Figure 1.
Type I spiral ganglion neuron physiology in the acutely explanted organ of Corti with cochlear ganglion. A, Schematic cross-section of the cochlear explant, showing the organ of Corti (right) and the peripheral neurites of type I SGNs (one highlighted in black) connected to somata in the cochlear ganglion (left). Each type I SGN is nonbranched and receives input from one IHC presynapse via a single, postsynaptic bouton-type connection. The synaptic region at the base of the IHC is enlarged in B. B, Intracellular patch-clamp recordings were made from the postsynaptic boutons, connected to their nonmyelinated neurites ≈30 μm in length, which exit the organ of Corti at the foramina nervosa. Beyond this small perforation in the basilar membrane (not on the scheme) are the NaV1.6-positive heminodes and the beginnings of the myelinated segments, and then several nodes of Ranvier before the cochlear ganglion. Due to the approach vector of the electrode, recorded boutons most likely innervated the hemisphere of the IHC that faced the cochlear ganglion (i.e., the 4 SGNs highlighted in black). Drawings are approximately to scale. C, In current-clamp mode, excitatory stimuli (e.g., arrow) were injected into boutons to measure the time course of depolarization and spike generation (top trace, left). Ca2+-dependent synaptic transmission (e.g., arrowheads) from IHCs evoked EPSPs and so-called spontaneously occurring action potentials. D, In the same recording in voltage-clamp mode, neurotransmitter release events from the IHC were measured as EPSCs of variable size and shape.