Myasthenia gravis immunoglobulin augments motor neuron survival without producing muscle paralysis.

Effects of sera or immunoglobulins from patients with acquired myasthenia gravis on motor neuron survival during critical stages of embryonic development were investigated in the trochlear nucleus-superior oblique muscle system of white Peking duck embryos. A significant increase in motor neuron survival occurred following application of myasthenia gravis sera or myasthenic immunoglobulin during the period of embryonic death of motor neurons. There was no reduction in limb or extraocular muscle movement in treated embryos. Trochlear motor neuron survival persisted after sera or immunoglobulin treatment was discontinued. The total number of muscle fibers and acetylcholine receptors were unchanged following immunoglobulin treatment. Myasthenic immunoglobulin is therefore unique in preventing motor neuron death without producing muscle paralysis and in promoting a prolonged augmentation of motor neuron survival. It is concluded that factors other than muscle activity may also control neuron survival during embryogenesis. Previous studies of myasthenic sera in muscle have shown effects only postsynaptically. This is the first demonstration that myasthenic immunoglobulin affects structures in the central nervous system.