Cochlear hair cells convert sound signals into receptor potentials and subsequently, at their afferent synapses with auditory nerve fibers, into firing rates that are relayed to the central nervous system. Hair cell ribbon synapses, like retinal ribbon synapses, are highly specialized for fast and continuous glutamate release. The presynaptic ribbon’s role is poorly understood, however, it has been proposed to support the continuous release of vast numbers of vesicles. The activity pattern of auditory nerve fibers is quite diverse, firing rates at rest can vary from less than 1 AP per s to 150 APs per s, and in response to sound, fibers activate with different thresholds and show diverse rate level functions. Auditory nerve fibers with different response patterns can contact the same inner hair cell in the cochlea. Therefore, properties of the auditory nerve fiber activity must be set at the individual hair cell ribbon synapses.

The Glowatzki lab studies the pre- and postsynaptic properties at inner hair cell ribbon synapses that set and modulate auditory nerve fiber properties. Mostly dendritic whole cell recordings from auditory nerve fibers directly where they contact the hair cell are used in excised cochlear tissue, sometimes parallel with hair cell recordings. Lately we have characterized the calcium dependence of release at the hair cell synapse and found it to be linear (Goutman and Glowatzki, 2007). We are now investigating the mechanisms and role of multivesicular release at the hair cell ribbon synapse. In my talk I will elaborate on different modes of release at individual synapses that may play a role in setting auditory nerve fiber properties.

Selected Publications:
Glowatzki, E., Fuchs, P.A. Transmitter release at the hair cell ribbon synapse. (2002) Nature Neuroscience (5) 2:147-154.

Pyott, S., Glowatzki, E., Trimmer, J., Aldrich, R., (2004) Extrasynaptic localization of inactivating BK channels in mouse inner hair cells. Journal of Neuroscience 24(43):9469-9474.

Glowatzki, E., Chen, N., Hiel, H., Jin, L., Yi, E., Tanaka, K., Ellis-Davies, J.C.R., Rothstein, J.D., Bergles, D.E. (2006) The glutamate-aspartate transporter (GLAST) mediates glutamate uptake at inner hair cell afferent synapses in the mammalian cochlea. Journal of Neuroscience 26(29):7659-64.

Tritsch, NX, Yi, E, Gale, JE, Glowatzki, E, Bergles, DE. The origin of spontaneous activity in the developing auditory system. Nature 2007, 450:50-55.

Seal, RP, Akil, O, Yi, E, Weber, CM, Grant, L, Yoo, J, Clause, A, Kandler, K, Noebels, JL, Glowatzki, E, Lustig LR, Edwards, RH, Sensorineural deafness and seizures in mice lacking vesicular glutamate transporter 3. Neuron 2008, 57(2):263-75.

Martinez-Monedero, R, Yi, E, Oshima, K, Glowatzki, E, Edge, ASB (2008) Differentiation of inner ear stem cells to functional sensory neurons. Developmental Biology 68(5):669-84.

For more information see our website - http://neuroseries.info.nih.gov