Evidence for gonadotropin-releasing hormone-like peptides in a cnidarian nervous system

There is increasing evidence that peptides of the gonadotropin-releasing hormone (GnRH) family, long considered a vertebrate preserve, are also present in invertebrate (molluscan) nervous systems. The possibility was examined that GnRHs are present and bioactive in cnidarians, considered to be representatives of the most primitive animals possessing a nervous system. Immunoreactive GnRH was detected in endodermal neurons of two anthozoans, the sea pansy Renilla koellikeri and the sea anemone Nematostella vectensis. In the sea pansy, immunoreactivity was detected throughout the autozooid polyps, including gamete-producing endoderm. High-performance liquid chromatography and radioimmunoassays of extracts from whole sea pansy colonies yielded two elution peaks exhibiting GnRH immunoreactivity with antisera raised against shark or mammalian GnRH. Vertebrate GnRHs as well as the two sea pansy GnRH-like factors inhibited the amplitude and frequency of peristaltic contractions in the sea pansy, and these actions were blocked by the LHRH analog [D-pGlu(1),D-Phe(2),D-Trp(3,6)]-LHRH. These results suggest that the GnRH family of neuropeptides is more widespread in metazoans than previously thought. Although our physiological data are preliminary, they point to a role for GnRHs as inhibitory modulators of neuromuscular transmission in the sea pansy.