Comparative distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) binding sites and PACAP receptor mRNAs in the rat brain during development.

Significant numbers of PACAP binding sites were detected as early as embryonic day 14 in the rat brain.

• The density of PACAP binding sites in germinative areas increased by 3- to 5-fold from embryonic day 14 to 21.
• From birth to postnatal day 12, PACAP binding sites gradually declined in all neuroepithelia except in the external granule cell layer of the cerebellum, where they remained high.
• Low to moderate densities of PACAP binding sites were observed in regions outside germinative areas, except for a high density in the internal granule cell layer of the cerebellum.
• The distribution of PAC1-R and VPAC1-R mRNAs closely mirrored the localization of PACAP binding sites, with PAC1-R mRNA being more concentrated than VPAC1-R mRNA.
• Intense expression of VPAC2-R mRNA was found in non-germinative brain regions, including the suprachiasmatic and ventral thalamic nuclei.

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