NEURONAL LOCALIZATION AND EVOKED RELEASE OF NOREPINEPHRINE IN THE CNIDARIAN RENILLA-KOELLIKERI

Neuronal release of norepinephrine (NE) in the sea pansy Renilla koell ikeri was investigated by searching for evidence 1) of neuronal locali zation of endogenous NE and 2) of synaptic-like release of exogenously supplied NE in sea pansy tissues. Measurements of endogenous NE by hi gh-performance liquid chromatography with electrochemical detection co rresponded with the visualization of specific NE immunoreactivity in s ix individual colonies thus sampled. Peroxidase-antiperoxidase immunoh istochemistry with antisera against NE-aldehyde-protein conjugates rev ealed that cellular NE immunostaining was predominantly associated wit h neurons and amoebocytes constituting the mesogleal nerve net. Transi ent increases of tritium outflow above background levels were evoked b y field electrical stimulation of colonial (rachis) tissues pre-loaded with 1 mu M [H-3]NE, under conditions that elicited nerve net-mediate d bioluminescence. This evoked release was largely reduced or abolishe d in a reversible manner by substituting high-magnesium or calcium-fre e seawater to normal seawater perfusate. Evoked release was significan tly enhanced by exogenous norepinephrine (50 mu M) and reduced in half or less by the alpha-adrenergic blockers phentolamine and yohimbine ( 10 mu M), thus providing support for the existence of an autoregulator y mechanism associated with release. These results suggest that neuron al, synaptic-like release of NE occurs in the nerve-net of the sea pan sy, a representative of the phylum (Cnidaria) in which the first nervo us systems of multicellular organisms are believed to have originated. (C) 1995 Wiley-Liss, Inc.