The effect of clipping guinea-pig hair and chronic radiodermatitis on diurnal (circadian) rhythms in epidermal labeling and mitotic indices

Modeling dermatophytosis: Guinea pig skin explants represent a highly suitable model to study Trichophyton benhamiae infections

Dermatophyte infections are a growing health concern worldwide with increasing patient numbers, especially in children. However, detailed knowledge about infection mechanisms and virulence factors are scarce. This study aimed to establish an infection model based on guinea pig skin explants mimicking the in vivo situation as closely as possible to survey the pathogenesis of dermatophytoses. A fundamental prerequisite was the detailed description of native guinea pig skin and its morphological changes during tissue culture because comprehensive data on guinea pig skin characteristics were not available. Skin explants were harvested from healthy, adult guinea pigs and transferred to cell culture inserts. One group was inoculated with defined suspensions of colony-forming units of zoonotic Trichophyton benhamiae isolates; others served as controls to assess the tissue viability during the 10-day culture. Samples were taken on days 3, 5, 7 and 10 and processed for histological and immunohistochemical analysis. Standard tissue culture conditions provoked acantholysis and regional orthokeratotic alterations. The reduced desquamation caused hyperkeratosis paralleled by hypogranulosis or regional hyperplasia. During T. benhamiae infection, keratinocyte proliferation came to a complete halt on day 5 whereas the number of terminal deoxynucleotidyl transferase dUTP nick end labeling assay-positive cells increased moderately up to day 7. Hyphae grew massively into the skin explants causing strong keratinolysis and tricholysis. By the end of the culture, complete disintegration of the basement membrane and dermal tissue was observed. A realistic and reliable skin infection model was established to study dermatophytoses in general and cutaneous T. benhamiae infections in particular.

A review and mathematical analysis of circadian rhythms in cell proliferation in mouse, rat, and human epidermis

The data from published studies of circadian rhythms in epidermal cell proliferation in mice, rats, and humans were reanalyzed. They were calculated as the percent difference from the mean at six timepoints over 24 h. Composite circadian rhythm curves were plotted from the combined data for each species for S-phase and M-phase. Each group of studies showed a general consensus on timing, and the composite curve showed a regular sinusoidal pattern. The rhythms in mice and rats were the same, whereas those in humans were in the opposite phase and had reduced amplitudes. In the rodents, S-phase peaked at about 3:30 A.M. and M-phase peaked at about 8:30 A.M. In humans S-phase peaked at about 3:30 P.M. and M-phase peaked at about 11:30 P.M. If the timing of the circadian rhythms in cell proliferation can be firmly established, it may be possible to schedule drug treatments to take advantage of the differences in cell proliferation rates at different times of day.

Effect of needle puncture and intradermal fluid injection on epidermal cell kinetics of albino guinea-pig skin

The flanks of male albino guinea pigs were used to study the effect of needle puncture with or without intradermal (id) injection of 0.1 ml fluid. The center of the raised bleb was marked and biopsies taken 1,4,8,24,50 and 72 hrs after needle puncture and 1 hr after intraperitoneal (ip) injection of tritiated thymidine (3H-TdR). There were no significant differences in labeling index (LI) or mitotic index (MI) 1 hr after id, ip, or subcutaneous (sc) injection nor in percent labeled mitoses, 7 hrs after id or ip injection. The earliest increase in LI (180% above control) occurred 12 hrs after needle puncture, peaked at 24 hrs (ca. 3X control), and returned to control level by 50 hrs. The area affected had a radius of about 5 mm from the point of needle entry or center of the bleb. Within 12 hrs after needle puncture, there was an increase in labeled cells primarily at the periphery of the bleb area, about 4 mm from the point of needle entry. By 24 hrs, the distribution of labeled cells had moved toward the bleb center (LI = 65%). The first increase in mitoses (MI = 2.5%) was seen 24 hrs after needle puncture. It is concluded that id injection introduces no significant error in LI or MI to 8 hrs after needle puncture. It does, however, trigger many noncycling basal cells into DNA synthesis after 8 hrs, and this may increase the rate of transit of these cells to the granular layer.