Age changes of motor innervation and acetylcholine receptor distribution on human skeletal muscle fibres.

Age changes of motor innervation and acetylcholine receptor (AChR) distribution on human intercostal muscle fibres (age 32-76 years) were investigated by using combined silver and acetylcholinesterase (AChE) staining method and [125I]alpha-bungarotoxin autoradiography. In the older subjects, (1) the number of preterminal axons entering an endplate and the length of endplate increased, and (2) the endplate was composed of a greater number of smaller conglomerates of AChRs, as compared with the younger subjects. In addition, (3) perijunctional AChRs were observed in the older subjects, but not in the younger ones. Linear relationships were observed between each of these parameters and age. These results suggest that there are gradual changes in the pre- and postsynaptic components of human skeletal muscle endplate over adult life.