PubMed · 3337645
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M B Katirji. 1988. SNAP recording technique.. https://pubmed.ncbi.nlm.nih.gov/3337645/
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Many materials have been used for artificial tubular prostheses to assist peripheral nerve gap reconstruction. However, the clinical use of these devices has been restricted because a microsurgical procedure requires specialized techniques and expensive equipment, such as operating microscope systems. Therefore the authors developed a new gluing method, without sutures, that uses freeze-dried alginate gel. A 7-mm gap in the sciatic nerve of rats was bridged with freeze-dried alginate gel. Regeneration was evaluated by electrophysiologic testing and histologic study. Eighteen weeks after surgery, functional reinnervation of motor and sensory nerves had occurred, as demonstrated by recovery of compound muscle action potentials (CMAP), compound nerve action potentials (CNAP), and somatosensory-evoked potentials (SEP). Histologically, many regenerated nerve fasciculi, including myelinated and unmyelinated fibers, were observed and the implanted alginate gel had disappeared. In conclusion, a gluing technique using alginate gel is a potential alternative to the conventional nerve autograft technique. Advantages include simple application and rapid repair. Freeze-dried alginate gel is a promising material for artificial nerve guides for peripheral nerves and also could be used for repair of disrupted pathways in central nervous tissue that is amorphous and cannot be sutured.
Neonatal spinal motor neurons are electrically and dye-coupled by gap junctions, but coupling is transient and disappears rapidly after birth. Here we report that adult motor neurons become recoupled by gap junctions after peripheral nerve injury. One and 4-6 weeks after nerve cut, clusters of dye-coupled motor neurons were observed among axotomized, but not control, lumbar spinal motor neurons in adult cats. Electrical coupling was not apparent, probably because of the electrotonic distance between dendrodendritic gap junctions and the somatic recording location. Analyses of gap junction protein expression in cat and rat showed that the repertoire of connexins expressed by normal adult motor neurons, Cx36, Cx37, Cx40, Cx43, and Cx45, was unchanged after axotomy. Our results suggest that the reestablishment of gap junctional coupling among axotomized adult motor neurons may occur by modulation of existing gap junction proteins that are constitutively expressed by motor neurons. After injury, interneuronal gap junctional coupling may mediate signaling that maintains the viability of axotomized motor neurons until synaptic connections are reestablished within their targets.
Synapse competition and elimination are widespread developmental processes, first demonstrated at neonatal neuromuscular junctions. Action potential activity was long shown to exert a powerful influence, but mechanisms and contribution relative to other factors are still not well understood. Here we show that replacement of natural motoneuronal discharge with synchronous activity suppresses elimination of polyneuronal innervation of myofibers. This requires the simultaneous chronic conduction block (tetrodotoxin) and distal electrical stimulation of motor axons during ectopic synaptogenesis in denervated adult soleus muscle. If in fact chronic stimulation is applied without central block of motor axons, the time course of synapse elimination is as fast as in control muscles undergoing natural activity. Our findings follow the prediction of Hebb's postulate and imply that asynchronous activity drives developmental synapse elimination in muscle. They further suggest that motoneurons could become transiently synchronized during development and regeneration, helping to establish the initial polyneuronal innervation.