Central administration of urocortin inhibits vasopressin release in conscious rats

Transcriptome Analysis Reveals Downregulation of Urocortin Expression in the Hypothalamo-Neurohypophysial System of Spontaneously Hypertensive Rats

The chronically increased blood pressure characteristic of essential hypertension represents an insidious and cumulative risk for cardiovascular disease. Essential hypertension is a multifactorial condition, with no known specific aetiology but a strong genetic component. The Spontaneously Hypertensive rat (SHR) shares many characteristics of human essential hypertension, and as such is a commonly used experimental model. The mammalian hypothalamo-neurohypophyseal system (HNS) plays a pivotal role in the regulation of blood pressure, volume and osmolality. In order to better understand the possible role of the HNS in hypertension, we have used microarray analysis to reveal differential regulation of genes in the HNS of the SHR compared to a control normotensive strain, the Wistar Kyoto rat (WKY). These results were validated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). One of the genes identified and validated as being downregulated in SHR compared to WKY was that encoding the neuropeptide urocortin (Ucn). Immunohistochemical analyses revealed Ucn to be highly expressed within magnocellular neurons of the PVN and SON, with pronounced localisation in dendritic projections containing oxytocin and vasopressin. When Ucn was overexpressed in the PVN of the SHR by in vivo lentiviral mediated gene transfer, blood pressure was unaffected but there were significant, transient reductions in the VLF spectra of systolic blood pressure consistent with an action on autonomic balance. We suggest that Ucn may act, possibly via dendritic release, to subtly regulate neurohumoral aspects of arterial pressure control.

The effects of the urocortins on the hypothalamic-pituitary-adrenal axis - similarities and discordancies between rats and mice

The urocortins (Ucn I, Ucn II and Ucn III) are structural analogues of corticotropin-releasing factor (CRF). The aim of our present experiments was to compare the effects of the urocortins on the hypothalamic-pituitary-adrenal (HPA) axis in rats and mice, including the hypothalamic adrenocorticotropic hormone (ACTH) secretagogues, such as CRF and arginine vasopressin (AVP). Therefore, male CFLP mice and male Wistar rats were injected intracerebroventricularly (icv) with 0.5, 1, 2 and 5 μg/2 μl of Ucn I, Ucn II or Ucn III. After 30 min the animals were decapitated, and then, hypothalamic CRF and AVP concentrations and plasma ACTH and corticosterone (CORT) levels were measured. All measurements were performed by enzyme-linked immunosorbent assays (ELISA), except that of the plasma CORT level, which was determined by chemofluorescent assay. Ucn I increased significantly the hypothalamic CRF and AVP concentrations in both rats and mice. Ucn II and Ucn III influenced significantly only the hypothalamic CRF concentration in rats, without affecting the hypothalamic AVP concentration. In contrast, Ucn II and Ucn III increased significantly only the hypothalamic AVP concentration in mice, without affecting the hypothalamic CRF concentration. The hypothalamic changes were reflected more or less accurately by changes of the plasma ACTH and CORT levels. The present experiments demonstrate that the urocortins regulate the HPA axis centrally via modulation of the hypothalamic ACTH secretagogues and that there are some similarities and discordancies between rats and mice regarding this regulation.

Corticotropin-Releasing Factor Receptors Modulate Oxytocin Release in the Dorsolateral Bed Nucleus of the Stria Terminalis (BNST) in Male Rats

The neuropeptide oxytocin (OT) plays an important role in the regulation of social and anxiety-like behavior. Our previous studies have shown that OT neurons send projections from the hypothalamus to the dorsolateral bed nucleus of the stria terminalis (BNST_dl), a forebrain region critically involved in the modulation of anxiety-like behavior. Importantly, these OT terminals in the BNST_dl express presynaptic corticotropin releasing factor (CRF) receptor type 2 (CRFR2). This suggests that CRFR2 might be involved in the modulation of OT release. To test this hypothesis, we measured OT content in microdialysates collected from the BNST_dl of freely-moving male Sprague-Dawley rats following the administration of a selective CRFR2 agonist (Urocortin 3) or antagonist (Astressin 2B, As2B). To determine if type 1 CRF receptors (CRFR1) are also involved, we used selective CRFR1 antagonist (NBI35965) as well as CRF, a putative ligand of both CRFR1 and CRFR2. All compounds were delivered directly into the BNST_dl via reverse dialysis. OT content in the microdialysates was measured with highly sensitive and selective radioimmunoassay. Blocking CRFR2 with As2B caused an increase in OT content in BNST_dl microdialysates, whereas CRFR2 activation by Urocortin 3 did not have an effect. The As2B-induced increase in OT release was blocked by application of the CRFR1 antagonist demonstrating that the effect was dependent on CRFR1 transmission. Interestingly, CRF alone caused a delayed increase in OT content in BNST_dl microdialysates, which was dependent on CRF2 but not CRF1 receptors. Our results suggest that members of the CRF peptide family modulate OT release in the BNST_dl via a fine-tuned mechanism that involves both CRFR1 and CRFR2. Further exploration of mechanisms by which endogenous OT system is modulated by CRF peptide family is needed to better understand the role of these neuropeptides in the regulation of anxiety and the stress response.

The effect of urocortin I on the hypothalamic ACTH secretagogues and its impact on the hypothalamic-pituitary-adrenal axis

Urocortin I (UCN I) is a structural analogue of corticotropin-releasing factor (CRF), which, together with arginine-vasopressin (AVP), are the principle adrenocorticotropic hormone (ACTH) secretagogues in mammals. The aim of the present study was to investigate the effects of UCN I on the hypothalamic CRF and AVP concentration and its impact on the hypothalamic-pituitary-adrenal (HPA) axis. First, male Wistar rats were injected intracerebroventricularly (ICV) with 0.5, 1, 2 and 5 μg of UCN I. After 30 min hypothalamic CRF and AVP concentrations were determined by immunoassays. In parallel, the trunk blood was collected and plasma ACTH and corticosterone concentration was determined by ELISA and chemofluorescent assay, respectively. Second, rats were pretreated ICV with selective antagonists of receptors being implicated in the regulation of the HPA axis (0.1 μg antalarmin for CRFR1, 1 μg astressin 2B for CRFR2 or 0.1 μg deamino-Pen1,Tyr2,Arg8-vasopressin for AVPR3) and treated ICV with the most effective dose of UCN I (5 μg). After 30 min plasma corticosterone concentration was determined by chemofluorescent assay. UCN I induced dose-dependent augmentation of the hypothalamic CRF and AVP concentration, associated with dose-dependent elevation of the plasma ACTH and corticosterone concentration. The most significant effect of UCN I on the plasma corticosterone concentration was inhibited by antalarmin, but was not influenced by astressin 2B or deamino-Pen1,Tyr2,Arg8-vasopressin. The present study demonstrates that UCN I modulates the concentration of the hypothalamic ACTH secretagogues in parallel with the concentration of the plasma ACTH and corticosterone. Our results suggest that UCN I may activate the HPA axis by stimulation of the hypothalamic CRF production, and this process is mediated by CRFR1, and not by CRFR2. UCN I may stimulate the AVP production, as well, but, based on the results with AVPR3 antagonist, this effect is not involved in the regulation of the HPA axis.

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.

Neuropeptides in anxiety modulation

This review is focused on the involvement of neuropeptides in the modulation of physiological and pathological anxiety. Neuropeptides play a major role as endogenous modulators of complex behaviours, including anxiety-related behaviour and psychopathology, particularly due to their high number and diversity, the dynamics of release patterns in distinct brain areas and the multiple and variable modes of interneuronal communication they are involved in. Manipulations of central neuropeptidergic systems to reveal their role in anxiety (and often comorbid depression-like behaviour) include a broad spectrum of loss-of-function and gain-of-function approaches. This article concentrates on those neuropeptides for which an involvement as endogenous anxiolytic or anxiogenic modulators is well established by such complementary approaches. Particular attention is paid to corticotropin-releasing hormone (CRH) and vasopressin (AVP) which, closely linked to stress, neuroendocrine regulation, social behaviour and learning/memory, play critical roles in the regulation of anxiety-related behaviour of rodents. Provided that their neurobiology, neuroendocrinology and molecular-genetic background are well characterized, these and other neuropeptidergic systems may be promising targets for future anxiolytic strategies.

Localization and physiological roles of urocortin

Urocortin, a 40 amino acid peptide, is a corticotropin-releasing factor (CRF) related peptide, and can bind to all three types of CRF receptors (CRF type 1, type 2a and type 2b receptors) with higher affinities for these receptors than CRF. Immunoreactivity of urocortin is widely distributed in central nervous, digestive, cardiovascular, reproductive, immune and endocrine systems. Urocortin plays important roles in appetite-suppression, immunomodulation, steroidogenesis in the ovary, maintenance of the placental function, labor, and cardioprotection via CRF receptors. Although urocortin has potent adrenocorticotropin (ACTH) releasing activity in vitro, endogenous urocortin does not act on pituitary ACTH secretion in vivo.

Urocortins and corticotropin releasing factor type 2 receptors in the hypothalamus and the cardiovascular system

In addition to urocortin (Ucn I), Ucn II and Ucn III were identified as endogenous ligands for corticotropin-releasing factor type 2 receptor (CRF2 receptor). CRF2 receptor is abundantly located in central hypothalamic ventromedial nucleus (VMH) and in peripheral cardiovascular system. In this mini-review, we focused on the roles of these urocortins and CRF2 receptor in the hypothalamus and the cardiovascular system. Ucn II mRNA was increased in the parvocellular part or the magnocellular part of the hypothalamic paraventricular nucleus (PVN) following immobilization stress or 3 days of water deprivation, respectively. Therefore, it is thought that Ucn II may modulate CRF and vasopressin synthesis in the PVN in a paracrine or autocrine fashion through PVN CRF2 receptor. The early and later phases of Ucn I-mediated feeding suppression may be CRF1 and CRF2 receptor-mediated events, respectively. Ucn II decreases food intake at a later phase, beyond 4 h post injection. A large dose of corticosterone increased plasma leptin and insulin levels as well as the levels of CRF2 receptor mRNA. Adrenalectomy, starvation, and immobilization each lowered plasma leptin and insulin levels and were associated with decrements in CRF2 receptor mRNA levels in the VMH. Peripheral injection of leptin increased VMH CRF2 receptor mRNA, as can induce reductions of food intake and body weight, indicating that circulating leptin is involved in the regulation of VMH CRF2 receptor mRNA expression. Therefore, it is also plausible that VMH CRF2 receptor transduces the anorexogenic effects of leptin as well as those of urocortins. The systemic administration of Ucn II decreases mean arterial pressure (arterial vascular tone) and causes tachycardia via vascular CRF2 receptor in rats, similar to the effects of Ucn I. Thus, CRF2 receptor seems to mediate cardioprotective effects of urocortins.

Effect of stress and adrenalectomy on urocortin II mRNA expression in the hypothalamic paraventricular nucleus of the rat

Urocortin II (Ucn II) is a novel corticotropin-releasing hormone (CRH)-related peptide discovered as a selective agonist for type-2 CRH receptor. In the rat or mouse brain, Ucn II mRNA shows weak expression mainly in the hypothalamic paraventricular nucleus (PVN) and the locus coeruleus (LC). Understanding the regulation of Ucn II mRNA expression under varying conditions provides new insights into central stress response. We examined expression of Ucn II mRNA in the PVN and LC following immobilization stress, water deprivation, and adrenalectomy. Rats subjected to immobilization stress exhibited a dramatic induction of Ucn II mRNA expression in the parvocellular part of the PVN at the end of 2 h of immobilization. In contrast, water deprivation for 3 days induced Ucn II mRNA expression mainly in the magnocellular part of the PVN. Although water-deprived rats showed a marked decrease in their food intake, pair-fed rats failed to alter PVN Ucn II mRNA expression, suggesting that osmotic stimuli per se, but not reduced food consumption during water deprivation, caused Ucn II mRNA induction in the magnocellular part of the PVN. Adrenalectomized rats failed to show an increase in Ucn II mRNA in the PVN when compared to sham-operated rats. Double-label in situ hybridization revealed colocalization of Ucn II mRNA in approximately 45% of the CRH mRNA-expressing cells in the parvocellular part of the PVN following immobilization, or colocalization in most of the vasopressin mRNA-expressing cells in the magnocellular part of the PVN following water deprivation. In the LC, no induction of Ucn II mRNA was observed in any of the three experimental conditions, indicating that the regulation of Ucn II mRNA expression was site-specific. The results show a stressor-specific regulation of Ucn II mRNA expression in the PVN and raise the possibility that Ucn II mRNA plays a modulatory role in stress-induced alteration of anterior and posterior pituitary function, depending on the type of stress.

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.

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.

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.

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.

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.

Behavioral and hormonal effects of centrally injected "anxiogenic" neuropeptides in growing pigs

Records of behavior (alertness, posture, oro-nasal responses, activity level, and vocalization pattern) were made in prepubertal pigs (n = 6) during a 60-min period following central injections of equimolar (21 nmol) doses of porcine CRH (pCRH), urocortin (UCN), octadecaneuropeptide (ODN), or saline vehicle (SAL). Blood samples were also collected at 15-min intervals before, during, and after the test, and used to determine plasma cortisol, prolactin, and growth hormone concentrations. The pigs became excited and highly active after pCRH, and to a lesser extent following UCN administration, but were subdued when given ODN or SAL. None of the peptides significantly affected prolactin or growth hormone release, but both UCN, and especially pCRH, increased cortisol concentrations. The emotional responses induced by pCRH and UCN are consistent with observations in rodents, which indicate that centrally administered CRH-like peptides have anxiogenic effects. In contrast, ODN, which inhibits benzodiazepine binding at the GABA(A) receptor and is anxiogenic in rodents, lowered plasma cortisol and had no overt behavioral effects. Hence, at the dose administered, there was no evidence to indicate that ODN acted as an anxiogen in this species.