CHANGES IN THE END-PLATE ACCUMULATION OF ACETYLCHOLINESTERASE DURING SYNAPSE ELIMINATION IN THE MOUSE

Focal accumulations of acetylcholinesterase (AChE; EC 3.1.1.7), cholin esterase (ChE, EC 3.1.1.8) and total cholinesterase (TChE; AChE + ChE) were examined in developing mouse diaphragm by using a modified Karno vsky/Roots staining method. The lengths of TChE and AChE reaction prod uct accumulations reached significant peaks on postnatal day (PD) 1 (P < 0.05), decreased to a minimum on PD 9 and then increased in proport ion to muscle fiber diameter (PD 9 to adult). The normalized area of a ccumulation (area of accumulation/fiber diameter) for AChE and TChE al so 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 elim ination, but rather increased in proportion to the postnatal growth of the muscle fiber. These results suggest that AChE is more sensitive t o neurotrophic influences than ChE; particularly during late embryonic and early postnatal periods of synapse elimination.