Distribution of gentamicin to the cochlea of the chicken embryo

Aminoglycoside antibiotics are ototoxic in mammals and birds, including recently hatched chicks, but chicken embryos are insensitive to the ototoxicity of gentamicin, kanamycin, and streptomycin. To determine whether or not the insensitivity is due to a lack of antibiotic distribution to the avian cochlea, the distribution of gentamicin to the cochlea of the White Leghorn chicken embryo was compared to the distribution to the cochlea of the recently hatched White Leghorn chick. Fertile eggs were injected with a maximally tolerated dose of gentamicin sulfate (0.1 mg/egg/day) on incubation days 10-18, and the chicks were injected subcutaneously with either 5 mg (non-ototoxic) or 100 mg (ototoxic) gentamicin sulfate/kg body weight on days 1-9 after hatching. Gentamicin sulfate was histochemically detected within the basilar papilla (the avian equivalent of the organ of Corti) in all treated chicken embryos and chicks by 1 day after the first injection, and the staining was intense after 3 days of treatment. By ultrastructural immunocytochemistry, mild, diffuse labeling for gentamicin sulfate was detected within the endoplasmic reticulum of short and tall hair cells of chicken embryos by incubation day 17. Moderate labeling of gentamicin sulfate was detected in the infracuticular region of lysosomes of hair cells in chicks receiving 5 treatments of gentamicin sulfate at 5.0 mg/kg body weight and after 1 treatment of gentamicin sulfate at 100 mg/kg body weight.(ABSTRACT TRUNCATED AT 250 WORDS)