Ontogeny of vasoactive intestinal peptide gene expression in rat brain.

Vasoactive intestinal peptide (VIP) expression was studied during rat brain development using in situ hybridization histochemistry with a 48mer, S35-ATP-labeled probe. First expression of VIP was found in the lateral thalamus at E17, in a region later recognized as the reticular nucleus. At E19, VIP mRNA was also found in the hypothalamus, especially the suprachiasmatic nucleus. The only other prenatal localizations were the cortex and the brainstem. VIP expression continously matured during the first three postnatal weeks, and adult-like patterns were found at P22, when cerebral cortex, ventrolateral and reticular thalamic nuclei, suprachiasmatic nucleus were the regions with most prominent VIP expression. These results demonstrate the relatively late appearance of VIP gene expression in the rat forebrain as compared with peptides like SRIF and CCK, suggesting it does not have a major role in early brain maturation.