Lead (Pb) is a major heavy metal that augments environmental pollution and is a health risk to living organisms. This study was performed to investigate the effect of lead on characteristics of planarian, Dugesia japonica. Briefly, planarians were cultivated in water containing different concentrations (0–400 mg/L) of Pb, and incubated for varying durations (1, 3, and 5 hr). After termination of the incubation time, motility and seizure-like behaviors (c-like, head-bop, snake-like, and screw-like) of the planarians were counted in fresh water. Results showed that increasing Pb concentration and time resulted in decreased motility of the planarians (p<0.05). Increasing concentrations of Pb also resulted in significant increase in the seizure-like behavioral patterns, in particular the c-like and head-bop behaviors. In order to examine eye regeneration, the head region was cut, and rest of the body was incubated in water in the absence or presence of Pb, until emergence of the eye extrusion. Formation of eye spots was initiated in amputated fragments of the control group (without Pb) on day 4 after incubation, whereas appearance of the eye spots was delayed in planarian exposed to 200 mg/L Pb. Moreover, immunohistochemistry revealed that formation of the optic nerve was delayed in planarians exposed to Pb. Thus, our studies determined that planarians exposed to high concentrations of Pb resulted in decreasing motility and induction of seizure-like behaviors, as well as delayed eye regeneration. Results of the current study therefore validate that exposure to lead has a negative effect on the lifespan of aquatic organisms and can cause disturbance of the nervous system in animals, thereby implying the possibility of threatening health.

This study was undertaken to evaluate the toxic effect of cadmium sulfate (Cds) on planarians (Dugesia japonica), and the suitability of planarians as an alternative animal model for toxicity studies. Planarians were exposed to varying concentrations of experimental solutions containing 0.1–25 mg/L Cds, and incubated for 1, 3, and 5 hrs. Motility, seizure-like behaviors (c-like, head-bop, snake-like, and screw-like) and regeneration ability of the amputated fragment were subsequently evaluated. Results showed decreased motility with increasing concentrations of Cds (p<0.05), with the lowest motility being observed at the highest concentration of 25 mg/L Cds. Results also indicate that seizure-like behavior patterns were significantly affected by increments in the Cds concentrations, especially the c-like and head-bop behaviors were notably increased. Compared to the control, the regeneration ability of the planarians was decreased in the experimental solutions containing Cds. Planarians exposed to Cds showed either delayed eye formation or no eye regeneration during incubation. Moreover, increased concentrations of Cds resulted in failure to regenerate and death of the planarians. In conclusion, this study confirm that the heavy metal Cds exerts a toxic effect on planarians. Furthermore, the performances of the planarians in the experimental period exhibit their suitability as an alternative animal model for toxicity studies.

Nicotine is a component of tobacco products and is one of the most commonly abused substances that leads to addiction. Therefore, the present study was performed to investigate the behavioral pattern and toxicity by nicotine exposure in planarians. Basically, planarians were exposed to different concentration of nicotine for 5 min. To investigate detoxification effect, planarians were exposed to nicotine for 5 min, and treated glycyrrhizin for 5 min, then motility and seizure-like behavior were observed for 5 min. As a result, the motility of nicotine-exposed planarians decreased approximately more than 50% compared to freshwater control. However, the motility of glycyrrhizin-exposed planarians recovered than nicotineexposed planarians. In the assessment of seizure-like behavioral pattern, planarians exposed to nicotine showed head-bop or c-like type rather than screw-like or snake-like patterns. However, planarians exposed to glycyrrhizin showed no seizure-like behavior. To examine the oxidative stress response, planarians were cultured in fresh water containing 1 mM nicotine for 1 day. Planarians were homogenized and extracted to assay the contents of reactive oxygen species (ROS), lipid hydroperoxides (LH), glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD). The result showed that a significantly higher level of ROS, LH indicated in planarians exposed to nicotine, on the other hand, glycyrrhizin-exposed planarians were significantly decreased ROS, LH levels. In conclusion, the motility decreased when planarians were exposed to nicotine, in a dose-dependent manner, whereas seizurelike behavior increased. Nicotine induced behavioral disturbances and cell toxicity in planarians were recovered by glycyrrhizin, suggesting a candidate substance for nicotine addiction treatment.