LOCALIZATION OF SOMATOSTATIN (SRIF) SSTR-1, SSTR-2 AND SSTR-3 RECEPTOR MESSENGER-RNA IN RAT-BRAIN BY IN-SITU HYBRIDIZATION

In situ hybridization histochemistry was performed to analyse the dist ribution of the messenger RNA (mRNA) of three putative somatostatin (S RIF) receptors in rat brain, using oligonucleotide probes derived from the cDNA coding for SSTR-1, SSTR-2, and SSTR-3 receptors. SSTR-1 sign als were found in layers V-VI of the cerebral cortex, in primary olfac tory cortex, taenia tecta, subiculum, entorhinal cortex, granular laye r of the dentate gyrus, amygdala and cerebellar nuclei. Signals for SS TR-2 were found in the frontal cerebral cortex (layers IV, V and VI), taenia tecta, claustrum, endopiriform nucleus, locus coeruleus, medial habenula, subiculum, granular cell layer of the dentate gyrus and amy gdala. High levels of SSTR-3 hybridization were found in the olfactory bulb, primary olfactory cortex, islands of Calleja, medial habenula, amygdala, granular layer of the dentate gyrus, various thalamic and po ntine nuclei and in the granular and Purkinje cell layers of the cereb ellum. The distribution of the hybridization signals of the oligoprobe s is consistent with the labelling of specific SRIF binding sites in r at brain. Especially SSTR-2 and SSTR-1 oligos seem to label regions in which SS-1 and SS-2 receptors, respectively, have been previously cha racterized in autoradiographical studies. The situation is less clear with SSTR-3 mRNA, since SRIF binding in adult rats is usually low or a bsent in cerebellum, although some cerebellar nuclei appear to be labe lled in the adult. The localization of SSTR-1, SSTR-2 and SSTR-3 mRNAs suggests that SRIF receptor subtypes in rat brain show profound diffe rences in their distribution and are involved in a variety of central, in addition to neuroendocrine, functions.