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Abstract:
A FOREIGN motor nerve transplanted on to an adult innervated muscle will not form functional neuromuscular synapses1, yet several experimental procedures, such as denervation or muscle crush, change the properties of the muscle membrane so that a foreign nerve can establish ‘ectopic’ synapses in a normally endplate-free region of the muscle2–4. The nerve thereby induces a localised area of high acetylcholine receptor (AChR) density in the extrajunctional membrane5. Denervated or previously crushed muscle fibres already have, before synapse formation, low density AChRs in the extrajunctional membrane6,7. The extrajunctional AChRs are different in a number of respects from those in the junctional membrane8–11. The question is, therefore, whether the AChRs of an ectopic synapse have properties similar to junctional or to extrajunctional AChRs.
