Shi-Yi Zhou

Low-affinity CCK-A receptors are coexpressed with leptin receptors in rat nodose ganglia: implications for leptin as a regulator of short-term satiety.

The paradigm for the control of feeding behavior has changed significantly. Research has shown that leptin, in the presence of CCK, may mediate the control of short-term food intake. This interaction between CCK and leptin occurs at the vagus nerve. In the present study, we aimed to characterize the interaction between CCK and leptin in the vagal primary afferent neurons. Single neuronal discharges of vagal primary afferent neurons innervating the gastrointestinal tract were recorded from rat nodose ganglia. Three groups of nodose ganglia neurons were identified: group 1 responded to CCK-8 but not leptin; group 2 responded to leptin but not CCK-8; group 3 responded to high-dose CCK-8 and leptin. In fact, the neurons in group 3 showed CCK-8 and leptin potentiation, and they responded to gastric distention. To identify the CCK-A receptor (CCKAR) affinity states that colocalize with the leptin receptor OB-Rb, we used CCK-JMV-180, a high-affinity CCKAR agonist and low-affinity CCKAR antagonist. As expected, immunohistochemical studies showed that CCK-8 administration significantly potentiated the increase in the number of c-Fos-positive neurons stimulated by leptin in vagal nodose ganglia. Administration of CCK-JMV-180 eliminated the synergistic interaction between CCK-8 and leptin. We conclude that both low- and high-affinity CCKAR are expressed in nodose ganglia. Many nodose neurons bearing low-affinity CCKAR express OB-Rb. These neurons also respond to mechanical distention. An interaction between CCKAR and OB-Rb in these neurons likely facilitates leptin mediation of short-term satiety.

Diabetic Visceral Hypersensitivity Is Associated With Activation of Mitogen-Activated Kinase in Rat Dorsal Root Ganglia

OBJECTIVE Diabetic patients often experience visceral hypersensitivity and anorectal dysfunction. We hypothesize that the enhanced excitability of colon projecting dorsal root ganglia (DRG) neurons observed in diabetes is caused by a decrease in the amplitude of the transient A-type K+ (IA) currents resulting from increased phosphorylation of mitogen-activated protein kinases (MAPK) and reduced opening of Kv4.2 channels. RESEARCH DESIGN AND METHODS We performed patch-clamp recordings of colon projecting DRG neurons from control and streptozotocin-induced diabetic (STZ-D) rats. Western blot analyses and immunocytochemistry studies were used to elucidate the intracellular signaling pathways that modulate the IA current. In vivo studies were performed to demonstrate that abnormal MAPK signaling is responsible for the enhanced visceromotor response to colorectal distention in STZ-D rats. RESULTS Patch-clamp studies demonstrated that IA current was diminished in the colon projecting DRG neurons of STZ-D rats. Western blot analysis of STZ-D DRG neurons revealed increases in phosphorylated MAPK and KV4.2. In diabetic DRG neurons, increased intracellular Ca2+ ([Ca2+]i), protein kinase C (PKC), and MAPK were involved in the regulation of IA current through modulation of Kv4.2. Hypersensitive visceromotor responses to colorectal distention in STZ-D rats were normalized by administration of MAPK inhibitor U0126. CONCLUSIONS We demonstrated that reduction of the IA current in STZ-D DRG neurons is triggered by impaired [Ca2+]i ion homeostasis, and this in turn activates the PKC-MAPK pathways, resulting in decreased opening of the Kv4.2 channels. Hence, the PKC-MAPK–Kv4.2 pathways represent a potential therapeutic target for treating visceral hypersensitivity in diabetes.

Ghrelin Induces Leptin Resistance by Activation of Suppressor of Cytokine Signaling 3 Expression in Male Rats: Implications in Satiety Regulation

The anorexigenic adipocyte-derived hormone leptin and the orexigenic hormone ghrelin act in opposition to regulate feeding behavior via the vagal afferent pathways. The mechanisms by which ghrelin exerts its inhibitory effects on leptin are unknown. We hypothesized that ghrelin activates the exchange protein activated by cAMP (Epac), inducing increased SOCS3 expression, which negatively affects leptin signal transduction and neuronal firing in nodose ganglia (NG) neurons. We showed that 91 ± 3% of leptin receptor (LRb) -bearing neurons contained ghrelin receptors (GHS-R1a) and that ghrelin significantly inhibited leptin-stimulated STAT3 phosphorylation in rat NG neurons. Studies of the signaling cascades used by ghrelin showed that ghrelin caused a significant increase in Epac and suppressor of cytokine signaling 3 (SOCS3) expression in cultured rat NG neurons. Transient transfection of cultured NG neurons to silence SOCS3 and Epac genes reversed the inhibitory effects of ghrelin on leptin-stimulated STAT3 phosphorylation. Patch-clamp studies and recordings of single neuronal discharges of vagal primary afferent neurons showed that ghrelin markedly inhibited leptin-stimulated neuronal firing, an action abolished by silencing SOCS3 expression in NG. Plasma ghrelin levels increased significantly during fasting. This was accompanied by enhanced SOCS3 expression in the NG and prevented by treatment with a ghrelin antagonist. Feeding studies showed that silencing SOCS3 expression in the NG reduced food intake evoked by endogenous leptin. We conclude that ghrelin exerts its inhibitory effects on leptin-stimulated neuronal firing by increasing SOCS3 expression. The SOCS3 signaling pathway plays a pivotal role in ghrelins inhibitory effect on STAT3 phosphorylation, neuronal firing, and feeding behavior.

Upregulation of bile acid receptor TGR5 and nNOS in gastric myenteric plexus is responsible for delayed gastric emptying after chronic high-fat feeding in rats

Chronic high-fat feeding is associated with functional dyspepsia and delayed gastric emptying. We hypothesize that high-fat feeding upregulates gastric neuronal nitric oxide synthase (nNOS) expression, resulting in delayed gastric emptying. We propose this is mediated by increased bile acid action on bile acid receptor 1 (TGR5) located on nNOS gastric neurons. To test this hypothesis, rats were fed regular chow or a high-fat diet for 2 wk. Rats fed the high-fat diet were subjected to concurrent feeding with oral cholestyramine or terminal ileum resection. TGR5 and nNOS expression in gastric tissue was measured by immunohistochemistry, PCR, and Western blot. Gastric motility was assessed by organ bath and solid-phase gastric emptying studies. The 2-wk high-fat diet caused a significant increase in neurons coexpressing nNOS and TGR5 in the gastric myenteric plexus and an increase in nNOS and TGR5 gene expression, 67 and 111%, respectively. Enhanced nonadrenergic, noncholinergic (NANC) relaxation, deoxycholic acid (DCA)-induced inhibition in fundic tissue, and a 26% delay in gastric emptying accompanied these changes. A 24-h incubation of whole-mount gastric fundus with DCA resulted in increased nNOS and TGR5 protein expression, 41 and 37%, respectively. Oral cholestyramine and terminal ileum resection restored the enhanced gastric relaxation, as well as the elevated nNOS and TGR5 expression evoked by high-fat feeding. Cholestyramine also prevented the delay in gastric emptying. We conclude that increased levels of circulatory bile acids induced by high-fat feeding upregulate nNOS and TGR5 expression in the gastric myenteric plexus, resulting in enhanced NANC relaxation and delayed gastric emptying.

67 Perturbing NMDA Receptor -PSD-95 Protein Interactions Prevents Selective Loss of Nitric Oxide Synthase (NOS) Containing Neuron and Improves Gastric Emptying in Diabetic Rats

Background. Although the pathogenesis of delayed gastric emptying, namely gastroparesis, is still unclear, diabetes mellitus is major etiology of gastroparesis. Decreased neuronal nitric oxide synthase (nNOS), which induces relaxation of gastric smooth muscle through the production of nitric oxide, is supposed to be one of the mechanisms of gastroparesis (Gastroenterology 113:1535, 1997). However, the effective treatment for gastroparesis has not been developed. While dyslipidemia is a risk factor of diabetic neuropathy, the defect of apolipoprotein E (apoE), a lipid transporter secreted from glial cell, decreased the expression of nNOS in the stomach (Dig Dis Sci. 57:1504, 2012). Furthermore, transplantion of neural stem cell into gastric antral wall was reported to improve delayed gastric emptying in nNOS knockout mouse (Gastroenterology 129:1817, 2005). The aim of the present study is to explore the role of apoE on gastric emptying and evaluate the effect of neural stem cell transplantation against the model of gastroparesis. Methods. The model of type2 diabetes, db/db mice, and apoE knockout mice, which is the model of arteriosclerosis and hyperlipidemia, were used. For measurement of gastric emptying, 0.48 mg of 13C-acetic acid with 0.15 ml liquid meal (Lacol®) was orally administered. The gastric half emptying time (t1/2) measured by 13C breath test was used for evaluation. The expression levels of nNOS, pan-neuronal marker, PGP 9.5, glial fibrillary acidic protein (GFAP), and glia derived neurotrophic factor (GDNF) were examined by immunohistochemistry andWestern blotting. Neural stem cells were isolated from ffLuc-transgenic mouse, which fluorescent protein, venus, and luciferase gene was fused (BBRC 419; 188, 2012). After tertiary neurosphere was formed, it was injected into gastric antral wall by glass needle. Results. Delayed gastric emptying was observed in 27% of db/db mice, while the levels of blood glucose and body weight were not significantly different. The expression of nNOS in gastric antrum and serum level of apoE were significantly decreased in db/db mice which presented delayed gastric emptying. In apoE knockout mice, the gastric emptying was also delayed compared with control. Although, the expression of PGP 9.5 was not changed, the expression of nNOS was significantly decreased in apoE knockout mice. Furthermore, the expression levels of GFAP and GDNF were significantly decreased in apoE knockout mice. Transplantation of neural stem cell significantly improved the delayed gastric emptying in apoE knockout mice. Conclusion. Neural stem cell transplantation restored the delayed gastric emptying in apoE knockout mice, suggesting a promising application of regenerative therapy against gastroparesis.