Immunohistochemical localization of the somatostatin sst(4) receptor in rat brain

The biological actions of the neuromodulator somatostatin are mediated through a family of G-protein-coupled receptors, of which five members, sst(1-5), have been identified. Although the messenger RNA distribution of the sst(4) receptor has been reported, no information about the distribution of the receptor protein in the central nervous system is available. We have therefore raised a polyclonal peptide antibody against a rat carboxy-terminal sst(4) peptide. The selectivity of the affinity-purified antibody was demonstrated by western blotting of membrane proteins isolated from Chinese hamster ovary-K1 cells expressing the recombinant sst(4) receptor and from the rat hippocampus. This resulted in both cases in the identification of a single band of approximately 42,000 mol. wt. Furthermore, the sst(4) receptor antibody selectively labelled Chinese hamster ovary-K1 cells expressing the recombinant sst(4) receptor in immunocytochemistry. No cross-reactivity was observed with other recombinant somatostatin receptors. Immunohistochemistry on adult rat brain sections showed the sst(4) receptor to have a widespread distribution. This included labelling of cell bodies as well as processes in the cerebral cortex, hippocampus and several nuclei in the brainstem. All signals were absent following antibody preabsorption with the synthetic sst(4) peptide. This study provides the first detailed analysis of the distribution of sst(4) receptor protein in the rat brain.