Ultrastructural localization of monoamines in nerve fibers of the pineal gland in golden hamsters.

Nerve terminals in the pineal glands of control, parachlorophenylalanine (PCPA)-, reserpine- and nialamide-administered hamsters were studied with glutaraldehyde-dichromate (GD) and formaldehyde-glutaraldehyde-dichromate (FGD) techniques in the electron microscope. In control pineals treated with the FGD or GD technique, clusters of electron dense reactive particles with a diameter of 20-30 nm, and mainly located in the perivascular space, were identified as dense cores of the small granulated vesicles (SGVs) in the pineal nerve fibers. After the administration of PCPA, the reactive cores were greatly decreased in number in the FGD-treated pineal blocks, whereas a lot of clusters of reactive cores were observed in the perivascular space in GD-treated specimens. After reserpine treatment, no reactive structures were revealed by GD or FGD technique. Reactive cores appeared to be increased in number and in electron density in GD- or FGD-treated pineals of hamsters after administration of nialamide. From the observations, it is concluded that the dense cores of SGVs in the pineal nerve fibers contain both primary catecholamines and 5-hydroxytryptamine although it was not determined whether both amines are located in the same or separate vesicles.