The impact of hearing experience on signal integration in the auditory brainstem: a c-Fos study of the rat

Abstract

In this study we investigated the pattern of c-Fos expression in anteroventral (AVCN) and dorsal cochlear nucleus (DCN) and central inferior colliculus (CIC) following electrical intracochlear stimulation (EIS) of anesthetized adult rats that were neonatally deafened. The animals never experienced acoustic sensations as their hair cells were destroyed by daily kanamycin injections between postnatal days 10 to 20, resulting in a rise of hearing threshold by about 90 dB. Unilateral EIS was applied through a cochlear implant inserted into the medial turn of the left cochlea and lasted for 45 or 73 min, 2, 3:15, or 5h. Following EIS at 50Hz, a high number of c-Fos positive nuclei were observed showing only marginal tonotopic order in ipsilateral AVCN, in DCN bilaterally, and in contralateral CIC. Quantifying the number of c-Fos positive nuclei in ipsilateral AVCN, we found a steady increase with stimulation time. By contrast, the population of neurons expressing c-Fos in DCN and CIC revealed a transient maximum at 73 min. A direct comparison with our previous study (Rosskothen-Kuhl, N., Illing, R.-B., 2010. Nonlinear development of the populations of neurons expressing c-Fos under sustained electrical intracochlear stimulation in the rat auditory brainstem. Brain Res. 1347, 33-41) reveals that absence of hearing experience has far-reaching consequences for the interneuronal communication within networks of the auditory brainstem. When hearing fails, EIS entails expression of c-Fos in populations of neurons that are much larger than normally, essentially disregard tonotopic order, and lack much of spatio-temporal variations seen in hearing-experienced rats.