Pancreatic polypeptide stimulates gastric acid secretion through a vagal mechanism in rats

Identification, characterization and feeding response of peptide YYb (PYYb) gene in grass carp (Ctenopharyngodon idellus)

The peptide YYb (PYYb) is a fish-specific peptide belonging to the neuropeptide Y (NPY) family. In the present study, the full-length cDNA sequence and genomic structure of PYYb (gcPYYb) from Ctenopharyngodon idellus have been isolated and characterized. The gcPYYb gene consists of three exons interspaced by two introns, opposing to the typical architecture of most NPY-family genes as well as its paralogs. Alignment of deduced amino acid sequence indicates that the fish PYYb is more variable compared to NPY and PYY as shown by more residue changes in teleosts lineage, suggesting mild selective pressure imposed on the peptide. Real-time quantitative PCR analysis shows the gcPYYb mRNA in developing larvae is increased during the mixed endo- and exogenous-feeding period and is widely distributed throughout the intestine of fully grown individuals. Following a single meal, the gcPYYb mRNA in foregut is increased at 3 h post-feeding and subsequently decreased before the foregut contents are cleared. These results suggest that the gcPYYb has an important role in the early life stages of grass carp and is involved in food intake by transmitting feeding-related signals.

Gut hormones and obesity: physiology and therapies

Over the past 30 years, it has been established that hormones produced by the gut, pancreas, and adipose tissue are key players in the control of body weight. These hormones act through a complex neuroendocrine system, including the hypothalamus, to regulate metabolism and energy homeostasis. In obesity, this homeostatic balance is disrupted, either through alterations in the levels of these hormones or through resistance to their actions. Alterations in gut hormone secretion following gastric bypass surgery are likely to underlie the dramatic and persistent loss of weight following this procedure, as well as the observed amelioration in type 2 diabetes mellitus. Medications based on the gut hormone GLP-1 are currently in clinical use to treat type 2 diabetes mellitus and have been shown to produce weight loss. Further therapies for obesity based on other gut hormones are currently in development.

Increased novelty-induced motor activity and reduced depression-like behavior in neuropeptide Y (NPY)-Y4 receptor knockout mice

There is growing evidence that neuropeptide Y (NPY) acting through Y1 and Y2 receptors has a prominent role in modulating anxiety- and depression-like behavior in rodents. However, a role of other Y-receptors like that of Y4 receptors in this process is poorly understood. We now investigated male Y2, Y4 single and Y2/Y4 double knockout mice in behavioral paradigms for changes in motor activity, anxiety and depression-like behavior. Motor activity was increased in Y2, Y4 and Y2/Y4 knockout mice under changing and stressful conditions, but not altered in a familiar environment. Y4 and Y2 knockout mice revealed an anxiolytic phenotype in the light/dark test, marble burying test and in stress-induced hyperthermia, and reduced depression-like behavior in the forced swim and tail suspension tests. In Y2/Y4 double knockout mice, the response in the light/dark test and in the forced swim test was further enhanced compared with Y4 and Y2 knockout mice, respectively. High levels of Y4 binding sites were observed in brain stem nuclei including nucleus of solitary tract and area postrema. Lower levels were found in the medial amygdala and hypothalamus. Peripheral administration of pancreatic polypeptide (PP) induced Y4 receptor-dependent c-Fos expression in brain stem, hypothalamus and amygdala. PP released peripherally from the pancreas in response to food intake, may act not only as a satiety signal but also modulate anxiety-related locomotion.

Effect of pancreatic polypeptide on rat dorsal vagal complex neurons

1. Pancreatic polypeptide (PP) microinjected into the dorsal vagal complex (DVC) elevates gastric activity through a vagal mechanism. Thus, it was hypothesized that PP alters the activity of nuclei comprising the DVC, i.e. the nucleus tractus solitarii (NTS) and the dorsal motor nucleus (DMN). 2. In vivo and in vitro approaches were used. For in vivo studies, micropipettes were used for recording and injecting vehicle or PP. Neurons were identified as NTS or DMN using orthodromic and antidromic activation, respectively, following vagal stimulation. Gastric-related DVC neurons were located using antral inflation. For in vitro studies, DMN neurons were recorded from medullary slices. 3. Of the twenty-eight NTS and DMN neurons identified, fifteen were activated, six inhibited and seven unaffected after PP microinjection. Forty-two gastric-related neurons were located in the DVC, of which twenty-five were stimulated by PP and seventeen exhibited no change. No gastric-related cells were inhibited. 4. For in vitro studies, 66% of DMN neurons were activated by PP (n = 27/47) while the remaining 33% were inhibited (n = 14/47). Similar results were obtained in normal or synaptic blockade media. 5. These results support the hypothesis that PP alters DVC neuronal activity, which may thereby lead to the previously observed alterations in gastric activity.