Functional differentiation of ganglion cells from multipotent progenitor cells in sliced retina of adult goldfish

Multipotent progenitor cells at the retinal margin of adult goldfish give r ise to all cell types in the rest of the retina. We took advantage of this spatial arrangement of progenitor and mature cells in slices of peripheral retina, to investigate the appearance and maturation of voltage-activated N a+ current. We divided the peripheral retina into three broad regions (marg inal, intermediate, and mature) on the basis of their morphological develop ment. Whole-cell patch-clamp recordings were performed in ruptured-patch mo de, so that cells from which currents were recorded could be identified by Lucifer Yellow fills. No voltage-activated Na+ current was detected in the slender, peripherally located marginal cells. Voltage-activated Na+ current s were detected in rounded cells found alongside or near marginal cells, fa cing the vitreal side of the retina. Some of these "intermediate cells" had a long axon-like process which ran along the vitreal surface. Intermediate cells adjacent to the marginal region tended to have smaller Na+ currents than intermediate cells closer to the mature region. On average, the maximu m Na+ current amplitude recorded from intermediate cells was roughly 6-fold smaller than that of mature ganglion cells. In addition, the activation th reshold of the Na+ current in intermediate cells was nearly 14 mV more posi tive than that of mature ganglion cells. The results indicate that voltage- activated Na+ current, as a possible marker of retinal ganglion cells, begi ns to develop well before these cells migrate to their adult position withi n the retina. J. Comp. Neurol. 419: 297-305, 2000. (C) 2000 Wiley-Liss, Inc .