الفهرس 
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Abstract
The organ of Corti is the receptor organ for hearing; it is described as “a masterpiece of cellular micro-architecture”, it is formed of inner and outer sensory hair cells and non sensory supporting cells as Deiter’s cells and pillar cells.
Presbycusis or age related hearing loss is one of the most common diseases affecting the aged. According to the National Institute of Deafness and Other Communication Disorders, one in three people above age 60 and half of those over 85 have hearing loss (2001).
There are four types of presbycusis: sensory (hair cell loss), neural (Spiral ganglia neuron SGN loss), metabolic (strial dysfunction) and cochlear conductive (changes in the stiffness of the basilar membrane). Strial presbycusis has been claimed by some to represent the major form that arises from the true ‘aging-like’ process.
The aim of the present work was to study the structure, the organization and the electrolyte changes in the organ of Corti associated with senility. Twenty male (caviacobaya) guinea pigs were used in this experiment; they were equally divided into young adult and senescent (senile) groups. The cochleae were extracted and processed for light microscope, scanning electron microscope, (EDAX) for electrolytes measurements and immunohistochemistry for apoptosis.
By light microscope, the organ of Corti showed vacuolation of inner hair cells, outer hair cells and their supporting cells with kinking of the basilar membrane. The stria vascularis showed ill-defined intermediate and basal cell layers, decreased vascularity and absence of its brownish pigmentation.
The spiral ligament showed loss of criss-cross pattern and decreasrd number of fibrocytes. The spiral ganglia showed degenerative changes, some neurons showed cytoplasmic ballooning while others were completely lysed leaving an empty spaces behind. The limbus lamina spiralis showed disorganization and a decrease in the number of its interdental cells.
The organ of Corti of the senescent (senile) group examined by SEM revealed a disorganization and distortion in the stereociliaof inner and outer hair cells with surface blebing with increased surface granularity.
The senescent (senile) stria vascularis showed also a striking positive immunoreactivity for tunnel apoptosis especially in its intermediate cell layer.
EDAX showed a characteristic significant elevation of Neiobium and Carbon in the senescent (senile) group on the contrary Calcium showed significant decrease in the senescent (senile) group compared to the adult group.
It could be thus concluded that, aging is a multifactorial process, in the cochlea aging of hair cells and supporting cells were also influenced by metabolic changes and a decrease in calcium and other minerals and ions level that affect the integrity of the endolymph and subsequently the cochlear cells and vice versa. Pollutants such as Niobium which was exceptionally discovered by EDAX in the present work could explain that pollutants could alter the microenvironment and add to the early degeneration of the organ of Corti. Neuronal changes in the spiral ganglion could be either concomitant or a result of hair cells and supporting cells destruction. The present work provides the experimental evidence suggesting that:
1- Alteration of the mineral contents seen in the sensory component of organ of Corti may be one of the earliest mechanisms of aberrations of hearing changes seen in presbycusis and restoration of the mineral contents may have ameliorated effect in hearing restoration .Future studies are necessary to evaluate the impact of restoring mineral ion homeostatic system.
2- The new technique, Scanning electron microscope (SEM) with (EDAX) Energy dispersive X-ray analysis gives a new point of view of pathophysiology of presbycusis and opens new perspectives in the study the effect of aging process on organ of Corti .However, further study is also required to evaluate and to identify the responsible mechanism for such minerals changes which may lead to better management of presbycusis.