Morphological and neurochemical diversity of neuronal nitric oxide synthase-positive amacrine cells in the turtle retina

The histochemistry of reduced nicotinamide adenine dinucleotide phosphate d iaphorase (NADPH-d) and immunoreactivity of neuronal nitric oxide synthase (nNOS-IR) can be demonstrated in various cell types of the vertebrate retin a. In this study, we have focused on characterizing the different NADPH-d-p ositive amacrine cell types in turtle retina. Cryostat sections were examin ed by confocal laser scanning microscopy for double immunofluorescence with antibodies against nNOS and either GABA or glycine. or by combining histoc hemistry with immunocytochemistry to obtain triple labeling with NADPH-d, G ABA, and glycine. Forty-eight percent of the NADPH-d-labeled amacrine cells colocalized GABA, 52% glycine. Here we show that two morphologically diffe rent types of amacrine cell are nNOS/glycine-IR and three types are nNOS/GA BA-IR. Antibodies against calretinin, parvalbumin, somatostatin, tyrosine h ydroxylase, and choline acetyltransferase did not colocalize with nNOS-IR o r NADPH-d-labeled amacrine cells, but 15% of the NOS-labeled amacrine cells showed immunoreactivity against calbindin. Only GABA has been seen to colo calize with NADPH-d in amacrine cells in previous reports in other species. The finding here of glycine colocalizing with NO-containing cells is novel . We suggest that NO, apart from its well known function in gap junction re gulation, can also modulate the release of both GABA and glycine in the tur tle retina.