Pinealocyte ultrastructure has been studied in four sterile, four pregnant and three fertile but non-pregnant females, and also in three reproductively active male pigmented Duncan Hartley guinea pigs. Synaptic ribbons are dense, rod-like structures with a linear arrangement of clear vesicles periodically spaced on both sides of the rodlet. Although these structures were observed in the pinealocytes of all of the animals studied, they were scarce and difficult to locate in tissue from the fertile, non-pregnant females and from the reproductively active males. They were numerous in the pineal glands of the pregnant and sterile females. Typically they lie perpendicular to the cell membrane of the pinealocyte polar process and in close proximity to a polar process of a neighboring cell. The increased incidence of synaptic ribbons in pinealocytes which appear to be in a heightened state of activity strongly suggests a function for this structure. Synaptic ribbons are also present in sensory systems such as rods and cones of the retina, hair cells of the organ of Corti and hair cells of the vestibular apparatus. This fact, plus the photoreceptor function of pinealocytes in lower vertebrates, lends credence to the possibility that this structure may serve a sensory or receptor function in the guinea pig gland.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.