Regularity of Discharge Constrains Models of Ventral Cochlear Nucleus Bushy Cells

Abstract

The bushy cells of the ventral cochlear nucleus (VCN) are characterized by two unusual features. The first is the large synaptic contact, the endbulb of Held, made by auditory nerve (AN) fibers on bushy cell somata (Brawer and Morest,’ 75; Lorente de No,’ 81; Ryugo and Fekete,’ 82). In the rostral anteroventral cochlear nucleus (AVCN), spherical bushy cells receive a small number of large endbulbs, as few as one to four per cell (Lorente de No,’ 81; Ryugo and Sento,’ 91). In the posterior AVCN and the anterior part of the posteroventral cochlear nucleus (PVCN), endbulbs are smaller (Brawer and Morest,’ 75; Lorente de No,’ 81; Rouiller et al.,’ 86). It is clear that the globular bushy cells in this region receive endbulbs from a larger number of AN fibers than the spherical cells of rostral AVCN, although current estimates of the number of endbulbs per cell are indirect (Spirou et al.,’ 90; Liberman,’ 91). Based on estimates of the total number of endbulbs in the globular bushy cell area (Ryugo and Rouiller,’ 88) and the number of globular bushy cells (Brownell,’ 75; Osen,’ 70), the number of endbulbs per cell has been estimated as about 17 (Spirou et al.,’ 90). In addition to endbulbs, both spherical and globular bushy cells receive smaller bouton terminals from AN fibers (Cant and Morest,’ 79; Lenn and Reese,’ 66; Lorente de No,’ 81; Ryugo and Sento,’ 91; Liberman,’ 91); these terminals increase the numbers of AN fibers per cell, but the contribution of these small terminals to postsynaptic processing is unclear, given their relatively small size compared to endbulbs.