Tuberculoventral cells of the dorsal cochlear nucleus of mice: intracellular recordings in slices

Abstract

1. Intracellular recordings were made from six tuberculoventral cells (also called vertical or corn cells) whose identity was confirmed by labeling with biocytin, with the aim of understanding their projection patterns and how their synaptic inputs and their intrinsic electrical properties shape their responses to activation of auditory nerve fibers. 2. The cell bodies, dendrites, and local axonal terminals of all six tuberculoventral cells lay in narrow bands, 70-100 microns wide and parallel to the path of auditory nerve fibers, in the dorsal cochlear nucleus (DCN). Terminals in the ventral cochlear nucleus (VCN) also lay in narrow bands, parallel to the path of auditory nerve fibers in either or both the anteroventral and posteroventral cochlear nuclei. 3. When depolarized with current, tuberculoventral cells fired regularly. The peaks of action potentials were usually overshooting and were followed by two afterhyperpolarizations, resembling other cells of the DCN. Unlike some other cells in the DCN, however, neither of the afterhyperpolarizations resulted in an undershoot of the resting potential in the presence of depolarizing currents stronger than 0.3 nA. The second afterhyperpolarization was more variable than the first. 4. Shocks to the auditory nerve evoked monosynaptic as well as polysynaptic excitation and weak polysynaptic inhibition. These results show that, in addition to receiving excitation directly through auditory nerve fibers, tuberculoventral cells also receive excitation through interneurons. 5. To locate the interneurons in the cochlear nuclei whose activation affects a tuberculoventral cell monosynaptically or polysynaptically, glutamate was applied focally to various loci in the VCN while responses were recorded in a target tuberculoventral cell that was subsequently labeled. Excitation of this tuberculoventral cell arose from a rostrocaudal band in the VCN. 6. The results are consistent with tuberculoventral cells receiving excitatory synaptic input from auditory nerve fibers and from T stellate cells in the VCN. They could be inhibited by D stellate cells in the VCN.