Preamputation and postamputation histology of the neonatal opossum hindlimb: implications for regeneration experiments.

Mammalian limbs generally do not regenerate, regardless of added hormonal or nervous stimulation, whether amputation occurs during fetal life or post-partum. The one exception, the newborn opossum, has been reported to regenerate the incompletely developed hindlimb (Mizell, '68). In an attempt to repeat and extend these earlier findings, we have examined the histology of the neonatal opossum hindlimb. After amputation on day 4 post-partum, we correlated the histology of the amputated segment with the histology of the remaining stump after a "regeneration time" of several weeks. Amputations through the middle of the hindlimb on day 4 did not transect the tibia and fibula because the rudiments of these bones are still almost completely inside the body wall. Midlimb amputations transected instead the tarsal rudiments or even phalangeal rudiments. Limb stumps were therefore left with distal skeletal rudiments which subsequently underwent further embryonic development and growth giving the erroneous impression of regeneration. Of 30 amputated hindlimbs, none showed regeneration.