An improved system for the control of dissolved oxygen in freshwater aquaria

A system for the removal and control of dissolved oxygen (DO) from freshwater was designed and constructed with aquarium-type fish studies in mind. Degassed water was obtained using a partial vacuum of -14 psi, and DO regulated at an aquarium scale using electronically controlled aeration with timed partial water renewal. The degassing system was capable of producing water with approximately 1.7 mg L(-1) DO within 10 min of operation, and 0.55 mg L(-1) after 2h. The control system was capable of maintaining DO levels of ca 0.8 mg L(-1) over 48 h in the absence of aeration and further capable of precisely controlling DO levels as low as 1.16+/-0.002 mg L(-1) (mean+/-SEM) with aeration over a 48 h period.     

ST/b and DBA/2 mice differ in brain alpha-bungarotoxin binding and alpha 7 nicotinic receptor subunit mRNA levels: a quantitative autoradiographic analysis

Inbred mouse strains vary in sensitivity to a number of behavioral and physiological effects produced by nicotine. Differences in sensitivity to nicotine are correlated with variance in the number of brain nicotinic receptors as measured in regionally dissected brain tissue. The studies reported here used quantitative autoradiography and in-situ hybridization methods to measure regional levels of alpha-bungarotoxin (alpha BTX) binding and alpha 7 mRNA levels. Two inbred mouse strains, ST/b and DBA/2, were compared because these strains differ maximally in sensitivity to nicotine-induced seizures and in alpha BTX binding measured in regional brain homogenates. The binding of alpha BTX was significantly greater in the St/b strain in 42 of 127 brain regions that were analyzed, and a trend towards increased binding was seen in many additional brain regions. The most consistent strain differences were found in hippocampal, thalamic and pontine nuclei. Strain differences in alpha 7 mRNA levels were also detected, but these were not as widespread as were the alpha BTX binding differences. The alpha 7 mRNA levels were significantly correlated with alpha BTX binding in both mouse strains which suggests that the strain differences in binding are related, in part, to the levels of alpha 7 mRNA.     

Serial measurements of body composition in obese subjects during a very-low-energy diet (VLED) comparing bioelectrical impedance with hydrodensitometry

Bioelectrical impedance analysis (BIA) is a convenient, inexpensive, and noninvasive technique for measuring body composition. BIA has been strongly correlated with total body water (TBW) and also has been validated against hydrodensitometry (HD). The accuracy and clinical utility of BIA and HD during periods of substantial weight loss remain controversial. We measured body composition in moderately and severely obese patients serially using both methods during a very-low-energy diet (VLED). Mean initial weight in these patients was 116 (+/-30) kg (range, 74-196 kg). Mean weight loss was 24 (+/-13) kg with a decrease in fat mass (FM) by HD of kg (p < 0.001) and a decrease in fat-free mass (FFM) of 3.6 kg (p < 0.05). Loss of FFM is best predicted by the rate (kg/wk) of weight loss (r2 = 0.86, p < 0.0001). FFM, as predicted from BIA equations, was highly correlated with FFM as estimated by HD during all testing sessions (r = 0.92-0.98). Although highly correlated, BIA overestimated FFM relative to HD and this difference appeared to be more pronounced for taller patients with greater truncal obesity. Although the discrepancy was no greater during weight-loss treatment, the level of disagreement was considerable. Therefore, the two methods cannot be used interchangeably to monitor relative changes in body composition in patients with obesity during treatment with VLED. The discrepancy between BIA and HD may be caused by body mass distribution considerations and by perturbations in TBW which affect the hydration quotient for FFM (BIA) and/or which affect the density constants for FFM and FM (HD).     

Nature of the Thermal pretransition of synthetic phospholipids: dimyristolyl- and dipalmitoyllecithin

The hydrated synthetic lecithins, dimyristoyl and dipalmitoyllecithins, undergo two thermal transitions, a broad low enthalpy "pretransition" prior to the sharp first-order "chain-melting" transition. Both phospholipids exhibit the same temperature-dependent structural changes associated with the thermal pretransition. At low temperatures, below the pretransition, a one-dimensional lamellar lattice is observed. The hydrocarbon chains are fully extended and tilted with respect to the plane of the lipid bilayer. The hydrocarbon chain packing displays a temperature dependence and the angle of tilt of the hydrocarbon chains decreases with increasing temperature, reaching a minimum value of 30 degrees at the pretransition temperature of both lecithins. The pretransition is associated with a structural transformation from a one-dimensional lamellar to a two-dimensional monoclinic lattice consisting of lipid lamellae distorted by a periodic ripple. The hydrocarbon chains remain tilted in the temperature range intermediate between the pretransition and chain-melting transition. The cell parameters of this two-dimensional lattice exhibit a compositional dependence. The a parameter (proportional to the lamellar repeat distance) increases with increasing water content, while the b parameter (a measure of the ripple periodicity) decreases with increasing water content. At the chain-melting transition, the hydrocarbon chains of the phospholipid melt and assume a liquid-like conformation and the lattice reverts to one-dimensional lamellar. These structural changes observed for dimyristoyl- and dipalmitoyllecithins may be a common feature of all synthetic lecithins exhibiting a thermal pretransition. The appearance of the pretransition and accompanying two-dimensional may arise from specific interactions between the choline moiety of the polar head group and the structured water matrix surrounding it.     

Frequency response analysis of the diaphragm in vivo

Frequency response analysis was used to determine the dynamic response characteristics of cat diaphragm under isovolumetric conditions at functional residual capacity (FRC) and at lung volumes above and below FRC. In apneic cats, sinusoidally modulated pulse rate patterns were applied to both phrenic nerves. Modulation frequencies over the range of 0.05-4 Hz were used. Amplitude ratio vs. frequency plots obtained at FRC for intratracheal, intraesophageal, and intragastric pressures were essentially flat at low frequencies but decreased at higher frequencies. Intratracheal and intraesophageal pressure responses were altered by changes in resting lung volume while intragastric pressure was not. The amplitude ratio was decreased at lung volumes above FRC but increased at volumes below FRC. Thus, lung volume significantly affected the input-output relations between phrenic nerve input and diaphragm muscle output. In all preparations studied, significant phase lags were present throughout the entire modulation frequency range. However, in contrast to the effect of lung volume on amplitude ratio, phase lag was not dependent on changes in lung volume.