Immunohistochemical localization of somatostatin receptor subtypes sst1 and sst2 in the rat retina.

PURPOSE To investigate the distribution of somatostatin receptor subtypes sst1 and sst2 in the rat retina by immunohistochemistry and to characterize further the neurotransmitters of the sst1- and sst2-immunoreactive cells. METHODS Polyclonal antibodies raised against sst1 and sst2 receptors were applied to 12-microm cryostat sections of rat retinas fixed in paraformaldehyde. Further, immunofluorescence double labeling was performed for the sst1 and sst2 receptors with somatostatin, tyrosine hydroxylase (TH) and glutamate decarboxylase (GAD). RESULTS Immunoreactivity for sst1 was present in somatostatinergic amacrine cells located in the inner nuclear layer (INL) and in displaced amacrine cells in the ganglion cell layer of the retina. Also, a small number of ganglion cells were sst1 immunoreactive. Immunoreactivity for sst2 was observed in many medium-sized amacrine cells in the middle part of the INL, with a central process projecting to the sublaminae of the inner plexiform layer. Furthermore, sst2 immunoreactivity was found in large amacrine cells of the INL. These cells also contained TH. Inner segments of cone receptors were stained with the sst2 antiserum. Immunostaining for sst2, and to a minor extent for sst1, was found in Müller cell fibers. None of the somatostatin receptors colocalized with GAD. CONCLUSIONS These findings suggest that the sst1 receptor may function as an autoreceptor on retinal somatostatinergic cells. The presence of sst2 receptors on the TH-immunoreactive amacrine cells indicates an influence of somatostatin on the secretion of dopamine in rat retina.