The Inner Ear
A third aggregate is focused on the inner ear, and particularly on the sensory hair cells in auditory end organs of birds and fish and relevant brainstem structures (Carr, Dooling, Popper, Ryals). Since hair cells in fishes and birds are homologous, it is possible to use the comparative method to explore issues related to inner ear function using the best model for each particular study. Popper is exploring hearing damage and recovery in fish from acoustic over exposure. While far less dramatic in birds than in fishes, both groups also show postembryonic proliferation of sensory cells that continues for an extended time. This occurs in the vestibular otolithic organs in birds, and at a much higher rate (up to several hundred cells per day per end organ) in otolithic organs of fish. These newly proliferated sensory cells are integrated into the function of the endorgans in both groups.
PEOPLE AND PROJECTS
brenda M. ryals (James Madison University) and Robert J. Dooling, Psychology
The Dooling and Ryals laboratories study hair cell regeneration and return of inner ear funcion after trauma extensively. Ryals and Dooling have explored the comparative functional significance of hair cell regeneration in several species of birds following both noise trauma and ototoxic drugs. We now have a much better understanding of species variation and the nature of functional recovery. There are a number of important species differences at the hair cell level in the responses of different species of birds to the same acoustic trauma. We know that much behavioral and anatomical recovery occurs but that functional recovery is never complete even though the hair cell numbers are back to normal and we are examining several aspects of the cellular basis of this lack of complete recovery.
The Belgian Waterslager (BWS) canary has an inherited developmental auditory disorder of the sensory epithelium involving missing and damaged hair cells. This species is constantly regenerating new hair cells and that increasing the rate of regeneration can "cure" some of the inherited threshold loss. This provides an interesting preparation for testing the role of antioxidant, steroids, and various other agents on these processes. Dr. Ryals has been analyzing morphological correlates of this increased sensitivity following synchronous hair cell regeneration. She has shown that the only significant change in the sensory epithelium in BWS following trauma and regeneration is an increase in the number of stereocilia per hair cell. These results strengthen the hypothesis that BWS hereditary hearing loss is a result of abnormal development of (or developmental cues for appropriate alignment of) stereocilia.
Arthur N. Popper, Biology (C-CEBH Director)
The Popper lab continues its work on ultrasound detection in fish which probably evolved so that these fish can detect their major predator, echolocating dolphins. Studies analyze the ultrastructure of the end organ, its development in contrast to the development of a more atypical vertebrate utricle (zebrafish), and physiological mechanisms involved in ultrasound detection.
