Expression of IGF‐I and insulin receptor genes in the rat central nervous system: A developmental, regional, and cellular analysis

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Abstract
Using a solution‐hybridization assay and specific oligonucleotidic probes, we have studied IGF‐I and insulin receptor mRNAs in the rat central nervous system during development. The expression of mRNAs was maximal at embryonic day 15 and 20 for IGF‐I receptors, and at embryonic day 20 and the day of birth for insulin receptors. After birth, the expression of both receptor transcripts decreased and reached minimal levels in the adult. At the time at which these transcripts were maximally expressed (embryonic day 20), the regional analysis indicated that IGF‐I receptor transcripts were widely distributed in the brain. In contrast, insulin receptor transcripts were restricted to certain areas in which they were coexpressed with the IGF‐I receptor transcripts. We next analyzed which cells at embryonic day 20 expressed those receptor transcripts. Late embryonic neurons, astrocytes, and neonatal progenitors of oligodendrocytes synthesized both IGF‐I and insulin receptor mRNAs after a short time in culture. However, astrocytes expressed preferentially IGF‐I receptor transcripts, while young progenitors for oligodendrocytes expressed high levels of insulin receptor transcripts. As a whole, our data indicate that during rat CNS development expression of IGF‐I and insulin receptors appears to be stage‐and cell‐specific. The differences observed between the expression of both receptors might point to a specific, but coordinative role of IGF‐I and insulin and their receptors during that time.