Increase of urocortin-like immunoreactivity in the rat hypothalamo-neurohypophysial system after salt loading and hypophysectomy

Centrally Projecting Edinger-Westphal Nucleus in the Control of Sympathetic Outflow and Energy Homeostasis

The centrally projecting Edinger-Westphal nucleus (EWcp) is a midbrain neuronal group, adjacent but segregated from the preganglionic Edinger-Westphal nucleus that projects to the ciliary ganglion. The EWcp plays a crucial role in stress responses and in maintaining energy homeostasis under conditions that require an adjustment of energy expenditure, by virtue of modulating heart rate and blood pressure, thermogenesis, food intake, and fat and glucose metabolism. This modulation is ultimately mediated by changes in the sympathetic outflow to several effector organs, including the adrenal gland, heart, kidneys, brown and white adipose tissues and pancreas, in response to environmental conditions and the animal's energy state, providing for appropriate energy utilization. Classic neuroanatomical studies have shown that the EWcp receives inputs from forebrain regions involved in these functions and projects to presympathetic neuronal populations in the brainstem. Transneuronal tracing with pseudorabies virus has demonstrated that the EWcp is connected polysynaptically with central circuits that provide sympathetic innervation to all these effector organs that are critical for stress responses and energy homeostasis. We propose that EWcp integrates multimodal signals (stress, thermal, metabolic, endocrine, etc.) and modulates the sympathetic output simultaneously to multiple effector organs to maintain energy homeostasis under different conditions that require adjustments of energy demands.

Increased oxytocin-monomeric red fluorescent protein 1 fluorescent intensity with urocortin-like immunoreactivity in the hypothalamo-neurohypophysial system of aged transgenic rats

To visualize oxytocin in the hypothalamo-neurohypophysial system, we generated a transgenic rat that expresses the oxytocin-monomeric red fluorescent protein 1 (mRFP1) fusion gene. In the present study, we examined the age-related changes of oxytocin-mRFP1 fluorescent intensity in the posterior pituitary (PP), the supraoptic nucleus (SON) and the paraventricular nucleus (PVN) of transgenic rats. The mRFP1 fluorescent intensities were significantly increased in the PP, the SON and the PVN of 12-, 18- and 24-month-old transgenic rats in comparison with 3-month-old transgenic rats. Immunohistochemical staining for urocortin, which belongs to the family of corticotropin-releasing factor family, revealed that the numbers of urocortin-like immunoreactive (LI) cells in the SON and the PVN were significantly increased in 12-, 18- and 24-month-old transgenic rats in comparison with 3-month-old transgenic rats. Almost all of urocortin-LI cells co-exist mRFP1-expressing cells in the SON and the PVN of aged transgenic rats. These results suggest that oxytocin content of the hypothalamo-neurohypophysial system may be modulated by age-related regulation. The physiological role of the co-existence of oxytocin and urocortin in the SON and PVN of aged rats remains unclear.

Urocortins are present in the rat testis

The synthesis and release of testosterone (T) depends both on circulating luteinizing hormone (LH) and on an array of testicular factors whose role remains incompletely understood. Corticotropin-releasing factor (CRF) had been reported in the rat testes, where it was thought to inhibit T secretion. However, the discovery that the CRF-related peptides urocortins (Ucns), of which there are currently three subtypes (Ucn 1, 2 and 3), cross-react with many reagents previously used to detect CRF, has cast doubt on this concept. Here we show that while CRF was readily measurable in rat hypothalami (which served as controls), signals for this peptide were barely detectable in total RNA extracted from the testes. On the other hand, microarray, RT-PCR and real-time quantitative RT-PCR (qRT-PCR) analyses all indicated strong signals for Ucn 1 in the male gonads, with weaker levels of Ucn 2 and 3 mRNA gene expression. Results obtained for Ucn 1 gene expression were corroborated by immunohistochemical detection, which appeared restricted to Leydig cells. Finally, to investigate possible changes in testicular Ucn 1 levels induced by homeostatic challenges, we measured them in rats exposed to alcohol. We observed that indeed, the intragastric injection of this drug significantly increased testicular Ucn 1, but not Ucn 2, Ucn 3, CRF, CRFR1 or CRFR2 mRNA levels. Collectively, these results provide novel information regarding the presence of CRF-like peptides in the adult male rat testis.

Footshock-induced urinary bladder hypersensitivity: role of spinal corticotropin-releasing factor receptors

Stress-induced hyperalgesia (SIH), a common clinical observation associated with multiple painful diseases including functional urinary disorders, presently has no mechanistic explanation. Using a footshock treatment, a classic stressor, to magnify physiological responses in a model of urinary bladder pain, we examined one potential group of mediators of SIH, the corticotropin-releasing factor (CRF)-related neuropeptides. Exposure to a footshock treatment produced bladder hypersensitivity in female Sprague-Dawley rats, manifested as significantly more vigorous visceromotor responses (VMRs) to urinary bladder distension (UBD) compared with rats that were exposed to a non-footshock treatment. This bladder hypersensitivity was significantly attenuated by blocking spinal CRF(2) receptors but not CRF(1) receptors. Furthermore, spinal administration of urocortin 2, a CRF(2) receptor agonist, augmented UBD-evoked VMRs in a way similar to what was observed after exposure to Footshock, an effect significantly attenuated by pretreatment with spinal aSVG30, a CRF(2) receptor antagonist. Surprisingly, neither spinal administration of CRF nor the CRF(1) receptor antagonist antalarmin had an effect on bladder nociceptive responses. The results of the present study not only provide further support for a role of stress in the exacerbation of bladder pain but also implicate spinal urocortins and their endogenous receptor, the CRF(2) receptor, as potential mediators of this effect.

PERSPECTIVE

This study presents evidence that spinal urocortins and CRF(2) receptors are involved in stress-induced hypersensitivity related to the urinary bladder. This provides a basis for investigating how urocortins mediate SIH, ultimately leading to more effective treatment options for patients with painful bladder syndromes as well as stress-exacerbated chronic pain.

Response of substances co-expressed in hypothalamic magnocellular neurons to osmotic challenges in normal and Brattleboro rats

The intention of this review is to emphasize the current knowledge about the extent and importance of the substances co-localized with magnocellular arginine vasopressin (AVP) and oxytocin (OXY) as potential candidates for the gradual clarification of their actual role in the regulation of hydromineral homeostasis. Maintenance of the body hydromineral balance depends on the coordinated action of principal biologically active compounds, AVP and OXY, synthesized in the hypothalamic supraoptic and paraventricular nuclei. However, on the regulation of water-salt balance, other substances, co-localized with the principal neuropetides, participate. These can be classified as (1) peptides co-localized with AVP or OXY with unambiguous osmotic function, including angiotensin II, apelin, corticotropin releasing hormone, and galanin and (2) peptides co-localized with AVP or OXY with an unknown role in osmotic regulation, including cholecystokinin, chromogranin/secretogranin, dynorphin, endothelin-1, enkephalin, ferritin protein, interleukin 6, kininogen, neurokinin B, neuropeptide Y, vasoactive intestinal peptide, pituitary adenylate cyclase-activating polypeptide, TAFA5 protein, thyrotropin releasing hormone, tyrosine hydroxylase, and urocortin. In this brief review, also the responses of these substances to different hyperosmotic and hypoosmotic challenges are pointed out. Based on the literature data published recently, the functional implication of the majority of co-localized substances is still better understood in non-osmotic than osmotic functional circuits. Brattleboro strain of rats that does not express functional vasopressin was also included in this review. These animals suffer from chronic hypernatremia and hyperosmolality, accompanied by sustained increase in OXY mRNA in PVN and SON and OXY levels in plasma. They represent an important model of animals with constantly sustained osmolality, which in the future, will be utilizable for revealing the physiological importance of biologically active substances co-expressed with AVP and OXY, involved in the regulation of plasma osmolality.

Chronic osmotic stimuli increase salusin-beta-like immunoreactivity in the rat hypothalamo-neurohypophyseal system: possible involvement of salusin-beta on [Ca2+]i increase and neurohypophyseal hormone release from the axon terminals

Salusin-alpha and -beta were recently discovered as bioactive endogenous peptides. In the present study, we investigated the effects of chronic osmotic stimuli on salusin-beta-like immunoreactivity (LI) in the rat hypothalamo-neurohypophyseal system. We examined the effects of salusin-beta on synaptic inputs to the rat magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus (SON) and neurohypophyseal hormone release from both freshly dissociated SONs and neurohypophyses in rats. Immunohistochemical studies revealed that salusin-beta-LI neurones and fibres were markedly increased in the SON and the magnocellular division of the paraventricular nucleus after chronic osmotic stimuli resulting from salt loading for 5 days and dehydration for 3 days. Salusin-beta-LI fibres and varicosities in the internal zone of the median eminence and the neurohypophysis were also increased after osmotic stimuli. Whole-cell patch-clamp recordings from rat SON slice preparations showed that salusin-beta did not cause significant changes in the excitatory and inhibitory postsynaptic currents of the MNCs. In vitro hormone release studies showed that salusin-beta evoked both arginine vasopressin (AVP) and oxytocin release from the neurohypophysis, but not the SON. In our hands, in the neurohypophysis, a significant release of AVP and oxytocin was observed only at concentrations from 100 nm and above of salusin-beta. Low concentrations below 100 nm were ineffective both on AVP and oxytocin release. We also measured intracellular calcium ([Ca(2+)](i)) increase induced by salusin-beta on freshly-isolated single nerve terminals from the neurohypophysis devoid of pars intermedia. Furthermore, this salusin-beta-induced [Ca(2+)](i) increase was blocked in the presence of high voltage activated Ca(2+)channel blockers. Our results suggest that salusin-beta may be involved in the regulation of body fluid balance by stimulating neurohypophyseal hormone release from nerve endings by an autocrine/paracrine mechanism.

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.

Urocortin 1 distribution in mouse brain is strain-dependent

Urocortin 1 has been implicated in a number of specific behaviors, which include energy balance, stress reactivity and ethanol consumption. To elucidate genetically influenced differences in the mouse urocortin 1 system, we performed immunohistochemical characterization of urocortin 1 distribution in C57BL/6J and DBA/2J mouse brain. Urocortin 1 analysis reveals strain-dependent differences in distribution of urocortin 1 immunoreactive neurons and neuronal fibers. In both strains, the highest number of urocortin 1-positive neurons was observed in the Edinger-Westphal nucleus and lateral superior olive. Urocortin 1-positive neurons were detected in the dorsal nucleus of the lateral lemniscus of DBA/2J mice, but were absent in the C57BL/6J strain. Differences in urocortin 1 fibers were detected in many areas throughout the brain, and were most apparent in the septal areas, thalamic areas, several midbrain regions, and medulla. Strain-dependent distribution of urocortin 1-containing cells and fibers suggests that differences in this neuropeptide system may underlie differences in behavior and physiological responses between these strains. Further, we found that in both mouse strains, urocortin 1 in the Edinger-Westphal nucleus and choline acetyltransferase are not coexpressed. We show that the urocortin 1-positive neurons of this brain area form a separate population of cells that we propose to be called the non-preganglionic Edinger-Westphal nucleus.

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.

Colocalization of urocortin and neuronal nitric oxide synthase in the hypothalamus and Edinger-Westphal nucleus of the rat

Different lines of studies suggest that both the corticotropin-releasing hormone-related peptide Urocortin I (Ucn) and the neuromodulator nitric oxide (NO) are involved in the regulation of the complex mechanisms controlling feeding and anxiety-related behaviors. The aim of the present study was to investigate the possible interaction between Ucn and NO in the hypothalamic paraventricular nucleus (PVN), an area known to be involved in the modulation of these particular behaviors. Therefore, we mapped local mRNA and peptide/protein presence of both Ucn and the NO producing neuronal NO synthase (nNOS). This investigation was extended to include the hypothalamic supraoptic nucleus (SON) and the Edinger-Westphal nucleus area (EW), the latter being one of the major cellular Ucn-expressing sites. Furthermore, we compared the two predominantly used laboratory rat strains, Wistar and Sprague-Dawley. Ucn mRNA and immunoreactivity were detected in the SON and in the EW. A significant difference between Wistar and Sprague-Dawley rats was found in mRNA levels in the EW. nNOS was detected in all brain areas analyzed, showing a significantly lower immunoreactivity in the PVN and EW of Sprague-Dawley versus Wistar rats. Contrary to some previous reports, no Ucn mRNA and only a very low immunoreactivity were detectable in the PVN of either rat strain. Interestingly, double-labeling immunofluorescence revealed that in the SON approximately 75% of all cells immunoreactive for Ucn were colocalized with nNOS, whereas in the EW only approximately 2% of the Ucn neurons were found to contain nNOS. These findings suggest an interaction between Ucn and NO signaling within the SON, rather than the PVN, that may modulate the regulation of feeding, reproduction, and anxiety-related behaviors.

Urocortin in the central nervous system of a primate (Cebus apella): sequencing, immunohistochemical, and hybridization histochemical characterization

The urocortin (UCN)-like immunoreactivity and UCN mRNA distribution in various regions of the nonprimate mammalian brain have been reported. However, the Edinger-Westphal nucleus (EW) appears to be the only brain site where UCN expression is conserved across species. Although UCN peptides are present throughout vertebrate phylogeny, the functional roles of both UCN and EW remain poorly understood. Therefore, a study focused on UCN system organization in the primate brain is warranted. By using immunohistochemistry (single and double labeling) and in situ hybridization, we have characterized the organization of UCN-expressing cells and fibers in the central nervous system and pituitary of the capuchin monkey (Cebus apella). In addition, the sequence of the prepro-UCN was determined to establish the level of structural conservation relative to the human sequence. To understand the relationship of acetylcholine cells in the EW, a colocalization study comparing choline acetyltransferase (ChAT) and UCN was also performed. The cloned monkey prepro-UCN is 95% identical to the human preprohormone across the matched sequences. By using an antiserum raised against rat UCN and a probe generated from human cDNA, we found that the EW is the dominant site for UCN expression, although UCN mRNA is also expressed in spinal cord lamina IX. Labeled axons and terminals were distributed diffusely throughout many brain regions and along the length of the spinal cord. Of particular interest were UCN-immunoreactive inputs to the medial preoptic area, the paraventricular nucleus of the hypothalamus, the oral part of the spinal trigeminal nucleus, the flocculus of the cerebellum, and the spinal cord laminae VII and X. We found no UCN hybridization signal in the pituitary. In addition, we observed no colocalization between ChAT and UCN in EW neurons. Our results support the hypothesis that the UCN system might participate in the control of autonomic, endocrine, and sensorimotor functions in primates.

Beneficial hemodynamic, endocrine, and renal effects of urocortin in experimental heart failure: comparison with normal sheep

OBJECTIVES

The goal of this study was to determine the bioactivity of urocortin (Ucn) in experimental heart failure (HF).

BACKGROUND

Urocortin may participate in cardiovascular function and pressure/volume homeostasis. Its effects in HF are unknown.

METHODS

Eight normal sheep and eight sheep with pacing-induced HF received ovine Ucn (10, 50, and 100 mg intravenous boluses at 2-h intervals) in vehicle-controlled studies.

RESULTS

Urocortin boluses dose-dependently increased plasma Ucn (p < 0.001). Pharmacokinetics were similar in normal and HF sheep with half-lives approximating 1.3 and 19.5 h for the first and second phases, respectively. In HF, cardiac output increased (twofold), while peripheral resistance, left atrial pressure (both 50% falls: p < 0.001), and mean arterial pressure (p < 0.05) fell. In normal sheep, changes in peripheral resistance and atrial pressure were blunted and in arterial pressure were directionally opposite. Urocortin induced persistent, dose-dependent falls (30% to 50%) in plasma vasopressin, renin activity, aldosterone, natriuretic peptides (all p < 0.001), and endothelin-1 (p < 0.05) in HF sheep, while adrenocorticotrophic hormone and cortisol levels rose acutely (both p < 0.001). In comparison, Ucn in normal sheep resulted in a similar rise in cortisol and fall in aldosterone, no significant effects on plasma renin activity and natriuretic peptides, and a rise in vasopressin. Urocortin produced dose-dependent, sustained increases in urine volume (twofold, p < 0.01), sodium excretion (>9-fold rise, p < 0.001), and creatinine clearance (p < 0.001) in HF sheep. No significant renal effects were observed in normal sheep.

CONCLUSIONS

Urocortin has profound and sustained hemodynamic, hormonal, and renal effects in experimental HF. Urocortin may have a role in pressure/volume homeostasis in HF and may provide a novel therapeutic approach to this disease.

Urocortin in the hypothalamic PVN increases leptin and affects uncoupling proteins-1 and -3 in rats

The hypothalamic paraventricular nucleus (PVN) plays a primary role in energy homeostasis, and urocortin (UCN) decreases feeding after injection into the PVN. Peripheral uncoupling proteins (UCPs) may influence energy metabolism. The effect of UCN administered into the PVN on UCPs is unknown. We injected PVN-cannulated rats with either UCN (200 pmol) or artificial cerebrospinal fluid (aCSF) at 0800, 2000, and again at 0800. An aCSF-injected group with food intake restricted to the level of UCN-treated animals was included to control for decreased feeding in the UCN-treated rats. Two hours after the final set of injections, rats were killed, and white adipose tissue, brown adipose tissue, and biceps femoris and acromiotrapezius muscle tissues were taken for analysis of UCP-1, -2, and -3. Trunk blood was collected for measurement of plasma leptin. Relative to food-restricted control animals, UCN in the PVN significantly increased plasma leptin and UCP-1 mRNA in brown adipose tissue and decreased UCP-3 mRNA in acromiotrapezius muscle, suggesting a role for PVN UCN in the regulation of energy balance.

Gene expression in the supraoptic nucleus

The magnocellular neurosecretory cells (MNCs) in the supraoptic nucleus (SON) express multiple kinds of genes, including not only the classical hormones arginine vasopressin (AVP) and oxytocin (OXT), but also other physiologically active substances including neuropeptides, their receptors, and nitric oxide (NO) synthase, the rate-limiting enzyme in the synthesis of NO under physiological condition. For example, osmotic stimuli such as dehydration and chronic salt loading cause a wide range of changes of the expression levels of the genes and marked induction of the expression of the genes in the SON. The expression of the NO synthase gene in the SON under physiological conditions is reviewed.

Increases in plasma ACTH and cortisol after hypertonic saline infusion in patients with central diabetes insipidus

To clarify the mechanism for the potentiation of CRH-induced ACTH response by the infusion of hypertonic saline, we investigated changes in plasma ACTH concentration after infusion of 5% hypertonic saline in five patients with untreated central diabetes insipidus (DI). Basal levels of plasma ACTH and cortisol in the DI group were not significantly different from those in normal control subjects. The infusion of hypertonic saline produced an increase in plasma arginine vasopressin (AVP) in controls, but did not elevate ACTH. However, in patients with DI, the plasma AVP concentration did not change, but circulating ACTH increased 3.6-fold (7.7 +/- 1.5 to 23.0 +/- 2.7 pmol/liter; P < 0.01), and plasma cortisol also increased significantly (298 +/- 99 to 538 +/- 124 nmol/liter; P < 0.05). Moreover, a positive correlation was observed between plasma ACTH and osmolality (r = 0.72; P < 0.005). These results indicate that ACTH secretion in DI patients is regulated by a mechanism distinct from that in healthy subjects. It seems possible that the increase in plasma osmolality promotes ACTH secretion in DI patients through AVP and/or urocortin via the hypophyseal portal system, independent of the AVP secretion from magnocellular neurons.

The role of CRH in behavioral responses to stress

Corticotropin-releasing hormone (CRH) and urocortin in the central nervous system affect behavior and can enhance behavioral responses to stressors. The action of CRH-related peptides is mediated through multiple receptors that differ markedly in their pharmacological profiles and anatomical distribution. Comparative pharmacology of CRH receptor agonists suggests that CRH, urocortin, sauvagine and urotensin consistently mimic, and CRH receptor antagonists consistently lessen, functional consequences of stressor exposure. Recently, important advances have been made in understanding the CRH system and its role in behavioral responses to stress by the development of specific CRH receptor antagonists, application of antisense oligonucleotides and development of transgenic mice lacking peptides and functional receptors. This review summarizes recent findings with respect to components of the CRH system and their role in stress-induced behavioral responses.

Expression of corticotropin releasing factor (CRF), urocortin and CRF type 1 receptors in hypothalamic-hypophyseal systems under osmotic stimulation

The expression of corticotropin releasing factor (CRF) and urocortin in hypothalamic magnocellular neurones increases in response to osmotic challenge. To gain a better understanding of the physiological roles of CRF and urocortin in fluid homeostasis, CRF, urocortin and CRF type 1 receptor (CRFR-1) gene expression was examined in the hypothalamic-hypophyseal system usingin situ and double-label in situ hybridization following chronic salt loading. CRFR-1 expression was further examined by immunohistochemistry and receptor binding. Ingestion of hypertonic saline by Sprague-Dawley rats for 7 days induced CRF mRNA exclusively in the oxytocin neurones of the magnocellular paraventricular nucleus (PVN) and the supraoptic nucleus (SON), but induced CRFR-1 mRNA in both oxytocin and vasopressin-containing magnocellular neurones. Hypertonic saline treatment also increased urocortin mRNA expression in the PVN and the SON. In the SON, urocortin was localized to vasopressin and oxytocin neurones but was rarely seen in CRF-positive cells. Changes in CRFR-1 mRNA expression in magnocellular neurones by hypertonic saline treatment were accompanied by changes in CRFR-1 protein levels and receptor binding. Hypertonic saline treatment increased CRFR-1-like immunoreactivity in the magnocellular PVN and SON, and decreased it in the parvocellular PVN. CRF receptor binding in the PVN and SON was also increased in response to osmotic stimulation. Finally, hypertonic saline treatment increased CRFR-1 mRNA, CRFR-1-like immunoreactivity and CRF receptor binding in the intermediate pituitary. These results demonstrate that the increase in the expression of CRF and urocortin message in magnocellular neurones induced by salt loading is accompanied by an increase in CRF receptor levels and binding in the hypothalamus and intermediate pituitary. Thus, CRF and urocortin may exert modulatory effects locally within magnocellular neurones as well as at the pituitary gland in response to osmotic stimulation.

Feeding inhibition by urocortin in the rat hypothalamic paraventricular nucleus

Ventricular administration of urocortin (UCN) inhibits feeding, but specific site(s) of UCN action are unknown. In the current studies we examined the effect of UCN in the hypothalamic paraventricular nucleus (PVN) on feeding. We tested UCN administered into the PVN in several paradigms: deprivation-induced, nocturnal, and neuropeptide Y (NPY)-induced feeding. We compared the effect of equimolar doses of UCN and corticotrophin releasing hormone (CRH) on NPY-induced and nocturnal feeding, determined whether UCN in the PVN produced a conditioned taste aversion (CTA) and induced changes in c-Fos immunoreactivity (c-Fos-ir) after UCN and NPY administration in the PVN. UCN in the PVN significantly decreased NPY and nocturnal and deprivation-induced feeding at doses of 1, 10, and 100 pmol, respectively. UCN anorectic effects lasted longer than those attributed to CRH. Ten and thirty picomoles UCN did not induce a CTA, whereas 100 pmol UCN produced a CTA. UCN (100 pmol) in the PVN neither increased c-Fos-ir in any brain region assayed nor altered c-Fos-ir patterns resulting from PVN NPY administration. These data suggest the hypothalamic PVN as a site of UCN action.

Urocortin and corticotropin-releasing factor receptor expression in the human colonic mucosa

Urocortin is a newly identified member of the CRF neuropeptide family. Urocortin has been found to bind with high affinity to CRF receptors. The present study investigated urocortin and CRF receptor expression in human colonic mucosa. Non-pathologic sections of adult colorectal tissues were obtained from patients with colorectal cancer at surgery. Urocortin expression was examined using immunohistochemistry and messenger (m) RNA in situ hybridization. Isolated lamina propria mononuclear cells (LPMC) and epithelial cells were also analyzed by flow cytometry for the characterization of urocortin-positive cells, and by RT-PCR for detection of urocortin, CRF, and CRF receptor mRNA. Urocortin peptide distribution at various stages of human development (n = 35, from 11 weeks of gestation to 6 years of age) was examined by immunohistochemistry using surgical and autopsy specimens. Immunoreactive urocortin and urocortin mRNA were predominantly detected in lamina propria macrophages. Urocortin peptide expression was detected from as early as three months of age, but not before birth or in neonates. Urocortin, CRF receptor type 1 and type 2 alpha mRNA were detected in LPMC. CRF receptor type 2 beta mRNA, a minor isoform in human tissues, was also detected in LPMC, but at lower levels. Urocortin is locally synthesized in lamina propria macrophages and may act on lamina propria inflammatory cells as an autocrine/paracrine regulator of the mucosal immune system. The appearance of urocortin after birth indicates that the exposure to dietary intake and/or luminal bacteria after birth may contribute to the initiation of urocortin expression in human gastrointestinal tract mucosa.

Urocortin, a member of the corticotropin-releasing factor family, in normal and diseased heart

In the present study we investigated the form of expression, action, second messenger, and the cellular location of urocortin, a member of the corticotropin-releasing factor (CRF) family, in the heart. Urocortin mRNA, as shown by quantitative RT-PCR analysis, is expressed in the cultured rat cardiac nonmyocytes (NMC) as well as myocytes (MC) in the heart, whereas CRF receptor type 2beta (CRF-R2beta), presumed urocortin receptor mRNA, is predominantly expressed in MC compared with NMC. Urocortin mRNA expression is higher in left ventricular (LV) hypertrophy than in normal LV, whereas CRF-R2beta mRNA expression is markedly depressed in LV hypertrophy compared with normal LV. Urocortin more potently increased the cAMP levels in both MC and NMC than did CRF, and its effect was more potent in MC than in NMC. Urocortin significantly increased protein synthesis by [(14)C]Phe incorporations and atrial natriuretic peptide secretion in MC and collagen and increased DNA synthesis by [(3)H]prolin and [(3)H]Thy incorporations in NMC. An immunohistochemical study revealed that urocortin immunoreactivity was observed in MC in the normal human heart and that it was more intense in the MC of the human failing heart than in MC of the normal heart. These results, together with the recent evidence of urocortin for positive inotropic action, suggest that increased urocortin in the diseased heart may modulate the pathophysiology of cardiac hypertrophy or failing heart, at least in part, via cAMP signaling pathway.

The neurobiology of urocortin

Urocortin (UCN) is a recently isolated 40 amino acid-containing neuropeptide that is the second endogenous mammalian ligand for the corticotropin-releasing factor (CRF) receptors. While UCN and CRF both display a similar high affinity for the CRF(1) receptor, the affinity of UCN for the CRF(2) receptor is more than 10-fold higher than that of rat/human CRF. UCN mRNA expression is highest in the Edinger-Westphal nucleus and lateral superior olive, with the most prominent terminal fields found in the lateral septum. Because of the higher relative affinity of UCN for the CRF(2) receptor and the corresponding neuroanatomical distribution of the highest density of UCN expression and innervation to brain regions preferentially expressing the CRF(2) receptor subtype, it has been hypothesized that UCN is the preferred endogenous ligand for the CRF(2) receptor. Following central administration, UCN has been demonstrated to produce behavioral and physiological effects that are qualitatively similar to CRF. Quantitatively, however, UCN appears to be a more potent suppressor of ingestive behavior (food and water intake) and a less potent inducer of anxiogenic behavior than CRF.

Vasopressin and oxytocin neurones of hypothalamic supraoptic and paraventricular nuclei co-express mRNA for Type-1 and Type-2 corticotropin-releasing hormone receptors

The presence of corticotropin-releasing hormone (CRH) receptors type-1 (CRHR-1) and type-2 (CRHR-2alpha) in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei, and the effects of i.c.v. injection of CRH and urocortin on arginine vasopressin (AVP) and oxytocin release, have suggested that CRH ligands have a role in osmoregulation. In this study, double labelling in situ hybridization using 35S-labelled CRHR-1 or CRHR-2alpha and digoxigenin-labelled AVP, oxytocin or CRH riboprobes was employed to examine the localization of CRHR-1 or CRHR-2alpha mRNA in the SON and PVN of control and osmotically stimulated rats. Rats received an i.p. hypertonic saline (1.5 M) injection or isotonic saline injection (controls), or 2% NaCl intake (salt loading) or tap water (controls) for 12 days. While CRHR-1 mRNA was undetectable in the SON and PVN in control rats, its expression was increased markedly at 4 h after i.p. hypertonic saline injection or after 12 days salt loading. Of the cells labelled with digoxigenin-AVP, 53% in the SON and 90% in the PVN coexpressed CRHR-1 mRNA after i.p. hypertonic saline injection. In oxytocinergic neurones, 73% in the SON and 91% in the PVN showed CRHR-1 autoradiographic grains higher than background levels after i.p. hypertonic saline injection. In addition, i.p. hypertonic saline induced CRHR-1 mRNA expression in digoxigenin-CRH stained cells in the parvocellular PVN. CRHR-2alpha transcripts were present in both the SON and PVN under basal conditions, and salt loading, but not acute i.p. hypertonic saline injection, further stimulated this expression. Double labelling in situ hybridization showed colocalization of CRHR-2alpha mRNA with AVP and oxytocin mRNA in the SON. These studies support a role for CRH and urocortin regulating the hypothalamo-neurohypophyseal system, and suggest a direct action of the peptides in the magnocellular neurones.

Urocortin in the ventromedial hypothalamic nucleus acts as an inhibitor of feeding behavior in rats

Urocortin (UCN), a member of the corticotropin-releasing factor (CRF) family, inhibits food intake when it is injected intracerebroventricularly in rats. To explore the site of action of UCN in feeding behavior, we examined the effects of injection of UCN into various hypothalamic nuclei on food and water intake in 24-h fasted rats. Injection of UCN into the ventromedial hypothalamic nucleus (VMH) significantly inhibited food and water intake over 3 h without sedative effect, but no significant effect was observed following injection either into the lateral hypothalamic area, or the paraventricular nucleus of the hypothalamus. To further explore the physiological significance of endogenous UCN of the VMH in feeding behavior, the effect of immunoneutralization of hypothalamic UCN on food intake was examined. Injection of anti-rat UCN rabbit gamma-globulin into the bilateral VMH in freely fed rats significantly potentiated food and water intake compared with rats that received normal rabbit gamma-globulin. These results suggest that endogenous UCN in the VMH exert inhibitory control on ingestive behavior.

Chronic administration of the triazolobenzodiazepine alprazolam produces opposite effects on corticotropin-releasing factor and urocortin neuronal systems

In view of the substantial preclinical evidence that supports a seminal role of central corticotropin-releasing factor (CRF) neuronal systems in the physiology and pathophysiology of stress and anxiety, it is reasonable to suggest that the anxiolytic properties of benzodiazepines are mediated, at least in part, via regulation of CRFergic function. To begin to test this complex hypothesis, we examined the effects of acute and chronic administration of the triazolobenzodiazepine agonist alprazolam on CRF peptide concentrations, receptor-binding density, and mRNA expression in the CNS. Additionally, we measured mRNA expression for urocortin, a recently discovered neuropeptide that is generally considered to be a second endogenous ligand for CRF receptors. Both acute and chronic alprazolam administration was found to decrease CRF concentrations within the locus coeruleus. Furthermore, chronic alprazolam decreased basal activity of the hypothalamic-pituitary-adrenal axis, CRF mRNA expression in the central nucleus of the amygdala, and CRF(1) mRNA expression and receptor binding in the basolateral amygdala. In marked contrast, urocortin mRNA expression in the Edinger-Westphal nucleus and CRF(2A) receptor binding in the lateral septum and ventromedial hypothalamus were increased. Similar findings of an inverse relationship between the CRF(1) and CRF(2A) receptor systems have been reported in an anxiety model based on adverse early-life experience, suggesting the intriguing possibility that CRF neuronal systems may be comprised of two separate, but interrelated, subdivisions that can be coordinately and inversely regulated by stress, anxiety, or anxiolytic drugs.

Increase of urocortin-like immunoreactivity in the supraoptic nucleus of Dahl rats given a high salt diet

Urocortin-like immunoreactivity (Ucn-LI) in the supraoptic nucleus (SON) of Dahl rats was examined. Dahl salt-sensitive (S) rats fed with a high salt diet developed hypertension. Numbers of Ucn-LI neurons in the SON in Dahl S on a high salt diet were markedly increased, compared with those in Dahl salt-resistant (R) rats on the same. Sporadic Ucn-LI neurons were found in the SON of both Dahl S and R on a normal diet. Numbers of Ucn-LI neurons in the SON of spontaneously hypertensive rat (SHR) and stroke-prone SHR, genetic models of hypertension, and control rats (Sprague-Dawley and Wistar-Kyoto) were similar. These results suggest that Ucn in the SON is associated with salt loading-induced hypertension rather than spontaneous hypertension.

Differential distribution of urocortin- and corticotropin-releasing factor-like immunoreactivities in the rat brain

Urocortin, a novel 40 amino acid neuropeptide, is a member of the corticotropin-releasing factor family. With 45% homology to corticotropin-releasing factor, urocortin binds with similar affinity to the corticotropin-releasing factor- and corticotropin-releasing factor-2 receptors and may play a role in modulating many of the same systems as corticotropin-releasing factor. To assess whether urocortin and corticotropin-releasing factor are localized in the same regions of the brain, we compared the distribution of urocortin- and corticotropin-releasing factor-like immunoreactivities in the rat central nervous system. Polyclonal antibodies to rat corticotropin-releasing factor and rat urocortin were generated and utilized to map the distribution of corticotropin-releasing factor- and urocortin-like immunoreactivities throughout the rat forebrain and brainstem. Characterization of the antibodies by radioimmunoassay showed no cross-reactivity with related peptides. Male Sprague-Dawley rats were treated with colchicine for 18-24 h. Following colchicine treatment, the rats were perfused with paraformaldehyde-lysine-periodate fixative and their brains removed. Serial coronal sections were taken throughout the rat brain and processed for either corticotropin-releasing factor- or urocortin-like immunoreactivity. Urocortin-like immunoreactivity shows a discrete localization within several regions including the supraoptic nucleus, the median eminence, Edinger-Westphal nucleus and the sphenoid nucleus. This is in contrast to the more abundant corticotropin-releasing factor-like immunoreactivity. Regions containing high levels of corticotropin-releasing factor immunoreactivity include the lateral septum, paraventricular nucleus of the hypothalamus, median eminence and locus coeruleus. There are a few regions that contain both urocortin-immunoreactive and corticotropin-releasing factor-immunoreactive cells, such as the supraoptic nucleus and the hippocampus. Therefore, urocortin and corticotropin-releasing factor appear to have different distribution patterns which may be indicative of their respective physiological functions.

Urocortin is not a significant regulator of intermittent electrofootshock-induced adrenocorticotropin secretion in the intact male rat

Urocortin (Ucn) is a newly identified mammalian member of the CRF family of peptides. Ucn activates CRF receptors (both CRF-R1 and CRF-R2) with greater potency than CRF itself, suggesting that Ucn may play an endogenous role in eliciting (at least some) CRF receptor-mediated events. Because the most characterized physiological function of CRF receptors is the activation of pituitary ACTH secretion, we have compared the effects and potential endogenous roles of CRF and Ucn in regulating plasma ACTH concentrations in intact male rats. Synthetic rat Ucn injected i.v. (0.09-9.0 nmol/kg) elicited ACTH secretion in a dose-dependent manner, causing greater ACTH secretion than CRF at each dose tested. The increases in plasma ACTH concentrations produced by CRF or Ucn were virtually abolished by pretreatment with the CRF receptor antagonist, astressin (3 mg/kg), and were partially attenuated (by 27-37%) by an antiarginine vasopressin serum. These data indicate that both Ucn and CRF elicit ACTH secretion via CRF receptor-dependent mechanisms, and that the ACTH-releasing activities of both CRF and Ucn are potentiated by endogenous arginine vasopressin. Intravenous administration of rabbit anti-Ucn serum, which inhibited ACTH secretion produced by Ucn, but not CRF, had no statistically significant effect on either resting (midday) plasma ACTH concentrations or the rise in ACTH levels elicited by 30 min of intermittent electrofootshocks. By contrast, treatment with a rabbit anti-CRF serum that specifically inhibited the ACTH response to CRF lowered plasma concentrations in control unstressed rats and largely prevented the plasma ACTH response to electrofootshocks. These data indicate that although Ucn is a more potent ACTH secretagogue than CRF in the intact male rat, it is not a major endogenous regulator of pituitary ACTH secretion under basal (midday) conditions or during acute footshock stress.

Urocortin expression in the human central nervous system

OBJECTIVE AND STUDY DESIGN

Urocortin is a recently identified neuropeptide of the corticotrophin-releasing factor (CRF) family in the mammalian brain and has been demonstrated to stimulate ACTH secretion from pituitary cells, but its expression in human brain tissue including the hypothalamus has not been examined. In this study, we first examined urocortin expression in the hypothalamus (20 cases) and pituitary stalks (17 cases) of human brain obtained from autopsy using immunohistochemistry and mRNA in situ hybridization.

RESULTS

Neither urocortin immunoreactivity nor mRNA hybridization signals were detected in the hypothalami and pituitary stalks while CRF immunoreactivity was detected in the paraventricular nuclei of the hypothalami in 10/20 cases and in nerve fibres of the stalks in 17/17 cases. These results indicate that urocortin does not act on the hypothalamo-pituitary-adrenal axis, at least not in the same manner as CRF in humans. We then examined urocortin expression in various portions of the brain in 7 cases. Both urocortin immunoreactivity and mRNA hybridization were detected in Purkinje cells of the cerebellum and anterior horn cells of the spinal cord in specimens examined. Urocortin expression was, however, variably seen in superior olivary nuclei (two out of six cases examined) and in the Edingar-Westphal nuclei (one out of three cases examined).

CONCLUSIONS

The distribution of urocortin in the human central nervous system suggests that urocortin may work as a neurotransmitter like other neuropeptides in the human.

Corticotropin-releasing factor but not urocortin is involved in adrenalectomy-induced adrenocorticotropin release

Urocortin, a new corticotropin-releasing factor (CRF)-related peptide, has been reported to have the ability to bind to CRF receptors and to stimulate adrenocorticotropin (ACTH) secretion from the rat anterior pituitary in vivo and in vitro. In this study, we examined the effect of intravenous administration of urocortin-antiserum to investigate the role of endogenous urocortin on ACTH secretion from rat anterior pituitary after adrenalectomy. Male Sprague-Dawley rats, which were maintained in a conscious and undisturbed condition, were administered non-immunized rabbit serum (NRS), CRF-antiserum or urocortin-antiserum at a volume of 1 ml/kg b.w. 15 min before the injection of secretagogues. Synthetic rat urocortin (2 microg/kg B.W.) increased plasma ACTH concentrations by about sixfold the basal concentration. The pretreatment with urocortin-antiserum but not CRF-antiserum abolished the urocortin-induced increase in plasma ACTH concentrations. In adrenalectomized rats, plasma ACTH concentrations were markedly increased at basal conditions, and rapidly reduced after the administration of CRF-antiserum. By contrast, administration of urocortin-antiserum did not alter ACTH secretion induced by adrenalectomy. Our results suggest that endogenous urocortin is unlikely to be involved in ACTH release in adrenalectomized rats.

Central administration of urocortin inhibits vasopressin release in conscious rats

Urocortin (UCN) is a new mammalian member of the corticotropin releasing factor (CRF) family and supposed to be an endogenous ligand for type 2 CRF receptors. Previous studies have revealed that UCN mRNA exists in the supraoptic nucleus (SON), and that water deprivation increases UCN immunoreactivity in SON. In this study, we examined the effect of centrally-administered UCN on arginine vasopressin (AVP) release in conscious rats. Intracerebroventricular (i.c.v.) injection of UCN (5.0 microg/rat) significantly attenuated AVP release induced by hyperosmolality at 30 min after the injection. In contrast, CRF (5.0 microg/rat) injected i.c.v. had no significant effect on AVP release. These results suggest that central UCN play an inhibitory role in osmoregulation of AVP release.

Urocortin-like immunoreactivity in the substantia nigra, ventral tegmental area and Edinger-Westphal nucleus of rat

Neurons showing intense urocortin-like immunoreactivity (Ucn-IR) were found immunohistochemically in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA), as well as in Edinger-Westphal nucleus (E-W), in the rat brain. Almost all Ucn-immunoreactive neuronal cell bodies in the SNc and VTA showed immunoreactivity for tyrosine hydroxylase. Injection of a retrograde tracer, colloidal gold-labeled WGAapoHRP, into the cervical spinal cord resulted in labeling of some E-W neurons with Ucn-IR. These findings suggest that Ucn is located in the cell bodies of dopaminergic neurons, as well as in the cell bodies of E-W neurons sending axons to the spinal cord.

Distribution of urocortin-like immunoreactivity in the central nervous system of the rat

Urocortin was recently cloned from the rat midbrain. Urocortin is a member of the corticotropin releasing factor (CRF) peptide family and shows 45% sequence identity to CRF and 63% sequence identity to urotensin. It binds with a high affinity to CRF1 and CRF2 receptors, resulting in the stimulation of their adenylate cyclase activity. We used a polyclonal antibody against rat urocortin to define the distribution of urocortin-like immunoreactivity in the rat central nervous system. Several immunostained cell bodies were found in the supraoptic, paraventricular, and ventromedial hypothalamic nuclei. A large number of neurons with urocortin-like immunoreactivity were seen in the dorsolateral tegmental nucleus, in the linear and dorsal raphe nuclei, and in the substantia nigra. The most abundant immunoreactive (ir) perikarya were found in the Edinger-Westphal nucleus. Some neurons showed immunoreactivity in the interstitial nucleus of Cajal, the nucleus of Darkeschewitsch, and the periaqueductal gray. A dense immunoreactive fiber network was found in the lateral septal area. Some faintly stained axon terminals were observed among urocortin-ir perikarya in the supraoptic and paraventricular nuclei, in the central and periaqueductal gray, and in the Edinger-Westphal nucleus. No fibers with urocortin-ir were seen in the median eminence or the posterior pituitary. The distribution of urocortin-ir overlapped with the expression of the mRNA for the CRF2 receptor in several brain areas. These data support the hypothesis that this peptide is the endogenous ligand for the CRF2 receptor. Urocortin has been implicated in various endocrine responses, such as blood pressure regulation, as well as in higher cognitive functions.

Regional distribution of urocortin-like immunoreactivity and expression of urocortin mRNA in the human brain

Regional distribution of urocortin-like immunoreactivity (UCN-LI) in the human brain was studied by radioimmunoassay and was compared with that of corticotropin-releasing hormone (CRH). In addition, the expression of UCN mRNA was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) method. UCN-LI was detected in every region of brain examined, including hypothalamus, pons, cerebral cortex, and cerebellum. The concentrations of UCN-LI in the human brain were approximately 3 pmol/g wet weight in any brain region, and no marked regional difference was noted. On the other hand, the highest concentrations of CRH-LI were found in the frontal cortex, temporal cortex, and hypothalamus and the lowest in the pons. Reverse phase high-performance liquid chromatography of the UCN-LI in the human brain extract showed two immunoreactive peaks; one peak eluting earlier and one in the position of synthetic human UCN. RT-PCR showed that UCN mRNA was expressed in every region of brain examined. These findings indicated that UCN and UCN mRNA were widely expressed in the human brain.

Corticotropin releasing factor receptor type II (CRF2) messenger ribonucleic acid levels in the hypothalamic ventromedial nucleus of the infant rat are reduced by maternal deprivation

The stress neurohormone corticotropin releasing factor (CRF) activates at least two receptor types. Expression of corticotropin releasing factor receptor type II (CRF2) has been demonstrated in the hypothalamic ventromedial nucleus (VMH) of the adult and developing rat, but the physiological functions of VMH-CRF2 have not been elucidated. The VMH has been documented as an important participant in the regulation of food intake and its interactions with the hypothalamic-pituitary-adrenal axis and circadian rhythms. Regulation of VMH-CRF2 may thus play a role in the interplay of physiological alterations in metabolic state with the neuroendocrine and anorexic effects of CRF. This study determined the regulation of CRF2-mRNA expression in infant rats by the physiological consequences of maternal deprivation, i.e., fasting and stress. Using in situ hybridization, maternally deprived pups had an average 62% reduction of VMH-CRF2-mRNA levels compared with stress-free controls. Maternal deprivation also resulted in elevated plasma corticosterone levels (3.8 +/- 0.3 vs. 1.3 +/- 0.1 microg/dl) and an average 5.7% body weight loss. This study demonstrates that maternal deprivation, via fasting and HPA activation, leads to a dramatic decrease of CRF2-mRNA levels in the VMH. These results are consistent with a role for CRF2 activation in mediating some of the complex interactions of CRF (or urocortin) with regulation of food intake in the developing rat.

Increase of urocortin-like immunoreactivity in the rat supraoptic nucleus after dehydration but not food deprivation

The effects of dehydration and food deprivation on urocortin-like immunoreactivity (Ucn-IR) in the rat supraoptic nucleus (SON) and the paraventricular nucleus (PVN) were examined by immunohistochemistry. Water deprivation for 48 h caused a significant increase in the number of Ucn-IR neurons in the SON, compared with control. Ucn-IR fibers and varicosities in the SON and the internal zone of the median eminence (ME) were increased, but a few and faint Ucn-IR neurons and fibers were observed in the PVN. On the other hand, food deprivation for 48 h caused a significant decrease in the number of Ucn-IR neurons in the SON, compared with control. Ucn-IR fibers and varicosities in the SON and the ME were fewer than those in controls. Ucn-IR neurons and fibers in the PVN were not detected after food deprivation. These results suggest that Ucn in the SON may be involved in the central regulation of water balance and nutrient homeostasis.