Effects of locomotor training on hindlimb regeneration in the urodele amphibian Pleurodeles waltlii

1. The effects of locomotor training on hindlimb regeneration were studied in the urodele amphibian Pleurodeles waltlii. 2. After amputation of one hindlimb at mid-femur, adult animals were subjec ted to regular training sessions (1 h daily, 5 days a week, over 8 months) of terrestrial stepping. 3. Eight months post-amputation, trained animals exhibited regenerated limb s of reduced size as compared to animals kept in their aquaria. Histologica l data showed an abnormal regeneration of both the femur and distal structu res (e.g. digit muscles, metatarsi and phalanges) while medial structures ( e.g. tibia and fibula) were totally reformed. The study of the electromyogr aphical activity in regenerated limbs during stepping and that of their ref lex responsiveness to electrical stimulation showed that both motor and sen sory innervations were functional in the limb stump of trained animals. 4. The regenerative capacity of the abnormal stumps was preserved since fol lowing a second amputation a quite normal hindlimb was regenerated in 3 mon ths, provided the re-amputated animals were not trained to terrestrial step ping. 5. The stress due to handling, change in locomotor medium (aquatic vs. terr estrial) and the friction of the wound epidermis with the ground were not i nvolved in the disruption of limb regeneration. 6. The locomotor pattern, the reflex responsiveness and the muscle fibre co mposition were similar in supernumerary forelimbs grafted on the back and i n normal forelimbs. However, the forelimbs regenerated normally even in ani mals subjected to locomotor supernumerary training while the hindlimb did n ot. It is concluded that the disrupting effects of locomotor training on li mb regeneration were localized to the the limb directly involved in locomot ion. 7. The mechanisms underlying, abnormal limb regeneration in animals subject ed to locomotor training are discussed.