Preferential expression of sst2A over sst2B somatostatin receptor splice variant in rat brain and pituitary

The expression of sst2A and sst2B somatostatin (SRIH) receptor splice variants was examined by polymerase chain reaction (PCR) in rat brain and pituitary. Two sets of primers chosen to recognize either both sst2A and sst2B or only the sst2B transcript yielded bands of the size predicted from the cloned sst2A and sst2B sequences in both mouse and rat tissue extracts. Accordingly, experiments carried out on mouse brain extracts and on AtT-20 pituitary cells yielded sst2A/sst2B expression ratios comparable to those previously published. As in the mouse, rat pituitary extracts contained both sst2A and sst2B transcripts. By contrast, various cerebral regions in which both sst2A and sst2B forms were detected in the mouse contained only sst2A form in rat brain, with the exception of the cerebral cortex which also showed weak sst2B expression. No sst2B mRNA was detected in the arcuate nucleus/median eminence complex, indicating that the sst2A form is the one that is associated with growth-hormone-releasing-hormone-containing neurons documented to express sst2 receptors in this region. Finally, only sst2A transcripts were detected in rat astrocytes in culture, suggesting that this form of the receptor is responsible for sst2-mediated effects of SRIH on these cells.