Hormonal content and ultrastructure of the disconnected neural lobe of the grass frog ( Rana pipiens)

Abstract

Based on changes in ultrastructure and vasotocin content, two postoperative phases can be distinguished in the neural lobes disconnected from the hypothalamus. During the first phase (first 2 days after transection) only very few axons start to degenerate, and the vasotocin content does not differ from that of the control glands. Axons filled with tubular formations are more numerous than in the controls. The second phase (6th to 9th postoperative days) is characterized by the degeneration of most of the neurosecretory axons and by a dramatic fall in the vasotocin content of the glands. During this phase, the number of Golgi complexes in the pituicytes increases considerably. Simultaneously, the appearance of well organized canaliculi lined by pituicytes is observed. A second cell type, in addition to pituicytes, is observed in the second phase. These cells have a charteristic nucleus and a cytoplasm mainly occupied by rough endoplasmic reticulum and lipid droplets. The pituicytic reorganization and the appearance of a new type of cell indicate that the chronically disconnected neural lobe is not a dead formation but a structure that may play some unknown functional role. The capillaries of the disconnected neural lobe are characterized by the widening of the endothelial fenestrations and the disappearance of their membrane, which results in a direct communication between the capillary lumen and the perivascular space. White blood cells are densely packed against the capillary walls, and most of these cells have processes that penetrate the endothelial openings and contact the perivascular basement membrane.