Hair growth pattern in nude mice.

Nude mice are not bald but instead show an 'abortive' reduced hair growth on different sites of the integument. An albino (NMRI-nu) and a pigmented (C57BL/6-nu) strain of nude mice were examined as to whether the regional distribution pattern of this anagen hair proliferation is subject to the same ontogenetic development as in hairy mice. Hairy mice of both strains served as a comparison. Hair distribution was documented macroscopically by drawing and photography in a total of 415 mice of both sexes up to 421 days of age. Because of the pigmentation of the growing anagen hair follicles, the growth areas in the pigmented nude mice were distinctly visible whereas in the albino mice they were roughly recognisable from the boundaries of hair covering. The regional distribution of the 'abortive' anagen hair pattern in both nude strains corresponded to the wave-like course of the adult hair generations of hairy mice. As in older hairy mice, the hair cycle duration in nude mice was prolonged from an age of 121-180 days, the hair growth areas appeared reduced and less symmetrically orientated. Differences of up to 33% in body mass between the lighter nude and +/nu mice made ontogenetic comparison impossible so that all information is based on direct pattern or age comparison. The significance of experiments on the skin and hair follicles of nude mice is further increased if litters are examined comparatively and the temporal and spatial dimension of the follicle proliferation is considered more carefully than has been the case until now.