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PubMed2005

Intraocular lens-capsular bag imaging with ultrahigh-resolution optical coherence tomography Pseudophakic human autopsy eyes.

PURPOSE: To compare in vitro ultrahigh-resolution optical coherence tomography (UHR OCT) cross-sectional images of the pseudophakic human autopsy eye with histology to evaluate the potential of this imaging technique for enhanced visualization of the anterior segment, especially the capsular bag, intraocular lens (IOL), and posterior capsule opacification (PCO) formation after cataract surgery. SETTING: Department of Medical Physics and Department of Ophthalmology, University of Vienna, Vienna, Austria, and Department of Oral and Maxillofacial Surgery Institute of Dentistry, University of Turku, Turku, Finland. METHODS: Ultrahigh-resolution OCT images were acquired from 7 pseudophakic human autopsy eyes using 1.4 microm axial x 3.0 microm transverse resolution. The axial resolution with UHR OCT is 1.4 microm compared to 10.0 microm with the commercially available OCT. Plastic-embedded histologic sections were obtained in precise alignment with the OCT tomograms. RESULTS: Ultrahigh-resolution OCT cross-sectional tomograms corresponded to the histologic sections. With the wavelength used (800 nm), the anterior and posterior capsules, area of lens epithelial cell growth and extracellular matrix proliferation, and IOL could be clearly visualized. The extent of capsular bag adhesion to the IOL could be detected, as well as the amount of PCO formation. CONCLUSIONS: The improved resolution makes UHR OCT a powerful tool in anterior segment imaging and evaluation of the capacity of IOL materials and models to induce capsular bag adhesion. Ultrahigh-resolution OCT may also help in determining the area of origin of PCO after cataract surgery.

Autopsy↗
PubMed2004

The use of photooxidized, mushroom-structured osteochondral grafts for cartilage resurfacing--a comparison to photooxidized cylindrical grafts in an experimental study in sheep.

OBJECTIVE: This article addresses the problem of structural design with osteochondral grafts used for cartilage resurfacing. METHODS: Photooxidized cylindrical or mushroom-shaped grafts were surgically implanted in the weight bearing area of the medial and lateral femoral condyles of eight sheep (condyles: N=8/group). Both types of photooxidized grafts contained no viable chondrocytes at the time of implantation. Results were evaluated at 2 and 6 months after surgical implantation of the grafts. Qualitative and quantitative evaluation of the subchondral bone area was performed using plastic embedded sections of non-decalcified bone and cartilage specimens and placing emphasis on graft anchorage, cyst-like lesions at the base of the cartilage junction and at the base of the graft in the subchondral bone region. Cartilage morphology was studied qualitatively focusing on viability of the graft and adjacent host cartilage, while a score system was developed for semi-quantitative evaluation of the overall articular cartilage performance. The semiquantitative scores and histomorphometrical measurements were subjected to statistical analysis using a factorial analysis of variance (ANOVA-test). RESULTS: The photooxidized mushroom-shaped grafts developed less fibrous tissue and cyst-like lesions in the subchondral bone area at 2 and 6 months compared to the cylindrical grafts. Areas of endochondral ossification and bone remodeling were noticeable in the mushroom structured grafts at 2 months, and also bone remodeling was more complete at 6 months than with the cylindrical grafts. Increased numbers of cells were seen in the basal remodeling zones of both graft types increased from the 2 months to the 6 months specimens, but mushroom structured grafts showed better results. In both graft types, however, the midzone of the cartilage matrix was still acellular at 6 months. Cells from the subchondral bone area started to penetrate the calcified cartilage zone and tide mark at 2 months and repopulated the old photooxidized cartilage matrix already at 6 months after implantation. Cartilage repopulation was dependent on a stable subchondral bone area in both types of grafts. Matrix degradation of the adjacent host cartilage was minimal at 2 and 6 months. At 6 months a junction between host and graft cartilage was already noticed in some of the mushroom-shaped grafts. CONCLUSION: This study confirmed the importance of the subchondral bone area for osteochondral graft survival. In addition it demonstrated that the structure of the graft influences considerably the architecture of the subchondral bone, and with this the possibility for the repopulation of the old cartilage matrix including the junction between the host and graft cartilage matrix.

Analysis of Variance↗
PubMed2005

Conical tomography II: A method for the study of cellular organelles in thin sections.

We have used conical electron tomography in order to reconstruct neuronal organelles in thin sections of plastic embedded rat somato-sensory cortical tissue. The conical tilt series were collected at a 55 degrees tilt and at 5 degrees rotations, aligned using gold particles as fiduciary markers, and reconstructed using the weighted back projection algorithm. After a refinement process based on projection matching, the 3D maps showed the "unit membrane pattern" along the entire reconstructed volume. This pattern is indicative of the bilayer arrangement of phospholipids in biological membranes. Based on Fourier correlation methods as well as the visualization of the "unit membrane" pattern, we estimated resolutions of approximately 4 nm. To illustrate the prospective advantages of conical tomography, we segmented "coated" vesicles in the reconstructed volumes. These vesicles were comprised of a central core enclosing a small lumen, and a protein "coating" extending into the cytoplasm. The "coated" vesicle was attached to the plasma membrane through a complex structure shaped as an arch where the ends are attached to the membrane and the crook is connected to the vesicle. We concluded that conical electron tomography of thin-sectioned specimens provides a powerful experimental approach for studying thin-sectioned neuronal organelles at resolution levels of approximately 4 nm.

Animals↗
PubMed2006

Local refinement: an attempt to correct for shrinkage and distortion in electron tomography.

A critical problem in electron tomography is the deformation of the specimen due to radiation, or "shrinkage," which interferes with image alignment and thereby limits resolution. Here, we describe a general strategy for refining preliminary reconstructions which allows the damage due to the shrinkage of plastic-embedded thin sectioned specimens (50-80 nm) to be corrected. The basic steps of the strategy involve: (a) the partition of the preliminary reconstruction into sub-volumes; (b) the extraction of corresponding sub-areas for each sub-volume from the micrographs of the tilt series; (c) the re-projection of each sub-volume according to the orientation parameters; and (d) the refinement of these parameters by correlating each sub-area to the corresponding computed projection. We tested the strategy by refining chemical synapses reconstructed from series imaged with conical, double and single tilt geometries. The results gathered with local refinement were evaluated by visually inspecting the structure of biological membranes in the maps. In an effort to quantify these improvements, we studied the refined maps using correlation criteria and mapped the corrections applied to the orientation parameters in each sub-volume of the reconstruction. Simulation experiments complemented the data gathered by correlation analysis. Based on these criteria, we concluded that local refinement significantly improves the overall quality of the reconstructions of chemical synapses calculated from series imaged with conical and double tilt geometries.

Image Enhancement↗
PubMed2004

Three-dimensional distributions of elements in biological samples by energy-filtered electron tomography.

By combining electron tomography with energy-filtered electron microscopy, we have shown the feasibility of determining the three-dimensional distributions of phosphorus in biological specimens. Thin sections of the nematode, Caenorhabditis elegans were prepared by high-pressure freezing, freeze-substitution and plastic embedding. Images were recorded at energy losses above and below the phosphorus L2,3 edge using a post-column imaging filter operating at a beam energy of 120 keV. The unstained specimens exhibited minimal contrast in bright-field images. After it was determined that the specimen was sufficiently thin to allow two-window ratio imaging of phosphorus, pairs of pre-edge and post-edge images were acquired in series over a tilt range of +/-55 degrees at 5 degrees increments for two orthogonal tilt axes. The projected phosphorus distributions were aligned using the pre-edge images that contained inelastic contrast from colloidal gold particles deposited on the specimen surface. A reconstruction and surface rendering of the phosphorus distribution clearly revealed features 15-20 nm in diameter, which were identified as ribosomes distributed along the stacked membranes of endoplasmic reticulum and in the cytoplasm. The sensitivity of the technique was estimated at < 35 phosphorus atoms per voxel based on the known total ribosomal phosphorus content of approximately 7000 atoms. Although a high electron dose of approximately 10(7)e/nm2 was required to record two-axis tilt series, specimens were sufficiently stable to allow image alignment and tomographic reconstruction.

Animals↗
PubMed2006

Quantification and thickness correction of EFTEM phosphorus maps.

We describe a method for correcting plural inelastic scattering effects in elemental maps that are acquired in the energy filtering transmission electron microscope (EFTEM) using just two energy windows, one above and one below a core edge in the electron energy loss spectrum (EELS). The technique is demonstrated for mapping low concentrations of phosphorus in biological samples. First, the single-scattering EELS distributions are obtained from specimens of pure carbon and plastic embedding material. Then, spectra are calculated for different specimen thicknesses t, expressed in units of the inelastic mean free path lambda. In this way, standard curves are generated for the ratio k0 of post-edge to pre-edge intensities at the phosphorus L2,3 excitation energy, as a function of relative specimen thickness t/lambda. Thickness effects in a two-window phosphorus map are corrected by successive acquisition of zero-loss and unfiltered images, from which it is possible to determine a t/lambda image and hence a background k0-ratio image. Knowledge of the thickness-dependent k0-ratio at each pixel thus enables a more accurate determination of the phosphorus distribution in the specimen. Systematic and statistical errors are calculated as a function of specimen thickness, and elemental maps are quantified in terms of the number of phosphorus atoms per pixel. Further analysis of the k0-curve shows that the EFTEM can be used to obtain reliable two-window phosphorus maps from specimens that are considerably thicker than previously possible.

Animals↗
PubMed2006

Electron tomography of ER, Golgi and related membrane systems.

A primary goal of cell biology is to uncover the mechanisms of cellular processes. A detailed structural understanding of the organelles and subcellular structures involved in these processes has often formed the foundation for the elucidation of their function. Electron tomography is a powerful technique for characterizing subcellular architecture and structural details in three dimensions. Electron tomography of cryofixed, freeze-substituted, and plastic-embedded samples allows three-dimensional visualization and display of dynamic, pleiomorphic structures at a resolution of approximately 7 nm in cell volumes up to approximately 25 microm(3). In this review, we describe the electron tomography protocols that we have employed to determine the 3D architecture of complex cellular structures, thereby gaining insights into their functional organization. We stress the need for studying specimens preserved by cryofixation methods to obtain accurate information on the geometry and size of cellular structures. We also discuss some of the challenges associated with the staining of certain types of membranes. Finally, we provide examples of how tomographic data can be analyzed, dissected, and displayed using the tools built into the IMOD software package.

Cell Membrane Structures↗
PubMed2006

Lysosomal accumulation of SCMAS (subunit c of mitochondrial ATP synthase) in neurons of the mouse model of mucopolysaccharidosis III B.

The neurodegenerative disease MPS III B (Sanfilippo syndrome type B) is caused by mutations in the gene encoding the lysosomal enzyme alpha-N-acetylglucosaminidase, with a resulting block in heparan sulfate degradation. A mouse model with disruption of the Naglu gene allows detailed study of brain pathology. In contrast to somatic cells, which accumulate primarily heparan sulfate, neurons accumulate a number of apparently unrelated metabolites, including subunit c of mitochondrial ATP synthase (SCMAS). SCMAS accumulated from 1 month of age, primarily in the medial entorhinal cortex and layer V of the somatosensory cortex. Its accumulation was not due to the absence of specific proteases. Light microscopy of brain sections of 6-months-old mice showed SCMAS to accumulate in the same areas as glycosaminoglycan and unesterified cholesterol, in the same cells as ubiquitin and GM3 ganglioside, and in the same organelles as Lamp 1 and Lamp 2. Cryo-immuno electron microscopy showed SCMAS to be present in Lamp positive vesicles bounded by a single membrane (lysosomes), in fingerprint-like layered arrays. GM3 ganglioside was found in the same lysosomes, but was not associated with the SCMAS arrays. GM3 ganglioside was also seen in lysosomes of microglia, suggesting phagocytosis of neuronal membranes. Samples used for cryo-EM and further processed by standard EM procedures (osmium tetroxide fixation and plastic embedding) showed the disappearance of the SCMAS fingerprint arrays and appearance in the same location of "zebra bodies", well known but little understood inclusions in the brain of patients with mucopolysaccharidoses.

Aging↗
PubMed1994

Ultrastructure of skeletal muscle fibers studied by a plunge quick freezing method: myofilament lengths.

We have set up a system to rapidly freeze muscle fibers during contraction to investigate by electron microscopy the ultrastructure of active muscles. Glycerinated fiber bundles of rabbit psoas muscles were frozen in conditions of rigor, relaxation, isometric contraction, and active shortening. Freezing was carried out by plunging the bundles into liquid ethane. The frozen bundles were then freeze-substituted, plastic-embedded, and sectioned for electron microscopic observation. X-ray diffraction patterns of the embedded bundles and optical diffraction patterns of the micrographs resemble the x-ray diffraction patterns of unfixed muscles, showing the ability of the method to preserve the muscle ultrastructure. In the optical diffraction patterns layer lines up to 1/5.9 nm-1 were observed. Using this method we have investigated the myofilament lengths and concluded that there are no major changes in length in either the actin or the myosin filaments under any of the conditions explored.

Actin Cytoskeleton↗
PubMed1998

Structural analysis of Alzheimer's beta(1-40) amyloid: protofilament assembly of tubular fibrils.

Detailed structural studies of amyloid fibrils can elucidate the way in which their constituent polypeptides are folded and self-assemble, and exert their neurotoxic effects in Alzheimer's disease (AD). We have previously reported that when aqueous solutions of the N-terminal hydrophilic peptides of AD beta-amyloid (A beta) are gradually dried in a 2-Tesla magnetic field, they form highly oriented fibrils that are well suited to x-ray fiber diffraction. The longer, more physiologically relevant sequences such as A beta(1-40) have not been amenable to such analysis, owing to their strong propensity to polymerize and aggregate before orientation is achieved. In seeking an efficient and inexpensive method for rapid screening of conditions that could lead to improved orientation of fibrils assembled from the longer peptides, we report here that the birefringence of a small drop of peptide solution can supply information related to the cooperative packing of amyloid fibers and their capacity for magnetic orientation. The samples were examined by electron microscopy (negative and positive staining) and x-ray diffraction. Negative staining showed a mixture of straight and twisted fibers. The average width of both types was approximately 70 A, and the helical pitch of the latter was approximately 460 A. Cross sections of plastic-embedded samples showed a approximately 60-A-wide tubular structure. X-ray diffraction from these samples indicated a cross-beta fiber pattern, characterized by a strong meridional reflection at 4.74 A and a broad equatorial reflection at 8.9 A. Modeling studies suggested that tilted arrays of beta-strands constitute tubular, 30-A-diameter protofilaments, and that three to five of these protofilaments constitute the A beta fiber. This type of structure--a multimeric array of protofilaments organized as a tubular fibril--resembles that formed by the shorter A beta fragments (e.g., A beta(6-25), A beta(11-25), A beta(1-28)), suggesting a common structural motif in AD amyloid fibril organization.

Amino Acid Sequence↗
PubMed1992

Ultrastructural detection of DNA within the nucleolus by sensitive molecular immunocytochemistry.

This paper describes a new technique for locating DNA on semithin or ultrathin sections of aldehyde-fixed and plastic-embedded cells or tissues. Sections were incubated in a medium containing bromodeoxyuridine (BUdR) triphosphate and terminal deoxynucleotidyltransferase. The labeled nucleotides bound at the surface of the sections were subsequently detected with an anti-BUdR antibody and immunoglobulin-gold complex. On semithin sections, labeled nucleotide detection was achieved by an amplification step with silver enhancement. This technique was applied to a wide variety of biological materials allowing a sensitive detection of DNA-containing structures, even where these are present in very low amounts. Examples of high resolution and sensitive detection include the DNA present in mitochondria, chloroplasts, mycoplasmas, and DNA viruses. Special attention focused on the location of DNA inside the nucleolus. In Ehrlich tumor cell nucleoli, DNA was detected in the fibrillar centers and not in the dense fibrillar component. Identical results were found in the nucleoli of other cell types. These results contradict earlier data but conform with other recent immunocytochemical observations concerning the correlation between structure and function in the nucleolus. This method provides a useful tool for investigations requiring highly precise correlations between a molecular function and a given ultrastructural morphology.

Animals↗
PubMed1995

Histomorphometry of the optic nerves of normal dogs and dogs with hereditary glaucoma.

The beagle dog with hereditary primary open-angle glaucoma, unlike other animal models of human glaucoma, possesses a slowly progressive, sustained elevation of intraocular pressure. The effects of this insidious elevation in intraocular pressure on the axons of the optic nerves of three beagles at early stages of glaucoma and two beagles with advanced signs of glaucoma were compared to the optic nerves of four age-matched normal dogs. Plastic embedded optic nerve cross-sections (1 micron) 1 mm posterior to the lamina cribrosa were osmicated and stained with Toluidine Blue. Axons from 0.2 to > 2.0 microns in diameter were counted and measured in 16 cross-sectional regions of equal size within the whole optic nerve using a computerized image analysis system. The mean optic nerve axon diameters in the normal, early glaucomatous, and advanced glaucomatous dogs were 1.53, 1.25 and 1.13 microns respectively. The average total optic nerve axon count in the normal dogs was 148,303. Approximately 16% of the total axonal fibers were counted in each nerve. The counts of optic nerve axons 2.0 microns or greater in diameter were reduced by up to 60% in the central regions of the optic nerves of affected beagles. The large diameter axons of the peripheral optic nerve of the beagle dogs with glaucoma were more resistant to the elevated intraocular pressure. The counts of axons > 0.6 to 0.8 micron in diameter were significantly increased in glaucomatous beagles.

Animals↗
PubMed1988

Morphologic studies of lymphocyte nuclei in follicular and diffuse mixed small- and large-cell (lymphocytic-histiocytic) lymphoma.

Twelve examples of mixed small- and large-cell lymphoma (eight follicular, one follicular and diffuse, and three diffuse) were investigated morphometrically using plastic-embedded tissue in order to study nuclear characteristics of lymphocyte populations in this form of non-Hodgkin's lymphoma (NHL) and to test morphologic bases for current NHL classification systems. This study illustrates that there are many inaccuracies, illusions, and misconceptions in the morphologic criteria currently used to classify mixed small- and large-cell lymphoma. A principal finding was that lymphocyte nuclear profiles in mixed-cell lymphomas tend to be smaller in size (P less than .005) and more irregular in shape (P = .0001) than the morphologically similar counterparts in germinal centers of lymph nodes with reactive hyperplasia. Intercase comparison of mixed small- and large-cell lymphomas revealed a considerable range of mean nuclear area values, some of which were within the size range of normal, small lymphocytes. At the magnifications used for morphometric assessment, a high proportion of lymphocyte nuclear profiles had shallow invaginations, but only a limited number of profiles (4% to 14%) had deep (cleaved) indentations. Contrary to current definitions for this subtype of NHL, lymphocytes with "small" nuclei had the same proportion of the nuclear diameter occupied by nuclear invaginations as lymphocytes with "large" nuclei and, in fact, mean nuclear invagination depth was shallower in "small" nuclei than in "large" nuclei. Furthermore, regardless of whether it is nuclear area or shape that is evaluated, lymphocytes in mixed-cell lymphoma do not separate into two populations of small-cleaved and large noncleaved cells. Morphometry reveals that only four of the 12 examples of mixed small- and large-cell lymphoma had a proportion of the lymphocytes in the size range of fully transformed germinal center lymphocytes that exceeded 25%, and none of the cases approached 50% even though the population of lymphocyte nuclei appearing "transformed," and therefore "large," ranged from 28% to 57%. Such results indicate that the large, noncleaved and cleaved component, as seen in histologic sections of mixed small- and large-cell lymphoma, do not have nuclei of uniform size and many, in fact, are not actually large. The morphometric findings indicate reasons for the poor observer reproducibility in classifying this subtype of NHL.

Cell Nucleus↗
PubMed2003

Biocompatibility and healing process of polyester meshes in the brain: in vivo examination in rats.

OBJECTIVES: To analyze the biocompatibility of multifilament polyester (PET) meshes used for the implantation of auditory brainstem implants in a standardized Wistar rat model (n=29). METHODS: The physical properties of the meshes were examined during surgery. Using a modified plastic embedding, the local tissue reaction and the stability of mesh position in the region of the fourth ventricle were evaluated in section series from day 3 to 64. The cellular reaction was further differentiated using transmission and scanning electron microscopy. RESULTS: PET meshes were stable for handling. However, sharp edges inevitably led to brainstem and cerebellar penetration in some cases. The meshes were preserved in situ in all section series. Positioning was stable with one exception. A sufficient fibroblast and collagen fiber encasement was reached after 14 days. In all cases, no further change was observed through day 64. The host-defense reaction was persistent and characterized by numerous macrophages and foreign-body giant cells. Bacterial infection occurred in three cases. CONCLUSIONS: PET meshes proved to have an acceptable biocompatibility regarding local-tissue reaction in the brain. Modified polymer structures should be developed to reduce risk of injury. Anti-inflammatory surface treatments and monofilament meshes could reduce the infection rate.

Animals↗
PubMed1984

The morphological development of the human fovea.

The development of the human fovea has been traced from 22 weeks gestation to 45 months postpartum using aldehyde-fixed, plastic embedded, serially-sectioned normal retinas. Five anatomical indicators of foveal maturity were used in this study: the shape of the foveal curvatures; the presence of the transient layer of Chievitz; the width of rod-free zone in the central retina; the width and length of the individual foveal cones; and the number and thickness of layers of nuclei within the fovea. The future fovea is identifiable at 22 weeks by the presence of a thick layer of ganglion cells and a photoreceptor layer containing only cones. By 1 week after birth, there is a shallow foveal depression, but the thick cones still lack outer segments and are only 1 cell deep in the fovea. The inner nuclear layer contains a thick transient layer of Chievitz. As judged by these anatomical criteria and compared to normal adult foveas similarly processed, the human fovea reaches maturity between 15 and 45 months of age.

Adolescent↗
PubMed1984

Recent advances in pathology as applied to orbital biopsy. Practical considerations.

Advances in pathology allow for more specific diagnoses of orbital disease. The authors discuss the value of awareness of advances in cytology, histochemistry, immunohistochemistry and electron microscopy as applied to orbital disease. Modern cytologic technique can aid in clearer visualization of cellular detail with improved diagnosis of thin needle aspiration biopsies. Histochemistry offers an increasing range of methods for identification of cellular and extracellular substances such as amyloid, fibrin, neuroglia, and collagen. Immunohistochemistry allows for identification of an ever-increasing number of component antigens including immunoglobulins, myoglobins, keratin, glial fibre protein, etc. Electronmicroscopic technique including plastic embedding allow for specific identification of lesions based on subcellular components and characteristic nuclear, cytoplasmic, membrane, basement membrane and stromal components. The value of these methods has been demonstrated with case presentations of "small round cell tumors" of the adult and child. In addition, the pathologic diagnosis of several rare lesions of the orbit including neuroendocrine carcinoma, histiocytosis X, simultaneously occurring poorly differentiated mucoepidermoid carcinoma of lacrimal gland and adenocarcinoma of the prostate are demonstrated to underline the advances in technology. Emphasis is placed on the management of biopsy material to maximize diagnostic potential.

Aged↗
PubMedDate not supplied

Pathology of otosclerosis: a review.

Otosclerosis is a bone disorder of unknown etiology confined to the otic capsule. Failure of remodeling of newly formed vascular, woven bone (otospongiosis) results in sclerotic bone (otosclerosis) with abnormal osteons. Involvement of the oval window causes conductive hearing loss. Electron microscopic, histochemical, and biochemical studies identify normal cellular and matrix components of otosclerotic bone without providing clues to the abnormal bone formation and resorption. Plastic-embedded, nondecalcified histologic sections with in vivo tetracycline labels permit the study of mineralization rates to separate this disorder from other bone dyscrasias that have similar histopathologic appearances. Characterization of the cells, matrix, and their mediators can yield an understanding of abnormalities that disorder bone.

Animals↗
PubMed2000

An anatomically based frequency-place map for the mouse cochlea.

An anatomically based frequency-place map was created for the mouse using C57BL/CBA F1 hybrids by matching noise-induced lesions in the organ of Corti with permanent hearing losses as determined by auditory brainstem response (ABR) thresholds. Twenty-six mice developed 'notched' ABR threshold shifts after exposure to an octave band of noise with a center frequency of 2 kHz at 120 dB SPL for 24 h, 4 kHz at 110 dB SPL for 4 h or 8 kHz at 100 dB SPL for 1 or 2 h. ABR thresholds were determined at several intervals post-exposure until thresholds stabilized (14-27 days). Once thresholds had stabilized, the mice were killed and their cochleas were prepared for phase-contrast microscopic examination as plastic-embedded flat preparations. Hair cell loss, stereocilia damage, and myelinated nerve fiber degeneration as a function of percentage distance from the cochlear apex were determined. Frequency-position matches could be made for 22 of the 26 mice by correlating areas of hair cell loss/stereocilia damage with permanent changes in ABR thresholds. These frequency-position data were fitted with the equation: % Distance from apex=56.6 log (f(Hz))-179.1; r(2)=0.810. This frequency-place function agrees well with Ehret's (1975) theoretical function based on critical bands and masked auditory thresholds.

Animals↗