The efferents interconnecting auditory inner hair cells

The work describes the system of efferent terminals that interconnect inner hair cells through a chain of direct somatic synapses organized in repetitive patterns. The efferent boutons were discovered in the apical turns of 12-day-old (hearing) mice. Clusters or short rows of vesiculated boutons are located between adjoining hair cells at the lower half of the receptors, close to their modiolar side. The individual endings, about 1.2 microns in diameter, adjoin inner hair cells and form one synapse per hair cell. On the hair cell side, the synaptic contact is apposed by a classical postsynaptic cisterna. Within a cluster of endings, some synapse simultaneously with either or both neighbouring inner hair cells. The efferent boutons also connect synaptically with each other and with other--different in type--vesiculated and nonvesiculated endings. These endings seem to derive from the climbing collaterals of the inner spiral bundle, and we believe them to be GABAergic.