Expression of somatostatin subtype 1 receptor in the rabbit retina

PURPOSE. To detect mRNAs for somatostatin (somatotropin release-inhibiting factor [SRIF]) receptor subtypes 1 to 5 (sst(1) through sst(5)) in rabbit r etinas by reverse transcription-polymerase chain reaction (RT-PCR) and to i nvestigate the distribution of sst(1) by single- and double-label immunocyt ochemistry. METHODS. Semiquantitative RT-PCR using sst-specific primers from mouse sequ ences was per formed. sst(1) was localized using a polyclonal antiserum dir ected to human sst(1) in cryostat sections of retinas from either normal or optic nerve-transected animals. Immunolabeled cell sizes and densities wer e measured in wholemounted retinas using computer-assisted image analysis. Double-label immunofluorescence was performed using the sst(1) antiserum in conjunction with monoclonal antibodies directed to SRIF, tyrosine hydroxyl ase (TH), parvalbumin (PV), or gamma-aminobutyric acid (GABA). RESULTS. With RT-PCR it was found that all five sst mRNAs were expressed in the rabbit retina, with highest levels of sst(1) mRNA. sst(1) immunolabeli ng was localized to amacrine cells in the proximal inner nuclear layer (INL ) of all retinal regions and to displaced amacrine cells in the ganglion ce ll layer (GCL) of the ventral retina. Some large sst(1)-immunoreactive (IR) somata were also present in the GCL. They were not observed after optic ne rve transection. Double-label immunofluorescence showed sst(1) expression b y all TH-IR amacrine cells and by other amacrine cells that were neither PV -IR nor GABA-IR. In addition, sst(1) was expressed by all SRIF-containing d isplaced amacrine cells. CONCLUSIONS. All five sst mRNAs are expressed in the rabbit retina. The loc alization of sst(1) suggests that it may mediate SRIF actions onto amacrine (including dopaminergic) and sparse ganglion cells. sst(1) expression in S RIF-IR cells suggests that this receptor may also act as an autoreceptor.