Plasticicy of cochlear nuclei following unilateral deafness due to cochlear ablation.
Abstract
The auditory system has been the subject on studies of its capability to develop plastic responses to different kinds of lesions. Regeneration has been observed in the peripheral portions of the system, with neogenesis of hair cells in avians, sometimes followed by functional rehabilitation, with electrophysiological confirmation. It has been also noticed the ocurrence of central auditory pathways disturbance, secondary to a peripheral damage, probably due to a plastic reaction to the lack of afferent signal.
This work had as main goals to develop an efficient experimental model of unilateral auditory deafferentation, through a mecanical lesion of the cochlea and to evaluate the occurrence of synaptic rearrangements after deafferentation in the cochlear nuclei, ipsilateral and contralateral to the lesion, by using Neo-Timm and Nissl-staining methods.
Surgical lesion of the right cochlea was conducted in 14 day post-natal rats. Their follow up was about ten weeks. Acoustic stimulation was performed once a week for the first four weeks, with another stimulation after a four weeks interval without stimuli. There were two control groups: not lesioned, but stimulated, and neither lesioned nor stimulated. Auditory brainstem evoked potentials were used to certify that the rats were unilaterally deaf.
The lesioned group showed suggestive plasticity, when compared either the two sides (ipsilateral and contralateral to the lesion) or each side with the control groups. The cochlear nuclei developed plastic responses, expressed as alterations in morphological features, such as different distribution of zinc granules.
Anatomical, physiological and neurochemical basis of these alterations were discussed.
