LARGE RETINAL GANGLION-CELLS THAT FORM INDEPENDENT, REGULAR MOSAICS IN THE RANID FROGS RANA-ESCULENTA AND RANA-PIPIENS

Population-based studies of ganglion cells in retinal flatmounts have helped to reveal some of their natural types in mammals, teleost fish and, recently, the aquatic mesobatrachian frog Xenopus laevis. Here, g anglion cells of the semiterrestrial neobatrachian frogs Rana esculent a and Rana pipiens have been studied similarly. Ganglion cells with la rge somata and thick dendrites could again be divided into three mosai c-forming types with distinctive stratification patterns. Cell dimensi ons correlated inversely with density, being smallest in the visual st reak. Cells of the alpha(a) mosaic (<0.2% of all ganglion cells) had t he largest somata at each location (often displaced) and their trees w ere confined to one shallow plane within sublamina a of the inner plex iform layer. In regions of high regularity, many trees were symmetric. Elsewhere, asymmetric, irregular trees predominated and their dendrit es, although sparsely branched, achieved consistent coverage by inters ecting in complex ways. Cells of the alpha(ab) mosaic were more numero us (approximate to 0.7%) and had large somata, smaller (but still larg e) trees, and dendrites that branched extensively in two separate shal low planes in sublaminae a and b. The subtrees did not always match in symmetry, and each subtree tessellated independently with its neighbo rs. Cells of the alpha(c) mosaic (approximate to 0.1%) had large, orth otopic somata and large, sparse trees (often asymmetric and irregular) close to the ganglion cell layer. Nearest-neighbor analyses and spati al correlograms confirmed that each mosaic was regular and independent . Densities, proportions, sizes, and mosaic statistics are tabulated f or all three types, which are compared with types defined by size and symmetry in R. pipiens, by discriminant analysis in R. temporaria, by physiological response in both, and by mosaic analysis in Xenopus and several teleosts. The variable stratification of these otherwise simil ar types across species is consistent with other evidence that stratif ication may be determined, in part, by functional interactions.