Effect of Amikacin on the Postnatal Development of the Cochlea in Albino Rats

Background: The cochlea is the anterior part of the labyrinth and its development is sensitive to large variety of noxious influences. Aim of the Work: This work was conducted to study the effect of amikacin on the postnatal development of cochlea in albino rats. Material and Methods: A total number of 30 albino rats were divided into two groups, a control group and an experimental group. The ages studied in this research were newborn, 7 days, 15 days, 1 month and 3 months postnatally in both control and experimental groups. The pregnant mothers of the experimental group received 250 mg/kg body weight of amikacin intraperitoneally daily from day 10 of gestation until the end of pregnancy. The same dose was given to the offsprings from day 1 until day 16 postnatally. The specimens were processed for histological study and stained with H&E. Ultrastructural study of the inner and outer hair cells and the large spiral ganglion cells was done through preparation of semithin and ultrathin sections. Morphometric measurements were performed to study the number of spiral ganglion cells in all the studied groups and were statistically analyzed. Results: This study revealed that the cochlea was still immature at birth and reached the adult appearance at the age of 15 days postnatally. The cochlear structures including the organ of Corti were found to be mature from the base to the apex of the cochlea. We observed that amikacin has no apparent effect on development of the cochlea in the newborn rats. In the 7-day-old rats, some degenerative changes appeared in the outer and inner hair cells. This effect became manifested in 15-day-old animals. Ultrastructural study of the outer hair cells showed peripheral condensation of nuclear chromatin with presence of many cytoplasmic vacuoles. At 1-month-age, there was disorganization of the organ of Corti, where atypical cells found in the region of the outer hair cells while the inner hair cells showed signs of degeneration. At the age of three months, there was complete destruction of the organ of Corti along the whole cochlea. Morphometric study for the number of the spiral ganglion cells showed highly significant decrease in the amikacin treated animals at the age of 15- day-old rats. This decrease became very highly significant at the age of one month and three months old amikacin treated rats  Conclusions: Amikacin has a damaging effect on the organ of Corti and so considered as one of the causes of sensory deafness. The effect of amikacin was manifested during the second postnatal week is corresponding to the period of maturity of the cochlea.