Localization of S1- and S2-like immunoreactivity in the nervous system of the brittle star Amphipholis squamata (Delle Chiaje 1828)

The recent isolation and characterization of the SALMFamide neuropeptides S1 (GFNSALMFamide) and S2 (SGPYSFNSGLTFamide) from the sea stars Asterias rubens aid Asterias forbesi have initiated numerous studies on their morphological localization and distribution within the phylum Echinodermata. It has been shown by immunocytochemistry and radioimmunoassay that these peptides are widely distributed in the nervous system of some asteroids, echinoids and ophiuroids. A physiological approach has also shown that S1 and S2 potentiate the luminescence of the small ophiuroid Amphipholis squamata. In the present study, S1- and S2-like immunoreactivity have been localized in A. squamata by immunocytochemistry on both wholemount preparations and histological sections. The results reveal a widespread neuronal distribution of S1-like immunoreactivity in the circumoral ring, radial nerve cord, and tube feet. S1-like immunoreactivity was found to be associated with axons and cell bodies in both the ectoneural and hyponeural components of the nervous system. S2-like immunoreactivity was detected only in the ectoneural plexus of the circumoral ring and radial nerve cord.