Autoradiographic visualization of binding sites for [3H]somatostatin in the rat brain.

[4-3H][Phe6]somatostatin-14 was used to localize somatostatin binding sites in the rat brain by tritium-film autoradiography. The distribution of binding sites using 0.7 nM [3H]somatostatin confirmed that previously described for iodinated tyrosyl analogues of somatostatin, with highest densities of sites in the cerebral cortex (particularly in laminae III-V), amygdala, lateral septal nucleus, hippocampus and claustrum. Investigation of the pharmacological specificity of the binding sites showed that somatostatin-28, but not its N-terminal dodecapeptide, somatostatin-28 (1-12) or des-Ala1[Gly2,Lys4,Asn5,Thr12,Ser13]somatostatin displaced [3H]somatostatin. Further examination of the binding inhibition characteristics, using a homogenate assay, suggested the presence of two classes of binding sites in the cerebral cortex, hippocampus, midbrain and striatum. The existence of sub-populations of somatostatin binding sites in the rat brain has implications for future studies on the physiological and pharmacological significance of somatostatin receptors in the central nervous system.