Modulatory influences on time-coding neurons in the ventral cochlear nucleus

Bushy cells of the ventral cochlear nucleus are time-coding neurons. They receive axosomatic synaptic terminals from the auditory nerve, the so-called endbulb of Held synapses and project to sound localization centers in the superior olivary complex. Bushy cells are specialized to maintain and even improve the temporal code contained in the auditory nerve activity. In the present review an overview is given of the dynamic features and convergent inputs that modulate the response of bushy cells to auditory stimuli. The biophysics and synaptic specializations and dynamics of these neurons were studied extensively. These studies will be reviewed briefly in the initial part of this paper. In addition to auditory nerve input, powerful but slow inhibitory inputs act on bushy cells. Studies on these inhibitory inputs to bushy cells are discussed as part of this review. Furthermore, evidence for four classes of additional or secondary inputs that also impinge on the bushy cells will be reviewed: 1) small auditory nerve boutons, 2) commissural connections that are either inhibitory or excitatory, 3) multimodal inputs from somatosensory nuclei and 4) descending modulatory axons employing monoaminergic transmitters all interact with the main auditory nerve input in the bushy cells. The present article aims at reviewing how complex the influences on neuronal processing are, already in this early stage of the auditory pathway. It is concluded that the various modulatory influences help to better adapt bushy cell coding functions to dynamics of the sensory world.