Note: Among cell populations of HF the folloving are the most important:
- Cells of epithelial origin: matrix trichocytes [M] and ORS [outer root sheath] cells.
- Cells of dermal origin: DP fibroblasts and dermal sheath [DS] fibroblasts.
The last play in HF predominantly regulation role, while the former represent mitotically active populations.


Model DP +DS +ORS represent a proximal segment of HF (i.e. closer to interfollicular epidermis), that consists of DS and ORS “tubes” with DP or DP fibroblasts implanted inside it.
1. Several experiments were done on vibrissae HF in situ. Dissected DPs were implanted in proximal segments of vibrissae HFs (their length was about _ of the length of initial HFs). In 70 % of HF segments with implanted DPs fibre production was noticed 18-25 days after operation. Length of produced hairs was 14 –73 % from normally expected. First histological signs of anagen in these HFs was noticed 14 days after transplantation. Causal relationship between DPs and HFs segments’ growth status at transplantation and subsequent growth fashion of regenerated HFs wasn’t analyzed.

R. F. OLIVER ., The experimental induction of whisker growth in the hooded rat by implantation of dermal papillae // J. Embriol. Exp. Morph. Vol.18 ., p. 43-51, 1967

2. Modified experiments, where DPs or derma fibroblasts were transplanted into HF segments after previous cultivation in vitro show the following:
53 % of HF segments with low-passage DP fibroblasts [from 1 to 3] regenerate vibrissae HFs with apparently normal length of growth cycle. Fibres were first visible at the end of 4-th week. At histology, in these HFs new DPs were identified. Their origin from implanted DP fibroblasts was confirmed by auto-radiography.
In no case HF segments with low-passage dermal fibroblasts produce fibres.

C. A. JAHODA ., K. A. HORNE ., & R. F. OLIVER . Induction of hair growth by implantation of cultured dermal papilla cells. // Nature . vol.311, p. 560-562. 1984


3. In more recent experiments the following results were obtained:
3 of 4 HF segments with implanted regenerate vibrissae HFs. . Length of produced fibres was 33 –40 % from normally expected.
53 % of HF segments with implanted low-passage DP fibroblasts regenerate HFs produce fibres Length of produced whiskers was 25 –57 % from normally expected. First fibres were noticed above skin level 4 weeks after transplantation. Growth cycle parameters of regenerated HFs preserved. At histology new HF bulbs were located below amputated HFs segments.
In no case, HF segments with implanted high-passage DP fibroblasts [from 6 to 15] regenerate new DPs and new HFs. This fail of DP fibroblasts to regenerate new DPs is in concordance with the fact, that high-passage DP fibroblasts lose in vitro aggregate behavior -so characteristic for low passage DP fibroblasts.
Low-passage dermal fibroblasts don’t regenerate new HFs, with the exception of 2 cases. In one case, produced fiber was of vibrissae type. It was suggested, that this new HF regenerate from HF segment that was too long. Other regenerated HF produce pelage type fiber. These unexpected results can be treated as shortcomings of operation technique.

C. A. JAHODA ., K. A. HORNE ., & R. F. OLIVER Whisker growth induced by implantation of cultured vibrissa dermal papilla cells in the adult rat .// J. Embriol. Exp. Morph. Vol.97., p. 11-124., 1986

4. Proximal lengths of mouse vibrissae HFs with DP implanted inside them were transplanted under kidney capsule. This system regenerated new HFs and fiber production started 28 days after transplantation. First growth cycle was 45 days long. Whiskers were thick and have medulla

YI KOBAYASHI , PH . D ., & NISHIMURA , B . S . Ectopic growth of mouse whiskers from implanted lengths of plucked vibrissa follicles . // // J. Invest. Dermatol . 1989 . vol . 92 . p. 278 – 282 .

These results show us, that in situ and at transplantation under kidney capsule ORS cells can produce new pool of matrix cells. This apparently takes place under the inductive influence of transplanted DP fibroblasts. Stem cells of bulge region are the prime target of DP influence and here new pool of cells, that are committed to become trichocytes of matrix and IRS is produced. By their proliferation status these cells are already transient amplifiers. This process mimic regeneration of new matrix under the inductive influence of DP at the beginning of each growth cycle in intact HFs.
Also, in system: DS +ORS +M lower DS is capable to regenerate structurally and functionally normal DP.