ABSTRACT
Models in which a single large systemic dose of gentamicin is used to cause near-synchronous hair cell (HC) loss in the basal end of the chick cochlea have proven increasingly useful in the study of HC regeneration. We quantified the amount of HC death, as a percentage of the length of the basilar papilla, following single doses of 200 mg/kg and 300 mg/kg of gentamicin in 23-day-old chicks. Following 200 mg/kg of gentamicin, there was total HC loss in the basal 18.0% of the sensory epithelium and partial HC loss in the basal 26.3%. Following 300 mg/kg of gentamicin, there was total HC loss in the basal 30.5% of the epithelium and partial HC loss in the basal 40.9%. The second goal of this study was to determine whether cannula implantation in the inner ear, and infusion of bromodeoxyuridine causes HC damage. We found that creation of a fistula in the labyrinth is not associated with HC damage, but that cannula implantation can cause HC death, and can also cause potentiation of gentamicin-induced HC death. Revision of the cannula and surgical technique to ensure minimal penetration into the labyrinth almost entirely eliminated these effects. We conclude that surgical technique is critical in experimental models in which the labyrinth is violated.
Subject(s)
Cochlea/drug effects , Ear, Inner/surgery , Gentamicins/toxicity , Hair Cells, Auditory/drug effects , Animals , Bromodeoxyuridine/administration & dosage , Bromodeoxyuridine/toxicity , Catheterization , Cell Death/drug effects , Chickens , Cochlea/pathology , Cochlea/physiology , Disease Models, Animal , Dose-Response Relationship, Drug , Epithelium/drug effects , Epithelium/pathology , Epithelium/physiology , Gentamicins/administration & dosage , Hair Cells, Auditory/pathology , Hair Cells, Auditory/physiology , RegenerationABSTRACT
Survival surgeries upon chicks are commonly used in auditory research. Appropriate anesthesia is usually obtained with intramuscular or intraperitoneal injections of systemic agents. These techniques have several drawbacks, including delayed onset of anesthesia, difficulty in adjusting the dosage to accomodate individual animals' different responses, prolonged recovery times, and in some cases substantial mortality. We present a technique of administering inhaled isoflurane via an endotracheal tube which we have used for over a year with excellent results. With this agent, onset of deep anesthesia is very rapid, dosage can be titrated readily, overdosage is survivable, complete recovery occurs within a few minutes and mortality is rare. This technique may be valuable for other auditory scientists performing survival surgery in avian species.
