Aged neuromuscular junctions in the extensor digitorum longus muscle of the rat as revealed by scanning electron microscopy

We examined the overall morphology of subneural apparatuses (SNAs) at neuromuscular junctions by scanning electron microscopy in the extensor digitorum longus muscle of aged (18 months) rats. Most of aged SNAs were mainly characterized by a large number (more than 20) of cup-like depressions (2-5 mu m in diameter) with numerous slit-like junctional folds about 0.1 mu m wide and 5 mu m at maximum length, while some SNAs consisted of a small number (fewer than 10) of depressions or poorly-developed gutters containing pit-like and/or slit-like junctional folds. Additionally, numerous slits were often found outside the depressions, possibly indicating the preexisting junctional folds persisted for a long time after the gutter-into-cup transformation of the SNAs. These structural changes of SNAs during ageing are discussed briefly.