Reformation of specific neuromuscular connections during axolotl limb regeneration: evidence that the first contacts are correct

Development ◽  
1988 ◽  
Vol 103 (2) ◽  
pp. 365-377
Author(s):  
S. Wilson ◽  
M. Jesani ◽  
N. Holder
Keyword(s):  
Spinal Cord ◽  
Horseradish Peroxidase ◽  
Limb Regeneration ◽  
Microscopic Analysis ◽  
Motor Neurone ◽  
Extensor Digitorum ◽  
Limb Muscle ◽  
Proximal Muscle ◽  
Electron Microscopic ◽  
Neuronal Tracing

Retrograde neuronal tracing with horseradish peroxidase was used to determine the position in the spinal cord of the motor neurone pools of a proximal (biceps) and a distal (extensor digitorum) limb muscle at various times during axolotl limb regeneration. It was found that from the earliest stages of muscle redifferentiation (as judged by light and electron microscopic analysis) the vast majority of axons innervating the regenerating muscles came from cells within the bounds of the normal motor neurone pool for each muscle. A few incorrect projections were noted in that the regenerating proximal muscle was sometimes innervated by some cells caudal to its normal motor neurone pool. The results are discussed in terms of mechanisms that may be operating in the regenerating limb to ensure that specific neuromuscular connections are made.

Reformation of the pattern of neuromuscular connections in the regenerated axolotl hindlimb

Development ◽  
1987 ◽  
Vol 99 (2) ◽  
pp. 221-230
Author(s):  
N. Stephens ◽  
N. Holder
Keyword(s):  
Spinal Cord ◽  
Horseradish Peroxidase ◽  
Detailed Analysis ◽  
Normal Control ◽  
Motor Neurone ◽  
Normal Position ◽  
Distal Limb ◽  
Neuronal Tracing ◽  
Limb Muscles ◽  
Motor Neurones

Retrograde neuronal tracing with horseradish peroxidase (HRP) was used to determine the position in the spinal cord of motor neurone pools innervating muscles in the regenerated axolotl hindlimb. This method allows a detailed analysis of the accuracy of reformation of neuromuscular connections. The results show that regenerated distal limb muscles are reinnervated by motor neurones in the same region of the cord as those that innervate normal control distal limb muscles but that proximal muscles are innervated by a mixture of motor neurones in a normal position and motor neurones in a region of the spinal cord that normally supplies innervation to distal limb muscles. This difference between the reinnervation of proximal and distal limb muscles suggests that axons destined for proximal muscles may not enter distal limb territory during reinnervation of the regenerated limb.

The pattern of innervation in serially duplicated axolotl limbs: further evidence for the existence of local pathway cues?

Development ◽  
1987 ◽  
Vol 100 (3) ◽  
pp. 479-487
Author(s):  
N. Stephens ◽  
N. Holder
Keyword(s):  
Spinal Cord ◽  
Horseradish Peroxidase ◽  
Local Environment ◽  
Retrograde Transport ◽  
Limb Muscle ◽  
Biceps Muscle ◽  
Motor Innervation ◽  
Nerve Sprouting ◽  
Correct Pattern ◽  
Motor Neurones

The innervation of the biceps muscle was examined in regenerated and vitamin A-induced serially duplicated axolotl forelimbs using retrograde transport of horseradish peroxidase. The regenerated biceps muscle becomes innervated by motor neurones in the same position in the spinal cord as the normal biceps motor pool. In previous experiments in which the innervation of a second copy of a proximal limb muscle was examined in serially duplicated limbs (Stephens, Holder & Maden, 1985), the duplicate muscle was found to become innervated by motor neurones that would normally have innervated distal muscles. In the present study, the innervation of the second copy of biceps was examined under conditions designed to encourage nerve sprouting from ‘correct’ biceps axons. Following either partial limb denervation or denervation coupled with removal of the proximal biceps, the second copy of the muscle was still innervated by inappropriate motor neurones, which again would normally innervate distal limb muscles. These results are interpreted as evidence for the necessity for an appropriate local environment for axonal growth to allow reformation of a correct pattern of motor innervation in the regenerated limb.

A horseradish peroxidase study of motorneuron pools of the forelimb and hindlimb musculature of the axolotl

1985 ◽  
Vol 224 (1236) ◽  
pp. 325-339 ◽  
Keyword(s):  
Spinal Cord ◽  
Horseradish Peroxidase ◽  
Transverse Plane ◽  
Extensor Digitorum ◽  
Limb Muscles ◽  
Axis Position ◽  
Rostrocaudal Axis ◽  
Flexor Digitorum

Motorneuron pools innervating axolotl limb muscles have been investi­gated by using the retrograde neuronal tracer horseradish peroxidase. Four muscles in the forelimb (biceps, anconeus, flexor digitorum and extensor digitorum) and four functionally equivalent muscles in the hindlimb (puboischiotibialis, iliotibialis, flexor digitorum and extensor digitorum) were studied. Motorneuron pools were characterized by using four criteria: position in the rostrocaudal axis; position of the median in the rostrocaudal axis; number of labelled cells; position of cells in the transverse plane of the spinal cord. Each pool was uniquely defined by the four characteristics, although overlap was found between pools. Two types of motorneuron were found in each pool, distinguished on the basis of size, shape and position in the spinal cord. The first type constituted the majority of cells in a pool, and occupied different positions in the transverse plane for each muscle. The second type was less common and always occupied a characteristic medial ventral position. These data will allow an assay of correct or incorrect innervation in experiments on the regeneration of specific neuromuscular connections in these animals.

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