ANCTIL, M.: Histamine immunoreactivity in the nervous system of the cnidarian Renilla koellikeri

Histamine (HA) appears to be present in the nervous system of many animal phyla, including Plathelminths, but has not been reported yet in Cnidaria, the lowest phylum in which nervous systems exist. The recent identification in the sea pansy Renilla koellikeri of a cloned G protein-coupled receptor exhibiting significant sequence similarity with HA receptors has prompted a search for histaminergic systems and functions in this cnidarian. An immunohistochemical investigation was undertaken using an antiserum raised in rabbit against a carbodiimide (EDAC) conjugate of HA and keyhole limpet hemocyanin. Immunoreactive elements were primarily observed in the mesogleal nervous system of the sea pansy, including numerous neurons of the nerve net and the relatively large granule-containing amoebocytes associated with the nerve net. In addition, neurons lying over the endodermal epithelium spread around the ovocytes and spermatophores were also immunoreactive. These results suggest that HA is used by the sea pansy as a neurotransmitter or modulator in nerve net activity, and that it may be involved in reproductive function. Attempts are currently made to identify specific sea pansy activities that are affected by HA. (Supported by NSERC of Canada)