Interactions between growth cones and neurites growing from different neural tissues in culture

We have previously used retinal and sympathetic explants to show that growth cones recognize and retract from specific neurites in culture (Kapfhammer et al., 1986). In an effort to determine the generality of this phenomenon and to see how many different neurite labels can be detected by it, we have studied interactions between individual growth cones and neurites extending from a variety of neural sources in vitro. Using most of the possible pairings between sympathetic, ciliary, dorsal root ganglion (DRG), retinal, and diencephalic neurons, we have found that in most instances: (1) Growth cones do not retract from neurites originating from the same tissue; (2) retinal growth cones do not retract from diencephalic neurites; (3) sympathetic, ciliary, and DRG growth cones, with one possible exception, do not retract from sympathetic, ciliary, or DRG neurites; (4) retinal growth cones retract from sympathetic, ciliary, and DRG neurites; (5) sympathetic, ciliary, and DRG growth cones retract from retinal neurites; and (6) sympathetic growth cones retract from diencephalic neurites. A simple hypothesis consistent with these results is that 2 labels exist--one associated with central neurites and another associated with peripheral neurites--and that peripheral growth cones are programmed to retract from the central label and central growth cones are programmed to retract from sympathetic, ciliary, and DRG neurites; (5) symevant to the separation of the CNS and PNS during development.