PEPTIDERGIC REGULATION OF CHROMATOPHORE FUNCTION IN THE EUROPEAN CUTTLEFISH SEPIA-OFFICINALIS

Color patterning in cephalopod molluscs involves activation of a perip heral chromatophore system that is under neuromuscular control. The co mplex behavior of individual chromatophores is mediated by a specific set of muscles, the chromatophore muscles, that receive direct innerva tion from the central nervous system. To date, glutamate is the only e xcitatory transmitter that has been proposed to act at the chromatopho re neuromuscular junction of cephalopods. We present data demonstratin g that the chromatophore muscles in the European cuttlefish Sepia offi cinalis are also regulated by the FMRFamide family of neuropeptides. U sing an in vitro chromatophore bioassay, it has been determined that s everal FMRFamide-related peptides (FaRPs) are potent exciters of the c hromatophore muscles, causing chromatophore expansion. Immunocytochemi cal analyses of the central nervous system using an FMRFamide antibody revealed the presence of FMRFamide-like immunoreactive cell bodies in the posterior chromatophore lobes, the region of the brain containing the chromatophore motoneurons of the fin and mantle, FMRFamide-like i mmunoreactivity was also seen in the periphery, in the nerves around t he chromatophores and in close apposition to the muscles in the chroma tophore layer of the fin, HPLC analysis of the fin dermis isolated fou r bioactive peaks that were FMRFamide-immunoreactive when tested on an immunoblot assay. Two of these peaks co-eluted with known FaRPs, FMRF amide and ALSGDAFLRFamide, a decapeptide isolated from squid. Taken to gether, these data suggest that the FaRPs are likely to be endogenous exciters of the chromatophore muscles in cephalopods.