Abstract
Quantitative histochemical procedures [O. H. Lowry and J. V. Passonneau, A Flexible System of Enzymatic Analysis (Academic, New York, 1972), pp. 219–260] have been applied together with a mapping approach to study the distributions of neurotransmitter systems in the cochlear nucleus. The methods involve quick‐freezing of tissue, followed by frozen sectioning, freeze‐drying, dissection of sections with microknives, weighing of samples on microbalances, and direct chemical assays in microliter volumes. Structures as small as 20 μM per edge can be chemically analyzed by these methods, and the histological locations of all samples are recorded, allowing direct comparisons with anatomical and physiological data for the same locations. The distributions of proposed transmitter amino acids and of the enzymes of acetylcholine metabolism have been mapped in the cochlear nuclei of rats and cats. The effects on these distributions of transections of anatomical pathways are being studied. Results so far suggest that, in the rat cochlear nucleus, most cholinergic synapses may be related to centrifugal, or feedback, pathways to the nucleus.
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