The ultrastructure of the human fetal pineal gland. II. Innervation and cell junctions.

The innervation of the pineal gland, the cell junctions in this organ and junctions between ependymal cells in the pineal recess were investigated in 27 human fetuses (crown-rump length 30-190 mm). Free nerve boutons containing clear and a few dense core vesicles were present in the pineal parenchyma and in the perivascular spaces. The boutons did not make "synaptic" contacts with the pinealocytes. No evidence for the presence of noradrenaline in the vesicles of nerve boutons was found. Gap junctions, intermediate-like junctions and desmosomes were frequently seen between the pinealocytes. Ruthenium red was used in three fetuses as an extracellular marker. The continuous endothelial cells surrounding the capillary lumen were connected by tight junctions. This indicates the presence of a blood-brain barrier. Tight junctions were present between the ependymal cells in the pineal recess. These junctions constitute an extracellular barrier between the pineal and the cerebrospinal fluid.