Gastric Inhibitory Polypeptide (GIP) Is Selectively Decreased in the Roux-Limb of Dietary Obese Mice after RYGB Surgery

Gastric inhibitory polypeptide (GIP, glucose-dependent insulinotropic polypeptide) is expressed by intestinal K cells to regulate glucose-induced insulin secretion. The impact of Roux-en Y bypass (RYGB) surgery on blood GIP is highly contraversial. This study was conducted to address the mechanism of controversy. GIP mRNA was examined in the intestine, and serum GIP was determined using Luminex and ELISA in diet-induced obese (DIO) mice. The assays were conducted in RYGB mice in fasting and fed conditions. Food preference, weight loss and insulin sensitivity were monitored in RYGB mice. In DIO mice, GIP mRNA was increased by 80% in all sections of the small intestine over the lean control. The increase was observed in both fasting and fed conditions. After RYGB surgery, the food-induced GIP expression was selectively reduced in the Roux-limb, but not in the biliopancreatic and common limbs of intestine in fed condition. Lack of stimulation by glucose or cholesterol contributed to the reduction. Jejunal mucosa of Roux-limb exhibited hypertrophy, but villous surface was decreased by the undigested food. Serum GIP (total) was significantly higher in the fasting condition, but not in the fed condition due to attenuated GIP response to food intake in RYGB mice. The GIP alteration was associated with chow diet preference, sustained weight loss and insulin sensitization in RYGB mice. RYGB increased serum GIP in the fasting, but not in the fed conditions. The loss of food-induced GIP response in Roux-limb of intestine likely contributes to the attenuated serum GIP response to feeding.     

In vitro and in vivo conjugation of dietary hydroxycinnamic acids by UDP-glucuronosyltransferases and sulfotransferases in humans

Hydroxycinnamic acids are a class of phenolic antioxidants found widely in dietary plants. Their biotransformation in the human organism primarily involves Phase II conjugation reactions. In this study, activities of UDP-glucuronosyltransferases (UGTs) and sulfotransferases (SULTs) towards major dietary hydroxycinnamic acids (caffeic, dihydrocaffeic, dihydroferulic, ferulic and isoferulic acids) were investigated. Conjugate formation was evaluated using human liver and intestinal S9 homogenates, and in vitro characterization was carried out using recombinant human UGTs and SULTs. Analysis of the kinetics of hydroxycinnamic acid conjugation in human S9 homogenates revealed that intrinsic clearance (V_max/K_m) is much greater for sulfation than for glucuronidation. Assessment of activity using a panel of recombinant human SULTs showed that SULT1A1 is most active in the sulfation of caffeic, dihydrocaffeic and isoferulic acids, while SULT1E1 is most active in the sulfation of ferulic and dihydroferulic acids. Only isoferulic acid was significantly glucuronidated by human liver S9 homogenates, explained by the high activity of liver-specific UGT1A9. Studies on the kinetics of active SULTs and UGTs demonstrated a markedly lower K_m for SULTs. To further corroborate our findings, we carried out an intervention study in healthy humans to determine the hydroxycinnamic acid conjugates in urine after consumption of hydroxycinnamate-rich coffee (200 ml). Analysis showed that sulfates are the main conjugates in urine, with the exception of isoferulic acid, which is mainly glucuronidated. These data suggest that sulfates are the predominant hydroxycinnamic acid conjugates in humans, and that SULT mediated sulfation is a major factor determining the bioavailability of hydroxycinnamic acids in vivo.     

The vagus nerve, food intake and obesity

Food interacts with sensors all along the alimentary canal to provide the brain with information regarding its composition, energy content, and beneficial effect. Vagal afferents innervating the gastrointestinal tract, pancreas, and liver provide a rapid and discrete account of digestible food in the alimentary canal, as well as circulating and stored fuels, while vagal efferents, together with the sympathetic nervous system and hormonal mechanisms, codetermine the rate of nutrient absorption, partitioning, storage, and mobilization. Although vagal sensory mechanisms play a crucial role in the neural mechanism of satiation, there is little evidence suggesting a significant role in long-term energy homeostasis. However, increasing recognition of vagal involvement in the putative mechanisms making bariatric surgeries the most effective treatment for obesity should greatly stimulate future research to uncover the many details regarding the specific transduction mechanisms in the periphery and the inter- and intra-neuronal signaling cascades disseminating vagal information across the neuraxis.     

Orexin inputs to caudal raphé neurons involved in thermal,cardiovascular, and gastrointestinal regulation

Orexin-expressing neurons in the lateral hypothalamus with their wide projections throughout the brain are important for the regulation of sleep and wakefulness, ingestive behavior, and the coordination of these behaviors in the environmental context. To further identify downstream effector targets of the orexin system, we examined in detail orexin-A innervation of the caudal raphé nuclei in the medulla, known to harbor sympathetic preganglionic motor neurons involved in thermal, cardiovascular, and gastrointestinal regulation. All three components of the caudal raphé nuclei, raphé pallidus, raphé obscurus, and parapyramidal nucleus, are innervated by orexin-A-immunoreactive fibers. Using confocal microscopy, we demonstrate close anatomical appositions between varicose orexin-A immunoreactive axon profiles and sympathetic premotor neurons identified with either a transneuronal retrograde pseudorabies virus tracer injected into the interscapular brown fat pads, or with in situ hybridization of pro-TRH mRNA. Furthermore, orexin-A injected into the fourth ventricle induced c-Fos expression in the raphé pallidus and parapyramidal nucleus. These findings suggest that orexin neurons in the hypothalamus can modulate brown fat thermogenesis, cardiovascular, and gastrointestinal functions by acting directly on neurons in the caudal raphé nuclei, and support the idea that orexins simultaneous stimulation of food intake and sympathetic activity might have evolved as a mechanism to stay alert while foraging.     

Die Wirkung von Hexachlorcyclohexanen bei Neurospora crassa inositolless

Ohne ZusammenfassungMeinem hochverehrten Lehrer, Herrn Prof. Dr. W. H. Schopfer () gewidmet.Inauguraldissertation der philosophisch-naturwissenschaftlichen Fakultät der Universität Bern zur Erlangung der Doktorwürde.     

Mechanical implications of pneumatic neck vertebrae in sauropod dinosaurs

The pre-sacral vertebrae of most sauropod dinosaurs were surrounded by interconnected, air-filled diverticula, penetrating into the bones and creating an intricate internal cavity system within the vertebrae. Computational finite-element models of two sauropod cervical vertebrae now demonstrate the mechanical reason for vertebral pneumaticity. The analyses show that the structure of the cervical vertebrae leads to an even distribution of all occurring stress fields along the vertebrae, concentrated mainly on their external surface and the vertebral laminae. The regions between vertebral laminae and the interior part of the vertebral body including thin bony struts and septa are mostly unloaded and pneumatic structures are positioned in these regions of minimal stress. The morphology of sauropod cervical vertebrae was influenced by strongly segmented axial neck muscles, which require only small attachment areas on each vertebra, and pneumatic epithelia that are able to resorb bone that is not mechanically loaded. The interaction of these soft tissues with the bony tissue of the vertebrae produced lightweight, air-filled vertebrae in which most stresses were borne by the external cortical bone. Cervical pneumaticity was therefore an important prerequisite for neck enlargement in sauropods. Thus, we expect that vertebral pneumaticity in other parts of the body to have a similar role in enabling gigantism.     

Biomarker discovery by imaging mass spectrometry: transthyretin is a biomarker for gentamicin-induced nephrotoxicity in rat

Adverse drug effects are often associated with pathological changes in tissue. An accurate depiction of the undesired affected area, possibly supported by mechanistic data, is important to classify the effects with regard to relevance for human patients. MALDI imaging MS represents a new analytical tool to directly provide the spatial distribution and the relative abundance of proteins in tissue. Here we evaluate this technique to investigate potential toxicity biomarkers in kidneys of rats that were administered gentamicin, a well known nephrotoxicant. Differential analysis of the mass spectrum profiles revealed a spectral feature at 12,959 Da that strongly correlates with histopathology alterations of the kidney. We unambiguously identified this spectral feature as transthyretin (Ser(28)-Gln(146)) using an innovative combination of tissue microextraction and fractionation by reverse-phase liquid chromatography followed by a top-down tandem mass spectrometric approach. Our findings clearly demonstrate the emerging role of imaging MS in the discovery of toxicity biomarkers and in obtaining mechanistic insights concerning toxicity mechanisms.     

Brain stem melanocortinergic modulation of meal size and identification of hypothalamic POMC projections

Metabolic, cognitive, and environmental factors processed in the forebrain modulate food intake by changing the potency of direct controls of meal ingestion in the brain stem. Here, we behaviorally and anatomically test the role of the hypothalamic proopiomelanocortin (POMC) system in mediating some of these descending, indirect controls. Melanotan II (MTII), a stable melanocortin 4 receptor (MC4R) and melanocortin 3 receptor (MC3R) agonist injected into the fourth ventricle near the dorsal vagal complex, potently inhibited 14-h food intake by decreasing meal size but not meal frequency; SHU9119, an antagonist, increased food intake by selectively increasing meal size. Furthermore, MTII injected into the fourth ventricle increased and SHU9119 tended to decrease heart rate and body temperature measured telemetrically in freely moving rats. Numerous alpha-melanocyte-stimulating hormone-immunoreactive axons were in close anatomical apposition to nucleus tractus solitarius neurons showing c-Fos in response to gastric distension, expressing neurochemical phenotypes implicated in ingestive control, and projecting to brown adipose tissue. In retrograde tracing experiments, a small percentage of arcuate nucleus POMC neurons was found to project to the dorsal vagal complex. Thus melanocortin signaling in the brain stem is sufficient to alter food intake via changing the potency of satiety signals and to alter sympathetic outflow. Although the anatomical findings support the involvement of hypothalamomedullary POMC projections in mediating part of the descending, indirect signal, they do not rule out involvement of POMC neurons in the nucleus tractus solitarius in mediating part of the direct signal.     

Gastrin-releasing peptide signaling plays a limited and subtle role in amygdala physiology and aversive memory

Links between synaptic plasticity in the lateral amygdala (LA) and Pavlovian fear learning are well established. Neuropeptides including gastrin-releasing peptide (GRP) can modulate LA function. GRP increases inhibition in the LA and mice lacking the GRP receptor (GRPR KO) show more pronounced and persistent fear after single-trial associative learning. Here, we confirmed these initial findings and examined whether they extrapolate to more aspects of amygdala physiology and to other forms of aversive associative learning. GRP application in brain slices from wildtype but not GRPR KO mice increased spontaneous inhibitory activity in LA pyramidal neurons. In amygdala slices from GRPR KO mice, GRP did not increase inhibitory activity. In comparison to wildtype, short- but not long-term plasticity was increased in the cortico-lateral amygdala (LA) pathway of GRPR KO amygdala slices, whereas no changes were detected in the thalamo-LA pathway. In addition, GRPR KO mice showed enhanced fear evoked by single-trial conditioning and reduced spontaneous firing of neurons in the central nucleus of the amygdala (CeA). Altogether, these results are consistent with a potentially important modulatory role of GRP/GRPR signaling in the amygdala. However, administration of GRP or the GRPR antagonist (D-Phe(6), Leu-NHEt(13), des-Met(14))-Bombesin (6-14) did not affect amygdala LTP in brain slices, nor did they affect the expression of conditioned fear following intra-amygdala administration. GRPR KO mice also failed to show differences in fear expression and extinction after multiple-trial fear conditioning, and there were no differences in conditioned taste aversion or gustatory neophobia. Collectively, our data indicate that GRP/GRPR signaling modulates amygdala physiology in a paradigm-specific fashion that likely is insufficient to generate therapeutic effects across amygdala-dependent disorders.     

Learning of submissive behavior in mice: A new model

The experience of winning or loosing fights plays an important role in subsequent aggressive or submissive behaviors. In this study agonistic behavior of male mice was chosen to investigate learning mechanisms in the context of a biologically meaningful situation.An ICR mouse introduced into a group of five C57BL/6 mice was attacked by mice of high social status (Fighter, F), but not by lower ranking animals (Non-Fighter, NF). On this basis the following model was developed to study learning of submissive behavior. Day 1 (baseline trial): An ICR mouse was introduced to a single NF-C57 mouse. Few submissive behaviors (crouch) were observed in naive ICR mice upon contact with NF-C57 mice. Day 2 (learning trial): The same ICR mouse was defeated by an F-C57 mouse until it showed defensive upright posture upon approach. This criterion was reached after a mean latency of 3.5 min and after being exposed to a mean number of 14 bites. Day 3 (retest trial): The same pairs as on day 1 confronted each other. Without being attacked, the ICR mouse showed a significant increase of submissive behavior (crouch, defensive sideways and upright) upon mere contact with the NF-C57 mouse when compared to day 1 and to control mice on day 3. Controls, confronted on all three days with NF-C57 mice, showed no increase in submissive behaviors.The results are discussed in terms of acquisition, memory, retrieval and extinction of learned submissive behavior. It is suggested that the mechanisms underlying learning of submissive behavior include generalization of conditioning and specific extinction processes. The further use of the learning scheme to assess drug effects is illustrated.