Circadian Phase Relationships of Thymidine-3h Uptake, Labeled Nuclei, Grain Counts, and Cell Division Rate in Rat Corneal Epithelium

Abstract

Significant differences in the uptake of thymidine-~H, percentage of labeled cells, numbers of grains per labeled nucleus, and mitotic rate were noted in rat corneal epithelium along a 24-hr time scale. These were demonstrated by injecting subgroups of five animals every hour during a 24-hr period with thymidine-3H, sacrificing thcm 2 hr later, and analyzing the corneal epithelium by scintillation counter and radioautographic techniques. The incrcasc in uptake during specific periods of the 24-hr time scale is attributed to an acceleration in the rate of DNA synthesis by individual cells and to an increase in the percentage of cclls in thc population activcly synthesizing DNA.

Circadian control of neurogenesis

“…Diurnal variation in cell proliferation has been documented in rodent and human studies of bone marrow (Smalland et al, 2002), gastrointestinal tract mucosa (Marra et al, 1994), epidermis (Brown, 1991), liver (Haus and Halberg, 1966), and cornea (Scheving and Pauly, 1967). However, our demonstration of circadian control of the neuronal cell cycle is the first example of light entrainment of neurogenesis (Bagay et al, 2001).…”

Damage to the Epithelial Basement Membrane in the Corneas of Diabetic Rabbits

“…No observa¬ tions were made during the first dark period of the light cycle to prevent disrup¬ tions of the normal circadian rhythm of corneal mitoses. 15 Computed planimetry of the lesions was performed on the projected slides (using an Apple II computer with an Apple Graphics Tablet). Lesion areas from both eyes were averaged so that each datum represented a single rabbit (two eyes) rather than a single eye.…”

Mitotic Nests in Human Vaginal Smears and Cultures of Amphibian Tissues

“…In other words, there is a limita tion on the size of a mitotic (and/or DNA synthesizing) nest because of in creasing asynchrony with increasing time. The relationship between the phenomenon of mitotic nest formation de scribed and discussed in this paper and other phenomena, such as waves of mitoses observed, for example, in experimental wound healing [10], during embryogenesis [5,14] and the circadian wave of mitosis which characterizes all mitotically labile tissues [12] requires clarification.…”