Facilitation and depression determine timing of synaptic responses at the IHC ribbon synapse

JUAN D. GOUTMAN

Huerta Grande, Córdoba

Congreso; XXVI Congreso Annual Sociedad Argentina de Investigación en Neurociencia; 2011

Sociedad Argentina de Investigación en Neurociencia

The auditory system must represent different features of the acoustic environment, including the temporal structure of incoming sounds. It is well established that auditory nerve fibers are able to fire at a particular phase of low-frequency periodic stimuli. This capacity is driven by the transmitter released from inner hair cells (IHC) in the cochlea and is known to occur regardless of the intensity of the stimulus. In the current study, we decided to investigate the mechanisms by which IHC are able to release neurotransmitter with constant timing even with stimuli of different intensities. We used simultaneous recordings from IHC and postsynaptic boutons of auditory nerve neurons. We firstly observed that with trains of square pulse at 250 Hz IHC released neurotransmitter with constant delay. Synaptic responsiveness was evaluated at the end of these trains of different intensities, observing that stronger stimuli produced deeper synaptic depression and longer delays. Therefore, during repetitive stimulations a given pulse promoted release by allowing Ca2+ in the cell, but simultaneously, provoked depression due to partial depletion of vesicles. We propose that an equilibrium would be established between pulse intensity and depression, determining a constant synaptic timing.