Transient expression of somatostatin sst2 receptors in rat cerebellar nuclei during development.

Adult rat cerebellar nuclei contain a single population of [125I][Leu8,D-Trp22,Tyr25]somatostatin-28 binding sites characterized as sst1 receptors. In the present study, we have investigated the evolution of somatostatin receptors in rat cerebellar nuclei during development by means of quantitative autoradiography on tissue sections. The binding of [125I][Leu8,D-Trp22,Tyr25]somatostatin-28, observed in the primordium of the medial cerebellar nuclei at embryonic day 17, reached a maximum at postnatal day 7 or 10 in the different nuclei. Thereafter, the density of binding sites gradually decreased to the adult level. Competition studies were performed using the somatostatin analogues CH-288 and MK-678 as specific sst1 and sst2 ligands, respectively. Partial inhibition of the radioligand binding by CH-288 and MK-678 revealed the presence of a predominant population of sst1 from embryonic day 19-28 day postnatal and a minor population of sst2 receptors. The use of [125I]MK-678 as a radioligand confirmed the presence of a transient population of sst2 receptors, suggesting that somatostatin could act on rat cerebellar nuclei via sst1 and/or sst2 receptors during development.