Similarly, OLETF rats demonstrate no deficit in gastric emptying relative to control rats (8), whereas streptozotocin-induced diabetic mice have accelerated gastric emptying (38). Serotonin is an amine mediator that is abundant in the gut wall. (pCaMKII). In PD rats, pCaMKII immunoreactivity was increased in duodenal 5-HT (P< 0.001), K (P< 0.01) and L (P< 0.01) cells in response to glucose; glucose-induced activation of all three cell types was significantly reduced in RD and 3MD compared with PD rats. Immunoreactivity for GLP-1, but not GIP, was significantly reduced in RD and 3MD compared with PD rats (P< 0.01). Administration of glucose significantly increased pCaMKII in enteric and vagal afferent neurons in PD rats; glucose-induced pCaMKII immunoreactivity was attenuated in enteric and vagal afferent neurons (P< 0.01,P< 0.001, respectively) in RD and 3MD. These data suggest that glucose sensing in enteroendocrine and enterochromaffin cells and activation of neural pathways is usually markedly impaired in UCD-T2DM rats. Keywords:5-hydroxytryptamine, intestinal glucose, incretin type 2 diabetes mellitus(T2DM) is usually associated with the Fenoldopam development of obesity and characterized by the impaired ability of gut hormones to regulate plasma levels of glucose and alterations in energy balance (10). A substantial portion of insulin secretion in response to oral ingestion of glucose is usually mediated via release of the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide (GLP-1). GIP and GLP-1 are released from K and L gut enteroendocrine cells (EECs), respectively, in response to luminal glucose and augment glucose-stimulated insulin secretion (20,25). However, patients with T2D demonstrate an impaired incretin response resulting in insufficient insulin secretion from the pancreatic -cell in response to ingestion of glucose (27). Whether this impairment of the incretin response in T2D is due to altered release of incretins and impaired incretin action at the pancreatic -cell has been an area of controversy. There is evidence that plasma levels of GIP following oral glucose are not different between healthy controls and patients with T2D, but that there is Fenoldopam a decrease in the release Fenoldopam of GLP-1 (39). However, other evidence suggests that decrease -cell response to incretin hormones in T2D patients (9). Thus altered function in gut endocrine cells may play a role in the pathogenesis of T2DM; however, in vivo studies looking at direct activation of these cell populations have been limited, in part, due to the difficulty in studying this cell population in vivo. Glucose-sensing mechanisms by K and L cells have been extensively studied using in vivo models and EEC lines and have identified a number of possible mechanisms. Recent studies using cultures of highly purified K or L cell culture have suggested that KATPchannels and possibly the sodium-glucose cotransporter SGLT-1 play a predominant role in glucose sensing (14,26,35). There is also evidence that taste transduction elements including the G protein-coupled sweet taste receptors T1R1/3 may also sense glucose in the gut (18). Luminal glucose also induces release of 5-hydroxytryptamine (5-HT) from enterochromaffin IL17B antibody (EC) cells in the gut wall. Receptors for 5-HT are expressed by many different cell types in the gut wall, and 5-HT activates intrinsic reflexes to regulate motor and secretory function. 5-HT also activates extrinsic, vagal afferent terminals located in the gut wall via 5-HT3receptors (5-HT3Rs) to activate a vago-vagal reflex to inhibit gastric emptying and stimulate pancreatic exocrine secretion (19,24). Interestingly, there is evidence that vagal efferent outflow can also influence the secretion of incretin hormones to maintain glucose homeostasis (4,29,37). Loss of vagal function also results in a reduced incretin effect, demonstrating the importance of peripheral neuroendocrine loop to regulate plasma glucose in the postprandial period (29). The UCD-T2DM rat is usually a relatively new animal model of human Fenoldopam T2DM demonstrating polygenic adult-onset obesity and insulin resistance accompanied by -cell dysfunction. It more closely models the pathophysiology of adult-onset T2DM Fenoldopam in humans than other rodent models of the disease (7). We hypothesized that in T2DM, glucose sensing in the gut wall would be impaired. During the onset and progression of T2DM, cellular activation of ECs and EECs in response to luminal glucose would be reduced along with diminished activation of the gut-brain axis. We have recently developed a method for measuring activation of gut EECs and ECs in situ, avoiding the use of either cell lines or isolated cell preparation (40). This technique uses detection of phosphorylated calcium calmodulin-dependent kinase II (pCaMKII) by immunohistochemistry as a marker of cellular activation. Moreover, the ability to conduct experiments in unanesthetized rats allows us to assess the activation of intrinsic and extrinsic neurons along the gut-brain axis. == MATERIALS AND METHODS == == == == Animals..