Corticotropin-releasing factor (CRF) induced anorexia is not influenced by a melanocortin 4 receptor blockage.

CRF and melanocortin (MSH/ACTH) peptides share a number of central effects including anorexia and grooming. The effects of CRF may be secondary, due to CRF's effects on melanocortin peptide release. We investigated if the newly discovered selective melanocortin 4 receptor antagonist HS014 could influence CRF induced anorexia and grooming. The data show that ICV administration of CRF (3 mg/rat), significantly reduced food intake, feeding time and feeding episodes whereas it increased grooming time and grooming episodes. HS014 (5 mg/rat), that previously has been shown to antagonize the anorectic effect and the excessive grooming induced by alpha-MSH, did however not influence any of the behavioral effects induced by CRF when the peptides were administered together. The data indicate that the anorectic and grooming effects of CRF are independent of pathways involving the MC4 receptors. These data suggest that the anorectic and grooming effect of CRF are not due to a secondary effect caused by increase in release of melanocortins acting on the central MC receptors.     

Effects of urocortin 2 and 3 on motor activity and food intake in rats

Urocortin 2 (Ucn 2) and Ucn 3 are new members of the corticotropin-releasing factor (CRF) family and bind selectively to the CRF type 2 receptor (CRF2). The effects of these peptides on behavioral changes induced by CRF were examined in rats. In a familiar environment, intracerebroventricular injection of Ucn 2 attenuated the stimulatory effect of CRF on motor activity, although it alone produced no effect. Ucn 3 suppressed motor activity and attenuated the stimulatory effect of CRF. In an open field, CRF decreased locomotion and rearing but increased grooming behavior. Ucn 2 attenuated the inhibition of locomotor activity induced by CRF without affecting other activities, such as rearing or grooming behavior. Ucn 3 had no effect on the behavioral changes induced by CRF, although it alone decreased locomotion and rearing in a manner similar to CRF. Ucn 2 was thus found to have an antagonistic effect on bi-directional motor activation induced by CRF, while Ucn 3 had a suppressive effect on motor activity. Both Ucn 2 and Ucn 3 suppressed food intake in freely-fed rats, but not immediately after injection. These results suggest that the CRF2 receptor is involved in motor suppressive effects as well as anxiolytic and anorectic effects of Ucn 2 and Ucn 3.     

Peripheral administration of CRF and urocortin: effects on food intake and the HPA axis in the marsupial Sminthopsis crassicaudata

The hypothalamic peptides corticotrophin releasing factor (CRF) and urocortin (UCN) decrease food intake and increase energy expenditure when administered either centrally or peripherally to rodents. The effects of CRF and UCN on food intake in other mammals (for example marsupials), however, are not known. Peripherally administered CRF induced cortisol release in the marsupial Sminthopsis crassicaudata via the CRF1 receptor, and central CRF administration potently decreased food intake, as in rodents. When peripherally administered, both CRF and UCN decreased food intake in S. crassicaudata, but UCN was considerably more potent ( approximately 50 fold) in this regard. The anorectic effects of CRF and UCN were not blocked by the CRF1 receptor antagonist antalarmin, suggesting that the peripheral effects of CRF and UCN on food intake are mediated primarily by the CRF2 receptor.     

Decreased behavioral effects of daily intracerebroventricular bombesin

Intracerebroventricular (ICV) bombesin increases grooming and decreases food intake in rats. We examined tolerance to these effects by administering a daily injection of either saline or 25 ng bombesin to rats for 8 days via lateral ventricular cannulas. Food intake and grooming were monitored. After 8 days bombesin no longer increased grooming or decreased food intake in bombesin-treated rats, but did increase grooming and decrease food intake in saline-treated rats. This development of behavioral tolerance conflicts with previous reports using larger doses and demonstrates that repeated small doses of ICV bombesin produce different effects from larger doses.     

Dorsomedial hypothalamic corticotropin-releasing factor mediation of exercise-induced anorexia

Running wheel access and resulting voluntary exercise alter food intake and reduce body weight. The neural mechanisms underlying these effects are unclear. In this study, we first assessed the effects of 7 days of running wheel access on food intake, body weight, and hypothalamic gene expression. We demonstrate that running wheel access significantly decreases food intake and body weight and results in a significant elevation of CRF mRNA expression in the dorsomedial hypothalamus (DMH) but not the paraventricular nucleus. Seven-day running wheel access also results in elevated arcuate nucleus and DMH neuropeptide Y gene expression. To assess a potential role for elevated DMH CRF activity in the activity-induced changes in food intake and body weight, we compared changes in food intake, body weight, and hypothalamic gene expression in rats receiving intracerebroventricular (ICV) CRF antagonist alpha-helical CRF or vehicle with or without access to running wheels. During a 4-day period of running wheel access, we found that exercise-induced reductions of food intake and body weight were significantly attenuated by ICV injection of the CRF antagonist. The effect on food intake was specific to a blockade of activity-induced changes in meal size. Central CRF antagonist injection further increased DMH CRF mRNA expression in exercised rats. Together, these data suggest that DMH CRF play a critical role in the anorexia resulting from increased voluntary exercise.     

Urocortin 1 reduces food intake and ghrelin secretion via CRF(2) receptors

Although it is known that urocortin 1 (UCN) acts on both corticotropin-releasing factor receptors (CRF(1) and CRF(2)), the mechanisms underlying UCN-induced anorexia remain unclear. In contrast, ghrelin, the endogenous ligand for the growth hormone secretagogue receptor, stimulates food intake. In the present study, we examined the effects of CRF(1) and CRF(2) receptor antagonists (CRF(1)a and CRF(2)a) on ghrelin secretion and synthesis, c-fos mRNA expression in the caudal brain stem, and food intake following intracerebroventricular administration of UCN. Eight-week-old, male Sprague-Dawley rats were used after 24-h food deprivation. Acylated and des-acylated ghrelin levels were measured by enzyme-linked immunosorbent assay. The mRNA expressions of preproghrelin and c-fos were measured by real-time RT-PCR. The present study provided the following important insights into the mechanisms underlying the anorectic effects of UCN: 1) UCN increased acylated and des-acylated ghrelin levels in the gastric body and decreased their levels in the plasma; 2) UCN decreased preproghrelin mRNA levels in the gastric body; 3) UCN-induced reduction of plasma ghrelin and food intake were restored by CRF(2)a but not CRF(1)a; 4) UCN-induced increase of c-fos mRNA levels in the caudal brain stem containing the nucleus of the solitary tract (NTS) was inhibited by CRF(2)a; and 5) UCN-induced reduction of food intake was restored by exogenous ghrelin and rikkunshito, an endogenous ghrelin secretion regulator. Thus, UCN increases neuronal activation in the caudal brain stem containing NTS via CRF(2) receptors, which may be related to UCN-induced inhibition of both ghrelin secretion and food intake.     

Comparison of the anorexigenic activity of CRF family peptides

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

The effects of chronic central administration of corticotropin-releasing factor on food intake, body weight, and hypothalamic-pituitary-adrenocortical hormones.

The effects of chronic central administration of corticotropin-releasing factor (CRF) on food intake, body weight, and hypothalamic-pituitary-adrenocortical hormones were investigated in rats. The infusion of ovine CRF at doses of 0.3 and 1.0 microgram/h continuously induced decrease in food intake and a suppression of body-weight gain for 7 days. The inhibition of body weight gain induced by CRF could not be accounted for solely by a decreased food intake since the suppression of body-weight gain in CRF-infused rats was significantly greater than that observed in rats which received the same amount of food as the CRF-infused rats. The content of proopiomelanocortin (POMC) -derived peptides in the anterior lobe of the pituitary as well as the plasma levels of ACTH and corticosterone (B) were significantly elevated in CRF-treated rats, and the CRF content in the hypothalamus was significantly decreased. These results suggest that chronic intracerebroventricular (icv) administration of CRF stimulates the synthesis and secretion of POMC-related peptides in the pituitary and suppresses food intake accompanied by inhibition of body weight gain. The results are similar to clinical and laboratory findings observed in patients with stress-induced anorexia.     

Effects of fourth ventricle bombesin injection on meal-related parameters and grooming behavior.

Injections of bombesin (BN) into the vicinity of the caudal brainstem suppress food intake in rats. In the present study, the food intake parameters [meal size (MS), intermeal interval (IMI), satiety ratio (SR)] affected by 4th ventricle BN injections were determined. Following a 15-h food deprivation, rats were administered 4th ventricle injections of saline (0.15 M) and BN in doses of 1, 5, 10, and 20 ng BN, and were then given access to sweetened milk. The animals' behaviors (feeding, resting, grooming, exploring) were scored every one min and milk intake every five min for 60 min following the injections. Fourth ventricle injections of 5 ng BN and greater reliably suppressed milk. intake. This reduction was reflected in a significant reduction in the MS. The IMI was not affected. As a result, the SR (IMI2/MS1), which is thought to represent the satiating property of food, was reliably greater following BN than following saline administration. The reduced food intake was accompanied by a significant increase in grooming behavior and a corresponding decrease in exploring. The amount of time spent resting (inactive) was similar following saline and all but the highest dose of BN. To demonstrate that the behavioral effects of BN were mediated by specific caudal brainstem BN receptors, 4th ventricle injections of [D-Phe12,Leu14]BN, a BN receptor antagonist, or saline preceded the 4th ventricle injection of 5 ng BN. Pretreatment with [D-Phe12,Leu14]BN reliably blocked the effects of BN on food intake and grooming.     

Differential monoaminergic, neuroendocrine and behavioural responses after central administration of corticotropin-releasing factor receptor type 1 and type 2 agonists

Corticotropin-releasing factor (CRF) mediates various aspects of the stress response. To differentiate between the roles of CRF(1) and CRF(2) receptor subtypes in monoaminergic neurotransmission, hypothalamic-pituitary-adrenocortical axis activity and behaviour we compared the effects of CRF and urocortin 1 with those of the selective CRF(2) receptor ligands urocortin 2 and urocortin 3. In vivo microdialysis in the rat hippocampus was used to assess free corticosterone, extracellular levels of serotonin (5-HT) and noradrenaline (NA), and their metabolites 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG), respectively. Intracerebroventricular (i.c.v.) injection of CRF and urocortin 1, 2 and 3 (1.0 microg) increased hippocampal levels of 5-HT and 5-HIAA. CRF and urocortin 1 increased NA and MHPG, whereas urocortin 2 and urocortin 3 elevated MHPG, but not NA levels. CRF and the urocortins induced an immediate increase in behavioural activity. CRF and urocortin 1 mainly caused grooming and exploratory behaviour. In contrast, urocortin 2 and urocortin 3 both induced exploratory behaviour, but not grooming, and increased time spent eating food pellets. All urocortins, but not CRF, suppressed food intake 4-6 h after injection. Hippocampal free corticosterone levels were elevated by CRF, urocortin 1 and 3, but not by urocortin 2. The time courses of the CRF- and urocortin 1-induced responses were significantly prolonged as compared to those of the CRF(2) receptor ligands. The stimulatory changes evoked by CRF and urocortin 1 were present up to 4-6 h after injection, whereas the effects of urocortin 2 and urocortin 3 returned to baseline within 2.5 h after injection. Pre-treatment with the selective antagonist antisauvagine-30 (5.0 microg, i.c.v.) confirmed that the effects of urocortin 3 were CRF(2) receptor-mediated. The differential time course of the monoaminergic, neuroendocrine and behavioural effects of CRF and urocortin 1, as compared to urocortin 2 and urocortin 3, and the specific behavioural pattern induced by the CRF(2) receptor ligands, suggest a distinct role for CRF(2) receptors in the stress response.     

Effects of dopaminergic system activation on feeding behavior and growth performance of the sea bass (Dicentrarchus labrax): A self-feeding approach

Dopamine is synthesized from l-dopa and subsequently processed into norepinephrine and epinephrine. Any excess neurotransmitter can be taken up again by the neurons to be broken down enzymatically into DOPAC. The effect of dopamine on mammalian food intake is controversial. Mice unable to synthesize central dopamine die of starvation. However, studies have also shown that central injection of dopamine inhibits food intake. The effect of dopaminergic system in the fish feeding behavior has been scarcely explored. We report that the inclusion of l-dopa in the diets results in the activation of sea bass central dopaminergic system but also in the significant increase of the hypothalamic serotonin levels. Dietary l-dopa induces a decrease of food intake and feed conversion efficiency that drives a decline of all growth parameters tested. No behavioral effects were observed after l-dopa treatment. l-dopa treatment stimulated central expression of NPY and CRF. It suggests that CRF might mediate l-dopa effects on food intake but also that CRF neurons lie downstream of NPY neurons in the hierarchical forebrain system, thus controlling energy balance. Unexpectedly, dietary administration of haloperidol, a D₂-receptor antagonist, cannot block dopamine effects but also induces a decline of the food intake. This decrease seems to be a side effect of haloperidol treatment since fish exhibited a decreased locomotor activity. We conclude that oral l-dopa inhibits sea bass food intake and growth. Mechanism could also involve an increase of hypothalamic serotoninergic tone.     

Antagonistic effect of somatostatin on corticotropin-releasing factor-induced anorexia in the rat

The effect of somatostatin on corticotropin-releasing factor (CRF)-induced anorexia was examined in rats. Intracerebroventricular (icv) administration of 0.11 nmol and 0.21 nmol ovine CRF significantly suppressed food intake of 24 h-starved rats. Icv administration of 0.31 nmol somatostatin 14 and somatostatin 28 partially reversed suppression of food intake induced by icv injection of 0.21 nmol CRF in 24 h-starved rats. These results suggest that somatostatin may counteract the suppressive effect of CRF on food intake within the central nervous system.     

Adrenal modulation of the inhibitory effect of corticotropin releasing factor on feeding

Corticotropin releasing factor (CRF) reduces food intake in rats after central administration. In these studies we examined whether the adrenal gland and the vagus were involved in CRF suppression of intake. One hour intake was reduced by a 5 μg (ICV) injection of CRF in sham but not adrenalectomized rats maintained on 0.9% NaCl. In a separate experiment on rats maintained on tap water, the inhibitory effect of CRF (5 μg) lasted at least 4 hours in sham rats whereas adrenalectomized rats did not significantly differ from controls. These experiments suggest that the adrenal gland modulates the feeding response to CRF. As replacement with corticosterone (0.75 mg/kg) in total adrenalectomized rats did not restore responsiveness to 5 or 10 μg of CRF, we next studied whether the adrenal medulla was responsible for the decreased responsiveness to CRF. In rats lacking the adrenal medulla only, food intake was reduced by a 5 μg injection of CRF; in sham rats, intake was significantly reduced by doses as low as 0.1 μg of CRF. An additional experiment examined the effect of gastric vagotomy on the CRF feeding response. Vagotomized rats were as responsive to 5 and 10 μg injections of CRF as sham rats, which suggests that the effect is not dependent on the vagus nerve. These findings indicate that the adrenal gland, primarily the medulla, plays an intermediate role in the reduction of food intake caused by central injections of CRF. This conclusion is consistent with the known effect of CRF on adrenomedullary discharge.     

CRF-induced excessive grooming behavior in rats and mice

We studied the grooming response to lateral ventricle injection of CRF in both rats and mice under similar conditions. One microgram of CRF ICV induced a pronounced increase (3- to 4-fold) in the frequency of self-grooming in rats, but only a much smaller (less than 20%) increase in mice. The minimum effective dose of CRF in rats was 300 ng. Although ACTH1-24 induced less grooming in mice than in rats, the difference in potency did not appear to be sufficient to explain the differences between the effectiveness of CRF in the two species. Whereas ACTH increased all types of grooming scored. CRF increased all forms of grooming except flank scratching with the hind limb. The major effect of CRF was to increase the number of episodes of grooming, whereas ACTH1-24 tended to prolong the length of individual episodes. The excessive grooming induced by ICV CRF was not affected by prior treatment with dexamethasone, suggesting that the increased grooming was not due to secondary release of ACTH from the pituitary. Nevertheless, ICV CRF might induce grooming by releasing MSH/ACTH from cerebral storage sites. CRF-induced grooming, like ACTH-induced grooming, was inhibited by naloxone pretreatment. Despite the small qualitative differences, CRF-induced grooming could be due to secondary release of ACTH.     

Involvement of corticotropin-releasing factor in restraint stress-induced anorexia and reversion of the anorexia by somatostatin in the rat

The mechanism by which restraint stress induces suppression of food intake and the influence of intracerebroventricular (icv) administration of somatostatin on the anorexia induced by restraint stress were examined in the rat. Ninety minutes of restraint stress reduced food intake of rats to approximately 60% that of control. Anorexia induced by 90 min restraint stress was partially reversed by icv administration of alpha-helical CRF (9-41), a corticotropin-releasing factor (CRF) antagonist, and completely reversed by anti-CRF gamma-globulin. These results provide further evidence in support of the theory that CRF is involved in the inhibitory mechanism of food intake in restraint stress. ICV administration of somatostatin 14 and SMS 201-995, an analog of somatostatin, also reversed restraint stress-induced anorexia. It is, therefore, suggested that somatostatin may counteract the suppressive action of CRF on food intake in stress.     

The hypothalamic-pituitary-interrenal axis and the control of food intake in teleost fish

Although environmental, social and physical stressors have been shown to inhibit food intake and feeding behavior in fish, little is known about the mechanisms that mediate the appetite-suppressing effects of stress. Since the hypothalamic-pituitary-interrenal (HPI) axis is activated in response to most forms of stress in fish, components of this axis may be involved in mediating the food intake reductions elicited by stress. Recent investigations into the brain regulation of food intake in fish have identified several signals with orexigenic and anorexigenic properties. Among these appetite-regulating signals are related neuropeptides that can activate the HPI axis, namely corticotropin-releasing factor (CRF) and urotensin I (UI). Central injections of CRF or UI, or treatments that result in an increase in hypothalamic CRF and UI gene expression, can elicit dose-dependent decreases in food intake that can be reversed by pre-treatment with a CRF-receptor antagonist. Evidence also suggests that cortisol, the end product of HPI activation in most fishes (i.e. Osteichthyes), may be involved in the regulation of food intake. Overall, while elements of the HPI axis may mediate some of the appetite-suppressing effects of stress, it is undetermined how either CRF-related peptides, cortisol, or other elements of the stress response interact with the complex circuitry of the hypothalamic feeding center.     

CRF-related peptides contribute to stress response and regulation of appetite in hypoxic rainbow trout

Hypoxia stress suppresses appetite in a variety of fish species, but the mechanisms mediating this response are not known. Therefore, given their anorexigenic and hypophysiotropic properties, we investigated the contribution of forebrain corticotropin-releasing factor (CRF) and urotensin I (UI) to the regulation of food intake and the hypothalamic-pituitary-interrenal (HPI) stress axis in hypoxic rainbow trout. Exposure to 50 and 35% O(2) saturation for 24 h decreased food intake by 28 and 48%, respectively. The 35% O(2) treatment also increased forebrain CRF and UI mRNA levels, plasma cortisol, and lactate. Exposure for 72 h to the same conditions resulted in similar reductions in food intake, increases in plasma cortisol proportional to the hypoxia severity, and increases in forebrain CRF and UI mRNA levels in the 50% O(2) treatment. Relative to saline-infused fish, chronic intracranial infusion of the CRF receptor antagonist alpha-helical CRF((9-41)) reduced the appetite-suppressing effects of 24-h exposure to 35% O(2) and blocked the hypoxia-induced increase in plasma cortisol. Finally, forebrain microdissection revealed that 50 and 35% O(2) exposure for 24 h specifically increases preoptic area CRF and UI mRNA levels in proportion to the severity of the hypoxic challenge and either has no effect or elicits small decreases in other forebrain regions. These results show that CRF-related peptides play a physiological role in regulating the HPI axis and in mediating at least a portion of the reduction in food intake under hypoxic conditions in rainbow trout and demonstrate that the response of forebrain CRF and UI neurons to this stressor is region specific.     

Inhibitory effect of ghrelin on food intake is mediated by the corticotropin-releasing factor system in neonatal chicks

It is known that, in rats, central and peripheral ghrelin increases food intake mainly through activation of neuropeptide Y (NPY) neurons. In contrast, intracerebroventricular (ICV) injection of ghrelin inhibits food intake in neonatal chicks. We examined the mechanism governing this inhibitory effect in chicks. The ICV injection of ghrelin or corticotropin-releasing factor (CRF), which also inhibits feeding and causes hyperactivity in chicks. Thus, we examined the interaction of ghrelin with CRF and the hypothalamo-pituitary-adrenal (HPA) axis. The ICV injection of ghrelin increased plasma corticosterone levels in a dose-dependent or a time-dependent manner. Co-injection of a CRF receptor antagonist, astressin, attenuated ghrelin-induced plasma corticosterone increase and anorexia. In addition, we also investigated the effect of ghrelin on NPY-induced food intake and on expression of hypothalamic NPY mRNA. Co-injection of ghrelin with NPY inhibited NPY-induced increase in food intake, and the ICV injection of ghrelin did not change NPY mRNA expression. These results indicate that central ghrelin does not interact with NPY as seen in rodents, but instead inhibits food intake by interacting with the endogenous CRF and its receptor.     

Endogenous corticotropin-releasing factor modulates feeding induced by neuropeptide Y or a tail-pinch stressor.

Previous work has characterized an anorexic action for endogenous, central nervous system corticotropin-releasing factor (CRF). Central injection of CRF decreases food intake induced pharmacologically by various appetite stimulants and a CRF antagonist attenuates restraint stress anorexia. Also, stressful physiological stimuli that are relevant to ingestive regulation, such as glucoprivation and protein nutrient deficiency, activate CRF systems. The present experiments examined the effects of exogenously administered CRF and a CRF antagonist, alpha-helical CRF(9-41), on spontaneous feeding induced by neuropeptide Y (NPY) and by a tail-pinch stressor. Pretreatment with a low dose of the CRF antagonist (1 microgram ICV) enhanced the hyperphagia induced by NPY while reducing the latency to begin feeding and increasing the duration of eating during tail pinch. Higher doses of alpha-hel CRF (5 and 25 micrograms ICV) exhibited diminishing or opposite effects. In contrast, CRF pretreatment (0.02, 0.1, and 0.5 microgram ICV) blocked the acquisition of tail-pinch feeding. Hence, while CRF administration impairs intake in these and other feeding paradigms, alpha-hel CRF actually facilitated dose dependently the intensity of the feeding response to NPY and tail pinch. These results suggest that endogenous CRF systems may play a role in modulating excessive feeding under conditions of evoked appetite and that brain CRF systems regulate feeding when excessive intake threatens to compromise the performance of other noningestive behaviors.