Auditory brainstem: Development and plasticity of GAP-43 mRNA expression in the rat

Abstract

Expression of the growth and plasticity associated protein GAP‐43 is closely related to synaptogenesis and synaptic remodeling in the developing as well as in the mature nervous system. We have studied the postnatal development of GAP‐43 mRNA expression in the auditory brainstem and determined the time course of its reexpression following deafening through cochlear ablation using a digoxigenin‐coupled mRNA probe. By the first postnatal day, GAP‐43 mRNA was expressed at high levels in all auditory brainstem nuclei. But whereas GAP‐43 mRNA is almost entirely lost in most of these nuclei in the adult animal, significant levels of this molecule are retained in the inferior colliculus and, most notably, in the lateral and medial superior olivary nucleus. As a consequence of unilateral cochleotomy, GAP‐43 mRNA rose dramatically in some neurons of the ipsilateral lateral superior olive, whereas the hybridization signal decreased in others. Using double staining protocols, we found that those olivary neurons that increase their level of GAP‐43 mRNA appear to be identical with the cells developing strong GAP‐43 immunoreactivity after cochleotomy. By combining axonal tracing with in situ hybridization, we proved that at least some of the cells with increased levels of GAP‐43 mRNA and protein are the cells of origin of olivocochlear projections. A substantial decrease of the level of GAP‐43 mRNA took place in the inferior colliculus contralateral to the lesioned cochlea. Our results led us to suggest that neurons in the superior olivary complex may play a crucial role in orchestrating auditory brainstem plasticity. J. Comp. Neurol. 412:353–372, 1999. © 1999 Wiley‐Liss, Inc.

Developmental changes of synaptic proteins expression within the hippocampal formation of the rat

“…A high level of GAP-43 appears during the periods of active growth of nerve cells. This is detected within axons during their elongation, thus a fibrous immunoreactivity is visible Ulfig et al 1999;Illing et al 1999). After the axonal growth is completed, when neurites begin to interact with their target cells, there is a shift from fibrous to punctate immunoreactivity (Benowitz et al 1983;McGuire et al 1988;Dani et al 1991;Yao et al 1993), which correlates with synaptogenesis.…”

Auditory brainstem activity in children with 9–30 months of bilateral cochlear implant use

“…Evidence from animal models suggests that a lack of binaural input during development results in extensive reorganization of the auditory brainstem pathways; connections from the cochlear nucleus to the ipsilateral inferior colliculus (IC) increase and connections to the contralateral inferior colliculus decrease (Illing et al, 1999;Nordeen et al, 1983). These changes are thought to result from a lack of competition from one side in brainstem nuclei which would normally receive inputs from either ear .…”

Predicting severity of cochlear hair cell damage in adult chickens using DPOAE input–output functions

“…In the auditory system, cochlear ablation can lead to substantial age-dependent alterations in the form and function of the CNS (Syka, 2002;Rubel and Fritzsch, 2002;Illing et al, 1999;Francis and Manis, 2000), including death of auditory brainstem neurons (Mostafapour et al, 2000;Tierney et al, 1997;Edmonds et al, 1999). Partial cochlear damage can also result in central auditory plasticity (Rajan et al, 1993;King et al, 2000;Park et al, 1999;Woolley et al, 2001;Willott, 1996).…”