LARGE RETINAL GANGLION-CELLS IN THE CHANNEL CATFISH (ICTALURUS-PUNCTATUS) - 3 TYPES WITH DISTINCT DENDRITIC STRATIFICATION PATTERNS FORM SIMILAR BUT INDEPENDENT MOSAICS

Retinal ganglion cells in the channel catfish (Ictalurus punctatus) we re retrogradely labelled, and those with the largest somata and thicke st primary dendrites were categorized by their levels of dendritic str atification. Three types were found, each forming a mosaic making up s imilar to 1% of the ganglion cell population. Using a system based on established sublaminar terminology, we call these the alpha-a (alpha(a )), alpha-b (alpha(b)), and alpha-c (alpha(c)) ganglion cell mosaics. Cells of the alpha(a) mosaic had large, sparsely branched trees in sub lamina alpha at 10-30% of the depth of the inner plexiform layer (IPL) , sclerad to those of all other large ganglion cells. Some alpha(a) so mata were displaced into the LPL or inner nuclear layer (INL) but belo nged to the same mosaic as their orthotopic counterparts. Cells of the alpha(b) mosaic had dendrites that branched a little more and arboriz ed in sublamina b at 50-60% of the IPL depth. Many also sent fine bran ches into sublamina alpha, and some were fully bistratified in a and b . The alpha(c) cells arborized in the most vitread sublamina, sublamin a c, at 80-95% of the IPL depth. The soma areas of the three types in the largest retina studied ranged between 139 mu m(2) and 670 mu m(2) with significant differencess in the order alpha(a) > alpha(c) greater than or equal to alpha(b). Analyses based on nearest-neighbour distan ce (NND) and on spatial auto- and cross-correlograms showed that each mosaic was statistically regular and independent of the others. Mosaic spacings were similar for each type, giving mean NNDs of 242-279 mu m in the largest retina and 153-159 mu m in a smaller one. Corresponden ces between these mosaics, previously defined large ganglion cell type s in catfish, and other mosaic-forming large ganglion cells in fish an d frogs are discussed along with their implications for neuronal class ification, function, development, and evolution. (C) 1995 Wiley-Liss, Inc.