BIPLEXIFORM GANGLION-CELLS, CHARACTERIZED BY DENDRITES IN BOTH OUTER AND INNER PLEXIFORM LAYERS, ARE REGULAR, MOSAIC-FORMING ELEMENTS OF TELEOST FISH RETINAE

Biplexiform ganglion cells were labelled by retrograde transport of HR P in five species of marine fish from the neoteleost acanthopterygian orders Perciformes and Scorpaeniformes. Their forms and spatial distri butions were studied in retinal flatmounts and thick sections. Biplexi form ganglion cells possessed sparsely branched, often varicose, dendr ites that ramified through the inner nuclear layer (INL) to reach the outer plexiform layer (OPL), as well as conventional arborizations in the most sclerad part of the inner plexiform layer (IPL). Their somata were of above-average size and were displaced into the vitread border of the INL. Mean soma areas ranged from 99 +/- 6 mu m(2) in Bathymast er derjugini (Perciformes) to 241 +/- 12 mu m(2) in Hexagrammos stelle ri (Scorpaeniformes), but were similar in each species to those of the outer-stratified alpha-like ganglion cells, whose dendritic trees occ upied the same IPL sublamina. In the best-labelled specimens, biplexif orm cells formed clear mosaics with spacings and degrees of regularity much like those of other large ganglion cells, but spatially independ ent of them. Biplexiform mosaics were plotted in three species, and an alyzed by nearest-neighbor distance and spatial correlogram methods. T he exclusion radius, an estimate of minimum mosaic spacing, ranged fro m 113 mu m in Hexagrammos stelleri, through 150 mu m in Ernogrammus he xagrammus (Perciformes), to 240 mu m in Myoxocephalus stelleri (Scorpa eniformes). A spatial cross-correlogram analysis of the distributions of biplexiform and outer-stratified alpha-like cells in Hexagrammos de monstrated the spatial independence of their mosaics. Similar cells we re previously observed not only in the freshwater cichlid Oreochromis spilurus (Perciformes) but also in the goldfish Carassius auratus (Cyp riniformes) which, being an ostariophysan teleost, is only distantly r elated. Thus, biplexiform ganglion cells may be regular elements of al l teleost fish retinae. Their functional role remains unknown.