Histochemical studies of sympathetic sprouting: Fluorescence morphology of noradrenergic axons

The importance of distinguishing between central and peripheral noradrenergic axons is evident from recent observations that sympathetic fibers will invade the central nervous system following specific lesions. The present paper reviews the normal histofluorescence appearance of peripheral and central NE fibers in several species as well as their appearance following experimental manipulations. The most striking differences between these two types of NE neurons is their axonal fluorescence morphology which is apparently determined by the target tissue, and their responsiveness to nerve growth factor (NGF). The latter may account for the remarkable growth of sympathetic axons into regions of the central nervous system denervated of cholinergic fibers. The use of glyoxylic acid in studying such sprouting is also discussed.