MET currents and otoacoustic emissions from mice with a detached tectorial membrane indicate the extracellular matrix regulates Ca2+ near stereocilia

The tectorial membrane (TM) is an acellular structure of the cochlea that is attached to the stereociliary bundles of the outer hair cells (OHCs), electromotile cells that amplify motion of the cochlear partition and sharpen its frequency selectivity. Although the TM is essential for hearing, its role is still not fully understood. In Tecta/Tectb−/− double knockout mice, in which the TM is not coupled to the OHC stereocilia, hearing sensitivity is considerably reduced compared with that of wild‐type animals. In vivo, the OHC receptor potentials, assessed using cochlear microphonics, are symmetrical in both wild‐type and Tecta/Tectb−/− mice, indicating that the TM does not bias the hair bundle resting position. The functional maturation of hair cells is also unaffected in Tecta/Tectb−/− mice, and the resting open probability of the mechanoelectrical transducer (MET) channel reaches values of ∼50% when the hair bundles of mature OHCs are bathed in an endolymphatic‐like Ca2+ concentration (40 μM) in vitro. The resultant large MET current depolarizes OHCs to near –40 mV, a value that would allow optimal activation of the motor protein prestin and normal cochlear amplification. Although the set point of the OHC receptor potential transfer function in vivo may therefore be determined primarily by endolymphatic Ca2+ concentration, repetitive acoustic stimulation fails to produce adaptation of MET‐dependent otoacoustic emissions in vivo in the Tecta/Tectb−/− mice. Therefore, the TM is likely to contribute to the regulation of Ca2+ levels around the stereocilia, and thus adaptation of the OHC MET channel during prolonged sound stimulation

The spatial aspects of fairness

As well as their family background, an individual's chances in life are determined by the opportunities available to them in their geographical context. This chapter therefore deals with the spatial aspects of fairness. It focuses, firstly, on socio-economic factors which are not randomly distributed in space (i.e. they have a geographical pattern). Secondly, it focuses, not on first nature geographical differences which cannot be changed (such as the presence of mountains), but on second nature geographical factors (such as access to basic services or hospitals) which can be altered and which are important in overcoming a region's natural disadvantages. It then links the two

Hair Cell Bundles: Flexoelectric Motors of the Inner Ear

Microvilli (stereocilia) projecting from the apex of hair cells in the inner ear are actively motile structures that feed energy into the vibration of the inner ear and enhance sensitivity to sound. The biophysical mechanism underlying the hair bundle motor is unknown. In this study, we examined a membrane flexoelectric origin for active movements in stereocilia and conclude that it is likely to be an important contributor to mechanical power output by hair bundles. We formulated a realistic biophysical model of stereocilia incorporating stereocilia dimensions, the known flexoelectric coefficient of lipid membranes, mechanical compliance, and fluid drag. Electrical power enters the stereocilia through displacement sensitive ion channels and, due to the small diameter of stereocilia, is converted to useful mechanical power output by flexoelectricity. This motor augments molecular motors associated with the mechanosensitive apparatus itself that have been described previously. The model reveals stereocilia to be highly efficient and fast flexoelectric motors that capture the energy in the extracellular electro-chemical potential of the inner ear to generate mechanical power output. The power analysis provides an explanation for the correlation between stereocilia height and the tonotopic organization of hearing organs. Further, results suggest that flexoelectricity may be essential to the exquisite sensitivity and frequency selectivity of non-mammalian hearing organs at high auditory frequencies, and may contribute to the “cochlear amplifier” in mammals

Untersuchungen zur Zytoarchitektur des Corti'schen Organs mittels LSM

Für die Modellbildung des Corti'schen Organs spielen frequenzabhängige Änderungen der Zellgrößen eine wichtige Rolle. In der Literatur sind nur fragmentäre Daten über dreidimensionale Geometrie von Haar-, und Stützzellen zu finden. Das Ziel dieser Studie war bisher nicht bekannte 3D-Darstellungen der Zytoarchitektur des Corti'schen Organs in drei Regionen mittels der konfokalen Laser Scanning Mikroskopie (KLSM) zu gewinnen. Nach der Entnahme der Innenohren von Meerschweinchen und Fixierung mittels 4% Formalinlösung wurden die Cochleae nach eigener Hemicochlea-Präparation zur Färbung vorbereitet. Die Färbung der Zellmembranen und der Kerne wurde mit Farbstoffen Phalloidin Alexa 488 und Hoechst durchgeführt. Die Untersuchung und Aufnahme der eingefärbten Präparate erfolgte mittels KLSM (Leica SP5). Für die Darstellung von Zellmembranen musste die Bilderstapel gefiltert und segmentiert werden. Dies erfolgte mit hauseigener Software "IPTools" (http://www.tu-dresden.de/medkhno/sites/wissenschaft/mittelohr/index.htm). Die daraus gewonnenen Daten wurden mit der Bildbearbeitungssoftware AMIRA dreidimensional rekonstruiert, und die Zellen wurden vermessen. Es ist gelungen, alle relevanten Zellen des Cortischen Organs in ihrer natürlichen topologischen Umgebung darzustellen und in 3D zu rekonstruieren. Nach vermessen der zellulären Strukturen wurden die Daten für ein frequenzabhängiges Abbild der Zytorachitektur des Corti'schen Organs erhalten. Die Hemicochlea-Präparation in Kombination mit den KLSM-Untersuchungen bringt akzeptable Ergebnisse zur 3D-Geometrie von zellulären Strukturen des Corti´schen Organs. Diese Daten können als sichere Basis für die zukünftigen numerischen Simulationsmodelle zur Mechanik des Corti'schen Organs dienen. Unterstützt durch: DFG ZA 249/4-

Facilitated non-invasive visualization of collagen and elastin in blood vessels

Multiphoton imaging is a powerful tool for three-dimensional visualization of extracellular matrix components such as collagen and elastin in fresh, nonfixed, and nonembedded tissues. We have previously published data on the induction of the second harmonic generation signal of collagen and autofluorescence of elastin using a tunable multiphoton laser system. Without staining, a second harmonic generation signal was detected for collagen when excited at wavelength lambda(ind ex) = 840 nm. Switching the excitation wavelength to 760 nm enabled visualization of elastic fiber structures. A limitation of this technology is the laser-tuning process that requires calibration of the system in between the studies. Now we have developed a facilitated method for studying tissues and tissue equivalents that enables simultaneous visualization of collagen and elastin structures using only a single excitation wavelength of 840 nm in combination with two different band-pass filters. This facilitated method will expand the range of application by reducing required time and expenses for the laser system without reducing its capability

Visualizing BDNF Transcript Usage During Sound-Induced Memory Linked Plasticity

Activity-dependent BDNF (brain-derived neurotrophic factor) expression is hypothesized to be a cue for the context-specificity of memory formation. So far, activity-dependent BDNF cannot be explicitly monitored independently of basal BDNF levels. We used the BLEV (BDNF-live-exon-visualization) reporter mouse to specifically detect activity-dependent usage of Bdnf exon-IV and -VI promoters through bi-cistronic co-expression of CFP and YFP, respectively. Enriching acoustic stimuli led to improved peripheral and central auditory brainstem responses, increased Schaffer collateral LTP, and enhanced performance in the Morris water maze. Within the brainstem, neuronal activity was increased and accompanied by a trend for higher expression levels of Bdnf exon-IV-CFP and exon-VI-YFP transcripts. In the hippocampus BDNF transcripts were clearly increased parallel to changes in parvalbumin expression and were localized to specific neurons and capillaries. Severe acoustic trauma, in contrast, elevated neither Bdnf transcript levels, nor auditory responses, parvalbumin or LTP. Together, this suggests that critical sensory input is essential for recruitment of activity-dependent auditory-specific BDNF expression that may shape network adaptation