Postembryonic expression of the serotonin phenotype in Helisoma trivolvis: comparison between laboratory-reared and wild-type strains

Abstract

In a laboratory-reared albino strain of the snail Helisoma trivolvis, the number of neurons expressing the serotonin phenotype increases markedly during postembryonic life. To address whether these latent changes occur selectively in the laboratory-reared strain, postembryonic expression of serotonin immunoreactivity was directly compared in laboratory-reared and wild-type specimens. The spatial pattern of serotonin-immunoreactive neurons was generally the same in the two strains. In contrast, the time course over which this pattern was generated was more prolonged in the wild types than in the laboratory-reared strain. The cerebral, left parietal, and visceral ganglia of laboratory-reared animals completed their postembryonic acquisition of serotonin-immunoreactive neurons by stage P10. Acquisition of serotonin-immunoreactive neurons after stage P10 occurred only in the pedal ganglia. In the wild types, addition of serotonin-immunoreactive neurons continued at least until stage P20 in all of the ganglia examined. Analysis of serotonergic clusters within the cerebral and pedal ganglia revealed distinct developmental patterns for individual clusters. Therefore, the acquisition of the serotonin phenotype during postembryonic life is a normal component of nervous system development in wild-type H. trivolvis.