Abstract
The present work describes a method for the histochemical demonstration of, and the differentiation between, norepinephrine and epinephrine at a fine structural level in cells of the adrenal medulla. The two catecholamines are definitely contained in granules which occur in two different cell types; one for norepinephrine, the other for epinephrine. No evidence could be adduced from the present material that norepinephrine material served as a precursor for epinephrine granules. Preliminary observations are included on the occurence of catecholamine-containing granules in neuronal processes of the hypothalamus.