Acta Otolaryngol 93: 205-210, 1982 PATTERNS OF HAIR CELL LOSS IN CHICK BASILAR PAPILLA AFTER INTENSE AUDITORY STrMULA TrONI Frequency Organization

Ten-day-old chicks were continuously exposed to pure tones (500, I 500, or 3000 Hz) at 125 dB SPL for 12 hours and sacrificed 10 days after exposure. The basilar papillae were embedded in plastic, sectioned and hair cells were counted at ~OO-!Lm intervals throughout the length of the papilla. The position of hair cell loss along the basilar membrane varied systematically as a log-linear function with the frequency of stimulation. This systematic relationship was used to predict the frequency organization of the chick basilar papilla. It is concluded that although the avian basilar papilla differs greatly in morphological detail from the mammalian cochlea, its response to intense acoustic stimulation is quite similar. The frequency organization of mammalian cochlea has been studied by analysing the location of hair cell loss along the basilar membrane following acoustic trauma (Schuhkneckt, 1953; Stockwell et al. 1969). A close correlation has been found between the location of hair cell loss and the site of maximum displacement of basilar membrane. Although the site of maximum basilar membrane displacement has been studied in avians (Bekesy, 1944), the location of hair cell loss as a function of the frequency of acoustic overstimulation has not previously been investigated. In the preceeding paper (Rubel & Ryals, .1981) we showed that the avian basilar papilla IS affected by acoustic overstimulation in a manner very similar to mammals when exposure duration and survival times are varied. In the present study we describe the position of hair cell loss in avian basilar papilla as a function of the frequency spectra of stimulation. In this way we provide a 'frequency map' of the avian cochlea and examine the correlation between maximum basilar membrane displacement described by Bekesy (1944) and the location of hair ceUloss.