The supraoptic nucleus and the supraopticohypophysial tract in the monkey (Macaca mulatta).

The observations here on Golgi material are based on the study of fortunate impregnations in one horizontally sectioned and one frontally sectioned series found in the collection of Golgi preparations of the adult monkey brains (Macaca mulatta) available in this laboratory. The soma of the large supraoptic neurons have jagged protrusions and irregular crevices which give their surfaces a craggy appearance. Also they have a few somatic spines. Their dendrites, which usually arise from two or three dendritic trunks, emerging from the cell body, are moderately branched and have occasional dendritic spines. The axon emerges from a conical elevation either on the soma or a dendrite and is directed towards the supraopticohypophysial tract. In the present material there are a few neurons of the supraoptic nucleus impregnated that are definitely smaller than the larger neurons. They have short beaded axons, ending in the supraoptic nucleus a short distance from their point of origin. In the horizontal sections the supraopticohypophysial tract fibers can be seen passing over the posterior aspect of the optic tract. In the frontal sections, this fan-shaped tract, wide above and constricted below, can be followed into the median eminence. Some of these axons in their intrahypothalamic course have short beaded collaterals. Electron micrographs reveal: (1) endings with spherical synaptic vesicles and endings with flattened synaptic vesicles synapsing on neurosecretory axons in the supraoptic nucleus; (2) a few myelinated fibers containing neurosecretory granules in the intrahypothalamic portion of the supraopticohypophysial tract. As can be seen in both Golgi and electron microscopic preparations the presence of fibrous astrocytes in the supraoptic nucleus and their abundance in the hypothalamic portion of the supraopticohypophysial tract is characteristic of this neurosecretory system. In the nucleus and in the tract processes of the fibrous astrocytes are intimately associated with neurosecretory fibers.