3D model of frequency representation in the cochlear nucleus of the CBA/J mouse

Abstract

The relationship between structure and function is an invaluable context with which to explore biological mechanisms of normal and dysfunctional hearing. The systematic and topographic representation of frequency originates at the cochlea, and is retained throughout much of the central auditory system. The cochlear nucleus (CN), which initiates all ascending auditory pathways, represents an essential link for understanding frequency organization. A model of the CN that maps frequency representation in 3D would facilitate investigations of possible frequency specializations and pathologic changes that disturb frequency organization. Toward this goal, we reconstructed in 3D the trajectories of labeled auditory nerve (AN) fibers following multiunit recordings and dye injections in the anteroventral CN of the CBA/J mouse. We observed that each injection produced a continuous sheet of labeled AN fibers. Individual cases were normalized to a template using 3D alignment procedures that revealed a systematic and tonotopic arrangement of AN fibers in each subdivision with a clear indication of isofrequency laminae. The combined dataset was used to mathematically derive a 3D quantitative map of frequency organization throughout the entire volume of the CN. This model, available online (http://3D.ryugolab.com/), can serve as a tool for quantitatively testing hypotheses concerning frequency and location in the CN.

Auditory responses to electric and infrared neural stimulation of the rat cochlear nucleus

“…Lateral stimulation positions in CN caused more activation in IC electrodes located dorsally (high electrode numbers), whereas medial CN stimulation positions caused more activation in IC recordings located ventrally (low electrode numbers). This pattern follows the mapping of low to high characteristic frequencies in CN (Muniak et al, 2013; Spirou et al, 1993) and in the IC (Richter et al, 2011; Ryan et al, 1982; Snyder et al, 2004). Some of the response patterns to electric stimulation were broader than those for acoustic stimulation (Fig.…”

“…Locations at ventrolateral positions of the DCN receive input from auditory nerve fibers of low characteristic frequencies and more dorsomedial sites receive input from higher characteristic frequencies (Fig. 3C, arrow; Muniak et al, 2013; Spirou et al, 1993). This innervation predicts that lateral stimulation locations would activate IC electrodes with high numbers, whereas medial locations would activate electrodes with low numbers.…”

Single-unit labeling of medial olivocochlear neurons: the cochlear frequency map for efferent axons

“…The CF-to-position mapping of MOC neurons described in the present study is one of many such tonotopic mappings in the auditory pathway (Clopton et al 1974;Ryan et al 1982;Friauf 1992;Muniak et al 2013). Present results suggest that the MOC mapping is similar to the auditorynerve fiber mapping, either indistinguishable from it (for MOC Ipsi units) or just apical to it (for MOC Contra units, although these data are more limited).…”

Age-related hearing loss: GABA, nicotinic acetylcholine and NMDA receptor expression changes in spiral ganglion neurons of the mouse

“…In old mice, ABR thresholds were found to be higher than 90 dB SPL, except for 12 and 16 kHz, which are generated in the middle turn of the cochlea (Muniak et al 2013). We analyzed the correlations between SGN density and ABR wave I responses, and the results revealed a positive correlation between SGN density and ABR wave I amplitude (Fig.…”