Histologic Methods and Interspecies Variations in the Laryngeal Histology of F344/N Rats and B6C3F1 Mice

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Abstract
The relatively high incidence and variety of lesions induced in the upper respiratory tract of rodents by inhalation of xenobiotics has resulted in considerable attention given to the microscopic anatomy of this area. Specific areas of the rodent laryngeal mucosa appear to be more sensitive to inhaled materials and more likely to contain cellular changes in response to injury. These include the epithelium covering the base of the epiglottis, ventral pouch, and the medial surfaces of the vocal processes of the arytenoid cartilages. There are few good landmarks for trimming rodent larynges to get consistent and accurate sections through these target areas. We have obtained consistently reproducible results by cutting transversely through the easily palpable cricothyroid notch and embedding the entire larynx anterior to this in paraffin with the cut surface against the face of the block. Multiple sections are cut from the caudal larynx toward the epiglottis, unstained sections examined microscopically for orientation, and sections from target areas selected for staining and histopathologic examination. Routine use of these methods for preparation and microscopic examination of sections of the larynx has revealed some variations in normal laryngeal anatomy between Fischer 344 (F344/N) rats and B6C3F1 mice.