Regional difference in epidermal thinning after skin denervation

Denervation of skin has a profound influence on epidermis; epidermal thinni ng was a consistent finding in rats. However, it is not clear whether the d egree of epidermal thinning was similar in the region receiving the same in nervation. In mice, how early epidermal nerves were degenerated after nerve injury remained unknown. To address these issues, we transected the sciati c nerve in mice and compared the changes of epidermal thickness in differen t areas of the hind foot skin. Epidermal nerves degenerated within 48 h aft er nerve transection, similar to what was observed in rats. Seven days afte r nerve transection, there was differential thinning of epidermis. The inte rpad area, in the center of the sciatic nerve-innervated region, exhibited the most profound degree of epidermal thinning (34.6 +/- 3.1 vs 47.8 +/- 2. 4 mu m, P < 0.01). The heel area, in the periphery of the sciatic nerve-inn ervated zone, did not show significant thinning of epidermis after denervat ion (37.3 +/- 4.8 vs 41.5 +/- 5.1 mu m, P > 0.05). The degree of epidermal thinning after denervation in the pad area was the intermediate one: with 9 8.8 +/- 4.8 vs 120.1 +/- 7.3 mu m, P < 0.02, in the rete pegs, and 51.1 +/- 4.1 vs 62.1 +/- 6.0 mu m, P < 0.02, in the dermal papilla. The differentia l thinning was obvious when the thickness of the denervated epidermis was n ormalized to that of the control epidermis with the ratios of 0.73 +/- 0.03 in the interpad area, 0.83 +/- 0.04 in the rete peg, 0.85 +/- 0.05 in the dermal papilla, and 0.92 +/- 0.05 in the heel. Epidermal thinning was rever sed by reinnervation of the epidermis after sciatic nerve crush (41.5 +/- 1 .5 vs 45.0 +/- 2.0 mu m in the interpad area, P > 0.05). These findings sug gest that sensory nerves exhibit trophic influences on the epidermis presum ably through the effects of diffusible factors. (C) 1998 Academic Press.