ABSTRACT
Freshwater planarians have a relatively well-organized central nervous system (CNS), which consists of the brain and the ventral nerve cords (VNCs). Recendy, several neural marker genes have been isolated by expressed sequence tag (EST) projects and DNA chip analysis and extensive molecular anatomical studies have been conducted using Dugesia japónica. Brain patterning and domain structure along the anterior-posterior axis and medial-lateral axis are regulated by wnt-family genes and Otx/otp-related genes, respectively, as in vertebrate brains. Neural connection patterns of each domain have been extensively analyzed by fluorescence dye tracing and visualization of each axon with monoclonal antibodies. In addition, several neuronal subtypes-such as dopaminergic, serotonergic and GABAergic-have been identified by whole mount in situ hybridization using genes for rate-limiting enzymes as probes and their axonal projections have been visualized.
