Quantitative analysis of damaging hair cells in cochleae of aging Fischer 344 rats / 解放军医学杂志

ABSTRACT

Objective To make a quantitative analysis of damaging hair cells,and investigate the progression pattern of cochlear pathology and the primary death pathway of hair cells in cochleae of aging Fischer 344 rats.Methods Thirty-two Fischer 344 rats were used in this experiment.The animals were assigned to two groupsrats in young group (n=13) were 3-4 months old,and in aging group (n=19) were 20-27 months old.Rats in aging group were further divided into two subgroups based on the animals' age20-23-month subgroup (n=13) and 24-27-month subgroup (n=7).The auditory brainstem response (ABR) thresholds of both ears elicited with tone bursts at 5,10,20 and 40 kHz were measured in both young,and aging Fischer 344 rats.Upon completion of the auditory test,animals were decapitated,and both left and right bullae were exposed.Following fixation,whole specimens comprising the basilar membrane with Corti organ were separated from the modiolus.Propidium iodide (PI),a popular DNA intercalating fluorescent probe was used to trace the morphological changes in hair cell nuclei,and a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was used to detect nuclear DNA fragmentation in the aging cochleae.Filamentous actin (F-actin),an important structural protein of outer hair cells (OHCs),was stained with FITC-labeled phalloidin to illustrate the morphologic viability of cuticular plate and the stereocilia for affirming the missed OHCs.Each Corti organ was thoroughly inspected from the apical to the basal turns of the cochlea under a fluorescence microscope.The numbers of damaging OHCs including missed nuclei,condensed nuclei and swollen nuclei were documented,and a cochleogram was drawn.Results There were significant thresholds at all tested frequencies between the young and aging rats (P