Identification of multiple somatostatin receptors in the rat somatosensorycortex during development

The present study was aimed at identifying somatostatin receptor subtypes o n the basis of their ligand-binding properties in the rat somatosensory cor tex during fetal and postnatal development. Characterization of somatostati n-binding sites was performed in individual cortical layers by using three radioligands and eight competitors with known selectivities for the five so matostatin receptor subtypes. Binding sites sensitive to sst2-selective lig ands were detected with high densities in the intermediate zone of the feta l cortex. From embryonic day 21 to 21 days postnatal (P21), mixed populatio ns of receptors were detected in the cortical plate and emerging layers I-V I. Putative sst2 receptors were detected throughout the entire period but d isplayed different affinities for somatostatin and analogs, and a different sensitivity to GTP, depending on the developmental stage and the cortical layer considered. High densities of binding sites exhibiting characteristic s of the sst1, sst3/5, and sst4 receptor subtypes were observed from P4 to P7, P7 to P14, and P7 to P21, respectively. In addition, each type of site exhibited a particular distribution pattern across the cortical layers that varied during the development. In the adult cortex, binding sites with sst 1 and sst2 receptor characteristics were predominant. This study provides e vidences of developmental expression windows of four sst receptor subtypes in selected areas of the rat cerebral cortex. (C) 2000 Wiley-Liss, Inc.