Synapse formation during embryogenesis on ganglion cells lacking a periphery

Abstract

1. The development of transmission was studied in chick ciliary ganglia that had been deprived of their periphery during early embryonic development.2. Peripherally deprived neurones in the ganglion differentiate in normal numbers and send functional axons into the post-ganglionic nerve.3. Ganglion cells lacking a periphery follow the normal developmental sequence sending out transient dendrites at the time ganglion cell synapses are formed, and later retracting them when calyces appear.4. Synapses, which appear functionally and ultrastructurally normal, form on all ganglion cells at the normal time and transmission is normal until Stage 34. Therefore information from the periphery is not required for ganglion cell synapse formation per se.5. From Stages 35 to 38 most cells die, so that only 8% of the original number of cells remain in the operated ganglion. Transmission fails in many cells during this same time, but precedes cell loss by only a short time, so that deafferentation probably does not contribute substantially to cell death.6. Both ciliary and choroid cells achieve full cytologic differentiation and are distinct from each other, indicating that the periphery is not required for the elaboration of the distinctive characteristics of these cells. Presynaptic fibres also differentiate into typical bouton as well as calyciform endings. Therefore, the type of preganglionic ending does not depend on ganglion cells establishing proper peripheral contacts.7. It has not been possible to ascertain whether ganglion cell specificity is affected by the periphery.8. Peripheral removal affects ganglion cell migration, so that two ganglia are formed. Approximately half of the cells migrate into the remnant optic cup forming a second misplaced ganglion. Ciliary and choroid cells occur in both ganglia and these cells go through the typical sequence of events described above.