RESEARCH ARTICLE Glycinergic axonal inhibition subserves acute spatial sensitivity to sudden increases in sound intensity Tom P Franken1,2*, Brian J Bondy3, David B Haimes3, Joshua H Goldwyn4, Nace L Golding3, Philip H Smith5, Philip X Joris1* 1Department of Neurosciences, Katholieke Universiteit Leuven, Leuven, Belgium; 2Systems Neurobiology Laboratory, The Salk Institute for Biological Studies, La Jolla, United States; 3Department of Neuroscience, University of Texas at Austin, Austin, United States; 4Department of Mathematics and Statistics, Swarthmore College, Swarthmore, United States; 5Department of Neuroscience, University of Wisconsin-Madison, Madison, United States Abstract Locomotion generates adventitious sounds which enable detection and localization of predators and prey. Such sounds contain brisk changes or transients in amplitude. We investigated the hypothesis that ill-understood temporal specializations in binaural circuits subserve lateralization of such sound transients, based on different time of arrival at the ears (interaural time differences, ITDs). We find that Lateral Superior Olive (LSO) neurons show exquisite ITD-sensitivity, reflecting extreme precision and reliability of excitatory and inhibitory postsynaptic potentials, in contrast to Medial Superior Olive neurons, traditionally viewed as the ultimate ITD-detectors. In vivo, inhibition blocks LSO excitation over an extremely short window, which, in vitro, required synaptically evoked inhibition. Light and electron microscopy revealed inhibitory synapses on the axon initial segment as the structural basis of this observation. These results reveal a neural vetoing mechanism with extreme temporal and spatial precision and establish the LSO as the primary *For correspondence: nucleus for binaural processing of sound transients.
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[email protected] (PXJ) Competing interests: The Introduction authors declare that no A key component of the neuron doctrine is the unidirectional propagation of action potentials, for- competing interests exist.