Distinct topographical localisation of two somatostatin receptor subpopulations in the human cortex.

The use of two different radioligands, [125I]Leu8, D-Tryp22,Tyr25-somatostatin-28 and the stable somatostatin octapeptide analog [125I]204-090, D-Phe-Cys[125I]Tyr-D-Trp-Lys-Thr-Cys-Thr(ol), allowed to differentiate between two somatostatin receptor subpopulations in the human cortex. In homogenates, octapeptide somatostatin analogs displaced only part of the somatostatin-28 radioligand with high affinity. Autoradiography showed that the receptor subpopulation labelled with [125I]204-090, which we named SS1, was preferentially localized in layers V and VI, whereas the subpopulation having low affinity for somatostatin octapeptides (named SS2), measured with somatostatin-28 radioligand, was concentrated in the superficial cortical layers (I-IV) and particularly enriched in parts of lamina IV.