Motile response patterns and ultrastructural observations of the isolated outer hair cell

The tonotopic organization of the mammalian cochlea is accompanied by structural gradients which include the somatic lengths of outer hair cells (OHCs). These receptors rest upon the vibrating portion of the basilar membrane and have been reported to exhibit motile responses following chemical and electrical stimulation. These movements were examined in detail in this dissertation. It was found that isolated OHCs cultured in vitro respond to chemical depolarization with slow tonic movements, and to electrical waveforms with bi-directional, frequency following movements extending from DC to at least 10 kHz.^ Slow contractions were also elicited following electrical stimulation, bath incubation in carbachol (a cholinergic agonist), and increases in extracellular K+ concentration as little as 50 mM.^ Isolated OHCs display anatomical features which are remarkable when contrasted with those prepared from intact receptor organs. A complex structure located between the cuticular plate and the nuclear membrane was consistently observed and was examined by serial cross-sections which revealed a network of non-membrane bound densities. This corresponded to a granular complex seen at the light microscope level. The complex was composed of dense regions of organelles, striated structures embedded within the core, and a circumferential network of microtubules residing in the peri-nuclear portion of the cell. In cells which had lost their nuclear attachment to the terminal synaptic body, the granular complex could be made to contract without effecting any change in cellular length, implying that the complex may be the driving force behind certain aspects of the motile response.^ Most cells displayed movements which revealed asymmetries analogous to those reported for OHC receptor potentials in vivo. The contraction phase (for longer cells) was shown to have a small time constant (approximately 400 microseconds) and saturated with limited displacements. The expansion phase had time constants as large as 1.3 milliseconds but yielded displacements as much as 60 percent larger than those seen for contractions.^ Additional waveform characteristics seen in the in vivo response could be emulated either by biasing the cell's resting length with either direct current, triggering contractions via large electrical displacements, or incubation with depolarizing compounds.^ Alternatively, short (20-30 um) cells revealed more linear response characteristics to the probe stimulus. Partial saturation was achieved and revealed a DC component which was opposite in polarity to that seen in longer cells. (Abstract shortened with permission of author.) ^

Poverty, Educational Attainment and Health Among America’s Children: Current and Future Effects of Population Diversification and Associated Socioeconomic Change

A complex of interrelated factors including minority status, poverty, education, health status, and other factors determine the general welfare of children in America, particularly in heavily diverse states such as Texas. Although racial/ethnic status is clearly only a concomitant factor in that determination it is a factor for which future projections are available and for which the relationships with the other factors in the complex can be assessed. After examining the nature of the interrelationships between these factors we utilize direct standardization techniques to examine how the future diversification of the United States and Texas will affect the number of children in poverty, the educational status of the householders in households in which children in poverty live and the health status of children in 2040 assuming that the current relationships between minority status and these socioeconomic factors continue into the future. In the results of the analyses, data are compared with the total population of the United States and Texas in 2040 assumed in the first simulation scenario, to have the race/ethnicity characteristics of 2008 and in the second those projected for 2040 by the U.S. Census Bureau for the nation and by the Texas State Data Center for Texas in 2040. The results show that the diversification of the population could increase the number of children in poverty in the United States by nearly 1.8 million more than would occur with the lower levels of diversification evident in 2008. In addition, poverty would become increasingly concentrated among minority children with minority children accounting for 76.2 percent of all children in poverty by 2040 and with Hispanic children accounting for nearly half of the children in poverty by 2040. Results for educational attainment show an increasing concentration of minority children in households with householders with very low levels of education such that by 2040, 85.2 percent of the increase in the number of children in poverty would be in households with a householder with less than a high school level of education. Finally, the results related to several health status factors show that children in poverty will have a higher prevalence of nearly all health conditions. For example, the number of children with untreated dental conditions could increase to more than 4 million in the United States and to nearly 500,000 in Texas. The results clearly show that improving the welfare of children in America will require concerted efforts to change the poverty, educational, and health status characteristics associated with minority status and particularly Hispanic status. Failing to do so will lead to a future in which America’s children are increasingly impoverished, more poorly educated, and less healthy and which, as a result, is an America with a more tentative future.