Occurrence, Distribution, and Physiological Function of Pituitary Adenylyl Cyclase- Activating Polypeptide in Invertebrate Species

The occurrence and distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) are summarized in invertebrate species with special attention to annelids, mollusks, and arthropods in this review. Furthermore, the role of PACAP is highlighted in physiological and behavioral processes of oligochaete (Lumbricus), gastropods (Helix, Lymnaea), insect (Drosophila), as well as malacostraca (Litopenaeus). Since its discovery PACAP has become increasingly recognized for its important and diversified roles in the central and peripheral nervous system and in several peripheral organs of a variety of vertebrate and invertebrate species. Twentysix years after its discovery, PACAP is now one of the most extensively studied neuropeptides both in invertebrate and vertebrate species. This review surveys the importance of PACAP or PACAP-like peptide(s) in invertebrates. The relevance of studies on lower vertebrates and invertebrates, which do not have a pituitary gland like higher vertebrate, is to contribute to the unraveling of fundamental effects of PACAP or PACAP-like peptide(s) and to provide a comparative view.