Modulation by dietary restriction in gene expression related to insulin-like growth factor-1 in rat muscle

Age-dependent expression of forkhead box O proteins in the duodenum of rats

The O subfamily of forkhead box (FoxO) proteins is the downstream effector of the insulin-like growth factor-1/phosphoinositide 3-kinase/protein kinase B (IGF-1/PI3K/PKB) signal pathway. The objective of the present study was to examine the expressions of three members of FoxO proteins, FoxO1, FoxO3a, and FoxO4 in the duodenum of Sprague-Dawley rats at different ages. The result demonstrated that the expression of FoxO4 in rat duodenum showed an age-dependent manner. At Day 21, there were no detectable localization and expression of FoxO4 in the duodenum, while, at Months 2 and 6, localization and expression of FoxO4 were distinct. In addition, FoxO4 staining was primarily concentrated in the cell nuclei of the lamina propria around the intestinal gland of the duodenum in 2-month-old rats, but was not detectable in the same area in 6-month-old rats. Our results showed also that although FoxO3a existed in the cytoplasm of the lamina propria at a low level at the 2- and 6-month marks, it was still not detectable at Day 21. Besides, FoxO1 was not detectable in all parts and stages. Taken together, our findings suggested that the cell-specific and age-dependent expressional patterns of FoxO4 and FoxO3a proteins in the duodenum play some roles in the development and growth performance of the rat duodenum.

Progress of Age-Related Changes in Properties of Motor Units in the Gastrocnemius Muscle of Rats

The mechanical properties of individual motor units in the medial gastrocnemius muscle, as well as the whole muscle properties and innervating motor nucleus, were investigated in dietary-restricted, male Fischer 344/DuCrj rats at ages of 4, 7, 12, 21/22, 27, 31, and 36 mo. The tetanic tension of the type S units continuously increased until the age of 36 mo. Those of type FF and FR units declined from 21/22 to 27 mo of age but did not change further while the whole muscle tension decreased greatly. The atrophy of muscle fibers, the decline in motoneuron number and axonal conduction velocity, and the decrease in the posttetanic potentiation of twitch contraction of motor units seemed to start after 21/22 mo of age and were accelerated with advancing age. Prolongation of twitch contraction time was evident for only type S and FR units in 36-mo-old rats. The fatigue index was greatly increased for type FF units in 36-mo-old rats. These findings indicated that the progress of changes in various properties occurring in the senescent muscle was different in terms of their time course and degree and also dependent on the types of motor unit. The atrophy and decrease in specific tension of muscle fibers affected the decline in tension output of motor units. This was effectively compensated for by the capture of denervated muscle fibers over time.

Effects of caloric restriction on development of the proximal growth plate and metaphysis of the caput femoris in spontaneously hypertensive rats: microscopic and computer-assisted image analyses

We previously demonstrated that caloric restriction (CR) reduced the prevalence of osteonecrosis in caput femoris of spontaneously hypertensive rats (SHR), a model of human Perthes' disease. The effects of CR on the development and pathology in the proximal femoral growth plate (GP) and adjacent structures in SHR were investigated by morphometric and computer-assisted image analyses. From 6 weeks of age, the food intake of SHR was restricted to 65% of the mean intake of ad libitum fed control SHR (SHR-AL). Wistar Kyoto rats (WKY), from which the SHR strain was isolated, fed ad libitum were also included as controls. CR reduced prevalence of chondromucinous degeneration and dysarray of cartilage cell columns in the GP, becoming prevalent between 10 and 20 weeks in the SHR-AL group, attaining the same levels of the WKY group. Thicknesses of non-calcifying cell columns in the GP were greater in the SHR-AL than WKY group; CR slightly reduced the thickness, but incompletely. Thicknesses of calcifying cell columns did not significantly differ among the three groups. CR decreased volume density and mean thicknesses of the trabecular bone in areas adjacent to GPs, and was greater in the SHR-AL than the WKY group. The present morphologic analysis suggested that CR ameliorates dysplastic changes of trabecular bones in areas adjacent to the GP, rather than modulating the ossification process in the GP. The CR paradigm might give insight into the pathogenesis of, and a therapeutic strategy for, human Perthes' disease.