Abstract
Evidence is cited demonstrating that the olivo-cochlear bundle is cholinergic. According to Dale's principle, all true collaterals of a cholinergic nerve might be expected to release acetyl-choline (ACh). The crossed olivo-cochlear bundle sends branches to the cochlear nucleus that appear to be collaterals whose final terminations are only incompletely described. The present study was designed to determine whether these branches from the olivo-cochlear bundle to the cochlear nucleus elaborate ACh in response to electrical stimulation and whether such ACh, collected from different parts of the cochlear nucleus might not indicate the distribution of the olivo-chochlear bundle-cochlear nucleus terminals. Fluid from the dorsal cochlear nucleus was collected by means of a cup placed on the surface of the cochlear nucleus. The ventral cochlear nucleus was perfused by means of a push-pull cannula. ACh-like activity, as determined by bioassay, was often present in control perfusate but electrical stimulation of the crossed olivo-cochlear bundle produced a statistically reliable increase in ACh-like activity in the dorsal cochlear nucleus perfusate. On the other hand, electrical stimulation of the crossed olivo-cochlear bundle produced a statistically reliable decrease in ACh-like activity in the ventral cochlear nucleus perfusate. The bioassay results of the ventral cochlear nucleus perfusates are confounded by the presence of non-ACh-like agonists in the control perfusates and ileum-relaxant agents in the “stimulated” perfusate. Of all possible interpretations, the favoured one is that the olivo-cochlear bundle-cochlear nucleus terminates largely in the superficial ventral cochlear nucleus near the dorsal cochlear nucleus collection cup and excites other neurones which secondarily release other transmitters found in the ventral cochlear nucleus perfusate.
Published Version
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