title: High Entrainment Constrains Synaptic Depression Levels of anIn vivoGlobular Bushy Cell Model.
abstract: Globular bushy cells (GBCs) located in the ventral cochlear nucleus are an essential part of the sound localization pathway in the mammalian auditory system. They receive inputs directly from the auditory nerve and are particularly sensitive to temporal cues due to their synaptic and membrane specializations. GBCs act as coincidence detectors for incoming spikes through large synapses-endbulbs of Held-which connect to their soma. Since endbulbs of Held are an integral part of the auditory information conveying and processing pathway, they were extensively studied. Virtually allin vitrostudies showed large synaptic depression, but on the other hand a fewin vivostudies showed relatively small depression. It is also still not well understood how synaptic properties functionally influence firing properties of GBCs. Here we show how different levels of synaptic depression shape firing properties of GBCs inin vivo-like conditions using computer simulations. We analyzed how an interplay of synaptic depression (0-70%) and the number of auditory nerve fiber inputs (10-70) contributes to the variability of the experimental data from previous studies. We predict that the majority of synapses of GBCs with high characteristic frequencies (CF > 500 Hz) have a rate dependent depression of less than 20%. GBCs with lower CF (<500 Hz) work also with strong depressing synapses (up to 50% or more). We also showed that synapses explicitly fitted toin vitroexperiments with paired-pulse stimuli did not operate properly inin vivo-like conditions and required further extension to capture the differences betweenin vitroandin vivoexperimental conditions. Overall, this study helps to understand how synaptic properties shape temporal processing in the auditory system. It also integrates, compares, and reconciles results of various experimental studies.
authors.affiliation: Bio-Inspired Information Processing, Technische Universität München München, Germany.
authors.forename: Marek
authors.initials: M
authors.lastname: Rudnicki
authors.affiliation: Bio-Inspired Information Processing, Technische Universität München München, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Hemmert
keywords: auditory pathway; cochlear nucleus; computational model; globular bushy cell; high-sync neurons; short term depression; sound localization; temporal processing