DISTRIBUTION OF SOMATOSTATIN RECEPTOR-1, RECEPTOR-2 AND RECEPTOR-3 MESSENGER-RNA IN RAT-BRAIN AND PITUITARY

In this study sequence-specific antisense oligonucleotide probes have been used to investigate the distribution of the mRNAs coding for the somatostatin receptor subtypes termed somatostatin receptor 1, somatostatin receptor 2 and somatostatin receptor 3 in the rat brain and pituitary using in situ hybridization techniques. The three receptor subtype mRNAs were found to be widely distributed in the brain with different patterns of expression, but with some overlap. Somatostatin receptor 1 mRNA was particularly concentrated in the cerebral and piriform cortex, magnocellular preoptic nucleus, hypothalamus, amygdala, hippocampus, and several nuclei of the brainstem. Somatostatin receptor 3 mRNA was very abundant in the cerebellum and pituitary (in contrast to somatostatin receptor 1), but it was also found in hippocampus, amygdala, hypothalamus and in motor nuclei of the brainstem. Somatostatin receptor 2 mRNA levels were very low relative to the other two mRNAs evaluated. Receptor 2 mRNA was observed in the anterior pituitary, and in the brain it was found in the medial habenular nucleus, claustrum, endopiriform nucleus, hippocampus, some amygdala nuclei, cerebral cortex and hypothalamus. None of the three somatostatin receptor mRNAs studied here was found in the caudate nucleus. Northern analysis revealed distinct sizes of mRNAs for each subtype, and displacement experiments showed that each probe sequence was subtype-specific.