Light and electron microscopic immunocytochemical demonstration of synthesis, storage, and release sites of the neuropeptide calfluxin in Lymnaea stagnalis.

The cerebral caudodorsal cells (CDC) of the pulmonate snail Lymnaea stagnalis control egg-laying and associated behaviors. They produce various peptides derived from two precursor molecules, proCDCH-I and II, one of which is calfuxin (CaFl). CaFL is involved in the control of the activity of a female accessory sex gland, the albumen gland. At the light microscope level, using an antibody raised against synthetic CaFl, immunoreactivity was demonstrated in all CDC somata as well as in the neurohemal CDC terminals in the periphery of the cerebral commissure and in the CDC axon collaterals in the inner region of the commissure. A group of small neurons in each cerebral ganglion was also immunopositive. At the ultrastructural level, secretory granules (SG) and large electron-dense granules (LG), formed by the Golgi apparatus and thought to be involved in intracellular degradation of secretory material, were clearly immunolabeled. The density of immunolabeling of LG was 3.3 times greater than that of SG, indicating that CaFl is preferentially packed into LG. In the LG, the density of immunolabeling with anti-alpha CDCP (alpha CDCP is also a peptide derived from proCDCH-I and II) was 10 times greater than in SG, suggesting that CaFl and alpha CDCP are processed and sorted in (quantitatively) different ways. In the neurohemal terminals SG release their CaFl-immunopositive contents into the hemolymph by the process of exocytosis, whereas collaterals release such contents into the intracellular space of the intercerebral commissure. It is proposed that neurohemally released CaFl acts upon the albumen gland, whereas CaFl released from the collaterals may influence the activity of central neurons.(ABSTRACT TRUNCATED AT 250 WORDS)