A GLOBULAR, NOT A SYMMETRICAL, FORM OF ACETYLCHOLINESTERASE IS EXPRESSED IN CHICK MOTOR-NEURONS - DOWN-REGULATION TOWARD MATURITY AND AFTERDENERVATION

In vertebrate neuromuscular junctions, the postsynaptic specialization s include the accumulation of acetylcholinesterase (AChE) at the synap tic basal lamina and the muscle fiber. Several lines of evidence indic ate that the presynaptic motor neuron is able to synthesize and secret e AChE at the neuromuscular junctions. By using anti-AChE catalytic su bunit, anti-butyrylcholinesterase (BuChE) catalytic subunit, and anti- AChE collagenous tail monoclonal antibodies, we demonstrated that the motor neurons of chick spinal cord expressed AChE in vivo and the pred ominant AChE was the globular form of the enzyme, Neither asymmetric A ChE nor BuChE was detected in the motor neurons. The molecular mass of AChE catalytic subunit in the motor neuron was similar to 105 kDa, wh ich was similar to that of the globular enzyme from low-salt extracts of muscle both of them were similar to 5 kDa smaller than the asymmetr ic AChE from high-salt extracts of muscle, The level of AChE expressio n in the motor neurons decreased, as found by immunochemical and enzym atic analysis, during the different stages of the chick's development and after nerve lesion. Thus, the AChE activity at the neuromuscular j unctions that is contributed by the presynaptic motor neurons is prima rily the globular, not the asymmetric, form of the enzyme, and these c ontributions decreased toward maturity and after denervation.