Motorneuron pools innervating muscles in vitamin A-induced proximal-distal duplicate limbs in the axolotl

Serially duplicated limbs containing two sets of proximal muscles were created in axolotls by vitamin A treatment. The innervation of three replicated proximal muscles was studied by using retrograde transport of horseradish peroxidase. These were the forelimb muscles biceps (seven cases) and anconeus (five cases) and the hindlimb muscle puboischiotibialis (five cases). In two cases (both of anconeus) innervation was from a correct motorneuron pool. In the other 15 cases the innervation was from an incorrect, distal limb muscle, motorneuron pool. These results are interpreted as evidence against long range signals between nerve and muscle controlling specific nerve regeneration. However, the data are compatible with models of axonal guidance that use local pathway cues.