EFFECTS OF CHRONIC PARALYSIS WITH ALPHA-BUNGAROTOXIN ON DEVELOPMENT OF INNERVATION

Chronic paralysis of the duck embryo with α-bungarotoxin increases the number of trochlear motor neurons that survive by decreasing the magnitude of embryonic cell death. The present study examined how such an increase in the motor neuron projection is accommodated at the peripheral target. The results indicate that the overall size of the duck superior oblique muscle was drastically reduced following chronic paralysis with α-bungarotoxin. The number of motor end-plates was reduced to about 25% of the control. Although the total number of end-plates was significantly reduced, their size was larger and they became innervated by far more nerve terminals than in the control. Thus, increased motor neuron survival occurred while the size of the periphery and the number of synaptic sites (end-plates) were greatly reduced. These observations suggest that the cause of embryonic cell death may not be related to the availability of adequate numbers of synapses with the periphery. They also suggest that the physiologic activity of the embryo may play a significant role in regulation of cell number in the developing nervous system. © 1979.