Distribution of somatostatin receptor 5 in mouse and bullfrog retinas

Abstract

Somatostatin (SRIF), as a neuroactive peptide in the CNS, may act as a neuromodulator through activation of five specific receptor subtypes (sst1–sst5). In this work we conducted a comparative study of the expression of sst5 in mouse and bullfrog retinas by immunofluorescence double labeling. Basically, the expression profiles of sst5 in the retinas of the two species were similar. That is, in the inner retina sst5 was localized to dopaminergic and cholinergic amacrine cells, stained by tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) respectively, and cells in the ganglion cell layer, whereas in the outer retina immunostaining for sst5 was observed in horizontal cells. However, a more widespread, abundant distribution of labeling for sst5, as compared to mouse retina, was seen in bullfrog retina: strong labeling for sst5 was diffusely distributed in both outer and inner plexiform layers (OPL and IPL) in the bullfrog retina, but the labeling was only observed in the IPL of the mouse retina. In addition, bullfrog photoreceptors, both rods and cones, but not mouse ones, were labeled by sst5. In combination with the experiments showing that SRIF-immunoreactivity was mainly found in the inner retina, our results suggest that SRIF, released from SRIF-containing cells in the inner retina, may play a neuromodulatory role in both outer and inner retina mediated by volume transmission via sst5 in bullfrog retina, while the SRIF action may be largely restricted to the mouse inner retina.