ABSTRACT
This study was aimed at to investigating the protective effect of a combined treatment with glial cell line derived neurotrophic factor (GDNF) and neurotrophin 3 (NT 3) on noise induced outer hair cell (OHC) damage. Guinea pigs were subjected to receiving infusion of an artificial perilymph containing GDNF (100ng/ml) and NT 3 (2 5?g/ml) into one cochlea via a mini osmotic pump. Three days later, the animals were exposed to a 4kHz narrow band noise at 115 dB SPL for 4h. The control animals received the same treatment except GDNF and NT 3. Thresholds of auditory brainstem responses (ABRs), elicited by clicks, were measured before and 3 days after the surgery of the pump implantation, and 10 days following noise exposure. Then, the subjects were sacrificed and the cochleas were stained with Hoechst 33342. The specimens were examined under a fluorescence microscope for quantitative assessment of the OHC nuclear morphology. The results showed that compared with the control animals, the drug treated ones had significant less swollen OHC nuclei ( P
ABSTRACT
To observe the morphological changes in hair cell nuclei in guinea pigs following noise exposure, guinea pigs were exposed to 4 kHz narrow band noise at 115 dB SPL for 4h. The cochleae were collected for the examination of the hair cell nuclei 14 days after the noise exposure. A fluorescent dye, Hoechst 33342,a fluorescent dye, was used to label the nuclear DNA and the specimens were examined under a fluorescence microscope for quantitative assessment of hair cell nuclear damage. There were three types of morphological changes in the damaged hair cell nuclei: nuclear swelling, nuclear condensation (karyopyknosis) and nuclear missing. Nuclear swelling was more frequent than nuclear missing. Nuclear condensation was less frequently found. The results suggested that complicated, long term and non synchronous biological processes might be involved in noise induced hair cell damage. A large number of hair cells with swollen nuclei, which might recover afte wards,still could be seen in the cochlea two weeks after noice exposure.