The ototoxic effects of gentamicin on the vestibular maculae in pigmented guinea pigs.

The normal density of the sensory hair cells of the utricular macula in pigmented guinea pigs was examined. The central region had a greater sensory cell density than the peripheral region. The effect of three different doses of gentamicin on the sensory hair cells was quantified. An increase in sensory cell damage was found with increasing doses of gentamicin. A differential regional sensitivity occurred. The central region was more vulnerable to gentamicin than the periphery. Only the central region of the saccular macula was examined, but no sensory cell losses were found with any of the dose regimes used. The utricular macula is therefore more sensitive to gentamicin than the saccular macula. This work was compared with a similar study using albino guinea pigs, and it was found that the pigmented animals are probably more resistant to ototoxic damage.

The ototoxic effects of different doses of gentamicin on the cochlea of pigmented guinea pigs.

The aims of this study were twofold: to obtain baseline data on gentamicin ototoxicity in the pigmented guinea pig, and to compare this data with an earlier study in the albino guinea pig. Animals were given ten consecutive daily doses, subcutaneously, of gentamicin at either 50, 75 or 100 mg/kg. Control animals received equivalent volumes of saline. After 3 weeks the animals were killed and their cochleae examined by light microscopy for hair cell damage. Hair cell damage was mapped onto cochleograms and subsequently quantified. Three sets of comparisons of hair cell damage were made: gentamicin group versus control group for each dose; comparisons between doses; pigmented animals versus albino animals. It was found that cochlear hair cell damage increased with increasing dose of gentamicin: 50 mg/kg was minimally ototoxic, 75 mg/kg was more ototoxic and 100 mg/kg was highly ototoxic, affecting a large extent of the spiral organ. There was a large (statistically significant) difference between the lower doses and the damage caused by 100 mg/kg. The pigmented-albino animal comparison showed albino guinea pigs to be more susceptible to gentamicin.