Classification of unit types in the anteroventral cochlear nucleus of laboratory mice

This report introduces a system for the objective physiological classification of single-unit activity in the anteroventral cochlear nucleus (AVCN) of anesthetized CBA/129 and CBA/CaJ mice. As in previous studies, the decision criteria are based on the temporal properties of responses to short tone bursts that are visualized in the form of peri-stimulus time histograms (PSTHs). Individual unit types are defined by the statistical distribution of quantifiable metrics that relate to the onset latency, regularity, and adaptation of sound-driven discharge rates. Variations of these properties reflect the unique synaptic organizations and intrinsic membrane properties that dictate the selective tuning of sound coding in the AVCN. When these metrics are applied to the mouse AVCN, responses to best frequency (BF) tones reproduce the major PSTH patterns that have been previously demonstrated in other mammalian species. The consistency of response types in two genetically diverse strains of laboratory mice suggests that the present classification system is appropriate for additional strains with normal peripheral function. The general agreement of present findings to established classifications validates laboratory mice as an adequate model for general principles of mammalian sound coding. Nevertheless, important differences are noted for the reliability of specialized endbulb transmission within the AVCN, suggesting less secure temporal coding in this high-frequency species.