Resonant and integration properties of principal LSO neurons

JIMENA BALLESTERO; ROBERTA DONATO; MICHIEL REMME; JOHN RINZEL; DAVID MCALPINE

San Diego, CA

Congreso; 37th annual midwinter research meeting of the association for research in otolaryngology; 2014

Association for Research in Otolaryngology

BackgroundNeurons in the medial superior olive (MSO) are specialised to extract information concerning the temporal fine structure of sounds underpinning sensitivity to interaural time differences (ITDs). Conversely, neurons in the lateral superior olive (LSO) neurons extract interaural level differences (ILDs) and ITDs conveyed in the envelope of high frequency sounds (envelope-ITDs). This implies that neurons in the auditory pathway should have the flexibility of extracting these different features either by circuit computation or by filtering inputs at the single cell level. We recently described an intrinsic resonance in the electrical response of principal cells in the MSO/LSO, for which the peak resonance frequency (fres) decreases as a neuron?s (presumed) characteristic frequency increases. Through a modelling approach we showed that this resonant gradient would underlie the transition from coding of temporal fine structure to coding of temporal envelope (Remme et. al. 2013 under revision). MethodsHere, we further explore the gradient in resonance across the LSO and its consequence for the integration properties of principal neurons. Patch-clamp, whole-cell recordings were made in LSO neurons from P14 rat and MSO neurons of P6-10 guinea pig brainstem slices. ResultsResonant properties of principal LSO and MSO neurons were evaluated by applying subthreshold current ZAP stimulus. As previously reported MSO neurons showed high fres (~400Hz) while LSO neurons showed either lower fres (~80Hz) or low pass profiles. By applying suprathreshold ZAP stimulus we showed that resonant neurons fire action potentials when the inputs frequency matches fres. Blocking either Kv1.1 channels or HCN channels abolished resonant responses, demonstrating a role for both of these currents in resonant behaviour. As previously reported all resonant neurons presented phasic firing. We tested whether spike initiation was triggered by a fix change in voltage (voltage threshold) or if depended the rate at which the voltage changed (slope threshold) by applying a family of depolarization ramps of decreasing slope. Tonically-firing neurons responded as voltage detectors while phasically-firing neurons were sensitive only to fast, rising inputs. Blocking Kv1.1 channels in phasic neurons abolished their slope sensitivity. ConclusionsOur data supports the MSO/LSO resonant gradient as a mechanism for filtering auditory inputs. Furthermore, we provide details on the molecular mechanism involved in the resonant response.