Abstract. The occurrence and distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) is 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 behavioural 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. Twenty-six 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.

Bending, twitching and quivering are different types of tentacle movements observed during olfactory orientation of the snail. Three recently discovered special muscles, spanning along the length of superior tentacles from the tip to the base, seem to be responsible for the execution of these movements. In this study we have investigated the ultrastructure, contractile properties and protein composition of these muscles. Our ultrastructural studies show that smooth muscle fibers are loosely embedded in a collagen matrix and they are coupled with long sarcolemma protrusions. The muscle fibers apparently lack organized SR and transverse tubular system. Instead subsarcolemmal vesicles and mitochondria have been shown to be possible Ca2+ pools for contraction. It was shown that external Ca2+ is required for contraction elicited by high (40 mM) K+ or 10-4 M ACh. Caffeine (5 mM) induced contraction in Ca2+-free solution suggesting the presence of a substantial intracellular Ca2+ pool. High-resolution electrophoretic analysis of columellar and tentacular muscles did not reveal differences in major contractile proteins, such as actin, myosin and paramyosin. Differences were observed however in several bands representing presumably regulatory enzymes. It is concluded that, the ultrastructural, biochemical and contractile properties of the string muscles support their special physiological function.

and increasing those of M3. In both cases, the modulation site was presynaptic. Serotonin (5-HT) at high concentration (10 -5 M) increased the amplitude of both the nerve-and the ACh-evoked contractions in all muscles. The relaxation rate was facilitated suggesting pre-and postsynaptic site of action. Our data provided evidence for a DAergic and 5-HTergic modulation of cholinergic nerves innervating flexor muscles of the tentacles as well as the muscles itself. These effects of DA and 5-HT may contribute to the regulation of sophisticated movements of tentacle muscles lacking inhibitory innervation.