Lead inhibits acquisition and retention learning in bullfrog tadpoles

Bullfrog, Rana catesbeiana, tadpoles were exposed to 0, 500, 625, 750 or 100 micrograms Pb/L as lead nitrate, and subjected to learning and retention tests. Tadpoles used in learning acquisition tests were exposed for six days (144 hours) and tadpoles used in retention tests were exposed for five days (120 hours). All tadpoles were conditioned, using shock avoidance, to associate illumination (conditioned stimulus) with shock (unconditioned stimulus). The mean latency to respond, the number of avoidances, and the differences in learning curves of the lead-exposed and control tadpoles were compared statistically. Learning acquisition tests showed increased latencies and fewer avoidances in lead-exposed as compared to control tadpoles. Retention tests showed increased latencies and fewer avoidances in tadpoles exposed to 625, 750 and 1000 micrograms Pb/L as compared to controls.