Biomedical subjects

Alejandro Rivas

Publications and source records attributed to Alejandro Rivas.

3 recordsLinked to original sources

PubMed2005

Efficient quantification of afferent cochlear ultrastructure using design-based stereology.

The afferent synapse between the auditory nerve fiber and the inner hair cell (IHC) represents a critical junction for hearing. Elucidation of the structure at this site will help establish the substrate for normal sound encoding as well as pathologic processes associated with hearing dysfunction. Previous applications of unbiased (design-based) stereological principles have expanded our knowledge of neuro-morphological changes evident with the light microscope. Applying these principles at the level of the synapse is a promising morphometric approach for the efficient sampling of large reference spaces with electron microscopy. This study tests the accuracy of using ultra-thin sections at a fixed interval, known as disector pairs, to quantify afferent innervation density. We analyzed the total numbers of afferent terminals, synaptic thickenings, and synaptic bodies associated with each IHC in the C57BL/6J mouse cochlea, and confirmed the accuracy of the stereological approach in comparison to three-dimensional reconstructions of serial alternate sections. The higher sampling efficiency of the disector pair method rapidly increases precision while also reducing the largest source of variability, inter-animal differences. We conclude that ultrastructural quantification of afferent innervation can be accomplished in the cochlea using efficient design-based stereology.

Animals↗

PubMed2005

Inner ear abnormalities in a Kcnq1 (Kvlqt1) knockout mouse: a model of Jervell and Lange-Nielsen syndrome.

HYPOTHESIS: Mice lacking functional KCNQ1 (previously known as KvLQT1) channels exhibit functional and structural abnormalities that indicate disturbed production of endolymph. BACKGROUND: Congenital deafness associated with cardiac conduction abnormalities (Jervell and Lange-Nielsen syndrome) is associated with dysfunctional KCNQ1/KCNE1 channel complex. This potassium channel plays a critical role in the production and homeostasis of endolymph by the stria vascularis. A preliminary report documented severe abnormalities of the scala media and vestibular compartments of a single mouse lacking functional KCNQ1 alleles. METHODS: Hearing thresholds were measured in three Kcnq1 knockout mice, two heterozygous mice, and one wild-type mouse by auditory brainstem response recordings using clicks, after which the temporal bones were removed. After fixation and dehydration, the ears were embedded in araldite, sectioned at 20-microm thickness, stained with toluidine blue on glass slides, and examined with the light microscope. RESULTS: Kcnq1 knockout mice were deaf and demonstrated circling behavior. They exhibited a marked atrophy of the stria vascularis, contraction of the endolymphatic compartments, and collapse and adhesion of surrounding membranes. There was a complete degeneration of the organ of Corti and an associated degeneration of the spiral ganglion. CONCLUSION: Kcnq1 knockout mice exhibit histopathologic findings that are comparable to those reported in human temporal bone cases of Jervell and Lange-Nielsen syndrome, and provide further evidence that KCNQ1 channel dysfunction can lead to congenital deafness in this syndrome.

Animals↗

PubMed2004

Two types of afferent terminals innervate cochlear inner hair cells in C57BL/6J mice.

Afferent synapses on inner hair cells (IHC) transfer auditory information to the central nervous system (CNS). Despite the importance of these synapses for normal hearing, their response to cochlear disease and dysfunction is not well understood. The C57BL/6J mouse is a model for presbycusis and noise-induced hearing loss because of its age-related hearing loss and susceptibility to acoustic over-exposure. In this context, we sought to establish normal synaptic structure in order to better evaluate synaptic changes due to presbycusis and noise exposure. Ultrastructural analysis of IHCs and afferent terminals was performed in a normal hearing 3-month-old C57BL/6J mouse at cochlear sites corresponding to 8, 16 and 32 kHz using semi-serial sections. A stereologic survey of random sections was conducted of IHCs in 11 additional mice. Two morphologically distinct groups of afferent terminals were identified at all 3 frequency locations in 11 out of 12 animals. "Simple" endings demonstrated classic features of bouton terminals, whereas "folded" endings were larger in size and exhibited a novel morphologic feature that consisted of a fully internalized double membrane that partially divided the terminal into two compartments. In many cases, the double membrane was continuous with the outer terminal membrane as if produced by an invagination. We still must determine the generality of these observations with respect to other mouse strains.

Afferent Pathways↗