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

Abstract

Amikacin belongs to the aminoglycoside group of antibiotics, which are bactericidal aminoglycosidic aminocyclitols. All aminoglycosides have a potential to induce severe and irreversible ototoxicity in the cochlea and vestibular organ. The cochlea is the anterior part of the labyrinth. The organ of Corti is composed of sensory cells and non-sensory cells (supporting cells). The sensory cells, the inner and outer hair cells are responsible for acoustic signals. The aim of this study was to demonstrate the effect of amikacin on the postnatal development of cochlea in albino rats. A total number of 30 albino rats were used in this work. They were divided into two groups, a control group and an experimental group. The ages studied in this research were newborn, 7, 15 days, 1 and 3 months postnatally in both control and experimental groups. The pregnant mothers of the experimental group received 250 mg kg-1 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. Animals were scarified using cervical dislocation method, under supervision of animal house veterinary doctor (Faculty of Medicine Cairo University). The remnant of animals was handled perfectly by animal house technician and destroyed in destruction room. The specimens were processed for ordinary histological study and stained with haematoxylin and eosin. Ultrastructural study of the inner and outer hair cells and the large spiral ganglion cells were done through preparation of semithin and ultrathin sections. The results of this study revealed that the cochlea was still immature at birth. It reached the adult appearance at the age of 15 days postnatally. In this work, it was found 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 the age of 1 month, there was disorganization of the organ of Corti. Atypical cells were found in the region of the outer hair cells while the inner hair cells showed signs of degeneration. At the age of 3 months, there was complete destruction of the organ of Corti along the whole cochlea. It is obvious from the previous study that amikacin has a damaging effect on the organ of Corti and so it could be considered as one of the causes of sensory deafness.