@inproceedings {Zhang1800_2016,
	year = {2016},
	author = {Zhang, Lichun and Stachowiak, Roksana and Köppl, Christine},
	title = {Loss of inner hair cell afferent synapses in aging gerbils},
	booktitle = {Assoc. Res. Otolaryng. MidWinter Meeting (ARO)},
	URL = {http://c.ymcdn.com/sites/www.aro.org/resource/resmgr/Abstract_Archives/UPDATED_2016_ARO_Abstract_Bo.pdf},
	abstract = {Background
Age-related hearing loss is well documented in gerbils more
than 2 years old. Outer hair cell (OHC) loss, mostly used as
an indicator of age-dependent hearing loss, is scattered and
mainly found in apical and basal half-turns. However, loss of
OHC is not well correlated with hearing loss, as assessed by
CAP thresholds. In addition, inner hair cells (IHC) are rarely
missing. A reduction in the number of synapses between
afferent neurons and IHC has been reported in ageing mice
(Sergeyenko, et al., J Neurosci., 2013, 33:13686-13694). In
gerbils, few studies have focused on synapses, mainly due
to technical difficulties with labeling (Meyer AC, et al. Nat
Neurosci, 2009, 12:444-453). In this study, we present reliable
pre- and postsynaptic immunoloabeling of afferent synapses
in gerbils of different ages. We followed changes in the
synapses with ageing, to investigate a potential mechanism
for age-related hearing loss.
Methods
Quiet-aged gerbils, 2 to 43 months old, were perfused
transcardially with 4% paraformaldehyde under deep
anesthesia with sodium pentobarbital. Cochleae were
harvested immediately after perfusion and decalcified in
0.5 M EGTA for 2 days at 4°C. An anti-CTBP2 antibody (BD
Biosciences, No. 612044) and an anti-GluR2 (Millipore MAB
397) were used to label presynaptic ribbons and postsynaptic
receptors, respectively. An anti-Myosin VIIa antibody (Proteus
Biosciences 25-6790) labeled hair cells. Four different
regions, located at 3.8, 5.19, 6.64, and 8.13 mm from the
apex, corresponding to 2, 4, 8 and 16 kHz respectively
(Müller M, Hear Res, 1996, 94:148–156) were examined with
confocal microscopy. At each location, structures co-labeled
with anti-CtBP2 and anti-GluA2 were defined as functional
afferent synapses and quantified.
Results
The staining methods for both pre- and post-synaptic markers
were reliable and repeatable at all ages. The total length of 6
cochleae analyzed to date was 11.6 ±0.45 mm. Preliminary
data showed that both the pre- and post- synaptic markers
decreased with age. At the 2 kHz region, afferent synapse
numbers changed from 21/IHC in gerbils between 2 and 17
months of age, to 10.6/IHC in 43 months old animals. At the
regions corresponding to 4, 8, and 16 kHz, synapse numbers
decreased more gradually with age.
Discussion
In conclusion, synapse loss occurs much earlier than OHC
loss in ageing gerbils and therefore could be a more reliable
indicator of age-related hearing loss. However, the relation
between synapse loss and age-related hearing loss still
needs clarification.
Funding
This research is supported by the program of Cluster of Excellence
“Hear4all”.}
}