2D D-bar reconstructions of human chest and tank data using an improved approximation to the scattering transform.

The D-bar method for electrical impedance tomography requires the computation of an intermediate function known as the scattering transform from the measured data. An approximation to the scattering transform utilizing the standard Green's function for the Laplacian was introduced for the 2D D-bar method in Mueller and Siltanen (2003 SIAM J. Sci. Comp. 24 1232-66) and tested on simple numerically simulated conductivity distributions. In this work, the approximation is implemented for experimental data for the first time. It is tested on both tank and human chest data, and the results demonstrate decreased blurring toward the boundary in the images than in images computed with the t(exp) approximation to the scattering transform.

Neuropeptide Y expression and endogenous leptin concentrations in a dietary model of obesity.

OBJECTIVE: To determine how leptin concentrations and neuropeptide (NPY) are regulated in a model of dietary obesity in relation to relative growth (RG) and relative food consumption (RFC). RESEARCH METHODS AND PROCEDURES: Sprague-Dawley rats were fed a moderately high-fat diet for 14 weeks over which time animals diverged into obesity-prone (OP) and obesity-resistant (OR) populations. RG rates and RFC were calculated weekly. Following the study, an adiposity index was calculated and arcuate nucleus (ARC) NPY expression was determined by in situ hybridization (ISH) or ribonuclease protection (RPA) assays. RESULTS: Body weights were greater in OP rats after 2 weeks on the diet compared to OR rats and remained different throughout the study. RG and RFC were greater in OP rats compared to OR rats only during the first 2 weeks of the study. Leptin concentrations rose in both groups during the experiment, but the increase was greater in OP rats than in OR rats. Insulin changes paralleled those for leptin. ARC NPY mRNA expression was not different between OP and OR rats as measured by ISH and RPA. DISCUSSION: Although NPY expression has been reported to be different initially in OP and OR rats, this difference dissipates following divergence of body weight. RFC and RG data suggest the initial NPY elevation may contribute to increased weight gain of OP rats during the first 2 weeks of the diet. Higher relative leptin concentrations in OP rats may be necessary to normalize differences in adiposity and apparent leptin and insulin resistance of OP rats.

Plasma growth hormone secretion is impaired in obesity-prone rats before onset of diet-induced obesity.

Sprague-Dawley rats, which become obese (obesity prone) when fed a moderately high-fat (MHF; 32.5% of kcal as fat) diet, have decreased growth hormone (GH) concentrations compared with obesity-resistant rats fed the same diet. To determine whether plasma GH concentrations are different in obesity-prone rats compared with obesity-resistant rats before diet-induced obesity occurs, total integrated GH concentrations were determined in male Sprague-Dawley rats before exposure to the MHF diet. After initial blood sampling, rats were fed an MHF diet for 15 wk, over which time the animals were separated into two discrete populations based on body weight gain. Analysis of GH in episodic blood samples showed that the obesity-prone group had a GH secretion deficit before the onset of obesity (115.2 +/- 12.9 ng . ml-1 . 200 min-1) compared with obesity-resistant rats (237.2 +/- 47.1 ng . ml-1 . 200 min-1). The GH concentration difference was due to a decrease in mean GH peak height in rats that later became obese (34.8 ng/ml) compared with rats that remained lean (74.2 ng/ml). The results suggest that GH secretion impairment exists before dietary challenge or onset of obesity and may contribute to the susceptibility to obesity observed in these animals.