagonized the hypotensive response to systemic urocortin (1.4 microg, i.v.), but did not block the pressor response to centrally administered urocortin (2.35 microg, i.c.v.). 3. K41498 was subsequently radio-iodinated, and in autoradiographic studies, specific (sensitive to rat urocortin, astressin and aSvg30, but insensitive to antalarmin) binding of (125)I-K41498 (100 pM) was detected in the heart and in selected brain regions including the nucleus tractus solitarius (NTS), spinal trigeminal nucleus, lateral septum and around the anterior and middle cerebral arteries. 4. Following unilateral nodose ganglionectomy, binding of (125)I-K41498 was reduced by 65% in the ipsilateral NTS, indicative of presynaptic CRF(2) receptors on vagal afferent terminals. 5. These data demonstrate that K41498 is a useful tool to study native CRF(2) receptors in the brain and periphery.

Appetite suppression and weight reduction by a centrally active aminosterol

The rise in obesity and its complications has generated enormous interest in the regulation of feeding and body weight. We show that a spermine metabolite of cholesterol (MSI-1436) decreases body weight, specifically fat, by suppressing feeding and preventing the reduction in energy expenditure, hormonal changes, and patterns of neuropeptide expression normally associated with weight loss. MSI-1436 enters the brain after peripheral injection and is more potent when injected into the cerebral ventricle (intracerebroventricular [ICV]). Systemic or ICV MSI-1436 administration induced similar patterns of Fos immunoreactivity in the brain, especially the paraventricular hypothalamic nucleus (PVN). This brain region integrates neural signals from hypothalamic and brain stem nuclei and regulates feeding behavior, autonomic function, and neuroendocrine function. Microinjection of MSI-1436 into the PVN potently suppressed feeding and reduced body weight for several days. Unlike caloric restriction, MSI-1436 decreased mRNA levels of agouti-related peptide and neuropeptide Y in the hypothalamus. These findings indicate that MSI-1436 acts in the brain to regulate food intake and energy expenditure, likely through suppression of orexigenic hypothalamic pathways.

Peripheral ghrelin selectively increases Fos expression in neuropeptide Y - synthesizing neurons in mouse hypothalamic arcuate nucleus

Ghrelin, a peptide isolated from the rat stomach, is the endogenous ligand of the growth hormone-secretagogue receptor and also known to have orexigenic effect. We examined the influence of intraperitoneal (i.p.) injection of ghrelin on food intake and brain neuronal activity in freely fed mice. Ghrelin (3, 10 or 30 microg/mouse) dose-dependently increased food intake by 0.8-, 1.6- and 2.6-fold, respectively, at 30 min post injection. Ghrelin (10 microg/mouse) induces Fos expression selectively in the ventromedial part of the hypothalamic arcuate nucleus (Arc). No change in Fos expression was observed in other hypothalamic and hindbrain nuclei. About 90% of the Fos-positive neurons in the Arc expressed neuropeptide Y (NPY) messenger RNA. These data indicate that NPY neurons in the Arc are likely the primary target mediating i.p. ghrelin induced orexigenic effect.

Visualization of functionally activated circuitry in the brain

We have used a transgenic approach to visualize functionally activated neurons and their projections. The transgenic mice contain a tau-lacZ fusion gene regulated by the promoter for c-fos, an immediate early gene that is rapidly induced in neurons after functional stimulation. Constitutive expression of beta-galactosidase (beta-gal), the lacZ product, was low and in accord with previous reports of c-fos expression. However, expression of beta-gal in positive neurons was clearly in cell bodies, axons, and dendrites. Treatment of the mice with kainic acid, a strong inducer of c-fos expression, resulted in high induction of beta-gal. beta-gal was induced in the same defined populations of neurons in the brain as those that express c-fos after kainic acid induction. Furthermore, the pattern of beta-gal expression within the neurons changed over time after kainic acid treatment. Early after kainate treatment, beta-gal was found mainly in cell bodies; at later times, expression extended further along the neuronal processes. This expression pattern is consistent with induction and anterograde transport of the Fos-Tau-beta-gal protein in the neurons. To test whether a functionally activated pathway could be visualized, transgenic mice were deprived of water, which activates nuclei involved in body fluid homeostasis. beta-gal induction was traced in neurons and their processes in the lamina terminalis, in magnocellular neurons of the supraoptic and paraventricular nuclei, and in their projections to the posterior pituitary gland. This strategy allowed the mapping of an activated osmoregulatory pathway. This transgenic approach may have general application in the mapping of functionally activated circuitry in the brain.

Hyperdynamic circulation in portal-hypertensive rats is dependent on central c-fos gene expression

Portal hypertension is associated with hyperdynamic circulation, but the pathogenesis remains unclear. To clarify the role of central cardiovascular regulatory mechanisms, several protocols were conducted in rats with portal hypertension due to portal vein stenosis (PVS). Neuronal activation was quantified by immunohistochemical staining for Fos, the protein product of the c-fos gene. Fos expression in several brain nuclei with cardiovascular-regulatory roles was examined at 1, 3, 5, and 10 days following PVS surgery. This was correlated with development of cardiovascular changes measured at the same time points. Finally, Fos expression in the nucleus tractus solitarius (NTS) was blocked by local microinjection of c-fos antisense oligonucleotides twice daily for 5 days following PVS. The results showed that Fos-positive neurons were significantly increased in the paraventricular nucleus of hypothalamus, supraoptic nucleus, ventrolateral medulla, and NTS, detectable at day 1 and persistently increased at every day examined in the PVS rats. However, the hyperdynamic circulation developed between days 3 to 5. Administration of c-fos antisense oligonucleotides eliminated the hyperdynamic circulation in PVS rats, but had no effect on sham-operated controls. We conclude that the activation of central cardiovascular-regulatory nuclei, through a c-fos-dependent pathway, is necessary for development of hyperdynamic circulation in portal-hypertensive rats.

Peripheral urocortin inhibits gastric emptying and food intake in mice: differential role of CRF receptor 2

Intraperitoneal urocortin inhibits gastric emptying and food intake in mice. We investigated corticotropin-releasing factor receptor (CRF-R) subtypes involved in intraperitoneal urocortin actions using selective CRF-R antagonists. Gastric emptying was measured 2 h after a chow meal, and food intake was measured hourly after an 18-h fast in mice. Urocortin (3 microg/kg ip) inhibited gastric emptying by 88%. The CRF-R1/CRF-R2 antagonist astressin B (30 microg/kg ip) and the selective CRF-R2 antagonist antisauvagine-30 (100 microg/kg ip) completely antagonized urocortin action, whereas the selective CRF-R1 antagonist CP-154,526 (10 mg/kg ip) had no effect. Urocortin (1-10 microg/kg ip) dose dependently decreased the 2-h cumulative food intake by 30-62%. Urocortin (3 microg/kg)-induced hypophagia was completely antagonized by astressin B (30 microg/kg ip) and partially (35 and 31%) by antisauvagine-30 (100 or 200 microg/kg ip). The CRF-R1 antagonists CP-154,526 or DMP904 (10 mg/kg ip) had no effect. Capsaicin did not alter urocortin-inhibitory actions while blocking the satiety effect of intraperitoneal CCK. These data indicate that intraperitoneal urocortin-induced decrease in feeding is only partly mediated by CRF-R2, whereas urocortin action to delay gastric emptying of a meal involves primarily CRF-R2.

Peripheral corticotropin-releasing factor and stress-stimulated colonic motor activity involve type 1 receptor in rats

BACKGROUND & AIMS

Corticotropin-releasing factor (CRF) exerts its action through CRF receptors 1 and 2 (CRF-R1 and CRF-R2). CRF has preferential affinity for CRF-R1, whereas urocortin displays high affinity for both. We investigated changes in colonic motor function after intraperitoneal (IP) injection of CRF-related peptides.

METHODS

Colonic motility was recorded in vivo in conscious rats equipped with electrodes chronically implanted in the cecum and proximal colon or in vitro in distal colon; fecal output was monitored in naive rats.

RESULTS

Rat CRF, rat urocortin, and amphibian sauvagine (10 microg/kg, IP) induced a new pattern of cecocolonic myoelectric activity characterized by clustered spike bursts of long duration; the percentage of occurrence was highest after CRF. The rank order of potency to increase fecal pellet output after IP peptide injection (0.3-10 microg/kg, IP) was CRF > urocortin = sauvagine. The CRF-R1/R2 antagonist astressin (33 microg/kg, IP) and the CRF-R1 antagonist CP-154,526 (20 mg/kg, subcutaneously) inhibited IP CRF-induced changes in cecocolonic myoelectric activity and IP CRF- and water avoidance stress-induced fecal output. In vitro, CRF injected into the inferior mesenteric artery increased distal colonic myoelectric activity compared with saline injection.

CONCLUSIONS

These results demonstrate that CRF acts peripherally to stimulate colonic motility and that CRF-R1 is primarily involved in mediating IP CRF/urocortin- and water avoidance stress-induced colonic motor response.