The effect of serum calcium levels on the rate of epidermal renewal in the rat

Sensory and motor denervation influence epidermal thickness in rat foot glabrous skin

Denervation in man often results in shiny, dry, thin skin. A previous study has shown that the epidermis of glabrous skin in the rat becomes approximately 40% thinner within 1 week following sciatic nerve transection, but which nerve fiber type or types influence epidermal thickness is unknown. In this study, we compared the effects on the epidermis of selective sensory, motor, and sympathetic denervation. Protein gene product 9.5 and calcitonin gene-related peptide immunocytochemical staining were used to determine the extent of denervation of epidermis, dermis, and sweat glands in the footpads. Epidermal thickness of the glabrous plantar skin of the foot was measured. To verify the specificity and reliability of each animal model, the relevant regions of the peripheral nervous system were examined by light or electron microscopy or both. Epidermal thickness decreased significantly following sciatic nerve transection (58% of control, P < 0.05) and dorsal root ganglionectomy (59%; P < 0.05). The thickness also decreased following lumbar ventral rhizotomy (61%; P < 0.01), destruction of lumbar spinal motor neurons (66%; P < 0.05), and botulinum toxin-induced paralysis of the tibialis anterior and gastrocnemius muscles (70%; P < 0.05). A slight decrease followed dorsal rhizotomy (84%; P < 0.01). In contrast, no significant alterations in epidermal thickness were detected following sham operation and sympathectomy. Epidermal thinning was paralleled by reductions in the amounts of transcripts for glyceraldehyde-3-phosphate dehydrogenase and beta-actin. These results suggest that selective loss of both sensory and motor fibers to the hind limb can contribute to reducing epidermal thickness in rat foot glabrous skin.

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.