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Electron microscopic observation of the neurons in superior cervical sympathetic ganglion was made on a total of 18 spontaneously hypertensive rats (OKAMOTO and AoKI), and 18 normotensive rats of Wistar strain. Evaluation of the findings was performed by quantitative estimation of cytoplasmic ultrastructure with an aid of linear analytical procedures. 2. The ultrastructural organization of neutrons in normal Wistar rats coincided with those of rats already described by certain authors. 3. The neuronsofthe S.H. rats showed submicroscopic features which did not differ in a basic way from those of normotensive control rats. By quantitative analyses of these neurons, however, the following disparate findings were noticed. (1) Granular endoplasmic reticulum was more abundant in the neurons of spontaneously hypertensive rats of all ages as compared with those of normotensive controls. Free ribosomes also showed a similar tendency. (2) Total mitochondrial volume was greater in the neurons of spontaneously hypertensive rats than in those of normotensives through all ages; no remarkable morphological abnormality of mitochondria was seen except for a slight swelling or cristolysis found in some of them. (3) Only in the spontaneously hypertensive rats of prehypertensive stage was the Golgi apparatus better developed than in the controls, though the same tendency was suggested through all ages. (4) More lysosomes were found in the spontaneously hypertensive rats than in the normotensives, being obvious especially in the older ones. 5. From these findings the possibility of higher metabolic level in the sympathetic neutrons and, in consequence, of the increase in sympathetic neuronal activity in the spontaneously hypertensive rats were discussed in relation to functional significance of neuronal ultrastructure.
Masao Matsumoto (Wed,) studied this question.