CELL-ADHESION MOLECULES REGULATING NEURITE GROWTH FROM AMACRINE AND ROD PHOTORECEPTOR CELLS

A great deal is now known about the cell adhesion molecules (CAMs) tha t are responsible for promoting the growth of ganglion cell axons as t hey project out of the retina through the optic nerve and finally to d istant targets in the brain. However, the CAMs important for regulatin g axon outgrowth from nonprojection neurons, such as amacrine cells an d rods, are not known. Such local circuit neurons extend their neurite s rather short distances on cellular surfaces not normally encountered by the ganglion cell axons. To study the mechanisms regulating axon o r dendrite growth from local circuit neurons, neurite outgrowth from a macrine cells and rod photoreceptor cells derived from the rat was exa mined in vitro on immunopurified forms of NCAM, L1, and N-cadherin, th ree well-characterized adhesive molecules found in the developing reti na. Either early (P3) or late (P10) postnatal amacrine cells grew neur ites on all three CAMs, but there were significant differences in the percentage of the amacrine cells that responded to each CAM. None of t he CAMs supported neurite outgrowth from early postnatal rods, but, su rprisingly, NCAM stimulated vigorous neurite extension from rods isola ted at postnatal day 10. Postnatal ganglion cells were also examined f or comparison and were found not to grow neurites on NCAM, but did gro w extensive processes on L1 and N-cadherin. These results show that NC AM, L1, and N-cadherin can promote neurite outgrowth from local circui t neurons, but that the effectiveness of any particular CAM is depende nt on the cell type and the developmental period.