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Step-down passive avoidance acquisition and 24 h retention performance were examined in adult rats given daily doses of either 0, 1, or 5 mg/kg cadmium (Cd) (as CdCl2) via the diet. Results indicated that subjects exposed to the 5 mg/kg Cd diet were less likely to step off a safe platform onto an electrified grid floor than controls. The 1 mg/kg subjects did not differ from controls on this acquisition task. None of the groups showed differential performances on a retention test administered 24 h after acquisition training. These results are discussed in terms of recent claims that Cd exposure enhances emotional reactivity in animals.

Conditioned suppression was examined for control (N = 8) and lead-treated (N = 8) adult rats. Treated animals were exposed daily to 10 mg/kg lead administered via the diet as lead acetate. 40 days of oporant lever press training on a multiple schedule using food as reward was given. Lever press training continued for an additional 5 days but during this period subjects experienced superimposed 3 min tone presentations followed by electric shock (1.3 mA, 1.5 s duration) to a grid floor. Tone presentations were observed to be significantly more disruptive of operant steady state responding for treated subjects as compared to controls. This finding supports earlier claims that lead exposure enhances emotionality.