PRIMARY AUDITORY afferent fibers transfer information regarding frequency, intensity, and timing to the central nervous system (CNS). The high temporal precision and indefatigable nature of the response is a result of pre- and postsynaptic specializations. Presynaptically the auditory hair cell contains an electron dense structure known has a synaptic ribbon which is a hallmark of sensory cells that respond to graded input. The synaptic ribbon is thought to play a role in vesicle trafficking and release as acute destruction1 of the ribbon or mutation2 of ribbon anchoring proteins alters release. Less is known about postsynaptic specializations.
My research is focused at this primary auditory synapse using the turtle auditory papilla as a model. The turtle auditory papilla is a robust mature hearing organ whose hair cells are innervated by a single afferent fiber which contains 20 to 50 synaptic contacts depending upon frequency position. In contrast mammalian inner hair cells have 15-20 afferent fibers per cell each with a single synapse. The auditory fibers in the turtle exhibit electrical resonance are tuned to frequencies of 30 to 700 Hz and show phase locking throughout the range. Tonotopic differences have been shown for the calcium currents, BK channels and the number of synapses.
We have characterized this synapse in terms of EM to define vesicles pools by location and correlated these pools with capacitance measurements to define release kinetics and vesicle trafficking. We developed a capacitance technique to measure release in real time (dual sine technique) and demonstrated two components of release, a linear component that varied with calcium influx and corresponds to a vesicle population near the synapse and a second superlinear component whose release was constant and required recruitment of vesicles from more distant pools.
Postsynaptic recordings from the afferent fiber in the turtle papilla have identified fast AMPA EPSCs that vary in amplitude by over 15X which exhibit stochastic release. Temporal summation of EPSCs across synapses in this multi-synapse fiber may be important in action potential generation. Currently I am performing paired patch clamp recordings of hair cell and afferent fiber to confirm and extend findings with Cm and single fiber recordings.
I have worked in the Ricci lab for over 13 years beginning at Louisiana State University in New Orleans and then chased by Hurricane Katrina to the bay area for the past seven years. My background is in insect physiology and I was with the DuPont Chemical Company for 17 years first doing mode of action studies with potential insecticides and supporting chemical synthesis programs and then at the DuPont-Merck joint venture where I was with the CNS group.
- Snellman et. al. Acute destruction of the synaptic ribbon reveals a role for the ribbon in vesicle priming. Nat Neurosci 2011 Jul 24;14(9):1135-41.
- Jing et. al. Disruption of the presynaptic cytomatrix protein bassoon degrades ribbon anchorage, multiquantal release, and sound encoding at the hair cell afferent synapse. 2013 J Neurosci. 2013 Mar 6;33(10):4456-67.