The development of synaptic connections between different segmental motoneurones and striated muscles in an axolotl limb

McGrath, P; Bennett, Maxwell R.

doi:10.1016/0012-1606(79)90280-x

Cited by 45 publications

(9 citation statements)

References 20 publications

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“…However, it is possible that a period of pathway modification might occur between the time of initial axonal outgrowth and St. 35-36. Experimental evidence in the amphibian limb (Lamb, 1976;McGrath & Bennett, 1979) and the chick wing (Pettigrew, Lindeman & Bennett, 1979) suggests that some incorrect projections are made and subsequently removed during normal embryogenesis. Further, these events occur just prior to and at the onset of motoneurone cell death periods in the cord.…”

Section: Axonal Pathwaysmentioning

confidence: 99%

Motoneurone projection patterns in the chick hind limb following early partial reversals of the spinal cord.

Lance‐Jones

Landmesser

1980

The Journal of Physiology

197

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1. The development of motoneurone projection patterns in the chick hind limb from reversed spinal cord segments was studied from the onset of axonal outgrowth (St. 24) to the establishment of mature connectivity patterns (St. 36). Approximately the first three lumbosacral cord segments were reversed along the anterior-posterior axis at St. 15-16. 2. Projection patterns from reversed cord segments were assessed electrophysiologically by direct spinal cord and spinal nerve stimulation and anatomically by retrograde horseradish peroxidase (HRP) labelling of motoneurones in St. 30-36 embryos. In younger embryos, paths taken by reversed axons were characterized by orthograde HRP labelling of motoneurones in specific reversed cord segments. 3. Lumbosacral motoneurones formed appropriate functional connexions with individual limb muscles in spite of anterior-posterior shifts in their spinal cord position aned consequent shifts in their spinal nerve entry point into the limb bud. Reversed motoneurones supplying individual hind limb muscles formed discrete nuclei in the transverse plane of the cord. Each nucleus and the lateral motor column as a whole showed reversed topographical characteristics when compared to control embryos. These observations were made before (St. 30) and after (St. 35-36) the major period of motoneurone cell death. 4. Correct connectivity resulted from specific alterations in axonal pathways within the plexus or major nerve trunks proximal to the branching of individual muscle nerves. Further such directed outgrowth was present from the earliest times that axons could be traced into the limb which is before the onset of motoneurone cell death and muscle cleavage. 5. It is concluded that motoneurones are specified to project to individual muscles or to follow particular pathways prior to motoneurone birthdays and limb bud formation. The establishment of specific motoneurone connectivity can not be accounted for by passive or mechanical guidance models alone. Rather, motoneurones must also actively respond to cues within the limb or interact among themselves on the basis of an early central specification.

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Section: Axonal Pathwaysmentioning

confidence: 99%

Motoneurone projection patterns in the chick hind limb following early partial reversals of the spinal cord.

Lance‐Jones

Landmesser

1980

The Journal of Physiology

197

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“…Some authors have claimed that the earliest connections were of a random nature, and that the mature pattern of connection is not established until after the period of cell death. On this basis, these authors concluded that the role of cell death is to weed out inappropriately connected motor neurons (McGrath and Bennett, 1979; Pettigrew et al, 1979). However, a number of studies have shown that properly patterned connections are established before the period of cell death (Landmesser and Morris, 1975; Lamb, 1976; Hollyday et al, 1977; Ashwell and Watson, 1983).…”

Section: Introductionmentioning

confidence: 99%

What Determines Motor Neuron Number? Slow Scaling of Facial Motor Neuron Numbers With Body Mass in Marsupials and Primates

Watson¹,

Provis²,

Herculano‐Houzel³

2012

The Anatomical Record

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How does the number of motor neurons in the brain correlate with the muscle mass to be controlled in the body? Numbers of motor neurons are known to be adjusted during development by cell death, but the change in the percentage of surviving motor neurons in response to experimental changes in target muscle mass is relatively small. Here we address the quantitative matching between final numbers of motor neurons in the facial nucleus and body mass (which we use as a proxy for the muscle mass). In 22 marsupial species, we found that the number of facial motor neurons is strongly correlated with body mass, and scales across species as a power function of body mass with a very small exponent of 0.184, which is close to the exponent found in primates from previously published data. With such an exponent, doubling the body mass is accompanied by a modest increase of only 14% in numbers of facial motor neurons, while halving body mass results in a decrease of only 12%. These numbers are remarkably similar to the 15-20% increase or 8% decrease in the number of spinal cord motor neurons that results from experimental or natural doubling or reducing by half the target muscle field of birds and amphibians. The scaling rule presented here might thus account for the quantitative matching of motor neurons to their target muscle mass in evolution. With this small scaling exponent, our data also raise the possibility that larger animals will have larger motor units.

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“…Such activity-based sorting mechanisms have been shown to be important in the refinement of orderly topographic maps and small receptive fields in sensory pathways during development and regeneration ( Wong, 1993;Cramer and Sur, 1995). Similar mechanisms may be responsible for the sharpening of compartmentalization of segmental inputs to muscles ( McGrath and Bennett, 1979;Brown and Booth, 1983;Bennett and Lavidis, 1984;Bennett and Ho, 1988;Callaway et al, 1989;Donohue and English, 1989;English, 1990;Gatesy and English, 1993;Ribchester, 1993). In the pectoralis, the refinement is extremely precise, occurring at the level of single motor units, which appear to constrict their projections during maturation by the loss of inputs at the edges of the projection (Grinnell and Harada, 1996).…”

Section: Discussionmentioning

confidence: 90%

Regeneration of specific innervation inXenopus pectoralis muscle

Harada¹,

Grinnell²

1996

J. Neurobiol.

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The development of synaptic connections between different segmental motoneurones and striated muscles in an axolotl limb

Cited by 45 publications

References 20 publications

Motoneurone projection patterns in the chick hind limb following early partial reversals of the spinal cord.

Motoneurone projection patterns in the chick hind limb following early partial reversals of the spinal cord.

What Determines Motor Neuron Number? Slow Scaling of Facial Motor Neuron Numbers With Body Mass in Marsupials and Primates

Regeneration of specific innervation inXenopus pectoralis muscle

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