ABSTRACT
Planaria are free-living flatworms and represent the most primitive example of centralization and cephalization of the nervous system along phylogeny. Several neurotransmitters such as dopamine, norepinephrine and serotonin which are present in the human brain have also been identified and investigated in the planaria nervous system. Dugesia gonocephala s.l. displays high concentrations of dopamine and lower amounts of norepinephrine. Moreover, the exposure to drugs acting on neural transmission causes specific and stereotyped behavioural patterns. Dopaminergic hyperstimulation rises cAMP and induces typical hyperkinesias, whereas dopaminergic blocking agents decrease cAMP and motility, suggesting similar neurochemical functional mechanisms in invertebrates as in mammals. The dopaminergic-cholinergic balance that was found in the planaria nervous system has been compared to that observed in the extrapyramidal system of mammals. For the above reported reasons, Dugesia gonocephala s.l. has been proposed as a reliable model to investigate neurotransmission and related human diseases.
