X-ray diffraction of reconstituted collagen fibers

The X-ray diffraction of fibers reconstituted from purified rat tail tendon collagen has been compared with that of native rat tail tendon. The axial structure is very similar in the two specimens, while the ordered lateral array found in the native state is only poorly reproduced in the reconstituted fiber. Thus, the axial order is determined by the collagen molecules alone, while the native lateral packing may depend, in part at least, on other tissue components.     

Collagen fibril morphology in developing chick metatarsal tendon: 2. Electron microscope studies

Transverse section of embryonic chick metatarsal tendons ranging in age from 11 days to 18 days fetal were examined by electron microscopy to determine both the diameters and the lateral arrangements of the cylindrical collagen fibrils. In early developmental stages, from 11 days to 14 days fetal, sharp unimodal distributions of diameters centred near 32 or 40 nm were observed, but increasingly heterogeneous diameters were seen with increasing age. The heterogeneous diameter distributions were not uniform, but showed discrete populations of preferred diameters. The centre-to-centre distance separating the fibrils in the early developmental stages was about twice the fibril diameter and constant with age. Comparison of X-ray diffraction results with these observations indicated that the saptial relationships of the structures are preserved during the preparative procedures for electron microscopy, but that a transverse shrinkage of 25–30% had occurred relative to the wet dimension.     

Melatonin injected into rat efficiently synchronizes the rhythm of protein synthesis in primary hepatocyte cultures isolated from this rat

Melatonin injected intraperitoneally into rat synchronizes the ultradian rhythm of protein synthesis after 100 min in primary hepatocyte cultures isolated from this rat, which are studied after 1 or 2 days. The effective synchronization concentrations of melatonin—0.01–0.02 μg per kg of rat weight—are three orders lower than melatonin doses used in clinical practice in human treatment.     

Constancy and variability in the content of DNA in cerebellar Purkinje cell nuclei. A cytophotometric study.

A cytophotometric study of DNA content in Purkinje cells of the cerebellum of rats, cats, chicken and humans (Feulgen staining) revealed that in a certain number of cells the amount of NDA ranged between the diploid and tetraploid level (H2C cells). The incidence of H2C Purkinje cells varied among the species studied. In rats, which were studied most thoroughly, these cells amounted on average to 3%. In some rats, as well as in some cats and chickens H2C Purkinje cells were entirely absent. In the group of animals possesing H2C Purkinje cells, great interindividual differences were observed. In rats for instance, the incidence of these cells varied from 1 to 23 per cent. Topographic analyses carried out in rat and human cerebellum revealed that H2C Purkinje cells occurred more frequently in the hemispheres than in the vermis. No significant differences were found in the number of H2C Purkinje cells in healthy and Kilham-DNA-virus infected rats. Densitometric analysis of the distribution of nuclear chromatin showed that H2C Purkinje cells were richer in condensed chromatin, especially in the region of the nucleolus, which apparently contains the hyperploid surplus of DNA. It is proposed that the phenomenon of DNA hyperdiploidy arises as a result of either incomplete S-phase in some immature Purkinje cell precursors or the amplification of some DNA sequences particularly those localized in the nucleolar region.