Laterality, intensity, and frequency of electrical intracochlear stimulation are differentially mapped into specific patterns of gene expression in the rat auditory brainstem

Abstract

Specific patterns of sensory activity may invoke neuroplastic remodelling in the young and adult mammalian brain. Among the indicators for the initiation of neuronal remodelling is the expression of immediate early genes (IEGs). The IEG c-Fos encodes a monomer of the transcription factor dimer AP-1 that triggers cascades of activity-dependent protein synthesis. In order to investigate activity-dependent neuroplasticity in the central auditory system, we applied unilateral electrical intracochlear stimulation (EIS), adjusted to evoke amplitudes of the auditory brainstem response corresponding to about 40 dB acoustic stimulation in adult urethane-anaesthetized rats for 2 h. The intracochlear electrode was baso-dorsally located and the stimulation was specified with respect to intensity (100 or 1500 impulses per min) and frequency (1.6, 50, 100 or 400 Hz). Following EIS, we detected and counted neurons in cochlear nucleus, superior olive, inferior colliculus, and medial geniculate body that initiate stimulation-dependent expression of the protein c-Fos. Unique patterns of gene expression emerged across the major auditory brainstem regions with respect to laterality, intensity, and frequency of EIS. These data suggest a potential of neuroplastic construction to be exploited by running a cochlear implant in humans one way rather than another.

• c-Fos
• cochlear implant
• immediate early genes
• plasticity