Whisker growth after removal of the dermal papilla and lengths of follicle in the hooded rat

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Abstract
The arrangement and mode of growth of the major vibrissae on the upper lip of the hooded rat has been studied. There was an antero-posterior gradation in rates of growth and club lengths produced in each of the vertical rows. The longest vibrissae were produced at the fastest rate in the larger follicles in the posterior vertical rows. There was a similar antero-posterior gradation in the times for a phase of growth throughout each of the vertical rows. There are no overall waves of growth on the upper lip; phases of growth are entered into by the vertical rows individually. The suggestion is made that the above behaviour may be related to the mode of development of the vibrissae in the embryo. A method has been described for the removal of the dermal papilla in situ and the removal of dermal papillae and various lengths of whisker root (‘root ends’) have been performed to determine the effects of these operations on whisker growth. After removal of dermal papillae, all 18 follicles produced generations of whiskers; 15 of these follicles produced vibrissae of normal or nearly normal length. After removal of root ends, whiskers of shorter than normal length were produced from 28 out of 37 follicles. Conclusive evidence was obtained that generations of vibrissae can be produced after complete removal of the dermal papilla. The degree of regeneration, as expressed by the length of post-operative whiskers produced, was apparently dependent on the amount of proximal follicle root removed.