Toxic effects of gentamicin on the basilar papilla in the lizard Calotes versicolor. A surface study

Poisonings in reptiles

Reptiles are increasingly being kept as pets in American households. The basic principles of emergency medicine are the same for all species, but reptilian species present special diagnostic challenges to veterinary clinicians when they become ill. Reptiles in captivity can become accidentally poisoned in a variety of ways. Veterinarians treating small animal emergencies must make an effort to familiarize themselves with the large body of literature and resources that are developing regarding both nontraditional exotic companion species and advances in toxicology.

Effects of noise and ototoxic drugs at the cellular level in the cochlea: a review

Currently available information concerning the cellular mechanisms involved in acoustic trauma and aminoglycoside ototoxicity is reviewed to shed some new light on the cellular events that may be related to functional impairment of the auditory organ. Based on the available data, the following postulations can be made concerning the cellular mechanisms involved. 1) The macromolecular disruption of the stereocilia and cuticular plates is the initial cellular event in acoustic trauma. This disruption would affect the micromechanics of the transduction process, leading to temporary threshold shift. Further cellular impairment would involve basic cellular functions such as the protein, lipid, and glucose synthesis needed for cell repair and survival, and such impairment would result in permanent cell injury or cell death, leading to permanent threshold shift. 2) It can be postulated that the cellular mechanisms involved in aminoglycoside ototoxicity include two events. The early event is the reversible blockage of the transduction channels from the endolymph side of the hair cells. The later event is the interference in such cellular functions as protein and/or phospholipid synthesis because of binding of aminoglycoside to the phospholipids and/or protein, leading to cell death. The latter event may be facilitated by penetration or membrane-mediated internalization of the aminoglycoside from the perilymph side of the hair cell.

Gentamicin-induced mitochondrial damage in inner ear sensory cells of the lizard Calotes versicolor

Earlier morphological and histochemical studies on the effects on inner ear sensory cells caused by aminoglycoside antibiotics have failed to give sufficient information of the genesis of these effects. The present study was focused on the phases of progessive mitochondrial changes in sensory cells of the the lizard basilar papilla induced by consecutive large doses of gentamicin. The mitochondria react by swelling, changes in the configuration and number of the cristae and formation of matrical inclusions. Myelin figures are a consistent finding in degenerating cells after gentamicin exposure. These are shown to be derived from changed mitochondria. The final product is an "onion-like" structure which is built of primitive membranes. There is a marked difference in reaction to the damage between individual mitochondria in the same cell. This difference is also evident between individual sensory cells in the same specimen. By studying the phases of the mitochondrial breakdown process in the sensory cell, some additional information on the changes in cell metabolism caused by ototoxic drugs, may be extracted.

Gentamicin-induced changes in RNA content in sensory and ganglionic cells in the hearing organ of the lizard Calotes versicolor. A cytochemical and morphological investigation

The effect of short-term administration of gentamicin on RNA content in isolated sensory and ganglionic cells in the hearing organ of the lizard Calotes versicolor was investigated. The effects of the drug on this biochemical parameter are compared with ultrastructural changes in sensory cells from the same material. In the first test group, daily intraperitoneal injections for 3 to 6 days resulted in a 30-50% decrease of the amount of RNA in sensory and ganglionic cells. No constant ultrastructural changes were recorded in the sensory cells at this point in time. A second test group received 3 or 5 injections of gentamicin and the animals were then left untreated for 21 days. The reduced RNA content persisted in both sensory cells and in ganglionic cells from animals that received 5 injections, whereas the content of RNA in ganglionic cells from lizards that received 3 injections was restored almost to control values at the end of this 21-day period. In the second test group, definite morphological derangements were observed in the sensory cells. The correlation between cytochemical and morphological findings as well as possible modes of action of gentamicin on inner ear ganglionic and sensory cell RNA content are discussed.

Comparative surface studies of ototoxic effects of various aminoglycoside antibiotics on the organ of Corti in the guinea pig. A scanning electron microscopic study

It was the purpose of this study to establish criteria for use in comparing the toxic effects of aminoglycosid antibiotics on the organ of Corti by means of scanning electron microscopy. Amikacin, Tobramycin and Gentamicin were administered twice a day subcutaneously for 10 days to healthy guinea pigs. One group of animals was sacrificed 1 day after completion of the treatment; the other group was allowed to survive 22 days. Depending upon the dosage of the administered drug, Amikacin (150 mg per kg body weight daily, corresponding to 10 times an average recommended human dose) caused pronounced outer hair cell damage even 1 day after the treatment was stopped. At this time Gentamicin and Tobramycin (150 mg per kg body weight daily, corresponding to 50 times an average human dose) showed less damage. After 22 days' survival, late toxic effects were found mainly in Gentamicin- and Tobramycin-treated animals. After 3 weeks, nearly total outer hair cell loss was found in the basal coil, while the 2nd and 3rd coils were often less severely damaged. At this time Amikacin-treated animals showed severe damage in all coils. 300 mg per kg body weight Amikacin (i.e. 20 times the average human dose) showed about the same toxic effect on sensory cells of the guinea pig as did 150 mg Gentamicin or Tobramycin per kg body weight. We are conscious of the fact that there are problems in correlating the weight of a drug and its probable toxic effect. In comparative animal experiments we consider it useful to standardize the time of exposure, the amount of drug administered (e.g. related to the human dose) and the survival time.