Immunoistochemical distribution and molecular expression of ocular receptors for Pituitary Adenylate Cyclase Activating Polypeptide (PACAP)

Purpose. To determine the mRNA expression and the immunohistochemical distribution of type-I PACAP receptors in the rat and rabbit eye. Methods. Freshly enucleated globes from Sprague-Dawley rats and albino rabbits were prepared for immunohistochemical studies and mRNA analysis. Antipeptide antibody, raised against the C-terminal intracellular domain of type-I PACAP receptors was used. Its specificity was verified by Western blot analysis. Reverse transcription-polymerase chain reaction (RT-PCR) was used to analyse the mRNAs of PACAP receptor splice variants. Results. PACAP receptor-like immunoreactivity (LI) was confined almost exclusively to the retina and ciliary body. In the retina, positive staining was present in the ganglionic, inner-plexiform and photoreceptor layers. In the ciliary body, a strong PACAP receptor-LI was observed in the epithelial cells covering the ciliary processes. RT-PCR analysis revealed the mRNA expression of the PACAP-R and PACAP-R-hop splice variants. Conclusions. The present results, together with the previous demonstration of PACAP binding sites and PACAP stimulated adenylate cyclase activity in the retina and ciliary body (Nilsson et al, Exp. Eye Res.,58:459,1994) suggest that PACAP may have specific functions in these tissues. In the retina, it could regulate retinal synaptic transmission and plasticity, whereas in the ciliary epithelium it may exert a role in the secretory process.