High-protein diet improves sensitivity to cholecystokinin and shifts the cecal microbiome without altering brain inflammation in diet-induced obesity in rats. Am J Physiol Regul Integr Comp Physiol 313: R473–R486, 2017. doi:10.1152/ajpregu.00105.2017.—High-protein diet (HPD) curtails obesity and/or fat mass, but it is unknown whether it reverses neuroinflammation or alters glucose levels, CCK sensitivity, and gut microbiome in rats fed a Western diet (WD)-induced obesity (DIO). Male rats fed a WD (high fat and sugar) for 12 wk were switched to a HPD for 6 wk. Body composition, food intake, meal pattern, sensitivity to intraperitoneal CCK-8S, blood glucose, brain signaling, and cecal microbiota were assessed. When compared with a normal diet, WD increased body weight (9.3%) and fat mass (73.4%). CCK-8S (1.8 or 5.2 nmol/kg) did not alter food intake and meal pattern in DIO rats. Switching to a HPD for 6 wk reduced fat mass (15.7%) with a nonsignificantly reduced body weight gain, normalized blood glucose, and decreased feeding after CCK-8S. DIO rats on the WD or switched to a HPD showed comparable microbial diversity. However, in HPD versus WD rats, there was enrichment of 114 operational taxonomic units (OTUs) and depletion of 188 OTUs. Of those, Akkermansia muciniphila (enriched on a HPD), an unclassified Clostridiales, a member of the RF39 order, and a Phascolarctobacterium were significantly associated with fat mass. The WD increased cytokine expression in the hypothalamus and dorsal medulla that was unchanged by switching to HPD. These data indicate that HPD reduces body fat and restores glucose homeostasis and CCK sensitivity, while not modifying brain inflammation. In addition, expansion of cecal Akkermansia muciniphila correlated to fat mass loss may represent a potential peripheral mechanism of HPD beneficial effects.

BackgroundRecent evidence from rat neuron-free mucosa study suggests that the membrane bile acid receptor TGR5 decreases colonic secretion under basal and stimulated conditions. As submucosal neurons are key players in secretory processes and highly express TGR5, we investigated their role in TGR5 agonist-induced inhibition of secretion and the pathways recruited.MethodsTGR5 expression and localization were assessed in rat proximal (pC) and distal (dC) colon by qPCR and immunohistochemistry with double labeling for cholinergic neurons in whole-mount preparations. The influence of a selective (INT-777) or weak (ursodeoxycholic acid, UDCA) TGR5 agonist on colonic secretion was assessed in Ussing chambers, in dC preparation removing seromuscular submucosal tissues, in the presence of different inhibitors of secretion pathways.Key ResultsTGR5 mRNA is expressed in full thickness dC and pC and immunoreactivity is located in colonocytes and pChAT-positive neurons. Addition of INT-777, and less potently UDCA, decreased colonic secretion in seromuscular stripped dC by -58.17 +/- 2.6%. INT-777 effect on basal secretion was reduced in neuron-free and TTX-treated mucosal-submucosal preparations. Atropine, hexamethonium, indomethacin, and L-NAME all reduced significantly INT-777's inhibitory effect while the 5-HT4 antagonist, RS-39604, and lidocaine abolished it. INT-777 inhibited stimulated colonic secretion induced by nicotine, but not cisapride, carbachol or PGE2.Conclusions & InferencesTGR5 activation inhibits basal and stimulated distal colonic secretion in rats by acting directly on epithelial cells and also inhibiting submucosal neurons. This could represent a counter-regulatory mechanism, at the submucosal level, of the known prosecretory effect of bile acids in the colon.

Corticotropin-releasing factor (CRF)-CRF1 receptor in the brain plays a key role in stress-related alterations of behavior including anxiety/depression, and autonomic and visceral functions. In particular, CRF1 signaling mediates hypersensitivity to colorectal distension (CRD) in various models (early life adverse events, repeated psychological stress, chronic high anxiety, postcolonic inflammation, or repeated nociceptive CRD). So far, knowledge of brain sites involved is limited. A recent article demonstrates in rats that CRF microinjected into the central amygdala (CeA) induces a hyperalgesic response to CRD and enhances the noradrenaline and dopamine levels at this site. The visceral and noradrenaline, unlike dopamine, responses were blocked by a CRF1 antagonist injected into the CeA. Here, we review the emerging role that CRF-CRF1 signaling plays in the CeA to induce visceral hypersensitivity. In the somatic pain field, CRF in the CeA was shown to induce pain sensitization. This is mediated by the activation of postsynaptic CRF1 receptors and protein kinase A signaling that increases N-methyl-d-aspartate receptor neurotransmission. In addition, the activation of tetraethylamonium-sensitive ion channels such as Kv3 accelerates repolarization and firing rate. Whether facilitation of pain transmission underlies CRF action in the CeA-induced visceral hypersensitivity will need to be delineated. CRF1 signaling in the CeA is also an important component of the neuronal circuitry inducing anxiety-like behavior and positioned at the interphase of the reciprocal relationship between pain and affective state. The hyperactivity of this system may represent the neuroanatomical and biochemical substrate contributing to the coexpression of hypersensitivity to CRD and mood disorders in subsets of irritable bowel syndrome patients.

Hintergrund/Einleitung: Ghrelin,ein aus 28 Aminosäuren bestehendes Peptidhormon,wird hauptsächlich im Magen gebildet und vermittelt seine Wirkung über den GHS-Rezeptor.Peripheres Ghrelin induziert eine Steigerung der Nahrungsaufnahme.In früheren Studien wurde gezeigt,dass peripher appliziertes Ghrelin im Gehirn allein im Ncl. arcuatus (NARC) die Expression von c-fos, einem etabliertem Marker neuronaler Aktivierung,induziert. Hierbei handelt es sich überwiegend um NPY-Neurone,für die propagiert wird,dass sie zum Paraventrikulären Nukleus des Hypothalamus (PVN) projizieren und an der Kontrolle von Nahrungsaufnahme beteiligt sind.Die Selektivität der Zunahme c-Fos-LI positiver Neurone im NARC ist überraschend,da GHS-Rezeptoren in weiteren Kerngebieten von Hypothalamus und Hirnstamm exprimiert werden,die an der Kontrolle der Nahrungsaufnahme beteiligt sind.

Brain somatostatin receptor 2 mediates the dipsogenic effect of central somatostatin and cortistatin in rats: role in drinking behavior. Am J Physiol Regul Integr Comp Physiol 307: R793–R801, 2014. 2014; doi:10.1152/ajpregu.00248.2014.—Intrace-rebroventricular injection of stable somatostatin (SST) agonists stimulates food and water intake in rats. We investigated the receptor subtype(s) involved in the dipsogenic effect of intracerebroventricular injection of SST agonists, mechanisms of action, and role. In nonfasted and non-water-deprived male rats with chronic intracerebroventricular cannula, intake of water without food or food without water was monitored separately to avoid any interactions compared with intracerebroventricular vehicle. SST-14 and cortistatin (CST-14) (1 (cid:2) g/rat icv) increased water intake by 3.1- and 2.7-fold, respec-tively, while both peptides did not alter food intake at 1 h postinjection in the light phase. By contrast, the stable pan-somatostatin agonist ODT8-SST (1 (cid:2) g/rat icv) increased both water and food intake by 4.9-and 3.7-fold, respectively. S-346-011, a selective receptor 2 (sst 2 ) agonist (1 (cid:2) g/rat icv) induced water ingestion, while sst 1 or sst 4 agonist, injected under the same conditions, did not. The sst 2 antagonist S-406-028 (1 (cid:2) g/rat icv) prevented the 1-h water intake induced by intracerebroventricular ODT8-SST and CST-14. Losartan (100 (cid:2) g/rat icv), an angiotensin receptor 1 (AT 1 ) antagonist, completely blocked the water consumption induced by intracerebroventricular ODT8-SST, whereas intracerebroventricular injection of S-406-028 did not modify the intracerebroventricular ANG II-induced dipsogenic response. The sst 2 antagonist reduced by 40% the increase of the 3-h water intake in the early dark phase. These data indicate that SST-14 and CST-14 interact with sst 2 to exert a potent dipsogenic effect, which is mediated downstream by angiotensin-AT 1 signaling. These data also indicate that sst 2 activation by brain SST-14 and/or CST-14 may play an important role in the regulation of drinking behavior.

Constipation and L‐dopa‐induced gastric dysmotility are common gastrointestinal (GI) symptoms in Parkinson's disease (PD). We investigated the novel ghrelin agonist, HM01 influence on GI motor dysfunctions in 6‐hydroxydopamine (6‐OHDA) rats.

Hunger and satiety are regulated in a complex fashion by a few food intake stimulatory (orexigenic) and a multitude of inhibitory (anorexigenic) factors produced in the periphery (mainly in the gastrointestinal tract) or directly in the brain. Within the brain, the hypothalamus plays a pivotal role as a production site of food intake regulatory factors. Importantly, this site integrates peripheral and central signaling factors to orchestrate food intake and in the long term body weight. Our knowledge on these regulatory pathways is not static but rather rapidly changing as new factors as well as up- and downstream signaling pathways of already known transmitters are uncovered. Hypothalamic nucleobindin2 (NUCB2), the precursor of nesfatin-1, was first described in 2006 and nesfatin-1 found to be a novel anorexigenic modulator of food intake and body weight. The initial report stimulated several groups to investigate the biological actions of nesfatin-1 and subsequent studies delineated the underlying brain mechanisms involved in its food reducing effect. Of interest was the demonstration that NUCB2 also exerts its anorexigenic action in the paraventricular nucleus of the hypothalamus and is regulated at this site by changes in metabolic status with a diurnal rhythm inversely related to that of feeding in rats. The present review describes the current state-of-knowledge on central nesfatin-1's effects on food intake and body weight and highlights important missing links regarding cellular signaling mechanisms involved in nesfatin-1's action.

Nesfatin-1 was discovered in 2006 and introduced as a potential novel anorexigenic modulator of food intake and body weight. The past years have witnessed increasing evidence establishing nesfatin-1 as a potent physiological inhibitor of food intake and body weight and unravelled nesfatin-1's interaction with other brain transmitters to exert its food consumption inhibitory effect. As observed for other anorexigenic brain neuropeptides, nesfatin-1 is also likely to exert additional, if not pleiotropic, actions in the brain and periphery. Recent studies established the prominent expression of the nesfatin-1 precursor, nucleobindin2 (NUCB2), in the stomach and pancreas, where nesfatin-1 influences endocrine secretion. This review will highlight the current experimental state-of-knowledge on the effects of NUCB2/nesfatin-1 on food intake, body weight and glucose homeostasis. Potential implications in human obesity will be discussed in relation to the evidence of changes in circulating levels of NUCB2/nesfatin-1 in disease states, the occurrence of genetic NUCB2 polymorphisms and - in contrast to several other hormones - the independence of leptin signalling known to be blunted under conditions of chronically increased body weight.

BACKGROUND:Chronic psychological stress-induced alterations in visceral sensitivity have been predominantly assessed in male rodents. We investigated the effect of acute and repeated water avoidance stress (WAS) on the visceromotor response (VMR) to colorectal distension (CRD) and the role of opioids in male and cycling female Wistar rats using a novel non-invasive manometric technique. METHODS:After a baseline VMR (1st CRD, day 0), rats were exposed to WAS (1 h day(-1) ) either once or for four consecutive days, without injection or with naloxone (1 mg kg(-1) ) or saline injected subcutaneously before each WAS session. KEY RESULTS:The VMR to CRD recorded on day 1 or 4 immediately after the last WAS was reduced in both females and males. The visceral analgesia was mainly naloxone-dependent in females, but naloxone-independent in males. In non-injected animals, on days 2 and 5, VMR was not significantly different from baseline in males whereas females exhibited a significant VMR increase at 60 mmHg on day 5. Basal CRD and CRD on days 1, 2, and 5 in both sexes without WAS induced similar VMR. CONCLUSIONS & INFERENCES:When monitored non-invasively, psychological stress induces an immediate poststress visceral analgesia mediated by an opiate signaling system in females while naloxone-independent in males, and hyperalgesia at 24 h after repeated stress only in females. These data highlight the importance of sex-specific interventions to modulate visceral pain response to stress.