Quantitative distribution of choline acetyltransferase and acetylcholinesterase activities in the rat cochlear nucleus.

Within the cochlear nucleus of the rat, as well as some nearby regions, quantitative histochemical mapping procedures were used to construct maps of the distributions of choline acetyltransferase and acetylcholinesterase activities. The results were in some ways consistent with results previously reported for cat, e.g., very low activities of both enzymes were found in the auditory nerve root, and also in the vestibular nerve root, except where acetylcholinesterase-positive centrifugal fibers are located, very high activities were found in the facial nerve system. In many ways, however, the results for the rat cochlear nucleus contrasted with those for the cat. Notably, choline acetyltransferase activities in some regions of the rat cochlear nucleus were as much as 30- to 60-fold higher than for the comparable regions in the cat, and both enzymes had much more uniform distributions in the rat cochlear nucleus than in the cat. The more prominent cholinergic system in the rat cochlear nucleus might relate to a proportionately larger population of cholinergic interneurons, or, more probably, a more significant innervation by cholinergic, centrifugal pathways, or both, as well as, perhaps, generally higher choline acetyltransferase activities in cholinergic neurons of rat.