Selective sympathetic denervation induced by 6-hydroxy-dopamine in the small intestine.

The structure of the nerve fibres in the intact and neurally isolated intestine of the cat was studied after 6-OHDA treatment by fluorescence and electron microscopy. A gradual disappearance of green fluorescence in the monoaminergic fibers was observed. Degeneration of nerve fibres containing 30--60 nm agranular and 30--60 nm densecore (granular) vesicles could be seen in all layers of the small intestine. Sporadically, degeneration of the presynaptic elements occurred also in the synapses of myenteric ganglia. A large number of degenerating fibres could be observed in close relation to blood vessels. These were thought to be monoaminergic because 6-OHDA selectively affected their terminals. In the chronically isolated small intestine degenerated nerve processes could not be observed following 6-OHDA treatment. It is concluded that the intrinsic nerve elements do not contain monoamines. Accordingly, the previously observed yellow fluorescence of the nerve elements of the isolated small intestine might be due to some other kind of neurotransmitter, possibly tryptamine.