ABSTRACT
We assessed cellular changes in one population of neurons of the cochlear nucleus associated with a form of genetic deafness in deaf dalmatians. Spheric cells from deaf dalmatians and age-matched control (hearing) dogs were analyzed morphometrically. The somatic silhouette of these cells was reduced by 22.1% to 38.1%. The effect on cell size was greater with increased duration of deafness. Because the deaf dalmatian exhibits progressive degeneration of the auditory periphery, shrinkage of spheric cells may reflect the initial influence of attenuated activity of auditory nerve fibers, and sensorineural degeneration with longer periods of deafness.
Subject(s)
Cochlear Nucleus/pathology , Deafness/congenital , Age Factors , Animals , Case-Control Studies , Cell Nucleolus/ultrastructure , Cell Nucleus/ultrastructure , Cell Size , Cytoplasm/ultrastructure , Deafness/genetics , Deafness/pathology , Disease Models, Animal , Disease Progression , Dogs , Evoked Potentials, Auditory, Brain Stem/physiology , Hearing/physiology , Hearing Loss/pathology , Nerve Degeneration , Nerve Fibers/pathology , Neurons/pathology , Nissl Bodies/ultrastructure , Nuclear Envelope/ultrastructure , Spiral Ganglion/pathology , Time Factors , Vestibulocochlear Nerve/pathologyABSTRACT
This study was undertaken to examine the effects of chronic high-rate stimulation on the eighth nerve and cochlea. Fifty-four male pigmented guinea pigs were deafened and implanted with single ball electrodes in scala tympani. Four groups of animals received chronic electrical stimulation at a level of 5 microCol/cm2/ph for 1000 h as follows: Group A: 1000 Hz, 100 microseconds/ph duration, 100 microA peak; Group B: 250 Hz, 100 microseconds/ph duration, 100 microA peak; Group C: 2750 Hz, 36 microseconds/ph duration, 250 microA peak; Group D: 250 Hz, 400 microseconds/ph duration, 25 microA peak. Also, two control groups received 20 min stimulation during weekly electrically evoked auditory brainstem response (eABR) measurement (Group E) and about 5 s stimulation (Group F) during a brief eABR 3 day postimplantation and at perfusion. On Day 50, animals were perfused, midmodiolar sections cut and a quantitative assessment of spiral ganglion cells (SGC) performed. All stimulated subjects showed a similar decrease in eABR thresholds and dynamic range over time. No stimulation conditions induced pathology. All stimulation conditions enhanced survival of SGCs compared to unimplanted ears and implanted non-stimulated ears (Group F). There were no statistically significant differences in SGC survival between any stimulated groups, including Group E stimulated once a week. In conclusion, high-rate stimulation, under the conditions of this study, provides no additional risks and the same benefits to SGC survival as low-rate stimulation.
Subject(s)
Cochlea/physiology , Deafness/physiopathology , Evoked Potentials, Auditory, Brain Stem/physiology , Vestibulocochlear Nerve/physiology , Animals , Auditory Threshold/physiology , Cochlea/innervation , Cochlear Implants/standards , Deafness/chemically induced , Deafness/surgery , Disease Models, Animal , Electric Stimulation , Electrodes, Implanted , Electrophysiology , Guinea Pigs , Hair Cells, Auditory, Inner/cytology , Hair Cells, Auditory, Inner/pathology , Hair Cells, Auditory, Outer/cytology , Hair Cells, Auditory, Outer/pathology , Male , Scala Tympani/physiology , Spiral Ganglion/cytology , Spiral Ganglion/pathology , Spiral Ganglion/physiology , Tectorial Membrane/pathologyABSTRACT
Mitosis of supporting cells has been shown to contribute to the cellular repopulation of the basilar papilla after acoustic trauma. In the present work we report data obtained with light and transmission electron microscopy after acoustic trauma in chicks. We report changes that occur in cell shape, surface morphology, intercellular junctions, nuclear shape and location, and cytoplasmic organization of supporting cells after trauma. The findings strongly suggest that supporting cells transdifferentiate and that the proliferative pattern is similar to interkinetic nuclear migration, as previously shown in the developing neural tube and basilar papilla. S-phase nuclei were positioned adjacent to the basement membrane, suggesting that interaction with the extracellular matrix may occur during the cell cycle. Supporting cells divided with the long axis of the spindle parallel to the reticular lamina and displayed no signs of intercellular communication during mitosis. This suggested to us that the fate of the progeny cells is determined prior to mitosis and that the progeny may be of identical phenotypic fate. Dividing cells had a smooth apical surface. The smooth surface may provide a marker to help identify dividing cells with scanning electron microscope analysis.
