The influence of early lead exposure on morphine reinforcement in the rat

Abstract

The effect of early lead burdens on morphine-seeking behavior was investigated in the albino rat. Several concentrations of lead acetate were administered to nursing mothers starting at 0, 7 or 14 days after birth, or provided directly to the pups in the drinking water after weaning, so that lead exposure was continuous for 3 successive weeks in each group. The off-spring were later tested for acquisition and maintenance of a goal-box preference based on morphine reinforcement. High lead burdens imposed before the second week of age resulted in a mild but significantly greater incidence of morphine-seeking responses, as well as retarded growth, compared with placebo-treated controls or animals treated at a later age. The data support the proposition that lead, introduced at a critical stage of development via the lactating mother, increases the potency of morphine reinforcement as a result of changes in cerebral dopaminergic activity. This effect may be mediated directly by the high lead burdens in the offspring, or indirectly by interfering with the mother's nursing capacity.