Morphological Assessment of Pathological Changes

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Abstract
Routine histological examination of the rat larynx, from inhalation toxicity and carcinogenicity studies, has been routinely performed in this laboratory for over 15 yr. This work has identified the larynx as an important target organ with a number of pharmaceuticals, industrial chemicals, agricultural chemicals, and environmental pollutants. The rat larynx contains 5 epithelial types: stratified squamous; low squamoid; respiratory; and 2 forms of pseudostratified cuboidal epithelium. Each epithelial type has a specific location within the relatively complex anatomical configuration of the larynx. The detection of induced changes requires a consistent, thorough and detailed histological examination in order to identify the often subtle changes in the distribution of these epithelial types. Induced lesions show distinct predilection sites, including the ventro-lateral regions anterior to the ventral pouch and the inner aspects of the arytenoid projections. Lesions commonly involve degeneration of the original epithelial cells with subsequent regeneration; hyperplasia and squamous metaplasia. In more severe reactions, the larynx may illustrate epithelial ulceration with exudation. To some extent the changes commonly observed are dependent upon the duration of the study and the dose level employed, rather than the individual compound. Recovery or regression of induced changes is variable and dependent upon the time scale involved and severity or type of initial lesion.