Heavy metals are released into the environment in increasing amounts from different natural and anthropogenic sources. Among them, cadmium contaminates aquatic habitats and represents a threat to Amphibians. To assess the risks of exposure to cadmium in the aquatic environment, we studied the survival rate of early tadpoles of Xenopus laevis under exposure to CdCl2 for 6 days in the concentration range between 0.15 and 150 µM of Cd2+. Tadpoles survived and reached stage 45 before feeding at all concentrations tested except 150 µM Cd2+, which significantly induced death. With an exposure of 15 µM Cd2+, tadpoles\' mean body length decreased, heart rate increased, fastest swimming speed decreased, and distance traveled was greater compared to unexposed controls. Additionally, a witness of neuronal normal development, the neural cell adhesion molecules (NCAM) expression, was decreased. Moreover, this cell-surface glycoprotein exhibited higher polysialylation, a post-translational modification capable to reduce cell adhesion properties and to affect organ development. Our study highlights the effects of Cd2+ on a series of parameters including morphology, physiology, and behavior. They emphasize the deregulation of molecular NCAM suggesting this effector is an interesting biomarker to detect cadmic toxicity in early tadpoles.

Xenopus laevis has a lateral line mechanosensory system throughout its full life cycle, and a previous study on prefeeding stage tadpoles revealed that it may play a role in motor responses to both water suction and water jets. Here, we investigated the physiology of the anterior lateral line system in newly hatched tadpoles and the motor outputs induced by its activation in response to brief suction stimuli. High-speed videoing showed tadpoles tended to turn and swim away when strong suction was applied close to the head. The lateral line neuromasts were revealed by using DASPEI staining, and their inactivation with neomycin eliminated tadpole motor responses to suction. In immobilized preparations, suction or electrically stimulating the anterior lateral line nerve reliably initiated swimming but the motor nerve discharges implicating turning was observed only occasionally. The same stimulation applied during ongoing fictive swimming produced a halting response. The anterior lateral line nerve showed spontaneous afferent discharges at rest and increased activity during stimulation. Efferent activities were only recorded during tadpole fictive swimming and were largely synchronous with the ipsilateral motor nerve discharges. Finally, calcium imaging identified neurons with fluorescence increase time-locked with suction stimulation in the hindbrain and midbrain. A cluster of neurons at the entry point of the anterior lateral line nerve in the dorsolateral hindbrain had the shortest latency in their responses, supporting their potential sensory interneuron identity. Future studies need to reveal how the lateral line sensory information is processed by the central circuit to determine tadpole motor behavior.NEW & NOTEWORTHY We studied Xenopus tadpole motor responses to anterior lateral line stimulation using high-speed videos, electrophysiology and calcium imaging. Activating the lateral line reliably started swimming. At high stimulation intensities, turning was observed behaviorally but suitable motor nerve discharges were seen only occasionally in immobilized tadpoles. Suction applied during swimming produced a halting response. We analyzed afferent and efferent activities of the tadpole anterior lateral line nerve and located sensory interneurons using calcium imaging.