Class I and class II ganglion cells of rabbit retina: quantitative analysis of dendritic branching patterns

Class I and class II ganglion cells, distinguished from one another in a companion paper, were analyzed in regard to their dendritic branching patterns by determination of: 1) mean "branching density" (BD), 2) "radial branching frequency" (RBF), and 3) "branch length distributions" (BLDs; Famiglietti [ 1992a] J Comp Neurol 324:295-321). Branching density of class II cells exceeded that of class I cells by a factor of two, when compared at the same retinal location, but declined with increasing distance from the visual streak (dvs). A one-bin difference in RBF between class I and class II cells was not statistically significant. BLDs are scatter-plots of individual preterminal and terminal branch lengths versus the distances of their origins from the soma. The parameters mp and mt, the slopes of regression lines fitted to the preterminal and terminal BLDs, respectively, were determined; mp, but not mt, was relatively independent of dvs, and was used empirically to determine a boundary value, mp = +5.0, separating "radiate" from "tufted" dendritic branching. Similarity of class I (mp = +8.6 +/- 4.6) and class II (mp = +1.4 +/- 5.2) cells did not allow a statistically significant separation of the two classes, based upon branching pattern alone; however, mp together with mt easily separated class I cells (mt = -17.8 +/- 10.0) and particularly "tufted" class II cells (mt = -16 +/- 9.3) from "tufted" class III.1 ganglion cells (Famiglietti, 1992a), with their qualitatively different, more regular branching (mp = +2.1 +/- 0.85; mt = +0.65 +/- 4.9).