Embryonic and postnatal mRNA distribution of five somatostatin receptor subtypes in the rat brain

Abstract

The messenger RNA (mRNA) expression of somatostatin (SRIF) receptors SSTR-1, SSTR-2, SSTR-3, SSTR-4 and SSTR-5 (called sst 1–5, now) was studied in rat brain between embryonic day 17 (E17) and post-natal day 5 (P5) by in situ hybridization histochemistry and compared to that of adult rats, sst 1 receptor mRNA expression was very low and restricted at E17, spread out at E18, to reach very high levels comparable to that of adult at P5 (e.g. in temia tecta, posteromedial cortical amygdaloid nucleus, subiculum). At E17 E18 , sst 2 receptor mRNA expression was low and limited (telencephalon); significant levels were present at P5 in allocortex, hippocampus, locus coeruleus, similarly to adult brain. sst 3 receptor mRNA was high at E17 in most brain regions, and almost as ubiquitous as in adult brain at P5. sst 4 receptor mRNA was apparently absent at E17, with low levelis in the hippocampus, amygdala and habenula at E18; a wider distribution, especially in the hippocampus and cerebral cortex was observed at P5, similar to that of adult, sst 5 receptor mRNA was not detected at E17 and negligible at E18; low levels were found in the cortex, hippocampus and cerebellum at P5. However, in adult brain, only the cerebellum and hind-brain showed some sst 5 receptor mRNA transcripts. The presence and distribution of SRIF receptor mRNAs differs substantially in embryo and adult brain. Some mRNAs are present throughout development, while others proceed only postnatally to the adult form. There are striking differences within and between the different SRIF receptor mRNAs, suggesting a role in neurogenesis for some SRIF receptors (e.g. sst 2). However, mRNA and protein levels do not necessarily correlate.