Intracerebroventricular urocortin 3 counteracts central acyl ghrelin-induced hyperphagic and gastroprokinetic effects via CRF receptor 2 in rats

Rare CRHR2 and GRM8 variants identified as candidate factors associated with eating disorders in Japanese patients by whole exome sequencing

Eating disorders (EDs) are a type of psychiatric disorder characterized by pathological eating and related behavior and considered to be highly heritable. The purpose of this study was to explore rare variants expected to display biological functions associated with the etiology of EDs. We performed whole exome sequencing (WES) of affected sib-pairs corresponding to disease subtype through their lifetime and their parents. From those results, rare single nucleotide variants (SNVs) concordant with sib-pairs were extracted and estimated to be most deleterious in the examined families. Two non-synonymous SNVs located on corticotropin-releasing hormone receptor 2 (CRHR2) and glutamate metabotropic receptor 8 (GRM8) were identified as candidate disease susceptibility factors. The SNV of CRHR2 was included within the cholesterol binding motif of the transmembrane helix region, while the SNV of GRM8 was found to contribute to hydrogen bonds for an α-helix structure. CRHR2 plays important roles in the serotoninergic system of dorsal raphe nuclei, which is involved with feeding and stress-coping behavior, whereas GRM8 modulates glutamatergic neurotransmission. Moreover, GRM8 modulates glutamatergic neurotransmission, and is also considered to have effects on dopaminergic and adrenergic neurotransmission. Thus, identification of rare and deleterious variants in this study is expected to increase understanding and treatment of affected individuals. Further investigation regarding the biological function of these variants may provide an opportunity to elucidate the pathogenesis of EDs.

Expression Patterns of the Neuropeptide Urocortin 3 and Its Receptor CRFR2 in the Mouse Central Auditory System

Sensory systems have to be malleable to context-dependent modulations occurring over different time scales, in order to serve their evolutionary function of informing about the external world while also eliciting survival-promoting behaviors. Stress is a major context-dependent signal that can have fast and delayed effects on sensory systems, especially on the auditory system. Urocortin 3 (UCN3) is a member of the corticotropin-releasing factor family. As a neuropeptide, UCN3 regulates synaptic activity much faster than the classic steroid hormones of the hypothalamic-pituitary-adrenal axis. Moreover, due to the lack of synaptic re-uptake mechanisms, UCN3 can have more long-lasting and far-reaching effects. To date, a modest number of studies have reported the presence of UCN3 or its receptor CRFR2 in the auditory system, particularly in the cochlea and the superior olivary complex, and have highlighted the importance of this stress neuropeptide for protecting auditory function. However, a comprehensive map of all neurons synthesizing UCN3 or CRFR2 within the auditory pathway is lacking. Here, we utilize two reporter mouse lines to elucidate the expression patterns of UCN3 and CRFR2 in the auditory system. Additional immunolabelling enables further characterization of the neurons that synthesize UCN3 or CRFR2. Surprisingly, our results indicate that within the auditory system, UCN3 is expressed predominantly in principal cells, whereas CRFR2 expression is strongest in non-principal, presumably multisensory, cell types. Based on the presence or absence of overlap between UCN3 and CRFR2 labeling, our data suggest unusual modes of neuromodulation by UCN3, involving volume transmission and autocrine signaling.

The transcripts of CRF and CRF receptors under fasting stress in Dabry's sturgeon (Acipenser dabryanus Dumeril)

Dabry's sturgeon (Acipenser dabryanus Dumeril, 1868) belongs to Sturgeon and is distributed throughout the mainstream of the upper Yangtze River. While there is little research onphysiological mechanism of Dabry's sturgeon, such as feeding regulation by the CRF system. At present, CRF is thought to regulate feeding via CRF receptors (CRF-Rs) in several mammals, but relatively few studies of CRF and feeding exist in teleosts. Herein, the transcripts of CRF and CRF-Rs under fasting stress in Dabry's sturgeon (Acipenser dabryanus Dumeril) have been explored. A full length Dabry's sturgeon CRF cDNA of 953 bp was identified, which contained a 447 bp open reading frame (ORF). A partial CRF-R1 cDNA of 1053 bp and CRF-R2 cDNA of 906 bp corresponding to the coding sequences (CDS) was obtained. In addition, analysis of the tissue distribution of CRF and CRF-Rs mRNAs revealed they were widely distributed in the central and peripheral nervous systems. Furthermore, periprandial (preprandial and postprandial), fasting, and re-feeding experiments revealed CRF mRNA was significantly increased 1 h and 3 h after feeding and CRF and CRF-Rs transcripts were significantly decreased after 10 days fasting, and significantly increased on re-feeding on day 10. These results suggest that CRF and CRF-Rs might regulate feeding by acting as satiety factors.

Hypothalamic mechanisms associated with corticotropin-releasing factor-induced anorexia in chicks

Central administration of corticotropin-releasing factor (CRF), a 41-amino acid peptide, is associated with potent anorexigenic effects in rodents and chickens. However, the mechanism underlying this effect remains unclear. Hence, the objective of the current study was to elucidate the hypothalamic mechanisms that mediate CRF-induced anorexia in 4 day-old Cobb-500 chicks. After intracerebroventricular (ICV) injection of 0.02 nmol of CRF, CRF-injected chicks ate less than vehicle chicks while no effect on water intake was observed at 30 min post-injection. In subsequent experiments, the hypothalamus samples were processed at 60 min post-injection. The CRF-injected chicks had more c-Fos immunoreactive cells in the arcuate nucleus (ARC), dorsomedial nucleus (DMN), ventromedial hypothalamus (VMH), and paraventricular nucleus (PVN) of the hypothalamus than vehicle-treated chicks. CRF injection was associated with decreased whole hypothalamic mRNA abundance of neuropeptide Y receptor sub-type 1 (NPYR1). In the ARC, CRF-injected chicks expressed more CRF and CRF receptor sub-type 2 (CRFR2) mRNA but less agouti-related peptide (AgRP), NPY, and NPYR1 mRNA than vehicle-injected chicks. CRF-treated chicks expressed greater amounts of CRFR2 and mesotocin mRNA than vehicle chicks in the PVN and VMH, respectively. In the DMN, CRF injection was associated with reduced NPYR1 mRNA. In conclusion, the results provide insights into understanding CRF-induced hypothalamic actions and suggest that the anorexigenic effect of CRF involves increased CRFR2-mediated signaling in the ARC and PVN that overrides the effects of NPY and other orexigenic factors.

Alpha-melanocyte stimulating hormone in ghrelin-elicited feeding and gut motility

This review evaluates published studies regarding alpha-melanocyte stimulating hormone (α-MSH) in ghrelin-elicited feeding and gut motility. We have sought to integrate all available evidences to provide a complete review on the properties of melanocortin receptors (MCR) and the potential clinical treatment of α-MSH after ghrelin-elicited feeding and gut motility. The available studies were grouped into four categories: food intake, gastric emptying, small intestinal transit, and colonic transit. As we describe, the literature provides evidence of the ability of ghrelin to increase food intake, gastric emptying, small intestinal transit, and colonic transit. α-MSH, which displays high affinity for the MC3 and MC4 receptors, can competitively activate MCRs with agouti-related protein stimulated by ghrelin, and partly attenuates the effect of acyl ghrelin on food intake. Central ghrelin-induced acceleration of gastric emptying is not mediated by MCRs, but the acceleration of the small intestinal transit is at least partly mediated via MCRs in the brain. Similar to fecal pellets and total fecal weight, distal colonic motility and secretion are partly mediated by MCRs in the brain. The interplay between acyl ghrelin and MCRs may provide a new therapeutic avenue to ameliorate anorexia and constipation.

Effects of burns on gut motor and mucosa functions

This review analyzed the published studies on the effects of thermal injury on gastrointestinal motility and mucosal damage. Our strategy was to integrate all available evidence to provide a complete review on the prokinetic properties of variable reagents and the potential clinical treatment of mucosal damage and gastrointestinal dysmotility after thermal injury. We classified the studies into two major groups: studies on gastrointestinal dysmotility and studies on mucosal damage. We also subclassified the studies into 3 parts: stomach, small intestine, and colon. This review shows evidence that ghrelin can recover burn-induced delay in gastric emptying and small intestinal transit, and can protect the gastric mucosa from burn-induced injury. Oxytocin and β-glucan reduced the serum inflammatory mediators, and histological change and mucosal damage indicators, but did not show evidence of having the ability to recover gastrointestinal motility. Using a combination of different reagents to protect the gastrointestinal mucosa against damage and to recover gastrointestinal motility is an alternative treatment for thermal injury.

α-melanocyte stimulating hormone modulates the central acyl ghrelin-induced stimulation of feeding, gastrointestinal motility, and colonic secretion

Background

Acyl ghrelin-induced intake depends on hypothalamic neuropeptide Y and agouti-related protein (AgRP) neurotransmitters. Intracerebroventricular (ICV) injection of AgRP increases feeding through competitive antagonism at melanocortin receptors. ICV administration of α-melanocyte stimulating hormone (α-MSH), a natural antagonist of AgRP, may modulate the acyl ghrelin-induced orexigenic effect.

Objective

This study aimed to investigate the modulating effect of α-MSH on the central acyl ghrelin-induced food intake, gastrointestinal motility, and colonic secretion in rats.

Methods and procedures

We examined the effects of α-MSH and acyl ghrelin on food intake, gastric emptying, small intestinal transit, colonic motility, and secretion in conscious rats with a chronic implant of ICV catheters.

Results

ICV injection of O-n-octanoylated ghrelin (0.1 nmol/rat) significantly increased the cumulative food intake up to 8 h (P<0.01), enhanced non-nutrient semi-liquid gastric emptying (P<0.001), increased the geometric center and running percentage of small intestinal transit (P<0.001), accelerated colonic transit time (P<0.05), and increased fecal pellet output (P<0.01) and total fecal weight (P<0.01). Pretreatment with ICV injection of α-MSH (1.0 and 2.0 nmol/rat) attenuated the acyl ghrelin-induced hyperphagic effect, fecal pellet output, and total fecal weight, while higher dose of α-MSH (2.0 nmol/rat) attenuated the increase in the geometric center of small intestinal transit (P<0.01). However, neither dose of α-MSH altered acyl ghrelin-stimulated gastroprokinetic effect, increase in the running percentage of small intestinal transit, nor accelerated colonic transit time.

Conclusion

α-MSH is involved in central acyl ghrelin-elicited feeding, small intestinal transit, fecal pellet output, and fecal weight. α-MSH does not affect central acyl ghrelin-induced acceleration of gastric emptying and colonic transit time in rats.

Correlation between colonic secretion and colonic motility in rats: Role of ghrelin

AIM

To explore the relationship between colonic secretory function and colonic motility.

METHODS

Using a rat model chronically implanted with intracerebroventricular (ICV) and cecal catheters, we validated the correlation between colonic secretion and colonic motor functions, as well as the role of ICV injection volume.

RESULTS

Compared to saline controls (5 μL/rat), ICV acyl ghrelin at 1 nmol/5 μL enhanced the total fecal weight, accelerated the colonic transit time, and increased the fecal pellet output during the first hour post-injection, while ICV des-acyl ghrelin at 1 nmol/5 μL only accelerated the colonic transit time. These stimulatory effects on colonic motility and/or secretion from acyl ghrelin and des-acyl ghrelin disappeared when the ICV injection volume increased to 10 μL compared with saline controls (10 μL/rat). Additionally, the ICV injection of 10 μL of saline significantly shortened the colonic transit time compared with the ICV injection of 5 μL of saline. The total fecal weight during the first hour post-injection correlated with the colonic transit time and fecal pellet output after the ICV injection of acyl ghrelin (1 nmol/5 μL), whereas the total fecal weight during the first hour post-injection correlated with the fecal pellet output but not the colonic transit time after the ICV injection of des-acyl ghrelin (1 nmol/5 μL).

CONCLUSION

Colonic secretion does not always correlate with colonic motility in response to different colonic stimulations. Acyl ghrelin stimulates colonic secretion.