No abstract

The responses of the gut hormone peptide YY (PYY) to food were investigated in 20 normal-weight and 20 obese humans in response to six test meals of varying calorie content. Human volunteers had a graded rise in plasma PYY (R2 = 0.96; P < 0.001) during increasing calorific meals, but the obese subjects had a lower endogenous PYY response at each meal size (P < 0.05 at all levels). The ratio of plasma PYY(1-36) to PYY(3-36) was similar in normal-weight and obese subjects. The effect on food intake and satiety of graded doses of exogenous PYY(3-36) was also evaluated in 12 human volunteers. Stepwise increasing doses of exogenous PYY(3-36) in humans caused a graded reduction in food intake (R2 = 0.38; P < 0.001). In high-fat-fed (HF) mice that became obese and low-fat-fed mice that remained normal weight, we measured plasma PYY, tissue PYY, and PYY mRNA levels and assessed the effect of exogenous administered PYY(3-36) on food intake in HF mice. HF mice remained sensitive to the anorectic effects of exogenous ip PYY(3-36). Compared with low-fat-fed fed mice, the HF mice had lower endogenous plasma PYY and higher tissue PYY but similar PYY mRNA levels, suggesting a possible reduction of PYY release. Thus, fasting and postprandial endogenous plasma PYY levels were attenuated in obese humans and rodents. The PYY(3-36) infusion study showed that the degree of plasma PYY reduction in obese subjects were likely associated with decreased satiety and relatively increased food intake. We conclude that obese subjects have a PYY deficiency that would reduce satiety and could thus reinforce their obesity.

Kisspeptin is the peptide product of the KiSS-1 gene and the endogenous agonist for the GPR54 receptor. Recent evidence suggests the kisspeptin/GPR54 system is a key regulator of the reproductive system. We examined the effect of intracerebroventricular (i.c.v.) and peripheral administration of the active kisspeptin fragment, kisspeptin-10, on circulating gonadotropins and total testosterone levels in adult male rats. The effect of kisspeptin-10 in-vitro on the release of hypothalamic peptides from hypothalamic explants and gonadotropins from anterior pituitary fragments was also determined. The i.c.v. administration of kisspeptin-10 dosedependently increased plasma luteinizing hormone (LH) and increased plasma follicle stimulating hormone (FSH) and total testosterone at 60 mins post-injection. In a separate study investigating the time course of this response, i.c.v. administered kisspeptin-10 (3nmol) significantly increased plasma LH at 10, 20 and 60 mins, FSH at 60 mins and total testosterone at 20 and 60 mins post-injection. Kisspeptin-10 stimulated the release of luteinizing hormone releasing hormone (LHRH) from invitro hypothalamic explants. Peripheral administration of kisspeptin-10 increased plasma LH, FSH and total testosterone. However, doses of 100-1000nM kisspeptin-10 did not influence LH or FSH release from pituitary fragments in-vitro. Kisspeptin therefore potently stimulates the hypothalamic-pituitary-gonadal (HPG) axis. These effects are likely to be mediated via the hypothalamic LHRH system. 2 IntroductionKisspeptin is a 54 amino acid peptide encoded by the tumour suppressor gene KiSS-1(1-4). Kisspeptin is thus also known as 'metastin' because of its antimetastatic properties (4,5). Using quantitative polymerase chain reaction, KiSS-1 mRNA expression has been demonstrated in the placenta and throughout the central nervous system (CNS), including the hypothalamus (3). Endogenous forms of kisspeptin 54, 14 and 13 amino acids in length have been isolated from human placenta. The common C terminal decapeptide shared by these forms, kisspeptin-10, is secreted by cultured human trophoblasts (6). In humans, circulating kisspeptin levels are 7000-fold higher than basal levels during the third trimester of pregnancy (7).All kisspeptin fragments, including kisspeptin-10, have a similar affinity and efficacy for the previously orphan G-protein-coupled receptor, GPR54 (1). GPR54 was originally isolated from rat brain (8) and is highly expressed in the rat and human CNS and peripheral tissues (1,8). GPR54 receptor mRNA is expressed in several rat brain regions, with highest expression in the hypothalamus and amygdala. Within the hypothalamus, GPR54 mRNA is highly concentrated in the arcuate nucleus, the lateral hypothalamic area and the dorsomedial nucleus (8). In the periphery it is highly expressed in the pituitary, placenta and pancreas (1,3). Peripheral administration of kisspeptin-10 increases plasma oxytocin levels in female rats (1).Recent reports suggest that the kisspeptin/GPR54 system is a...

The exocytosis of AMPA receptors is a key step in long-term potentiation (LTP), yet the timing and location of exocytosis and the signaling pathways involved in exocytosis during synaptic plasticity are not fully understood. Here we combine two-photon uncaging with two-photon imaging of a fluorescent label of surface AMPA receptors to monitor individual AMPA receptor exocytosis events near spines undergoing LTP. AMPA receptors that reached the stimulated spine came from a combination of preexisting surface receptors (70-90%) and newly exocytosed receptors (10-30%). We observed exocytosis in both the dendrite and spine under basal conditions. The rate of AMPA receptor exocytosis increased ∼5-fold during LTP induction and decayed to the basal level within ∼1 min, both in the stimulated spine and in the dendrite within ∼3 μm of the stimulated spine. AMPA receptors inserted in the spine were trapped in the spine in an activity-dependent manner. The activity-dependent exocytosis required the Ras-ERK pathway, but not CaMKII. Thus, diffusive Ras-ERK signaling presumably serves as an important means for signaling from synapses to dendritic shafts to recruit AMPA receptors into synapses during LTP.two-photon imaging | synaptic plasticity L ong-term potentiation (LTP) at CA1 synapses in the hippocampus, a cellular model for learning and memory, is initiated by the influx of Ca 2+ through NMDA-type glutamate receptors (NMDAR) into dendritic spines. The insertion of AMPA-type glutamate receptors (AMPAR) into the postsynaptic site and the associated enlargement of dendritic spines are believed to be critical for LTP induction (1-3). The insertion of AMPARs is likely a multistep process including the exocytosis of AMPARs from endosomes to extrasynaptic membranes, lateral diffusion of receptors into the synapse, and anchoring there (1, 4-11). The location of exocytosis during LTP is under some debate, with reports of exocytosis exclusively in the dendrite (9, 10, 12), as well as reports of exocytosis both in the spine and dendrite (13-16). The relative timing of AMPAR exocytosis during LTP is still ambiguous (11).The signaling cascades linking spine Ca 2+ elevation and AMPAR trafficking have been extensively studied, and a myriad of signaling molecules have been identified (1,(17)(18)(19). However, which signaling pathways underlie specific processes (e.g., exocytosis or anchoring) of AMPAR trafficking remains elusive. Recent studies using two-photon fluorescence lifetime imaging have show that different signaling pathways have different spatiotemporal dynamics during LTP: activity of Ca 2+ /calmodulin-dependent kinase II (CaMKII) is restricted to the stimulated synapse, whereas Ras signaling diffuses out of the stimulated spine and spreads along the dendrite over ∼5 μm (20,21). Each step of AMPAR trafficking should have a specific spatiotemporal pattern dependent on its upstream signaling.Here we image individual exocytosis events near spines in organotypic slices with subsecond temporal resolution using highsensitivity two-p...