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Muscle spindle reinnervation following phenol block
1Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.
Cells, Tissues, Organs
|June 27, 2000
Summary
Phenol nerve blocks for spasticity cause complete muscle spindle denervation. Sensory reinnervation occurs within six weeks, but motor (gamma) reinnervation is significantly delayed or incomplete.
Area of Science:
- Neuroscience
- Peripheral Nerve Regeneration
- Muscle Physiology
Background:
- Phenol injections are clinically used to manage spasticity via chemical denervation.
- Muscle spindles are crucial sensory receptors within muscles, providing feedback on muscle length and tension.
Purpose of the Study:
- To investigate the effects of phenol nerve block on the innervation of muscle spindles.
- To evaluate the timeline of sensory and motor reinnervation of muscle spindles after phenol treatment.
Main Methods:
- Peripheral nerve phenol block was simulated in rats using a 7% phenol solution on the lateral plantar nerve.
- Muscle spindles in plantar lumbrical muscles were analyzed at 4 and 6 weeks post-phenol block.
- Immunohistochemistry was employed to assess spindle integrity and reinnervation using antibodies for slow tonic myosin and neurofilament protein.
Main Results:
- Four weeks post-phenol block, muscle spindles showed reduced immunoreactivity and were mostly denervated (>80%), with some receiving only afferent innervation.
- No efferent (gamma) innervation was observed in spindles at the 4-week mark.
- By six weeks, nearly all spindles (>90%) exhibited afferent reinnervation, while only 38% showed gamma motor reinnervation.
Conclusions:
- Phenol nerve block leads to complete denervation of muscle spindles.
- Sensory reinnervation of muscle spindles is relatively rapid following phenol treatment.
- Motor (gamma) reinnervation of muscle spindles is either incomplete or substantially delayed after phenol nerve block.