Some Components of the Serotonergic System in the Eyes of Two Species of Freshwater Molluscs

Labeling of 5-HT-immunoreactive structures was performed on eye slices of freshwater molluscs Lymnaea stagnalis and Pomacea canaliculata . In the periocular region of both species an increased density of 5-HTergic fibers forming structurally distinct plexuses and partially penetrating into the retina was detected. Transcription of serotonin receptor genes was detected in eye tissues: two types in L. stagnalis and three in P. canaliculata . Its relative level is significantly upregulated compared with central ganglia of the nervous system and tentacles. Additionally transcription of the 5HT transporter gene was recorded in P. canaliculata tissues.The obtained results are discussed in terms of a possible serotonergic mechanism of modulation of processes in the retina of gastropods.