Development and differentiation of neuronal subsets in asexually reproducing Microstomum lineare. Immunocytochemistry of 5-HT, RF-amide and SCPB.

The development of immunoreactivity (IR) in the nervous system of asexually reproducing Microstomum lineare has been studied by a combination of simultaneous and double immunostaining with antisera to 5-HT and RF-amide, as well as with monoclonal antibodies to SCPB (molluscan small cardioactive peptide). Immunoreactivity appears in a distinct sequential order. 5-HT antigenicity in the postpharyngeal commissure indicates the initiation of the development of a new zooid. The development of a new brain and pharyngeal plexus always starts in connection to the parental nerve cords. Significantly different developmental patterns are observed for the IR to 5-HT and RF-amide, whereas IR to SCPB has the same localization as that to RF-amide, but appears both weaker and later during the development. Influences of the immunoreactive substances on the asexual reproduction and the feeding behaviour are discussed.