Distribution and Molecular Evolution of the Neuropeptide Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and its Receptors in the Lizard Podarcis sicula (Squamata, Lacertidae).

The presence of the pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors PAC1, VPAC1, and VPAC2 was studied in the lizard Podarcis sicula gastrointestinal and respiratory tissues. The expression and distribution of this neuropeptide was investigated using RT-PCR, immunohistochemistry, and in situ hybridization techniques. RT-PCR showed that several tissues of this reptile synthesize an mRNA encoding for PACAP. Performing in situ hybridization and immunohistochemistry, we found a wide distribution of PACAP and its mRNA in intestine, stomach, liver, and lung. PACAP receptors possess a specific distribution in both gastrointestinal and respiratory system. Further, we analyzed the conservation of PACAP amino acid sequence demonstrating that this peptide in the lizard is very similar to that of other vertebrates. Our findings suggest that also in reptiles an effective PACAP system is present and that it could be implicated in some essential physiological functions as a result of its high conservation amongst vertebrates.