Comparison of Methods for the Histological Evaluation of Odontocete Spiral Ganglion Cells

SIMPLE SUMMARY: Hearing is arguably the primary sensory and communication channel for cetaceans. The study of diverse physiological and pathological events involving this system, requires standardized and reliable protocols for processing valuable and scarce samples such as the ears of cetaceans. As part of our research, standardized tissue processing protocols were developed in order to improve our knowledge regarding the anatomy and pathological changes of this sensorial system, including the nervous structures of the ear. The results obtained suggest that ethylenediaminetetraacetic acid (EDTA)-based decalcifying solutions are key for correct evaluation of bony tissue structures such as the ear of cetaceans. ABSTRACT: Cetaceans greatly depend on their hearing system to perform many vital activities. The spiral ganglion is an essential component of the auditory pathway and can even be associated with injuries caused by anthropogenic noise. However, its anatomical location, characterized by surrounding bony structures, makes the anatomical and anatomopathological study of the spiral ganglion a difficult task. In order to obtain high-quality tissue samples, a perfect balance between decalcification and the preservation of neural components must be achieved. In this study, different methodologies for spiral ganglion sample preparation and preservation were evaluated. Hydrochloric acid had the shortest decalcification time but damaged the tissue extensively. Both formic acid and EDTA decalcification solutions had a longer decalcification time but exhibited better preservation of the neurons. However, improved cell morphology and staining were observed on ears pretreated with EDTA solution. Therefore, we suggest that decalcifying methodologies based on EDTA solutions should be used to obtain the highest quality samples for studying cell morphology and antigenicity in cetacean spiral ganglion neurons.