QUANTITATIVE-DETERMINATION AND DISTRIBUTION OF THE MYOTROPIC NEUROPEPTIDE ORCOKININ IN THE NERVOUS-SYSTEM OF ASTACIDEAN CRUSTACEANS

For quantitative determinations of orcokinin, an indirect, noncompetit ive sandwich ELISA was developed. This ELISA is highly specific for or cokinin and the detection limit is 1 fmol. In three astacidean species (Orconectes limosus, Homarus americanus, and Astacus astacus) orcokin in immunoreactivity (OK-IR) was measurable in all parts of the nervous system. Upon normalization to the protein content of the tissue (pmol /mg protein), concentrations were shown to be in the same range in all three species. The distribution of OK-IR in the nervous system is als o very similar in the three species. In Orconectes limosus the followi ng values were obtained (in pmol/mg protein): cerebral ganglion 215, o ptic ganglia in the eyestalk 38, subesophageal ganglion 182. The thora cic ganglia have lower concentrations (35-72) and the abdominal gangli a (AG) 1-5 even lower ones (11-17). In the AG 6 of Orconectes, from wh ich the innervation of the hindgut arises, concentrations are approxim ately five times higher than in the other AG. In hindgut tissue, relat ively high concentrations of 22 pmol/mg were measured, which is in agr eement with the demonstrated function of orcokinin as a hindgut excita tory substance. Markedly elevated levels of orcokinin were observed in the AG 6 of Astacus, but not in Homarus. Orcokinin could also be meas ured consistently and reliably in the hemolymph, where its concentrati on is approximately 1 X 10(-11) M. These results show that orcokinin m ay be released into the hemolymph and may act as a hormone, in additio n to its role as a locally acting neurotransmitter/modulator.