Vasomotor axons of the lacrimal glands of monkeys and the ultrastructural identification of sympathetic terminals

Summary The ultrastructure of the perivascular axon terminals of the lacrimal gland in monkeys is investigated electronmicroscopically. Evidence is presented to show that axon terminals populated with small granular vesicles (300 to 500 Å) are sympathetic. Large granular vesicles (650 to 1,000 Å) are present in both sympathetic and parasympathetic terminals.Lacrimal arterioles have both sympathetic and parasympathetic axon terminals disposed between the adventitia and media, which do not form neuro-effector junctions. Capillaries and venules are sparsely innervated. Both parasympathetic and sympathetic axons are shown to innervate capillaries.Results from degeneration studies show that sympathetic and parasympathetic terminal axons lie within the cytoplasm of single Schwann cells.