Neostigmine-induced end-plate proliferation in the rat. A study using supra-vital methylene blue.

The supra-vital methylene blue technique was used to study motor end-plate morphology in 21 BD-1X rats, treated for 7 to 16 weeks with oral neostigmine bromide, and in five control animals. Motor endings of treated animals showed preterminal, terminal, and ultraterminal sprouting and an increase in mean end-plate length (p less than 0.001). These changes were most prominent after 14 weeks of treatment. After 16 weeks of therapy, mean end-plate length decreased and the proliferative abnormality became less evident. The adverse effect of neostigmine on motor end-plates may have clinical relevance in the management of myasthenia gravis and may be partly responsible for the end-plate abnormalities previously reported in this disease.