Changes in cochlear electrical stimulation induced Fos expression in the rat inferior colliculus following deafness

Fos immunoreactive (IR) staining was used to examine changes in excitatory neuronal activity in the rat inferior colliculus (IC) between normal hearin g and 21 day deaf rats evoked by basal or apical monopolar cochlear electri cal stimulation. The location of evoked Fos IR neurons was consistent with expected tonotopic areas. The number of Fos IR cells increased as stimulati on intensity increased in both normal and 21 day deaf animals. Stimulation at 1.5 x threshold evoked fewer Fos IR cells in 21 day deafened animals com pared to normal hearing animals. At 5 x and above, however, significantly i ncreased numbers of Fos IR neurons (in a larger grouping) were evoked in 21 day deafened animals compared to normal hearing animals. Another group of animals had 7 days of deafness followed by 14 days of chronic basal cochlea r electrical stimulation. In this group basal monopolar stimulation at 5 x evoked not only a greater number of Fos IR neurons, compared to normal hear ing animals, but the location of their grouping was slightly shifted to a m ore dorso-lateral region in the contralateral IC, compared to the normal he aring and 21 day deaf groups. These observations indicate that both deafnes s and chronic electrical stimulation may alter central auditory processing. (C) 2000 Elsevier Science B.V. All rights reserved.