FUNCTIONAL-MORPHOLOGY OF THE LIGHT YELLOW CELL AND YELLOW CELL (SODIUM INFLUX-STIMULATING PEPTIDE) NEUROENDOCRINE SYSTEMS OF THE POND SNAILLYMNAEA-STAGNALIS

Neuroendocrine light yellow cells of the pond snail Lymnaea stagnalis express a neuropeptide gene encoding three different peptides. The mor phology of the cell system has been studied by in situ hybridization, using two synthetic oligonucleotides encoding parts of light yellow ce ll peptides I and III, and by immunocytochemistry with antisera to syn thetic light yellow cell peptide II and to two fragments of light yell ow cell peptide I. One large cluster of light yellow cells was observe d in the ventro-lateral protrusion of the right parietal ganglion, sma ller clusters lying in the posterior dorsal part of this ganglion and in the visceral ganglion. The cells had an extended central neurohaema l area. Immunopositive axons projected into all nerves of the ganglia of the visceral complex, into the superior cervical and the nuchal ner ves, and into the connective tissue surrounding the central nervous sy stem. Axon tracts ramified between the muscle cells of the walls of th e anterior aorta and of smaller blood vessels. Peripheral innervation by the light yellow cell system was only found in muscular tissue of t he ureter papilla. The antisera to the two peptide fragments of light yellow cell peptide I not only stained the light yellow cells, but als o the identified yellow cells, which have previously been shown to pro duce the sodium influx-stimulating neuropeptide. The latter cells were negative to the in situ hybridization probes and antisera specific to the light yellow cell system. It is therefore unlikely that the yello w cells express the light yellow cell neuropeptide gene. Nevertheless, the cells contain a neuropeptide sharing antigenic determinants with light yellow cell peptide I, Our observations support the hypothesis t hat light yellow cells are involved in maintaining the shape of the an imal via the regulation of ion- and water-balance processes and blood pressure.