Neural Responses to Injury: Prevention, Protection and Repair; Volume 6: Protecting the Auditory System and Prevention of Hearing Problems

Book excerpt: The experimental animals used during this period for the project, Neural Responses to Injury: Prevention, Protection, and Repair, Subproject: Protecting the Auditory System and Prevention of Hearing Problems, are as follows: Species, Guinea Pig, Number Allowed, 276, Number Used, 83, LSU IACUC# 1061. ANIMAL PROJECT: The SPECIFIC MMS of this study are to demonstrate and explore mechanisms for preventing the effects of intense sound. In years 01, and 02 we discovered that continuous, ipsilateral primary stimulation (CM-LIPS) will produce complex changes in the mechanics of the cochlea, possibly related to toughening In year 03 we discovered that ATP is involved in generating this complex mechanics. We extended the noise exposure studies and found that continuous noise is less effective than interrupted noise in inducing "toughing" Cellular mechanism studies discovered that ATP kills outer hair cells in vitro and in vivo, indicating that ATP may be a key player in noise-induced deafness and toughening. HUMAN PROJECT: We have found that binaural noise suppresses linear click evoked emissions twice as much as ipsilateral noise and 3 times as much as contralateral noise. However, subjects with noise exposure often show poor or reduced emissions when the stimulus is a click. Of 20 subjects enrolled and 13 completely tested so far in the multi-day protocol, subjects with noise exposure effects at higher frequencies show MORE suppression at and around 1500 Hz than do subjects with no hearing loss. This may support the original hypothesis in this program that "Noise Tender Ears" will show different emission suppression patterns from ears that are tough.