Cobalt chloride can be injected into an identified nerve cell body in an insect ganglion and reacted with ammonium sulfide to stain the soma and its branches with a black precipitate. The stained cell body and its branches throughout the neuropil are visible in both the light and electron microscope. In whole mount preparations, the resolution of neurites within the neuropil is of a quality that permits the comparison of branching patterns between cells and during various functional states.

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Adult male albino rats were assigned randomly to control (CON) and weight-lifting (WL) groups. The WL rats were subjected to a progressive weight-lifting program against high resistance for 8 weeks. During the last 2 weeks, each WL rat lifted a load equal to 130% of its body weight. The mean weight of the adductor longus muscle was significantly increased in the WL group ( p < 0.05). This increased muscle weight was shown to be due to an increase in the number of fibers per unit cross-sectional area ( p < 0.05), and the mean sizes of both fast-twitch oxidative glycolytic and slow-twitch oxidative fibers were significantly smaller in the WL rats than in the CON rats (p < 0.05). Light and electron microscopic examination showed that five out of eight WL rats exhibited longitudinally split muscle fibers, while only one CON rat had a few centrally placed nuclei. The splitting process appeared as either a "pinching-off" of a small segment from the parent fiber or an invagination of the sarcolemma deep into the muscle fiber in a plane parallel to the sarcomeres. There were preliminary indications that this work-induced fiber-splitting process may be a physiological adaptation of muscle to the stress of exercise.

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A quantitative ultrastructural study was performed to determine the changes in the neurosecretory neurons of the supraoptic (SON) and circularis (NC) nuclei following 4-24 h of water deprivation (WD) and subsequent rehydration (12 and 24 h). In both nuclei, the amount of direct soma-somatic contact increased throughout WD, apparently by retraction of fine glial processes from between the cells. Rehydration reversed these changes. The number of smaller (less than 1600 A) neurosecretory granules (NSG's) decreased in both nuclei at 4 h of WD but returned to control levels by 24 h of WD and remained so during rehydration. Larger (less than 1600 A) NSG's decreased in number at 4 h of WD in SON and then returned to control levels by 24 h of WD and remained the same throughout rehydration. In NC, these NSG's did not change in number with WD, but significantly increased between 12 and 24 h of rehydration. No cells with dilated rough endoplasmic reticulum were seen in NC during this study. In SON, however, the percentage of such cells increased at 4 and 12 h of dehydration only to decrease to control levels at 24 h of dehydration and throughout rehydration. Lysosomes decreased at 4 h of dehydration in SON and returned to control levels thereafter. In NC, lysosomes tended to decrease with dehydration and increase with rehydration. These findings indicate that detectable morphological changes take place in the course of alterations in hydration state that are well within the physiological range.

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