Abstract
Sensory brain regions show neuroplastic changes following deficits or experimental augmentation of peripheral input during a neonatal period. We have previously shown reorganization of cortical tonotopic maps after neonatal cochlear lesions or exposure to an enhanced acoustic environment. Such experiments probe the cortex and show reorganization, but it is unclear if such changes are intrinsically cortical or reflect projections from modified subcortical regions. Here, we ask whether an enhanced neonatal acoustic environment can induce midbrain (inferior colliculus (IC)) changes. Neonatal chinchillas were chronically exposed to a 70 dB SPL narrowband (2 ± 0.25 kHz) sound stimulus for 4 weeks. In line with previous studies, we hypothesized that such exposure would induce widening of the 2 kHz tonotopic map region in IC. To probe c-fos expression in IC (central nucleus), sound-exposed and nonexposed animals were stimulated with a 2 kHz stimulus for 90 minutes. In sound-exposed subjects, we find no change in the width of the 2 kHz tonotopic region; thus, our hypothesis is not supported. However, we observed a significant increase in the number of c-fos-labeled neurons over a broad region of best frequencies. These data suggest that neonatal sound exposure can modify midbrain regions and thus change the way neurons in IC respond to sound stimulation.
Highlights
The objective of this study is to examine the effects of a frequency-enhanced neonatal acoustic environment on c-fos expression patterns in the auditory midbrain
We have shown that chronic stimulation with a tonal stimulus results in a band of c-fos-labeled neurons in inferior colliculus (IC) that corresponds to the tonotopic map functionally verified using single-unit electrophysiological recordings [26]
We have previously demonstrated a viable c-fos labelling protocol for the chinchilla [26]. We use this method here to study neuroplastic change in sound frequency representation in IC following rearing in an enhanced acoustic environment
Summary
The objective of this study is to examine the effects of a frequency-enhanced neonatal acoustic environment on c-fos expression patterns in the auditory midbrain (inferior colliculus). Many studies have revealed alterations in sensory cortical representation after deafferentation or enhanced sensory stimulation. Seminal work on such neuroplasticity has been made in visual cortex [1, 2], in somatosensory cortex [3], and in auditory cortex [4]. We have observed tonotopic map changes in the inferior colliculus (IC) of the chinchilla auditory midbrain as a result of neonatal partial cochlear deafferentation [7]. Studies have revealed midbrain plasticity after augmented auditory stimulation during a neonatal
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