Characterization of various nervous tissues of the chick embryos through responses to chronic application and immunocytochemistry of beta-bungarotoxin.
beta-Bungarotoxin (beta-BT) was applied to chick embryos at 3-day intervals beginning on the fourth day of incubation to investigate ultrastructurally the effects of chronically and massively applied beta-BT on various nervous tissues and muscles. On the twenty-first day of incubation, spinal cords of beta-BT treated embryos were conspicuously decreased in size. Ventral root fibers dorsal root fibers, white matter, and motor neurons disappeared. Although spinal ganglia and sympathetic trunk ganglia were completely absent, Auerbach's and Meissner's ganglia nerve cells in the small intestine and adrenal medullary cells were not affected. In retinas of beta-BT treated animals ganglion cells and optic nerve fibers disappeared, but photoreceptor cells, bipolar cells and horizontal cells remained intact. Furthermore, olfactory nerve cells and their unmyelinated nerve fibers ensheathed by Schwann cells were quite undamaged. Skeletal muscles degenerated, whereas cardiac muscles were unaffected. In the present study various nervous tissues of the twenty-first day normal chick embryos were incubated with beta-BT and target cells of beta-BT were detected directly by the reaction with horseradish peroxidase labelled anti beta-BT guinea pig IgG. Motor nerve cells in the spinal cords, spinal and sympathetic ganglia nerve cells, ganglion cells and some nerve cells at the inner part of the inner nuclear layer in the retinas were positively stained, whereas Auerbach's and Meissner's ganglia nerve cells in the small intestine, adrenal medullary cells, photoreceptor cells, bipolar cells and horizontal cells in the retina and olfactory nerve cells were negative. Thus the present study shows the beta-BT has extensive destructive effects on various nerve cells which were revealed to be target neurons of beta-BT by immunocytochemistry. Those nerve cells, affected by beta-BT and positively stained with immunocytochemical reaction were supposed to have different characteristics from unaffected cells. One of the differences between these affected cells and unaffected cells may be whether there exist binding sites for beta-BT on the plasma membrane or not. The possibility of the use of beta-BT to characterize various nervous tissues is presented in the present study.