ABSTRACT
Abstract
Introduction:
Noise-induced hearing loss is one of the most common forms of
sensorineural hearing loss. Nevertheless, the mechanisms of
noise-induced hearing loss are still not fully understood.
Objective:
To investigate the dynamics of inflammatory responses in the mammalian
cochlea following
noise trauma at two different times, once during the
light cycle and once during the dark.
Methods:
We challenged C57BL/6J
mice with moderate, continuous
noise trauma at either 9 a.m. or 9 p.m. Auditory function, histological changes in
hair cells, and modifications in
gene expression levels of inflammatory mediators were assessed at specific
time points. Shifts in
auditory brainstem response thresholds were measured at 1, 3, 7 and 14 days after
noise exposure to
measure potential
noise-induced hearing loss. Cochlear basilar-
membrane immunofluorescent
staining was performed at 3 and 14 days after
noise exposure. The
mRNA levels of several inflammatory mediators were measured via
quantitative real-time polymerase chain reaction before (pre) and after (0, 3, 12, 24 and 72 h)
noise exposure.
Results:
We found that all
noise-exposed
mice developed a temporary threshold shift and that there were no significant differences between daytime and nighttime
noise exposures in terms of inducing
hearing-threshold shifts. Similarly, we did not detect significant histological changes in
hair cells between these two groups. However, we discovered an interesting phenomenon in that the peak
mRNA levels of
IL-1β,
IL-6, CCL2 and TNF-α were higher in day
noise-exposed
mice compared to those in night
noise-exposed
mice, and these
mRNA levels subsided more slowly in day
noise-exposed
mice.
Conclusion:
Overall, these observations suggest that the circadian timing of
noise exposure has a significant effect on
noise-induced inflammatory responses in the
mouse cochlea and that a greater inflammatory response might occur after daytime exposure.