Types of junctions encountered in aged muscles as a result of the two-color bungarotoxin experiments
| Status of AChR labeling/status of AChR plaque | ||||
|---|---|---|---|---|
| First weak, second strong | First strong, second strong | |||
| AChR fragmented | AChR smooth | AChR fragmented | AChR smooth | |
| Central nuclei present | 6a | 0 | 7b | 0 |
| Central nuclei absent | 0 | 0 | 133c | 25d |
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Data are from 171 NMJs examined in three muscles at 25–32 months of age, 2 weeks following vital application of first-color bungarotoxin and at the time of application of second color. Numerical entries are given superscripts that indicate their interpretation as follows.
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↵aSix (4%) NMJs on fibers that experienced a degeneration/regeneration episode in the postsynaptic segment in the 2 week period; all have central nuclei.
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↵bSeven (4%) NMJs on fibers that experienced a degeneration/regeneration episode in the postsynaptic segment prior to start of the 2 week period but not so long ago that central nuclei have completed their migration to the periphery; central nuclei are present.
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↵cOne hundred thirty-three (78%) NMJs on fibers that experienced a degeneration/regeneration episode in the postsynaptic segment more than ∼30 d before; these have no central nuclei.
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↵dTwenty-five (15%) NMJs that appear “young” and are located on fibers that, in contrast to all the NMJs above, have never experienced degeneration/regeneration of the postsynaptic segment of muscle fiber; these have no central nuclei.
