Selective targeting of somatostatin receptor 3 to neuronal cilia

Recently, five members of the somatostatin receptor family have been cloned . However, little is known about their cellular and subcellular localizatio n in the central nervous system. Using specific anti-peptide antisera, we o bserved somatostatin receptor 3-like immunoreactivity in many brain regions , including the cerebral cortex, hippocampus, hypothalamus, amygdala and ce rebellum. In all of these regions (except for the cerebellar cortex), somat ostatin receptor 3-like immunoreactivity was selectively targeted to 4-8-mu m-long rod-shaped profiles which did not co-localize with axonal or dendri tic markers. One immunoreactive profile was always associated with one neur onal cell body. This staining pattern was resistant to colchicine treatment and showed a closely overlapping distribution with somatostatin receptor 3 messenger RNA, suggesting that the receptor protein is not transported ove r long distances. Electron microscopic analysis revealed that somatostatin receptor 3-like immunoreactivity is localized to the plasma membrane of neu ronal cilia which extended into an intercellular pocket and showed a 9+0 fi lament pattern in their basal body and proximal segments. Thus, somatostatin receptor 3 demonstrates a unique example of a G-protein- coupled receptor not localized to "classical" pre- or postsynaptic sites, b ut selectively targeted to neuronal cilia. The presence of the somatostatin receptor 3 receptor on neuronal cilia suggests that these presumably non-m otile cilia may not merely represent developmental remnants, but rather fun ction as chemical sensors of the immediate milieu. (C) 1999 IBRO. Published by Elsevier Science Ltd.