A QUANTITATIVE AUTORADIOGRAPHICAL STUDY ON THE DISTRIBUTION OF SOMATOSTATIN SST(2) RECEPTORS IN THE RAT CENTRAL-NERVOUS-SYSTEM USING [I-125] BIM-23027

The kinetic properties, steady state binding characteristics and autor adiographic distribution of the somatostatin (SRIF) sst(2) receptor-se lective ligand, [I-125]-BIM-23027, have been investigated in the rat c entral nervous system. Analysis of kinetic, saturation and competition binding data in rat hippocampal membranes was consistent with [I-125] -BIM-23207 binding to a single population of non-interacting binding s ites. Competition studies, using different SRIF ligands, suggested tha t [I-125]-BIM-23027 was binding to sites similar to that of the recomb inant sst(2) receptor. The rank order of affinity for displacing speci fic binding was BIM-23027=SRIF>L-362855>>BIM-23056. There was a widesp read distribution of [I-125]-BIM-23027 binding sites in the rat centra l nervous system. The highest density of binding was observed in the d entate gyrus, medial habenular, amygdala, claustrum and lateral septum as well as in the piriform, cingulate and parietal cortex. The cervic al and lumbar spinal cord also displayed moderate levels of binding lo calized to the substantia gelatinosa. The cellular localization of [I- 125]-BIM-23027 binding was found to be associated with dendritic termi nal fields. In contrast, the cellular signal for sst(2) receptor mRNA was restricted to cell somata. The widespread distribution of [I-125]- BIM-23027 binding sites within the brain suggests that receptors simil ar to the recombinant sst(2) receptor may mediate a variety of differe nt physiological effects within the central nervous system. Copyright (C) 1996 Elsevier Science Ltd.