Morphology and function of Bast’s valve: additional insight in its functioning using 3D-reconstruction

The utriculo-endolymphatic valve was discovered by Bast in 1928. The function of Bast’s valve is still unclear. By means of orthogonal-plane fluorescence optical sectioning (OPFOS) microscopy 3D-reconstructions of the valve and its surrounding region are depicted. The shape of the duct at the utricular side is that of a flattened funnel. In the direction of the endolymphatic duct and sac this funnel runs into a very narrow duct. The valve itself has a rigid ‘arch-like’ configuration. The opposing thin, one cell-layer thick, utricular membrane is highly compliant. We propose that opening and closure of the valve occurs through movement of the flexible base/utricular membrane away from and toward the relatively rigid valve lip

The frog inner ear: picture perfect?

This is the accepted manuscript of a paper published in the Journal of the Association for Research in Otolaryngology (2015) DOI: 10.1007/s10162-015-0506-zMany recent accounts of the frog peripheral auditory system have reproduced Wever's (1973) schematic cross-section of the ear of a leopard frog. We sought to investigate to what extent this diagram is an accurate and representative depiction of the anuran inner ear, using three-dimensional reconstructions made from serial sections of Rana pipiens, Eleutherodactylus limbatus and Xenopus laevis. In Rana, three discrete contact membranes were found to separate the posterior otic (=endolymphatic) labyrinth from the periotic (=perilymphatic) system: those of the amphibian and basilar recesses and the contact membrane of the saccule. The amphibian 'tegmentum vasculosum' was distinguishable as a thickened epithelial lining within a posterior recess of the superior saccular chamber. These features were also identified in Eleutherodactylus, but in this tiny frog the relative proportions of the semicircular canals and saccule resemble those of ranid tadpoles. There appeared to be a complete fluid pathway between the right and left periotic labyrinths in this species, crossing the cranial cavity. Xenopus lacks a tegmentum vasculosum and a contact membrane of the saccule; the Xenopus ear is further distinguished by a lateral passage separating stapes from periotic cistern and a more direct connection between periotic cistern and basilar recess. The basilar and lagenar recesses are conjoined in this species. Wever's diagram of the inner ear of Rana retains its value for diagrammatic purposes, but it is not anatomically accurate or representative of all frogs. Although Wever identified the contact membrane of the saccule, most recent studies of frog inner ear anatomy have overlooked both this and the amphibian tegmentum vasculosum. These structures deserve further attention.The authors wish to thank Emanuel Mora for his help and support with this project. Dave Simpson kindly provided the Xenopus specimens. The CT scan of Xenopus was made by Alan Heaver of the University of Cambridge Department of Engineering, with thanks going also to Norman Fleck for the use of his equipment. The authors are very grateful to Dolores Bozovic, Alan D. Grinnell, Tammy Hoang, Victoria Sandoval and Felix E. Schweizer for facilitating the Rana CT scan, which was made by Ting-Ling Chang at the UCLA School of Dentistry, Division of Advanced Prosthodontics. Stephan Kamrad helped with translations. The research of JMS and PvD was supported by the Heinsius Houbolt Foundation and is part of the research programme Healthy Ageing and Communication of the Department of Otorhinolaryngology at the University Medical Center Groningen. Finally, the authors wish to thank the reviewers and editors of the manuscript for their very helpful comments

A Bast-like valve in the pigeon?

The first description of the presence of a utriculo-endolymphatic valve in human fetuses was given by Bast in 1928. Since then this valve-like structure is called Bast’s valve. Its exact function has not yet been established. The general opinion is that it has a protective function by having the possibility to separate the superior endolymphatic compartments of the labyrinth from the inferior compartment. Phylogenetically seen birds are the first vertebrates with a cochlear duct and a distinct inferior and superior part of the labyrinth. A structure in the pigeon inner ear, resembling Bast’s valve in mammals, is described

Mechanics of the exceptional anuran ear

The anuran ear is frequently used for studying fundamental properties of vertebrate auditory systems. This is due to its unique anatomical features, most prominently the lack of a basilar membrane and the presence of two dedicated acoustic end organs, the basilar papilla and the amphibian papilla. Our current anatomical and functional knowledge implies that three distinct regions can be identified within these two organs. The basilar papilla functions as a single auditory filter. The low-frequency portion of the amphibian papilla is an electrically tuned, tonotopically organized auditory end organ. The high-frequency portion of the amphibian papilla is mechanically tuned and tonotopically organized, and it emits spontaneous otoacoustic emissions. This high-frequency portion of the amphibian papilla shows a remarkable, functional resemblance to the mammalian cochlea

Caloric Stimulation of the Vestibular System of the Pigeon under Minimal Influence of Gravity

Vestibular microphonics in response to acoustical stimulation were recorded in cochlea-deprived pigeons. Endolymph flow in the semicircular canals alters this response. A caloric stimulus was applied to the horizontal canal or the posterior vertical canal close to the ampulla. To minimize the influence of gravity, the canal being studied was positioned in the horizontal plane. Local temperature changes were generated with an electrically heated miniature copper probe, producing an approximately trapezoidal temperature profile. Because of the opposite hair cell polarization in the horizontal and the vertical ampulla, we could prove that the observed effects were of (hydro-)mechanical origin and were not caused by a direct effect of sensory epithelium temperature change. The first effect of temperature increase was an utriculopetal endolymph flow, as predicted by the 'expansion theory'

Three-dimensional reconstruction of the pigeon inner ear

Three-dimensional reconstructions of the inner ear of the pigeon (Columba livia domestica), from two-dimensional images, obtained with (conventional) light microscopy or orthogonal-plane fluorescence optical sectioning (OPFOS), are presented. The results are compared with available information on the dimensions and orientation of the semicircular canals

FREQUENCY-SELECTIVE RESPONSE OF THE TECTORIAL MEMBRANE IN THE FROG BASILAR PAPILLA

The frog's basilar papilla is a useful study object for cochlear mechanics, because of it's relatively simple anatomy and functionality. We investigated the displacement amplitudes of the basilar papilla's tectorial membrane in response to stimulation of the oval window at various frequencies within the auditory range of the Northern leopard frog. From Our measurement data we find that the tectorial membrane exhibits a frequency selective response. The peak response was found to occur at 1500Hz in correspondence with known data for the response of auditory nerve fibers from the organ.From these data we conclude that; mechanical timing contributes significantly to the frequency selectivity of the frog's basilar papilla</p

Three-dimensional reconstruction of the guinea pig inner ear, comparison of OPFOS and light microscopy, applications of 3D reconstruction

Three-dimensional (3D) reconstruction of anatomical structures can give additional insight into the morphology and function of these structures. We compare 3D reconstructions of the guinea pig inner ear, using light microscopy and orthogonal plane fluorescence optical sectioning microscopy. Applications of 3D reconstruction of the inner ear are further explored. For each method two bullas were prepared for 3D reconstruction. Both methods are explained. In general, the 3D reconstructions using orthogonal plane fluorescence optical sectioning microscopy are superior to light microscopy. The exact spiral shape of the cochlea could be reconstructed using orthogonal plane fluorescence optical sectioning microscopy and the length of the basilar membrane measured. When a resolution of 20 mu m is sufficient, orthogonal plane fluorescence optical sectioning microscopy is a superior technique for 3D reconstruction of inner ear structures in animals

Vestibular microphonic potentials in pigeons

Electrical responses to acoustic stimuli were measured by placing thin wire electrodes in the vestibular system of a pigeon model. Responses were measured after extirpation of the cochlea and the application of tetrodotoxin to the perilymphatic space. Responses seen were comparable to those of known cochlear microphonic potentials. These findings indicate that acoustic stimuli can evoke microphonic potentials in the vestibular system of the pigeon. We also found that vibrational amplitudes of less than 1 nm were sufficient to evoke a vestibular microphonic potentia