Angiotensin II receptor subtype gene expression and cellular localization in the retina and non-neuronal ocular tissues of the rat.

In addition to its function as a peripheral hormone, angiotensin II (AngII) has been shown to act as a neuromodulator in various brain regions. AngII effects are mediated by two major AngII receptor subtypes, AT1 and AT2, and different AT1 receptor isoforms AT1A and AT1B are described in rat brains. The purpose of the present study was to analyse the expression pattern of AT receptors in different parts of the rat eye with special emphasis on the retina. Specific primers were constructed and the gene expression of AngII receptor subtypes was investigated by means of reverse transcription-polymerase chain reaction (RT-PCR). An antibody was used for cellular localization of AT1 receptor in the retina. AT2 receptor mRNA was localized by in situ hybridization (ISH). We examined the retinas of different developmental stages as well as non-neuronal ocular tissues, e.g. choroid and anterior uveal tract of rats (Brown Norway and Wistar strain), for the gene expression of AT receptors. Our results show that AT1A and AT2 mRNAs are expressed in rat choroid, iris/ciliary body and retinas, whereas AT1B mRNA is not expressed in the retina but in all other ocular tissues under investigation. AT1 receptor immunohistochemistry of the retina showed strong labelling in the ganglion cell layer (GCL), and some cells in the inner nuclear layer (INL), suggesting putative ganglion cell but also amacrine cell labelling. In the retina, ISH for AT2 mRNA revealed labelling in the GCL and a faint labelling in the inner nuclear layer. No AT2 ISH-signal was found in the other ocular tissues. These data suggest that there is a specific distribution pattern of AT receptors in rat ocular tissues, especially in the retina. The expression of AT receptors on retinal ganglion cells confirms the AngII action on these cell types and supports the role of AngII as a retinal neurotransmitter or neuromodulator.