Reticular Lamina Research Articles

A Serial-Parallel Panoramic Filter Bank as a Model of Frequency Decomposition of Complex Sounds in the Human Inner Ear

We consider that the outer hair cells of the inner ear together with the local structures of the basilar membrane, reticular lamina and tectorial membrane form the primary filters (PF) of the second order. Taking into account a delay in transmission of the excitation signal in the cochlea and the influence of the Reissner membrane, we design a signal filtering system consisting of the PF with the common PF of the neighboring channels. We assess the distribution of the central frequencies of the channels along the cochlea, optimal number of the PF constituting a channel, natural frequencies of the channels, damping factors and summation weights of the outputs of the PF. As an example, we present a filter bank comprising 20 Gaussian-type channels each consisting of five PF. The proposed filtering system can be useful for designing cochlear implants based on biological principles of signal processing in the cochlea.

Postnatal Development of the Lamina Reticularis in Primate Airways

The basement membrane zone (BMZ) appears as three component layers: the lamina lucida, lamina densa, and lamina reticularis. The laminas lucida and densa are present during all stages of development. The lamina reticularis appears during postnatal development. Collagens I, III, and V form heterogeneous fibers that account for the thickness of the lamina reticularis. Additionally, there are three proteoglycans considered as integral components of the BMZ: perlecan, collagen XVIII, and bamacan. Perlecan is the predominant heparan sulfate proteoglycan in the airway BMZ. It is responsible for many of the functions attributed to the BMZ, in particular, trafficking of growth factors and cytokines between epithelial and mesenchymal cells. Growth factor binding sites on perlecan include FGF-1, FGF-2, FGF-7, FGF-10, PDGF, HGF, HB-EGF, VEGF, and TGF-beta. Growth factors pass through the BMZ when moving between the epithelial and mesenchymal cell layers. They move by rapid reversible binding with sites on both the heparan sulfate chains and core protein of perlecan. In this manner, perlecan regulates movement of growth factors between tissues. Another function of the BMZ is storage and regulation of FGF-2. FGF-2 has been shown to be involved with normal growth and thickening of the BMZ. Thickening of the BMZ is a feature of airway remodeling in asthma. It may have a positive effect by protecting against airway narrowing and air trapping. Conversely, it may have a negative effect by influencing trafficking of growth factors in the epithelial mesenchymal trophic unit. However, currently the significance of BMZ thickening is not known.

Distortion product emissions from a cochlear model with nonlinear mechanoelectrical transduction in outer hair cells

A model of cochlear mechanics is described in which force-producing outer hair cells (OHC) are embedded in a passive cochlear partition. The OHC mechanoelectrical transduction current is nonlinearly modulated by reticular-lamina (RL) motion, and the resulting change in OHC membrane voltage produces contraction between the RL and the basilar membrane (BM). Model parameters were chosen to produce a tonotopic map typical of a human cochlea. Time-domain simulations showed compressive BM displacement responses typical of mammalian cochleae. Distortion product (DP) otoacoustic emissions at 2f(1)-f(2) are plotted as isolevel contours against primary levels (L(1),L(2)) for various primary frequencies f(1) and f(2) (f(1)<f(2)). The L(1) at which the DP reaches its maximum level increases as L(2) increases, and the slope of the "optimal" linear path decreases as f(2)/f(1) increases. When primary levels and f(2) are fixed, DP level is band passed against f(1). In the presence of a suppressor, DP level generally decreases as suppressor level increases and as suppressor frequency gets closer to f(2); however, there are exceptions. These results, being similar to data from human ears, suggest that the model could be used for testing hypotheses regarding DP generation and propagation in human cochleae.

Influence of hair bundle configuration on biomimetic hair sensor sensitivity.

Hair cells are the sensory receptors of the auditory system. When the stereocilia (hair buddles) sitting on top of the hair cells are stimulated, a current flows through the hair cell transducing mechanical stimuli into electrical response. For the outer hair cell (OHC), the hair bundles are stimulated by displacement of the tectorial membrane relative to the reticular lamina. For the inner hair cell (IHC), the hair bundles are stimulated by force due to motion of the fluid around the hair bundle. In addition, OHC and IHC hair bundles are shaped differently. In this paper, biomimetic micromachined hair sensors are designed, fabricated, and tested to investigate how the configurations of the hair bundles affect the sensitivity of the hair sensor. These hair sensors use a capacitive scheme and have different hair configurations including the W and U shape representing OHC and IHC hair bundles. Computational results achieved to date indicate that sensitivity can be strongly affected by the placement of the engineered hair bundles. Microfabrication and experimental work are ongoing.

Organ of Corti Micromachine Enables Hair Bundles to Deform the Stiff Basilar Membrane

The organ of Corti (OC) is a highly organized structure in the mammalian cochlea that houses the sensory hair cells. It is believed that the OC functions to optimize force transmission from the outer hair cell (OHC) to the basilar membrane and the inner hair cell. Recent studies reveal that the OC cannot be considered as a rigid body and has a complex mode of deformation. We developed a 3-D finite element model of the OC to dissect its mechanics. Geometric and mechanical information was taken from the gerbil cochlea at 2 and 10 mm from the stapes, positions encoding high and low frequencies respectively, and in each case several hundred microns longitudinal extent was simulated. The model included all structurally significant components: OHCs, pillar cells, Deiters cells and reticular lamina. The model was validated by reproducing experimental results on point stiffness and longitudinal space constant measured at the basilar membrane and response to current steps through the OC. Deformation of the OC by two different active OHC forces (the OHC somatic force and the stereociliary-based force) was then simulated. A surprising result was that despite smaller magnitude, the stereociliary-based force (0.1and 0.7 nN at apex and base) was nearly as effective as the somatic force (10 nN) in displacing the basilar membrane. The results also suggested that for the active forces to work efficiently the radial stiffness of the tectorial membrane must be comparable to or greater than the hair bundle stiffness. Funded by NIH RO1 DC01362.

Sound Transduction in the Mammalian Outer Hair Cells: Prestin Activity is Required for Proper Deflection of the Stereocilia Bundle

The outer hair cell (OHC) body is capable of prestin-driven electromotility leading to force generation that increases the vibration of the hearing organ critical for auditory sensitivity. At the cell's apex, the stereocilia bundle deflects as a unit during sound stimulation (Fridberger et al, 2006). Such a deflection converts nanometric displacements into electrical signals transmitted to the auditory nerve. Very little is however known about how sound stimuli cause the bundle to deflect, especially, the possible contribution of prestin-induced cell body vibrations to this deflection has never been investigated. Here we investigated the influence of the membrane protein prestin activity on the bundle deflection, in an intact ear preparation from the Guinea pig. Prestin was previously shown to be specifically inactivated by salicylate and tributyltin. Using an approach combining rapid confocal imaging and optical flow-based computation, the bundle deflection was studied under simultaneous sound stimulus administered at 50-350HZ, a frequency band typical of OHCs vibrations in the apex of the cochlea. To our surprise and irrespective of the prestin inhibitor used, sound-induced bundle deflection drastically increases, specifically, near the best frequency whose position was altered. Likewise, the vibration of the bundle tip intensified. Moreover, the shape of the bundle deflection's pattern was affected. Our data challenge the general assumption that prestin inactivation decreases the vibrations of the cochlear's structures. Because no consistent change was observed for vibrations of the reticular lamina, the increase in the bundle deflection may be caused by a robust vibration of the top. The data suggest that prestin motor's activity regulates the tuning of the bundle vibrations and may explain how the stereociliary and saumatic amplifiers interact during sound transduction in the mammalian ear.

Vocal Fold Nodules: Morphological and Immunohistochemical Investigations

The objective of this study was to investigate the morphological and immunohistochemical characteristics of vocal fold nodules. The study design was prospective and retrospective. For the histological study, we reviewed 15 slides from the surgical cases of vocal fold nodules, in which we analyzed epithelium, basal membrane (bm), and lamina propria. For the transmission and scanning electron microscopy (TEM, SEM) studies, five new cases on vocal fold nodules were included. Immunohistochemistry study was carried out in the 15 specimens, using antifibronectin, antilaminin, and anticollagen IV antibodies. The main histological alterations were epithelial hyperplasia (73.33%), basement membrane thickening (86.66%), edema, and fibrosis (93.33%). SEM--reduction in mucous lacing and increase in the desquamating cells, without epithelial erosion. TEM--hyperplasia of the epithelium, enlargement of the intercellular junctions, which was filled by fluid, subepithelial thickening of the lamina reticularis, and break points in the basal membrane. Immunohistochemistry--we identified greater immunoexpression of fibronectin on the basal membrane, on the lamina propria, and around the vessels. Antilaminin and anticollagen IV antibodies showed higher pigmentation on the endothelium of the vessels than that on the basal membrane. In vocal fold nodules, combined assessment using light microscopy, electron microscopy, and immunohistochemistry can reveal important morphological details useful in characterizing these lesions.

Rethinking the Pathogenesis of Asthma

Asthma research has focused primarily on allergic pathways on the basis that the majority of asthma is associated with atopy, the recruitment of the Th2-type T cell, the cytokines, and the chemokines that are released on exposure to allergens, and the IgE pathway. However, despite considerable investment by industry, targeting these pathways has not resulted in new treatments being developed beyond blockade of cysteinyl leukotrienes and IgE and improvements in inhaled corticosteroids and beta(2)-adrenoceptor bronchodilators. Increasingly, it is recognized that asthma is a heterogeneous disorder, and while important, allergen sensitization is only one component of the disease, with many other environmental and genetic factors playing a role. In addition, these factors act locally on a susceptible airway epithelium that is both structurally and functionally deficient. It may be worthwhile to focus on increasing the resilience of the airways to environmental insults in addition to improving strategies that modify adaptive immunity or suppress inflammation.

Outer hair cell electromechanical properties in a nonlinear piezoelectric model

A nonlinear piezoelectric circuit is proposed to model electromechanical properties of the outer hair cell (OHC) in mammalian cochleae. The circuit model predicts (a) that the nonlinear capacitance decreases as the stiffness of the load increases, and (b) that the axial compliance of the cell reaches a maximum at the same membrane potential for peak capacitance. The model was also designed to be integrated into macro-mechanical models to simulate cochlear wave propagation. Analytic expressions of the cochlear-partition shunt admittance and the wave propagation function are derived in terms of OHC electro-mechanical parameters. Small-signal analyses indicate that, to achieve cochlear amplification, (1) nonlinear capacitance must be sufficiently high and (2) the OHC receptor current must be sensitive to the velocity of the reticular lamina.

The Role of Leukotrienes in Airway Remodeling

Asthma is an inflammatory disorder of the airways that has been typified by its bronchospastic component. New attention has been directed to the long-term changes in asthmatic airways as indicated by the accelerated rate of lung function decline occurring in these patients despite therapy with inhaled corticosteroids. These structural changes in the airway wall, termed airway remodeling, are now thought to be a key component in the pathophysiology of asthma. Airway remodeling is characterized by thickening of the lamina reticularis with deposition of collagen and other extracellular matrix proteins leading to subepithelial fibrosis and increased airway goblet cells causing mucus hypersecretion. Of note, there is myofibroblast proliferation and increased airway smooth muscle mass caused by both hyperplasia and hypertrophy of smooth muscle cells. While an important role for cysteinyl leukotrienes (CysLTs) in the pathogenesis of airway inflammation and bronchoconstriction in asthma has been well-established, the specific role of CysLTs in airway remodeling is less clear. This aim of this review is to summarize the data from mouse models of asthma as well as limited human studies that demonstrate a key role for CysLTs in allergen-induced mucus hypersecretion, thickening of the lamina reticularis, and subepithelial fibrosis in the lungs. We will also focus on the interaction between CysLTs and cytokines/growth factors that mediate these changes in epithelial cells, smooth muscle cells, vasculature, and other structural components of the lungs in patients with asthma.

TGF-β1 Induces Human Bronchial Epithelial Cell-to-Mesenchymal Transition in Vitro

The subepithelial fibrosis component of airway remodeling in asthma is mediated through induction of transforming growth factor-beta1 (TGF-beta1) expression with consequent activation of myofibroblasts to produce extracellular matrix proteins. The number of myofibroblasts is increased in the asthmatic airway and is significantly correlated with the thickness of lamina reticularis. However, much is still unknown regarding the origin of bronchial myofibroblasts. Emerging evidence suggests that myofibroblasts can derive from epithelial cells by an epithelial-to-mesenchymal transition (EMT). In this study we investigated whether TGF-beta1 could induce bronchial epithelial EMT in the human bronchial epithelial cell. Cultured human bronchial epithelial cells, 16HBE-14o, were stimulated with 10 ng/ml TGF-beta1. Morphologic changes were observed and stress fiber by actin reorganization was detected by indirect immunostaining. The expression of alpha-SMA (alpha-smooth muscle actin) and the epithelial cell marker E-cadherin were detected in those 16HBE-14o cells after TGF-beta1 stimulation for 72 h, using immunostaining and RT-PCR. The contents of collagen I were determined by radioimmunoassay, and the levels of endogenous TGF-beta1 were measured with ELISA. Human bronchial epithelial cells stimulated with TGF-beta1 were converted from a "cobblestone" epithelial structure into an elongated fibroblast-like shape. Incubation of human bronchial epithelial cells with TGF-beta1 induced de novo expression of alpha-SMA, increased formation of stress fiber by F-actin reorganization, and loss of epithelial marker E-cadherin. Moreover, a significant increase in the levels of collagen I and endogenous TGF-beta1 released from bronchial epithelial cells stimulated with TGF-beta1 were observed. These results suggested that human bronchial epithelial cells, under stimulation of TGF-beta1, underwent transdifferentiation into myofibroblasts.

What can we learn about airway smooth muscle from the company it keeps?: Fig. 1—

In severe and fatal asthma dramatic changes in airway structure have been described, collectively referred to as remodelling 1, 2. Current dogma dictates that remodelling reflects aberrant repair in response to ongoing inflammation and injury. However, the interplay between inflammation and remodelling, and, more importantly, between airway structure and function remains elusive, such that we remain uncertain whether these changes protect the airways from the effects of inflammation or are integral to disease progression. To begin to unravel this conundrum we need to recognise the complexity and heterogeneity of asthma. The asthma paradigm comprises several domains, including ongoing symptoms, the presence of variable airflow obstruction and airway hyperresponsiveness. Together with such disordered airway physiology, most subjects with asthma have evidence of a chronic inflammatory response that is typically, but not exclusively, eosinophilic, with the presence of mast cells within the airway smooth muscle bundle 3–5. In addition, there is often evidence of structural remodelling of the airway wall with thickening of the reticular lamina, mucus gland hyperplasia, increased vasculature, and increased airway smooth muscle hyperplasia and hypertrophy. Importantly, some features of remodelling, particularly thickening of the lamina reticularis, can occur early on in disease and even in some children prior to the onset of asthma 6. In contrast, other aspects of the remodelling process have been associated with disease duration 7. In addition to structural and inflammatory cells, the airway wall is comprised of extracellular matrix, the composition of which varies between different compartments in the airway wall, between asthma versus health, and across disease severity. This matrix is not a benign bystander that simply constitutes the scaffold to build airway structures and allow inflammatory cell trafficking, but can alter …

Airway modeling and remodeling in the pathogenesis of asthma

Asthma remains a severe health problem since current therapies are directed to suppressing, rather than preventing or reversing, the primary disease process. Clearly, a greater understanding of the pathogenesis of asthma is critical to the development of better therapeutic modalities. In this review, we discuss the recent advancements in research targeting the role of airway remodeling in asthma. Epithelial fragility and abnormalities are being recognized as important facets of asthma, as are other features of remodeling such as angiogenesis, goblet cell hyperplasia and thickened lamina reticularis. Significantly, these anomalies occur early in disease pathogenesis. However, their impact on disease severity remains unclear. Although an altered immune response is undoubtedly important to the pathogenesis of asthma, there is increasing evidence that the tissue-specific manifestations occur independently of inflammation and significantly impact on disease development and severity.

Glucocorticoid actions on airway epithelial responses in immunity: Functional outcomes and molecular targets

Research on the biology of airway epithelium in the last decades has progressively uncovered the many roles of this cell type during the immune response. Far from the early view of the epithelial layer simply as a passive barrier, the airway epithelium is now considered a central player in mucosal immunity, providing innate mechanisms of first-line host defense as well as facilitating adaptive immune responses. Alterations of the epithelial phenotype are primarily involved in the pathogenesis of allergic airways disease, particularly in severe asthma. Appreciation of the epithelium as target of glucocorticoid therapy has also grown, because of studies defining the pathways and mediators affected by glucocorticoids, and studies illustrating the relevance of the control of the response from epithelium in the overall efficacy of topical and systemic therapy with glucocorticoids. Studies of the mechanism of action of glucocorticoids within the biology of the immune response of the epithelium have uncovered mechanisms of gene regulation involving both transcriptional and posttranscriptional events. The view of epithelium as therapeutic target therefore has plenty of room to evolve, as new knowledge on the role of epithelium in immunity is established and novel pathways mediating glucocorticoid regulation are elucidated.

Sound-Evoked Radial Strain in the Hearing Organ

The hearing organ contains sensory hair cells, which convert sound-evoked vibration into action potentials in the auditory nerve. This process is greatly enhanced by molecular motors that reside within the outer hair cells, but the performance also depends on passive mechanical properties, such as the stiffness, mass, and friction of the structures within the organ of Corti. We used resampled confocal imaging to study the mechanical properties of the low-frequency regions of the cochlea. The data allowed us to estimate an important mechanical parameter, the radial strain, which was found to be 0.1% near the inner hair cells and 0.3% near the third row of outer hair cells during moderate-level sound stimulation. The strain was caused by differences in the motion trajectories of inner and outer hair cells. Motion perpendicular to the reticular lamina was greater at the outer hair cells, but inner hair cells showed greater radial vibration. These differences led to deformation of the reticular lamina, which connects the apex of the outer and inner hair cells. These results are important for understanding how the molecular motors of the outer hair cells can so profoundly affect auditory sensitivity.

Contribution of outer hair cell bending to stereocilium deflection in the cochlea

The outer hair cell (OHC) in the cochlea is believed to actively enhance the cochlear sensitivity and frequency selectivity. Besides the well-known axial length change of the OHC, the bending mode of the OHC may also contribute to the stereocilium deflection. To investigate the contribution of the OHC bending to the stereocilium deflection, and the active process in the cochlea, we develop a simple kinematic model of the organ of Corti, consisting of the reticular lamina, the stereocilia and tectorial membrane. The electrically evoked axial length change and bending of the OHC are simulated, and their contributions to the stereocilium deflection are obtained. At the apical turn of the cochlea, the bending mode of the OHC results in stereocilium deflection comparable to that due to the axisymmetric length change of the OHC. At the basal turn, the contribution of the bending mode to the stereocilium deflection becomes insignificant compared to that of the axisymmetric mode.

Imaging Electrically Evoked Micromechanical Motion within the Organ of Corti of the Excised Gerbil Cochlea

The outer hair cell (OHC) of the mammalian inner ear exhibits an unusual form of somatic motility that can follow membrane-potential changes at acoustic frequencies. The cellular forces that produce this motility are believed to amplify the motion of the cochlear partition, thereby playing a key role in increasing hearing sensitivity. To better understand the role of OHC somatic motility in cochlear micromechanics, we developed an excised cochlea preparation to visualize simultaneously the electrically-evoked motion of hundreds of cells within the organ of Corti (OC). The motion was captured using stroboscopic video microscopy and quantified using cross-correlation techniques. The OC motion at ∼2–6 octaves below the characteristic frequency of the region was complex: OHC, Deiter’s cell, and Hensen’s cell motion were hundreds of times larger than the tectorial membrane, reticular lamina (RL), and pillar cell motion; the inner rows of OHCs moved antiphasic to the outer row; OHCs pivoted about the RL; and Hensen’s cells followed the motion of the outer row of OHCs. Our results suggest that the effective stimulus to the inner hair cell hair bundles results not from a simple OC lever action, as assumed by classical models, but by a complex internal motion coupled to the RL.

Epithelial Cell Proliferation Contributes to Airway Remodeling in Severe Asthma

Despite long-term therapy with corticosteroids, patients with severe asthma develop irreversible airway obstruction. To evaluate if there are structural and functional differences in the airway epithelium in severe asthma associated with airway remodeling. In bronchial biopsies from 21 normal subjects, 11 subjects with chronic bronchitis, 9 subjects with mild asthma, and 31 subjects with severe asthma, we evaluated epithelial cell morphology: epithelial thickness, lamina reticularis (LR) thickness, and epithelial desquamation. Levels of retinoblastoma protein (Rb), Ki67, and Bcl-2 were measured, reflecting cellular proliferation and death. Terminal deoxynucleotidyl-mediated dUTP nick end labeling (TUNEL) was used to study cellular apoptosis. Airway epithelial and LR thickness was greater in subjects with severe asthma compared with those with mild asthma, normal subjects, and diseased control subjects (p=0.009 and 0.033, respectively). There was no significant difference in epithelial desquamation between groups. Active, hypophosphorylated Rb expression was decreased (p=0.002) and Ki67 was increased (p<0.01) in the epithelium of subjects with severe asthma as compared with normal subjects, indicating increased cellular proliferation. Bcl-2 expression was decreased (p<0.001), indicating decreased cell death suppression. There was a greater level of apoptotic activity in the airway biopsy in subjects with severe asthma as compared with the normal subjects using the TUNEL assay (p=0.002), suggesting increased cell death. In subjects with severe asthma, as compared with subjects with mild asthma, normal subjects, and diseased control subjects, we found novel evidence of increased cellular proliferation in the airway contributing to a thickened epithelium and LR. These changes may contribute to the progressive decline in lung function and airway remodeling in patients with severe asthma.

In vitro culture of porcine respiratory nasal mucosa explants for studying the interaction of porcine viruses with the respiratory tract

The mucosal surface of the respiratory tract is a common site of entry of many viruses. Molecular and cellular aspects of the interactions of respiratory viruses with the respiratory nasal mucosa are largely unknown. In order to be able to study those interactions in depth, an in vitro model was set up. This model consists of porcine respiratory nasal mucosa explants, cultured at an air–liquid interface. Light microscopy, scanning electron microscopy and transmission electron microscopy, combined with morphometric analysis and a fluorescent Terminal deoxynucleotidyl transferase mediated dUTP Nick End Labelling (TUNEL) staining were used to evaluate the effects of in vitro culture on the integrity and viability of the explants. The explants were maintained in culture for up to 60 h post-sampling without significant morphometric (epithelial thickness, epithelial morphology, thickness of the lamina reticularis, continuity of the lamina densa, relative amounts of collagen and nuclei) changes and changes in viability. The potential to infect the explants was demonstrated for two porcine respiratory viruses of major importance: suid herpesvirus 1 and swine influenza virus H1N1. In conclusion, this in vitro model represents an ideal tool to study interactions between infectious agents and porcine respiratory nasal mucosa.

Effect of infrasound on cochlear damage from exposure to a 4 kHz octave band of noise

Infrasound (i.e., <20 Hz for humans; <100 Hz for chinchillas) is not audible, but exposure to high-levels of infrasound will produce large movements of cochlear fluids. We speculated that high-level infrasound might bias the basilar membrane and perhaps be able to minimize noise-induced hearing loss. Chinchillas were simultaneously exposed to a 30 Hz tone at 100 dB SPL and a 4 kHz OBN at either 108 dB SPL for 1.75 h or 86 dB SPL for 24 h. For each animal, the tympanic membrane (TM) in one ear was perforated (∼1 mm 2) prior to exposure to attenuate infrasound transmission to that cochlea by about 50 dB SPL. Controls included animals that were exposed to the infrasound only or the 4 kHz OBN only. ABR threshold shifts (TSs) and DPOAE level shifts (LSs) were determined pre- and post-TM-perforation and immediately post-exposure, just before cochlear fixation. The cochleae were dehydrated, embedded in plastic, and dissected into flat preparations of the organ of Corti (OC). Each dissected segment was evaluated for losses of inner hair cells (IHCs) and outer hair cells (OHCs). For each chinchilla, the magnitude and pattern of functional and hair cell losses were compared between their right and left cochleae. The TM perforation produced no ABR TS across frequency but did produce a 10–21 dB DPOAE LS from 0.6 to 2 kHz. The infrasound exposure alone resulted in a 10–20 dB ABR TS at and below 2 kHz, no DPOAE LS and no IHC or OHC losses. Exposure to the 4 kHz OBN alone at 108 dB produced a 10–50 dB ABR TS for 0.5–12 kHz, a 10–60 dB DPOAE LS for 0.6–16 kHz and severe OHC loss in the middle of the first turn. When infrasound was present during exposure to the 4 kHz OBN at 108 dB, the functional losses and OHC losses extended much further toward the apical and basal tips of the OC than in cochleae exposed to the 4 kHz OBN alone. Exposure to only the 4 kHz OBN at 86 dB produces a 10–40 dB ABR TS for 3–12 kHz and 10–30 dB DPOAE LS for 3–8 kHz but little or no OHC loss in the middle of the first turn. No differences were found in the functional and hair-cell losses from exposure to the 4 kHz OBN at 86 dB in the presence or absence of infrasound. We hypothesize that exposure to infrasound and an intense 4 kHz OBN increases cochlear damage because the large fluid movements from infrasound cause more intermixing of cochlear fluids through the damaged reticular lamina. Simultaneous infrasound and a moderate 4 kHz OBN did not increase cochlear damage because the reticular lamina rarely breaks down during this moderate level exposure.