Changes in the endplate accumulation of acetylcholinesterase during synapse elimination in the mouse

Focal accumulations of acetylcholinesterase (AChE; EC 3.1.1.7), cholinesterase (ChE, EC 3.1.1.8) and total cholinesterase (TChE; AChE+ChE) were examined in developing mouse diaphragm by using a modified Karnovsky/Roots staining method. The lengths of TChE and AChE reaction product accumulations reached significant peaks on postnatal day (PD) 1 (P < 0.05), decreased to a minimum on PD 9 and then increased in proportion to muscle fiber diameter (PD 9 to adult). The normalized area of accumulation (area of accumulation/fiber diameter) for AChE and TChE also decreased by 19% (P < 0.05) between PD 3 and PD 7. In contrast, ChE focal accumulation did not decrease during the period of synapse elimination, but rather increased in proportion to the postnatal growth of the muscle fiber. These results suggest that AChE is more sensitive to neurotrophic influences than ChE; particularly during late embryonic and early postnatal periods of synapse elimination.