LOCALIZATION OF THE SOMATOSTATIN RECEPTOR SST2A IN RAT-BRAIN USING A SPECIFIC ANTIPEPTIDE ANTIBODY

Biological actions of somatostatin are exerted via a family of recepto rs, for which five genes recently have been cloned. However, none of t hese receptor proteins has been visualized yet in the brain. In the pr esent study, the regional and cellular distribution of the somatostati n sst(2A) receptor was investigated via immunocytochemistry in the rat central nervous system by using an antibody generated against a uniqu e sequence of the receptor protein. Specificity of the antiserum was d emonstrated by immunoblot and immunocytochemistry on rat brain membran es and/or on cells transfected with cDNA encoding the different sst re ceptor subtypes. In rat brain sections, sst(2A) receptor immunoreactiv ity was concentrated either in perikarya and dendrites or in axon term inals distributed throughout the neuropil. Somatodendritic labeling wa s most prominent in the olfactory tubercle, layers II-III of the cereb ral cortex, nucleus accumbens, pyramidal cells of CA1-CA2 subfields of the hippocampus, central and cortical amygdaloid nuclei, and locus co eruleus. Labeled terminals were detected mainly in the endopiriform nu cleus, deep layers of the cortex, claustrum, substantia innominata, su biculum, basolateral amygdala, medial habenula, and periaqueductal gra y. Electron microscopy confirmed the association of sst(2A) receptors with perikarya and dendrites in the former regions and with axon termi nals in the latter. These results provide the first characterization o f the cellular distribution of a somatostatin receptor in mammalian br ain. The widespread distribution of the sst(2A) receptor in cerebral c ortex and limbic structures suggests that it is involved in the transd uction of both pre- and postsynaptic effects of somatostatin on cognit ion, learning, and memory.