In situ localization of neuronal nitric oxide synthase (nNOS) mRNA in the rat retina

We performed a comparative study on the distribution of neuronal nitric oxide synthase (nNOS) immunoreactivity and mRNA in a normal rat retina using immunocytochemistry and in situ hybridization technique. As in previous studies, we found NOS immunoreactive (NOS-IR) cells and fibers in inner and outer plexiform layers (IPL and OPL), inner nuclear layer (INL) and inner photorecetptor segment (IPS). However, very little nNOS-IR could be detected in groups of amacrine cells and ganglion cells localized in ganglion cell layer (GCL). However, in situ hybridization showed that intense NOS mRNA signals were mainly found in the GCL and INL while weak or no mRNA signals were detected in IPL, OPL, outer nuclear layer (ONL) and IPS. This difference suggests that nNOS proteins may be transported through axons into the terminals in the IPL and OPL after they were synthesized with nNOS mRNA templates in the INL. In the case of nNOS mRNA in GCL, synthesizing nNOS proteins may move outside the eyeball and carry out tasks in central nervous system. The difference of nNOS mRNA and nNOS IR means that the complete concurrence of nNOS IR and in situ hybridization results may not always occur in the rat retina.