Effects of Inner Ear Damage on the Cholinergic System in the Cochlear Nucleus
The aim of this dissertation was to provide some biochemical evidence relevant to previous functional studies by measuring muscarinic receptor binding and choline acetyltransferase (ChAT) activity following cochlear ablation and intense tone exposure. The ChAT activity in the rat cochlear nucleus (CN) had a characteristic distribution pattern. Significant gradients of ChAT activity were found in all dissected regions. These chemical gradients suggest that descending cholinergic input to the CN is widely distributed and tonotopically organized. After cochlear ablation, bilateral increases in ChAT were found in the anteroventral CN (AVCN) and dorsolateral granular region (G-AVCN) 1 mo after lesion. However, there was no change in the dorsal CN (DCN). In the lateral superior olive, there was a sustained decrease ipsilateral to the lesion after cochlear ablation, By contrast, ChAT activity in the ventral nucleus of the trapezoid body had a tendency to decrease bilaterally in 1 mo and 2 mo survival animals. Except for similar ChAT activities in granular regions, ChAT activity was 2-3-fold lower in the hamster CN than in the rat. Eight days after tone exposure, significant increases over control were found in the AVCN and fusiform soma layer of DCN on the exposed side. In addition, ChAT activities in the G-AVCN, in AVCN, and in deep layer of DCN (DCNd) ipsilateral to the exposure were higher than contralateral values. Two months after tone exposure, ChAT activity in the ipsilateral DCNd was still higher than the contralateral value. Changes of ChAT in the CN may underlie pathophysiological conditions. Analysis of 1-[N-methyl-3H]scopolamine binding in the ventral CN after cochlear ablation demonstrated significant asymmetry in muscarinic receptor binding in 2 mo survival rats, with higher density on the lesion side. The lesion side was 67% higher in the AVCN and 70% higher in the posteroventral CN. In the DCN, increased binding on the lesion side relative to contralateral was significant in DCNf and DCNd in the 1 mo and 2 mo survival animals. The asymmetry was more obvious in the DCNd. The [3H]NMS binding pattern in the DCNf changed from a patchy pattern in control rats to a more diffuse pattern on the lesion side.
School:University of Toledo Health Science Campus
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:cochlear nucleus cholinergic system receptor binding choline acetyltransferase
Date of Publication:01/01/2004