Direct histological validation of diffusion tensor MRI in formaldehyde-fixed myocardium.

Diffusion tensor MRI is emerging as a rapid, nondestructive method to map myocardial fiber organization. It accurately measures myofiber orientation in hearts bathed in or perfused with cardioplegic solution. This study shows it also accurately maps the fibrous architecture of formalin-fixed hearts. Fiber orientations obtained by MRI and histology at the same locations in an excised portion of rabbit ventricle differed on average by 3.7 degrees (SD = 6.4 degrees, N = 70), a closer correspondence than achieved with previous preparations. The longer acquisition times afforded by fixed-heart imaging provides better accuracy, and should enable high-resolution reconstruction of the entire ventricular architecture. Magn Reson Med 44:157-161, 2000.     

Enhancement of Viability of Fat Grafts in Nude Mice by Endothelial Progenitor Cells

BACKGROUND: A recent discovery showed that endothelial progenitor cells (EPCs) could augment collateral vessel growth to ischemic tissues. OBJECTIVE: The objective was to demonstrate the effects of EPCs on the vasculogenesis and survival of free transplanted fat tissues in nude mice. METHODS: EPCs from human donors were cultured in vitro for 7 days. Human fat tissues were injected subcutaneously into the scalps of 20 6-week-old nude male mice. EPCs stained with CM-DiI were mixed with the transplanted fat tissues and injected into the mice. EBM-2 medium was used as control group. The animals were euthanized 15 weeks after the procedure. Graft volume were measured, and histologic evaluation was performed. The central part of fat tissues was histologically evaluated 15 weeks after the fat injection. RESULTS: The survival volume of the experimental group was significantly greater than that of the control group (p< .05). Less cyst formation and fibrosis was obtained in the experimental group. Histologic evaluation of the central part of fat tissues 15 weeks after the fat injection showed that capillary densities increased markedly in the experimental group mice. CONCLUSION: The results indicate that EPCs have the ability to enhance the survival and the quality of the transplanted fat tissues.     

Breast feeding and the dietary habits of children in rural Somalia

Breast feeding and dietary habits were studied prospectively in a cohort of children under the age of five years in a rural Somali community. The median duration of breast feeding was 19.5 months. However, all the children also received cow's milk by cup from the first day of life and onwards. Energy supplements (mainly sugar and oil) as well as additional water were given daily from early infancy. Staples, protein-rich foods (beans and meat), vegetables and fruits were usually introduced when the children reached the age of 12-18 months. There was a seasonal variation with the lowest intake of protein-rich and vitamin-rich foods during the rains in May to June. Thus, there was a complete absence of exclusive breast feeding. Energy-reinforced cow's milk and human milk dominated the diet up to the age of one year. Staples were mixed with oil and supplemented with milk, thereby leading to a much higher energy density in the complementary food than is usually the case in African communities.     

Single-tone intensity discrimination based on auditory-nerve rate responses in backgrounds of quiet, noise, and with stimulation of the crossed olivocochlear bundle

We use simple statistical models of the firing patterns of high, medium, and low spontaneous rate auditory-nerve fibers to study mechanisms which determine the overall dynamic range of the auditory periphery. The models relate experimentally measured rate response properties of fibers with best frequency (BF) near 8.0 kHz to their ability to encode changes in BF tone level by changes in discharge rate in backgrounds of quiet and noise, with and without electrical stimulation of the crossed olivocochlear bundle (COCB). Application of the models to the BF tone rate responses of auditory-nerve fibers in backgrounds of quiet shows that optimum processing of the rate responses of fibers with BF near 8.0 kHz yields performance in the intensity discrimination task meeting or exceeding that of human subjects over an 80 dB range of levels. By defining a statistical measure of dynamic range, we confirm the results of Costalupes et al. (1984) demonstrating that masking noise shifts the dynamic range of auditory-nerve fibers to higher stimulus levels, thus preventing rate saturation. However, model analysis shows that masking noise also produces large reductions of dynamic range as well as large increases in the minimum intensity difference that can be encoded by the rate responses of single and ensembles of fibers. Electrical stimulation of the COCB can restore auditory-nerve fiber dynamic range and sensitivity to changes in BF tone level in noise backgrounds, in some cases to roughly that observed in backgrounds of quiet.     

Alternative oxygen therapeutics: products, status of clinical trials, and future prospects

Alternative oxygen therapeutics are oxygen carriers that can potentially replace red blood cell transfusion in clinical instances in which banked blood is unavailable or unsafe. Most of the candidate solutions have been based on hemoglobin, derived from animals, outdated banked human blood, or recombinant systems. Other solutions are based on perfluorocarbons. In contrast to hemoglobin, which chemically binds oxygen, perfluorocarbons carry oxygen as a dissolved gas. Most of the products of either category developed over the past two decades have failed attempts at regulatory approval for clinical use, but their development has led to a large body of research that has defined the way oxygen is normally delivered to tissues. From this research, a new generation of products is emerging, designed specifically to target oxygen to the tissues in most need. It is possible that one or more of the earlier products may be approved by regulatory agencies in 1 or 2 years. However, a universally compatible and safe product most likely will be unavailable for several more years.     

Intracellular ionic concentration by calibration from fluorescence indicator emission spectra,its relationship to the K(d), F(min), F(max) formula,and use with Na-Green for presynaptic sodium

The emission spectra calibration curves for a fluorescence indicator and the F(min), F(max), and K(d) formula were shown to be related. Using the known calibrated fluorescence emitted by Sodium Green (Na-Green) and photo-multiplier-tube quantum efficiency, we calculated the detection signal over a range of sodium concentrations. The calculated calibration curves were compared for optical filters passing a narrow band, medium band or full spectrum. We found that a method based on the full emission spectrum was the most appropriate. Given a known resting concentration of intracellular sodium, calibrated readings can be converted to concentration values. This method is applicable to any fluorescence indicator when curves for emission spectra over a range of concentrations are available. We measured sodium concentration changes during trains of action potentials (APs) at a crayfish motor axon's presynaptic terminals injected with Na-Green. During low frequency AP trains, net sodium increases asymptotically with frequency. Average net Na-flux per AP decreases for increasing terminal size. The terminals of crayfish motor axon have surface area to volume ratio which is 7700 times larger than for squid. Thus, in comparison to squid, crayfish terminals exhibit a larger change in [Na(+)](i) during equivalent AP activity.