Ghrelin and the Hyposomatotropism of Obesity

Objective: Human obesity is characterized by growth hormone (GH) deficiency, which appears primarily related to a central pattern of obesity and is reverted on weight loss. As yet, the metabolic basis of the GH deficiency remains to be elucidated. The recently discovered endogenous ligand for the GH secretagogue receptor, ghrelin, stimulates GH secretion when administered to rodents or healthy humans. It may thus be hypothesized that low ghrelin levels underlie the hyposomatropism in obesity. Research Methods and Procedures: We have tested this hypothesis in individuals with widely varying body mass and fat distribution and evaluated whether the improved GH concentrations on weight loss are associated with enhanced ghrelin levels. Results: Both plasma GH and ghrelin levels were reciprocally related with body mass index (r = −0.67, p < 0.001). However, whereas 24-hour GH secretion was negatively related to the visceral fat area (r = −0.72, p < 0.01), ghrelin levels showed a positive relationship with the visceral fat area (r = 0.49, p < 0.02). Weight loss resulted in increased GH secretion (median 24-hour GH area under the curve: 1983 vs. 4024 mU/day before and after weight loss, respectively; p < 0.01) but did not affect ghrelin levels. No relationship could be found between GH and ghrelin plasma levels in obese subjects when comparing diurnal concentration profiles. Discussion: We showed that plasma ghrelin and GH levels are both reciprocally related with body mass index, but no causative relationship could be demonstrated between low ghrelin levels and the hyposomatropism in human obesity.     

Using eggshell membranes as a DNA source for population genetic research

In the context of population genetic research, a faster and less invasive method of DNA sampling would allow large-scale assessments of genetic diversity and genetic differentiation with the help of volunteer observers. The aim of this study was to investigate the usefulness of eggshell membranes as a DNA source for population genetic research, by addressing eggshell membrane DNA quality, degeneration and cross-contamination. To this end, a comparison was made with blood-derived DNA samples. We have demonstrated 100% successful DNA extraction from post-hatched Black-tailed Godwit (Limosa limosa) eggshell membranes as well as from blood samples. Using 11 microsatellite loci, DNA amplification success was 99.1% for eggshell membranes and 97.7% for blood samples. Genetic information within eggshell membrane DNA in comparison to blood DNA was not affected (F _ST = −0.01735, P = 0.999) by degeneration or possible cross-contamination. Furthermore, neither degeneration nor cross-contamination was apparent in total genotypic comparison of eggshell membrane DNA and blood sample DNA. Our research clearly illustrates that eggshell membranes can be used for population genetic research.     

Sulphur and sulphate reduction with acetate and propionate in an aerobic process for sulphide removal

Summary Sulphide production rates of sulphur-and sulphate-reducing bacteria up to 50 mg per biomass support particle per day were observed in an aerated sulphide-removal reactor with polyurethane (PUR) foam as carrier material. The optimal pH and temperature for the sulphide-producing bacteria were 8.0 and 30°C respectively. Raschig rings and four types of cube-shaped PUR particles were tested as carrier materials. When using PUR particles, the sulphide production rate was always between 3% and 4% of the sulphide removal rate, dependent on the dimensions and pore size of the polyurethane support particles. With the Raschig rings this ratio was only 2% and for reactors in which no carrier materials were present it was even lower (0.6%). Media containing different mixtures of acetate, propionate, sulphur and sulphate inoculated under anoxic conditions with sludge from the aerated reactor showed the presence of acetate-degrading sulphur-reducing, but not of acetate-degrading sulphate-reducing, bacteria. With propionate as sole electron donor no degradation occurred in the presence of sulphur within 2 weeks, whereas sulphate-dependent propionate oxidation started after 5–6 days incubation. Bacteria were isolated and resembled Desulfuromonas acetoxidans and Desulfobulbus propionicus morphologically and physiologically.     

Concentrations of NaCl and sucrose: equality in perceived taste intensity

Results from previous studies suggest that sucrose and NaClsolutions have an equal perceived taste intensity when the molarconcentration of sucrose is 1.5–1.75 times the molar concentrationof NaCl. However, according to other studies, sucrose and NaClsolutions taste equally strong when their molar concentrationsare about equal. This issue was further pursued using the methodof constant stimuli, where subjects matched the perceived tasteintensity of NaCl solutions to five sucrose references and viceversa. The results concur with previous findings that sucroseand NaCl solutions have equal perceived taste intensities whenthe molar concentration of sucrose is 1.5–1.75 times themolar concentration of NaCl.     

Robust emergence of small-world structure in networks of spiking neurons

Spontaneous activity in biological neural networks shows patterns of dynamic synchronization. We propose that these patterns support the formation␣of a small-world structure—network connectivity␣optimal for distributed information processing. We␣present numerical simulations with connected Hindmarsh–Rose neurons in which, starting from random connection distributions, small-world networks evolve as a result of applying an adaptive rewiring rule. The rule connects pairs of neurons that tend fire in synchrony, and disconnects ones that fail to synchronize. Repeated application of the rule leads to small-world structures. This mechanism is robustly observed for bursting and irregular firing regimes.     

A psychophysical investigation of Beidler's mixture equation

Beidler's mixture equation (1971) describes the relationshipbetween the concentration and composition of a binary mixtureand the magnitude of the neural response. Later this equationwas generalized to a psychophysical level. The purpose of thepresent study is to show that Beidler's mixture equation canbe tested appropriately with indirect psychophysical methods,without the necessity of making assumptions about the magnitudeof the maximum responses to the single compounds which constitutethe mixture. Experiments were carried out using glucose andfructose as tastants. Concentrations of fructose and three equiratiomixture types containing glucose and fructose were matched inperceived sweetness intensities to five different glucose concentrationsusing the method of constant stimuli. The results showed thatBeidler's mixture equation describes accurately the taste interactionbetween glucose and fructose at low sweetness levels. At highsweetness levels the taste system is more efficient, as couldbe expected on the basis of Beidler's mixture equation, becausethe experimentally determined mixture concentrations were lowerthan those predicted by the mixture equation. The findings suggestthat glucose and fructose share common receptors, but that eitherone or both have additional secondary binding mechanisms.