Changes in the avian cochlea after single high-dose gentamicin

Purpose: Define the time course of functional and anatomical damage and sub sequent recovery (by regeneration) of hair cells in the chicken inner ear a fter a single high-dose of gentamicin. Materials and Methods: Broiler chicks were given a single intraperitoneal d ose (200 mg/kg) of gentamicin (n = 39) or saline (n = 39). Functional statu s was evaluated with auditory brainstem response (ABR) thresholds before in jection and before sacrifice at 2, 5, 9, 16, 21, 28, and 70 days postinject ion. The cochleae were then examined with scanning electron microscopy (SEM ) to assess the extent of damage along the cochlea and absolute hair cell n umbers in the basal 15% of the cochlea (high-frequency region). Results: Considerable variability between animals was seen for both ABR and SEM changes. Damage was maximal at 5 days postinjection with an average AB R threshold shift of 12 dB (range -10 to 50 dB) and basal cochlear damage o f 28% (range 12%-57%). Hair cell counts were significantly decreased in the basal 15% of the cochlea at 5 days. Hair cell regeneration resulted in rap id anatomical and functional recovery, but evidence of hair cell disorganiz ation persisted at 70 days despite improved thresholds. Conclusion: A single high dose of gentamicin produces a significant but var iable anatomical and functional insult in the chick cochlea. Hair cell rege neration results in rapid but incomplete recovery. Copyright (C) 2000 by W. B. Saunders Company.