DISTRIBUTION OF SEROTONIN-LIKE IMMUNOREACTIVITY IN THE CENTRAL NERVOUS SYSTEM OF THE PERIWINKLE,LITTORINA LITTOREA(GASTROPODA, PROSOBRANCHIA, MESOGASTROPODA)

Abstract

The distribution of serotonin-like immunoreactivity was determined in whole-mounted ganglia of the central nervous system of the prosobranch snail, Littorina littorea, with the goal of establishing a basis for cellular comparisons between different gastropod nervous systems. While general similarities appear to exist with other species, the nervous system of Littorina appears to differ markedly from the nervous systems of the pulmonate and the opisthobranch gastropods with regard to its relatively large number of small, serotonergic cell bodies. Over 1500 cells in Littorina were tentatively identified as serotonergic. These cells and their processes were distributed through all the major ganglia, but the vast majority of immunoreactive cell bodies were found in the pedal ganglia. Most cells in the central nervous system were identified only as members of clusters, however, a few could be reliably identified as consistent individuals between preparations. Further histological and physiological studies are needed on prosobranch nervous systems before evolutionary relationships can be established at the cellular level with pulmonate or opisthobranch nervous systems.