Transfer Properties of the Hair Cell-Afferent Fiber Synapse

Erica C. Keen

OAI: oai:digitalcommons.rockefeller.edu:student_theses_and_dissertations-1117

The perception of sound is initiated in the inner ear by the conversion of vibrational energy into a neural code, a transduction process achieved by the chemical synapses of hair cells in the auditory periphery. Thus, the operation of the hair cellâs presynaptic active zone is key to understanding auditory transduction. However, the lack of suitable experimental systems in which to investigate both the presynaptic and postsynaptic aspects of this synapse with high resolution has limited our understanding of its functional characteristics. This work describes the development of a novel in vitro preparation of the amphibian papilla from Rana catesbeiana that provides electrical access to the pre- and postsynaptic elements of the hair cellâs afferent synapse. The transfer properties of this ribbon-type synapse have been explored with a variety of electrophysiological techniques, including whole-cell recordings, capacitance measurements, and iontophoresis. Glutamate is released from hair cells in response to Ca2+ influx through L-type Ca2+ channels and is detected by AMPA receptors in postsynaptic fibers. Gradations in the extent of presynaptic stimulation are encoded by a linear increase in the postsynaptic response with respect to the presynaptic Ca2+ current, a relation imparted primarily by an increase in the frequency of release events. Both spontaneous and evoked postsynaptic signals are stereotyped in waveform but highly variable in amplitude. Determination of the size of the quantal response provides compelling evidence that the majority of these events are multiquantal. Multiquantal events may originate from individual active zones and do not typically saturate postsynaptic receptors, thus suggesting that they may have functional significance. The results presented in this study are most consistent with compound exocytosis as the dominant form of transmitter release at individual hair-cell active zones.

auditory transduction auditory hair cells amphibian papilla Rana catesbeiana Life Sciences