Comparative analysis of patch lesions in the chick inner ear following acoustic trauma: optical versus scanning electron microscopy.

Neonatal chicks were exposed to an octave band noise with a center frequency of 1.5 kHz at 116 dB SPL for 4 hours. Seven days following overstimulation, the birds were sacrificed. Their basilar papillae were removed, fixed in 4% paraformaldehyde, and processed in two steps. First, the ears were immunostained with a supernatant of mouse anti-tectorial membrane antibodies, followed by a diaminobenzidine process. Examinations of the papillae under an optical stereo microscope revealed a patch site with a partially regenerated tectorial membrane (referred to as the honeycomb). After the optical studies, the same ears were post-fixed in 1% osmium tetroxide, dehydrated in ethanol, and processed for scanning electron microscopy (SEM). SEM examinations demonstrated a honeycomb-covered patch lesion in the papilla. Patch lesion perimeters were traced from both the optical and SEM images, and patch areas were calculated. Also, papilla height was measured at the midpoint of the inner ear in both groups. These calculations showed that the patch area and papilla height had shrunk by approximately 37% and 33%, respectively, following the SEM methodology. The decrease in these dimensions may be attributed to several steps required for the SEM specimen preparation, such as critical point drying.