NADPH-DIAPHORASE NEURONS IN THE RETINA OF THE HAMSTER

NADPH-diaphorase-positive neurons have been demonstrated in the inner nuclear layer and ganglion cell layer of the retina of different mamma lian species, but so far no experiments have been conducted to identif y whether these cells are amacrine cells and/or retinal ganglion cells . We attempted to solve this problem by studying the NADPH-diaphorase- positive neurons in the hamster retina. From the NADPH-diaphorase hist ochemical reaction, two distinct types of neurons in the hamster retin a were identified. They were named ND(g) and ND(i) cells. The ND(g) ce lls were cells with larger somata, ranging from 10 to 21 mu m in diame ter with a mean of 15.58 mu m (S.D. = 2.59). They were found in the ga nglion cell layer only. The ND(i) cells were smaller, with the somata ranging from 7 to 11 mu m and having the mean diameter of 8.77 mu m (S .D. = 1.24). Most of the ND(i) cells were found in the inner nuclear l ayer, and only very few could be observed in the inner plexiform layer . On average, there were 8,033 ND(g) and 5,051 ND(i) cells in the gang lion cell layer and inner nuclear layer, respectively. Two experiments were performed to clarify whether any of the NADPH-diaphorase neurons were retinal ganglion cells. Following unilateral optic nerve section , which leads to the retrograde degeneration of retinal ganglion cells , the numbers of both ND(g) and ND(i) cells did not change significant ly for up to 4 months. In addition, when retinal ganglion cells were p relabeled retrogradely (horseradish peroxidase or fluorescent microsph eres) and retinas were then stained for NADPH diaphorase, no double-la beled neurons were detected. These results indicated that the NADPH-di aphorase neurons in the hamster retina were the amacrine cells in the inner nuclear layer and displaced amacrine cells in the ganglion cell layer. Dendrites of the ND(g) and ND(i) cells were found to stratify i n sublaminae 1, 3, and 5 of the inner plexiform layer, with a prominen t staining in the sublamina 5. The possible importance of this arrange ment in the rod pathway is also discussed. (C) 1994 Wiley-Liss, Inc.