ULTRASTRUCTURE OF NEUROSECRETORY CELLS IN THE SUPRAOPTIC NUCLEUS OF THE DOG AND RAT

The hypothalamo-neurohypophysial systems of the dog and rat have been investigated with the electron microscope. The best preparations were obtained from anaesthetized animals cooled to about 7°.

Neuronal cell bodies in the supraoptic nuclei of the dog were characterized both by their size, by their occasional proximity to the capillary basement membranes, and by their content of electron-dense, membrane-bound inclusions measuring between 750 and 3000 å in diameter. Similar inclusions, measuring between 800 and 2400 å in diameter, characterized nerve terminals in the infundibular process. These inclusions are the same size as those found to be associated with high antidiuretic activity in samples taken from the posterior pituitary and from the hypothalamus of the dog, and could therefore be the vehicles of antidiuretic hormone. It has been calculated that in the dog these inclusions, if they contain antidiuretic hormone, are numerous enough in the neuronal cell body for the latter to constitute the only site of hormone synthesis.

Similar secretory neurones were found in the supraoptic nucleus of the rat. They were more difficult to identify than in the dog, for they contained fewer inclusions of the size which filled nerve terminals in the infundibular process.