NADPH-diaphorase reactivity in adult and developing cat retinae.

We have examined the distribution and size of nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase reactivity in adult and developing cat retinae. From late gestation E (embryonic day) 58 to adulthood, NADPH-diaphorase reactivity was detected in amacrine cells with somata located in the inner nuclear layer (INL) and ganglion cell layer (GCL) and in processes spreading in the middle strata of the inner plexiform layer (IPL). Reactivity was also present in small rounded profiles located in the outer plexiform layer (OPL) and thought to be cone pedicles. The number of NADPH-diaphorase reactive cells present in adult retinae was about 40,000, 75% of these somata were located in the GCL, the remainder in the INL. At birth, however, there was more than double this number of labelled somata (85,000), the total gradually declining to reach adult values by P (postnatal day) 25. This loss of NADPH-diaphorase reactive somata may be partly explained by natural cell death (apoptosis) or by loss of the active diaphorase from the cells. The density distributions of NADPH-diaphorase reactive cells in the INL and GCL of retinal wholemounts reached maxima in regions slightly inferior to the area centralis at all ages studied. The principal topographical difference between adult and developing retinae was that the density gradient of NADPH-diaphorase reactive cells was steeper in adults than at younger ages. During early development, the somal and dendritic field diameters of NADPH-diaphorase reactive cells at the area centralis were about the same size as those in the periphery; by adulthood, cells in the periphery were larger. The change in the somal diameter gradient apparently emerged because of a reduction in somal size of the centrally located cells. The change in the dendritic diameter gradient emerged because of a greater growth of peripheral cells as compared to central cells. We suggest that NADPH-diaphorase may have a role in the formation of synapses in the developing IPL.