Electron microscopy of silver-stained core-like structures in metaphase chromosomes.

Chinese hamster metaphase chromosomes, stained with ammoniacal silver and examined by electron microscopy, were covered with fine silver grains of variable size. In addition, many chromosomes contained linear aggregates of silver grains running continuously from one end of each chromatid to the other, forming a core-like structure. Extensive deposits of silver were observed over the nucleolar organizers and the centromeric regions, and the silver precipitate in the latter region appeared to be a localized differentiation of the core-like structure. The silver cores ranged from thin to thick and continuous to discontinuous elements in different chromosomes. This extreme variability suggests that these cores are not true structural components of chromosomes. The amount of silver deposit over any given chromosome region may simply reflect the concentration of chromatin in that region of the chromosome. The silver-stained core-like structure probably reflects an underlying difference in the concentration of chromatin in the central and peripheral region of each chromatid. Such differences in chromatin concentration may be induced during the prolonged hypotonic treatment required for the subsequent visualization of cores.

Silver stained core-like structures in chinese hamster metaphase Chromosomes.

Chinese hamster metaphase chromosomes, subjected to prolonged hypotonic pretreatment and subsequently stained with ammoniacal silver, contained a darkly-stained core-like structure in each chromatid, surrounded by a halo of dispersed chromatin which was pale yellow to brown in color. The core was variable in its appearance, ranging from a continuous linear configuration to a spiral structure or a discontinuous, particulate structure. Within the centromeric regions, the cores frequently appeared more intensely stained than elsewhere in the chromosome. The nucleolus organizers also stained darkly and appeared to be attached to the core-like structures. It remains to be determined whether the cores represent a real component of metaphase chromosome structure, or whether they are artifacts resulting from abnormal chromatin aggregation arising at the time of chromosome preparation.

Cytogenetic effects of delta-9-tetrahydrocannabinol (delta9-THC) on hamster bone marrow.

Single s.c. injections of 10 or 1000 mg/kg of delta9-THC did not induce discernable chromosomal damage but caused significant mitotic inhibition in the bone marrow of Syrian hamsters.