Home cage behavior and lead treatment in rhesus monkeys: a comparison with open-field behavior

Nursery-reared rhesus monkeys were treated with no (n = 4) or moderate levels of lead (n = 4) during the first postnatal year. Mean blood lead levels peaked at 55 micrograms/dl at 5 weeks of age, averaged 36 micrograms/dl for the remainder of the first year postpartum, and declined to < or = 5 micrograms/dl for the 4 monkeys by 2.3 years of age. Previously, the lead-treated monkeys exhibited increased environmental exploration and decreased inactivity in a nonhuman primate version of the open field when tested at 4, 5, and 6 years of age (5,6). The current study was designed to assess behavior in the home cage of these monkeys at 6 years of age to determine: (a) whether the increased exploration was specific to the open field, and (b) any lead-related behavioral alterations specific to the home cage. Each monkey was observed twice weekly for 10 weeks and the duration and frequency of 17 behaviors were recorded. Lead treatment did not result in significant alterations in any of the six behaviors which occurred with enough frequency to warrant analysis. As a whole, all monkeys were either inactive or engaged in self-grooming for a large proportion of the test session. Less frequent were behaviors such as locomotion, environmental exploration, and self-directed behaviors. The distribution of behavioral activities in the home cage differed from that in the open field. Potential reasons for the expression of significant lead-related effects in the open field and not in the home cage are discussed as well as the differences in distribution of behavioral activities.