Techniques for the observation and measurement of red blood cell velocity in vessels of the guinea pig cochlea

Fluorescence techniques combined with intravital microscopy provide a powerful approach to the study of cochlear blood microcirculation. In the current study, fluorescein isothiocyanate conjugated to high molecular weight dextrans was added to plasma to enhance the visual contrast of flowing blood in microscopic images from the guinea pig cochlea. Photometric signals, obtained from video pictures of the blood vessels, provided a means to continuously measure red cell velocity by using crosscorrelation algorithms to extract the time delay for moving features of the image. Alternatively, a small amount of fluorescently-labeled red blood cells (RBCs) were added to the vascular volume to serve as natural indicators of whole blood flow. The speed of these cells was measured by video photometric detection of the time required for the cells to pass between two predetermined positions in the television image. RBCs can be made fluorescent by chemical bonding of a fluorochrome to the cell membrane or by internal loading of the cell with an inert fluorochrome. Labeled RBCs provide a means to determine blood velocity in capillaries having extremely poor optical contrast, a situation which is generally the case for relatively thick tissues such as the lateral wall of the membranous labyrinth.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26885/1/0000451.pd

Electrical Impedance of Isolated Amnion

The electrical impedance of the guinea pig amniotic membrane was measured, under standardized conditions, over the frequency range of 20 to 7000 cycles/second. This impedance can be represented analytically by a simple frequency-dependent function which is precisely of the form of the Debye relaxation equation. The observed data exhibit a broad dispersion centered at a frequency of 1050 cycles/second and a narrow distribution of time constants centered about 152 microseconds, both effects being due to the polydisperse nature of amniotic tissue. If the narrow time-constant distribution is approximated by a single time constant, amnion impedance can be simulated by a simple electrical circuit of frequency-independent elements. The Maxwell-Wagner interfacial treatment, although successfully adapted for cell suspensions, is shown to lose its quantitative significance in the case of the tightly structured amnion. In addition, determinations were made on the chemical composition of amniotic fluid, fetal blood and urine, and maternal blood and urine; the DC potential across the amniotic membrane was also measured

Three-dimensional current flow in a large-scale model of the cochlea and the mechanism of amplification of sound

The mammalian inner ear uses its sensory hair cells to detect and amplify incoming sound. It is unclear whether cochlear amplification arises uniquely from a voltage-dependent mechanism (electromotility) associated with outer hair cells (OHCs) or whether other mechanisms are necessary, for the voltage response of OHCs is apparently attenuated excessively by the membrane electrical filter. The cochlea contains many thousands of hair cells organized in extensive arrays, embedded in an electrically coupled system of supporting cells. We have therefore constructed a multi-element, large-scale computational model of cochlear sound transduction to study the underlying potassium (K+) recirculation. We have included experimentally determined parameters of cochlear macromechanics, which govern sound transduction, and data on hair cells' electrical parameters including tonotopical variation in the membrane conductance of OHCs. In agreement with the experiment, the model predicts an exponential decay of extracellular longitudinal K+ current spread. In contrast to the predictions from isolated cells, it also predicts low attenuation of the OHC transmembrane receptor potential (−5 dB per decade) in the 0.2–30 kHz range. This suggests that OHC electromotility could be driven by the transmembrane potential. Furthermore, the OHC electromotility could serve as a single amplification mechanism over the entire hearing range