Identification of putative egg-laying hormone containing neuronal systems in gastropod molluscs

Of gastropod molluscs, only in the Aplysiidae and the Lymnaeidae have the genes encoding the respective egg-laying hormones been cloned and the neurons controlling egg laying and egg-laying behavior been identified. Immunocytochemistry, using antibodies raised against alpha-CDCP (one of the neuropeptides encoded on the egg-laying hormone gene of Lymnaea stagnalis), identified neurons in various species of gastropods. In the basommatophoran snail, Biomphalaria glabrata, large and small neurons were observed in areas of the central nervous system similar to where immunoreactive cells exist in L. stagnalis, i.e., in the cerebral and pleural ganglia. In the stylommatophoran snail (Helix aspersa) and the slug (Limax maximus), large immunopositive neurons occur in the visceral and right parietal ganglia. In L. maximus, small immunoreactive neurons were found in the cerebral ganglia while in H. aspersa similar cells were observed intermingled with the large cells in the visceral and right parietal ganglia. Similar to the situation in L. stagnalis, in the female part of the reproductive tract of B. glabrata, L. maximus, and A. californica, but not in H. aspersa, neurons and/or fiber tracts are present. The results indicate that egg-laying hormone precursor molecules of gastropod molluscs are phylogenetically closely related. The alpha-CDCP antiserum may allow the identification of hitherto unknown egg-laying regulating systems of gastropod molluscs.