Cellular Localization of Monoamines in the Spinal Cord

Abstract

The cellular localization of monoamines in the spinal cord of the mouse and the rat has been studied with the use of a fluorescence method for histochemical demonstration of certain cate‐cholamines and tryptamines in combination with a pharmacological approach and transection experiments. Strong evidence was obtained for the view that noradrenaline (NA) and 5‐hydroxytryptamine (5‐HT) are localized in special systems of nerve tracts which from supraspinal centers descend in the lateral and anterior funiculi to terminate in the gray matter and which belong to monoaminergic neurons. The amines show a massive accumulation in the terminal part of the nerve fibres. This strongly indicates that both amines serve as synaptic transmitters in the spinal cord. Many nerve terminals containing NA or 5‐HT are present in the anterior horns. They are more scarce in the posterior horns. Terminals of both kinds are highly concentrated in the sympathetic lateral column where most—if not all—of the nerve cells are surrounded by them. They originate—at least mainly—from a tract descending in the dorsolateral funiculi. This localization of the descending fibres suggests that they arc identical with the inhibitory fibres going to the sympathetic column.