Treatment with 6-hydroxydopamine in planaria ( Dugesia gonocephala s.l.): morphological and behavioral study

Morpho-functional and behavioral effects of exposure to 6-hydroxydopamine (OHDA)-HCl (24 μg/ml per day for 24 h and 7 days) were studied in planarias ( Dugesia gonocephala s.l.). Exposure to 6-OHDA-HCl for 24 h produced hypokinesia of the specimens. These behavioral changes were more pronounced, leading to complete immobility, after 7 days of exposure to the neurotoxin. Moreover, specimens exposed to 6-OHDA-HCl for 24 h and 7 days failed to show any behavioral response to nomifensine, thus furnishing evidence of the damage of presynaptic dopamine terminals. Exposure to 6-OHDA-HCl for 24 h significantly reduced cathecolamine content in neuropil region, as demonstrated by histochemistry, and electron-dense presynaptic vesicles, as observed on electron microscopy examination. All these alterations were significantly more pronounced and were accompanied by swelling and strong increase of electron-density in cytoplasm of numerous neurons after exposure to the neurotoxin for 7 days. This appears to be the first demonstration of the neurotoxic effects of 6-OHDA-HCl in flatworms.