OHCs: Synapses

Synaptic organization at the OHC base

R. Pujol

The basal pole of an OHC is contacted by large vesiculated terminals of the medial efferent system. Amongst these efferent synapses can be found one or two little dendritic boutons (green arrow) of a spiral afferent fibre (type II neurons).

This type of organisation is characteristic of most of the OHCs in that part of the cochlea that codes for the mid- and high frequencies (2 to 20 kHz).
d = Deiters' cell; o = OHC
scale bar : 1 µm

M. Lenoir

OHC in the basal turn of a rat cochlea.

A large vesiculated terminal contacts the base of an OHC (o), which is itself in close contact with the Dieters' cell (d); green arrows indicate two small afferent dendritic boutons.

The zoom (right) allows good visualisation of the postsynaptic cistern (blue arrows) and the presynaptic microvesicles, often arranged in small packets close to the membrane.

scale bar: 1 µm

High magnification of synapses between OHC (o) and the type II afferent dendrites (a)

R. Pujol

On serial sectioning, one often encounters an invagination of a spiral afferent dendritic bouton (a) in the OHC (o).   On both sides, membrane densifications (yellow arrows) can be seen. Some vesicles are seen on the presynaptic side (blue arrow).   Below, one can see the internal covering of the endocytic vesicle (red arrow). scale bars: 250 nm scale bar: 250 nm