Electron Microscopy of the Rat Hypothalamic Neurosecretory System : I. The Supraoptic Nuclei of Normal and Dehydrated Rats

The supraoptic neurosecretory nucleus of the rat hypothalamus both in the normal and experimental condition induced by the administration of trypan blue was observed with the electron microscope.1. The perikaryon of the neurosecretory cell contains rodlike mitochondria, rough-surfaced endoplasmic reticulum and well-developed GOLGI apparatus, small neurosecretory granules, multivesicular bodies and large dense inclusion bodies which are considered to be a type of lysosomes. After treatment with trypan blue, an increased number of large dense bodies was noticed. They are variable in shape and size and heterogeneous in texture. Additional types of inclusion bodies which are similar in morphology to the so-called autophagic vacuoles or cytolysomes were frequently observed in the perikaryon of neurosecretory cells of the experimental animals. Furthermore, the number of the neurosecretory granules increased markedly after the trypan blue injection, and most of them were observed in the vicinity of the GOLGI apparatus.2. The supraoptic nucleus contains many unmyelinated and a few myelinated axons as well as various types of nerve terminals. After the treatment with trypan blue, dark inclusion bodies which are similar in appearance to those found in the perikaryon could be frequently observed also in the axons and terminals.3. The supraoptic neurosecretory nucleus contains three kinds of neuroglia cells, namely, the astrocytes, oligodendrocytes and microglial cells. The astrocytes are characterized by their clear cytoplasmic matrix with a small amount of endoplasmic reticulum. The GOLGI apparatus and mitochondria are also poorly developed. The heterogeneous dense bodies occourring in the normal astrocytes appear to increase in number after injection of trypan blue. The oligodendrocytes are identified by their moderately dense cytoplasm. Some oligodendrocytes also contain the heterogeneous inclusion bodies which are similar in appearance to those found in the astrocytes. The microglial cells characterized by their extremely high overall density often contain large dense bodies surrounded by a single membrane which are markedly increased in number after trypan blue injection. In such an experimental condition, the microglial cells are more frequently observable than in the normal rat hypothalamus.4. The blood capillaries in the hypothalamic neurosecretory region consist of the endothelium, basement membranes and pericytes. The cytoplasm of both the endothelial cells and the pericytes of the rat given trypan blue frequently contains dark inclusion bodies which are surrounded by a limiting membrane and are heterogeneous in texture.5. The possible relationships between the action of trypan blue on the neurosecretory cells in the hypothalamus and the teratogenic effect of this dyestuff were discussed.