THE EFFECTS OF POST-GANGLIONIC AXOTOMY ON SELECTIVE SYNAPTIC CONNEXIONS IN THE SUPERIOR CERVICAL GANGLION OF THE GUINEA-PIG

J. Physiol., 1979 · DOI: · Published: March 20, 1979

Simple Explanation

The study investigates how nerve damage (axotomy) affects the connections in a specific nerve cluster (superior cervical ganglion) in guinea pigs. Specifically, it looks at how cutting the nerve fibers after the ganglion (post-ganglionic axotomy) changes the way different parts of the spinal cord influence the organs connected to the ganglion. Normally, stimulating different spinal cord levels has different effects on organs like the eye. The research explores whether damaging the nerve fibers changes this selective influence, and if the nerve cells in the ganglion change their connections when they have to re-establish links with the body. The findings suggest that after nerve damage, the original selective connections are not accurately re-established. The ganglion cells do not seem to change their fundamental properties even when they connect to new targets, indicating a permanent identity of these cells.

Study Duration

3 months

Participants

Adult guinea-pigs (250-400 g)

Evidence Level

Not specified

Key Findings

1
Post-ganglionic axotomy leads to a loss of the normal differential effectiveness of stimulating different thoracic ventral roots on end-organ responses, particularly in the eye.
2
Despite the abnormal end-organ responses, the segmental innervation of individual ganglion cells appeared largely normal after recovery from axotomy. Cells were innervated by a contiguous subset of spinal segments with a dominant segment, similar to unoperated animals.
3
Post-ganglionic axons do not regenerate selectively to their original peripheral targets. This was evidenced by the lack of predictable differences in segmental innervation of neurones running to different destinations in cervical spinal nerves after axotomy.

Research Summary

This study examines the impact of post-ganglionic axotomy on synaptic connections within the superior cervical ganglion of guinea pigs, focusing on whether altering a neuron's target leads to compensatory changes in its innervation. The key finding is that post-ganglionic regeneration is less precise than preganglionic regeneration. Axons regrow without preference for their original peripheral targets, and ganglion cells do not change their segmental innervation in response to novel peripheral innervation. The results suggest that ganglion cells possess a permanent identity that determines their segmental innervation, irrespective of the targets they innervate, and that specificity in neural connectivity relies on axon guidance and selective synaptogenesis.

Practical Implications

Nerve Regeneration Strategies

The findings highlight the challenges in achieving precise nerve regeneration after injury, suggesting that interventions may need to focus on improving axon guidance to original targets.

Understanding Neural Plasticity

The study contributes to the understanding of neural plasticity by demonstrating that certain aspects of neuronal identity, such as segmental innervation, may be more fixed than previously thought, even in the face of significant peripheral changes.

Targeted Therapies

The research suggests that therapies aimed at altering neuronal connections may need to consider the inherent properties of neurons and the limitations of re-specification after injury.

Study Limitations

1
The study focuses on positional attributes of innervation and does not assess the accuracy of post-ganglionic re-innervation with respect to modality.
2
The study cannot definitively rule out the possibility that contiguity and segmental dominance after recovery from axotomy represent neither the original preference, nor a novel preference retrogradely imposed from the periphery.
3
The experiments primarily address adult neurons, and the findings may not be directly applicable to developmental events or the specification of segmental innervation during ontogeny.

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