Tonotopic gradient of intrinsic and synaptic properties in the rat principal LSO neurones

JIMENA BALLESTERO; ROBERTA DONATO; SIMON FOSTER; DAVID MCALPINE

Baltimore

Congreso; Thirty-sixth annual midwinter research meeting of the association for research in otolaryngology; 2013

Association for Research in Otolaryngology

BackgroundThe lateral superior olive (LSO) and medial superior olive (MSO) are the first nuclei in the ascending auditory pathway that encode binaural information. The classical view of the function of the LSO is that it encodes interaural leveldifferences by weighting excitatory and inhibitory inputs originating from the ipsilateral and contralateral cochlear nucleus respectively. Nevertheless, it has been shown that LSO neurons are heterogeneous both in their intrinsic properties (Barnes-Davies et al., 2004; Remme et al., 2012) as well as in their synaptic inputs (Tsuchitani 1977). Moreover, some of these characteristics vary along the tonotopic axis. In addition, it has been shown that LSO neurons are capable of encoding interaural time differences in the envelope of high frequency sounds (Joris and Yin 1995). Therefore, it has become clear in recent LSO neuronal models the importance of including this heterogeneity to fully understand the encoding properties of the LSO. The aim of the present work is to study the intrinsic electrical properties of principal LSO neurones and the characteristics of their synaptic inputs along the tonotopic axis.MethodsPatch clamp whole cell recordings were made in LSO cells from P14 rat brainstem slices. Resonant properties of pLSO neurones were evaluated applying a current ZAP stimulus. Synaptic activity was evoked by use of a concentric bipolar stimulator placed at the fibre bundle that projects from the ipsilateral AVCN to the LSO.ResultsWe demonstrate a gradient of resonances in the rat LSO where most of the pLSO cells from the lateral limb exhibit a peak resonance around 300 Hz while all the medial ones exhibit low-pass profiles. To further investigate the pLSO cells intrinsic ability to process high frequency inputs, action potentials were evoked either by injecting current pulses or by synaptic stimulation at rates ranging from 50 to 700 Hz. ConclusionOur data indicate a gradient in resonance filter properties along the presumed tonotopic gradient of the LSO of the rat that could underpin a transition in neural coding from one favouring extraction of temporal information conveyed in the stimulus envelope to one favouring the extraction of stimulus energy (level).