SYNAPSE FORMATION IN INTACT INNERVATED CUTANEOUS-PECTORIS MUSCLES OF THE FROG FOLLOWING DENERVATION OF THE OPPOSITE MUSCLE

J. Physiol., 1979 · DOI: · Published: January 1, 1979

Simple Explanation

When one muscle in a frog is denervated, the nerves of the corresponding muscle on the opposite side sprout and create new connections. This study investigates the source and pathway of the signal that causes this sprouting. The experiment found that the signal for sprouting and synapse formation comes from the damaged nerve cells, not from the denervated muscle tissue itself. The signal travels within the spinal cord to reach the intact motor nerve cells on the opposite side. The extent and timing of new synapse formation depend on the severity and location of the nerve injury. More severe injuries closer to the spinal cord lead to faster and greater synapse formation.

Study Duration

8-56 Weeks

Participants

Rana pipiens frogs, 5 cm body length

Evidence Level

Not specified

Key Findings

1
Denervation of one cutaneous-pectoris muscle induces the formation of new synapses in the intact innervated muscle on the opposite side.
2
The formation of new synapses is independent of denervated muscle fibers or degenerating axons peripheral to the site of axotomy.
3
The number of new synapses formed depends on the type of lesion to the motor nerve on the opposite muscle.

Research Summary

Denervation of one cutaneous-pectoris muscle of the frog induces the formation of new synapses in the intact innervated muscle on the opposite side. The formation of the new synapses in the intact muscle is independent of the presence of denervated muscle fibres or degenerating axons peripheral to the site of axotomy. These results suggest that the signal for sprouting and synapse formation may arise in the damaged nerve cells, central to the site of axotomy, and then be communicated transneuronally within the spinal cord to the intact motoneurones on the opposite side.

Practical Implications

Central Nervous System Plasticity

Demonstrates the capacity of the central nervous system to reorganize and form new connections in response to injury, even in distant, uninjured areas.

Neurotrophic Interactions

Highlights the potential role of trophic factors released by injured nerve cells in influencing the behavior and connectivity of intact neurons.

Rehabilitation Strategies

Suggests that therapeutic interventions targeting the injured nerve cells and spinal cord may promote beneficial plasticity and recovery in cases of nerve damage or denervation.

Study Limitations

1
The study was conducted on frogs, and the findings may not be directly applicable to mammals or humans.
2
The electrophysiological method used may underestimate the incidence of polyneuronal innervation.
3
The exact nature of the signal for sprouting and synapse formation remains unclear.

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