Ultrastructure of cisternal synapses on outer hair cellsof the mouse cochlea
Copyright © 2013 Wiley Periodicals, Inc., A Wiley Company
- Accepted manuscript online: 9 OCT 2013 12:38PM EST
- Manuscript Revised: 20 SEP 2013
- Manuscript Accepted: 20 SEP 2013
- Manuscript Received: 14 JUL 2013
- NIDCD R01 DC001508 and P30 DC005211.
- NIDCD. Grant Numbers: R01 DC001508, P30 DC005211.
- Cited By
‘C’ (cisternal) synapses with a near membrane postsynaptic cistern are found on motor neurons and other central neurons where their functional role is unknown. Similarly structured cisternal synapses mediate cholinergic inhibition of cochlear hair cells via α9α10-containing ionotropic receptors and associated calcium-activated (SK2) potassium channels, providing the opportunity to examine the ultrastructure of genetically-altered cisternal synapses. Serial section electron microscopy was used to examine efferent synapses of outer hair cells (OHCs) in mice with diminished or enhanced cholinergic inhibition. The contact area of efferent terminals, the appositional area of the postsynaptic cistern, the distance of the cistern from the plasma membrane, and the average width of the cisternal lumen were recorded. The synaptic cisterns of wildtype OHCs were closely aligned (14 nm separation) with the hair cell membrane and co-extensive with the micrometers-long synaptic terminals. The cisternal lumen averaged 18 nm so that the cisternal volume was approximately 30% larger than that of the cytoplasmic space between the cistern and the plasma membrane. Synaptic ultrastructure of α9L9’T knock-in OHCs (‘AChR gain of function’) were like those of wildtype littermates except that cisternal volumes were significantly larger. OHCs of SK2 knockout mice had few small efferent terminals. Synaptic cisterns were present, but smaller than those of wildtype littermates. Taken together, these data suggest that the cistern serves as a sink or buffer to isolate synaptic calcium signals. J. Comp. Neurol., 2013. © 2013 Wiley Periodicals, Inc.