Effects of spaceflight on the proliferation of jejunal mucosal cells

The mitotic indices, villus heights, and crypt depths were determined in each of three jejunal regions (proximal, middle, and distal) for five animals each in the flight, vivarium, and synchronous groups. Because of the rapid turnover of intestinal mucosal cells and the delay in recovering the flight animals, it is not known whether the proliferation of jejunal mucosal cells is affected by microgravity conditions associated with spaceflight. However, since there were no consistent differences between animals in the flight group and those in the synchronous and vivarium control groups, it appears that any effects of microgravity on the turnover of jejunal mucosal cells are short-lived. Thus, this study represents an initial step in determining the effects of microgravity on the proliferation and turnover of intestinal mucosal cells.     

Spatial scaling of allometry for terrestrial,mammalian carnivores

A regression slope of –0.75 between log₁₀ density and log₁₀ body mass is thought to express equivalence of energy conversion among species' populations of similar taxonomic and trophic status. Using larger sample sizes than the usual 1–3 density estimates per species, we estimated a regression slope of –0.71 for terrestrial mammalian carnivores. We investigated the sampling variation in this estimate, and those derived from smaller intra-specific subsets, using 1000-iteration bootstrap analyses to obtain 90% confidence intervals. As expected, these widened as random subsets were reduced in size, but always contained the postulated –0.75. However, log₁₀ density also declined as 3/4 of the log₁₀ spatial extent of study area, and study area accounted for virtually all of the variation in density that was previously thought due to body mass. We removed the effect of study area by using the species-specific regression models between density and study area to predict density at a common scale of 400 km². These common-scale densities regressed against body mass with a slope of –0.16, but separated into body mass classes less than and greater than 11 kg, they produced slopes that were not significantly different from zero. We show that the allometry of density could be a case of circular logic, whereby body mass has influenced the investigator's choice of study area, and the resulting scale-dependent densities are related back to body mass. To test the allometry hypothesis, the effect of study area on density estimates needs to be removed. This requires conducting larger-scale studies of the smaller-bodied species so that all species compared are represented by an average study area that is near the common scale. Furthermore, study sites need to be selected and designed to represent more than the local detail in species' density.     

Migration of myogenic cells in the rat extensor digitorum longus muscle studied with a split autograft model

Summary The ability of myogenic cells to migrate perpendicular to the long axis of freely autografted muscles was examined. Rat extensor digitorum longus muscles were divided, and one half was devitalized by repeated freezing in liquid nitrogen while the other half was kept viable in physiologic saline. The halves were reunited with sutures and grafted back into the original muscle bed. At intervals between 5 and 25 days the grafts were removed and examined histologically for the presence of myotubes within the devitalized region. Myotubes were first seen in the devitalized half 10 days postgrafting with the maximum number of myotubes observed after 12 to 15 days. These results indicate that myogenic cells are capable of migration perpendicular to the long axis of the muscle fibers in an autograft.