Immunocytochemical identification of serotoninergic neurons in planaria Girardia tigrina

Abstract

Flatworms occupy an important position among simple organisms, which were first in the evolution having bilateral symmetry and centralized nervous system. This paper provides evidence of the presence of a biogenic amine serotonin in free-living flatworms planarians Girardia tigrina (Turbellaria, Platyhelminthes). Using immunohistochemical method, fluorescence and confocal laser scanning microscopy, we have identified serotonin neurons and their fibers using planarian whole-mount preparations and got important information about distribution of serotoninergic components in their body. Information on the number and size of serotonin-immunopositive neurons in the brain ganglion of G. tigrina and on the distribution density of serotoninergic neurons in the central nervous system of worms is presented for the first time. The published data concerning the serotoninergic signalization in flatworms are briefly overviewed.